Ohlmann J, Hüttermann J
Fachrichtung Biophysik und Physikalische Grundlagen, Medizin Universität des Saarlandes, Homburg/Saar, Germany.
Int J Radiat Biol. 1993 Apr;63(4):427-36. doi: 10.1080/09553009314550581.
Free radical formation by reaction of water radiolysis intermediates produced by X-irradiation in aqueous glasses containing 7 M BeF2 at 77 K with pyrimidine and purine constituents of DNA (10 mM) was studied by electron paramagnetic resonance (EPR) spectroscopy. Reactions of electrons and .OH radicals were observed; H. form a minority and their contribution was difficult to establish. The electrons form substrate radicals at 77 K, while .OH radicals, stabilized in the matrix at 77 K, become mobile at about 140K and in part react with solute molecules. The radicals formed by both reactions were characterized after isolation of the corresponding components by thermal annealing up to about 190 K and spectra simulation using literature parameters whenever possible. The spectra from cytosine gave strong evidence for heteroatom protonation following electron addition while those from adenine were somewhat less clear. The spectra of uracil and all methylated pyrimidines gave no evidence for the protonation state of the electron adduct. For the .OH radical, the reaction with uracil and cytosine was found to be addition to the 5,6-double bond, in line with studies using aqueous solutions. For all methylated pyrimidines, however, H-abstraction from the methyl group was dominant. .OH addition to adenine was found to take place at C2.
利用电子顺磁共振（EPR）光谱研究了在77 K下含有7 M BeF₂的水性玻璃中，X射线辐照产生的水辐射分解中间体与DNA的嘧啶和嘌呤成分（10 mM）反应形成自由基的情况。观察到了电子和·OH自由基的反应；H·占少数，其贡献难以确定。电子在77 K时形成底物自由基，而在77 K的基质中稳定的·OH自由基在约140 K时变得可移动，并部分与溶质分子反应。通过热退火至约190 K分离相应成分，并尽可能使用文献参数进行光谱模拟后，对两种反应形成的自由基进行了表征。胞嘧啶的光谱有力地证明了电子加成后杂原子的质子化，而腺嘌呤的光谱则不太清晰。尿嘧啶和所有甲基化嘧啶的光谱没有给出电子加合物质子化状态的证据。对于·OH自由基，发现它与尿嘧啶和胞嘧啶的反应是加成到5,6-双键上，这与在水溶液中的研究一致。然而，对于所有甲基化嘧啶，从甲基上夺取氢是主要反应。发现·OH加成到腺嘌呤的位置是C2。
