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在密度泛函B3LYP/6-311G~(**)水平下,对14种气相和水相中可能存在的2,6-二硫代黄嘌呤异构体进行了几何构型全自由度优化,并计算出它们的总能量、焓、熵、吉布斯自由能。Onsager反应场溶剂模型用于水相的计算,计算结果表明,2,6-二硫代黄嘌呤在气相和水相中主要以双硫酮形式存在。在气相和水相中,硫酮-N(7)(H)均比硫酮-N(9)(H)稳定,计算结果同已有实验结果一致。2,6-二硫代黄嘌呤互变异构的熵效应小,对互变异构平衡没有显著影响,而焓变对互变异构产生了主要影响。较详细地讨论了水溶剂化作用对异构体的能量、几何结构、电荷分布和偶极矩的影响。溶剂化自由能与异构体的偶极矩存在相关性。并且以在水相中最稳定的两种异构体为对象,采用超分子模型探讨了它们与水分子之间氢键作用的情况。
In the B3LYP / 6-311G ~ (**) density functional theory, all the 2,6-dithioxanthine isomers in 14 kinds of gas and water phases were optimized in their geometrical configurations. And calculate their total energy, enthalpy, entropy, Gibbs free energy. The Onsager reaction field solvent model was used to calculate the water phase. The calculated results show that 2,6-dithioxanthine is mainly in the form of dithione in the gas phase and aqueous phase. In both gas phase and aqueous phase, thione-N (7) (H) is more stable than thioketone-N (9) (H), and the calculated results are consistent with the experimental results. The entropic effect of 2,6-dithioxanthine tautomerism is small, which has no significant effect on the tautomerism balance, while the enthalpy change has a major effect on the tautomerism. The effects of water solvating on the energy, geometry, charge distribution and dipole moment of isomers are discussed in more detail. There is a correlation between solvation free energy and dipole moment of isomers. In addition, the two most stable isomers in the aqueous phase are used as targets, and the supramolecular model is used to investigate the hydrogen bonding between them and water molecules.