中文摘要：

用密度泛函B3LYP方法在6-311＋G＊＊基组水平上对鸟嘌呤及顺（cis-）、反式（anti-）-6-烷基鸟嘌呤（O6-AlkylG）与DNA碱基（胸腺嘧啶T、胞嘧啶C、腺嘌呤A、鸟嘌呤G）的氢键二聚体结构进行了优化.在MP2/cc-pVXZ（X=D,T）//B3LYP/6-311＋G＊＊水平上,采用完全基组外推方法校正了氢键二聚体的相互作用能,并用完全均衡校正法（CP）校正了基组重叠误差（BSSE）.在B3LYP/6-311＋G＊＊水平上计算了各氢键碱基对的全电子波函数,并用分子中的原子理论（AIM）分析了碱基间的弱相互作用.计算结果显示,鸟嘌呤6-O烷基化改变了碱基间的氢键作用模式,使碱基对发生了明显的螺旋桨式扭转和不同程度的位移,碱基间的电子密度分布和氢键作用能明显减小.O6-AlkylG对DNA碱基间的氢键作用是去稳定化的,去稳定化影响的顺序为GC〉GG〉GA≈GT.计算结果与文献给出的实验结论基本一致.

英文摘要：

The geometries of hydrogen-bond dimers between DNA bases （adenine, thymine, guanine and cytosine） and guanine, cis-O6-alkylguanine and trans-O6-alkylguanine have been optimized at the B3LYP/6-311＋G＊＊ level. The complete basis-set extrapolation method was employed at the MP2/ cc-pVXZ（X=D,T）//B3LYP/6-311＋G＊＊ levels in order to obtain more accurate interaction energies. Coun- terpoise correction （CP） scheme was also used to take into account of basis set superposition error （BSSE）. The all-electron wave functions of these dimers were calculated at the B3LYP/6-311＋G＊＊ level and the weak interactions were analyzed by atoms in molecules （AIM） method. The calculation results show that the alkylation of O6-guanine can lead to changes of hydrogen-bond interactions between DNA base-pairs, which results in propeller torsions and various displacements between two bases. Furthermore, the obvious decreases in interaction energies and electron densities of base-pair can also be attributed to the alkylation of guanine. Evidently, the alkylation of O6-guanine destabilizes the hydrogen-bond interactions of DNA base-pairs, and the destabilization effect decreases in the order of GCGGGA≈GT. Our calculation results are basically in agreement with the experiments.