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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.
