RESUMO
This work aims to determine the roles of reactive oxygen species HOâ and HO2- in the bleaching of melanins by alkaline hydrogen peroxide. Experiments using melanosomes isolated from human hair indicated that the HOâ radical generated in the outside solution does not contribute significantly to bleaching. However, studies using soluble Sepia melanin demonstrated that both HO2- and HOâ will individually bleach melanin. Additionally, when both oxidants are present, bleaching is increased dramatically in both rate and extent. Careful experimental design enabled the separation of the roles and effects of these key reactive species, HOâ and HO2-. Rationalisation of the results presented, and review of previous literature, allowed the postulation of a simplified general scheme whereby the strong oxidant HOâ is able to pre-oxidise melanin units to o-quinones enabling more facile ring opening by the more nucleophilic HO2-. In this manner the efficiency of the roles of both species is maximised.