EPR and spin-trapping investigation of free radicals from the reaction of 4-methoxybenzenediazonium tetrafluoroborate with melanin and melanin precursors

EPR spectroscopy and spin-trapping method were used to examine the interaction of synthetic 3,4-dihydroxyphenylalanine (DOPA) melanin (DM) and its precursors, with 4-methoxybenzenediazonium tetrafluoroborate, 4-MeO-PhN2BF4. A one electron-transfer mechanism facilitates the reaction of DM, catechol, 3,4-dihydroxybenzoic acid, 3,4-dihydroxyhydrocinnamic acid, 3, 4-dihydroxyphenylalanine, and 6-hydroxydopamine with 4-MeO-PhN2+. Hydroquinones and semiquinone radicals enhanced the homolysis of diazonium salts to produce aryl radicals.