水液相环境下苯丙氨酸分子的手性对映体转变机理

Chiral Enantiomer Transition Mechanism of Phenylalanin Molecule in Water Liquid Environment

在MP2/6-311++g(3df,2pd)/WB97X-D/6-311++G(d,p)双水平,结合自洽反应场理论的SMD模型方法,对标题反应进行了研究.反应通道研究发现:水液相环境下苯丙氨酸(Phe)分子手性对映体转变反应在质子直接迁移时有2个通道,水分子(簇)作质子迁移媒介时有3个通道.势能面计算表明:水液相环境与气相环境比较,质子从α-碳向羰基氧直接迁移的内禀能垒小幅升高,质子从α-碳向氨基氮直接迁移的内禀能垒小幅降低;2个水分子簇作媒介时,质子从α-碳向羰基氧迁移的内禀能垒小幅升高,质子从α-碳向氨基氮迁移的内禀能垒显著降低.水液相环境下Phe分子手性对映体转变反应的优势通道是α-氢以氨基氮为桥迁移,质子直接迁移时反应的活化能是260.36kJ·mol^-1,2个水分子簇作质子迁移媒介时反应的活化能是107.64kJ·mol^-1.结果表明,水液相环境下水分子(簇)的催化可以使Phe分子实现手性对映体转变.

The chiral enantiomer transition mechanism of phenylalanin molecule has been investigated in water liquid environment,by means of both MP2/6-311++g(3 df,2 pd)∥WB97 X-D/6-311++G(d,p)methods and SMD model method of self-consistent reaction field theory.The research reveals that there are two channels in the direct migration of protons for chiral enantiomer transformation reaction of Phe molecule in water liquid environment.There are three channels through water molecules(cluster)act as proton transport media for this transformation reaction.The calculation of potential energy surfaces indicate the internal energy barrier for direct migration of protons fromα-C to carbonyl oxygen is slightly increased,the intrinsic energy barrier for protons transfer fromα-C to amino nitrogen is weakly reduced when the water liquid environment is compared with the gas environment.Furthermore,the internal energy barrier for protons transfer fromα-C to carbonyl oxygen is slightly increased,the intrinsic energy barrier for protons transfer from α-C to amino nitrogen is significantly reduced because of two water molecules cluster as proton transfer medium.The transfer process ofα-H across the aminonitrogen bridge is the dominant reaction path for chiral enantiomer transformation of Phe molecule in water liquid environment.The activation energy of the direct transport of protons is 260.36 kJ·mol^-1,the activation energy is 107.64 kJ· mol^-1 because of two water molecules cluster as proton transfer medium.The results confirmed that the catalysis of water molecules(cluster)can facilitate Phe molecule accomplish chiral enantiomer transformation in water liquid environment.