title: Metal-independent production of hydroxyl radicals by halogenated quinones and hydrogen peroxide: an ESR spin trapping study.
abstract: The metal-independent production of hydroxyl radicals (*OH) from H(2)O(2) and tetrachloro-1,4-benzoquinone (TCBQ), a carcinogenic metabolite of the widely used wood-preservative pentachlorophenol, was studied by electron spin resonance methods. When incubated with the spin trapping agent 5,5-dimethyl-1-pyrroline N-oxide (DMPO), TCBQ and H(2)O(2) produced the DMPO/*OH adduct. The formation of DMPO/*OH was markedly inhibited by the *OH scavenging agents dimethyl sulfoxide (DMSO), ethanol, formate, and azide, with the concomitant formation of the characteristic DMPO spin trapping adducts with *CH(3), *CH(CH(3))OH, *COO(-), and *N(3), respectively. The formation of DMPO/*OH and DMPO/*CH(3) from TCBQ and H(2)O(2) in the absence and presence, respectively, of DMSO was inhibited by the trihydroxamate compound desferrioxamine, accompanied by the formation of the desferrioxamine-nitroxide radical. In contrast, DMPO/*OH and DMPO/*CH(3) formation from TCBQ and H(2)O(2) was not affected by the nonhydroxamate iron chelators bathophenanthroline disulfonate, ferrozine, and ferene, as well as the copper-specific chelator bathocuproine disulfonate. A comparative study with ferrous iron and H(2)O(2), the classic Fenton system, strongly supports our conclusion that *OH is produced by TCBQ and H(2)O(2) through a metal-independent mechanism. Metal-independent production of *OH from H(2)O(2) was also observed with several other halogenated quinones.
authors.affiliation: Linus Pauling Institute, Oregon State University, Corvallis, OR 97331, USA.
authors.forename: Ben-Zhan
authors.initials: BZ
authors.lastname: Zhu
authors.forename: Hong-Tao
authors.initials: HT
authors.lastname: Zhao
authors.forename: Balaraman
authors.initials: B
authors.lastname: Kalyanaraman
authors.forename: Balz
authors.initials: B
authors.lastname: Frei
mesh_terms: D002614:Chelating Agents; D002703:Chloranil / Q000737:chemistry* / Q000378:metabolism; D003300:Copper; D003497:Cyclic N-Oxides / Q000737:chemistry* / Q000378:metabolism; D004578:Electron Spin Resonance Spectroscopy; D006861:Hydrogen Peroxide / Q000737:chemistry* / Q000378:metabolism; D017665:Hydroxyl Radical / Q000737:chemistry / Q000378:metabolism*; D007501:Iron; D015394:Molecular Structure; D013113:Spin Labels
chemical_list: D002614:Chelating Agents; D003497:Cyclic N-Oxides; C045076:Fenton's reagent; D013113:Spin Labels; D002703:Chloranil; D017665:Hydroxyl Radical; D003300:Copper; D006861:Hydrogen Peroxide; D007501:Iron