title: Interaction of melanin with carbon- and oxygen-centered radicals from methanol and ethanol.
abstract: The interaction of dopa-melanin (DM) and cysteinyldopa-melanin (CDM) with carbon- and oxygen-centered radicals generated by benzophenone-photosensitized hydrogen abstraction from ethanol, or by pulse radiolysis of aqueous solutions of methanol and ethanol, is reported. Photosensitized formation of carbon-centered radicals and their interaction with melanin was monitored by electron paramagnetic resonance (EPR) spin trapping using DMPO, and via the melanin free radical signal itself. In the pulse radiolysis experiments, the interaction of DM or CDM with hydroxymethyl, hydroxyethyl, and the corresponding methanol peroxyl radical was monitored by recording time-dependent changes of the melanin absorbance at selected wavelengths. The data indicate that both melanins are good scavengers of carbon-centered radicals, with corresponding rate constants in the range of 10(7) to 10(8) M-1 s-1. Significantly, compared to DM, CDM is also an exceptionally efficient scavenger of oxygen-centered radicals derived from methanol with corresponding rate constants of 2.7 x 10(4) and 2 x 10(6) M-1 s-1 for DM and CDM, respectively. The results are discussed with reference to the potential role of melanin in protecting the integrity of melanosomes by inhibiting peroxidation of lipid components of the organelle membrane.
authors.affiliation: Department of Chemistry, Keele University, Staffordshire, UK.
authors.forename: R
authors.initials: R
authors.lastname: Dunford
authors.forename: E J
authors.initials: EJ
authors.lastname: Land
authors.forename: M
authors.initials: M
authors.lastname: Rozanowska
authors.forename: T
authors.initials: T
authors.lastname: Sarna
authors.forename: T G
authors.initials: TG
authors.lastname: Truscott
mesh_terms: D001577:Benzophenones / Q000494:pharmacology; D002244:Carbon / Q000737:chemistry*; D003497:Cyclic N-Oxides; D004295:Dihydroxyphenylalanine / Q000737:chemistry; D004298:Dopamine / Q000031:analogs & derivatives / Q000737:chemistry; D004578:Electron Spin Resonance Spectroscopy; D000431:Ethanol / Q000737:chemistry*; D005609:Free Radicals; D008543:Melanins / Q000737:chemistry*; D000432:Methanol / Q000737:chemistry*; D010100:Oxygen / Q000737:chemistry*; D017319:Photosensitizing Agents / Q000494:pharmacology; D011675:Pulse Radiolysis; D013113:Spin Labels; D014466:Ultraviolet Rays
chemical_list: D001577:Benzophenones; D003497:Cyclic N-Oxides; D005609:Free Radicals; D008543:Melanins; D017319:Photosensitizing Agents; D013113:Spin Labels; D000431:Ethanol; D004295:Dihydroxyphenylalanine; C047723:benzophenone; C017245:5,5-dimethyl-1-pyrroline-1-oxide; D002244:Carbon; C047408:5-S-cysteinyldopamine; D010100:Oxygen; D004298:Dopamine; D000432:Methanol