Bleaching of melanin pigments. Role of copper ions and hydrogen peroxide in autooxidation and photooxidation of synthetic dopa-melanin.

摘要: Bleaching of eumelanin has been studied in model systems consisting synthetic dopa-melanin and various concentrations hydrogen peroxide, molecular oxygen, copper(II) ions at neutral alkaline pH. The data show that pH, the dark, metal-ion-free melanin is very resistant to oxidation by peroxide. However, rate bleaching melanin, induced H2O2 significantly accelerated illumination from UVA-visible light. Bound-to-melanin also accelerates with efficiency dependent on concentration oxygen. It suggests possible involvement melanin-copper complexes Fenton-like processes. formation hydroxyl radicals during concluded basis electrochemical detection hydroxylation products salicylate used as OH scavenger. Redox conversion bound-to-melanin copper was monitored EPR spectroscopy direct measurement melanin-Cu(II) complexes. shown melanin-copper(I) were readily oxidized either oxygen or indicate a complex process two distinct stages, reversible hydroquinone moieties followed irreversible reactions monomers lead degradation polymer.