Abstract
The possible involvement of low-barrier hydrogen bonds (LBHBs) in enzyme catalysis has attracted wide attention in recent years. The initial proposal of the existence of special short and strong hydrogen bonds (SSHBs) in enzymatic active sites was based on experimental findings of unique physicochemical properties. The character of a LBHB is based on the shape of the potential energy surface that is the hydrogen atom lies in a double minimum potential well with zero-point vibrational energies the same as or above the barrier height, it is a LBHB. When metal ions exist in hydrogen-bonding systems, their interaction will affect the systems directly or indirectly. This thesis reports the theoretical investigation on the effect of main group metal cations on the LBHB of 4,5-dimethyl-1H-imidazole (DMim) and acetate (Ac), and all calculations were done at B3LYP or RMP2 level. The complex [DMim-H-Ac]1□ is a normal hydrogen-bonding system, and the character of the hydrogen bond will become a LBHB while Li+、Ca2+、Sr2+ or Ba2+ is added to [DMim-H-Ac]1□ complex. We find the charge transfer from [DMim-H-Ac]1□ complex to the metal ion is very small by NBO charge analysis. The analysis of the two relative energy surfaces between [M-DMim-H-Ac]Z□ (M=Li+、Na+、K+、Rb+、Cs+、Ca2+、Sr2+、Ba2+) complex and [DMim-H-Ac]1□ complex constructed by removing metal ions of [M-DMim-H-Ac]Z+ shows that metal ions affect the hydrogen-bonding system by long-distance stabilization. The ability of long-distance stabilization is according to metal ionic size : in the aspect of alkali metal ionic systems : Li+＞Na+＞K+＞Rb+＞Cs+ system； in the aspect of alkaline metal ionic systems : Ca2+＞Sr2+＞Ba2+ system. The most important interaction between the metal ion and [DMim-H-Ac]1□ complex is coulombic interaction by analyzing the binding energy between the metal ions and [DMim-H-Ac]1□ complex.