Mechanistic insights into the bleaching of melanin by alkaline hydrogen peroxide.
This work aims to determine the roles of reactive oxygen species HO∙ and HO2-in the bleaching of melanins by alkaline hydrogen peroxide. Experiments using melanosomes isolated from human hair indicated that the HO∙ radical generated in the outside solution does not contribute significantly to bleaching. However, studies using soluble Sepia melanin demonstrated that both HO2-and HO∙ 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, HO∙ and HO2-. Rationalisation of the results presented, and review of previous literature, allowed the postulation of a simplified general scheme whereby the strong oxidant HO∙ 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.
Department of Chemistry, University of York, Heslington, York YO10 5DD, United Kingdom.
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Smith
Department of Chemistry, University of York, Heslington, York YO10 5DD, United Kingdom.
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Garrett
Department of Chemistry, University of York, Heslington, York YO10 5DD, United Kingdom.
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Naqvi
Department of Chemistry, University of York, Heslington, York YO10 5DD, United Kingdom.
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Fülöp
Procter & Gamble Service GmbH, Sulzbacher Str. 40, 65824 Schwalbach am Taunus, Germany.
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Godfrey
The Procter & Gamble Company, Mason Business Center, 8700 Mason Montgomery Road, Mason, OH 45040, United States.
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Marsh
Department of Chemistry, University of York, Heslington, York YO10 5DD, United Kingdom. Electronic address: victor.chechik@york.ac.uk.
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Chechik
D000818:Animals; D000863:Antacids / Q000737:chemistry; D029941:Fish Proteins / Q000378:metabolism*; D006197:Hair / Q000378:metabolism*; D006801:Humans; D006861:Hydrogen Peroxide / Q000737:chemistry / Q000378:metabolism*; D007501:Iron / Q000737:chemistry; D008543:Melanins / Q000378:metabolism*; D008544:Melanocytes / Q000502:physiology*; D020460:Melanosomes / Q000378:metabolism*; D010084:Oxidation-Reduction; D017382:Reactive Oxygen Species / Q000378:metabolism; D049833:Sepia; D012880:Skin Pigmentation
D000863:Antacids; C045076:Fenton's reagent; D029941:Fish Proteins; D008543:Melanins; D017382:Reactive Oxygen Species; D006861:Hydrogen Peroxide; D007501:Iron
Fenton chemistry; Hydrogen peroxide; Hydroxyl radical; Melanin bleaching; Reactive oxygen species; Superoxide