水环境下具有氨基和羧基间双氢键的缬氨酸旋光异构及羟自由基致损伤的机理

摘要

在MP2/6-311 ++G(2df,pd)//B3LYP/6-31 +G(d,p)双理论水平,采用自洽反应场(SCRF)理论的smd模型方法,对标题反应进行了研究.反应通道研究表明:水环境下缬氨酸的旋光异构可以在3个通道a、b和c实现,分别是质子以水分子簇为媒介以氨基氮、羰基氧和羧基为桥梁,从α-碳的一侧迁移到另一侧;水分子辅助羟自由基抽氢致缬氨酸损伤发生在a通道.势能面计算表明:2个和3个水分子簇作氢迁移媒介时,水分子簇对旋光异构反应的氢迁移过程有极好的催化作用,使反应能垒相对裸反应大幅降低,水溶剂效应在a通道有较好的助催化作用,对b和c通道影响不大.水分子辅助羟自由基抽氢致缬氨酸损伤气相反应能垒较低,水溶剂效应对此反应有较大的阻碍作用.%The mechanism of optical isomerization of valine molecules with dual-hydrogen bonds between amino and carboxyl groups and the damage induced by hydroxyl radicals in water environment were stud-ied by using MP2/6-311 ++G(2df,pd)//B3LYP/6-31 +G(d,p)dual-theory and SMD model method for self consistent reaction field(SCRF)theory.The study of reaction channels showed that there were three channels a,b and c in the optical isomer reaction of valine in water environment.Using water cluster as medium,the protons transfered from one side of the α-carbon to the other side with N atom of amino group,O atom of carbonyl group and carboxyl group as bridges.The hydrogen abstraction reaction which damaged the valine molecules happened in channel a,and the water molecules were assistants. The potential energy surface calculation showed that when two or three water clusters were used as hydro-gen transport medium,they acted a good catalytic action on the process of hydrogen-transfer of Optical I-somerization,and reduced the barrier of reaction vs naked reaction.Water solution effect had good cata-lytic activity in channel a,but catalytic activities were not obvious in channel b and c.The reaction bar-rier of hydrogen abstraction reaction which damaged the valine molecules with water molecules as assis-tants was low.The water solution effect has a big impediment effect on this reaction.