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Pulse Radiolysis of 5-Substituted Uracils : Substituent Effects on Radical Reactivity

5-取代尿嘧啶的脉冲放射分解：取代基对自由基反应性的影响

基本信息

批准号：
07651002
负责人：
FUJITA Shin-ichi
金额：
$ 1.41万
依托单位：
UNIVERSITY OF OSAKA PREFECTURE
依托单位国家：
日本
项目类别：
Grant-in-Aid for Scientific Research (C)
财政年份：
1995
资助国家：
日本
起止时间：
1995 至 1996
项目状态：
已结题

项目摘要

Effects of substituents on the reactivity of 5-substituted uracils were investigated experimentally and theoretically to get molecular and mechanistic insights into the biological damages by ionizing radiation. In 1995 the reaction of various 5-substituted uracils with hydroxyl radicals, which were generated as the primary active species in the radiolysis of N_2O-saturated aqueous solution, and the reactivity of intermediate radicals were explored to characterize the damages of pyrimidine bases by indirect action of radiation. In 1996 the dynamic behavior in the formation and conversion to radicals of radical cation intermediates derived from 5-substituted uracils was determined in relation to direct action of radiation, for correlating the reactivity of the intermediates with their structures. The followings are the main results.(1) The regioselectivity of hydroxyl radical addition to the C (5)-C (6) double bond of 5-substituted uracils, that was strongly affected by the 5-substituent structures, was evaluated quantitatively by a redox titration method in the pulse radiolysis.(2) The mechanism by which hydroxylated 5-substituted uracil-6-yl radicals undergo elimination of 5-substituents to produce hydroxyl radicals was demonstrated.(3) The structure-reactivity relationship of radicals was determined on the basis of the experimental data from pulse and steady-state radiolyses to clarify the 5-substituent effect on the reactivity of 5-substituted uracils and the related radicals.(4) The dynamic behavior and the reactivity of radical cations derived from one-electron oxidation of 5-substituted uracils and the related allyl radicals were characterized.(5) The N (1) -C (5) -linked dimers of 5-substituted uracils as produced by head-to-tail recombination of the allyl radicals were quantified to clarify the 5-substituent effect on the G-value of the dimerization.

通过实验和理论研究取代基对5-取代尿嘧啶反应性的影响，以期对电离辐射生物损伤的分子机理有深入的了解。1995年，研究了各种5-取代尿嘧啶与n22o饱和水溶液辐射分解中产生的主要活性物质羟基自由基的反应，以及中间自由基的反应活性，以表征辐射间接作用对嘧啶碱的损伤。1996年测定了5-取代尿嘧啶衍生的自由基阳离子中间体在辐射的直接作用下形成和转化为自由基的动力学行为，以将中间体的反应性与其结构联系起来。以下是主要结果。(1)采用脉冲辐射分解氧化还原滴定法定量评价了5取代脲嘧啶的C (5)-C(6)双键羟基自由基加成的区域选择性，该区域选择性受5取代基结构的强烈影响。(2)证实了羟基化的5-取代尿嘧啶-6-基自由基通过消除5-取代基产生羟基自由基的机理。(3)根据脉冲和稳态辐射裂解实验数据，确定了自由基的构效关系，阐明了5取代基对5取代脲嘧啶及其相关自由基的反应性的影响。(4)表征了5-取代尿嘧啶及其烯丙基自由基单电子氧化生成的自由基阳离子的动力学行为和反应活性。(5)对烯丙基自由基头尾复合产生的5-取代尿嘧啶N (1) -C(5)键二聚体进行了定量分析，明确了5-取代基对二聚反应g值的影响。