Herak J N, Hüttermann J
Department of Pharmacy and Biochemistry, University of Zagreb, Yugoslavia.
Int J Radiat Biol. 1991 Sep;60(3):423-32. doi: 10.1080/09553009114552281.
Polycrystalline samples of several nucleic acid bases co-crystallized with small amounts of thioanalogues as impurities were X-irradiated at 77 K and investigated by electron paramagnetic resonance (EPR) spectroscopy for sulphur (S)-centered radicals. Anhydrous cytosine, cytosine monohydrate and cytosine hydrochloride with 0.01-1% incorporated thiocytosine gave strong EPR signals characteristic of S-centered radicals, with spectroscopic parameters different from those for irradiated thiocytosine alone. Likewise, in guanine hydrochloride doped with thioguanine (0.1-1%), strong signals of the radicals associated with thioguanine were observed. For the thymine-thiothymine systems (anhydrous and monohydrate) no characteristic S-centered radicals were observed after the same treatment. This was also the case for samples from non-matching bases and thiols (e.g. cytosine-thioguanine or guanine-thiocytosine), for combinations in the form of frozen glasses or frozen aqueous solutions and for almost all freeze-dried samples composed of the bases containing a small amount of thioanalogues. These observations are discussed in terms of the long-range migration of holes within the stacked base systems.
将几种与少量硫代类似物作为杂质共结晶的核酸碱基的多晶样品在77 K下进行X射线辐照，并通过电子顺磁共振（EPR）光谱对以硫（S）为中心的自由基进行研究。含有0.01 - 1%掺入硫代胞嘧啶的无水胞嘧啶、一水合胞嘧啶和盐酸胞嘧啶产生了以S为中心的自由基的强EPR信号，其光谱参数与单独辐照硫代胞嘧啶的不同。同样，在掺杂有硫鸟嘌呤（0.1 - 1%）的盐酸鸟嘌呤中，观察到了与硫鸟嘌呤相关的自由基的强信号。对于胸腺嘧啶 - 硫代胸腺嘧啶体系（无水和一水合物），在相同处理后未观察到特征性的以S为中心的自由基。对于不匹配的碱基和硫醇的样品（如胞嘧啶 - 硫鸟嘌呤或鸟嘌呤 - 硫代胞嘧啶）、以冷冻玻璃或冷冻水溶液形式的组合以及几乎所有由含有少量硫代类似物的碱基组成的冻干样品也是如此。根据堆叠碱基系统内空穴的长程迁移对这些观察结果进行了讨论。
