水液相下两性α丙氨酸K+配合物旋光异构的理论研究

Theoretical Study on the Optical Isomerization of Amphotericα-Alanine and K+Complexes in Water-Liquid Phase Environment

采用密度泛函理论的M06-2X方法,结合自洽反应场理论的SMD模型方法,研究了水液相下两性S型α丙氨酸与一价钾离子配合物(S-α-Ala·K^(+))的旋光异构.反应通道研究发现:S-α-Ala·K^(+)旋光异构反应有a、b和c 3个通道,a是质子只以羰基氧为桥迁移;b是α氢迁移到羰基氧后,质子再从质子化氨基向α碳迁移;c是质子从质子化氨基迁移到羰基氧后,再以氨基氮为桥迁移.势能面计算表明:隐性溶剂效应下,c通道具有优势,决速步能垒是241.7 kJ·mol^(-1);a和b通道为劣势通道,具有共同的决速步能垒261.3 kJ·mol^(-1).显性溶剂效应下,a、b和c 3个通道的决速步能垒基本相同,大约在136.6至142.0 kJ·mol^(-1)之间.结果表明:水液相下S-α-Ala·K^(+)的旋光异构反应进行的极其缓慢,生命体利用S-α-Ala·K^(+)同补K^(+)和丙氨酸具有较好的安全性.

The M06-2X method of density functional theory combined with the SMD model method of self consistent reaction field theory was used to study the optical isomerization of amphoteric S-α-Ala complex with monovalent potassium(S-Ala·K^(+))in water-liquid phase environment.Reaction channel research found that the optical isomerization of S-Ala·K^(+)has three channels a,b and c.The proton was transferred with carbonyl oxygen as the bridge in channel a;In channel b,the proton transferred toα-C from protonation amino afterα-H was transferred to carbonyl oxygen.In channel c,the proton is transferred to carbonyl oxygen from protonation amin and then transfers with amino nitrogen as a bridge.The potential energy surface shows that the channel c has the most advantage under the effect of recessive solvent and the energy barrier of the rate-determining step is 241.7 kJ·mol^(-1);channel a and b are inferior channels and they have the common energy barrier of the rate-determining step is 261.3 kJ·mol^(-1).Under the effect of explicit solvent,the energy barrier of the rate-determining step of a,b and c channels is basically the same,between 136.6 and 142.0 kJ·mol^(-1).The results show that the optical isomerization of S-A·K proceeds very slowly.It's safe for living organisms to use S-A·K supplement K^(+)and alanine simultaneously.