Electron spin resonance and intermediate neglect of differential overlap molecular orbital study of the .pi. cations of (hydroxymethly)uracil and (hydroxymethyl)cytosine. Evidence for internal hydrogen bonding
Electron spin resonance and intermediate neglect of differential overlap molecular orbital study of the .pi. cations of (hydroxymethly)uracil and (hydroxymethyl)cytosine. Evidence for internal hydrogen bonding
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电子自旋共振和中间忽略微分重叠分子轨道研究.pi。
DOI：
10.1021/j100227a023
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发表时间：
1983
期刊：
影响因子：
--
通讯作者：
M. McGlashen
中科院分区：
文献类型：
--
作者：
M. Sevilla;M. McGlashen
那个... pi..- Cl/sub 2//sup -/进攻5-（羟甲基）尿嘧啶（HOMeU）和5-（羟甲基）胞嘧啶（HOMeC）产生阳离子自由基.伽马.. -辐照的碱性12 M LiCl和低温下在碱性8 M NaClO/sub 4/glass中的光电离。对这些自由基的ESR谱的分析表明，每一个自由基都是由一个或多个原子组成的。pi..-随着温度升高，阳离子自由基可能通过氮质子化状态的变化而转化为另一种物质。例如，5-（羟甲基）尿嘧啶阳离子显示两个羟甲基的28.5-G平均分裂。beta..在退火时转化为36-G分裂的质子。退火后发现的分裂和狭窄的线宽是暗示的配置，这是分子内刚性和稳定的分子内氢键从羟基质子的4-位氧。那个... pi.. 5-（羟甲基）胞嘧啶的阳离子转化为在环外氮上具有相当大的自旋密度的自由基，这再次显示了分子内氢键的强有力证据。最终的自由基被发现是从.. pi..-通过亚甲基质子的去质子化，形成（羟甲基）尿嘧啶和（羟甲基）胞嘧啶的阳离子自由基。INDO计算结果pi..（羟甲基）尿嘧啶的阳离子作为羟基取向的函数显示，在3-位氮去质子化后，与4-位氧的氢键的强度增加3倍。因此，氢键被预测为基本上稳定的。pi..-阳离子自由基«少
The ..pi..-cation radicals of 5-(hydroxymethyl)uracil (HOMeU) and 5-(hydroxymethyl)cytosine (HOMeC) have been produced by Cl/sub 2//sup -/ attack in ..gamma..-irradiated basic 12 M LiCl and photoionization in basic 8 M NaClO/sub 4/ glasses at low temperatures. Analysis of the ESR spectra found for these radicals shows that each of the ..pi..-cation radicals converts to another species probably by a change in a nitrogen protonation state as the temperature is raised. For example, 5-(hydroxymethyl)uracil cation shows a 28.5-G average splitting for the two hydroxymethyl-group ..beta.. protons which convert upon annealing to a 36-G splitting. The splittings and the narrowness of the line widths found after annealing are suggestive of a configuration which is intramolecularly rigid and stabilized by a intramolecular hydrogen bond from the hydroxyl proton to the 4-position oxygen. The ..pi.. cation of 5-(hydroxymethyl)cytosine converts to a radical with substantial spin density on the exocyclic nitrogen which again shows strong evidence for intramolecular hydrogen bonding. Final radicals are found to be produced from the ..pi..-cation radicals of (hydroxymethyl)uracil and (hydroxymethyl)cytosine by deprotonation of a methylene proton. INDO calculations for the ..pi.. cation of (hydroxymethyl)uracil as a function of orientation of the hydroxyl group show that the hydrogen bond to the 4-positionmore » oxygen increases in strength by a factor of 3 upon deprotonation at the 3-position nitrogen. The hydrogen bond is therefore predicted to substantially stabilize the ..pi..-cation radical.« less