title: Characterization of semiquinone free radicals formed from stilbene catechol estrogens. An ESR spin stabilization and spin trapping study.
abstract: Electron spin resonance spectroscopy has been used to detect, characterize, and to infer structures of o-semiquinones derived from stilbene catechol estrogens. Radicals were generated enzymatically using tyrosinase and were detected as their Mg2+ complexes. It is suggested that initial hydroxylation of stilbene estrogen gives a catechol estrogen in situ; subsequent two-electron oxidation of the catechol to the quinone, followed by reverse disproportionation, leads to the formation of radicals. Consistent with this mechanism, o-phenylenediamine, a quinone trapping agent, inhibits formation of o-semiquinones. A competing mechanism of radical production involves autoxidation of the catechol. Hydroxyl radicals are shown to be produced in this system via a mechanism involving reduction of iron and copper complexes by stilbene catechols. Possible differences in the reactivity of stilbene ortho- and para-semiquinones are discussed.
authors.affiliation: Department of Radiology, Medical College of Wisconsin, Milwaukee 53226.
authors.forename: B
authors.initials: B
authors.lastname: Kalyanaraman
authors.forename: R C
authors.initials: RC
authors.lastname: Sealy
authors.forename: J G
authors.initials: JG
authors.lastname: Liehr
mesh_terms: D016227:Benzoquinones; D003497:Cyclic N-Oxides; D004028:Dienestrol / Q000031:analogs & derivatives / Q000378:metabolism; D004054:Diethylstilbestrol / Q000031:analogs & derivatives / Q000378:metabolism; D004578:Electron Spin Resonance Spectroscopy; D002393:Estrogens, Catechol / Q000378:metabolism*; D005609:Free Radicals; D006589:Hexestrol / Q000031:analogs & derivatives / Q000378:metabolism; D008274:Magnesium / Q000378:metabolism; D015394:Molecular Structure; D014442:Monophenol Monooxygenase / Q000378:metabolism; D010084:Oxidation-Reduction; D011809:Quinones; D013113:Spin Labels; D013267:Stilbenes / Q000378:metabolism*
chemical_list: D016227:Benzoquinones; D003497:Cyclic N-Oxides; D002393:Estrogens, Catechol; D005609:Free Radicals; D011809:Quinones; D013113:Spin Labels; D013267:Stilbenes; D006589:Hexestrol; C025232:semiquinone radicals; C017245:5,5-dimethyl-1-pyrroline-1-oxide; D004054:Diethylstilbestrol; D014442:Monophenol Monooxygenase; D008274:Magnesium; D004028:Dienestrol