水液相下α-丙氨酸Co(Ⅱ)旋光异构的密度泛函理论研究

Density Functional Theory Study on the Optical Isomerism ofα-Alanine Co(Ⅱ)in Water-Liquid Phase Environment

采用密度泛函理论的M06和MN15方法,结合自洽反应场理论的SMD模型方法,研究了两性及中性α-丙氨酸(α-Ala_1和α-Ala_2)与Co^(2+)配合物在水液相下的旋光异构。α-Ala_1·Co^(2+)可在4个通道(a、b、c和d)实现旋光异构:a通道是质子以羧基底部的氧为桥迁移;b通道是α-氢迁移至羧基底部的氧后,质子在纸面内从氨基向α-碳迁移;c通道是质子以羧基上部的氧为桥迁移;d通道是α-氢迁移至羧基上部的氧后,质子在纸面内从氨基向α-碳迁移。α-Ala_2·Co^(2+)的旋光异构有2个通道(a和b):a通道是其异构成α-Ala_1·Co^(2+)后,再按α-Ala_1·Co^(2+)异构的方式进一步异构;b通道是质子以羰基氧和甲基碳为桥迁移。势能面计算表明:α-Ala_1·Co^(2+)在a和b通道的旋光异构具有优势,隐性溶剂效应下决速步能垒为283.1 kJ/mol,显性溶剂效应下该能垒降至120.3 kJ/mol;α-Ala_2·Co^(2+)在a通道的旋光异构具有优势,决速步能垒与α-Ala_1·Co^(2+)在a和b通道旋光异构的能垒相同。结果表明,水液相下α-丙氨酸Co(Ⅱ)很难发生旋光异构。

The optical isomerism of amphoteric and neutralα-alanine(α-Ala_1 andα-Ala_2)and Cocomplexes was studied in water-liquid phase environment by means of M06 and MN15 methods based on density functional theory and SMD model method of self consistent reaction field theory.The study shows that the optical isomerization ofα-Ala_1·Cohas four channels a,b,c and d.In channel a,the proton transfers with the oxygen at the bottom of the carboxyl group as a bridge.In channel b,the proton transfers toα-C from amino group inside the paper afterα-H is transferred to the oxygen at the bottom of the carboxyl group.In channel c,the proton transfers with the oxygen on the upper part of the carboxyl group as a bridge.In channel d,the proton transfers toα-C from amino group inside the paper afterα-H is transferred to the oxygen on the upper part of the carboxyl group.The optical isomerization ofα-Ala_2·Co^(2+)has two channels a and b.In channel a,α-Ala_2·Co^(2+)isomerizes toα-Ala_1·Co^(2+)followed by the isomerization ofα-Ala_1·Co^(2+).In channel b,the protons transfer with carbonyl oxygen and methyl carbon as bridges.The potential energy surface shows that the optical isomerization ofα-Ala_1·Co^(2+)in channel a and b has the most advantage.Under the recessive solvent effect,the energy barrier of the rate-determining step is 283.1 k J/mol.The energy barrier drops to 120.3 k J/mol under the effect of explicit solvent.The optical isomerization ofα-Ala_2·Co^(2+)in channel a has the most advantage.The energy barrier of the rate-determining step is the same as that ofα-Ala_1·Co^(2+)in channel a and b.The results show thatα-alanine Co(Ⅱ)is difficult to racemize in water-liquid phase.