新型羟基和醌碳自由基产生的分子机理

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.

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

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.