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用密度泛函理论研究了胞嘧啶(Cyt)-巴比妥酸(BA)分子间相互作用,以期从理论上预测巴比妥酸类物质对核酸可能产生的影响。在B3LYP/6-311G~(**)理论水平上优化复合物构型,得到5个Cyt-BAl,8个Cyt-BA2和9个Cyt-BA3稳定复合物,经基组重叠误差和零点振动能校正后,发现在3个系列中最稳定的复合物分别是Cyt-BAl-Ⅳ,Cyt-BA2-Ⅲ和Cyt-BA3-Ⅷ,其结合能各自为53.98,96.48和92.50 kJ/mol,相互作用能主要由氢键贡献。Cyt与BA2-Ⅲ、BA3-Ⅸ以三氢键,其余均以二氢键形成复合物,其稳定性与氢键强度关系非常密切。分析自然键轨道而揭示相互作用的本质。用统计热力学求出常温下从单体形成复合物的热力学性质的变化,发现除Cyt-BA3-Ⅰ、Ⅱ、Ⅵ外,Cyt与BA均可在常温下形成复合物。
The interaction between cytosine (Cyt) -barbituric acid (BA) was studied by density functional theory in order to theoretically predict the possible effect of barbiturates on nucleic acids. The structure of the complex was optimized at B3LYP / 6-311G ~ (**) theoretical level. Five Cyt-BAl, eight Cyt-BA2 and nine Cyt-BA3 stable complexes were obtained. After calibration, the most stable complexes in the three series were found to be Cyt-BAl-IV, Cyt-BA2-III and Cyt-BA3-VIII with binding energies of 53.98, 96.48 and 92.50 kJ / mol, respectively The effect can mainly be contributed by hydrogen bonding. Cyt and BA2-Ⅲ, BA3-Ⅸ to three hydrogen bonds, the rest are two hydrogen bonds to form a complex, its stability and hydrogen bond strength are closely related. Analysis of the natural bond orbit reveals the nature of the interaction. The thermodynamic properties of the complex formed from monomer at room temperature were calculated by statistical thermodynamics. It was found that Cyt and BA could form complexes at room temperature except Cyt-BA3-Ⅰ, Ⅱ and Ⅵ.