气相环境下丙氨酸Ca^2+配合物的手性转变机理及水分子的催化作用

Chiral transition mechanism of Ala and Ca^2+ complexes in gas phase and catalysis of water molecules

采用基于密度泛函理论的M06方法,研究了气相环境下2种稳定构型的丙氨酸(Ala)与Ca^2+配合物的手性转变及水分子的催化。研究发现,Ala_1·Ca^2+的手性转变有a和b 2个通道,a通道是α-氢只以羰基氧为桥迁移;b通道是α-氢迁移到羰基氧后,氨基上的质子在纸面内侧向α-碳迁移。Ala_2·Ca^2+的手性转变有a、b、c、d 4个通道,a和b通道分别是羧基内质子迁移后,α-氢只以羰基氧为桥迁移和α-氢迁移到羰基氧接质子从氨基氮向α-碳迁移;c通道是钙与氮的配位键断裂后,α-氢向氨基氮迁移;d通道是钙与氮的配位键断裂后,Ala_2·Ca^2+向Ala_1·Ca^2+异构,再接Ala_1·Ca^2+的手性转变。势能面计算表明,Ala_1·Ca^2+手性转变的a通道具有优势,总包能垒为134.8 kJ·mol^-1,Ala_2·Ca^2+手性转变的d通道具有优势,总包能垒为235.3 kJ·mol^-1;水分子的催化使能垒分别降至40.8和141.3 kJ·mol^-1。结果表明,Ca^2+对Ala的手性转变具有催化作用,水分子对丙氨酸Ca^2+配合物的手性转变具有极好的催化作用。

The catalysis of water molecules and the chiral transition of two stable configurations of alanine(Ala)and Ca^2+ complexes in gas phase have been studied using the M06 method based on density functional theory.The study shows that the Ala_1·Ca^2+ chiral transition has two pathways a and b.In pathway a,α-H is transferred merely using carbonyl O atom as a bridge.In pathway b,the proton on the amino group transfers to α-C from inside paper after α-H is transferred to carbonyl O atom.The Ala_2·Ca^2+ chiral transition has four pathways a,b,c and d.In pathway a,α-H is transferred merely using carbonyl O atom as a bridge after the transition of proton on the carboxyl group.In pathway b,α-H is transferred to carbonyl O atom and then proton transfers from the amino group N atom to α-C after the transition of proton on the carboxyl group.In pathway c,α-H is transferred to the amino group N atom after the coordination bond between calcium and nitrogen is broken.In pathway d,the coordination bond between calcium and nitrogen is broken and Ala_2·Ca^2+ is isomerized to Ala_1·Ca^2+,then Ala_1·Ca^2+ achieves the chiral transition.The potential energy surface calculation shows that the dominant pathway of the chiral transition of Ala_1·Ca^2+ is pathway a,and the total energy barrier is 134.8 kJ·mol-1.The dominant pathway of the chiral transition of Ala_2·Ca^2+ is pathway d,and the total energy barrier is 235.3 kJ·mol^-1.The catalysis of water molecules then reduces them to 40.8 kJ·mol^-1 and 141.3 kJ·mol^-1 respectively.The results show that Ca^2+has a catalytic effect on the chiral transition of Ala,and water molecule has an excellent catalytic effect on the chiral transition of Ala and Ca^2+ complexes.