精氨酸侧链和核酸碱基间离子氢键作用强度分析

Ionic Hydrogen Bonding Between Arginine Side Chain and Nucleic Acid Bases

采用MP2/6-31+G(d,p)方法优化得到了22个由精氨酸侧链与碱基尿嘧啶、胸腺嘧啶、胞嘧啶、鸟嘌呤及腺嘌呤形成的氢键复合物的气相稳定结构,使用包含BSSE校正的MP2/aug-cc-p VTZ方法计算得到了复合物的气相结合能,通过MP2/6-31+G(d,p)方法和PCM模型优化得到了复合物的水相稳定结构,采用MP2/aug-cc-p VTZ方法和PCM模型计算得到了复合物的水相结合能.研究发现,精氨酸侧链与碱基间的离子氢键作用强度与单体间电荷转移量、氢键临界点电子密度及二阶作用稳定化能密切相关.与中性氢键相比,离子氢键作用具有更显著的共价作用成分.研究还发现,精氨酸侧链和碱基间形成的氢键复合物的稳定性次序可以通过氢键受体碱基分子上氧原子和氮原子的质子化反应焓变进行预测,质子化反应焓变越负,形成的氢键复合物越稳定.

The optimal structures of twenty-two hydrogen-bonded complexes composed of one charged arginine side chain molecule and one nucleic acid base in gas phase were obtained at the MP2/6-31 ＋G（ d,p） level.The binding energies in gas phase were evaluated at the MP2/aug-cc-p VTZ level including basis set superposition error（ BSSE） correction. The optimal structures for these hydrogen-bonded complexes in water solvent were further obtained by using PCM model combined with the MP2/6-31 ＋ G（ d,p） method. The binding energies in water solvent were evaluated by using PCM model combined with the MP2/aug-cc-p VTZ method.It is found that the ionic hydrogen bonding strength between the arginine side chain and one of the five nucleic acid bases highly correlates to the charge transfer between the two monomers,the electron density at the hydrogen bond critical point,and the second-order stabilization energy. Compared to the neutral hydrogen bond,the ionic hydrogen bond exhibits more significant covalent character. It is also found that the stability of the hydrogen-bonded complexes can be predicted according to the enthalpy change of the protonation reaction of the nucleic acid bases. The more negative the enthalpy change of the protonation reaction,the more stable the hydrogen-bonded complexes.