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首页> 外文期刊>The journal of physical chemistry, A. Molecules, spectroscopy, kinetics, environment, & general theory >Computational study of the deamination reaction of cytosine with H2O and OH-
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Computational study of the deamination reaction of cytosine with H2O and OH-

机译：胞嘧啶与H2O和OH-脱氨反应的计算研究

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The mechanism for the deamination reaction of cytosine with H2O and OH- to produce uracil was investigated using ab initio calculations. Optimized geometries of reactants, transition states, intermediates, and products were determined at RHF/6-31G(d), MP2/6-31G(d), and B3LYP/6-31G(d) levels and for anions at the B3LYP/ 6-31+ G(d) level. Single- point energies were also determined at B3LYP/6-31+ G(d), MP2/GTMP2Large, and G3MP2 levels of theory. Thermodynamic properties (Delta E, Delta H, and Delta G), activation energies, enthalpies, and free energies of activation were calculated for each reaction pathway that was investigated. Intrinsic reaction coordinate analysis was performed to characterize the transition states on the potential energy surface. Two pathways for deamination with H2O were found, a five-step mechanism (pathway A) and a two-step mechanism (pathway B). The activation energy for the rate-determining steps, the formation of the tetrahedral intermediate for pathway A and the formation of the uracil tautomer for pathway B, are 221.3 and 260.3 kJ/mol, respectively, at the G3MP2 level of theory. The deamination reaction by either pathway is therefore unlikely because of the high barriers that are involved. Two pathways for deamination with OH- were also found, and both of them are five-step mechanisms. Pathways C and D produce an initial tetrahedral intermediate by adding H2O to deprotonated cytosine which then undergoes three conformational changes. The final intermediate dissociates to product via a 1-3 proton shift. Deamination with OH-, through pathway C, resulted in the lowest activation energy, 148.0 kJ/mol, at the G3MP2 level of theory.
机译：使用从头算研究了胞嘧啶与H2O和OH-脱氨基反应生成尿嘧啶的机理。在RHF / 6-31G（d），MP2 / 6-31G（d）和B3LYP / 6-31G（d）含量下确定了反应物，过渡态，中间体和产物的最佳几何形状，在B3LYP / 6-31 + G（d）等级。还确定了B3LYP / 6-31 + G（d），MP2 / GTMP2Large和G3MP2理论水平的单点能量。对于所研究的每个反应路径，计算了热力学性质（ΔE，ΔH和ΔG），活化能，焓和活化自由能。进行本征反应坐标分析以表征势能表面上的过渡态。发现了使用H2O进行脱氨的两条途径，即五步机理（途径A）和两步机理（途径B）。在G3MP2的理论水平上，速率确定步骤的活化能，途径A的四面体中间体的形成和途径B的尿嘧啶互变异构体的活化能分别为221.3 kJ / mol和260.3 kJ / mol。由于涉及高障碍，因此不可能通过任一途径进行脱氨基反应。还发现了用OH-脱氨基的两条途径，它们都是五步机理。途径C和D通过向去质子化的胞嘧啶中加入H2O产生初始的四面体中间体，然后经历三个构象变化。最终中间体通过1-3质子移位解离为产物。在G3MP2的理论水平上，通过途径C用OH-进行脱氨基反应可得到最低的活化能，为148.0 kJ / mol。

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