重庆大学生物有机化学-第四章-酶化学-第一节

di re cti o n of dip ole mo m e nt
O C HH
Form al de hy de m = 2.33 D
共价键的断裂
均裂
A
B
hv
A
B
（一对电子平均分给两个原子或原子团）
R CH 3
异裂
a or b
C
D
极性溶剂
离子型反应分为亲核与亲电反应:
C
+D
C +D
R+, CH3+ 碳正离子，可作为亲电试剂 R-, CH3- 碳负离子，可作为亲核试剂
These molecules have polar bonds, but each has a zero dipole moment（非极 性分子含有极性键，但分子总的偶极距为0）
OCO
Carbon dioxide m =0 D
F
BF
F
Boron trifluoride m =0 D
Cl
C
Cl
Bo n d D ipole Bond (D)
H-C 0.3 H-N 1.3 H-O 1.5
H-S 0.7
C-F 1.4 C-Cl 1.5 C-Br 1.4
C-I 1.2
C-O 0.7 C=O 2.3
C-N 0.2 C=--N 3.5
Polar and Nonpolar Molecules（极性和非极性分子）
Shapes of a Set of 2p Atomic Orbitals
Three-dimensional shapes of 2p atomic orbitals
Hybrid Orbitals
Hybridization of orbitals (L. Pauling)
the combination of two or more atomic orbitals forms a new set of atomic orbitals, called hybrid orbitals
生物化学家通过生化方法研究生命过程，这些方法包括酶纯化和分析，在体放射性同位素示踪剂 研究。
Reaction or synthetic mechanisms
Biological related molecules
Bioorganic chemistry
Create new compounds
有机化学的基本概念补充
sp3 Hybrid Orbitals
each sp3 hybrid orbital has two lobes of unequal size
the sign of the wave function is positive in one lobe, negative in theБайду номын сангаасother, and zero at the nucleus
•化学键类型 •共价键 •极性 •碳原子成键时的杂化及形状 •顺反异构 •对映异构及旋光性
有机化合物中共价键理论
价键理论 （1） 价键的形成可看作是原子轨道的重叠或电子配对的结果，如：
x
x C x + 4H
.
x
H x
Hx C xH x
H H CH
H
H
（形成键的电子对在成键前是属于一个原子时，形成的键称配价键，存在
Transition state (T.S.) theory过渡态理论
The function of a catalyst is to provide a new reaction pathway in which the rate-determining限速的 (slowest) step has a lower free energy自由能 of activation than the rate-determining step of the uncatalyzed reaction. （酶 的作用是提供一种新的反应途径，在这条途径中，限速步骤具有更低的活化能）
Overlap of hybrid orbitals can form two types of bonds depending on the geometry of overlap
bonds are formed by “direct” overlap bonds are formed by “parallel” overlap
己醛糖有4个手性碳原子，有16种对映异构体，常见的葡萄糖溶 液中绝大多数葡萄糖分子形成两种环状的旋光异构体。
Chapter 4 Enzyme Chemistry
酶化学
o授课安排
o一般催化剂的概念及催化机理 o酶作为特殊的生物催化剂的特点及催化机理
Introduction to catalysis（催化剂简介）
sp2 Hybrid Orbitals
the axes of the three sp2 hybrid orbitals lie in a plane and are directed toward the corners of an equilateral triangle
the unhybridized 2p orbital lies perpendicular to the plane of the three hybrid orbitals
有机化学家开发可更好的理解有机反应机理的合成方法，并创造新物质。
Biochemists study life processes by means of biochemical methodology: enzyme purification and assay, radioisotopic tracer studies in in vivo system.
other and to the line created by the axes of the two sp hybrid orbitals
Bonding in Acetylene, C2H2
顺反异构
H C
H3C
CH3 C
H
H C
H3C
H C
CH3
许多昆虫的信息素具有1个或多个碳 碳双键，通常存在顺反异构。一种 热带雌蚕蛾会分泌“蚕蛾醇”的性 信息素吸引同类雄蛾。蚕蛾醇有多 种顺反异构体，其中只有A能传递 信息。
nuclei（是价键原子上的电荷乘以两价键原子核间的距离） Table shows average bond dipole moments of selected covalent bonds（下表显示了一些
共价键的平均偶极距）
Bond Dipole Bond (D )
Bond Dipole Bond (D )
Classification of catalyst and catalysis（催化剂和催化反应的分类）
异相催化和均相催化
Catalysts may be classified as heterogenous异相的, or not in solution and homogenous均相的, or limited to one phase, in which a surface or phase boundary is absent.
O
H
H
W at e r m = 1.85D
N
H
H
H
Am mo ni a m = 1.47D
di re cti o n of dip ole mo m e nt
Polar and Nonpolar Molecules
formaldehyde has polar bonds and is a polar molecule
Basic concepts基本概念
Catalyst: A catalyst is any substance that alters the speed of a chemical reaction without itself undergoing change. A catalyst may either increase or decrease the velocity of a chemical reaction. As catalysts, enzymes need only be present in small amounts. 催化剂是改变化学反应速度，同时它自己在反应前后不产生没有任何变 化的物质。一种催化剂可能增加或降低化学反应的速度。酶作为催化剂， 仅少量就能达到效果。
Shapes of 1s and 2s Orbitals
Probability distribution (2) for 1s and 2s orbitals showing an arbitrary boundary surface containing about 95% of the electron density
旋光异构
两种分子式相同的有机分子，其空间结构互为镜 像，且不能完全重叠，即成为对映异构体。这种分 子称为手性分子。手性分子有旋光性。手性分子中 具有与4个不同原子（或原子团）相连接的碳原子 （手性碳原子）。
甘油醛存在1个手性 碳原子，有两种D型 和L型对映异构体， 它们的旋光性恰好 相反。
L-丙氨酸、D-丙氨酸
Cl
Cl
Carbon tetrachloride
m =0 D
Polar and Nonpolar Molecules
These molecules have polar bonds and are polar molecules（极 性分子含有极性键，而且分子总的偶极距不为0）
di re cti o n of dip ole mo m e nt
We deal with three types of hybrid orbitals
sp3 (one s orbital + three p orbitals) sp2 (one s orbital + two p orbitals) sp (one s orbital + one p orbital)
the four sp3 hybrid orbitals are directed toward the corners of a regular tetrahedron at angles of 109.5°
sp3 Hybrid Orbitals
orbital overlap pictures of methane, ammonia, and water
Bonding in Ethylene
Bonding in Formaldehyde
sp Hybrid Orbitals
two lobes of unequal size at an angle of 180° the unhybridized 2p orbitals are perpendicular to each
电子得失时则形成离子键。）
共用两对电子形成双键，其余类推：
H HC
H CH
HH CC
HH
Polar Covalent Bonds（极性共价键）
Bond dipole moment (m)（偶极距）:
a measure of the polarity of a covalent bond（是对共价键极性的一种量化，是一个矢量） the product of the charge on either atom of a polar bond times the distance between the
生物化学是一门交叉学科。从本质上来说，生物有机化学是应用化学手段去理解生化过程。如， 生物膜是如何工作的，大脑是如何工作的？
Organic chemists develop synthetic methodology to better understand organic mechanisms and create new compounds.
生物有机化学 第四章 酶化学 第一节
Bioorganic Chemistry
•Why study bioorganic chemistry? •How to study bioorganic chemistry?
Bioorganic chemistry is a discipline that is essentially concerned with the application of the tools of chemistry to the understanding of biochemical process. For example, how does a biological membrane work? How does a brain work?