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首页> 外文期刊>The journal of physical chemistry, A. Molecules, spectroscopy, kinetics, environment, & general theory >Hydrogen Atom Addition to Cytosine, 1-Methylcytosine, and Cytosine-Water Complexes. A Computational Study of a Mechanistic Dichotomy
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Hydrogen Atom Addition to Cytosine, 1-Methylcytosine, and Cytosine-Water Complexes. A Computational Study of a Mechanistic Dichotomy

机译：氢原子添加到胞嘧啶，1-甲基胞嘧啶和胞嘧啶-水复合物中。机械二分法的计算研究

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摘要

Combined ab initio and density functional theory calculations at the B3-MP2/6-311++G(3df,2p) level of theory are used to investigate the structures and energetics of radicals produced by hydrogen atom addition to cytosine tautomers, 1-methylcytosine, and cytosine-water complexes. H-atom adducts to the N-3 positions are the most stable radical isomers derived from cytosine tautomer (1), 1-methylcytosine, and cytosine-water complexes in the gas phase. Solvent effects on radical stabilities are addressed by calculation that use the polarizable continuum model. Solvation by bulk water favors C-5 and C-6 adducts which have free energies in eater that are comparable to those of the N-3 adducts. H-atom additions to the C-5 positions have the lowest activation energies for all cytosine derivatives under study and are predicted to be kinetically predominant. H-atom additions to the N-3 and C-6 positions are solvent dependent. In the absence of solvation, N-3 is more reactive than C-6 in cytosine and 1-methylcytosine. Water complexation increases the activation energy for H-atom addition to N-3 and results in a reactivity reversal for the N-3 and C-6 positions.
机译：结合从头算和密度泛函理论在B3-MP2 / 6-311 ++ G（3df，2p）上的理论计算来研究氢原子添加到胞嘧啶互变异构体1-甲基胞嘧啶中产生的自由基的结构和能量和胞嘧啶-水复合物。 N-3位的H原子加合物是在气相中衍生自胞嘧啶互变异构体（1），1-甲基胞嘧啶和胞嘧啶-水复合物的最稳定的自由基异构体。通过使用可极化连续体模型进行计算，可以解决溶剂对自由基稳定性的影响。用大量水溶剂化有利于C-5和C-6加合物，它们在进料器中具有的自由能与N-3加合物的自由能相当。对于正在研究的所有胞嘧啶衍生物，C-5位上的H原子加成具有最低的活化能，并且被认为在动力学上占优势。 N-3和C-6位置的H原子加成取决于溶剂。在没有溶剂化的情况下，在胞嘧啶和1-甲基胞嘧啶中，N-3比C-6更具反应性。水络合增加了H原子加到N-3上的活化能，并导致N-3和C-6位置的反应性反转。

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