The tensile behavior of an oxide dispersion strengthened copper-niobium composite 96

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The Psychology of Human Behavior

The Psychology of Human Behavior The psychology of human behavior is a complex and multifaceted topic that has been the subject of study and debate for centuries. Understanding the factors that influence human behavior is crucial for various fields such as psychology, sociology, and even business. From the influence of genetics and biology to the impact of social and environmental factors, there are numerous perspectives to consider when exploring the psychology of human behavior. One important perspective to consider when examining human behavior is the role of genetics and biology. Research in the field of behavioral genetics has shown that genetic factors can play a significant role in shaping an individual's behavior. For example, studies have found that certain genetic variations are associated with an increased risk of developing mental health disorders such as depression and anxiety. Additionally, research in the field of neuroscience has shown that the structure and function of the brain can also influence behavior. For example, abnormalities in certain brain regions have been linked to impulsive and aggressive behavior. Understanding the genetic and biological factors that contribute to human behavior is important for developing effective interventions and treatments for behavioral and mental health disorders. In addition to genetics and biology, social and environmental factors also play a crucial role in shaping human behavior. Social psychologists have long been interested in understanding how social norms, cultural values, and interpersonal relationships influence behavior. For example, research has shown that individuals are more likely to engage in prosocial behavior when they are in the presence of others. Similarly, studies have found that individuals from collectivist cultures are more likely to prioritize the needs of the group over their individual needs. Environmental factors such as poverty, access to education, and exposure to violence can also have a significant impact on behavior. For example, children who grow up in poverty are more likely to experience chronic stress, which can have long-term effects on their behavior and mental health. Understanding the social and environmental factors that influence behavior is important for developing interventions that promote positive behavior and well-being. Another perspective to consider when examining human behavior is the role of cognitive processes.Cognitive psychologists are interested in understanding how individuals perceive, process, and interpret information from their environment. For example, research has shown that individuals are more likely to remember information that is emotionally salient. Additionally, cognitive biases such as confirmation bias and availability heuristic can influence decision-making and behavior. Understanding the cognitive processes that underlie behavior is important for developing interventions that promote rational decision-making and critical thinking. Furthermore, the study of human behavior also encompasses the role of emotions and motivation. Emotions play a crucial role in shaping behavior, as they influence how individuals perceive and respond to their environment. For example, research has shown that individuals are more likely to engage in risky behavior when they are experiencing strong emotions such as anger or fear. Similarly, motivation is a key factor in driving behavior, as individuals are more likely to engage in a behavior if they are motivated to do so. For example, individuals are more likely to engage in healthy behaviors such as exercise and diet if they are motivated by a desire to improve their health. Understanding the role of emotions and motivation in behavior is important for developing interventions that promote positive behavior change. In conclusion, the psychology of human behavior is a complex and multifaceted topic that encompasses a wide range of perspectives. From the influence of genetics and biology to the impact of social and environmental factors, there are numerous factors to consider when examining human behavior. Understanding the various perspectives that contribute to human behavior is important for developing interventions and treatments that promote positive behavior and well-being. By considering the role of genetics, biology, social and environmental factors, cognitive processes, and emotions and motivation, researchers and practitioners can gain a more comprehensive understanding of human behavior and develop effective strategies for promoting positive behavior change.。

环二硫醚制法2

Synthesis of cyclic mono-and bis-disulﬁdes and their selective conversion to mono-and bis-thiosulﬁnatesEmilie Bourl e s,a Rodolphe Alves de Sousa,a Erwan Galardon,a Mohamed Selkti,bAlain Tomas b and Isabelle Artaud a,*a Laboratoire de Chimie et Biochimie Pharmacologique et Toxicologique,UMR8601,CNRS Universit e´Paris5,45rue des Saints P e res,75270Paris Cedex06,Franceb Laboratoire de Cristallographie et RMN Biologiques,UMR8015,CNRS Universit e´Paris5,4avenue de l’Observatoire,75270Paris cedex06,FranceReceived8November2006;revised27December2006;accepted2January2007Available online4January2007Abstract—Twelve-membered ring pseudopeptidic cyclic disulﬁdes have been prepared by iodine oxidation of the parent dithiols.However, oxidation of N,N0-(1,2-phenylene)bis(2-mercapto-2-methylpropanamide)afforded a25/75mixture of cyclic mono-and bis-disulﬁdes that were separated by selective precipitation in CHCl3.The cyclic bis-disulﬁde was selectively prepared by iodine oxidation of the Ni complex of this dithiol and crystallized.Its crystal structure was solved by X-ray diffraction.All these cyclic mono-or bis-disulﬁdes were selectively converted to cyclic mono-and bis-thiosulﬁnates upon stoichiometric oxidation with dimethyldioxirane at low temperature.1H NMR of the cyclic bis-thiosulﬁnate revealed the presence of four isomers,two couples of stereoisomers,as expected from the insertion of two oxygen atoms in this compound,one on each disulﬁde bond.The two couples of cis/trans isomers were separated by preparative TLC and identiﬁed after alkaline cleavage of the two S(O)–S bonds and metalation with Ni(II).As HOÀattack is selective for the sulﬁnyl sulfur,the nature of the Ni complexes obtained is a signature of each couple of stereoisomers.Ó2007Elsevier Ltd.All rights reserved.1.IntroductionRecently glutathion has been reported to be converted to di-sulﬁde-S-oxides under oxidative stress conditions.1These reactive sulfur oxidized species can then react with nucleo-philes in proteins such as free thiols2or zinc bound thiolates leading to glutathionylation of proteins or zinc metallothio-neins.3Thisﬁnding emphasizes that more generally disul-ﬁde-S-oxides might play an important role in biology.This requires developing the synthesis of new disulﬁde mono-oxides(thiosulﬁnates)or dioxides(thiosulfonates).Herein we report the synthesis of cyclic mono-and bis-disulﬁdes from the parent dithiols and their further oxidation into cyclic disulﬁde-S-oxide and cyclic bis(disulﬁde-S-oxides) (bis(thiosulﬁnates)).2.Results and discussionThe linear dithiols N2S2H4,1a,1b,and1c,shown in Scheme 1,are the precursors of10-or12-membered ring disulﬁdes 2a,2b,and2c,respectively.While the synthesis of1b has been previously described,4the synthetic route for the dipep-tide1c is outlined in Scheme2.Acylation of o-phenylenedi-amine with2equiv of S-benzyl-protected N-Boc-cysteine afforded the S-protected dithiol,which was further debenzyl-ated with Na in liquid pound1a was prepared2R21a, n = 0, R2 = Me1b, n = 1, R1 = H, R2 = Me1c, n = 1, R1 = NHBoc, R2 = H2a2b2cNH SOSNH S SOHNHNOO3a+Et3N / I23Scheme1.Synthesis of disulﬁdes.Keywords:Cyclic disulﬁde;Disulﬁde-S-oxide;Thiosulﬁnate;Bis(disulﬁde-S-oxides);Bis-thiosulﬁnates.*Corresponding author.Tel.:+33(1)42862189;fax:+33(1)42868387;e-mail:isabelle.artaud@univ-paris5.fr0040–4020/$-see front matterÓ2007Elsevier Ltd.All rights reserved.doi:10.1016/j.tet.2007.01.002Tetrahedron63(2007)2466–2471in situ from the bis(S -acetylated)form of 1a 5after depro-tection with K 2CO 3in MeOH.Oxidative cyclization of the dithiols 1with iodine in CHCl 3in the presence of triethylamine 6affords cyclic mono-disul-ﬁdes 2and bis-disulﬁde 3a (Scheme 1)depending on the size of the N 2S 2H 4chelate,while oxidation of 1b and 1c provides 2b and 2c as the only products identiﬁed by 1H NMR.At this stage,we tried to remove the Boc protection of 2c by an acidic treatment,but this results in a poorly soluble species that was difﬁcult to characterize further.Oxidation of 1a leads to a mixture of the cyclic mono-and bis-disulﬁdes 2a and 3a ,in a 25/75ratio.Fortunately,2a and 3a could be easily separated by repeated crystallizations from CHCl 3,2a being only sparingly soluble in this solvent.The 10-atom chelate 1a does not favor the ring closure into 2a whose structure appears to be rigid and twisted in solution as shown by the lack of any symmetry revealed by 1H NMR analysis.The methyl protons are split into two groups (6H each)appearing at two different chem-ical shifts.In contrast,the methyl protons of the bis(di-sulﬁde)3a are equivalent and appear as a single resonance,showing the larger ﬂexibility of the dimer in solution.Oxidation of dithiols usually provides mixtures of cyclic di-sulﬁdes containing one or more disulﬁde bridges depending on the reaction conditions.Thus,oxidation with iodine under high-dilution conditions 7or using thiol-disulﬁde interchange reactions 8are reported to provide monomeric disulﬁdes and higher disulﬁde-containing species,respectively,but these reactions are either not very selective,or afford by-products.Interestingly,selective synthesis of bis(disulﬁde)-tetramine macrocycles from the parent dithiol/diamine precursor has been described either when using vanadyl spe-cies as oxidizing agent 9or by oxidative coupling of Ni(II)or Cu(II)complexes of the linear tetradentate N 2S 2ligand.10,11In this latter case,the cleanest synthesis was described by Fox et al.11Iodine oxidation of the diamine/dithiolate nickel(II)or copper(II)complexes followed by removal of the metal led to the unique and selective formation of the bis(disulﬁde)in high yield.11To get a larger amount of 3a ,this method was applied to the oxidation of the diamidato dithiolato nickel(II)complex of 1a ,prepared as previously described by Kr €u ger and Hanss.12Compound 3a was iso-lated in almost quantitative yield and subjected to crystalli-zation by slow evaporation of a CH 2Cl 2solution.A view of its X-ray crystal structure is shown in Figure 1.As other cyclic bis(disulﬁdes),73a adopts a cage conforma-tion with a center of symmetry.The metric parameters of the disulﬁdes (S1–S2i ,S1–C1,and S2–C10distancesof 2.0294(9),1.856(2),and 1.864(3)A˚,respectively;C1–S1–S2i and C10–S2–S1i bond angles of 106.31(8) and 105.65(8) ,respectively)compare well with those of struc-turally related 20-membered ring disulﬁdes such as a tetrabenzo-tetrathia-tetraazacycloeicosane 13or an octa-methyl-diperhydrobenzo-tetrathia-tetraazacycloeicosane.11Two features characterize the structure of 3a ,namely,(i)avery short cross cage distance S1–S1i of 3.393(1)A˚,which puts the two sulfur atoms within van der Waals contact and (ii)a quite large value of the C1–S1–S2i –C10i torsion angle (111.9(1) ).This value,which has been established to be 80–85 in strain-free disulﬁdes,14is indicative of the stability of the disulﬁdes.Torsion angles can be compared within cyclic disulﬁdes of the same size.In that regard,the value deter-mined in 3a is slightly larger than that found in the structure described by Fox et al.(110.1(2) ).11Replacement of the two 1,2-diamino-cyclohexyl groups in this structure by two phthalamide groups in 3a is likely to account for the increase of the torsion as well as for the short cross cage distance revealed in 3a .The second part of this work deals with the oxidation of di-sulﬁdes 2and bis(disulﬁde)3a into cyclic mono-and bis-thiosulﬁnates.While oxidation of linear disulﬁdes is well documented,only a few papers describe the oxidation of cyclic disulﬁdes into cyclic thiosulﬁnates 15and to the best of our knowledge,there is no report on the oxidation of cyclic bis(disulﬁdes).Dimethyldioxirane (DMD)was chosen as a clean oxidant since acetone was the only by-product after oxygen transfer.The solvent used was either acetone or a mixture of CH 2Cl 2/acetone,when the starting product was only sparingly soluble in acetone at the low temperature required for the reaction.In these conditions,the cyclic disulﬁdes 2were completely and selectively converted with 1equiv of DMD to the monothiosulﬁnate 4(Scheme 3).Oxidation of the bis(disulﬁde)3a was performed in a CH 2Cl 2/acetone mixture at À50 C with 2equiv of DMD (Scheme 4).1H NMR analysis of the raw material isolatedSCOOH NH HN S S OOBocHNNHBocPhPh1ciii Scheme 2.Synthesis of dithiol 2c :(i)i -BuOCOCl/o -phenylenediamine/NMP;(ii)Na/NH 3.S1S2iC1C11C12O3C2N1C3C4C5C6C7C8N2O4C9C10C13C14S2S1iC10iFigure 1.ORTEP view of the cyclic bis(disulﬁde)3a showing 50%proba-bility displacement ellipsoids.Selected bond distances (A ˚):S1–C1:1.856(2),S2–C10: 1.864(3);selected bond angles ():C1–S1–S2i :106.31(8),C10–S2–S1i :105.65(8);[i:1Àx ,1Ày ,1Àz ].2467E.Bourl e s et al./Tetrahedron 63(2007)2466–2471after oxidation of3a shows the existence of four different products in the same amount.ESI+MS analysis of this mix-ture shows only two peaks at m/z653and675,corresponding to the incorporation of two oxygen atoms in the four products (653,[M+H]+;675[M+Na]+).The IR spectrum does not show strong bands in the range1100–1300cmÀ1as expected for thiosulfonates RS(O2)–SR,but exhibits only one strong stretching frequency at1082cmÀ1supporting the formation of thiosulﬁnates.The two oxygens can be incorporated either on both sulfur atoms of the same disulﬁde bond,or on one sul-fur atom of each disulﬁde bond leading,respectively,to vic-disulfoxides or bis(thiosulﬁnates).Only two stereoisomers are expected in the case of vic-disulfoxides and four isomers, as observed by1H NMR,in the case of thiosulﬁnates.These four isomers correspond to two couples of cis/trans stereoiso-mers,resulting from the incorporation of one oxygen atom at S1and S3,or S1and S4,leading to5a(cis/trans)and6a(cis/ trans),respectively.Moreover our compounds being stable at rt,we can rule out deﬁnitively the possible involvement of vic-disulfoxides,whose S–S bond is relatively weak,and which are only stable at low temperature.16a Such com-pounds have been isolated in unusual structures such as bridged bicyclic a-disulfoxides16b and more recently as tetra-thiolane-2,3-dioxides.15c,d Despite several attempts,we did not succeed in separating the four isomers but two clean fractions were isolated after separation over preparative TLC(SiO2,RP-18).The upper fraction contained two stereoisomers in a1/1ratio while the lower fraction contained the other two stereoisomers in a35/65ratio.The different ratio in both couples of stereoiso-mers after separation arises from the slight difference in mi-gration of the two slow-migrating isomers and by the quite arbitrary cut-off,the in-between fraction being a mixture of the four isomers.A deﬁnitive assignment of the1H NMR spectrum of each fraction to cis/trans5a or cis/trans6a being difﬁcult,we used an indirect evidence to do this attribution.In a recent paper,17we have shown that alkaline cleavage of the S(O)–S bond in4b selectively takes place at the sulﬁnyl sulfur as previously described for related compounds(Eq.1),18lead-ing after insertion of Co(III)to the corresponding mixed thiolate/sulﬁnate complex.17R S S+ 2 HO-RSO- + RS-O-H2Oð1ÞThis reaction was then applied to the metalation of4a and4b with Ni(II)with the same selectivity toward mixed thiolate/sulﬁnate derivatives(paper in preparation). To characterize and attribute the regioisomers to each fraction,the two collected fractions were subjected to alkaline cleavage of both S(O)–S bonds followed by Ni(II) insertion in the opened structures.By comparison with an authentic sample prepared from4a,a unique square planar complex with a mixed thiolate/sulﬁnate environment, {Ni[N2S(SO2)]}2À,was obtained from the lower fraction, indicating clearly that it corresponds to the mixture of stereoisomers6a cis and trans.Treatment of the upper fraction leads to a1/1mixture of bis(thiolate)and bis(sulﬁ-nate)nickel complexes consistent with the mixture of stereoisomers5a cis and trans.The IR spectra of {Ni[N2S(SO2)]}2Àand{Ni[N2S(SO2)]}2Àdisplay two bands between1000and1200cmÀ1,assigned to n(SO)asym and n(SO)sym stretching typically observed in S-bonded metal sulﬁnate complexes.For an O-bonded sulﬁnate,only one strong vibration around1000cmÀ1is expected.Because the yields of pure isomers5a and6a were very low,this has hampered the attempts to get crystal structures of the re-sulting Ni complexes.Finally,an assignment of the1H NMR signals to6a1and6a2(cis or trans isomer)was possible on the basis of their relative intensities since these two com-pounds are in35/65ratio.However,5a1and5a2being in a1/1ratio,a complete attribution of the signals to5a1and 5a2was not possible.3.ConclusionIn conclusion,we have described efﬁcient syntheses of cyclic mono-and bis-disulﬁdes and their selective conver-sions to thiosulﬁnates and bis-thiosulﬁnates with dimethyl-dioxirane as oxidant.In addition,we propose a simple method to identify the two regioisomers derived from the 20-membered ring cyclic bis(thiosulﬁnates),which can be applied to other cyclic pseudopeptidic bis(thiosulﬁnates).2a, n = 0, R2 = Me2b, n = 1, R1 = H, R2 =Me2c, n = 1, R1 = NHBoc, R2 = H 4a 4b 4cScheme3.Synthesis of mono-thiosulﬁnates.22Scheme4.Cyclic bis(thiosulﬁnates)and their conversion to Ni complexes:(i)4equiv Et4NOH,DMF,À40 C;(ii)2equiv NiCl2;(iii)4equiv Et4NOH.2468 E.Bourl e s et al./Tetrahedron63(2007)2466–24714.Experimental4.1.Dithiol1cTo a THF solution(20mL)of S-benzyl-N-Boc-L-cysteine (1.1g, 3.53mmol)and N-methylmorpholine(442m L, 4mmol),isobutyl chloroformate(521m L,4mmol)was added dropwise at0 C and the mixture was stirred for 1h.o-Phenylenediamine(173mg, 1.6mmol)in THF (25mL)was slowly added at rt.After stirring overnight, the solution wasﬁltered and the solvent evaporated to dry-ness.Ethyl acetate was then added and the solution was washed with water,saturated aq NaCl,water,dried over Na2SO4,and concentrated in vacuo.Puriﬁcation by column chromatography over silica gel(CH2Cl2/AcOEt95/5)gave the S-benzyl intermediate.Yield:72%(800mg).1H NMR (CDCl3,250MHz)d1.46(s,18H),2.9(m,4H),3.74(m, 4H),4.39(m,2H),5.39(m,2H),7.17–7.46(m,16H),8.46 (s,2H).Mass(CI+,NH3)m/z695[M+1]+;712[M+NH4+]. Anal.Calcd for C36H48N4O6S2:C,62.22;H,6.67;N,8.06. Found:C,62.09;H,6.82;N,8.17.The S-benzyl derivative (800mg,1.15mmol)dissolved in THF(3mL)was stirred with anhydrous ammonia(50mL).An excess of sodium (4–10equiv)was then added until persistence of a blue color for1h.After addition of NH4Cl,and removal of NH3and THF,aq HCl(0.1M)was added and the acidic solution was extracted with AcOEt.The organic layer was washed with brine,dried over Na2SO4,and concentrated in vacuo. Yield:86%(510mg).Compound1c:1H NMR(250MHz, CDCl3)d1.49(s,18H),1.65(m,2H),2.83–3.17(m,4H), 4.5(m,2H),5.59(m,2H),7.2(m,2H),7.13–7.46(m, 2H),8.63(s,2H).Mass(CI+,NH3)m/z515[M+1]+;532 [M+NH4+].Anal.Calcd for C22H34N4O6S2:C,51.34;H, 6.66;N,10.89.Found:C,51.14;H,6.86;N,10.77.4.2.2-Mercapto-N-[2-(2-mercapto-2-methyl-propionyl-amino)-phenyl]-2-methyl-propionamide1aA0.07M methanol solution of thioacetic acid S-{1-[2-(2-acetylsulfanyl-2-methyl-propionylamino)-phenyl-carba-moyl]-1-methyl-ethyl}ester5was deprotected in methanol with K2CO3(2.2equiv).After stirring overnight under ar-gon,the solution was acidiﬁed with an ethereal solution of HCl(g)(2equiv).After removal of the solvents and dissolu-tion of the solid in a large volume of EtOAc,the solution was washed with water and dried over MgSO4.Evaporating the solvent in vacuo afforded1a in quantitative yield.1H NMR(250MHz,CD2Cl2)d1.31(s,3H),1.60(s,6H), 1.71(s,6H),7.28(m,2H),7.42(m,2H).Yield from 443mg of the thioacetic derivative,95%(324mg).4.3.Typical procedure for synthesis of disulﬁdes0.13M solutions of dithiol1and I2(1equiv relative to1)in CHCl3were added dropwise and simultaneously,under argon,into a0.26M solution of triethylamine(2equiv relative to1)in CHCl3.Then the solution was washed with saturated aq Na2S2O3,aq HCl(0.1N),and water and the solvent was removed.In the case of1a,2a and3a were isolated by selective precipitation of2a in CHCl3leading to a25/75ratio of2a/3a. Compounds2b and2c were puriﬁed by column chromato-graphy over silica gel using dichloromethane/ethyl acetate mixtures as eluants(7/3for2b and8/2for2c).4.3.1.7,7,10,10-Tetramethyl-5,12-dihydro-8,9-dithia-5,12-diaza-benzocyclodecene-6,11-dione2a.IR(ATR): 3300(NH),1653(amide),1503,1441,747.1H NMR (250MHz;DMSO-d6)d1.56(s,6H),1.59(s,6H),7.2(m, 2H),7.35(m,2H),9.13(s,2H NH).Mass(ESI+)m/z333 [M+Na]+.Anal.Calcd for C14H18N2O2S2$0.5H2O:C, 52.64;H,6.00;N,8.77.Found:C,52.44;H,5.56;N,8.8. Yield from240mg of1a,24%(58mg).4.3.2.8,8,11,11-Tetramethyl-5,7,8,11,12,14-hexahydro-9,10-dithia-5,14-diaza-benzocyclododecene-6,13-dione 2b.1H NMR(250MHz,CDCl3)d1.49(s,12H),2.64(s,4H), 7.18(m,2H),7.41(m,2H),8.24(s,2H NH).Anal.Calcd for C16H22N2O2S2:C,56.77;H,6.55;N,8.28.Found:C,56.76; H,6.48;N,8.09.Yield starting from4.47g of1b:61%(2.71g).4.3.3.(12-tert-Butoxycarbonylamino-6,13-dioxo-5,6,7,8,11,12,13,14-octahydro-9,10-dithia-5,14-diaza-benzocyclododecen-7-yl)-carbamic acid tert-butyl ester 2c.1H NMR(250MHz,CDCl3)d1.47(s,18H),3.22–3.38 (m,4H),4.57(m,2H),5.52(s,2H NH),7.22–7.36(m,4H), 8.34(s,2H).Anal.Calcd for C22H32N4O6S2$AcOEt$H2O: C,50.47;H,6.84;N,9.05.Found:C,50.71;H,7.05;N,8.86.Yield starting from400mg of1c:58%(231mg).4.3.4.7,7,10,10,19,19,22,22-Octamethyl-5,12,17,24-tetra-hydro-8,9,20,21-tetrathia-5,12,17,24-tetraaza-dibenzo-[a,k]cycloeicosene-6,11,18,23-tetraone3a.IR(ATR, cmÀ1):3306(NH),1670(amide),1527,1472,747.1H NMR (250MHz,CDCl3)d1.66(s,24H),7.0(m,4H),7.26(m,4H), 8.73(s,4H NH).Anal.Calcd for C28H36N4O4S4$H2O:C, 52.64;H,6.00;N,8.77.Found:C,53.36;H,6.00;N,8.77. Mass(FAB+)m/z621[M+1]+.Yield from240mg of1a, 75%(180mg).4.4.Typical procedure for synthesis of thiosulﬁnates4 Disulﬁde2was dissolved in acetone(0.02M for2b)or in a60/40v/v mixture of CH2Cl2/acetone(3mM for2a)and DMD(0.08M in acetone,1equiv)was added dropwise at À40 C under argon.Removal of the solvents afforded thethiosulﬁnates4in almost quantitative yields.4.4.1.7,7,10,10-Tetramethyl-8-oxo-5,7,8,12-tetrahydro-8l4,9-dithia-5,12-diaza-benzocyclodecene-6,11-dione4a. IR(ATR,cmÀ1):1662,1506,1089(S]O),749.1H NMR (250MHz,CDCl3)d1.69(s,3H),1.71(s,3H),1.75(s, 3H), 1.96(s,3H),7.19(m,2H),7.37(m,2H).Mass (FAB+)m/z327.2[M+1]+.1H NMR(250MHz,DMSO-d6) d1.53(s,3H),1.76(s,6H),7.18(m,2H),7.37(m,2H), 9.18(s,1H NH),9.76(s,1H NH).13C NMR(500MHz, DMSO-d6)d16.32,22.15,25.57,28.17,54.78,70.24, 128.27,128.53,129.23,135.55,167.63,172.64.Mass(FAB+) m/z327[M+1]+.Anal.Calcd for C16H22N2O3S2$1/6CH2Cl2: C,49.66;H,5.40;N,8.16.Found:C,49.57;H,5.24;N,8.56. Yield from200mg of2a,97%(217mg).4.4.2.8,8,11,11-Tetramethyl-9-oxo-5,8,9,11,12,14-hexa-hydro-7H-9l4,10-dithia-5,14-diaza-benzocyclododecene-6,13-dione4b.IR(ATR,cmÀ1):1665,1527,1070(S]O), 733.1H NMR(250MHz,DMSO-d6)d1.45(s,3H),1.61 (s,3H),1.65(s,6H),2.78–2.9(m,2H),3.1–3.2(m,2H), 7.17(m,2H),7.3(m,2H),8.95(s,1H NH),9.67(s,1H NH).2469E.Bourl e s et al./Tetrahedron63(2007)2466–247113C NMR(500MHz,CDCl3)d24.04,24.84,30.70,31.80,45.66,49.54,52.36,63.10,126.46,127.00,130.96,131.70,167.30,168.76.Anal.Calcd for C16H22N2O3S2$0.5H2O:C, 53.31;H,6.34;N,7.77.Found:C,53.33;H,6.16;N,7.56. Yield from500mg of2b,94%(508mg).4.4.3.(12-tert-Butoxycarbonylamino-6,10,13-trioxo-5,7, 8,10,11,12,13,14-octahydro-6H-9,10l4-dithia-5,14-di-aza-benzocyclododecen-7-yl)-carbamic acid tert-butyl ester4c.The product was puriﬁed byﬂash chromatography (SiO2,CH2Cl2/AcOEt60/40).IR(ATR,cmÀ1):1692,1660, 1076(S]O),756.1H NMR(250MHz,CDCl3)d1.47(s,18H),3.52–3.83(m,4H),4.53–4.59(m,1H),4.87(s,1H), 5.69–5.77(m,2H NH),7.13–7.65(m,4H Ar),8.58(s,1H NH), 8.64(s,1H NH).13C NMR(500MHz,CDCl3)d28.32, 37.36,51.62,53.70,57.99,80.81,124.00,125.39,126.40,127.00,127.59,128.31,128.97,130.74,154.97,167.00, 168.24.Anal.Calcd for C22H32N4O7S2$0.5AcOEt:C, 50.33;H,6.34;N,9.78.Found:C,50.62;H,6.42;N,9.45.Yield from50mg of2c,63%(35mg).4.5.Bis-thiosulﬁnates5a and6aTo a CH2Cl2/acetone(30/70v/v mixture)solution of3a, cold DMD in acetone(2equiv)was added dropwise at À50 C.1H NMR analysis of the mixture isolated after re-moval of the solvents revealed the unique presence of5aand6a in a1/1ratio.Mass(ESI+)m/z653[M+H]+;675 [M+Na]+.Anal.Calcd for C28H36N4O6S4$0.5H2O:C, 50.81;H,5.63;N,8.46.Found:C,50.79;H,5.88;N,8.29. Yield from205mg of3a,96%(260mg of5a and6a).Com-pounds5a and6a were separated by three successive migra-tions on preparative TLC silica gel60F254(1mm)eluted with hexane/AcOEt(4/6v/v mixture).4.5.1.7,7,10,10,19,19,22,22-Octamethyl-8,21-dioxo-5,7, 8,12,17,21,22,24-octahydro-8l4,9,20,21l4-tetrathia-5, 12,17,24-tetraaza-dibenzo[a,k]cycloeicosene-6,11,18,23-tetraone5a.Two isomers5a1and5a2unrespectively cis and trans in a1/1ratio.1H NMR(250MHz,CDCl3) d1.93,1.89,1.87,1.85,1.76,1.60(s,6Â3H),1.76(s,6H), 6.88,6.95,7.16,7.61(m,8H Ar5a1),6.86,6.94,7.65,7.2 (m,8H Ar5a2),7.08(m)not attributed,8.40,8.85(s, 2Â2H NH5a1),8.37,8.90(s,2Â2H NH5a2).IR(ATR, cmÀ1):3272,1650(amide),1513,1082(S]O),747.Yield from42mg of the mixture5a/6a,14%(6mg).4.5.2.7,7,10,10,19,19,22,22-Octamethyl-8,20-dioxo-5,7, 8,12,17,19,20,24-octahydro-8l4,9,20l4,21-tetrathia-5, 12,17,24-tetraaza-dibenzo[a,k]cycloeicosene-6,11,18,23-tetraone6a.Two isomers6a1and6a2unrespectively cis and trans in a7/3ratio.1H NMR(250MHz,CDCl3)d6a1: 1.95,1.78,1.74,1.72(s,4Â3H),7.14,7.66(m,2Â4H), 8.60(m,4H);d6a2:1.98,1.84,1.77,1.66(s,4Â3H), 7.66,7.14(m,2Â4H),8.54(s,4H).Yield from42mg of the mixture5a/6a,47%(20mg).4.6.Typical procedure for characterization of the stereoisomers5a and6aTo a DMF solution of5a or6a atÀ40 C wasﬁrst added,un-der a stream of argon and stirring,Et4NOH(1M in MeOH,4equiv)to cleave the S(O)–S bonds and to produce the sulﬁnates and the thiolates.A concentrated DMF solution of NiCl2(2equiv)was then added and immediately4equiv of Et4NOH to deprotonate the amides.The solution was then allowed to warm to rt.After removal of the solvents in vacuo,the complexes were isolated upon precipitation at0 C from CH3CN into diethylether and characterized by1H NMR.Synthesis and spectroscopic characterizations of[Ni(N2S2)](Et4N)2are described in Ref.12.{Ni[N2S(SO2)]}(Et4N)2:IR(ATR,cmÀ1):1588(C]O), 1154and1034(SO2),1173,1001(Et4N).1H NMR (250MHz,CD3CN)d1.18(m,24H),1.27(s,6H),1.45(s, 6H),3.24(q,J¼7.3Hz,16H),6.62(m,2H),8.58(m,2H). Anal.Calcd for C60H56N4NiO4S2$1.5H2O:C,52.48;H, 8.66;N,8.16.Found C,52.57;H,8.65;N,8.37.{Ni[N2(SO2)2]}(Et4N)2:IR(ATR,cmÀ1):1599,1562, 1180,1170,1057,1031.1H NMR(250MHz,CD3OD) d 1.26(t,J¼7.3Hz,24H), 1.45(s,12H), 3.26(q, J¼7.3Hz,16H),6.75(m,2H),8.47(m,2H).Mass(ESIÀ) m/z560(50%)[{Ni[N2(SO2)2]}(Et4N)]À.Anal.Calcd for C60H56N4NiO6S2$H2O$0.5CH3CN:C,50.99;H,8.21;N, 8.63.Found:C,50.82;H,8.09;N,8.60.4.7.X-ray crystallography for3aFormula C28H36N4O4S4;monoclinic,space group P21/a;a¼11.958(2),b¼10.662(2),c¼13.373(2)A˚,b¼116.15(1) ,V¼1530.4(4)A˚3,Z¼2.The structure was solved by SHELXS9719and reﬁned using SHELXL97.20The hy-drogen atoms were positioned geometrically and reﬁned rid-ing on their carrier atom with isotropic thermal displacement parametersﬁxed at1.2times those of their parent atoms. Convergence was reached at R1¼0.0636for2733reﬂections (I>2s(I)),wR2¼0.186for all data and S¼0.934for185pa-rameters.The residual electron density in theﬁnal difference Fourier does not show any feature above0.698eA˚À3and be-lowÀ0.571eA˚À3.An ORTEP21view is given in Figure1. Crystallographic data(excluding structure factors)have been deposited with the Cambridge Crystallographic Data Center as supplementary publication DC249662. Copies of the data can be obtained,free of charge,on appli-cation to CCDC,12Union Road,Cambridge,CB21EZ,UK [fax:+44(0)1223336033or e-mail:deposit@ccdc.cam. ]References and notes1.Giles,G.I.;Jacob,C.Biol.Chem.2002,383,375–388.2.Huang,K.P.;Huang,F.L.Biochem.Pharmacol.2002,64,1049–1056.3.Giles,G.I.;Tasker,K.M.;Collins,C.;Giles,N.M.;O’Rourke,E.;Jacob,C.Biochem.J.2002,364,579–585.4.Rat,M.;Alves de Sousa,R.;Vaissermann,J.;Leduc,P.;Mansuy,D.;Artaud,I.J.Inorg.Biochem.2001,84,207–213.5.Chatel,S.;Chauvin,A.S.;Tuchagues,J.P.;Leduc,P.;Bill,E.;Chottard,J.C.;Mansuy,D.;Artaud,I.Inorg.Chim.Acta2002, 336,19–28.6.Goodrow,M.H.;Musker,W.K.Synthesis1981,6,457–459.7.Houk,J.;Whitesides,G.M.Tetrahedron1989,45,92–102.2470 E.Bourl e s et al./Tetrahedron63(2007)2466–24718.(a)Ranganathan,S.;Muraleedharan,K.M.;Bharadwaj,P.;Chatterj,I.D.;Karle,I.Tetrahedron2002,58,2861–2874;(b)Ranganathan,S.;Muraleedharan,K.M.;Vairamani,M.;Kunwar,A.C.;Sankar,mun.2002,314–315.9.(a)Tsagkalidis,W.;Rehder,D.J.Biol.Inorg.Chem.1996,507–514;(b)Tsagkalidis,W.;Rodewald, D.;Rehder, D.Inorg.Chem.1995,34,1943–1945.i,C.-H.;Reibenspies,J.H.;Darensbourg,M.Y.Chem.Commun.1999,2473–2474.11.Fox,S.;Stibrany,R.T.;Potenza,J.A.;Knapp,S.;Shugar,H.J.Inorg.Chem.2000,39,4950–4961.12.Hanss,J.;Kr€u ger,H.-J.Angew.Chem.,Int.Ed.1998,37,360–363.13.Chan,T.-L.;Poon,C.-D.;Mak,T.C.W.Acta Crystallogr.1986,C42,897–900.14.Jorgensen,F.S.;Snyder,.Chem.1980,45,1015–1020.15.(a)Kice,J.L.;Large,G.B.Tetrahedron Lett.1965,3537–3541;(b)Juaristi,E.;Cruz-Sanchez,.Chem.1988,53,3334–3338;(c)Oshida,H.;Ishii,A.;Nakayama,J.Tetrahedron Lett.2002,43,5033–5037;(d)Oshida,H.;Ishii,A.;Nakayama,.Chem.2004,69,1695–1703.16.(a)Freeman,F.;Angeletakis,C.N.J.Am.Chem.Soc.1983,105,4039–4049;(b)Folkins,P.L.;Harpp,D.N.J.Am.Chem.Soc.1993,115,3066–3070.17.Bourl e s,E.;Alves de Sousa,R.;Galardon,E.;Giorgi,M.;Artaud,I.Angew.Chem.,Int.Ed.2005,44,6162–6165. 18.(a)Kice,J.L.;Liu,.Chem.1979,44,1918–1923;(b)Oae,S.;Takata,T.;Kim,Y.H.Tetrahedron Lett.1977,48,4219–4222.19.Sheldrick,G.M.SHELXS97.Program for Solution of CrystalStructures;University of G€o ttingen:G€o ttingen,Germany, 1990.20.Sheldrick,G.M.;Schneider,T.R.SHELXL:High ResolutionReﬁnement,Methods in Enzymology,277;Carter,C.W.,Jr., Sweet,L.M.,Eds.;Academic:San Diego,CA,1997;pp319–343.21.Johnson,C.K.ORTEP.A Thermal Ellipsoid Plotting Program;Oak Ridge National Laboratories:Oak Ridge,TN,1976.2471E.Bourl e s et al./Tetrahedron63(2007)2466–2471。

氧化态势英文

氧化态势英文Oxidation SituationThe world we live in is a delicate balance of various chemical reactions, and one of the most crucial among them is the process of oxidation. Oxidation, a fundamental chemical reaction, plays a pivotal role in shaping the very fabric of our existence, from the air we breathe to the energy that powers our lives. In this essay, we will explore the intricacies of oxidation and its far-reaching implications on our planet and our daily lives.At its core, oxidation is a chemical reaction in which a substance loses electrons, resulting in an increase in its oxidation state. This process is ubiquitous in nature, occurring in everything from the rusting of metal to the cellular respiration that sustains life. The importance of oxidation cannot be overstated as it is integral to numerous essential processes that sustain our world.One of the most well-known examples of oxidation is the rusting of iron. When iron is exposed to air and moisture, it undergoes a series of chemical reactions that cause it to slowly deteriorate and transform into a reddish-brown substance known as iron oxide. Thisprocess not only affects the structural integrity of the metal but also has significant implications for industries that rely on iron-based materials. Engineers and architects must account for the effects of oxidation when designing structures, vehicles, and infrastructure to ensure their longevity and safety.Beyond the realm of industry, oxidation also plays a crucial role in the natural world. In the atmosphere, the process of oxidation is responsible for the formation of ozone, a gas that shields the Earth from the harmful effects of ultraviolet radiation. Ozone, created through the interaction of oxygen molecules and solar energy, acts as a protective layer, filtering out these damaging rays and maintaining a habitable environment for life on our planet.Oxidation also lies at the heart of the carbon cycle, a fundamental process that regulates the exchange of carbon between the Earth's various systems, including the atmosphere, biosphere, and lithosphere. Through the process of photosynthesis, plants absorb carbon dioxide from the air and, using the energy from the sun, convert it into organic compounds, releasing oxygen in the process. This oxygen is then utilized by living organisms, including humans, in the process of cellular respiration, where it is combined with glucose to produce energy. The carbon, in turn, is released back into the atmosphere as carbon dioxide, completing the cycle.The delicate balance of this cycle is crucial for maintaining the Earth's atmospheric composition and climate. Disruptions to the carbon cycle, often caused by human activities such as the burning of fossil fuels, can lead to an imbalance in the levels of greenhouse gases, contributing to climate change and its far-reaching consequences.Oxidation also plays a crucial role in the human body, where it is responsible for the generation of energy through the process of cellular respiration. In this process, oxygen is used to break down glucose and other organic compounds, releasing the energy stored within these molecules. This energy is then used to power the various functions of the body, from the beating of the heart to the firing of neurons in the brain.However, the process of oxidation can also have negative consequences for the human body. Excessive oxidation, known as oxidative stress, can lead to the formation of harmful free radicals, which can damage cells and contribute to the development of various diseases, including cancer, heart disease, and neurodegenerative disorders. To combat this, the body has developed a complex system of antioxidants, which work to neutralize these free radicals and maintain a healthy balance of oxidation within the cells.The importance of oxidation extends far beyond the realms ofindustry, the natural world, and human health. In the field of energy production, oxidation plays a crucial role in the generation of electricity and the powering of various technologies. The burning of fossil fuels, for example, is a process of oxidation that releases the energy stored within these compounds, which can then be harnessed to generate electricity and power our homes, businesses, and transportation systems.Similarly, the development of renewable energy sources, such as solar and wind power, also relies on the principles of oxidation. In the case of solar power, the interaction between photons of light and the electrons in solar cells leads to the generation of an electrical current, a process that is fundamentally driven by the principles of oxidation and reduction.As we look to the future, the understanding and management of oxidation will become increasingly crucial in addressing the pressing challenges facing our world. From the development of more efficient and sustainable energy sources to the design of materials that are resistant to corrosion, the ability to harness and control the power of oxidation will be key to ensuring a brighter and more sustainable future for all.In conclusion, the oxidation situation is a complex and multifaceted phenomenon that permeates every aspect of our lives, from thenatural world to the technological innovations that power our societies. By deepening our understanding of this fundamental chemical process, we can unlock new possibilities for addressing the challenges of our time and shaping a better tomorrow for generations to come.。

routine练习题

routine练习题一、词汇练习1. 选择正确的单词填空：1. I usually _______ to work bus.2. She _______ her homework every evening.A. doesB. doC. does not doD. doesn't do3. They _______ a movie last night.A. watchB. watchesC. watchedD. watching2. 选择正确的词组：1. I _______ (go, going) to the gym this morning.2. He _______ (be, is) late for school again.3. She _______ (do, does) her homework every day.3. 选择正确的形容词：1. This is a _______ (good, bad) book.2. She is a _______ (smart, silly) girl.3. The weather is very _______ (hot, cold) today.二、语法练习1. 选择正确的时态：1. I _______ (go, went) to the park yesterday.2. She _______ (be, was) happy when she received the gift.3. They _______ (do, did) their homework last night.2. 选择正确的语态：1. The teacher _______ (teach, is taught) Mr. Wang.2. The book _______ (write, is written) a famous author.3. The letter _______ (send, is sent) to her last week.3. 选择正确的连词：1. I _______ (go, am going) to the movies, _______ (because, because of) I have free time.2. She _______ (like, likes) coffee, _______ (but, but) she doesn't like tea.3. I _______ (finish, finished) my homework, _______ (so, so) I can go out now.三、阅读理解1. 阅读短文，回答问题：1. What is the main idea of the passage?2. Who is the main character in the story?3. What happens at the end of the passage?2. 阅读文章，判断正误：1. The story is about a boy who goes to the park every weekend.2. The boy meets his friends at the park and they play games together.3. The boy goes home after playing games with his friends.3. 阅读文章，找出关键信息：1. What is the author's favorite color?2. Why does the author like this color?3. What does the author think about other colors?四、写作练习1. 介绍动物的名字和种类。

Principles of Plasma Discharges and Materials Processing9

CHAPTER8MOLECULAR COLLISIONS8.1INTRODUCTIONBasic concepts of gas-phase collisions were introduced in Chapter3,where we described only those processes needed to model the simplest noble gas discharges: electron–atom ionization,excitation,and elastic scattering;and ion–atom elastic scattering and resonant charge transfer.In this chapter we introduce other collisional processes that are central to the description of chemically reactive discharges.These include the dissociation of molecules,the generation and destruction of negative ions,and gas-phase chemical reactions.Whereas the cross sections have been measured reasonably well for the noble gases,with measurements in reasonable agreement with theory,this is not the case for collisions in molecular gases.Hundreds of potentially signiﬁcant collisional reactions must be examined in simple diatomic gas discharges such as oxygen.For feedstocks such as CF4/O2,SiH4/O2,etc.,the complexity can be overwhelming.Furthermore,even when the signiﬁcant processes have been identiﬁed,most of the cross sections have been neither measured nor calculated. Hence,one must often rely on estimates based on semiempirical or semiclassical methods,or on measurements made on molecules analogous to those of interest. As might be expected,data are most readily available for simple diatomic and polyatomic gases.Principles of Plasma Discharges and Materials Processing,by M.A.Lieberman and A.J.Lichtenberg. ISBN0-471-72001-1Copyright#2005John Wiley&Sons,Inc.235236MOLECULAR COLLISIONS8.2MOLECULAR STRUCTUREThe energy levels for the electronic states of a single atom were described in Chapter3.The energy levels of molecules are more complicated for two reasons. First,molecules have additional vibrational and rotational degrees of freedom due to the motions of their nuclei,with corresponding quantized energies E v and E J. Second,the energy E e of each electronic state depends on the instantaneous con-ﬁguration of the nuclei.For a diatomic molecule,E e depends on a single coordinate R,the spacing between the two nuclei.Since the nuclear motions are slow compared to the electronic motions,the electronic state can be determined for anyﬁxed spacing.We can therefore represent each quantized electronic level for a frozen set of nuclear positions as a graph of E e versus R,as shown in Figure8.1.For a mole-cule to be stable,the ground(minimum energy)electronic state must have a minimum at some value R1corresponding to the mean intermolecular separation (curve1).In this case,energy must be supplied in order to separate the atoms (R!1).An excited electronic state can either have a minimum( R2for curve2) or not(curve3).Note that R2and R1do not generally coincide.As for atoms, excited states may be short lived(unstable to electric dipole radiation)or may be metastable.Various electronic levels may tend to the same energy in the unbound (R!1)limit. Array FIGURE8.1.Potential energy curves for the electronic states of a diatomic molecule.For diatomic molecules,the electronic states are speciﬁedﬁrst by the component (in units of hÀ)L of the total orbital angular momentum along the internuclear axis, with the symbols S,P,D,and F corresponding to L¼0,+1,+2,and+3,in analogy with atomic nomenclature.All but the S states are doubly degenerate in L.For S states,þandÀsuperscripts are often used to denote whether the wave function is symmetric or antisymmetric with respect to reﬂection at any plane through the internuclear axis.The total electron spin angular momentum S (in units of hÀ)is also speciﬁed,with the multiplicity2Sþ1written as a preﬁxed superscript,as for atomic states.Finally,for homonuclear molecules(H2,N2,O2, etc.)the subscripts g or u are written to denote whether the wave function is sym-metric or antisymmetric with respect to interchange of the nuclei.In this notation, the ground states of H2and N2are both singlets,1Sþg,and that of O2is a triplet,3SÀg .For polyatomic molecules,the electronic energy levels depend on more thanone nuclear coordinate,so Figure8.1must be generalized.Furthermore,since there is generally no axis of symmetry,the states cannot be characterized by the quantum number L,and other naming conventions are used.Such states are often speciﬁed empirically through characterization of measured optical emission spectra.Typical spacings of low-lying electronic energy levels range from a few to tens of volts,as for atoms.Vibrational and Rotational MotionsUnfreezing the nuclear vibrational and rotational motions leads to additional quan-tized structure on smaller energy scales,as illustrated in Figure8.2.The simplest (harmonic oscillator)model for the vibration of diatomic molecules leads to equally spaced quantized,nondegenerate energy levelse E v¼hÀv vib vþ1 2(8:2:1)where v¼0,1,2,...is the vibrational quantum number and v vib is the linearized vibration frequency.Fitting a quadratic functione E v¼12k vib(RÀ R)2(8:2:2)near the minimum of a stable energy level curve such as those shown in Figure8.1, we can estimatev vib%k vibm Rmol1=2(8:2:3)where k vib is the“spring constant”and m Rmol is the reduced mass of the AB molecule.The spacing hÀv vib between vibrational energy levels for a low-lying8.2MOLECULAR STRUCTURE237stable electronic state is typically a few tenths of a volt.Hence for molecules in equi-librium at room temperature (0.026V),only the v ¼0level is signiﬁcantly popula-ted.However,collisional processes can excite strongly nonequilibrium vibrational energy levels.We indicate by the short horizontal line segments in Figure 8.1a few of the vibrational energy levels for the stable electronic states.The length of each segment gives the range of classically allowed vibrational motions.Note that even the ground state (v ¼0)has a ﬁnite width D R 1as shown,because from(8.2.1),the v ¼0state has a nonzero vibrational energy 1h Àv vib .The actual separ-ation D R about Rfor the ground state has a Gaussian distribution,and tends toward a distribution peaked at the classical turning points for the vibrational motion as v !1.The vibrational motion becomes anharmonic and the level spa-cings tend to zero as the unbound vibrational energy is approached (E v !D E 1).FIGURE 8.2.Vibrational and rotational levels of two electronic states A and B of a molecule;the three double arrows indicate examples of transitions in the pure rotation spectrum,the rotation–vibration spectrum,and the electronic spectrum (after Herzberg,1971).238MOLECULAR COLLISIONSFor E v.D E1,the vibrational states form a continuum,corresponding to unbound classical motion of the nuclei(breakup of the molecule).For a polyatomic molecule there are many degrees of freedom for vibrational motion,leading to a very compli-cated structure for the vibrational levels.The simplest(dumbbell)model for the rotation of diatomic molecules leads to the nonuniform quantized energy levelse E J¼hÀ22I molJ(Jþ1)(8:2:4)where I mol¼m Rmol R2is the moment of inertia and J¼0,1,2,...is the rotational quantum number.The levels are degenerate,with2Jþ1states for the J th level. The spacing between rotational levels increases with J(see Figure8.2).The spacing between the lowest(J¼0to J¼1)levels typically corresponds to an energy of0.001–0.01V;hence,many low-lying levels are populated in thermal equilibrium at room temperature.Optical EmissionAn excited molecular state can decay to a lower energy state by emission of a photon or by breakup of the molecule.As shown in Figure8.2,the radiation can be emitted by a transition between electronic levels,between vibrational levels of the same electronic state,or between rotational levels of the same electronic and vibrational state;the radiation typically lies within the optical,infrared,or microwave frequency range,respectively.Electric dipole radiation is the strongest mechanism for photon emission,having typical transition times of t rad 10À9s,as obtained in (3.4.13).The selection rules for electric dipole radiation areDL¼0,+1(8:2:5a)D S¼0(8:2:5b) In addition,for transitions between S states the only allowed transitions areSþÀ!Sþand SÀÀ!SÀ(8:2:6) and for homonuclear molecules,the only allowed transitions aregÀ!u and uÀ!g(8:2:7) Hence homonuclear diatomic molecules do not have a pure vibrational or rotational spectrum.Radiative transitions between electronic levels having many different vibrational and rotational initial andﬁnal states give rise to a structure of emission and absorption bands within which a set of closely spaced frequencies appear.These give rise to characteristic molecular emission and absorption bands when observed8.2MOLECULAR STRUCTURE239using low-resolution optical spectrometers.As for atoms,metastable molecular states having no electric dipole transitions to lower levels also exist.These have life-times much exceeding10À6s;they can give rise to weak optical band structures due to magnetic dipole or electric quadrupole radiation.Electric dipole radiation between vibrational levels of the same electronic state is permitted for molecules having permanent dipole moments.In the harmonic oscillator approximation,the selection rule is D v¼+1;weaker transitions D v¼+2,+3,...are permitted for anharmonic vibrational motion.The preceding description of molecular structure applies to molecules having arbi-trary electronic charge.This includes neutral molecules AB,positive molecular ions ABþ,AB2þ,etc.and negative molecular ions ABÀ.The potential energy curves for the various electronic states,regardless of molecular charge,are commonly plotted on the same diagram.Figures8.3and8.4give these for some important electronic statesof HÀ2,H2,and Hþ2,and of OÀ2,O2,and Oþ2,respectively.Examples of both attractive(having a potential energy minimum)and repulsive(having no minimum)states can be seen.The vibrational levels are labeled with the quantum number v for the attrac-tive levels.The ground states of both Hþ2and Oþ2are attractive;hence these molecular ions are stable against autodissociation(ABþ!AþBþor AþþB).Similarly,the ground states of H2and O2are attractive and lie below those of Hþ2and Oþ2;hence they are stable against autodissociation and autoionization(AB!ABþþe).For some molecules,for example,diatomic argon,the ABþion is stable but the AB neutral is not stable.For all molecules,the AB ground state lies below the ABþground state and is stable against autoionization.Excited states can be attractive or repulsive.A few of the attractive states may be metastable;some examples are the 3P u state of H2and the1D g,1Sþgand3D u states of O2.Negative IonsRecall from Section7.2that many neutral atoms have a positive electron afﬁnity E aff;that is,the reactionAþeÀ!AÀis exothermic with energy E aff(in volts).If E aff is negative,then AÀis unstable to autodetachment,AÀ!Aþe.A similar phenomenon is found for negative molecular ions.A stable ABÀion exists if its ground(lowest energy)state has a potential minimum that lies below the ground state of AB.This is generally true only for strongly electronegative gases having large electron afﬁnities,such as O2 (E aff%1:463V for O atoms)and the halogens(E aff.3V for the atoms).For example,Figure8.4shows that the2P g ground state of OÀ2is stable,with E aff% 0:43V for O2.For weakly electronegative or for electropositive gases,the minimum of the ground state of ABÀgenerally lies above the ground state of AB,and ABÀis unstable to autodetachment.An example is hydrogen,which is weakly electronegative(E aff%0:754V for H atoms).Figure8.3shows that the2Sþu ground state of HÀ2is unstable,although the HÀion itself is stable.In an elec-tropositive gas such as N2(E aff.0),both NÀ2and NÀare unstable. 240MOLECULAR COLLISIONS8.3ELECTRON COLLISIONS WITH MOLECULESThe interaction time for the collision of a typical (1–10V)electron with a molecule is short,t c 2a 0=v e 10À16–10À15s,compared to the typical time for a molecule to vibrate,t vib 10À14–10À13s.Hence for electron collisional excitation of a mole-cule to an excited electronic state,the new vibrational (and rotational)state canbeFIGURE 8.3.Potential energy curves for H À2,H 2,and H þ2.(From Jeffery I.Steinfeld,Molecules and Radiation:An Introduction to Modern Molecular Spectroscopy ,2d ed.#MIT Press,1985.)8.3ELECTRON COLLISIONS WITH MOLECULES 241FIGURE 8.4.Potential energy curves for O À2,O 2,and O þ2.(From Jeffery I.Steinfeld,Molecules and Radiation:An Introduction to Modern Molecular Spectroscopy ,2d ed.#MIT Press,1985.)242MOLECULAR COLLISIONS8.3ELECTRON COLLISIONS WITH MOLECULES243 determined by freezing the nuclear motions during the collision.This is known as the Franck–Condon principle and is illustrated in Figure8.1by the vertical line a,showing the collisional excitation atﬁxed R to a high quantum number bound vibrational state and by the vertical line b,showing excitation atﬁxed R to a vibra-tionally unbound state,in which breakup of the molecule is energetically permitted. Since the typical transition time for electric dipole radiation(t rad 10À9–10À8s)is long compared to the dissociation( vibrational)time t diss,excitation to an excited state will generally lead to dissociation when it is energetically permitted.Finally, we note that the time between collisions t c)t rad in typical low-pressure processing discharges.Summarizing the ordering of timescales for electron–molecule collisions,we havet at t c(t vib t diss(t rad(t cDissociationElectron impact dissociation,eþABÀ!AþBþeof feedstock gases plays a central role in the chemistry of low-pressure reactive discharges.The variety of possible dissociation processes is illustrated in Figure8.5.In collisions a or a0,the v¼0ground state of AB is excited to a repulsive state of AB.The required threshold energy E thr is E a for collision a and E a0for Array FIGURE8.5.Illustrating the variety of dissociation processes for electron collisions with molecules.collision a0,and it leads to an energy after dissociation lying between E aÀE diss and E a0ÀE diss that is shared among the dissociation products(here,A and B). Typically,E aÀE diss few volts;consequently,hot neutral fragments are typically generated by dissociation processes.If these hot fragments hit the substrate surface, they can profoundly affect the process chemistry.In collision b,the ground state AB is excited to an attractive state of AB at an energy E b that exceeds the binding energy E diss of the AB molecule,resulting in dissociation of AB with frag-ment energy E bÀE diss.In collision b0,the excitation energy E b0¼E diss,and the fragments have low energies;hence this process creates fragments having energies ranging from essentially thermal energies up to E bÀE diss few volts.In collision c,the AB atom is excited to the bound excited state ABÃ(labeled5),which sub-sequently radiates to the unbound AB state(labeled3),which then dissociates.The threshold energy required is large,and the fragments are hot.Collision c can also lead to dissociation of an excited state by a radiationless transfer from state5to state4near the point where the two states cross:ABÃðboundÞÀ!ABÃðunboundÞÀ!AþBÃThe fragments can be both hot and in excited states.We discuss such radiationless electronic transitions in the next section.This phenomenon is known as predisso-ciation.Finally,a collision(not labeled in theﬁgure)to state4can lead to dis-sociation of ABÃ,again resulting in hot excited fragments.The process of electron impact excitation of a molecule is similar to that of an atom,and,consequently,the cross sections have a similar form.A simple classical estimate of the dissociation cross section for a level having excitation energy U1can be found by requiring that an incident electron having energy W transfer an energy W L lying between U1and U2to a valence electron.Here,U2is the energy of the next higher level.Then integrating the differential cross section d s[given in(3.4.20)and repeated here],d s¼pe24021Wd W LW2L(3:4:20)over W L,we obtains diss¼0W,U1pe24pe021W1U1À1WU1,W,U2pe24021W1U1À1U2W.U28>>>>>><>>>>>>:(8:3:1)244MOLECULAR COLLISIONSLetting U2ÀU1(U1and introducing voltage units W¼e E,U1¼e E1and U2¼e E2,we haves diss¼0E,E1s0EÀE11E1,E,E2s0E2ÀE1EE.E28>>>><>>>>:(8:3:2)wheres0¼pe4pe0E12(8:3:3)We see that the dissociation cross section rises linearly from the threshold energy E thr%E1to a maximum value s0(E2ÀE1)=E thr at E2and then falls off as1=E. Actually,E1and E2can depend on the nuclear separation R.In this case,(8.3.2) should be averaged over the range of R s corresponding to the ground-state vibrational energy,leading to a broadened dependence of the average cross section on energy E.The maximum cross section is typically of order10À15cm2. Typical rate constants for a single dissociation process with E thr&T e have an Arrhenius formK diss/K diss0expÀE thr T e(8:3:4)where K diss0 10À7cm3=s.However,in some cases E thr.T e.For excitation to an attractive state,an appropriate average over the fraction of the ground-state vibration that leads to dissociation must be taken.Dissociative IonizationIn addition to normal ionization,eþABÀ!ABþþ2eelectron–molecule collisions can lead to dissociative ionizationeþABÀ!AþBþþ2eThese processes,common for polyatomic molecules,are illustrated in Figure8.6.In collision a having threshold energy E iz,the molecular ion ABþis formed.Collisionsb andc occur at higher threshold energies E diz and result in dissociative ionization,8.3ELECTRON COLLISIONS WITH MOLECULES245leading to the formation of fast,positively charged ions and neutrals.These cross sections have a similar form to the Thompson ionization cross section for atoms.Dissociative RecombinationThe electron collision,e þAB þÀ!A þB Ãillustrated as d and d 0in Figure 8.6,destroys an electron–ion pair and leads to the production of fast excited neutral fragments.Since the electron is captured,it is not available to carry away a part of the reaction energy.Consequently,the collision cross section has a resonant character,falling to very low values for E ,E d and E .E d 0.However,a large number of excited states A Ãand B Ãhaving increasing principal quantum numbers n and energies can be among the reaction products.Consequently,the rate constants can be large,of order 10À7–10À6cm 3=s.Dissocia-tive recombination to the ground states of A and B cannot occur because the potential energy curve for AB þis always greater than the potential energycurveFIGURE 8.6.Illustration of dissociative ionization and dissociative recombination for electron collisions with molecules.246MOLECULAR COLLISIONSfor the repulsive state of AB.Two-body recombination for atomic ions or for mol-ecular ions that do not subsequently dissociate can only occur with emission of a photon:eþAþÀ!Aþh n:As shown in Section9.2,the rate constants are typically three toﬁve orders of magnitude lower than for dissociative recombination.Example of HydrogenThe example of H2illustrates some of the inelastic electron collision phenomena we have discussed.In order of increasing electron impact energy,at a threshold energy of 8:8V,there is excitation to the repulsive3Sþu state followed by dissociation into two fast H fragments carrying 2:2V/atom.At11.5V,the1Sþu bound state is excited,with subsequent electric dipole radiation in the ultraviolet region to the1Sþg ground state.At11.8V,there is excitation to the3Sþg bound state,followedby electric dipole radiation to the3Sþu repulsive state,followed by dissociation with 2:2V/atom.At12.6V,the1P u bound state is excited,with UV emission tothe ground state.At15.4V,the2Sþg ground state of Hþ2is excited,leading to the pro-duction of Hþ2ions.At28V,excitation of the repulsive2Sþu state of Hþ2leads to thedissociative ionization of H2,with 5V each for the H and Hþfragments.Dissociative Electron AttachmentThe processes,eþABÀ!AþBÀproduce negative ion fragments as well as neutrals.They are important in discharges containing atoms having positive electron afﬁnities,not only because of the pro-duction of negative ions,but because the threshold energy for production of negative ion fragments is usually lower than for pure dissociation processes.A variety of pro-cesses are possible,as shown in Figure8.7.Since the impacting electron is captured and is not available to carry excess collision energy away,dissociative attachment is a resonant process that is important only within a narrow energy range.The maximum cross sections are generally much smaller than the hard-sphere cross section of the molecule.Attachment generally proceeds by collisional excitation from the ground AB state to a repulsive ABÀstate,which subsequently either auto-detaches or dissociates.The attachment cross section is determined by the balance between these processes.For most molecules,the dissociation energy E diss of AB is greater than the electron afﬁnity E affB of B,leading to the potential energy curves shown in Figure8.7a.In this case,the cross section is large only for impact energies lying between a minimum value E thr,for collision a,and a maximum value E0thr for8.3ELECTRON COLLISIONS WITH MOLECULES247FIGURE 8.7.Illustration of a variety of electron attachment processes for electron collisions with molecules:(a )capture into a repulsive state;(b )capture into an attractive state;(c )capture of slow electrons into a repulsive state;(d )polar dissociation.248MOLECULAR COLLISIONScollision a 0.The fragments are hot,having energies lying between minimum and maximum values E min ¼E thr þE affB ÀE diss and E max ¼E 0thr þE af fB ÀE diss .Since the AB Àstate lies above the AB state for R ,R x ,autodetachment can occur as the mol-ecules begin to separate:AB À!AB þe.Hence the cross section for production of negative ions can be much smaller than that for excitation of the AB Àrepulsive state.As a crude estimate,for the same energy,the autodetachment rate is ﬃﬃﬃﬃﬃﬃﬃﬃﬃﬃﬃﬃﬃM R =m p 100times the dissociation rate of the repulsive AB Àmolecule,where M R is the reduced mass.Hence only one out of 100excitations lead to dissociative attachment.Excitation to the AB Àbound state can also lead to dissociative attachment,as shown in Figure 8.7b .Here the cross section is signiﬁcant only for E thr ,E ,E 0thr ,but the fragments can have low energies,with a minimum energy of zero and a maximum energy of E 0thr þE affB ÀE diss .Collision b,e þAB À!AB ÀÃdoes not lead to production of AB Àions because energy and momentum are not gen-erally conserved when two bodies collide elastically to form one body (see Problem3.12).Hence the excited AB ÀÃion separates,AB ÀÃÀ!e þABunless vibrational radiation or collision with a third body carries off the excess energy.These processes are both slow in low-pressure discharges (see Section 9.2).At high pressures (say,atmospheric),three-body attachment to form AB Àcan be very important.For a few molecules,such as some halogens,the electron afﬁnity of the atom exceeds the dissociation energy of the neutral molecule,leading to the potential energy curves shown in Figure 8.7c .In this case the range of electron impact ener-gies E for excitation of the AB Àrepulsive state includes E ¼0.Consequently,there is no threshold energy,and very slow electrons can produce dissociative attachment,resulting in hot neutral and negative ion fragments.The range of R s over which auto-detachment can occur is small;hence the maximum cross sections for dissociative attachment can be as high as 10À16cm 2.A simple classical estimate of electron capture can be made using the differential scattering cross section for energy loss (3.4.20),in a manner similar to that done for dissociation.For electron capture to an energy level E 1that is unstable to autode-tachment,and with the additional constraint for capture that the incident electron energy lie within E 1and E 2¼E 1þD E ,where D E is a small energy difference characteristic of the dissociative attachment timescale,we obtain,in place of (8.3.2),s att¼0E ,E 1s 0E ÀE 1E 1E 1,E ,E 20E .E 28>><>>:(8:3:5)8.3ELECTRON COLLISIONS WITH MOLECULES 249wheres 0%p m M R 1=2e 4pe 0E 1 2(8:3:6)The factor of (m =M R )1=2roughly gives the fraction of excited states that do not auto-detach.We see that the dissociative attachment cross section rises linearly at E 1to a maximum value s 0D E =E 1and then falls abruptly to zero.As for dissociation,E 1can depend strongly on the nuclear separation R ,and (8.3.5)must be averaged over the range of E 1s corresponding to the ground state vibrational motion;e.g.,from E thr to E 0thr in Figure 8.7a .Because generally D E (E 0thr ÀE thr ,we can write (8.3.5)in the forms att %p m M R 1=2e 4pe 0 2(D E )22E 1d (E ÀE 1)(8:3:7)where d is the Dirac delta ing (8.3.7),the average over the vibrational motion can be performed,leading to a cross section that is strongly peaked lying between E thr and E 0thr .We leave the details of the calculation to a problem.Polar DissociationThe process,e þAB À!A þþB Àþeproduces negative ions without electron capture.As shown in Figure 8.7d ,the process proceeds by excitation of a polar state A þand B Àof AB Ãthat has a separ-ated atom limit of A þand B À.Hence at large R ,this state lies above the A þB ground state by the difference between the ionization potential of A and the electron afﬁnity of B.The polar state is weakly bound at large R by the Coulomb attraction force,but is repulsive at small R .The maximum cross section and the dependence of the cross section on electron impact energy are similar to that of pure dissociation.The threshold energy E thr for polar dissociation is generally large.The measured cross section for negative ion production by electron impact in O 2is shown in Figure 8.8.The sharp peak at 6.5V is due to dissociative attachment.The variation of the cross section with energy is typical of a resonant capture process.The maximum cross section of 10À18cm 2is quite low because autode-tachment from the repulsive O À2state is strong,inhibiting dissociative attachment.The second gradual maximum near 35V is due to polar dissociation;the variation of the cross section with energy is typical of a nonresonant process.250MOLECULAR COLLISIONS。

酚与氯化胆碱形成低共熔溶剂

Separation and Puriﬁcation Technology 63(2008)710–715Contents lists available at ScienceDirectSeparation and PuriﬁcationTechnologyj o u r n a l h o m e p a g e :w w w.e l s e v i e r.c o m /l o c a t e /s e p p urShort communicationHighly efﬁcient extraction of phenols and aromatic amines into novel ionic liquids incorporating quaternary ammonium cationVladimir M.Egorov,Svetlana V.Smirnova,Igor V.Pletnev ∗Department of Chemistry,M.V.Lomonosov Moscow State University,1/3Leninskiye gory,119992Moscow,Russiaa r t i c l e i n f o Article history:Received 13May 2008Received in revised form 26June 2008Accepted 28June 2008Keywords:Ionic liquidsLiquid–liquid extraction PhenolsAromatic aminesa b s t r a c tTwo novel hydrophobic room temperature ionic liquids (RTIL)incorporating quaternary ammonium cations:tetrahexylammonium dihexylsulfosuccinate (THADHSS)and trioctylmethylammonium salicylate (TOMAS)have been obtained.The mutual solubility of the both RTILs with water and their Reichardt’s polarity index have been measured.The extraction of aromatic amines and phenols into novel RTILs and two 1-alkyl-3-methylimidazolium bis (triﬂuoromethanesulfonyl)amides has been studied.The depen-dences of RTIL–water distribution ratio for the studied liquids on the phase volume ratio,the time of phase contact,pH value of aqueous solutions and the solute concentration have been obtained.In some cases,the solute distribution ratios for ammonium-based RTILs are as high as n ×104that is much greater than for imidazolium ones.Notably,unlike the case of imidazolium-based RTILs,the quantitative extraction into ammonium RTILs is achieved even at the phase volume ratio V RTIL :V w =1:20.©2008Elsevier B.V.All rights reserved.1.IntroductionRoom temperature ionic liquids (RTIL),which are organic or organoelement salts liquid at room temperature,have nowadays a growing diversity of applications in chemistry and technology [1,2].The advantages of room temperature ionic liquids include wide liq-uid range,high heat capacity,high thermal and chemical stability [3,4].As opposed to conventional organic solvents,most RTILs are non-ﬂammable,have low vapor pressure and good electrochemical properties (electric conductivity,wide electrochemical window)[2–5].It is important that modiﬁcation of cationic or anionic parts of RTIL may enable a ﬁne-tuning of physical and chemical properties [6,7].Room temperature ionic liquids is an attractive alternative to conventional organic solvents in organic synthesis [1],catalysis [8],biopolymers processing [9–11],electrochemistry and electro-analysis [5,12–14],biochemistry [15],analytical chemistry [16].Furthermore,RTILs have a considerable potential as extraction sol-vents and may serve as a key to the design of more environmentally benign separation processes.However,the most abundant 1,3-dialkylimidazolium ionic liq-uids have some limitations on use,the most important being their high cost.That is why the search for new cheaper ionic liquids with improved characteristics is of current interest.As was indicated∗Corresponding author.Tel.:+74959395464;fax:+74959394675.E-mail address:pletnev@analyt.chem.msu.ru (I.V.Pletnev).elsewhere [17,18],some quaternary ammonium or phosphonium-based RTILs look the promising alternative:they are relatively cheap and easy to synthesize;some of them are water-immiscible and suitable for solvent extraction.A large number of publications devoted to liquid–liquid sep-arations with the use of RTILs have appeared within last years.The applications include extraction of simple substituted arenes [19,20],alcohols [21],carboxylic acids [22,23],and metal ions [24,25];aromatics/aliphatics separations [26,27]and fuel desul-furization [28,29].Extraction of various biological substances is another popular subject [30–32].It is worthy of mention that the majority of papers employ only imidazolium-based RTILs as extrac-tion solvents.Gathering a large array of experimental data on the extraction of representative solutes into different RTILs may give a useful information about the inﬂuence of solute/solvent structure on the partitioning of organic compounds.Phenols and aromatic amines may well serve as such representative solutes,since a wide vari-ety of substituted compounds are readily available to examine the role of structural details.Additionally,the data on the extraction of phenols have been previously reported for dialkylimidazolium hexaﬂuorophosphate RTILs (our work [33]),and the extraction of phenols and amines has been reported for tetraﬂuoroborate ones [34].We report herein on the synthesis and properties of two novel hydrophobic RTILs incorporating quaternary ammo-nium cations,tetrahexylammonium dihexylsulfosuccinate (THADHSS)and trioctylmethylammonium salicylate (TOMAS).1383-5866/$–see front matter ©2008Elsevier B.V.All rights reserved.doi:10.1016/j.seppur.2008.06.024V.M.Egorov et al./Separation and Puriﬁcation Technology63(2008)710–715711These two RTILs along with two imidazolium-based RTILs,1-hexyl-3-methylimidazolium and1-decyl-3-methylimidazolium bis(triﬂuoromethanesulfonyl)amides(HMImTf2N and DMImTf2N, respectively),have been tested as extraction solvents for recovery of aromatic amines and phenols from aqueous solution.2.Experimental2.1.ReagentsTetrahexylammonium bromide(Aldrich,99%),Aliquat®336 (trioctylmethylammonium chloride,Aldrich),sodium dihexylsul-fosuccinate(Technolog Ltd.,Russia),sodium salicylate(Panreac, RFE,USP,BP,Ph.Eur.),and2,6-diphenyl-4-(2,4,6-triphenylpyridin-1-yl)-phenolate monohydrate(Reichardt’s dye,Sigma–Aldrich, 70%)were used as received.1-Hexyl-3-methylimidazolium bis(triﬂuoromethanesulfonyl)amide(99%)was purchased at Sol-vent Innovation GmbH,Germany.1-Decyl-3-methylimidazolium bis(triﬂuoromethanesulfonyl)amide was synthesized in the Dr.A.V.Yatsenko’s group at the Department of Chemistry of the MSU.The studied solutes,phenol,4-nitrophenol,2,4-dinitrophenol,2,6-dinitrophenol,picric acid,1-naphthol,2-naphthol,aniline hydrochloride,p-toluidine,3-nitroaniline,and tryptamine hydrochloride were of reagent grade purity.Potas-sium ferrocyanide,4-aminoantipyrine,amidopyrine(analytical reagent grade),and iron(III)sulfate(reagent grade)were used for spectrophotometrical measurements.Nitric and sulfuric acids (0.1and3M),potassium hydroxide(0.1and3M),phosphate(pH 6.86)and borate(pH9.18)buffer solutions were used for pH anic solvents,acetone(reagent grade),acetoni-trile(HPLC grade),chloroform(reagent grade)were used without additional puriﬁcation.Water was freshly distilled before use.2.2.Preparation of quaternary ammonium RTIL2.2.1.Tetrahexylammonium dihexylsulfosuccinate19.42g(0.05mol)of sodium dihexylsulfosuccinate(NaDHSS) was dissolved in80ml of water at50◦C upon shaking.After complete dissolution of NaDHSS,equimolar amount(21.73g)of tetrahexylammonium bromide was added to the solution.The mixture was stirred for20min forming two phases where upper phase is RTIL.Aqueous phase was separated and RTIL phase was repeatedly rinsed with triple volume of fresh water10times upon vigorous shaking.The presence of NaBr in wash water was mon-itored by reaction with silver nitrate.After that the upper phase was collected and centrifuged for several hours to settle the emul-sion of water.A clear,colorless,viscous liquid was obtained.1H NMR(500MHz,CDCl3,␦/ppm relative to TMS):0.88(t;18H),1.33 (m;36H),1.55(m;12H),3.2(m;12H),4.1(m;3H).13C NMR (126MHz,DMSO-d6,␦/ppm relative to TMS):13.64,13.69,13.71 (CH3);20.91,21.76(C*H2CH3);21.87,24.82,24.85,25.34,27.95, 27.99,30.47,30.75,30.82(various CH2CH2);34.01(OOCC*H2CH);57.63(CHSO3);61.30(CH2N);63.89(CH2O);168.31,170.97(COOR).2.2.2.Trioctylmethylammonium salicylate40.42g(0.1mol)of trioctylmethylammonium chloride (Aliquat®336)was dissolved in200ml of acetone,and equal molar amount of sodium salicylate(16.01g)was added to the solution.The mixture was shaken for5h and left overnight.After that the precipitate wasﬁltered off and acetone was evaporated fromﬁltrate using rotary evaporator.The obtained RTIL was then rinsed with distilled water10times,and the upper RTIL phase was then centrifuged for several hours to settle the emulsion of water.Elemental analysis of the product yielded zero inorganic ash content.A clear,slightly yellowish,viscous liquid was obtained.1H NMR(500MHz,CDCl3,␦/ppm relative to TMS):0.88(t;9H),1.22(m;30H),1.53(m;6H),2.98(s;3H),3.13(m;6H),6.86(t;1H),6.92(d;1H),7.38(t;1H),7.88(d;1H),15.6(s;1H).13C NMR (126MHz,DMSO-d6,␦/ppm relative to TMS):13.80(C*H3C);21.93 (C*H2CH3);21.25,25.68,28.27,28.32,31.04(various CH2CH2);47.41(CH3N);60.50(CH2N);115.35,115.62,120.73,129.73,130.88 (aromatic C);163.17(COH);171.00(COO).1H and13C NMR data were recorded with NMR spectrometer DRX500(Bruker,Germany).2.3.Polarity measurementsFor solvatochromic polarity measurements a pinch of Reichardt’s dye on the tip of a spatula was added to3ml of studied solvent in a glass test-tube.If necessary,the mixture was ultrasonicated to completely dissolve the dye.After that the UV–vis spectrum of the solution was measured relative to distilled water(SF103spectrophotometer,Akvilon,Russia).The Dimroth–Reichardt polarity parameter E T(30)was calculated using the following equation:E T(30),kcal mol−1=28591max(1) where max is a maximum absorbance wavelength[35].2.4.Solubility measurementsThe solubility of THADHSS in water was measured conductimet-rically.A solution of THADHSS was prepared by dissolving a known amount of THADHSS in0.5L of deionized water.Then a series of cal-ibration solutions was made by dilution of the above solution,and their conductivity and the conductivity of the saturated THADHSS solution were measured.The solubility of TOMAS in water was determined spectroﬂuo-rometrically by salicylate( ex=305nm, em=405nm).The measurement of water content in water-saturated quater-nary ammonium RTILs was made using coulometric Karl Fischer titrator“Expert-007”(Econiks-Expert,Russia).2.5.Extraction procedureThe extraction was carried out in10ml polypropylene cen-trifuge test-tubes at ambient temperature(20±3◦C).The proper volumes of RTIL and pH-adjusted aqueous solution of studied com-pound were placed in a test-tube and shaken for the time necessary for extraction equilibrium to be achieved.Unless otherwise men-tioned,the phase volume ratio V IL:V w was1:3for imidazolium and 1:20for quaternary ammonium RTILs.After the necessary shaking time had elapsed,the systems with quaternary ammonium RTIL were centrifuged for2min(the centrifugation is not imperative but desirable as quaternary ammonium RTILs tend to adhere onto walls of test-tube after shaking).After that the necessary volume of aqueous phase was taken,and pH value was measured(pH-meter pH-410;combined glass microelectrode ESLK-13.7,Akvilon,Rus-sia).Finally,the determination of the solute in the aqueous phase was performed.The recovery(R,%)and the distribution ratio(D)of a solute were calculated using the following equations:R(%)=1−C wC0w100(2) D=C oC w=R100−RV wV o(3) where C0w and C w are the initial and equilibrium concentrations of the studied solute in aqueous phase,respectively(mol L−1),V w and712V.M.Egorov et al./Separation and Puriﬁcation Technology63(2008)710–715V o denote the volumes of aqueous and RTIL phases,respectively (ml).The studied solutes were monitored spectrophotometrically or spectroﬂuorometrically[36,37].Spectroscopic measurements were performed using spectrophotometer UV-2201or spectroﬂuorime-ter RF-5301PC(Shimadzu,Japan),quartz cells.Concentrations of nitrocompounds were determined by their own absorbance after adding3M KOH to pH11–12.The absorbance was measured at400nm(4-nitrophenol),359nm(2,4-dinitrophenol),360nm (2,6-dinitrophenol),356nm(picric acid),365nm(3-nitroaniline). For spectrophotometrical determination of phenol and naphthols, 1.0ml of borate buffer solution(pH9.18),0.1ml of2%wt aque-ous K3Fe(CN)6,and0.1ml of2wt%aqueous4-aminoantipyrine were added to2.5ml of the studied solution.After5min,the absorbance was measured at510nm.For determination of aromatic amines,1ml of phosphate buffer solution,0.3ml of0.1M aqueous amidopyrine and1ml of2wt%K3Fe(CN)6were added to2.5ml of amine solution.After20min,the absorbance was measured at535nm.Tryptamine was determined spectroﬂuorimetrically at ex=279nm( em=359nm).Spectrophotometrical determination of salicylate in aqueous solutions after contact with TOMAS was car-ried out using freshly prepared5×10−3mol L−1(Fe3+)solution of iron(III)sulfate;2ml of5×10−3mol L−1Fe3+solution were added to2ml of salicylate solution(pH2–3);the absorbance was mea-sured at525nm[36].3.Results and discussion3.1.Properties of the quaternary ammonium RTILsTOMAS and THADHSS are clear liquids with densities slightly less than1g cm−3(0.945and0.975,respectively).Freezing points of the both RTILs are below−10◦C.The liquids are immiscible with water.1H and13C NMR spectra conﬁrmed the identity of the obtained RTILs,and the molar cation–anion ratio calculated from1H NMR data was exactly1:1for the both RTILs.Solubility of THADHSS in water was found to be (8.6±0.2)×10−5mol L−1.Solubility of TOMAS is(2.0±0.2)×10−4mol L−1.These values are up to two orders of magnitude lower than that of common hydrophobic imidazolium-based RTILs[38].This signiﬁcantly decreases a possible RTIL loss during extraction.The obtained RTILs are hydrolytically stable at pH2–13.Solubility of water in THADHSS and TOMAS is ca.5and7wt%, respectively(Karl Fischer titration).After shaking the RTILs with water,no emulsiﬁcation was observed in both aqueous and RTIL phases.3.2.Polarity of THADHSS and TOMASPolarity is an important property of a solvent,which affects dif-ferent types of interactions between solvent and solute molecules. There exist several experimental methods for quantitative eval-uation of polarity:inverse gas chromatography,kinetic method, refractive index measurement[39].One of the most popular approaches refers to solvatochromism measured for a speciﬁc probe molecule,in particular,Reichardt’s betaine dye.The maxi-mum absorbance wavelength of this dye lies in visible spectrum and strongly depends on the nature of a solvent.In the present study we have measured the Dimroth–Reichardt’s polarity E T(30)of the novel RTILs,and three commonly used organic solvents(acetone,acetonitrile,and chloroform).The results along with literature data are shown in Table1.Table1max and E T(30)values for several solventsSolvent max(nm)E T(30)(kcal mol−1)Acetone67842.2Acetonitrile63045.4Chloroform69841.0 Dichloromethane[40]70040.8HMImTf2N[41]55251.8BMImPF6[40]a54552.5THABzO[35]b65143.9Ethanol[40]54652.4THADHSS(satd.with H2O)61546.5TOMAS(satd.with H2O)59348.2a1-Butyl-3-methylimidazolium hexaﬂuorophosphate.b Tetrahexylammonium benzoate.The E T(30)values for THADHSS and TOMAS are close to each other and comparable with those for the other known ammonium-based RTILs[35].As compared to imidazolium-based RTILs(typical E T(30)values are in between49and60[35]),the novel ionic liquids are less polar.All the measurements and literature data are given for room temperature.It is important to mention that the E T(30)values were measured for water-saturated THADHSS and TOMAS,as they are directly related to the polarity of solvents in extraction conditions.On the basis of polarity measurements one may conclude that the novel RTILs would have solvation/extraction proper-ties different from both conventional extraction solvents and imidazolium-based ionic liquids.As is shown below(see extrac-tion data in Section3.4),there exists no quantitative relationship between E T(30)and extraction efﬁciency for corresponding RTIL. However,one may note that the lower E T(30)value the more efﬁ-cient is extraction,in general.3.3.Extraction studies3.3.1.Optimization of extraction conditionsThe inﬂuence of phase contact time,phase volume ratio and concentration of an inorganic electrolyte(NaCl)on the distribution ratio has been studied on the example of2,4-dinitrophenol.The appropriate values of theﬁrst two parameters are shown in Table2.As can be seen from Table2,the time of phase contact,which is necessary to achieve extraction equilibrium,is less for the qua-ternary ammonium RTILs.Previously our group has shown that the optimal phase contact time for extraction into imidazolium-based ionic liquids weakly depends on the structure of extracted polar aromatic compound[33].That is why,and also for conditions uni-ﬁcation,in all the further experiments the phase contact time for all systems was15min.Like for the other previously studied imidazolium-based RTILs[33],the distribution ratio of2,4-dinitrophenol into both HMImTf2N and DMImTf2N dramatically decreases with increasing phase volume ratio.The3:1phase volume ratio has been chosen as optimal in order to maintain an acceptable distribution coefﬁcientTable2Phase contact time and phase volume ratio for extraction of2,4-dinitrophenol (5×10−4mol L−1;pH2)RTIL Phase contacttime(min)Phase volumeratio(V w:V RTIL) THADHSS520:1TOMAS1020:1HMImTf2N153:1DMImTf2N153:1V.M.Egorov et al./Separation and Puriﬁcation Technology 63(2008)710–715713and at the same time to minimize the quantity of RTIL,which is necessary for an extraction run.On the contrary,in the case of quaternary ammonium RTILs,the distribution ratio of 2,4-dinitrophenol weakly depends on the phase volume ratio up to 50:1.The value 20:1has been chosen for further experiments with the both quaternary ammonium RTILs in order to decrease the consumption of RTIL while sustaining a good recovery.The concentration of introduced inorganic electrolyte (NaCl)from 5×10−4to 0.5mol L −1has practically no effect on the dis-tribution ratio of 2,4-dinitrophenol.3.3.2.The effect of pH on the recovery of aromatic compoundsAll the studied solutes can be divided into two types based on their acid-base behaviour:phenols and aromatic amines.3.3.2.1.Extraction of phenols.The pH dependence of the distribu-tion ratio of unsubstituted phenol for all studied RTILs is shown in Fig.1.As can be seen,the maximal distribution ratio is observed at acidic pH,where the molecular form of phenol is predomi-nant.Upon the increase in pH the recovery of phenol into the imidazolium-based RTILs dramatically decreases,and at pH >12becomes negligible (R <10%).This is a typical behaviour for parti-tioning of phenol into imidazolium RTILs [33,34].The extraction ability of HMImTf 2N is close to that of DMImTf 2N (though less hydrophobic HMImTf 2N has a small advantage).The distribution ratios of phenol for the ammonium-based RTILs are approximately 0.5and 1order of magnitude (TOMAS and THADHSS,respectively)higher than for the imidazolium-based RTILs.The observed pH dependence of extraction clearly shows that phenol is preferably partitioned into all RTILs in undissociated (molecular)form.However,even at pH 12the recovery of phenol into the ammonium RTILs remains rather signiﬁcant (R ∼40–50%,see Fig.1).In the case of nitrophenols pH value has small effect on the recovery into quaternary ammonium RTILs,whereas pH depen-dences of distribution ratio of nitrophenols into imdazolium-based RTILs have a trend similar to that for phenol.The aforementioned results clearly point to the possibility of phenolates extraction (anion-exchange)into the quaternary ammonium RTILs,in addi-tion to extraction of a neutral solute.Naturally,the contribution of ion-exchange recovery of ionized phenols should be higher at pH >pK a of solute.Expectedly,the efﬁciency of anion-exchange extraction into the quaternary ammonium RTILs is higher for more hydrophobic nitrophenols than for phenol.The similarbehaviourFig.1.The effect of pH on distribution ratio of phenol (1×10−4mol L −1)into differ-entRTILs.Fig.2.The increase of salicylate concentrations in aqueous phase after extraction at various pH (solid line)in comparison to calculated initial concentration of 2,4-dinitrophenolate (C total =5×10−4mol L −1;dashed line)in aqueous phase.has been previously observed for the partitioning of picric acid between water and BMImPF 6[33].In order to conﬁrm a contribution of anion exchange to extraction,the concentration of salicylate in aqueous phase after extraction of 2,4-dinitrophenol (5×10−4mol L −1)into TOMAS was monitored.Evidently,anion-exchange extraction of dinitrophe-nolate should be accompanied by a release of stoichiometric quantity of RTIL anion,salicylate,to an aqueous phase.The measured concentration of salicylate after extraction at differ-ent pH was compared with the concentration of salicylate in solutions,which had also been in contact with TOMAS but did not contain 2,4-dinitrophenol (pH values of these solu-tion pairs were approximately the same).Corresponding plot is presented in Fig.2(concentration of 2,4-dinitrophenolate in aqueous phase is calculated with the use of literature pK a ,see Table 3).As can be seen,the increase in aqueous salicylate concentra-tion is higher at higher pH;at pH >7it is nearly equal to the total concentration of 2,4-dinitrophenol.Note that at pH >72,4-dinitrophenol exists mostly as anion,and its recovery into TOMAS is ca.100%.In other words,the increase of aqueous salicylate concen-tration exactly matches the concentration of extracted solute.This proves that the anion exchange mechanism is operative at pH >pK a (solute).3.3.2.2.Extraction of aromatic amines.The extraction of four aro-matic amines into RTILs has been investigated.Fig.3presents theTable 3Extraction of the studied phenols and aromatic amines into quaternary ammonium RTILs (V w :V RTIL =20:1)SolutepK a [42]log D log P OW [43,44]THADHSSTOMAS Phenol10.0 2.5 2.1 1.464-Nitrophenol 7.14 3.6 3.4 1.912,4-Dinitrophenol 4.08 4.1 3.5 1.672,6-Dinitrophenol 4.15 4.0 3.6 1.372,4,6-Trinitrophenol 0.69 3.9 3.8 1.331-Naphthol 9.85 3.8 3.4 2.852-Naphthol 9.63 3.7 3.2 2.70Aniline4.63 1.9 1.80.903-Nitroaniline 2.47 2.3 2.3 1.37p-Toluidine5.07 2.0 2.0 1.39Tryptamine10.23.52.61.55714V.M.Egorov et al./Separation and Puriﬁcation Technology 63(2008)710–715Fig.3.The effect of pH on distribution ratio of aniline (1×10−4mol L −1)into differ-ent RTILs.pH dependence of the distribution ratio of aniline for all studied RTILs.Three of the studied amines incorporate NH 2group bonded to an aromatic ring,and one (tryptamine)has an aliphatic NH 2group and indole aromatic ring.The pH dependence of extraction of aniline into imidazolium-based RTILs is typical for amines [33,34].Noteworthy,a less hydrophobic HMImTf 2N is a better extraction solvent for aniline than DMImTf 2N.The extraction of aniline into THADHSS and TOMAS is much better than into imidazolium-based RTILs.The characteristic trend of pH dependence for the extraction of aniline,p-toluidine,and m-nitroaniline into the novel RTILs is observed.Tryptamine is efﬁciently extracted into both THADHSS and TOMAS,but at the optimal pH the distribution ratio of tryptamine for THADHSS is approximately one order of magnitude higher than for TOMAS.For all the ionic liquids studied,the pH proﬁle of aniline extrac-tion is similar to that common for molecular solvents (i.e.efﬁcient extraction takes place at pH >pK a of amine),which is indicative of neutral solute recovery.Unlike phenols,aromatic amines are poorly extracted in ionizedform.parison of distribution data for RTIL/water and 1-octanol/water systems (the trendline is shown for HMImTf 2N).parison of distribution ratios of several compounds for THADHSS and TOMAS (see also Table 3).parative analysis of the extraction resultsThe results obtained in the present work show that the newly obtained quaternary ammonium-based RTILs are much more efﬁ-cient extraction solvents towards the studied aromatic compounds than common imidazolium-based RTILs.The extraction data for non-nitrated phenols and aromatic amines show that the maximal recovery is achieved for molecular forms of these compounds,the decrease in recovery closely corresponding to the respective pK a values.The data on partitioning of the studied phenols and aro-matic amines into quaternary ammonium RTILs are summarized in Table 3.The partitioning of neutral substituted aromatic molecules into imidazolium-based RTILs is often attributed to speciﬁc ␲–␲inter-actions between imidazolium ring and aromatic ring of extracted compound [19,45]or to the ability of imidazolic proton at C2to form hydrogen bonds [46].However,in the case of THADHSS and TOMAS such interactions are unlikely.We suggest that dispersive interactions of solute molecules with cation of RTIL may be a driv-ing force for the preferential partitioning of phenols and aromatic amines into quaternary ammonium RTILs.It is interesting to correlate distribution ratio of organic com-pounds with 1-octanol/water partition coefﬁcients,log P OW .Fig.4shows plot of logarithm of the maximal distribution ratio for the studied compounds (log D )into different RTILs vs.log P OW [43,44].As is clearly seen,the extraction ability of the imidazolium-based RTILs is inferior to the extraction ability of the novel quaternary ammonium RTILs and,in some cases,to that of 1-octanol.Noteworthy,there is a correlation between log P OW and log D for imidazolium-based RTILs (see a trendline in Fig.4).This corresponds well to the literature data [19,33].However,for the novel RTILs a log D –log P OW correlation is poor.This may be because of difference in extraction mechanisms between imidazolium and quaternary ammonium RTILs.At the same time,there exists a good correlation between log D obtained for the same solutes with use of THADHSS and TOMAS (Fig.5).This suggests that solvation/extraction patterns for the two ammonium RTILs be similar (note that,in general,THADHSS is more efﬁcient extraction solvent than TOMAS).4.ConclusionsTwo novel quaternary ammonium based room temperature ionic liquids (THADHSS and TOMAS)have been synthesized andV.M.Egorov et al./Separation and Puriﬁcation Technology63(2008)710–715715characterized.The Dimroth–Reichardt’s polarities of the novel RTILs,E T(30),are higher than those for the studied molecular sol-vents,but less than for imidazolium ionic liquids.Extraction of11aromatic compounds(phenols and aro-matic amines)into two imidazolium-based RTILs(HMImTf2N and DMImTf2N)and into the novel RTILs has been studied.The best recovery into the novel RTILs has been observed for nitrophenols and naphthols.The recovery of the aforementioned compounds is high(>50%at V IL:V w=1:20)in the whole studied pH range. For phenols at pH>pK a(solute)the contribution of ion-exchange mechanism to partitioning has been observed.In the case of imidazolium-based RTILs the best recovery is achieved for molec-ular form of solutes,the recovery of ionic forms being poor.It has been demonstrated that the extraction abilities of THADHSS and TOMAS well correlate with each other.Generally, THADHSS is more efﬁcient extraction solvent towards the studied compounds than TOMAS.At the same time,it has been shown that the novel RTILs are more efﬁcient extraction solvents than common imidazolium-based RTILs.AcknowledgementsWe are grateful to Dr.A.V.Yatsenko for providing a sample of DMImTf2N.Thanks are also due to Prof.S.I.Petrov for performing Karl Fischer titration,and to M.Khrenova for THADHSS solubil-ity measurements.This work was partially funded by the Russian Foundation for Basic Research(project N05-03-32976)and INTAS (project N05-1000008-8020).References[1]P.Wasserscheid,T.Welton(Eds.),Ionic Liquids in Synthesis,Wiley-VCHVerlagGmbH&CoKgaA,2002.[2]I.V.Pletnev,S.V.Smirnova,K.S.Khachatryan,V.V.Zernov,Russ.Chem.J.58(2004)51–57.[3]T.Welton,Chem.Rev.99(1999)2071–2083.[4]H.L.Ngo,K.Le Compte,L.Hargens,A.B.McEwen,Thermochim.Acta357(2000)97–102.[5]M.C.Buzzeo,R.G.Evans,pton,ChemPhysChem.5(2004)1106–1120.[6]J.G.Huddleston,A.E.Visser,W.M.Reichert,H.D.Willauer,G.A.Broker,R.D.Rogers,Green Chem.3(2001)156–164.[7]J.D.Holbrey,K.R.Seddon,J.Chem.Soc.,Dalton Trans.(1999)2133–2134.[8]T.Welton,Coord.Chem.Rev.248(2004)2459–2477.[9]R.P.Swatloski,S.K.Spear,J.D.Holbrey,R.D.Rogers,J.Am.Chem.Soc.124(2002)4974–4975.[10]V.M.Egorov,S.V.Smirnova,A.A.Formanovsky,I.V.Pletnev,Yu.A.Zolotov,Anal.Bioanal.Chem.387(2007)2263–2269.[11]H.Xie,S.Zhang,S.Li,Green Chem.8(2006)630–633.[12]J.D.Wadhawan,U.Schroder,A.Neudeck,et al.,J.Electroanal.Chem.493(2000)75–83.[13]C.Villagrán,L.Aldous,pton,et al.,J.Electroanal.Chem.588(2006)27–31.[14]N.V.Shvedene,D.V.Chernyshov,M.G.Khrenova,A.A.Formanovsky,V.E.Baulin,I.V.Pletnev,Electroanalysis18(2006)1416–1421.[15]S.Park,R.J.Kazlauskas,Curr.Opin.Biotechnol.14(2003)432–437.[16]M.Koel,Crit.Rev.Anal.Chem.35(2005)177–192.[17]N.Nishi,T.Kawakami,F.Shigematsu,M.Yamamoto,T.Kakiuchi,Green Chem.8(2006)349–355.[18]J.-P.Mikkola,P.Virtanena,R.Sjöholm,Green Chem.8(2006)250–255.[19]J.G.Huddleston,H.D.Willauer,R.P.Swatloski,A.E.Visser,R.D.Rogers,Chem.Commun.(1998)1765–1766.[20]E.Bekou,D.D.Dionysiou,R.-Y.Qian,G.D.Botsaris,ACS Symp.Ser.856(2003)544–560.[21]A.Fadeev,M.Meagher,mun.(2001)295–296.[22]J.Marták,ˇS.Schlosser,Chem.Pap.60(2006)395–398.[23]S.Carda-Broch,A.Berthod,D.W.Armstrong,Anal.Bioanal.Chem.375(2003)191–199.[24]S.Dai,Y.H.Ju,C.E.Barnes,J.Chem.Soc.,Dalton Trans.(1999)1201–1202.[25]A.E.Visser,R.P.Swatloski,W.M.Reichert,et al.,mun.(2001)135–136.[26]M.L.Dietz,J.A.Dzielawa,szak,B.A.Young,M.P.Jensen,Green Chem.5(2003)682–685.[27]A.Arce,M.J.Earle,H.Rodríguez,K.R.Seddon,Green Chem.9(2007)70–74.[28]W.-H.Lo,H.-Y.Yang,G.-T.Wei,Green Chem.5(2003)639–642.[29]C.Huang,B.Chen,J.Zhang,Z.Liu,Y.Li,Energy Fuels18(2004)1862–1864.[30]S.V.Smirnova,I.I.Torocheshnikova, A.A.Formanovsky,I.V.Pletnev,Anal.Bioanal.Chem.378(2004)1369–1375.[31]C.He,S.Li,H.Liu,K.Li,F.Liu,J.Chromatogr.A.1082(2005)143–149.[32]J.-H.Wang,D.-H.Cheng,X.-W.Chen,Z.Du,Z.-L.Fang,Anal.Chem.79(2007)620–625.[33]K.S.Khachatryan,S.V.Smirnova,I.I.Torocheshnikova,N.V.Shvedene,A.A.For-manovsky,I.V.Pletnev,Anal.Bioanal.Chem.381(2005)464–470.[34]B.Y.Pei,J.Wang,K.Wu,Y.Zhao,J.Fan,Z.Phys.Chem.221(2007)825–835.[35]C.Reichardt,Green Chem.7(2005)339–351.[36]I.M.Korenman,Photometricheskiy analiz.Metody opredeleniya organich-eskikh soedineniy(Photometric Analysis.Methods for Determination of Organic Compounds),Khimiya,Moscow,1970(in Russian).[37]R.E.Galian,A.V.Veglia,R.H.de Rossi,Analyst123(1998)1587–1591.[38]N.V.Shvedene,S.V.Borovskaya,V.V.Sviridov,E.R.Ismailova,I.V.Pletnev,Anal.Bioanal.Chem.381(2005)427–430.[39]C.Reichardt,Solvents and Solvent Effects in Organic Chemistry,Wiley-VCH,Weinheim,2003.[40]K.A.Fletcher,I.A.Storey,A.E.Hendricks,Sh.Pandey,S.Pandey,Green Chem.3(2001)210–215.[41]B.R.Mellein,S.N.V.K.Aki,dewski,J.F.Brennecke,J.Phys.Chem.B111(2007)131–138.[42]E.P.Serjeant,B.Dempsey,Ionization Constants of Organic Acids in AqueousSolution,Pergamon,Oxford,1979.[43]NCI database:http://129.43.27.140/ncidb2/.[44]Ya.I.Korenman,Koefﬁtsienty raspredeleniya organicheskikh soedineniy(Dis-tribution Coefﬁcients of Organic Compounds),Voronezh University Press, Voronezh,Russia,1992(in Russian).[45]J.Liu,Y.Chi,J.Peng,et al.,J.Chem.Eng.Data49(2004)1422–1424.[46]J.F.Huang,P.Y.Chen,I.W.Sun,S.P.Wang,Inorg.Chim.Acta320(2001)7–11.。

不对称自由基反应英文

不对称自由基反应英文Asymmetric Radical Reactions: An Insight into Their Mechanism and Applications.Introduction.Asymmetric radical reactions have emerged as a powerful tool in organic synthesis, enabling the synthesis of chiral compounds with high enantiomeric purity. These reactions differ significantly from their symmetric counterparts, as they involve the generation and utilization of chiral radicals. These chiral radicals can undergo a range of reactions, including substitution, addition, and cyclization, leading to the formation of enantiomerically enriched products.Mechanism of Asymmetric Radical Reactions.The mechanism of asymmetric radical reactions typically involves three key steps: radical generation, chiralitytransfer, and radical termination.Radical Generation.The first step involves the generation of a radical species. This can be achieved through various methods, such as photolysis, thermal decomposition, or redox reactions. The generated radical can be chiral or achiral, depending on the starting materials and the conditions used.Chirality Transfer.The second step involves the transfer of chirality from a chiral auxiliary or catalyst to the radical species. This chirality transfer can occur through covalent or non-covalent interactions between the catalyst/auxiliary and the radical. The nature of these interactions determines the stereoselectivity of the reaction.Radical Termination.The final step involves the termination of the radicalspecies, leading to the formation of the desired product. This termination can occur through various mechanisms, such as coupling with another radical species, hydrogen atom abstraction, or disproportionation.Applications of Asymmetric Radical Reactions.Asymmetric radical reactions have found widespread applications in various fields of organic synthesis, including the synthesis of natural products, pharmaceuticals, and functional materials.Synthesis of Natural Products.Natural products often possess complex chiral structures, making their synthesis challenging. Asymmetric radical reactions have proven to be effective tools for the synthesis of such chiral natural products. For example, the use of chiral radicals generated from appropriate precursors has enabled the enantioselective synthesis of alkaloids, terpenes, and amino acids.Pharmaceutical Applications.The enantiomers of chiral drugs often differ significantly in their biological activities, making it crucial to control their enantiomeric purity. Asymmetric radical reactions can be used to synthesize enantiomerically enriched chiral drugs with high selectivity. This approach has been successfully applied to the synthesis of various drugs, including anti-inflammatory agents, anticancer agents, and antiviral agents.Functional Materials.Chiral materials possess unique physical and chemical properties that make them useful in various applications, such as displays, sensors, and catalysts. Asymmetricradical reactions can be used to synthesize chiral building blocks for the preparation of such materials. For instance, chiral polymers can be synthesized by utilizing asymmetric radical polymerization reactions, leading to the formation of materials with controlled chirality and tailored properties.Conclusion.Asymmetric radical reactions have emerged as powerful tools for the synthesis of enantiomerically enriched chiral compounds. Their unique mechanism, involving chirality transfer from a chiral catalyst/auxiliary to the radical species, enables high selectivity and enantiopurity in the product. The widespread applications of asymmetric radical reactions in organic synthesis, particularly in the synthesis of natural products, pharmaceuticals, and functional materials, highlight their importance in modern chemistry.Future Perspectives.Despite the significant progress made in the field of asymmetric radical reactions, there are still numerous challenges and opportunities for further exploration.Improving Selectivity and Efficiency.One of the key challenges in asymmetric radical reactions is achieving high selectivity and efficiency. While significant progress has been made in this area, there is still room for improvement. Future research could focus on developing new chiral catalysts/auxiliaries that can promote asymmetric radical reactions with higher selectivity and efficiency.Expanding the Scope of Reactions.Currently, the scope of asymmetric radical reactions is limited by the availability of suitable precursors and the reactivity of the generated radicals. Future research could aim to expand the scope of these reactions by developing new methods for generating radicals with desired functionalities and reactivities.Applications in Sustainable Chemistry.In the context of sustainable chemistry, asymmetric radical reactions offer an attractive alternative to traditional synthetic methods. By utilizing renewableresources and mild reaction conditions, asymmetric radical reactions could contribute to the development of more sustainable synthetic routes for the preparation of chiral compounds.Integration with Other Techniques.The integration of asymmetric radical reactions with other techniques, such as photocatalysis, electrochemistry, and microfluidics, could lead to the development of new and innovative synthetic methods. By combining the advantages of these techniques, it may be possible to achieve even higher selectivity, efficiency, and scalability in asymmetric radical reactions.In conclusion, asymmetric radical reactions have emerged as powerful tools for the synthesis of enantiomerically enriched chiral compounds. While significant progress has been made in this area, there are still numerous opportunities for further exploration and development. Future research in this field could lead tothe discovery of new and innovative synthetic methods with improved selectivity, efficiency, and sustainability.。

化学专英试题及答案

化学专英试题及答案一、选择题（每题2分，共10分）1. The term "stoichiometry" refers to the:A. Study of chemical reactionsB. Calculation of amounts of reactants and products in chemical reactionsC. History of chemistryD. Physical properties of substances2. Which of the following is not a state of matter?A. SolidB. LiquidC. GasD. Energy3. The SI unit for the amount of substance is the:A. CoulombB. JouleC. MoleD. Newton4. In the periodic table, elements are arranged in order of increasing:A. Atomic massB. Atomic numberC. ElectronegativityD. Ionization energy5. The process of converting a solid to a liquid is called:A. SublimationB. VaporizationC. MeltingD. Decomposition二、填空题（每空1分，共10分）1. The chemical symbol for the element oxygen is ________.2. The law that states that the volume of a gas is directly proportional to the number of molecules is known as________'s law.3. The process of a substance changing from a liquid to a solid is called ________.4. The pH scale ranges from ________ to ________, with 7 being neutral.5. A compound that releases hydrogen ions when dissolved in water is known as an ________.三、简答题（每题5分，共20分）1. Explain what is meant by the term "valency" in chemistry.2. Describe the difference between a physical change and a chemical change.3. What is the significance of the Avogadro's number in chemistry?4. Discuss the role of catalysts in chemical reactions.四、计算题（每题10分，共20分）1. If 5 moles of a gas occupy 22.4 liters at standard temperature and pressure (STP), calculate the volume occupied by 10 moles of the same gas at STP.2. A 1.5 M solution of hydrochloric acid (HCl) is mixed witha 3.0 M solution of sodium hydroxide (NaOH) in a 1:1 volume ratio. Calculate the molarity of the resulting solution.五、实验题（每题15分，共30分）1. Describe a laboratory procedure to test for the presence of chloride ions in a solution.2. Outline the steps to prepare a standard solution of potassium permanganate (KMnO4) for titration.答案：一、选择题1. B2. D3. C4. B5. C二、填空题1. O2. Boyle3. Solidification4. 0, 145. Acid三、简答题1. Valency refers to the combining power of an element, which is the number of hydrogen atoms it can combine with or replace in a chemical reaction.2. A physical change is a change in the state or form of a substance without altering its chemical composition, while a chemical change involves a transformation that results in theformation of new substances.3. Avogadro's number (6.022 x 10^23) is significant becauseit represents the number of particles (atoms, molecules, ions, etc.) in one mole of a substance.4. Catalysts are substances that increase the rate of a chemical reaction without being consumed in the process, thus facilitating the reaction without altering the overall chemical equilibrium.四、计算题1. 44.8 liters2. 0.75 M五、实验题1. To test for chloride ions, add a small amount of silver nitrate solution to the test solution. If a white precipitate forms, it indicates the presence of chloride ions.2. To prepare a standard solution of KMnO4, dissolve a known mass of the compound in a minimal amount of distilled water, then dilute it to a known volume in a volumetric flask. The concentration can be calculated using the mass and volume of the solution.。

成都2024年07版小学六年级第六次英语第3单元测验试卷

成都2024年07版小学六年级英语第3单元测验试卷考试时间：100分钟（总分:100）B卷考试人：_________题号一二三四五总分得分一、综合题(共计100题)1、听力题：A horse is known for its ______ and speed.2、填空题：The ______ (潜力) of plants for healing is still being researched.3、听力题：A thermometer measures ______.4、听力题：The chemical formula for hydrogen peroxide is ________.5、填空题：The ________ was a major event in the history of the United States.6、听力题：The chemical formula for bismuth(III) oxide is __________.7、What is the capital of Japan?A. SeoulB. BeijingC. TokyoD. Bangkok8、What is the capital of Germany?A. BerlinB. MunichC. FrankfurtD. Hamburg9、听力题：She has a ________ (passion) for art.In a double replacement reaction, two compounds exchange _____ to form new products.11、填空题：I want to be a _______ (职业) when I grow up. It’s my dream job.12、听力题：The _______ of an object can be influenced by its shape and size.13、填空题：I like to play with my ________ (拼插玩具) to create new shapes.14、填空题：I enjoy planting _____ (多肉植物).15、听力题：Acids have a sour taste and can turn blue litmus paper ______.16、听力题：Saturn is famous for its beautiful ______.17、填空题：My sister loves to __________ (进行科学实验).18、填空题：The platypus is one of the few mammals that lay ________________ (蛋).19、听力题：Gravity pulls objects ______ to the ground.20、What do we call the imaginary line that runs from the North Pole to the South Pole?A. LatitudeB. LongitudeC. EquatorD. Meridian答案:D21、选择题：What do we call the main meal of the day?A. BreakfastB. LunchC. DinnerD. SnackWhat is the name of the famous composer known for his symphonies?A. Ludwig van BeethovenB. Wolfgang Amadeus MozartC. Johann Sebastian BachD. Pyotr Ilyich Tchaikovsky23、听力题：A solid has a definite ______ and volume.24、What do you call a person who creates visual art?A. ArtistB. DesignerC. PainterD. Sculptor答案:A25、填空题：The __________ was a time when the world faced a global pandemic. (流感大流行)26、What is the name of the famous ancient city in Greece?A. RomeB. AthensC. CairoD. Istanbul答案: B27、听力题：I like to listen to ___. (music)28、听力题：I can _______ (dance) well.29、听力题：A liquid that can dissolve a solute is called a _______.30、听力题：In a galvanic cell, chemical energy is converted into _____ energy.31、听力题：The apple tree is _______ (full) of fruit.32、What is the capital of the Galápagos Islands?a. Puerto Ayorab. San Cristóbalc. Puerto Villamild. Puerto Baquerizo Moreno答案:d33、听力题：My grandma loves to make ____ (sauces).34、填空题：I help my mom _______ (买菜) every weekend.35、Which of these is a common dairy product?A. BreadB. CheeseC. PastaD. Rice答案:B36、What do we call a baby dog?A. KittenB. PuppyC. CubD. Calf答案:B. Puppy37、填空题：The discovery of ________ has changed our understanding of physics.38、填空题：My cat enjoys chasing ______ (小虫) in the garden.39、听力题：Animals that are active at night are called __________.40、填空题：The __________ (历史的价值认知) shape our identities.41、填空题：I like to collect ______ (漫画书) featuring my favorite superheroes.42、What do we call the study of the weather?A. BiologyB. MeteorologyC. GeographyD. Climatology答案:B43、填空题：The __________ (历史的多元性) enrich dialogue.44、选择题：What do you call the act of producing food?A. AgricultureB. FarmingC. HorticultureD. All of the above45、听力题：The main function of lipids is to store _____.46、What do we call a song that tells a story?A. PoemB. BalladC. NovelD. Play答案:B47、填空题：_____ (土壤) composition affects how plants grow.48、填空题：I like to ______ (参与) in art competitions.49、听力题：A reaction that requires energy input is called an ______ reaction.50、填空题：I like to _______ my friends at school.51、What do we call the distance between two points?A. LengthB. WidthC. HeightD. Depth答案: A52、听力题：The capital of Iran is __________.53、Which animal is known for building dams?A. BeaverB. RabbitC. SquirrelD. Fox答案:A. Beaver54、How many months are in a year?A. 10B. 11C. 12D. 1355、填空题：I have a ________ that helps me build things.56、听力题：My ______ enjoys hiking in the mountains.57、听力题：My cousin is a ______. She loves to play video games.58、填空题：I like to watch ________ (电影) with my family.59、听力题：A mixture of sand and salt can be separated using ________.60、填空题：The _____ (狐狸) is often portrayed in fables.61、填空题：At the fair, I won a ________ (玩具熊) by throwing rings. It was a ________ (好运气).62、填空题：The scientist conducts _____ (实验) in the lab.63、Which of these animals can swim?A. CatB. DogC. FishD. Bird64、What is the main purpose of a museum?A. To entertainB. To educateC. To sell goodsD. To provide shelter答案:B65、What do you call the process of washing clothes?A. CleaningB. WashingC. DryingD. Folding答案: A66、选择题：What is the name of the famous painting of a woman with a mysterious smile?A. The Starry NightB. The ScreamC. The Mona LisaD. Girl with a Pearl Earring67、What do you call a large, slow-moving animal with a shell?A. TortoiseB. TurtleC. SnailD. Armadillo答案:A68、Which one of these is a flying insect?A. AntB. ButterflyC. SpiderD. Snail69、填空题：I want to paint my ________ bright red.70、选择题：What is the name of the superhero who wears a cape?A. BatmanB. Spider-ManC. Iron ManD. All of the above71、听力题：A turtle has a hard __________ for protection.72、填空题：I have a special ________ that keeps me company.73、听力题：My brother is interested in ____ (engineering).The ice cream is ________ (冷).75、填空题：My mom enjoys __________ (与朋友聚会) on weekends.76、听力题：The library has many ______. (books)77、选择题：What do we call the time of year when the leaves change color?A. WinterB. SpringC. AutumnD. Summer78、听力题：The chemical reaction that occurs in batteries involves _______ reactions.79、听力题：The chemical formula for sodium sulfate is _____.80、听力题：The baby is _____ in the stroller. (sitting)81、填空题：My friend is __________ (大方的).82、填空题：The jackrabbit can run very _________ (快).83、What is the name of the toy that spins on the ground?A. FrisbeeB. TopC. Yo-yoD. Kite84、听力题：Chemical equations show the ______ of reactions.85、填空题：The ________ (沙漠) is hot and dry.86、听力题：She is _____ (running) a race.I have a pet _____ (金鱼) in a bowl at home.88、选择题：What do you call a person who studies stars?A. BiologistB. AstronomerC. GeologistD. Chemist89、填空题：I enjoy watching ______ (电影) that tell inspiring stories.90、What is the term for the outer layer of the Earth?A. MantleB. CrustC. CoreD. Surface答案:B91、听力题：The children are _____ in the classroom. (talking)92、听力题：A ____ is a small mammal that loves to dig.93、填空题：_____ (小草) can grow in small spaces.94、听力题：Acids release hydrogen ions (H⁺) in a _____ (solution).95、What do we breathe?A. WaterB. AirC. FoodD. Light答案:B96、填空题：A _____ (植物生活) reflects the interdependence of all life forms.97、What is 2 x 3?A. 5B. 6C. 7D. 8答案:B98、填空题：This girl, ______ (这个女孩), is very athletic.99、填空题：I like to _______ my bike.100、听力题：In chemistry, a phase is a distinct _____ of matter.。

现象学及其效应英语

现象学及其效应英语English Answer:1. Introduction.Phenomenology is a philosophical and psychological movement that emphasizes the first-person perspective and the importance of lived experience. It is based on the idea that all knowledge is rooted in our own subjective experiences and that we can only understand the world through our own perceptions.2. Phenomenological Method.The phenomenological method involves bracketing all assumptions about the world and focusing on the immediate and unmediated experience of things. This is done by suspending judgment and simply describing the things we experience in the moment.3. Phenomenological Reduction.Phenomenological reduction is a process of bracketing or suspending all beliefs and assumptions about the worldin order to get to the pure essence of things. This can be done by imagining a "phenomenological epoché," in which we put all of our beliefs and assumptions in parentheses and simply focus on the things themselves.4. The Phenomenological Subject.The phenomenological subject is the first-person perspective that is the source of all experience. This is not a fixed or unchanging self, but rather a fluid andever-changing stream of consciousness.5. The Phenomenological World.The phenomenological world is the world as it is experienced by the subject. This is not an objective world that exists independently of the subject, but rather a world that is constituted by the subject's own experiences.6. The Phenomenological Attitude.The phenomenological attitude is an attitude of openness and curiosity towards the world. This attitude involves letting go of all preconceived notions and simply experiencing the world as it is.7. Phenomenology in Psychology.Phenomenology has had a significant impact on psychology, leading to the development of qualitative research methods such as phenomenological interviewing and participant observation. These methods allow researchers to gain a deeper understanding of the subjective experiences of individuals.8. Phenomenology in Philosophy.Phenomenology has also been a major influence on philosophy, leading to the development of new philosophical approaches such as existentialism and hermeneutics. Theseapproaches emphasize the importance of the human experience and the need for understanding the world from the perspective of the individual.9. Phenomenology in Other Fields.Phenomenology has also had an impact on other fields such as sociology, anthropology, and literary criticism. In these fields, phenomenology has been used to gain a deeper understanding of the subjective experiences of individuals and the ways in which these experiences shape the social world.10. Conclusion.Phenomenology is a powerful philosophical and psychological approach that has had a significant impact on a wide range of fields. It is a method for understanding the world from the first-person perspective and for gaining a deeper understanding of the subjective experiences of individuals.Chinese Answer:1. 介绍。

Self-trapped excitons at the quartz(0001) surface¤

Self-trapped excitons at the quartz(0001)surface ¤J.Song,ab R.M.VanGinhoven,ab L.R.Corrales b and H.Jonsson *a a Department of Chemistry 351700,University of W ashington ,Seattle W A 98195-1700,USAb EMSL ,PaciÐc Northwest National L aboratory ,Richland W A 99352,USA Recei v ed 2nd August 2000First published as an Ad v ance Article on the web 6th No v ember 2000We have studied self-trapped excitons in a -quartz using density functional theory (DFT),both in the crystal and at the (0001)surface.The excitons are triplet excited states that distort the crystal locally.They have a long lifetime,of the order of a millisecond,and become thermally equilibrated.We have calculated the drop in the exciton energy as it approaches the surface from the interior of the crystal.In the subsurface layer of the ÈOH terminated (0001)surface,the energy has dropped by 0.7eV.Another 0.4eV drop occurs as the exciton enters the surface layer,where it breaks o†an OH radical.The drop in energy can be understood from the greater ease of structural distortion at the surface.These calculations illustrate that excitons formed in the bulk could migrate out to the surface and form chemically active surface species.Molecules adsorbed at the surface could also serve as traps for the excitons and could,in principle,be induced to undergo structural or chemical transitions.I.IntroductionPhotoexcitation of oxides can lead to various interesting processes.Recently,much attention has been paid to photocatalysis,in particular on surfaces.There,electronic excitations created TiO 2by photon absorption cause chemical reaction to occur on the oxide surface.1Also,metal oxide particles dispersed in aqueous solutions and exposed to gamma irradiation have been shown to induce radiolysis of water.2,3Clearly,studies of the electronic excitations formed in oxides due to photon absorption,the mechanism of energy transfer and subsequent chemical processes are of great interest.Silica,is a particularly simple and stable oxide which could serve as a model system for SiO 2,studying such photoexcitation processes,although the photon energy required for excitation is too large for large-scale applications.Silica has become widely used as oxide support in model studies of metal/oxide catalysts.4,5Photoinduced defects can also play a role in various silica-based appli-cations such as protective layers on electronic devices,optical Ðbers,and immobilization matrices for hazardous waste.6,7Excitons can play an important role in the long-time evolution of silica.It has been found that triplet state,self-trapped excitons (STE)in quartz have a long lifetime,of the order of milliseconds,before recombining and giving o†blue luminescence.8h 14It has been speculated that STEs can ¤Electronic Supplementary Information available.Colour versions of Fig.1,5and 6are given.See /suppdata/fd/b0/b006289h/DOI:10.1039/b006289h Faraday Discuss .,2000,117,303È311303This journal is The Royal Society of Chemistry 2001(lead to Si ÈO bond breaking and degradation of the silica network.There are also indications that defects can be made mobile and/or anneal out in the presence of excitons.Previous theoretical work has shown that an STE binds to an oxygen vacancy in quartz with a 3eV binding energy and reduces the di†usion activation barrier of the vacancy from 4eV to less than 2eV.15In this article,an overview of results obtained from DFT calculations of STEs in a -quartz is given and new results on STEs at the quartz (0001)surface are presented.Our calculations indi-cate that STEs formed in the quartz crystal would tend to thermally di†use out towards the surface,where surface ÈOH groups can get broken o†to form OH radicals.A competing process would be the thermal activation into a di†erent STE,which is near the singlet Ètriplet crossing,and subsequent non-radiative decay.We Ðrst discuss the methodology used in the calculations,and then the results obtained on STEs in the quartz crystal and,Ðnally,at the quartz surface.II.DFT calculations of STEsA large system is needed to represent STEs in quartz because the self-trapping involves large displacements of atoms and substantial elastic strain.Calculations of such systems can only be handled at an approximate level.High level calculations can only be applied to small clusters with a few atoms.For the highly reliable CCSD(T)method,a single unit is already a large SiO 2calculation.A theoretical study of STEs in quartz must,therefore,Ðnd some practical balance between the approximations in the methodology and errors due to small system size.While DFT applies only to the ground electronic state,16it is possible to study the STEs in quartz because they are triplet states.With a constraint on the spin (two more electrons with spin up than spin down)in a spin-polarized DFT calculation,the lowest triplet state is the lowest energy state available.The basic theorem of DFT,the Hohenberg ÈKohn theorem,holds within the triplet subspace.The calculated atomic forces can be used to relax the atomic structure to local minima on the triplet energy surface,each minimum corresponding to a triplet state exciton.17,18The development of functionals for DFT has,however,mainly focused on singlet states:19There is little experience on how well they can be applied to higher spin states.We have carried out tests of various functionals by calculating singlet Ètriplet (S ÈT)splittings in small clusters where well established wavefunction-based methods can be carried out for comparison.17,20These tests indicate that the PW91functional underestimates the S ÈT splitting in cases where the triplet state is delocalized.Then the semi-local description of exchange becomes problematic in the triplet state.This underestimate is most severe for the perfect crystal,where the calculated S ÈT splitting is6.1eV but the experimental estimate is 8.3eV.10This is consistent with the typical underestimate of band gaps in DFT.The B3LYP functional is more accurate as it involves exact exchange rather than just the semi-local description employed in PW91.The S ÈT splittings are predicted to be larger,and close to,although somewhat smaller than,those calculated by the CCSD(T)method.17,20The inclusion of exact exchange,however,makes it extremely costly to implement B3LYP in calculations where periodic boundary conditions are applied (and the evaluation of atomic forces at that level of theory has not yet been developed).21The B3LYP functional can only be applied to Ðnite clusters at the present time.We have,therefore,developed a procedure where DFT/B3LYP cluster calcu-lations are used to improve on the triplet state energetics of the DFT/PW91conÐgurations that are subject to periodic boundary conditions to eliminate surface e†ects.This is illustrated in Fig.1.The atomic conÐguration is obtained by relaxation of the triplet state using DFT/PW91calcu-lations.Clusters of varying size,up to are then snipped out of the relaxed conÐguration,Si 8O 25,centered on the STE and the edge atoms (chosen to be O-atoms)are then capped with H-atoms to terminate dangling bonds.The direction of the O ÈH bonds is the same as the direction of the broken O ÈSi bonds and are chosen to have a bond length of 0.8to get a similar charge on the A edge O-atoms as interior O-atoms.The S ÈT splitting is calculated at both the PW91and B3LYP level and the di†erence gives the B3LYP correction which is added to the S ÈT splitting calculated using PW91and periodic boundary conditions.The correction is only important for the highly delocalized triplet states (1.2eV for quartz and 0.6eV for the most delocalized STE).This pro-cedure gives an estimate of the triplet-state energy surface which appears to be in good agreement with experimental measurements.304Faraday Discuss .,2000,117,303È311Fig.1The 72atom quartz conÐguration used in the DFT/PW91calculations.Periodic boundary conditions are applied.Calculations have also been carried out on clusters snipped out of the 72atom conÐguration.The outermost atoms in the cluster are O atoms,which get capped with H atoms to reduce surface e†ects.Various wavefunction-based calculations as well as DFT calculations have been carried out for the clusters to assess the accuracy of the quasi-local PW91functional in describing the triplet state and to estimate corrections to the DFT/PW91results.The plane-wave-based spin-polarized DFT calculations were carried out with the VASP code,22using ultrasoft pseudopotentials.23The energy cuto†was 29Ry for the wavefunction and 68Ry for the electron density.The PW9124exchange-correlation functional was used.The importance of using a gradient-dependent density functional rather than the local density approximation when studying silica has been demonstrated by Hamann.25The bulk quartz calculations were done on a 72atom cell (eight unit cells)including just the !point in the k-point sampling.Additional k-points were found to have insigniÐcant e†ect on both structure and singlet Ètriplet splittings.Two kinds of Si ÈO bonds are found in a -quartz.The DFT calculations predict bond lengths of 1.619and 1.615as compared with experimental estimates of 1.612and 1.607A ,A .26Low-energy electron di†raction (LEED)measurements of the (0001)surface of quartz have shown the unreconstructed (1]1)conÐguration to be stable up to 600¡C where a (3]1)or (1]3)reconstruction takes place.27The electronic structure of the surface has been studied by energy loss spectroscopy reÑection (REELS)28where it was found that the surface band gap is 8.8eV,which is very similar to the bulk band gap.29The surface calculations were done with a slab where the upper and lower surface were terminated with ÈOH groups.The surface in contact with water would be expected to be hydroxylated.A total of 84atoms were used in the slab calcu-lations The bottom two layers of Si and O atoms in the slab were held Ðxed in the (Si 20O 48H 16).perfect quartz conÐguration,but other atoms in the slab were allowed to move and relax to a minimum energy conÐguration.The capping O ÈH bonds in the bottom layer were pointed in the direction of the broken O ÈSi points,and the O ÈH distance was chosen to be 0.8to bring the A charge on the O atoms to a similar value as that of bulk O atoms.The B3LYP calculations were carried out using Gaussian basis sets,both the 6-31G*and 6-31G*]s @for the Si and O atoms while H atoms were represented with minimal basis.The cluster corrections were converged both with respect to cluster size and basis set.III.Excitons in the quartz crystalFig.2shows the cluster carved out of the perfect quartz crystal conÐguration.An isosurface for the excess spin density in the triplet state is also shown.The distribution of the excess spin density is quite even over the whole cluster and is largest at the O-atoms.The exciton in perfect quartz isFaraday Discuss .,2000,117,303È311305Fig.2A cluster representing quartz.The 0.02electron isosurface of the excess spin density of Si 8O 25H 18A ~3the triplet state calculated using DFT/B3LYP is shown.The excess spin density mainly resides on the O-atoms and is evenly distributed over the cluster,indicating a highly delocalized exciton.highly delocalized.By breaking the symmetry in various ways and relaxing the system in the triplet state,we have been able to identify three di†erent local minima corresponding to local distortions of the lattice,i .e .STEs.Previously,Fisher,Hayes and Stoneham presented a model for STE in quartz obtained from unrestricted Hartree ÈFock (UHF)calculations on small silica clusters and We (Si 5O 4Si 2O 7).30have found very similar STE conÐguration in our DFT calculations,which have been carried out using signiÐcantly larger clusters,The self-trapping mainly involves the displacement Si 8O 25H 16.of an oxygen atom by 0.96resulting in a formally broken Si ÈO bond (2.5We will refer to A ,A ).this structure as STE-Oc.The S ÈT splitting calculated by the B3LYP corrected DFT is 2.8eV,in excellent agreement with the experimentally measured luminescence,2.6È2.8eV 10h 12(while UHF calculations give S ÈT splitting of 1.6eV).The S ÈT splitting predicted by the DFT calculations seems,therefore,to be quite accurate.When one of the Si ÈO bonds in the 72atom bulk crystal conÐguration is rotated in such a way as to formally break another Si ÈO bond and the system is then relaxed in the triplet state using DFT/PW91,a di†erent STE also involving displacements of mainly O-atoms,is obtained.The structure,captured in a cluster carved out of the 72atom conÐguration,is shown in Fig.3,along with an isosurface of the excess spin density.We will refer to this as STE-Ob.It turns out to beFig.3One of the O-displaced self-trapped excitons,STE-Ob,in a cluster snipped out of a 72Si 8O 25H 18atom bulk conÐguration.The excess spin density is shown (analogous toFig.2)and illustrates a distribution of the hole over the three oxygen atoms while the excited electron is mainly to be found at the adjacent Si atom.Two O-atoms get displaced appreciably,by 0.6and 0.5and the Si-atom gets displaced by 0.2The A ,A .lattice relaxations extend over a large region and no bond is formally broken.306Faraday Discuss .,2000,117,303È311slightly lower in energy in the DFT/PW91calculations,but slightly higher in B3LYP corrected calculations.The distortion involves roughly equally large displacements of two oxygen atoms(by A)0.6and0.5bonded to the same Si atom,as well as displacements of the adjacent Si atoms(byA),Aup to0.25in such a way that three SiÈO bonds are stretched to1.76but not broken.17,18 The singlet and triplet state energy for quartz and the STEs is shown in Fig.4.The luminescence of this STE predicted by the B3LYP corrected calculation is4.3eV.The triplet state surface is veryÑat in this region.In fact,a minimum energy path between these two STEs has a barrier of only0.2eV even though large displacements are involved(one O-atom gets displaced by0.7A A.and another by0.6TheÑatness of the triplet state surface suggests that several local minima, i.e.STEs,may exist and that the system is quiteÑoppy in the excited state,consistent with the large width(ca.1eV)and complex shape of the measured luminescence peak.Luminescence has also been observed at4.0eV in low temperature experiments(at80K),but was tentatively ascribed to defects or impurities.10Our results indicate that there may be an intrinsic STE contri-bution to the emission around4.0eV.Both the emissions centered at2.8and4.0eV seem to have more than one origin,as can be seen from the dependence of the line shape on the excitation energy.12The barrier to go from STE-Ob to STE-Oc is predicted to be on the order of0.2eV(see Fig.4).This estimate was obtained byÐnding the minimum energy path between STE-Ob and STE-Oc(using the Nudged Elastic Band method,31using DFT/PW91,and then applying the B3LYP cluster correction.The low barrier between the STEs and the energetic preference for STE-Oc suggest that room temperature experiments would only be able to detect the2.8eV luminescence.The third STE we have identiÐed mainly involves a displacement of a Si atom.We will refer to it as STE-Si.This STE is obtained when the quartz crystal structure is distorted by displacing one oxygen atom by0.2in the direction of a SiÈO bond and the system is then relaxed in the triplet AAstate using DFT/PW91.In the end,a Si atom has moved by0.9through the plane of three of its neighboring O-atoms.STE-Si turns out to be close to a crossing of the singlet and triplet surfaces. This,we have veriÐed by CAS-SCF calculations.The system is,therefore,expected to undergo non-radiative energy transfer to the singlet ground state if it gets trapped in STE-Si.This bringsFig.4A slice of the triplet and singlet energy surfaces including the perfect quartz crystal conÐguration and the three STEs found in bulk.The conÐgurations are ordered with delocalization of the excess spin density increasing to the left.The conÐgurations were obtained by relaxation of a72atom system subject to periodic boundary conditions using DFT/PW91.A minimum energy path was calculated between the STE-Ob and STE-Oc.Clusters were then snipped out and used to get an improved estimate of the energetics using DFT/ B3LYP calculations,which include exact exchange.The correction is only signiÐcant for the more delocalized states:quartz and STE-Ob.The triplet state surface shows two local minima,the STE-Oc and STE-Ob conÐgurations.The lower energy one has SÈT splitting of2.8eV in close agreement with experimentally measured luminescence.An experimentally observed reduction in the intensity of the2.8eV luminescence with increasing temperature can be explained by the thermal activation from the STE-Oc state to the STE-Si state which is near a SÈT crossing and,therefore,leads to non-radiative decay.Faraday Discuss.,2000,117,303È311307the system back to the perfect crystal state,in agreement with experiments which show that decay of excitons does not lead to structural changes in quartz (unlike amorphous where 1/100SiO 2STEs lead to Si ÈO bond breaking 11).We have studied several possible paths that can take the system from STE-Oc to STE-Si,but in all cases tested to date the system preferred to make the transition through the perfect quartz conÐguration (which at the PW91level is the lowest energy conÐguration,making it hard to calculate a minimum energy path for the transition).Our best estimate of the energy barrier for a thermal transition from STE-Oc to STE-Si is 0.5eV (see Fig.4).Experiments on the temperature dependence of the luminescence intensity have indicated that the system can get thermally activated from the luminescent STE state to a new state from where the system is quenched non-radiatively.10,14The experimentally estimated activation barrier is 0.4eV.The STE-Si state we have found could very likely provide this non-radiative mechanism.The predicted activation energy for the process is even in close agreement with the experimental value.Our calculations,which are summarized in Fig.4,give a microscopic picture of the scenario deduced qualitatively from experimental measurements.14IV.Excitons at the quartz (1000)surfaceIn order to study the behaviour of the STEs near the surface of quartz,we have carried out DFT/PW91calculations on a quartz slab described above and shown in Fig.5.Both sides of the slab are terminated by O-atom layers and capped with H-atoms to saturate dangling bonds.Because of the small thickness of the slab,which is limited by the large computational e†ort in the DFT calculations,it is only possible to represent the STE in the surface and subsurface layers in this slab.A displacement of an O-atom in the second layer gives a STE which is quite similar to the STE-Ob in the crystal.The di†erence is that one of the three stretched bonds,the one pointing towards the surface,becomes longer (1.78while the other two become shorter (1.72as A )A )compared with the STE-Ob in the interior of the crystal.The Si-atom is also displaced more thanFig.5A side view of the 84atom cell used to represent a quartz slab with an ÈOH terminated (Si 20O 48H 16)(0001)surface.Atoms in the bottom two layers are Ðxed in the quartz conÐguration (the capping O ÈH bonds pointing in the direction of the broken O ÈSi points).Other atoms are allowed to relax in the DFT/PW91calculation.The STE is in the surface layer and has broken an OH radical o†the surface layer (top left).308Faraday Discuss .,2000,117,303È311Fig.6The energy of the STE in bulk quartz,near and at the(0001)surface.In the subsurface layer,the STE has dropped in energy by0.7eV as compared with the bulk.In the surface layer,where the STE results in an OH radical being broken o†,the energy drops further by0.4eV.in the crystal,by0.5The calculated SÈT splitting has dropped by0.7eV as compared with A.bulk.This represents a drop in the triplet state energy and/or a rise in the singlet energy.It is difficult to compare the singlet state energy between the crystal and slab conÐgurations,because the two are so di†erent.We will assume here that the singlet state energy of the STE conÐguration is the same in the second layer as in bulk quartz.The triplet state energy is,then,lower by0.7eV in the subsurface layer(see Fig.6).In the surface layer,a similar displacement of an O-atom and subsequent structural relaxation leads to a SiÈO bond rupture and spontaneous formation of an OH radical.The triplet state energy is0.4eV lower than in the subsurface layer and now the singlet state energy has increased signiÐcantly so the SÈT splitting is only0.5eV.This likely represents a non-radiative channel.It is reasonable to expect this drop in the triplet state energy since the energetic cost of distortions of the lattice becomes smaller near the surface where atoms are able to move more freely.This suggests that STEs formed in bulk quartz will tend to di†use out to the surface.Since the lifetime of STEs in quartz is on the order of1ms,and the di†usion barrier is estimated from our calcu-lations to be on the order of0.5eV,the STEs could di†use over a large distance at temperatures around room temperature.The transition into the STE-Si state and subsequent non-radiative decay would be a competing process,however,and in the end it may be that only a small region near the surface feeds STEs into the surface.We have also carried out calculations for the(0001)surface with Si2O double bond recon-structed states.The Si2O terminated surface is produced from the hydroxylated surface by remo-ving the hydrogen atoms on the top surface.ToÐnd an STE state a perturbation to the lattice structure is introduced,as in the crystal case.On the reconstructed surface having Si2O double bonds,two distinct silicon-displaced STEs are found,but the oxygen-displaced STE,STE-Ob, does not appear to exist on this particular surface.The two silicon-displaced STEs have emission energies of1.0and2.5eV.The former is more stable,is likely a non-radiative channel and the Si2O bond has stretched from1.5to1.7A.At this point in time,B3LYP corrections have not been applied to the surface STE conÐgu-rations,but it seems clear from the comparison of the STE-Ob calculations for bulk,subsurface and surface layers that the SÈT splitting decreases as the STE approaches the surface.V.DiscussionOur calculations indicate that as the exciton approaches the surface,the energy is lowered.The increased stability of the STEs at the surface can be ascribed to the lower energetic cost of theFaraday Discuss.,2000,117,303È311309structural distortions favored by the triplet state.The formation of an OH radical at the hydroxyl-ated surface provides one possible mechanism for chemical processes induced by STEs.Experi-mental studies have,for example,demonstrated that radiolysis events can occur when metal oxide particles dispersed in aqueous solutions are exposed to gamma irradiation.2,3Also,one of the proposed mechanisms for photocatalysis at surfaces involves the production of surface TiO 2hydroxyl radicals but from self-trapped holes rather than excitons.1While most STEs are probably formed in the interior of the crystal,far from the surface,it is possible that thermal di†usion can bring the STEs to the surface.It is not clear what the thermal di†usivity of STEs in quartz is.If the perfect crystal is the optimal transition state for the STE hopping from one site to another,our calculations suggest an activation energy of 0.5eV.This is likely an underestimate since the energy of the perfect crystal in the triplet state is underestimated by the DFT calculations,even at the B3LYP level.It is also possible that a lower energy path exists for the STE to hop from one site to another,bypassing the perfect crystal conÐguration.The perfect crystal transition state is highly delocalized and a single thermally activated di†usion hop can in principle bring the exciton a long distance away from the initial STE location.The thermally activated transition to the STE-Si state,which is right at a crossing of the singlet and triplet surface and leads to non-radiative decay,is in competition with the di†usion of the STE.Assuming again the perfect crystal is the transition state,our calculations predict a barrier of 0.5eV,in very good agreement with experimental measurements (0.4eV).The relative activation energy for di†usion and transition into the non-radiative state a†ects,of course,strongly to what extent STEs formed in bulk can fuel surface processes.For some oxides the thermal di†usion mechanism may be active but not for others.VI.AcknowledgementsThis work was supported by the Environmental Management Science Program,Office of Environmental Management,DOE (JS),and the Division of Chemical Sciences,DOE Office of Basic Energy Sciences (LRC),and by DOE-BES grant DE-FG03-99ER45792(RVG,HJ).The calculations were performed on a parallel IBM SP computer at the William R.Wiley Environ-mental Molecular Sciences Laboratory,a national scientiÐc user facility sponsored by DOE Office of Biological and Environmental Research,located at PaciÐc Northwest National Laboratory.References1M.R.Ho†mann,S.T.Martin,W.Choi and D.W.Bahnemann,Chem .Rev .,1995,95,89.2N.G.Petrik,A.B.Alexandrov,T.M.Orlando and A.I.Vall,T rans .Am .Nucl .Soc .,1999,81,101.3 A.B.Alexandrov,A.Y.Bychkov,A.I.Vall,N.G.Petrik and V.M.Sedov,Russ .J .Phys .Chem .,1991,65,1604.4I.Zuburtikudis and H.Saltsburg,Science ,1992,258,1337.5(a )X.Xu and D.W.Goodman,J .Phys .Chem .,1993,97,683;(b )X.Xu and D.W.Goodman,J .Phys .Chem .,1993,97,7711.6S.Rico,in T he Physics and Chemistry of and the Interface ,ed.C.R.Helms and B.E.Deal,SiO 2SiÈSiO 2Plenum,New York,1988,p.75.7W.J.Weber et al .,J .Mater .Res .,1998,13,1434.8T.Tanaka,T.Eshita,K.Tanimura and N.Itoh,Cryst .L attice Defects Amorph .Mater .,1985,11,221.9J.H.Stathis and M.Kastner,Phys .Rev .B ,1987,35,2972.10 C.Itoh,K.Tanimura,N.Itoh and M.Itoh,Phys .Rev .B ,1989,39,11183.11N.Itoh,T.Shimizu-Iwayama and T.Fujita,J .Non -Cryst .Solids ,1994,179,194.12K.S.Song and R.T.Williams,Self -T rapped Excitons ,Springer,Berlin,2nd edn.,1996,p.281.13W.Hayes,M.J.Kane,O.Salminen,R.L.Wood and S.P.Doherty,J .Phys .C ,1984,17,2943.14M.Georgiev and N.Itoh,J .Phys .:Condens .Matter ,1990,2,10021.15J.Song,L.R.Corrales,G.Kresse and H.Jonsson,submitted to Phys .Rev .L ett .16(a )P.Hohenberg and W.Kohn,Phys .Rev .B ,1964,136,864;(b )W.Kohn and L.J.Sham,Phys .Rev .A ,1965,140,1133.17J.Song,H.and L.R.Corrales,Nucl .Instrum .Methods Phys .Res .,Sect .B ,2000,166,167453.Jonsson 18L.R.Corrales,J.Song,R.M.VanGinhoven and H.in NAT O Advanced Studies Institute Pro -Jonsson,ceedings on ““Defects in Silica and Related Dielectrics ÏÏ,ed.G.Pacchioni,in press.19W.Kohn,A.D.Becke and R.G.Parr,J .Phys .Chem .,1996,100,12974.20R.Van Ginhoven,J.Song,M.Dupuis,K.A.Peterson,L.R.Corrales and H.to be published.Jonsson,310Faraday Discuss .,2000,117,303È31121M.Stadele,M.Moukara,J.A.Majewski and P.Vogl,Phys.Rev.B,1999,59,10031.22(a)G.Kresse and J.Hafner,Phys.Rev.B,1993,47,558;(b)G.Kresse and J.Hafner,Phys.Rev.B,1994,Furthmu ller,49,14251;(c)G.Kresse and put.Mater.Sci.,1996,6,16;(d)G.Kresse and J.Furthmu ller,Phys.Rev.B,1996,55,11169.23 D.Vanderbilt,Phys.Rev.B,1990,41,7892.24J.P.Perdew,in Electronic Structure of Solids,ed.P.Ziesche and H.Eschrig,1991.25 D.R.Hamann,Phys.Rev.L ett.,1996,76,660.26W.Hayes and T.J.L.Jenkin,J.Phys.C:Solid State Phys.,1986,19,6211.27 F.Bart and M.Gautier,Surf.Sci.,1994,311,L671.28 F.Bart,M.Gautier,F.Jollet and 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Exploring the Behavior of Gases and Liquids

Exploring the Behavior of Gases andLiquidsIntroductionGases and liquids are two of the three states of matter, the other being solids. While solids have a definite shape and volume, gases and liquids both have variable shapes and volumes. However, there are key differences in their behavior that make them distinct from each other. In this article, we will explore the behavior of gases and liquids and their properties.Properties of GasesGases are characterized by their ability to fill any container they are placed in. This is due to the fact that the particles in a gas are far apart and move at high speeds in all directions. While gases have no definite shape, they do have a definite volume, which is determined by the size and shape of the container they are in.The behavior of a gas can be described using the ideal gas law, which relates the pressure, volume, temperature, and number of particles of a gas. The ideal gas law assumes that gases are composed of infinitely small particles that have no volume and do not interact with each other. While this is not entirely accurate for real gases, it is a useful approximation for many situations.One of the key properties of gases is pressure. Pressure is the force per unit area that a gas exerts on the walls of its container. The pressure of a gas can be increased by increasing the number of particles, increasing the temperature, or decreasing the volume of the container.Another important property of gases is temperature. Temperature is a measure of the average kinetic energy of the particles in a gas. When the temperature of a gas is increased, the particles move faster and collide with each other more frequently, which increases the pressure.Properties of LiquidsUnlike gases, liquids have a definite volume but no definite shape. This is because the particles in a liquid are close together and are attracted to each other, which allows a liquid to take on the shape of its container. While liquids are not compressible like gases, they can still be affected by changes in temperature and pressure.The behavior of a liquid can be described using several properties, including surface tension, viscosity, and boiling point. Surface tension is the property of a liquid that causes it to form a curved surface at the boundary with the air. This is due to the cohesive forces between the particles in the liquid.Viscosity refers to the resistance of a liquid to flow. The viscosity of a liquid is determined by the size and shape of its particles and their degree of attraction to each other. Liquids with high viscosity, like honey or molasses, flow slowly, while liquids with low viscosity, like water or gasoline, flow easily.The boiling point of a liquid is the temperature at which it changes from a liquid to a gas. This is determined by the strength of the attractive forces between the particles in the liquid. Liquids with weaker attractive forces, like alcohol, have a lower boiling point than liquids with stronger attractive forces, like water.ConclusionIn summary, the behavior of gases and liquids is determined by their properties and the intermolecular forces between their particles. Gases have no definite shape but a definite volume, while liquids have a definite volume but no definite shape. Understanding the behavior of gases and liquids is important in many fields, including chemistry, physics, and engineering. By exploring these properties and their effects, we can gain a deeper understanding of the natural world around us.。

The properties and behavior of chiral materials

The properties and behavior of chiralmaterialsChirality is a fundamental property of many molecules and materials, referring to their asymmetry in mirror reflection. Chiral molecules and materials have opposite handedness, or enantiomers, that cannot be superimposed onto each other. This results in important differences in their physical and chemical properties, as well as their behavior in various environments. In this article, we will discuss the properties and behavior of chiral materials, including their optical, magnetic, and electronic properties, as well as their applications in medicine, chemistry, and materials science.Optical properties of chiral materialsOne of the most important properties of chiral materials is their optical activity, or the ability to rotate the polarization plane of polarized light. This phenomenon, known as optical rotation or circular dichroism (CD), is due to the interaction between chiral molecules and the electromagnetic field of light. The magnitude and direction of the optical rotation depend on the nature and concentration of the chiral molecules, as well as the wavelength and intensity of the incident light.Chiral materials also exhibit CD, which is the differential absorption of left- and right-circularly polarized light. This CD can be measured by spectrophotometers, which analyze the intensity and wavelength dependence of the transmitted or reflected light. CD spectra of chiral molecules and materials provide valuable information about their structure, conformation, and interactions with other molecules. In addition, CD can be used for the detection and quantification of chiral compounds, as well as the monitoring of chemical reactions and protein folding.Magnetic properties of chiral materialsAnother intriguing property of chiral materials is their magnetic behavior, which arises from their asymmetry in spin and orbital angular momentum. Chirality can inducemagnetic moments, or moments of polarization, that give rise to magnetic fields and interactions. This results in various magnetic phenomena, such as magnetochiral dichroism (MChD), magnetic circular dichroism (MCD), and magneto-optical Kerr effect (MOKE).MChD is the differential absorption of light by chiral materials in the presence of a magnetic field. This effect can be used to distinguish enantiomers and measure their magnetic moments. MCD is related to the linear dichroism of chiral materials in the presence of a magnetic field, and can provide information about the magnetic anisotropy and orbital contribution of chiral molecules. MOKE is the rotation of the polarization plane of light reflected by chiral materials in the presence of a magnetic field, and is used for the imaging and manipulation of magnetic structures.Electronic properties of chiral materialsChirality also affects the electronic properties of materials, especially their conductivity and transport. This is due to the breaking of the spatial symmetry and the formation of energy bands with non-zero Berry curvature, which leads to the topological effects, such as the quantum Hall effect and the anomalous Hall effect. In addition, chirality can influence the bandgap and optical absorption of semiconductors and nanomaterials, as well as the stability and reactivity of chemical bonds.Applications of chiral materialsChiral materials have important applications in various fields, such as medicine, chemistry, and materials science. In medicine, chiral drugs and biomolecules have different pharmacological and toxicological properties, depending on their enantiomeric composition. Chiral separations and analyses are therefore crucial for drug development, quality control, and clinical diagnosis. In addition, chiral materials can be used for the design and fabrication of sensors, catalysis, and energy storage devices.In chemistry, chiral catalysts and reagents are widely used for asymmetric synthesis and chromatography, which enable the selective and efficient production of chiral molecules and materials. Chirality also plays a crucial role in the self-assembly andsupramolecular chemistry of biomolecules, such as DNA, peptides, and lipids. Chiral materials can also serve as templates and scaffolds for the synthesis of nanomaterials and devices with controlled size, shape, and functionality.In materials science, chiral materials have attracted much attention due to their unique physical and chemical properties, as well as their potential for novel applications. Chiral metamaterials and photonic crystals, for example, have been used for the manipulation and control of light at the nanoscale. Chiral liquid crystals and polymers have been employed for display and communication technologies, as well as for biomedical and environmental engineering. Chiral materials have also been explored for energy conversion and storage, such as in solar cells, batteries, and supercapacitors.ConclusionChiral materials exhibit fascinating properties and behavior, which have stimulated much research and applications in various fields. Their optical, magnetic, and electronic properties provide valuable insights into their structure, conformation, and interactions with other molecules. Their applications in medicine, chemistry, and materials science have broadened our knowledge and advances in these fields. With the increasing demand for functional materials and devices, chiral materials are expected to play increasingly important roles in the future.。

规则与行为英语作文高中

In high school,students are expected to adhere to a set of rules and exhibit appropriate behaviors that contribute to a positive learning environment.These rules and behaviors not only shape the students conduct within the school premises but also lay the foundation for their future interactions in society.Title:Rules and Behaviors in High SchoolRespect for Authority:High school students should show respect to all authority figures,including teachers, administrators,and support staff.This respect is demonstrated through politeness, attentiveness in class,and compliance with instructions.Attendance and Punctuality:Regular attendance and punctuality are crucial for academic success.Students are expected to be in class on time and to inform the school if they are unable to attend due to illness or other legitimate reasons.Academic Honesty:Cheating,plagiarism,and other forms of academic dishonesty are strictly prohibited. Students are encouraged to complete their work independently and to seek help from teachers or tutors if they are struggling.Dress Code:Adhering to the schools dress code is a sign of respect for the institution and its community.Students should wear clean,appropriate clothing that does not distract from the learning process.Classroom Behavior:Students should actively participate in class discussions,listen attentively,and avoid disruptive behaviors such as talking out of turn,using electronic devices without permission,or engaging in side conversations.Respect for Peers:Treating fellow students with kindness and respect is essential.This includes avoiding bullying,namecalling,and any form of discrimination based on race,gender,religion,or other personal characteristics.Use of School Facilities:Students are expected to take care of school property and facilities.This includes keeping classrooms and common areas clean,reporting any damages,and using equipmentresponsibly.Extracurricular Participation:Participation in extracurricular activities is encouraged as it helps students develop teamwork,leadership,and time management skills.However,students must also balance these activities with their academic responsibilities.Health and Safety:Students must follow all health and safety guidelines set by the school,including those related to physical education,laboratory work,and emergency procedures.Communication:Effective communication with teachers,peers,and school administrators is key.Students should feel comfortable expressing their concerns,asking questions,and providing feedback in a respectful manner.Civic Responsibility:High school students should be aware of their role as future citizens and act accordingly. This includes being environmentally conscious,understanding the importance of voting, and participating in community service.Personal Development:High school is a time for personal growth and selfdiscovery.Students are encouraged to explore their interests,set goals,and develop a strong sense of self.By following these rules and behaviors,high school students can create a supportive and conducive learning environment that prepares them for success in higher education and beyond.。

The Behavior of Liquid Mixtures at the Nanoscale

The Behavior of Liquid Mixtures at theNanoscaleNanoscale science has become one of the most promising research fields in recent years. With the development of nanotechnology, the behavior of liquid mixtures at the nanoscale has attracted much attention from researchers. Understanding the fundamental properties and behaviors of liquid mixtures at the nanoscale is an essential step toward designing and developing new materials with improved properties and characteristics.At the nanoscale, the liquid mixture properties can differ significantly from those at the macroscopic level. The surface area-to-volume ratio is much higher, and thermal and diffusion processes dominate. In particular, the surface energy of the solid-liquid interface plays a fundamental role in the behavior of liquid mixtures at the nanoscale.The behavior of liquid mixtures at the nanoscale has significant implications in several fields, including material science, chemical engineering, and biotechnology. One of the primary applications of nanoscale science is in developing advanced materials with enhanced properties. For example, researchers have used nanotechnology to enhance the performance of polymers, such as increased strength, thermal stability, and water repellency, by manipulating the behavior of liquid mixtures at the nanoscale.In addition, the behavior of liquid mixtures at the nanoscale can impact the performance of nanoscale devices. For example, the properties of liquid mixtures in microfluidic devices depend strongly on the surface energy of the device's walls. By controlling the surface energy of the walls, researchers can manipulate the behavior of the liquid mixture in microfluidic devices and optimize their performance.The behavior of liquid mixtures at the nanoscale can also play a crucial role in drug delivery systems. In recent years, researchers have used nanoscale science to develop new drug delivery systems with improved efficiency and targeting. By manipulating the surface energy of nanoparticles, researchers can control the behavior of liquid mixtures within the nanoparticle and enhance the delivery of drugs to specific targeted cells.The behavior of liquid mixtures at the nanoscale can also impact the behavior of biological systems. For example, the behavior of liquid mixtures can affect the interactions between proteins and other biomolecules. By manipulating the properties of liquid mixtures at the nanoscale, researchers can develop new methods for diagnosing and treating diseases.In conclusion, the behavior of liquid mixtures at the nanoscale is a significant research area with implications in several fields, including material science, chemical engineering, and biotechnology. By understanding the fundamental properties and behavior of liquid mixtures at the nanoscale, researchers can develop new materials and devices with enhanced performance and develop new methods for diagnosing and treating diseases. The potential applications of nanoscale science in the future are vast, and researchers from different fields will continue to make significant contributions to the understanding and manipulation of liquid mixtures at the nanoscale.。

219401800_传统咸肉加工过程中羟基十八碳二烯酸的变化及其与脂肪氧化的关系

刘裕，徐佳美，李金玲，等. 传统咸肉加工过程中羟基十八碳二烯酸的变化及其与脂肪氧化的关系[J]. 食品工业科技，2023，44（13）：79−84. doi: 10.13386/j.issn1002-0306.2022090002LIU Yu, XU Jiamei, LI Jinling, et al. Changes of Hydroxy-octadecanodienoic Acids and Its Relationship with Lipids Oxidation during Traditional Salted Meat Processing[J]. Science and Technology of Food Industry, 2023, 44(13): 79−84. (in Chinese with English abstract). doi: 10.13386/j.issn1002-0306.2022090002· 研究与探讨 ·传统咸肉加工过程中羟基十八碳二烯酸的变化及其与脂肪氧化的关系刘　裕1,2，徐佳美2，李金玲2，李鹏鹏2，马晶晶2，耿志明1,2, *，王道营1,2, *，徐为民1,2（1.江苏大学食品与生物工程学院，江苏镇江 212013；2.江苏省农业科学院农产品加工研究所，江苏南京 210014）摘　要：本文通过跟踪传统咸肉加工过程中理化指标、脂肪氧合酶（Lipoxygenase ，LOX ）以及羟基十八碳二烯酸（HODEs ）等的变化，研究LOX 活性和HODEs 含量、异构体构成的关系，并初步探讨咸肉加工中酶促和非酶促氧化模式演替规律。

结果表明，咸肉加工过程中LOX 活性呈现先升高后缓慢下降的趋势，HODEs 的总量缓慢上升，13-HODEs/9-HODEs 之比从1.31下降到1.13；LOX 活性和13-HODEs/9-HODEs 比值之间具有极显著正相关性（r =0.942，P <0.01）；LOX 作用下的酶促氧化在传统咸肉加工初期的脂质氧化中占有主导地位，随后其作用不断下降，在加工中、后期逐渐被自由基等诱导的自动氧化所取代。

Oxidation protection of CC–SiC composites by an

Journal of the European Ceramic Society 25(2005)577–587Oxidation protection of C/C–SiC composites by an electrophoretically deposited mullite precursorT.Damjanovi´c a ,∗,Chr.Argirusis a ,G.Borchardt a ,H.Leipner b ,R.Herbig b ,G.Tomandl b ,R.Weiss caTechnische Universität Clausthal,Institut für Metallurgie,Robert-Koch-Str.42,38678Clausthal-Zellerfeld,Germany b TU Bergakademie Freiberg,Institut für Keramische Werkstoffe,Gustav-Zeuner-Str.3,09596Freiberg,Germanyc Schunk Kohlenstofftechnik GmbH,Rodheimer Str.59,35452Heuchelheim,GermanyReceived 10October 2003;received in revised form 22March 2004;accepted 3April 2004Available online 20July 2004AbstractElectrophoretic deposition (EPD)is a suitable technique to produce mullite layers for acceptable oxidation protection of C/C–SiC bining sol–gel synthesis of 3Al 2O 3·2SiO 2mullite through hydrolysis and condensation of tetraethoxysilane (TEOS)and aluminum-tri-sec -butylate (Al-(OBu)3)with EPD yields sufﬁciently thick and homogeneous layers,which transform into mullite at 1300◦C.The protectiveness of the deposited mullite layers was tested in air in the temperature range 1300◦C ≤T ≤1550◦C by means of isothermal thermogravimetric analysis for up to 200h.The experimental data can be described by a phenomenological model of the (reduced)oxidation rate of the SiC layer underneath the outer mullite layer,which suggests that transport of carbon monoxide through mullite and silica is rate paring the oxidation rate of electrophoretically coated C/C–SiC samples to that of uncoated reference samples clearly demonstrates that mullite offers a signiﬁcant improvement to the oxidation resistance of the reference material.©2004Elsevier Ltd.All rights reserved.Keywords:Mullite;C/C–SiC;Composites;Electrophoretic deposition;Sol–gel processes1.IntroductionThe starting industrial material (Schunk Kohlenstofftech-nik GmbH,Heuchelheim,Germany)is a SiC coated carbon-reinforced carbon composite (C/C)in the form of thin slabs with average dimensions 20mm ×20mm ×2mm.The SiC layer is deposited by chemical vapour deposition (CVD)after the C/C substrate has ﬁrst been capillary inﬁl-trated with liquid silicon.As the CVD process takes place at high temperatures cracks develop in the SiC layer after cooling down to room temperature,which close again after renewed heating above 1100◦C.For short-term oxidation the resulting protective SiO 2layer is a suitable diffusion barrier but it degrades during prolonged service beyond 1300◦C.Furthermore,silica is not sufﬁciently resistant against erosion and chemical reactions with other compo-nents in the system (e.g.,ﬂue ash in power plants or steels in hardening cases for tool production).It is,therefore,∗Corresponding author.E-mail address:tanja.damjanovic@tu-clausthal.de (T.Damjanovi´c ).necessary to coat the SiC layer with more protective oxidesthan silica.Mullite ceramics are promising candidate materials for high temperature applications and oxidation protection of C/C–SiC composites.1–4Mullite satisﬁes all essential re-quirements for a refractory oxide layer on top of a C/C–SiC composite and has the corresponding mechanical proper-ties:similar low thermal expansion coefﬁcient (average val-ues for CTE of SiC and mullite in the temperature range 20◦C <T <1000◦C are:SiC:6.1×10−6K −1,mul-lite:4.4×10−6K −1),low thermal conductivity,excellent creep resistance,good chemical stability and low oxygen diffusivity.5,6Mullite coated SiC exhibits excellent oxida-tion resistance in dry air by forming a slowly growing native SiO 2scale under the mullite layer.Depending on the SiO 2content and on temperature mullite forms a low viscosity grain boundary ﬁlm which can close cracks and pores,thus offering a certain self-healing capacity.Plasma spraying or dip coating processes are mostly used to produce mullite layers from mixed oxide or mullite suspensions or from sol–gel systems,7,8respectively.The0955-2219/$–see front matter ©2004Elsevier Ltd.All rights reserved.doi:10.1016/j.jeurceramsoc.2004.04.005578T.Damjanovi´c et al./Journal of the European Ceramic Society25(2005)577–587sol–gel synthesis,however,represents a method to prepareultrapure and nano-sized mullite.Bulk ceramics obtainedfrom powders prepared this way reach nearly theoreticaldensity and have mullitization temperatures below1500◦C.9This paper demonstrates the possibility to prepare amullite precursor sol via chemical processing from whichelectrophoretic deposition(EPD)on C/C–SiC compositesproduces dense mullite coatings after sintering at1300◦C,which considerably improve the protectiveness of the pri-mary,SiC coating.2.Synthesis of the mullite precursor solProgress in the synthesis of chemically homogeneousmulticomponent oxides is particularly indebted to sol–gelscience.10,11However,it is well-known that hydrolysis andpolycondensation of silicon alkoxides are very slow com-pared to those of aluminium,and it is difﬁcult to achieve ahomogeneous co-polymerization.This may be reached byvery slow hydrolysis12,13of both alkoxides,by prehydroly-sis of the silicon alkoxide,14or by modifying the aluminiumalkoxide by a chelating group to reduce its reactivity.15,16Reagent grade chemicals used were alkoxides of Si andAl,tetraethoxysilane(TEOS;C8H20O4Si,VWR Interna-tional,p.a.)and Al(OBu)3(C12H27AlO3,VWR Interna-tional,p.a.),respectively,and isopropyl alcohol(C3H7OH,VWR International,p.a.)as a solvent.Due to the pronounceddifference in the reactivity of both alkoxides,acetylacetone(AcAc,VWR International,p.a.)was added as a chelatingagent inhibiting the condensation of Al(OBu)3.TEOS as aslower reacting precursor was prehydrolyzed with water ofdifferent pH values(pH2,6,10)adjusted by the additionof hydrochloric acid and ammonia.For the synthesis of suitable mullite precursors the con-centration of the separate alkoxide solutions,the pH of water(pH2,6,10),the molar ratio of the water to TEOS(r W= 2–10)and the concentration of acetylacetone were varied(0.01–1M)in order to obtain a series of different mulliteprecursor sols,whose electrokinetic properties were to beinvestigated systematically later on.The synthesis of Al(OBu)3–isopropanol solution was per-formed in a glove box so as to avoid uncontrollable at-mospheric moisture.Al(OBu)3was dissolved in isopropylalcohol on stirring,and acetylacetone was added into theAl(OBu)3solution until aﬁnal concentration0.1M wasreached.In the meantime,the separate solution of TEOSwas prepared.This reaction was performed in air becauseof the lower reactivity of the Si alkoxide.TEOS was prehy-drolyzed for1h by addition of water of deﬁned pH.The ad-dition of water was controlled by an automatic titrator(736GP Titrino,Metrohm,Germany).The interval of titrationwas10s and theﬂow rate was2ml min−1.Theﬁnal mullite precursor sol was obtained under con-trolled addition of the Al(OBu)3solution to the TEOSsol in a ratio corresponding to stoichiometric mullite (3Al2O3·2SiO2).Final mixing of both sols was performed in air with the Al(OBu)3sol covered with a paraﬁlm to avoid additional hydrolysis by atmospheric moisture.According to the mullite composition,a larger volume of Al(OBu)3 solution had to be mixed with a smaller volume of the TEOS solution.It would be technically easier to add the TEOS solution to the Al(OBu)3solution but this sequence leads to higher local concentrations of Al and induces in-homogeneities and phase separation in theﬁnal sol.Due to this fact,the Al(OBu)3solution was added in small volume increments to the TEOS solution.The addition was per-formed in volume increments of0.1ml,with aﬂow rate of 1ml min−1in intervals of10s,by an automatic titrator.The TEOS sol was stirred during the addition of the Al(OBu)3 solution,and the whole experiment was performed at room temperature.From the systematic investigations to optimize the above mentioned parameters of the sol–gel synthesis(concentra-tion of alkoxide solutions,pH value,amount of water needed for prehydrolysis of TEOS and amount of chelating agent), two promising experimental procedures were identiﬁed: (i)Synthesis of a mullite precursor sol was possibleunder the following conditions:concentration of alkoxide–isopropanol solutions is10vol.%,pH7(dis-tilled water),r W=2,addition of acetylacetone(c=0.1M).This precursor will be further denoted as MP1in the text.(ii)Synthesis of a mullite precursor sol with alkoxide–isopropanol solutions of10vol.%,pH2(adjusted by addition of HCl),r W=10and addition of acety-lacetone(c=0.1M).Due to the higher amount of water added for the hydrolysis of TEOS and prolonged co-polymerization of both alkoxides,we obtained a particulate sol suitable for the electrophoretic deposi-tion of the mullite precursor.This precursor will be further denoted as MP2in the text.3.Characterization of the mullite precursorsThe characterization of the stability and the mobility of the two mullite precursors prepared as described in Section2,was carried out by electrokinetic sonic anal-ysis(ESA-8000,MATEC Applied Sciences,USA).The average particle size of the synthesized mullite precur-sors MP1(d50≈20nm)and MP2(d50≤50nm),was estimated by means of transmission electron microscopy (TEM).The ESA measurements gave an ESA amplitude of7.80␮Pa m V−1(corresponding to a zeta-potential value ofζ=5.2mV)for the mullite precursor MP1and of 22.59␮Pa m V−1(ζ=15.1mV)for the mullite precursor MP2.Because of its low conductivity MP1was not suitable for the electrophoretic deposition,in contrast to MP2.In order to get information about the thermal behaviour of the precursors,as well as to determine structural changes asT.Damjanovi´c et al./Journal of the European Ceramic Society 25(2005)577–587579a function of the annealing regimes,XRD (Siemens D5000diffractometer),DTA/TG (Shimadzu Thermal Analyzer)and 29Si and 27Al MAS NMR (Bruker MSL 300MHz spectrom-eter)studies were performed.For the mullite precursor MP1the DTA/TG peak at 996.5◦C corresponded to mullite formation which was conﬁrmed by means of XRD analysis.This means that the obtained precursor sol was a single phase with both alkoxides mixed on a molecular scale leading to mullite crystallization at T ≤1000◦C.For the mullite precursor MP2,XRD investigations showed that the precursor remains amorphous up to approx-imately 1000◦C.The DTA/TG peak at 1129◦C corresponds to the formation of an alumina spinel also conﬁrmed by XRD.After a heat treatment at 1250◦C,according to XRD phase analysis,crystalline mullite is formed.According to the literature 16higher mullitization temperatures (T ≥1250◦C)indicate that the synthesized mullite precursor MP2is diphasic already in the sol state.These conclusions on the homogeneity of the synthesized mullite precursors were conﬁrmed by means of NMR analy-sis.The NMR results on the two different mullite precursors described above can explain the different mullitization tem-peratures.The detected chemical shifts and the respective signal assignments 17are given in Table 1.For a homogeneous mullite precursor a mullite-like Si surrounding,i.e.,Si(4Al)units should be present in the NMR spectra.The preliminary stage of the mullite pre-cursor MP1(heat-treated at 550◦C)and the ﬁnally formed sol–gel mullite from MP1at 1300◦C fulﬁl this expectation,whereas the non-crystalline phase from the mullite precur-sor MP2at 550◦C causes a broad signal in the spectrum.The peak maxima for both thermal stages of MP1(Fig.1a and c )are in the region for Si(4Al).The spectrum of the MP2precursor at 550◦C (Fig.1b )shows signiﬁcant evi-dence for silicon surrounded by less than four OAl groups,which triggers the formation of SiO 2rich and SiO 2deﬁ-cient domains in the annealed precursor.This ﬁnally results in higher mullitization temperatures than for the (more homogeneous)precursor MP1.Numerous 27Al NMR studies of aluminium-containing amorphous xerogels of oxide glasses have revealed the presence of three different aluminium environments.18Alu-minium nuclei in octahedral and tetrahedral environmentsTable 1Results of 29Siand27Al solid state NMR measurementsSample29SiMAS or CP/MASNMR 21chemical shift (ppm)Assignment of 29Si chemical shifts 27AlSATRAS NMR 22chemical shift (ppm)Assignment of27Alchemical shiftsMP2(550◦C)−75to –115(max.–99.2)Si(2Al) 3.4CN 6 CN 4(shoulder),CN 5present MP1(550◦C)−70to –112(max.–87.6)Si(4Al)26.1,2.0CN 5strongest signal CN 6 CN 4MP1(1300◦C)−86.1,shoulder –89,−93.3Si(3Al),Si(4Al)42.4,1.9CN 6∼CN 4,CN 4shoulder29SiNMR measuring conditions:MSL 300MHz,Larmor frequency 59.627MHz,CP time 5ms;27Al NMR measuring conditions:MSL 300MHz,Larmor frequency :co-ordination number of Al;CP/MAS NMR:cross polarization/magic angle spinning NMR spectroscopy;SATRAS NMR:satellite transition NMRspectroscopy.Fig.1.29Si solid state NMR:(a)CP/MAS spectrum of the preliminary stage of MP1(550◦C),(b)CP/MAS spectrum of MP2(550◦C)and (c)CP/MAS spectrum of MP1(1300◦C).give rise to characteristic chemical shifts of 0and 60ppm,respectively.The third species at 30ppm has been attributed to an [AlO 5]environment because its chemical shift lies between those of [AlO 6]and [AlO 4]and is very similar to the signal observed in well-known pentacoordinated Al compounds.Recently,it has been suggested by Schmücker and Schneider 19that in Al 2O 3-rich aluminium silicate gels and glasses with compositions close to mullite,this signal may arise from some tricluster [AlO 4]units.Taylor and Holland 20have related the aluminium coor-dination in aluminosilicate gels to their homogeneity,sug-gesting that Al(4)sites exist in regions of uniform Al/Si dis-persion and reﬂect the efﬁcient incorporation of aluminium into the tetrahedral silicate network.Less homogeneous regions containing discrete alumina-rich and silica-rich domains are believed to result in an increased proportion of Al(6)sites.By comparing the values of the composite quadrupolar coupling constant and of the isotropic chemical shift for the intermediate peaks in a mullite glass precursor and in crystalline mullite Bodart et al.18conﬁrmed that metastable aluminium atoms are present in the mullite glass precursor in an essentially pentacoordinated environment.Jaymes et al.21also suggested that the concentration of hexacoordinated Al atoms in single phase precursors prac-tically completely disappears before mullite crystallization at 980◦C.In diphasic precursors the aluminosilicate phase580T.Damjanovi´c et al./Journal of the European Ceramic Society25(2005)577–587has a higher content in AlO6octahedra,resulting in the crystallization of a spinel phase.The27Al NMR spectra22of the preliminary stage of the mullite precursor MP1,the mullite obtained from the precursor MP1after heating to1300◦C and the mullite precursor MP2show three Al signals assigned to different co-ordination numbers(CN)for each sample(Table1). From the results presented in Table1it is obvious that the mullite precursor MP2which is suitable for EPD has in its amorphous structure at550◦C a high concen-tration of hexacoordinated Al atoms.These Al(6)sites exist as a result of inhomogeneties at the Al–Si mixing scale and,according to this,MP2crystallizes into mullite at temperatures only above1250◦C.On the other hand, the mullite precursor MP1at550◦C has the strongest NMR signal for pentacoordinated aluminium which ac-cording to Schmücker and Schneider19acts as mullite nucleus because of a locally decreased activation energy. This precursor crystallizes directly into mullite below 1000◦C without formation of spinel,but is unfortunately unsuitable for electrophoretic deposition,as mentioned above.4.EPD of mullite from the precursor solAs the uniformity of the deposited layer is strongly de-pendent on the homogeneity of the surrounding electrical ﬁeld,23,24the following experimental set-up for EPD was chosen(Fig.2):•The substrate(C/C–SiC composite)was placed vertically in the mullite precursor sol with its surface parallel to the counter electrodes made of stainless steel.•Both the substrate and the counter electrodes were of pla-nar geometry.•The distance between the counter electrodes and the sub-strate was keptﬁxed at10mm.•The surface of the counter electrodes(40mm×60mm) was larger than the surface of the substrate(20mm×20mm),which yields a reasonably uniform electricalﬁeld near the substrate.•In order to avoid electrode marks on the substrate the position of the point contacts was changed before each individual deposition step.The topography of the sample surface was investigated with a surface proﬁler(Alpha-Step500,Tencor).The rough-ness of the surface25is characterized by the following param-eters:the average roughness,Ra=3.71␮m,and the max-imum peak-valley amplitude called total indicator run-out, TIR=50.02␮m.As explained above only the precursor MP2was suitable for our purposes and EPD was performed cathodically with different voltages and durations of deposition.The best per-formance of the deposited layer regarding the adhesion of the green layer to the C/C–SiC substrate after drying,wasFig.2.Experimental set-up for EPD of the mullite precursor. achieved with15V cm−1and15and30s deposition time. Under these conditions the deposited mass is directly pro-portional to the deposition time.The average mass gain per deposition cycle at15V cm−1and15or30s was0.16and 0.37mg cm−2,respectively.All C/C–SiC substrates were coatedﬁve-times with a sintering step between each depo-sition step at1300◦C(mullitization temperature obtained from XRD investigations on the mullite precursor MP2)in an atmosphere of99.996%Ar for2h.After theﬁnal sin-tering step the deposited layers were investigated by means of secondary electron microscopy(SEM)in order to obtain information about the thickness of the deposited layer and its composition.On the presented SEM micrograph(Fig.3)the deposited mullite layer is shown for the EPD conditions of15V/15s. According to the SEM micrograph,it is obvious that for the chosen EPD conditions the obtained layer adheres well to the surface of the substrate.The EDX analysis at the indicated spot showed a composition close to3/2-mullite.5.Thermogravimetric analysis of the oxidation rate in airThe protectiveness of the electrophoretically deposited mullite layers against isothermal oxidation in air in the tem-perature range from1300to1550◦C was investigated byT.Damjanovi´c et al./Journal of the European Ceramic Society25(2005)577–587581Fig.3.SEM micrograph of the cross-section of the electrophoretically deposited mullite layer on C/C–SiC at15V cm−1for15s(1×:EDX analysis spot).means of thermogravimetry(TG).The results are given in Table2.The experimentally obtained values for the oxidation rate of the mullite coated C/C–SiC samples were interpreted with the help of a phenomenological model whose basic version had been originally developed in our group by Fritze et al.1 for pulsed laser deposited mullite layers.According to this model(see Fig.4a),the samples exhibit a mass gain in the whole temperature range,due to the passive oxidation of the SiC layer.The formation of SiO2overcompensates the mass loss due to CO formation according to the reaction:SiC+32O2→SiO2+CO(1) The model will be applied to two situations,named case A and case B in the following.Table2Practical linear rate constants,k L,and practical parabolic rate constants, k P,for T≤1350◦C and for T≥1400◦C.The experimental values were, respectively,determined with the help of Eqs.(14)and(16)T(◦C)k L(mg cm−2h−1)k0L(mg cm−2h−1) H a(kJ mol−1) 1300 1.72×10−3 1.53×1083301350 3.74×10−3k P(mg2cm−4h−1)k 0P(mg cm−4h−1)1400 4.91×10−5 1.12×107362±66 1450 1.61×10−41500 1.90×10−41550 5.00×10−4Case A:The rate-limiting step is assumed to be trans-port of oxygen through the protective layer composed of the mullite layer and a native SiO2layer growing under-neath.Under the assumption that mullite does not substan-tially dissolve in the silica scale,the time(t)dependent thickness of the growing SiO2layer,x S(t),is obtained as follows:1With the atomic or ionic oxygenﬂux densities j M and j S in the mullite(M)and in the silica layer(S),respectively, j M=−˜D M c MRT∂µO∂x M(2a) j S=−˜D S c SRT∂µO∂x S(2b)the formal molecularﬂux density,j O2,of oxygen can be derived as follows:j O2=12j M=12j S=14˜D S c S˜D M c M˜D S c S x M+˜D M c M x S| µO2|RT(3)where˜D S,˜D M is the effective chemical diffusivity of oxy-gen O,(O2−or O2),in vitreous(or polycrystalline)SiO2and in polycrystalline mullite;x S(t),x M is the thickness of the silica layer and of the mullite layer;c S,c M is the molar con-centration of oxygen in silica and in crystalline3/2-mullite;µO is the chemical potential of oxygen(=1/2µO2); µO2 is the difference of the chemical potential of oxygen(seeFig.4a:µO2(I)−µO2(III)).582T.Damjanovi´c et al./Journal of the European Ceramic Society 25(2005)577–587Fig.4.(a and b)Schematic representation of the variation of the chemicalpotential of O 2and CO in the layer system mullite-SiO 2according to the case A (oxygen diffusion rate determining)and case B (CO diffusion rate determining),respectively.According to Eq.(1)the growth rate of the silica layer at the interface III is given by the following expression:d x S (t)d t =23V m ,SiO 2j O 2(4)which,together with Eq.(3),yields after integration:x S (t)=α(1+βt)−1 (5)where the parameters αand βare deﬁned as follows:α=213V m ,M V m ,S ˜DS ˜D M xM β=1696 V m ,S V m ,M 2| µO 2|RT 1x 2M ˜D 2M˜DS (7)where V m ,S ,V m ,M is the molar volume of silica and of mul-lite,respectively.As long as the growing SiO 2layer is much thinner than the deposited mullite layer (short oxidation times,i.e.,βt 1),oxygen diffusion through the mullite layer is the rate limitingstep and the oxidation kinetics is linear.Eq.(5)reduces to:x S (t)=12αβt =136V m ,S V m ,M | µO 2|RT ˜DM x Mt =k L t (8)withk L =136V m ,S V m ,M | µO 2|RT ˜DM x M(9)as the linear rate constant,which is directly proportional tothe oxygen diffusion coefﬁcient in the mullite layer,˜DM ,and inversely proportional to the thickness of the mullite layer,x M .Longer oxidation times (βt 1)lead to thicker SiO 2layers,and transition from the linear to the parabolic growth law will occur:x S (t)=αβ1/2t 1/2= 23| µO 2|RT˜D S 1/2t 1/2= 2k P √t(10)The parabolic rate constant k P is deﬁned as:k P =12α2β=13| µO 2|RT˜D S (11)and is directly proportional to the oxygen diffusion coefﬁ-cient in the SiO 2layer,˜DS .In agreement with the exper-iments this simple model shows that after long times the oxidation kinetics become parabolic.For the evaluation of the TG data,the oxidation rate can be expressed in terms of the mass change rate:1A 0d ( m sample )d t =ρS 3d x S d t =ρS 6αβ√1+βt (12)where A 0is the total (geometrical)surface of the sample,ρS the density of amorphous silica or ␤-cristobalite,respec-tively.For short oxidation times (βt 1)Eq.(12)yields a constant oxidation rate:1A 0d ( m sample )d t =ρS 6αβ=kL(13)which,after integration,yields a linear time dependency for the mass change: m sample A 0=kL t (14)with k L as a practical linear rate constant (for TG experi-ments).For longer oxidation times (βt 1)we obtain from Eq.(12)a time dependent oxidation rate:1A 0d ( m sample )d t =ρS 6α√β√t= k P 2t (15)which,after integration,yields a parabolic time dependency for the mass change: m sample A 02=2kP t (16)T.Damjanovi´c et al./Journal of the European Ceramic Society 25(2005)577–587583Table 3Calculated rate constants T (◦C)k L(mg cm −2h −1)k 0L(mg cm −2h −1) H a (kJ mol −1)1300 1.85×10−1 1.38×101135713504.30×10−1k Pfrom Eq.(18)with ˜D S from Eq.(19)after Rodriguez-Viejo et al.27:vitreous SiO 2k P(mg 2cm −4h −1)k 0P(mg 2cm −4h −1)1400 1.05×10−27.37×1073151450 2.03×10−21500 3.78×10−21550 6.78×10−2k Pfrom Eq.(18)with ˜D S from Eq.(20)after Rodriguez-Viejo et al.27:␤-cristobalitek P(mg 2cm −4h −1)k 0P(mg 2cm −4h −1)1400 2.80×10−3 4.0×10104211450 6.74×10−31500 1.54×10−21550 3.38×10−2Case A:Oxygen diffusion rate determining;k Lfrom Eq.(17)with ˜D Meff from Eq.(24)after Fielitz et al.5,6,26with k Pas a practical parabolic rate constant (for TG exper-iments).With the working Eqs.(17)and (18):kL =1318M S V m ,M | µO 2|RT ˜D M x M =ρS 3k L (17)k P=ρ2S 913| µO 2|RT ˜D S =ρ2S 9k P(18)oxidation rate constants can be calculated from diffu-sivity data for the linear and for the parabolic growth regime,respectively,and can be compared with experi-mentally obtained values (see Tables 2and 3)depending on the given oxidation time and temperature.For the mo-lar volume of mullite and for the densities of the vitreous silica and of ␤-cristobalite,respectively,the following values were adopted:V m ,M =134.81cm 3mol −1,ρam =2.2g cm −3,ρcr =2.27g cm −3,M S =60.082g mol −1is the molar mass of SiO 2.The thickness of the EPD–mullite layer was x M =7.5␮m (for EPD at 15V/15s).For the diffusion data for oxygen in single crystalline 2/1-mullite 5and polycrystalline 3/2-mullite,6,26in amor-phous silica and in ␤-cristobalite,27respectively,the follow-ing data set was used:SiO 2:see Rodriguez-Viejo et al.27D am =1.1×10−6exp −333kJ mol−1RT(m 2s −1)(19)D cr =5.6×10−4exp −439kJ mol−1RT(m 2s −1)(20)Mullite :see Fielitz et al.5,6,26D V =3.71×10−5exp−(433±21)kJ mol−1RT(m 2s −1)(21)D GB =6.2×10−3exp−(363±25)kJ mol−1RT(m 2s −1)(22)As has been shown,5there is only a small difference in the bulk diffusivity,D V ,measured in 2/1-mullite and in 3/2-mullite.For our calculations,we used an effective tracer diffusiv-ity,D Meff ,for the oxygen transport in polycrystalline mul-lite:D Meff =D V 1+4δd D GBD V(23)where δ≈1nm is the grain boundary thickness and d ≈35nm is the grain size,which was determined from XRD peak broadening.Inserting the values for δand d in Eq.(23)together with the data for volume and grain boundary tracer diffusion of oxygen in polycrystalline mullite,we get the following ex-pression for D Meff :D Meff =3.7×10−5e −(433±21)kJ mol−1/RT ×(1+19.1e (70±46)kJ mol−1/RT)(m 2s −1)(24)i.e.,D Meff (1573K)≈4×103D V (1573K).The calculated values of k L and k Pgiven in Table 3were obtained by setting ˜D S =D am (from Eq.(19))or ˜DS =D cr (from Eq.(20))and ˜DM =D Meff (from Eq.(24)).The value of µO 2is estimated as follows:the standard Gibbs energy of formation for the reaction in Eq.(1), G ◦1,can be expressed by the corresponding standard Gibbs en-ergies of formation for SiO 2,SiC and CO 28:G ◦1= G ◦SiO 2− G ◦SiC + G ◦CO(25)The equilibrium condition at the SiO 2/SiC interface (III)leads to:e − G ◦1/RT =a CO (III )a 3/2O 2(III )(26)with a CO ,a O 2being the activities of CO and O 2,respectively.In general,a CO (III)will be lower than unity.If,for the sake of simplicity,we set a CO (III )=1,we obtain:a O 2(III )=(e G ◦1(T)/RT )2/3(27)i.e.,µO 2RT =ln 0.2−23 G ◦1RT(28)for oxidation in air (a O 2(I )=0.2).In the temperature range under study,1573K ≤T ≤1823K, µO 2/RT varies between 39.84and 33.32.。

以功能化有机硅碳纳米管生产新型碳基流体

以功能化有机硅碳纳米管生产新型碳基流体表面功能化的简单或复杂的分子的碳纳米管是一个值得而又具有挑战性的任务。

我们的目标是设计在胶体，电子，高分子复合材料，传感器和药物输送[1,2]中的具有应用潜力的新材料。

由纳米管核心以及与之相连的壳形修饰分子组成的表面功能化碳纳米管,代表一种独特的一类混合动力系统。

通过使表面功能化碳纳米管与每个单独的成分进行化合，形成单一均相体系，进而获得设计的特殊性能。

与表面相连的分子鞘的物理、化学性质对于混合物的最终性能，起到至关重要的作用。

然而，为实现这些目标人们已经进行了具有重要意义的探索。

其中，最近的努力就是致力于合成具有更加复杂行为与性质的新型碳纳米管衍生物。

通常情况下，功能化碳纳米管表现出固体状的行为，在无溶剂或介质的条件下，不接受任何宏观的固体，液体的过渡。

最近，有报道称通过在纳米管上连接短树冠--灵活的聚苯乙烯链，合成了可溶的功能化碳纳米管。

最近，据报道通过在纳米管上连接短树冠--灵活的聚苯乙烯链，合成了可溶的功能化碳纳米管。

在进一步扩展碳基流体范围的努力中，本文提供了一种基于硅功能化碳纳米管的新体系。

碳纳米管是首先被氧化，然后进行环氧有机硅反应。

与此前公布的PEG尾混合不同，新的硅功能化碳纳米管衍生在室温已经是液体，而且包含的碳纳米管的显著较高的数额，即85％ W / W。

具有异常高含量碳纳米管的流体与环境条件相结合的行为显示出巨大的优势，并可能被证明有助于在一个潜在范围的应用[5,6]。

整体合成包括两个步骤（图1）。

第一步包括用食人鱼洗液氧化水碳纳米管。

后者，导致切割碳纳米管的表面上有亲核组（- COOH，- OH）修饰的末端开口。

在第二个步骤中，添加了液体，环氧终止硅。

羧酸和羟基的表面氧化反应，经亲核性攻击含环氧乙烷环硅胶终止链，产生一个永久性的共价附件。

虽然大部分的硅胶是以共价形式连接碳纳米管,但部分被硅聚合物链包裹的管子并不能完全排除。

反应的第一步，需要一定的时间在表面上集聚足够浓度的亲核集团来满足碳纳米管的氧化处理。

现象学英语

现象学英语Phenomenal 英文版:In today's interconnected world, English has emerged as the lingua franca, a bridge for communication across diverse cultures and nations. The phenomenon of English is not just about the language itself but also about the cultural, economic, and social implications that come with its widespread use. This article delves into the multifaceted aspects of English as a global language and offers insights into mastering it for effective communication.The Rise of English as a Global LanguageThe spread of English is often attributed to thehistorical reach of the British Empire, followed by the cultural and economic influence of the United States. Today, English is the primary language of international business, science, technology, and diplomacy. It is also the most widely taught second language in the world, with an estimated 1.5 billion learners.Cultural Exchange and EnglishAs a medium for cultural exchange, English allows for the sharing of ideas, art, and literature across borders. It has also absorbed words and phrases from many other languages, enriching its vocabulary and reflecting its adaptability.Learning English is not just about grammar and vocabulary;it's also about understanding the cultural nuances that accompany the language.The Digital Age and EnglishThe advent of the internet and social media has further cemented English's status as the language of the digital world. Most online content is in English, making it essential for anyone looking to participate in global online communities or access information from around the globe.Strategies for Mastering English1. Consistent Practice: Regular engagement with the language through speaking, writing, reading, and listening is crucial for improvement.2. Immersive Learning: Surrounding oneself with English, whether through media, travel, or conversation, can significantly enhance language acquisition.3. Formal Education: Structured learning through courses and certifications can provide a solid foundation in grammar and vocabulary.4. Technology: Utilizing language learning apps, online resources, and social media can make learning more accessible and interactive.5. Cultural Immersion: Understanding the cultural contextof the English-speaking world can lead to a more profound understanding of the language.The Future of English as a Global LanguageThe future of English as a global language seems assured, given its entrenched role in international communication. However, the language continues to evolve, with new words and usages being adopted from the cultures it interacts with.ConclusionMastering English is more than just learning a language;it's about embracing a tool for global interaction. AsEnglish continues to be a phenomenon in itself, those who invest in learning it gain access to a world of opportunities, ideas, and people. The journey to proficiency is a rewarding one, offering not just linguistic skills but also a deeper connection to the global community.。

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* Corresponding
author.
concurrent loss in thermal conductivity. An attractive and viable approach or mechanism for improving the strength of copper is to introduce a fine dispersion of a second-phase into the matrix material, resulting in a dispersion strengthened CDS) alloy [5-S]. Oxides are the most common second-phase particles used to strengthen the copper matrix, but nitrides, borides and carbides have also been used as candidates. In fact, for optimum strengthening, the second-phase oxide dispersion strengthened particles must be extremely small and the interparticle spacing small [7]. Copper matrices containing fine dispersions are particularly attractive for their excellent combinations of thermal and electrical conductivities, strength retention at elevated temperatures, and overall microstructural stability [6-81. Since the early 1970’s a patented family of dis-
persion strengthened copper emerged and became commercially available under the trade name GlidCopR [7,8]. An attractive feature of this material was an intrinsic ability to resist softening, while concurrently retaining its strength and conductivity properties even after continuous exposure to elevated temperatures approaching the melting point of the matrix. The much superior properties of the oxide dispersion strengthened copper material arises from the competing influences of size and distribution of the insoluble submicroscopic aluminum oxide (Al,O,) particles in a high-purity copper matrix. These particles range in size from 3 to 12 nm with an interparticle spacing of 30 to 100 nm and a particle density of the order of 10’6-10’7 cmm3 [7,8]. The Al,O, particles are hard, and chemically and thermally stable at elevated temperatures. On account of their chemically inert nature they exert little influence on the electrical conductivity of the matrix material. Besides, the insoluble Al,O, particles retain their original size, distribution and spacing even after prolonged exposure to elevated temperatures. The overall thermal stability of the dispersed particles is largely responsible for their excellent resistance to softening. Furthermore, since the volumetric percentage of the dispersed Al,O, particles is small, the physical properties, namely: (a) melting point, (b) density and (c) coefficient of thermal expansion of the oxide dispersion strengthened copper matrix, are very similar to those of pure copper, while the modulus of elasticity and strength are substantially higher [7,8]. Additional improvements in the properties of GlidCopR were achieved through the controlled addition of elemental niobium [9,10]. The niobium reinforcements are distributed uniformly in an internally oxidized, dispersion strengthened copper matrix. The unique properties of GlidCopR AL- 15 coupled with the refractory metal characteristics of niobium results in a composite material that is potentially viable for use as resistance-welding electrodes and tooling. The composite powder mixture is consolidated in the same manner as conventional dispersion strengthened copper powder, to produce a variety of shapes. The objective of this paper is to document the microstructure, tensile deformation and fracture behavior of a dispersion strengthened copper-niobium composite.
00167-577X/96/$12.00 Copyright PII SO 167-577X(96)0009 l-2
0 1996 Elsevier Science B.V. All rights reserved.
424
T.S. Sricatsan et al. /Materials
Letters 28 (1996) 423-429
Received 15 March 1996; accepted 28 March bium particulate reinforced aluminum oxide (Al,O,) dispersion strengthened copper composite is an attractive and emerging engineering material for applications requiring high strength, high thermal and electrical conductivities and resistance to softening at elevated temperatures. In this paper, the microstructure and tensile behavior of the composite is examined. The strength of the material marginally decreases at elevated temperatures with a concomitant improvement in ductility. The composite microstructure maintained a high value of the yield strength/ultimate tensile strength ratio. The fracture behavior of the composite is examined in light of intrinsic microstructural effects, nature of loading and deformation characteristics of the matrix.
’ Department of Mechanical Engineering, The Unicersi@ of Akron, Akron, OH 44325.3903. USA
’ SCM Metal Products Inc., 2601 Week Drive, Research Triangle Park, NC 29909-2166, USA