Nitroxides as redox probes of melanins: dark-induced and photoinduced changes in redox equilibria

Journal Article · Wed May 15 04:00:00 EDT 1985 · Arch. Biochem. Biophys.; (United States)

DOI:https://doi.org/10.1016/0003-9861(85)90830-6· OSTI ID:5012645

Sarna, T; Korytowski, W; Sealy, R C

The interaction of nitroxide free radicals and their reduced products (hydroxylamines) with synthetic and natural melanins has been studied. Electron spin resonance spectroscopy was used to measure changes in radical concentration in the dark and during irradiation with visible or uv light. Some reduction of nitroxide occurs in the dark, and is reversible: the nitroxide can be completely regenerated by the one-electron oxidant ferricyanide. The kinetics of the process depend strongly on radical charge and pH. For positively charged nitroxides the rate is much faster than for either neutral or anionic radicals. At pH 10 the rate is about 20 times faster than at pH 5. Oxidation of hydroxylamine also can occur so that a redox equilibrium is established. The equilibrium constant has been estimated for the reaction between a nitroxide and melanin from autoxidation of 3,4-dihydroxyphenylalanine. Results are also dependent upon the type of melanin used and chemical modification (oxidation or reduction) of the melanin. Redox equilibria are altered during irradiation with either visible or uv light. Rapid oxidation of hydroxylamine to nitroxide is apparent, together with a slower reduction of nitroxide. Action spectra for these processes are related to those for melanin radical production and oxygen consumption in nitroxide-free melanin systems. Reduction of nitroxide is inhibited by oxygen, suggesting a competition between nitroxide and oxygen for photoinduced reducing equivalents.

• OSTI ID: 5012645
• Journal Information: Arch. Biochem. Biophys.; (United States), Journal Name: Arch. Biochem. Biophys.; (United States) Vol. 1; ISSN ABBIA
• Country of Publication: United States
• Language: English

Related Subjects

560111* -- Radiation Effects on Biochemicals-- In Vitro-- (-1987)
63 RADIATION, THERMAL, AND OTHER ENVIRON. POLLUTANT EFFECTS ON LIVING ORGS. AND BIOL. MAT.
AMINES
BIOLOGICAL HALF-LIFE
CHALCOGENIDES
CHEMICAL REACTIONS
CHEMISTRY
ELECTROMAGNETIC RADIATION
ELECTRON SPIN RESONANCE
HYDROXY COMPOUNDS
HYDROXYLAMINE
MAGNETIC RESONANCE
MELANIN
NITROGEN COMPOUNDS
NITROGEN OXIDES
ORGANIC COMPOUNDS
ORGANIC NITROGEN COMPOUNDS
OXIDATION
OXIDES
OXYGEN COMPOUNDS
PHOTOCHEMISTRY
PIGMENTS
RADIATIONS
REDOX REACTIONS
RESONANCE
ULTRAVIOLET RADIATION