5-甲基胞嘧啶水解反应机理的理论研究

Theoretical Study on the Hydrolysis Reaction Mechanism of 5-methylcytosine

采用密度泛函理论方法,在B3LYP/6-31G**水平下研究了5-甲基胞嘧啶(m5C)水解反应的微观机理和势能剖面.计算结果表明,5-甲基胞嘧啶的水解反应有两条反应途径:(A)水分子进攻m5C生成中间体IM1,然后氨分子充当桥生成终产物胸腺嘧啶;(B)水分子进攻m5C首先生成四配位的中间体IM2,然后中间体分解成终产物胸腺嘧啶和氨分子.能量计算结果表明,5-甲基胞嘧啶的水解反应决速步的活化能垒较高,在自发状态下,5-甲基胞嘧啶的水解反应难于进行.

The hydrolysis reaction mechanism and potential energy surface of 5-methylcytosine （ m5 C） were inves- tigated using density functional theory （DFT） at the B3LYP/6-31 G ＊ ＊ level. The results show that the hydrolysis reaction of m5 C includes two pathways： （A）With the water attacking at m5 C, thymine is formed; （B） This pathway is as- sociated with a tetracoordinated intermediate formed and decomposed. Because the hydrolysis reaction of m5 C has a higher barrier, the hydrolysis reaction of m5 C does not take place for the opening system, which is agreement with the experimental result. The present calculations have rationalized and verified all the possible reaction channels.