α-丙氨酸限域在扶椅型 SWBNNT（9，9）与水复合环境下的手性转变机制

摘要

用量子化学 ONIOM（B3LYP／6－311＋＋G（3df，3pd）：UFF）∥ONIOM（B3LYP／6－31＋G（d，p）：UFF）方法，研究α-Ala 在 SWBNNT（9，9）与水复合环境的手性转变。分子结构计算表明：反应物 S 型α-Ala 和中间体INT1在 SWBNNT（9，9）与水复合环境，与单体相比，氢转移断的 O-H 和 C-H 键都略长，H 与其要转移到的目标原子 O 的距离均短很多。反应通道研究发现：在 SWBNNT（9，9）与水复合环境下，α-Ala 手性转变有4条路径，每条路径上氢转移都能以1个或2个水分子为媒介实现。势能面计算发现：手性转变反应的最高能垒来自 H 从手性 C 向羰基 O 转移的过渡态；在氨基先异构接着羧基 H 转移和 H 从手性 C 向羰基 O 转移顺次实现的路径，并以2H2 O 为氢转移媒介时最高能垒被降到最小值153．8 kJ·mol －1。比只在 SWBNNT（9，9）内的302．7 kJ·mol －1明显降低，比只在水环境的167．8 kJ·mol －1也有所降低。结果表明：SWBNNT（9，9）与水复合环境，对α-Ala 手性转变有较好的催化作用。%The chiral transition mechanism of α-alanine confined in the armchair SWBNNT (9,9)/water complex environment was studied using the method of quantum chemistry (ONIOM(B3LYP/6 -31 1 ++G(3df,3pd):UFF)∥ ONIOM(B3LYP/6 -31 +G(d,p):UFF))in the paper.The result indicated that,compared s-type α-Ala and intermediate INT1 in the SWBNNT(9,9)/water complex environment with monomer molecules,the bond lengths between oxygen and hydrogen,as well as carbon and hydrogen involving hydrogen transfer were all slightly increased.However,the distance between oxygen and hydro-gen was significantly shorten under the same condition.It was found that there were four reaction paths in SWBNNT(9,9).Furthermore,the processes of hydrogen transfer were all realized by the way which made one or two water molecules as bridge.The maximum energy barriers of every path were always coming from transition state where hydrogen transferred from chiral carbon to carbonyl through measure-ment of the potential energy surfaces of chiral reaction.The minimum of maximum energy barriers was 1 53.8 kJ·mol -1 in the process that Amino heterogeneous firstly,then successively hydrogen transferred inside the carboxyl and hydrogen transferred from chiral carbon to carbonyl oxygen through two water mol-ecules as bridge.Corresponding to chiral transition of α-Ala in SWBNNT(9,9)only,the minimum of maximum energy barriers was 302.7 kJ·mol -1 which obviously reduced.Moreover,corresponding to chiral transition of α-Ala in water environment only,the minimum of maximum energy barriers was 1 67.8 kJ·mol -1 that also reduced.The results showed that the SWBNNT(9,9)/water complex environment provided a preferable catalytic action for chiral transition of α-Ala.