α-Ala限域在扶手椅型SWCNT(9,9)与水复合环境下的手性转变机制

The Chiral Shift Mechanism ofα-Ala Confined in the Complex Environment of Armchair SWCNT(9,9) and Water

采用量子化学ONIOM(B3LYP/6-31+G(d,p):UFF)方法,研究了限域在SWCNT(9,9)与水复合环境下α-Ala的手性转变机理.反应通道研究发现:α-Ala在SWCNT(9,9)与水复合环境下有两个手性转变通道,一是手性碳上的氢以水分子为桥梁直接转移到羰基氧上,再经过一系列过程完成手性转变;二是氢先在羧基内以水分子为桥梁转移,而后手性碳上的氢以水分子为桥梁转移到羰基氧上,再经过一系列过程完成手性转变.反应过程势能面计算发现:S型α-Ala在SWCNT(9,9)内分别以1个和2个水分子作为桥梁实现氢转移,最高能垒都来自氢从手性碳转移到羰基氧的过渡态.与单体情形相比较,在第一通道最高能垒从326.5kJ·mol-1降到192.2和164.5kJ·mol-1,在第二通道最高能垒从320.3kJ·mol-1降到175.5和154.3kJ·mol-1.结果表明SWCNT(9,9)与水的复合环境对α-Ala手性转变过程的限域影响,是使氢转移反应的能垒比单体和只限域在SWCNT(9,9)的情形明显降低,且比单纯水环境下也有所降低.

Abstract： The chiral shift mechanism of ocAla is researched by using the method of quantum chemistry ONIOM （B3LYP/6-31＋G（d, p）： UFF） which confined in complex environment of armchair SWCNT （9,9） and water. From the reaction channels, we find that, there are two shift reaction channels during the chiral shift in the complex environment. The first one is from the process that hydrogen on the ehiral carbon directly transfers to carbonyl oxygen which makes water molecules as bridge. After a series of processes, the chiral transition is completed. The second one is from the process that hydrogen firstly transfers inside carboxyl, then transfers from chiral carbon to carbonyl oxygen which makes water molecules as bridge. Finally after a series of processes, the chiral transition is completed. From the potential energy surface, we find that S-type a.-Ala achieves hydrogen transfer respectively by making one and two water molecules as bridge. Compared with the monomer, the highest energy barrier of two channels are both from the transition states that hydrogen on the chiral carbon transfers to carbonyl oxygen. The highest energy in the first channel declines from 326. 5 kJ · mo1-1 to 192. 2 and 164.5 kJ · mol 1 respectively. The highest energy in the second channel declines from 320. 3 kJ ·mo1-1 to 175.5 and 154. 3 kJ ·mol 1 respectively. The results show that： The complex environment which includes SWCNT （9, 9） and water presents confined influence on chiral transition of ccAla. The energy barriers of hydrogen transfer are significantly lower than that in monomer and only domain in SWCNT （9,9）, as well as lower than that under the water environment.