5-甲基胞嘧啶-BH3复合物构型及异构化机理的理论研究

用B3LYP/6-311＋G(d)及MP2/6-311＋G(d)计算方法, 对5-甲基胞嘧啶与BH₃所形成复合物及异构化反应进行了研究, 获得了6种复合物及4个异构化过渡态. 在考虑基组重叠误差校正基础上, 得到了结合能及变形能等信息, 并用自然键轨道分析法讨论了其相互作用情况. 结果表明, BH₃与5-甲基胞嘧啶中N(3), O及N(4)相连形成稳定复合物a, b₁, b₂和c, 其结合能分别为104.58, 92.25, 63.49和43.41 kJ?mol^－1; 复合物a, b₁, b_2, c和d既可通过BH₃与5-甲基胞嘧啶不同部位结合直接生成, 也可通过BH₃整体迁移实现相互转化; 甲基化对复合物稳定性及相互异构化能垒无明显影响.

Theoretical Study on the Structures and Isomerization Mechanisms of 5-Methylcytosine-BH3 Complexes

The structures and isomerization reactions of 5-methylcytosine-BH₃ complexes have been investigated by the B3LYP and MP2 methods with 6-311＋G(d) basis set. 6 complexes and 4 transition states were located. Natural bond orbital analysis was performed to reveal the origin of intermolecular interaction. To obtain the accurate binding energies and potential energy surface, single point energy calculations and BSSE correction were performed. The results indicate that a, b₁, b₂ and c with BH₃ directly combining N(3), O or N(4) are stable complexes with the binding energies of 104.58, 92.25, 63.49 and 43.41 kJ?mol^－1, respectively. The complexes may be formed with BH₃ directly combining to 5-methylcytosine as well as with BH₃ entirely transferring on 5-methylcytosine-BH₃. The influence of cytosine methylation was not obvious on stabilization orders and the energy barriers of isomerization.