2-羟基咪唑在气相和水中的异构平衡和质子迁移的从头算计算和Monte Carlo模拟  

Ab initio Calculation and Monte Carlo Simulation on Tautomerism and Proton Transfer of 2-Hydroxyimidazole in Gas Phase and Water

作　　者：张慧[1] 薛英[1] 谢代前[1,2] 鄢国森[1] 

机构地区：[1]四川大学化学学院教育部绿色化学和技术重点实验室 [2]南京大学化学系理论与计算化学研究所,南京210093

出　　处：《化学学报》2005年第9期791-796,i001,共7页Acta Chimica Sinica

基　　金：国家自然科学基金面上项目(No.20473055);教育部高校青年教师奖资助项目.

摘　　要：采用从头算方法在MP2/6-31+G*水平上研究了2-羟基咪唑分子在孤立分子和一水合物的异构体的相对稳定性和可能的质子迁移反应,分析了一个水分子的参与对2-羟基咪唑分子异构体的相对稳定性和质子迁移速率的影响,采用MonteCarlo模拟方法研究了反应体系在水溶液中反应的溶剂化效应.结果表明:2-羟基咪唑分子的孤立分子和一水合物的最稳定异构体相同,都为酮式.直接质子迁移反应在水溶液中活化能垒有轻微增加,但产物能量得到降低;水助催化质子迁移反应在水溶液中的活化能垒和产物能量都得到明显降低.综合气相和水相的计算结果,2-羟基咪唑水助催化的质子迁移反应较易进行,且在水溶液中进行容易,可以很容易被实验观察到.The relative stabilities and probable proton transfer in isolated and monohydrated 2-hydroxyimidazole molecules have been studied in gas phase using ab initio (MP2/6-31+G*) method. The results show that the keto tautomer is the relatively stable structure in isolated and monohydrated states. Monte Carlo simulation with free energy perturbation technique has been used to study the proton transfer reaction in water. The calculated free energy of activation of direct proton transfer reaction in water was found to be higher than that in gas phase by 1.71 kJ center dot mol(-1) though the free energy of tautomerism in water is lower than that in the gas phase by 5.55 kJ center dot mol(-1). The reduction of free energies of activation and tautomerism in the water-assisted proton transfer path was found to be significant due to the solvent effect of water. All the results show that the water-assisted proton transfer reaction of 2-hydroxymidazole could occur easily in gas phase and water and they could be observed easily experimentally.

关 键 词：Carlo模拟 咪唑 羟基 气相 质子迁移反应 相对稳定性 平衡 从头算方法 溶剂化效应 水溶液 迁移速率 反应体系 模拟方法 计算结果 实验观察 异构体 水合物 助催化 MP2 水分子 孤立 能垒 活化 能量 产物 酮式 水相 

分 类 号：O626[理学—有机化学]