水溶液中胞嘧啶阳离子自由基降解反应机理的理论研究

Theoretical Study of Degradation Reaction Mechanism of Cytosine Cation Radicals in Aqueous Solution

用密度泛函理论以C^(+)…6H_(2)O,C(H);∶C^(+)…4H_(2)O为计算模型从理论上研究了2’-脱氧胞嘧啶核苷(dC)及i-Motif结构中胞嘧啶阳离子自由基(C^(+))的脱质子反应和水合反应。计算结果表明,在自由dC中,C^(+)主要发生脱质子反应和异构化反应,而在i-Motif结构中,C^(+)主要发生水合反应,i-Motif结构中C^(+)水合反应的速率会慢于自由dC中C^(+)脱质子和异构化。导致自由dC及i-Motif结构中C^(+)反应机理不一样的原因是i-Motif结构中C(H);与C^(+)之间的氢键阻碍了C^(+)脱质子产物的异构化。

The deprotonation and hydration reaction of cytosine cation radicals(C^(+))in 2’-deoxycytidine(dC)and in i-motif DNA have been investigated by density functional theory(DFT)calculations using C^(+)…6 H_(2)O and C(H);:C^(+)…4 H_(2)O as computational models,respectively.The results showed that,for free dC,the deprotonation and isomerization reactions mainly occurred for C^(+).While for i-motif DNA,the predominant reaction for C^(+) was hydration.The reaction rate of C^(+) hydration in i-motif DNA was slower than that of C^(+) deprotonation and isomerization in free dC.It was also shown that the C^(+) reaction mechanism in free dC and i-motif DNA was different,and that the hydrogen bond between C(H);and C^(+) in i-motif DNA would prevent the isomerization of C^(+) deprotonated products.