Hüttermann J, Lange M, Ohlmann J
Fachrichtung Biophysik und Physikalische Grundlagen der Medizin, Universität des Saarlandes, Homburg/Saar, Germany.
Radiat Res. 1992 Jul;131(1):18-23.
Frozen aqueous solutions of 1 M thymidine-5'-monophosphate were X-irradiated 77 K. The free radicals formed were analyzed by electron spin resonance spectroscopy between 77 K and about 260 K and were shown to result nearly exclusively from electron reaction at 77 K forming the thymine base anion, which converts into the well known 5-thymyl radical upon annealing. Primary oxidation of the substrate was not detectable. A minority species denoted TOH., which appeared at about 200 K, was suggested to result from OH. addition to carbon C6 of the base, perhaps via intermediate oxidation involving H2O2 or from direct reaction of OH. with the base. Another minority species at 77 K up to about 150 K, which was strongly enhanced by H2O2, was shown to be the allyl radical formed by reaction of the OH. with the methyl group. Support for this was given from experiments using BeF2 glasses. The possible spectral features for the cation of dTMP were extracted from aqueous pastes of the Ca2+ salt at 77 K. The mechanistic aspects derived from the results are in conflict with previous assumptions and are discussed for DNA model compounds and DNA.
1 M 胸苷-5'-单磷酸的冷冻水溶液在77 K下进行X射线辐照。通过电子自旋共振光谱在77 K至约260 K之间对形成的自由基进行分析，结果表明几乎所有自由基都是在77 K时通过电子反应形成胸腺嘧啶碱基阴离子产生的，该阴离子在退火时会转化为著名的5-胸腺嘧啶自由基。底物的初级氧化无法检测到。一种在约200 K出现的少数物种标记为TOH.，据推测是由于OH. 加成到碱基的C6碳原子上形成的，可能是通过涉及H2O2的中间氧化过程，或者是OH. 与碱基的直接反应。另一种在77 K至约150 K出现的少数物种，在H2O2存在下会强烈增强，结果表明是由OH. 与甲基反应形成的烯丙基自由基。使用BeF2玻璃进行的实验为此提供了支持。在77 K下从Ca2+盐的水性糊剂中提取了dTMP阳离子可能的光谱特征。从结果得出的机理方面与先前的假设相冲突，并针对DNA模型化合物和DNA进行了讨论。
