THE REACTION OF MELATONIN WITH PEROXYNITRITE - FORMATION OF MELATONINRADICAL-CATION AND ABSENCE OF STABLE NITRATED PRODUCTS

Peroxynitrite is capable of hydroxylating and nitrating aromatic speci es. However, nitromelatonin is not found as a final product when melat onin was allowed to react with peroxynitrite either in the presence or absence of added bicarbonate. In the absence of bicarbonate, the two major products formed are 6-hydroxymelatonin and 5-methoxy-2-hydro-pyr roloindole, and the latter is the only major product with excess bicar bonate. A transient purple intermediate with a maximum absorbance at a bout 520 nm is observed upon mixing solutions containing peroxynitrite and melatonin. These observations indicate that the melatoninyl radic al cation is formed in the peroxynitrite/melatonin reaction, providing a direct evidence for the one-electron oxidation ability of peroxynit rite. The melatoninyl radical cation also is observed with excess bica rbonate. (C) 1998 Academic Press.