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Metal-independent decomposition of hydroperoxides by halogenated quinones: detection and identification of a quinone ketoxy radical. Proc Natl Acad Sci U S A 2009 Jul 14;106(28):11466-71

Date

06/27/2009

Pubmed ID

19556549

Pubmed Central ID

PMC2710671

DOI

10.1073/pnas.0900065106

Scopus ID

2-s2.0-67650886071 (requires institutional sign-in at Scopus site)   94 Citations

Abstract

We have shown recently that halogenated quinones could enhance the decomposition of hydroperoxides and formation of alkoxyl/hydroxyl radicals through a metal-independent mechanism. However, neither the proposed quinone enoxy radical intermediate, nor the major reaction products were unambiguously identified. In the present study, one of the major reaction products between 2,5-dichloro-1,4-benzoquinone (DCBQ) and t-butylhydroperoxide (t-BuOOH) was isolated and purified by semipreparative HPLC, and identified as 2-hydroxy-3-t-butoxy-5-chloro-1,4-benzoquinone [CBQ(OH)-O-t-Bu], which is the rearranged isomer of the postulated quinone-peroxide reaction intermediate. The formation of CBQ(OH)-O-t-Bu was found to be inhibited by the spin trapping agent 5,5-dimethyl-1-pyrroline N-oxide (DMPO), and concurrently, a new DMPO adduct with 1-chlorine isotope peak clusters at m/z 268 was observed. Further electron spin resonance (ESR) spin-trapping, (1)H-NMR and HPLC/Fourier transform ion cyclotron resonance (FTICR) mass spectrometric studies with oxygen-17-labeled and unlabeled hydrogen peroxide strongly suggest that the radical trapped by DMPO is a carbon-centered quinone ketoxy radical, which is the spin isomer of the proposed oxygen-centered quinone enoxy radical. Analogous results were observed when DCBQ was substituted by other halogenated quinones. This study represents the first detection and identification of an unusual carbon-centered quinone ketoxy radical, which provides direct experimental evidence to further support and expand our previously proposed mechanism for metal-independent decomposition of hydroperoxides by halogenated quinones.

Author List

Zhu BZ, Shan GQ, Huang CH, Kalyanaraman B, Mao L, Du YG

Author

Balaraman Kalyanaraman PhD Professor in the Biophysics department at Medical College of Wisconsin




MESH terms used to index this publication - Major topics in bold

Benzoquinones
Chromatography, High Pressure Liquid
Cyclic N-Oxides
Electron Spin Resonance Spectroscopy
Hydrocarbons, Halogenated
Mass Spectrometry
Models, Chemical
Molecular Structure
tert-Butylhydroperoxide