朱本占研究員在自由基化學(xué)研究方面又取得重要進展,，其有關(guān)“過氧化氫和鹵代醌不依賴于金屬離子存在型的羥基自由基產(chǎn)生分子機理”的研究發(fā)表在國際著名的綜合性學(xué)術(shù)期刊美國《國家科學(xué)院院刊》（PNAS）上。
羥基自由基（HO·）被公認是生物系統(tǒng)中最具活性的活性氧物種,，能導(dǎo)致生物體內(nèi)DNA,，蛋白質(zhì)和脂質(zhì)氧化損傷,。目前，關(guān)于羥基自由基的產(chǎn)生機理,，最被廣泛接受的是過渡金屬離子催化的Fenton反應(yīng),。朱本占等曾發(fā)現(xiàn)五氯酚的代謝產(chǎn)物之一四氯苯醌與H2O2反應(yīng)可產(chǎn)生羥基自由基，其特別之處在于此過程不依賴于金屬離子的存在,。但其潛在的分子機理仍不清楚,。
以電子自旋共振結(jié)合二級自由基自旋捕獲技術(shù)為手段，通過研究發(fā)現(xiàn)：四氯苯醌（TCBQ,，五氯酚等環(huán)境污染物的有毒代謝產(chǎn)物）,，而不是相應(yīng)的半醌負離子自由基（TCSQ·-）對羥基自由基的產(chǎn)生極其重要。TCBQ和H2O2反應(yīng)的主要產(chǎn)物采用電噴霧-四極桿飛行時間質(zhì)譜儀鑒定為三氯羥基-1,，4-苯醌（TrCBQ-OH）的離子形式,。研究還發(fā)現(xiàn)，反應(yīng)產(chǎn)物TrCBQ-OH中的氧原子來自于H2O2,。 基于這些數(shù)據(jù)和分析,，提出以下假設(shè)：TCBQ和H2O2反應(yīng)產(chǎn)生羥基自由基不是通過一種依賴于半醌的有機Fenton反應(yīng)進行，而是通過下述機理：H2O2對TCBQ進行親核攻擊,，形成一種三氯氫過氧基-1,，4-苯醌（TrCBQ-OOH）中間產(chǎn)物，這種中間產(chǎn)物能均裂產(chǎn)生羥基自由基和三氯羥基-1,4-苯醌自由基（TrCBQ-O·）,。TrCBQ-O·隨后能歧化形成三氯羥基-1,4-苯醌的離子形式（TrCBQ-O-）,。
上述反應(yīng)途徑展示了一種新型的羥基自由基產(chǎn)生機理：羥基自由基的形成不需要具有氧化還原活性的過渡金屬離子參與，也不需要光照,，輻射和高溫加熱,。該機理能部分解釋許多殺蟲劑（如多氯代酚，六氯苯和橙色劑等）的致癌性,，這些物質(zhì)能在體內(nèi)代謝成四氯,，三氯，二氯和一氯苯醌,。（來源：中國科學(xué)院生態(tài)環(huán)境研究中心）
生物谷推薦原始出處：
（PNAS）,，March 6, 2007 | vol. 104 | no. 10 | 3698-3702，Ben-Zhan Zhu, Balz Frei
Mechanism of metal-independent decomposition of organic hydroperoxides and formation of alkoxyl radicals by halogenated quinones
Ben-Zhan Zhu*,,, Hong-Tao Zhao, Balaraman Kalyanaraman, Jun Liu*, Guo-Qiang Shan*, Yu-Guo Du*, and Balz Frei
*State Key Laboratory of Environmental Chemistry and Ecotoxicology, Research Center for Eco-Environmental Sciences, Chinese Academy of Sciences, Beijing 100085, People's Republic of China; Linus Pauling Institute, Oregon State University, Corvallis, OR 97331; and Biophysics Research Institute, Medical College of Wisconsin, Milwaukee, WI 53226
Edited by Jack Halpern, University of Chicago, Chicago, IL, and approved December 18, 2006 (received for review July 2, 2006)
The metal-independent decomposition of organic hydroperoxides and the formation of organic alkoxyl radicals in the absence or presence of halogenated quinones were studied with electron spin resonance (ESR) and the spin-trapping agent 5,5-dimethyl-1-pyrroline N-oxide (DMPO). We found that 2,5-dichloro-1,4-benzoquinone (DCBQ) markedly enhanced the decomposition of tert-butylhydroperoxide (t-BuOOH), leading to the formation of the DMPO adducts with t-butoxyl radicals (t-BuO) and methyl radicals (CH3). The formation of DMPO/t-BuO and DMPO/CH3 was dose-dependent with respect to both DCBQ and t-BuOOH and was not affected by iron- or copper-specific metal chelators. Comparison of the data obtained with DCBQ and t-BuOOH with those obtained in a parallel study with ferrous iron and t-BuOOH strongly suggested that t-BuO was produced by DCBQ and t-BuOOH through a metal-independent mechanism. Other halogenated quinones were also found to enhance the decomposition of t-BuOOH and other organic hydroperoxides such as cumene hydroperoxide, leading to the formation of the respective organic alkoxyl radicals in a metal-independent manner. Based on these data, we propose a mechanism for DCBQ-mediated t-BuOOH decomposition and formation of t-BuO: a nucleophilic attack of t-BuOOH on DCBQ, forming a chloro-t-butylperoxyl-1,4-benzoquinone intermediate, which decomposes homolytically to produce t-BuO. This represents a mechanism of organic alkoxyl radical formation not requiring the involvement of redox-active transition metal ions.
