溶液环境中水对甲酰胺质子迁移影响的密度泛函研究

甲酰胺酮式和烯醇式的互变异构(FM→FA)可被视为DNA中生物碱基点突变的一个模型. 使用B3LYP密度范函的计算方法, 在B3LYP/6-311++G**的基组条件下运用SCRF溶液模型研究了溶液环境对甲酰胺互变异构的影响. 研究表明, 从水分子对甲酰胺异构的作用进行划分, 分子的周围有三个不同的区域, 和气态计算结果一致, 在一些区域中, 水对异构起到了催化的作用; 而在其它区域中, 水分子却能阻碍反应的进行,保护酮式, 同时溶液环境的存在也使两种作用得到了加强和削弱. 溶液状态下的质子转移研究将会对水分子对中心分子的异构化研究提供参考, 同时也部分解释了试验中酮式比例高于烯醇式的现象.

Density Functional Studies on Formamide's Water-influenced Proton Transfer in Solution

The interconversion process between keto and enol forms of formamide (FM→FA) can be regarded as a model for tautomerization of larger nucleic acid base, which may be responsible for the spontaneous point mutation in DNA. The present paper describes a study of structural tautomer interconversion and the relative stabilizing influences of water for formamide-H2O and the enol form formamidic acid-H2O in aqueous solution. The solvent effects were considered by explicit water molecule within SCRF framework. In the vicinity of formamide (FM) and formamidic acid(FA), three different regions are considered, full geometry optimizations of these complexes were carried out at B3LYP/6-311++G * * using self-consistent isodensity polarized continuum model (SCIPCM). The calculated results indicate that water in two of them can protect formamide from tautomerizing, while in the third one works oppositely,exactly the same as the situations in gas phase. However, comparing with the transition in gas phase, the protective and assistive effects induced by the explicit water are greatly altered. The calculated results shed more light on the water's influence on the proton transfer and offer a new insight into the structural tautomer interconversion of FM.