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采用密度泛函B3LYP方法在6-311+G~(**)级别上对2-硫代黄嘌呤气相和水相中较稳定的两个构型2TX(1,3,7)和2TX(1,3,9)及可能的8种离子构型进行了几何构型全优化和频率分析,水相优化选用IEFPCM模型,单点能计算采用CPCM溶剂模型并选取UAKS空穴方法。为了获得较精确的能量,在MP2/6-311+G~(**)级别下各物种分别在两相中进行了单点能计算。根据所计算的溶剂化吉布斯自由能进一步得到了水相4种相对稳定的离子异构体的pK_a值,理论计算结果与实验值基本一致,从而揭示了水溶剂中2-硫代黄嘌呤的电离活性部位和离子构型的存在形式。
Two stable 2TX (1, 3, 7) and 2TX (1) groups of 2-thioxanthine in gas phase and aqueous phase were analyzed by density functional theory B3LYP at 6-311 + , 3,9) and possible eight kinds of ion configuration geometry optimization and frequency analysis, IEFPCM model selection for the water phase optimization, single-point calculation using CPCM solvent model and select the UAKS hole method. In order to obtain more accurate energy, each species under the MP2 / 6-311 + G ~ (**) level was calculated in two phases separately. According to the calculated solvation Gibbs free energy, the pK_a values of four relatively stable ionic isomers of the aqueous phase are further obtained. The theoretical calculation results are in good agreement with the experimental values, revealing that the 2-thioxanthine Of the ionically active sites and the ion configuration of the existing form.