Grand A, Morell C, Labet V, Cadet J, Eriksson L A
Laboratoire Lésions des Acides Nucléiques, DRFMC/SCIB, UMR-E 3 (CEA/UJF), CEA-Grenoble, 17 rue des Martyrs, 38054 Grenoble Cedex 9, France.
J Phys Chem A. 2007 Sep 20;111(37):8968-72. doi: 10.1021/jp0737799. Epub 2007 Aug 28.
The reactions between either a hydrogen atom or a hydroxyl radical and 5-methylcytosine (5-MeCyt) are studied by using the hybrid kinetic energy meta-GGA functional MPW1B95. *H atom and *OH radical addition to positions C5 and C6 of 5-MeCyt, or *OH radical induced H-abstraction from the C5 methyl group, are explored. All systems are optimized in bulk solvent. The data presented show that the barriers to reaction are very low: ca. 7 kcal/mol for the *H atom additions and 1 kcal/mol for the reactions involving the *OH radical. Thermodynamically, the two C6 radical adducts and the *H-abstraction product are the most stable ones. The proton hyperfine coupling constants (HFCC), computed at the IEFPCM/MPW1B95/6-311++G(2d,2p) level, agree well with B3LYP results and available experimental and theoretical data on related thymine and cytosine radicals.
采用杂化动能元广义梯度近似泛函MPW1B95研究了氢原子或羟基自由基与5-甲基胞嘧啶(5-MeCyt)之间的反应。探索了氢原子和羟基自由基加成到5-MeCyt的C5和C6位,或羟基自由基诱导从C5甲基上夺取氢的反应。所有体系均在本体溶剂中进行了优化。给出的数据表明反应势垒非常低:氢原子加成反应约为7千卡/摩尔,涉及羟基自由基的反应为1千卡/摩尔。从热力学角度看,两个C6自由基加合物和氢夺取产物是最稳定的。在IEFPCM/MPW1B95/6-311++G(2d,2p)水平计算的质子超精细偶合常数(HFCC)与B3LYP结果以及有关胸腺嘧啶和胞嘧啶自由基的现有实验和理论数据吻合良好。