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

Journal Article · Wed May 15 00:00:00 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), Vol. 1
• Country of Publication: United States
• Language: English

Related Subjects

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