质子化和低能电子俘获对N-糖苷键解离性质影响的理论研究

Theoretical Study of Protonation and Low-energy Electron Attachment Effects on Cleavage and Hydrolysis of the N-Glycosidic Bond

采用B3LYP密度泛函方法,在6-311++G(2d,2p)基组水平上,对3种嘌呤核苷体系及其N7-质子化和低能电子俘获形成的衍生物结构性质、键解离能、水解机理进行了计算调查.计算结果显示,质子化嘌呤核苷与中性嘌呤核苷的水解机理并不相同,且质子化可以明显减少N-糖苷键离子解离通道所需要的能量,降低其水解活化能,稳定水解产物,极大地促进N-糖苷键的水解.与质子化作用类似,嘌呤核苷俘获低能电子,也能显著地降低N-糖苷键的键解离能,显著地影响嘌呤核苷的稳定性.

Although remarkable progresses of inosine-adenosine-guanosine nucleoside hydrolases have been made in recent years,the mechanistic details for the cleavage of N-glycosidic bond are still unclear. Herein, the equilibrium geometries, bond dissociation ener- gies,and hydrolysis mechanisms of N-glycosidic bonds in three types of purine nucleosides and their protonated and electron-attached derivatives have been investigated by B3LYP/6-311＋ ＋ G（2d, 2p） calculations. The present results show that protonation can re- markably reactivate the N-glycosidic bond and reduce the activation barrier for its cleavage and hydrolysis. Similarly, low-energy elec- tron attachment to the purine moiety can make N-glycosidic bond easier to break. Significant effects of protonation and excess electron on the mechanistic details and reaction thermodynamic properties also have been observed.