基于氨基做质子迁移桥梁水环境下蛋氨酸分子的旋光异构

Optical isomerism mechanism of methionine molecule in water based on amino group as proton transfer bridge

采用密度泛函理论的B3LYP方法、微扰理论的MP2方法和自洽反应场(SCRF)理论的smd模型方法,研究了2种稳定构型蛋氨酸分子的标题反应。反应历程研究发现:构型1旋光异构经历2个基元反应,构型2旋光异构经历5个基元反应。势能面计算表明:构型1和2的决速步骤分别是第1和第2基元反应。水气相环境下决速步能垒分别是124.4和128.7 kJ·mol^(-1),液相环境下决速步能垒分别是104.9和105.2 kJ·mol^(-1),远低于裸环境的决速步能垒264.2和266.1 kJ·mol^(-1)。气相环境下表观活化能分别是140.8和155.0 kJ·mol^(-1),液相环境下表观活化能分别是97.9和98.9 kJ·mol^(-1)。结果表明:水分子和水溶剂对蛋氨酸旋光异构反应的质子迁移过程具有较好的催化和助催化作用。水汽环境下蛋氨酸会损伤,蛋氨酸的旋光异构可以在水液相环境下缓慢实现。

The optical isomerism reaction of two kinds of the most stable configurations of methionine molecules with amino group as proton transfer bridge were explored by using the B3LYP method of density functional theory and the MP2 method of perturbation theory.The study of reaction process showed that optical isomerism of configuration 1 goes through 2 elementary reactions and configuration 2 goes through 5 elementary reactions.Calculations of potential energy surface pointed out that the step-determining of configuration 1 is first elementary reaction and configuration 2 is second elementary reaction.The step-determining energy barriers are 124.4 and 128.7 kJ·mol^（-1） in gaseous water environment and they are 104.91 and 105.2 kJ·mol^（-1） in liquid water environment,respectively,far lower than the energy barriers of 264.2 and 266.1 kJ·mol^（-1） in the bare environment.The apparent activation energies are 140.8and 155.0 kJ·mol^（-1） in gaseous water environment and they are 97.9 and 98.9 kJ·mol^（-1） in liquid water environment,respectively.The results showed that water molecules and water solvents have good catalytic effects on the optical isomerism of methionine molecule the in proton transfer process.The methionine can be damaged in water environment.The optical isomerism of methionine molecule can be slowly realized in liquid water environment.