新型羟基和醌碳自由基产生的分子机理

A Novel Mechanism for Metal-Independent Production of Hydroxyl Radicals and Carbon-Centered Quinone Ketoxy Radicals

羟基自由基(.OH)被公认是生物系统中最具活性的活性氧物种,能导致生物体内DNA等生物大分子氧化损伤.目前,最被广泛接受的.OH的产生机理是过渡金属离子催化的Fenton反应.五氯酚(PCP)是一种重要的生物杀灭剂,主要用作木材保护.采用电子自旋共振二级自旋捕获等分析手段,发现H2O2和五氯酚的代谢产物之一四氯苯醌(TCBQ)能通过不依赖于金属离子的途径产生.OH;进一步的研究发现是TCBQ,而非其相应的半醌自由基对.OH的产生极其重要.基于这些数据和分析,提出以下新型.OH产生分子机理:H2O2对TCBQ进行亲核攻击形成不稳定的三氯氢过氧基苯醌中间产物,其可均裂产生.OH.综合采用电子自旋共振自旋捕获和其他分析方法,第1次检测到一种新型的以碳为中心的醌自由基.

The hydroxyl radical（· OH） has been considered to be one of the most reactive oxygen species produced in biological systems.It has been shown that · OH can cause oxidative damage to DNA and other macromolecules.One of the most widely accepted mechanisms for · OH production is through the transition metal-catalyzed Fenton reaction.Pentachlorophenol（PCP） has been widely used as a wood preservative.Using electron spin resonance（ESR） secondary spin-trapping methods,we found that · OH can be produced by H2O2 and tetrachloro-1,4-benzoquinone（TCBQ）（one of the major carcinogenic metabolites of PCP） independent of transition metal ions.Further studies showed that TCBQ,but not its corresponding semiquinone radical,the tetrachlorosemiquinone radical,is essential for · OH production.Based on these data,we propose that · OH production by H2O2 and TCBQ is through the following novel mechanism： a nucleophilic attack of H2O2 to TCBQ,forming a trichloro-hydroperoxyl-1,4-benzoquinone intermediate,which decomposes homolytically to produce · OH.Through complementary application of ESR spin-trapping and other methods,we also detected and identified,for the first time,a novel carbon-centered quinone ketoxy radical.