Evidence of an electron-transfer mechanism in the peroxynitrite-mediated oxidation of 4-alkylphenols and tyrosine

The mechanism of interaction of the peroxynitrite with some 4-alkylphenols and tyrosine was mainly studied by means of ESR spectroscopy and product analysis. The radical intermediates, detected as spin adducts to the 5-diethoxyphosphoryl-5-methyl-1-pyrroline N-oxide (DEPMPO), were identified as carbon-centered radicals to the benzene ring. The reaction seems to proceed via an electron transfer process (ET), most likely mediated by a NOx derivative, leading to the intermediacy of a phenoxyl-type radical as proved by the detection of the corresponding Pummerer-type ketone. No evidence of the formation of hydroxyl radicals, due to the homolytic cleavage of the peroxynitrite at physiological pH was obtained, even though DEPMPO hydroxyl spin adducts were detected: the latter most likely arises from the direct attack of the spin trap by the oxidant species. The possible involvement of HCO(3)(-)/CO(2), i.e., the formation of the nitrosoperoxycarbonate, ONOOCO(2)(*)(-), was also investigated.