胞嘧啶水化去氨基反应机理的理论研究

Theoretical Study on the Hydrolytic Deamination Reaction Mechanism of Cytosine

用量子化学密度泛函方法,在B3LYP/6-31G**水平下研究了胞嘧啶的水化去氨基的反应机理.研究表明,胞嘧啶的水化去氨基的反应是分步进行的,首先发生水解反应生成四配位的中间体,接着脱去氨基生成终产物尿嘧啶.势能面研究表明,氨分子充当桥时尿嘧啶的醇式与其烯酮式结构转化容易发生.但胞嘧啶的水化去氨基反应的决速步活化能较高,反应不容易进行.

The hydrolytic deamination reaction mechanism of cytosine （C） has been theoretically investigated at the B3LYP/6-31G ^＊ ＊ level. It is found that the hydrolytic deamination reaction of C may proceed in a stepwise way, in which a tetracoordinated intermediate is formed firstly by the hydrolysis reaction, followed by the deamination reaction with C--N broken and C = O formed. The study on the potential energy surface showed that NH3 molecule as a shuttle facilitates H transfer between keto form and enol form of hypoxanthine. However, the deamination reaction of C does not take place because of a higher barrier for the opening system, which is agreement with the experimental result.