Asp分子手性对映体转变机理及水的催化作用

用色散校正密度泛函WB97X D方法、 微扰理论的MP2方法和自洽反应场的SMD模型方法, 研究两种天冬氨酸(Asp)分子在优势反应通道的手性对映体转变、 水分子催化及溶剂效应. 结果表明： Asp分子经α 羧羟基、 β 羧羟基、 β 羧基和R 基旋转及质子从α 碳向氨基氮、 质子从氨基氮向α 碳和羧基内质子迁移的一系列过渡态, 实现了手性对映体转变, 并得到几种不同构型的旋光异构产物； 具有2条较强单氢键和2条中等强度单氢键的Asp分子在优势通道旋光异构的内禀能垒分别为258.5,253.8 kJ/mol, 均来自α 氢向氨基氮迁移的过渡态； 2个水分子簇的催化使其能垒分别降至133.3,134.3 kJ/mol, 水溶剂环境下分别降至106.3,107.8 kJ/mol. 表明水分子簇的催化可使Asp分子缓慢实现手性对映体转变, 水溶剂化效应可加快反应速度.

Mechanism of Chiral Enantiomer Transition ofAsp Molecule and Catalysis of Water

Using the dispersion correction density functional WB97X D method, the MP2 method of perturbation theory and the SMD model method of self consistent reactionfield, we studied the chiral enantiomer transition of two aspartic acid (Asp) molecule in dominant reactionchannels, the catalysis and the solvent effect of water molecules. The results show that the chiral enantiomer transition is realized by a series of Asp transition states of the rotation of α carboxyhydroxyl, β carboxyhydroxyl, β carboxyl and R group and proton transport from α carbon to amino nitrogen, from amino nitrogen to α carbon and in carboxyl groups, and several kinds of optical isomerism products with different configurations are obtained. The intrinsic energy barriers of Asp molecules with two strong single hydrogen bonds and two moderate strength single hydrogen bonds in the dominant channel are 2585, 2538 kJ/mol,respectively, which are derived from the transition states of transfer of α hydrogen to amino nitrogen, and that are reduced to 133.3, 134.3 kJ/mol bythe catalysis of two water clusters, and to 106.3, 107.8 kJ/mol in water solvent environment, respectively. Therefore, the chiral enantiomer transition of Asp molecules can be realized slowly by the catalysis of watermolecular clusters, and the reaction rate can be accelerated by the water solvent effect.