中国科学院生态环境研究中心, 环境化学与生态毒理学国家重点实验室, 北京100085

State Key Laboratory of Environmental Chemistry and Eco-toxicology, Research Center for Eco-Environmental Sciences, Chinese Academy of Sciences, Beijing 100085, China

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 DNA, protein, and lipid oxidation. One of the most widely accepted mechanisms for •OH production is the transition metal- catalyzed Fenton reaction. Pentachlorophenol (PCP) has been widely used as a wood preservative. Using the salicylate hydroxylation assay and electron spin resonance (ESR) 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 (TCSQ•), is essential for •OH production. The major reaction product between TCBQ and H₂O₂ was identified to be the ionic form of trichloro-hydroxy-1, 4-benzoquinone (TrCBQ-OH), and H₂O₂ was found to be the source and origin of the oxygen atom inserted into the reaction product TrCBQ-OH. Based on these data, we propose that •OH production by H₂O₂ and TCBQ is not through a semiquinone-dependent organic Fenton reaction, but rather through the following novel mechanism: a nucleophilic attack of H₂O₂ on TCBQ, forming a trichloro- hydroperoxyl-1, 4-benzoquinone (TrCBQ-OOH) intermediate, which decomposes homolytically to produce •OH. These findings represent a novel mechanism of •OH formation not requiring the involvement of redox-active transition metal ions, and may partly explain the potential carcinogenicity of widely used biocides such as PCP and other polyhalogenated aromatic environmental pollutants.

国家重点基础研究发展计划(编号: 2008CB418106)、国家自然科学基金(批准号: 20777080, 20877081, 20747001, 20890112, 20621703)和中国科学院“百人计划”资助项目