几种稳定构型精氨酸分子的手性转变反应机理及水溶剂化效应

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种最稳定构型的精氨酸分子的手性转变机理及水溶剂化效应.研究发现标题反应有3条通道a、b和c.对于构型1,分别是手性碳上的质子以氨基、羰基和氨基联合以及羧基和氨基联合为桥迁移.对于构型2,分别是手性碳上的质子只以氨基为桥、羧基异构后再以氨基为桥迁移及以羧基和氨基联合作桥迁移.势能面计算表明:构型1的主反应通道都是a,决速步自由能垒分别为268.2kJ·mol~(-1),来源于质子从手性碳向氨基氮迁移的过渡态.构型2的主反应通道是b,决速步自由能垒为239.3kJ·mol~(-1),来源于质子从手性碳向氨基氮迁移的过渡态.水溶剂效应使构型2的主反应通道决速步自由能垒降到95.7kJ·mol~(-1).结果表明:随着温度的升高,构型2先手性转变;水溶剂对精氨酸的手性转变有极好的催化作用.

Chiral Conversion Mechanism and Water Solvation Effect of Several Arginine Molecules of Stable Configurations

The chiral conversion mechanism and water solvation effect of three kinds of the most stable configurations of arginine molecules were researched by using the B3LYP method of density functional theory,the MP2 method of perturbation theory,and smd model method of self consistent reaction field theory.The study of reaction channels shows that there are three channels a,b and c in the title reaction.For the configuration 1,the proton of the chiral carbon is transferred with amino group,carbonyl/amino groups and carboxyl/amino groups as the bridge,respectively.For the configuration 2,the proton is transferred directly with amino group as the bridge,then carboxyl isomerism,the proton is transferred with amino group and carboxyl/amino groups as the bridge,respectively.Calculations of potential energy surface show that channel a is the dominant reaction path in the configuration 1,step-determining Gibbs free energy barriers are 268.2 kJ · mol-1,which are generated by the transition state of proton transfer from the chiral carbon to the amino N.In addition,channel b is the dominant reaction path in the configuration 2,step-determining Gibbs free energy barrier is 239.3 kJ · mol-1 that is generated by the transition state of proton transfer from the chiral carbon to the amino N.The water solvation effect enables the step-determining energy barrier is reduced to 95.7 kJ · mol-1 for the dominant reaction path in the configuration 2.The results show that chiral conversion of the configuration 2 is achieved with the increase temperature.The water environment has an excellent catalytic effect on the arginine optical isomerization.