气相环境下Cu2+催化α-丙氨酸手性对映体转变的机理

Mechanism of Chiral Enantiomer Transition of α-Alanine Catalyzed by Cu2+ Ions in Gas Phase

采用基于密度泛函理论的ɷB97X-D和M06方法,研究了气相环境下Cu2+催化α-丙氨酸(α-Ala)分子两种稳定构型的手性对映体转变。对于构型1的手性转变反应考察了4个通道(ai,aj,ak和b),ai、aj和ak通道分别是羟基旋转后α-H以氨基氮、铜及与铜配位的羰基氧为桥迁移;b通道是羟基氢向氨基氮迁移后α-H向羰基氧迁移,接着质子从质子化氨基向α-C迁移。对于构型2的手性转变反应考察了α-H以氨基氮为桥迁移的通道。势能面计算表明:对于构型1,aj通道具有优势,决速步骤的内禀能垒为120.3 kJ·mol^-1,构型2在决速步骤的内禀能垒为189.0 kJ·mol^-1。结果表明:相对于孤立环境下α-Ala分子的手性转变,气相环境下Cu2+对α-Ala分子的手性转变反应具有较好的催化作用。

The chiral enantiomer transition of two stable conformations ofα-alanine(α-Ala)molecules catalyzed by Cu2+ions in gas phase was studied by means ofɷB97X-D and M06 methods based on density functional theory.For the chiral transition of Con⁃figuration 1,four channels(ai,aj,ak and b)were investigated.Among which,after hydroxyl rotationα-H is transferred in channel ai,aj and ak using amino N as a bridge,copper and carbonyl oxygen coordinated with copper,respectively.Furthermore,α-H is transferred to carbonyl O after hydroxyl H transferred to amino N,and then proton is transferred from protonated amino toα-C.As for Configuration 2,the channel,whereα-H is transferred using amino N,is investigated in the chiral transition reaction.The potential energy surface shows that for Configuration 1,the channel aj is more advantageous and the energy barrier of the rate-de⁃termining step is 120.3 kJ·mol^-1,and that is 189.0 kJ·mol^-1 for Configuration 2.The results indicate that Cu2+ions in gas phase have a better catalytic effect on the chiral transition ofα-Ala molecules compared withα-Ala molecules in isolated environment.