苯丙氨酸分子的手性对映体转变机理及水分子（簇）的催化作用

在MP2/6 311++G(3-df,2pd-)//WB97X-D/6-311++G(-d,p-)双水平研究苯丙氨酸(Phe)分子的手性对映体转变机理, 并用分子中的原子理论(AIM)分析驻点的成键特征. 结果表明： 经过羧羟基旋转、 质子迁移、 碳 碳键旋转和氨基翻转的一系列过渡态, Phe分子在质子以氨基氮为桥梁迁移的通道a和以羰基氧与氨基氮顺次为桥梁迁移的通道b内, 实现了手性对映体转变; 当2个水分子簇作为质子迁移媒介时, 在通道b中增加了质子仅以羰基氧为桥梁迁移的反应路径； 通道a具有优势, 速控步骤的内禀能垒为25971 kJ/mol, 反应的表观能垒为27026 kJ/mol； 2个水分子簇催化使速控步骤的内禀能垒降至126.47 kJ/mol, 反应的表观能垒降至80.80 kJ/mol; 考虑零点振动能后, 质子从氨基氮向羰基氧迁移的能垒消失. 即水分子（簇）催化可使Phe分子实现手性对映体转变.

Mechanism of Chiral Enantiomer Transition of PhenylalanineMolecules and Catalysis of Water Molecules (Clusters)

We studied mechanism of chiral enantiomer transition ofphenylalanine （Phe） molecules and catalysis of water molecules (clusters) at the MP2/6-311++G(3-df,2pd-)/WB97X-D/6-311++-G(-d,p-) level, and the bonding characteristics of the stationary points were analyzed by the atomic theory in molecules (AIM). The results show that the chiral enantiomer transition of Phe molecule is realized through a series of transition states of carboxyl hydroxyl rotation, proton transfer, carbon carbon bond rotation and amino turnover. The protons are transferred with amino nitrogen as the bridge in channela, and in channel b with carbonyl oxygen and amino nitrogen as the bridge. When two water molecules clusters are used as proton transfer medium,the reaction path of photon tranfer only with carbonyl oxygen as the bridge is added in channel b. The channela has the advantage, where the intrinsic energy barrier of the rate determining step is 25971 kJ/mol and the apparent energy barrier is 27026 kJ/mol. The intrinsic energy barrierof the rate determining step is reduced to 126.47 kJ/mol by the catalysis of two water clusters, and the apparent energy barrier is reduced to 80.80 kJ/mol. When zero point vibration energy is considered, the enery barrier of proton transfer from amino nitrogento carbonyl oxygen disappears. The chiral enantiomeric transition of Phe molecules can be realized by the catalysis of water molecules (clusters).