核酸中碱基的氢键作用机理及电子特征理论研究

Theoretical studies on hydrogen bonding action mechanism and electronic properties of the base in nucleic acid

采用耦合簇量子化学方法 CCSD/aug-cc-pVDZ研究了嘧啶与嘌呤之间的相互作用,利用基函数叠加误差法(BSSE)消除相互作用能误差,并进行了几何结构优化;采用Gaussian 03程序包中的NBO程序分析了二阶稳定化能及自然键轨道.与此同时,应用约化密度函数(RDG)填色等值面图对体系进行了图形化分析,分析了氢键相互作用所在的空间位置和相对强度,以及氢键相互作用的性质,以进一步了解二者的相互作用.结果表明,嘧啶-嘌呤体系的相互作用属于闭合壳层静电相互作用.电子密度跃迁矩阵分析结果表明,激发区域主要集中在N原子和O原子处,涉及的空间广度很大,第一激发态主要涉及前线分子轨道,属于σ→π*或n→π*类型跃迁.

The interactions between pyrimidine and purine were investigated with CCSD/aug-cc- pVDZ quantum chemical method, the interaction energies were corrected while basis function equilibrium correction method was adopted to eliminate the overlapping error of the base groups, and the geometric structure was optimized. Besides, the second-order stabilization e- nergies and natural bond orbitals were analyzed with NBO program attached in Gaussian 03 program package. In the meantime, for further exploration of the interactions between pyrimi- dine and purine, reduced density gradient color-filled iso-surface map was adopted for graphical analyses of pyrimidine-purine system and visualizing the positions and strengths of hydrogen bonding as well as revealing the nature of hydrogen bonding interactions. Results indicate that the interactions of pyrirnidine-purine system belong to closed-shell electrostatic interactions. E- lectron density transition matrix analysis shows that the excitation area mainly concentrates on N and O atoms and involves a very large breadth of space. Moreover, the first excited state mainly involves the frontier molecule orbitals, belonging toα→π＇orn→π＇ type transition.