Nishimoto S, Ide H, Wada T, Kagiya T
Int J Radiat Biol Relat Stud Phys Chem Med. 1983 Dec;44(6):585-600. doi: 10.1080/09553008314551651.
The effect of 20 electron-affinic compounds including nitroimidazoles, nitrofurans, nitrobenzenes, and quinones on the radiation-induced reaction of thymine in aqueous solution was studied under deaerated and N2O-saturated conditions. The radiolysis of thymine in aerated aqueous solution was also performed for comparison. Thymine decomposition was depressed to some extent by the addition of electron-affinic compounds in both deaerated and N2O-saturated solutions, while promoted in aerated solution. The radiolyses with varying concentration of misonidazole indicated that the depression of thymine decomposition can be attributed to a competition between thymine and electron-affinic compounds for the reactions with .OH. Among the radiolysis products, the formation of thymine glycol was remarkably promoted by the addition of electron-affinic compounds. Irrespective of structures of the electron-affinic compounds, the G-value of thymine glycol increased in sigmoidal form with increasing one-electron reduction potential of the electron-affinic compounds and attained the ultimate values of ca. 1.1 and 1.8 in deaerated and N2O-saturated solutions, respectively. The results are in accord with one-electron oxidation of the hydroxythymyl radical, produced by the reaction of thymine with .OH, to the corresponding cation by electron-affinic compounds. The so-formed hydroxythymine cation undergoes solvolytic substitution to give thymine glycol. Based on the ultimate G-values of thymine glycol, the difference in reactivity between hydroxythymine-5-yl and 6-yl radicals toward electron-affinic compounds is discussed.
研究了包括硝基咪唑、硝基呋喃、硝基苯和醌在内的20种亲电子化合物在除气和N₂O饱和条件下对水溶液中胸腺嘧啶辐射诱导反应的影响。还进行了曝气水溶液中胸腺嘧啶的辐射分解以作比较。在除气和N₂O饱和溶液中，添加亲电子化合物都能在一定程度上抑制胸腺嘧啶分解，而在曝气溶液中则促进其分解。不同浓度米索硝唑的辐射分解表明，胸腺嘧啶分解的抑制可归因于胸腺嘧啶和亲电子化合物对与·OH反应的竞争。在辐射分解产物中，添加亲电子化合物显著促进了胸腺嘧啶二醇的形成。无论亲电子化合物的结构如何，胸腺嘧啶二醇的G值都随着亲电子化合物单电子还原电位的增加呈S形增加，在除气和N₂O饱和溶液中分别达到约1.1和1.8的最终值。结果与胸腺嘧啶与·OH反应产生的羟基胸腺嘧啶自由基被亲电子化合物单电子氧化为相应阳离子一致。如此形成的羟基胸腺嘧啶阳离子发生溶剂解取代反应生成胸腺嘧啶二醇。基于胸腺嘧啶二醇的最终G值，讨论了羟基胸腺嘧啶-5-基和6-基自由基对亲电子化合物反应性的差异。
