基于氨基作为质子迁移桥梁的蛋氨酸分子旋光异构机理

Optical Isomerism Mechanism of Methionine Molecule Based on Amino Group as Proton Transfer Bridge

采用密度泛函理论的B3LYP方法和微扰理论的MP2方法,研究两种最稳定构型的蛋氨酸分子(Met)基于氨基作为质子迁移桥梁的旋光异构反应.结果表明:基于氨基作为质子迁移桥梁的蛋氨酸分子旋光异构反应有2条通道a和b;构型1的主反应通道为通道a,决速步骤为第1基元反应,自由能垒为264.2kJ/mol,由质子从手性C直接向氨基N迁移的过渡态产生;构型2的主反应通道也为通道a,决速步骤为第2基元反应,自由能垒为266.1kJ/mol,由羧基异构后质子从手性C向氨基N迁移的过渡态产生;两种构型的Met分子旋光异构速控步骤的反应速率常数分别为3.04×10^(-34),1.41×10^(-34) s^(-1).

We studied the optical isomerism reaction of two kinds of the most stable configurations of methionine molecules based on amino group as proton transfer bridge by using the B3LYP method of density functional theory and the MP2 method of perturbation theory.The results show that there are two channels a and b in the optical isomerism reaction of methionine molecules based on amino group as proton transfer bridge.The dominant reaction channel of the configuration one is channel a,the rate-determining step is the first elementary reaction,and the free energy barrier is 264.2kJ/mol that is generated by the transition state of proton transfer from the chiral C to the amino N.The dominant reaction channel of the configuration two is the channel a,the rate-determining step is the second elementary reaction,and the free energy barrier is 266.1kJ/mol that is generated by the transition state of proton transfer from the chiral C to the amino N after carboxyl group isomerism.The reactionrate constants of the optical isomerism rate-determining step of two configurations of methionine molecules are 3.04×10^（-34）,1.41×10^（-34） s^（-1）,respectively.