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首页> 外文期刊>The journal of physical chemistry, A. Molecules, spectroscopy, kinetics, environment, & general theory >Hole Transfer and Differential Radical Recombination in X-Irradiated Doped Crystalline DNA Model Systems
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Hole Transfer and Differential Radical Recombination in X-Irradiated Doped Crystalline DNA Model Systems

机译：X射线辐射掺杂的结晶DNA模型系统中的空穴转移和微分自由基重组。

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摘要

Radiation induced hole transfer and differential recombination of radicals at room temperature and lower temperatures (77 and 12 K) have been studied in crystals of cytosine·HCl doped with 5-methylcytosine·HCl doped with 5-methylcytosine·HCl (doping level 0.25-1.1 mol%). The main oxidation product stabilized in the doped crystals at room temperature is an allylic radical, called the 3αH radical, which is formed in the 5-methylcytosine dopant by net H-abstraction from the methyl group. This radical has previously been observed in various crystalline cytosine nucleosides and nucleotides shown to contain 5-methylated impurities, and it is of interest to investigate why this radical is formed in disproportionately large yields. Two effects are important in this respect. First, the 3αH radical in the present system is far less prone to recombination than the initially formed cytosine radicals, rendering the relative yield of this radical much greater than expected from the concentration of the dopant in the crystals. Second, as 5-methylcytosine has a lower ionization potential than cytosine, the 3αH radical may in addition be formed by hole transfer from oxidized cytosine to 5-methylcytosine followed by deprotonation at the methyl group. A simple model is presented which isolates the effect of such hole transfer on the relative radical yields from the effect of differential recombination. On the basis of the experimental data, and according to this model, the 3αH radical most probably is formed by fast hole transfer and radical trapping upon irradiation at room temperature. At lower irradiation temperatures the model predicts that the 3αH radical is not the dominant oxidation radical in crystalline 5-methylcytosine.
机译：在掺有5-甲基胞嘧啶的胞嘧啶·HCl·掺有5-甲基胞嘧啶·HCl（掺杂水平0.25-1.1）的胞嘧啶·HCl晶体中，研究了室温和较低温度（77和12 K）下辐射诱导的空穴转移和自由基的差异重组。 mol％）。在室温下稳定在掺杂晶体中的主要氧化产物是被称为3αH的烯丙基自由基，它是通过从甲基上净吸氢而在5-甲基胞嘧啶掺杂剂中形成的。先前已经在各种晶体胞嘧啶核苷和核苷酸中观察到了该自由基，这些核苷和核苷酸显示含有5-甲基化杂质，因此研究为什么以不成比例的大产率形成该自由基是很有意义的。在这方面有两个作用很重要。首先，本系统中的3αH自由基比最初形成的胞嘧啶自由基更不易于重组，使该自由基的相对产率比晶体中掺杂剂的浓度所期望的要高得多。其次，由于5-甲基胞嘧啶的电离电势比胞嘧啶低，因此3αH自由基还可以通过从氧化的胞嘧啶向5-甲基胞嘧啶的空穴转移然后在甲基上去质子化而形成。提出了一个简单的模型，该模型将这种空穴转移对相对自由基产率的影响与差分重组的影响隔离开来。根据实验数据，并根据该模型，最有可能通过快速空穴传输和在室温下照射时捕获自由基而形成3αH自由基。在较低的辐射温度下，该模型预测3αH自由基不是晶体5-甲基胞嘧啶中的主要氧化自由基。

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