物理化学学报 >> 2004, Vol. 20 >> Issue (12): 1455-1458.doi: 10.3866/PKU.WHXB20041211

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2-硫代黄嘌呤互变异构体的密度泛函理论计算

李宝宗   

  1. 苏州大学化学化工学院,苏州　215006
  • 收稿日期:2004-04-15 修回日期:2004-06-30 发布日期:2004-12-15
  • 通讯作者: 李宝宗 E-mail:ymguo@suda.edu.cn

Density Functional Theory Calculations on 2-thioxanthine Tautomers

Li Bao-Zong   

  1. School of Chemistry and Chemical Engineering,Suzhou University,Suzhou　215006
  • Received:2004-04-15 Revised:2004-06-30 Published:2004-12-15
  • Contact: Li Bao-Zong E-mail:ymguo@suda.edu.cn

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摘要： 在密度泛函B3LYP/6-311G**水平上,对14种气相和水相中可能存在的2-硫代黄嘌呤互变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-硫代黄嘌呤在气相和水相中主要以酮式结构形式存在,与已有实验结果一致.在气相和水相中,酮式结构—N(7)(H)均比酮式结构—N(9)(H)更稳定.2-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的影响,而焓变对互变异构却产生了主要的影响.水溶剂化自由能与异构体的气相偶极矩存在相关性.另外,较详细地考察了2-硫代黄嘌呤与6-硫代黄嘌呤的相对稳定性.

关键词: 2-硫代黄嘌呤, 　异构体, 　密度泛函理论, 　自洽反应场方法, 　偶极矩

Abstract: Molecular structures of fourteen 2-thioxanthine tautomers were calculated by the B3LYP /6-311G** method, both in the gas and aqueous phases, with full geometry optimization. The Onsager solvate theory model was employed for aqueous solution calculations. The structures, total energy, standard enthalpy, standard entropy and standard Gibbs free energy were obtained. The calculations show that 2-thioxanthine existing as the thione(keto) forms is the predominant tautomer in the gas and aqueous phases. The thione(keto)-N(7)(H) tautomer is more stable than the thione(keto)-N(9)(H) tautomer in the gas and aqueous phases. The results are in good agreement with available experimental results. The entropy effect on the Gibbs free energy of 2-thioxanthine base is very small and there is little significance for the tautomeric equilibria of the base.The enthalpic term is dominant in the determination of tautomeric equilibria. The free energy of solvation is well correlated with the dipole moments of 2-thioxanthine tautomer. Additionally, the relative stabilities of 2-thioxanthine tautomers and 6-thioxan thine ones were examined.

Key words: 2-thioxanthine, 　Tautomer, 　Density functional theory, 　Self-consistent reaction field method, 　Dipole moment