Free radicals in melanin-cationic porphyrin complexes in the dark and under light irradiation.
Electron Paramagnetic Resonance (EPR) spectroscopy was employed in the study of the interaction between L-3,4-dihydroxyphenylalanine (L-Dopa) melanin and the cationic porphyrins meso-tetrakis(1-methylpyridinium-4yl)-porphyrin (TMPyP), meso-tetrakis-(1-benzylpyridinium-4-yl)-porphyrin (TBzPyP), and their respectives complexes ZnTMPyP and ZnTBzPyP. By monitoring signal intensities and progressive microwave power saturation it was shown that the interaction increases the equilibrium concentration of free radicals in L-Dopa melanin in the dark. The extent of increase is dependent on the presence of molecular oxygen and on the type of porphyrin. Not all interacting sites available for complexation in L-Dopa melanin are involved in the formation of free radicals. It was also observed that the interaction with porphyrins promotes an increase in the number of photoinduced free radicals in L-Dopa melanin during illumination with visible light.
Ridente
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Instituto de Física da Universidade de São Paulo, Brazil.
Azzellini
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GC
Ito
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D004295:Dihydroxyphenylalanine / Q000031:analogs & derivatives* / Q000737:chemistry / Q000528:radiation effects; D004578:Electron Spin Resonance Spectroscopy; D005609:Free Radicals; D008652:Mesoporphyrins / Q000737:chemistry / Q000528:radiation effects*; D008872:Microwaves; D015394:Molecular Structure; D010084:Oxidation-Reduction; D010100:Oxygen / Q000737:chemistry; D010777:Photochemistry; D011166:Porphyrins / Q000737:chemistry* / Q000528:radiation effects; D015032:Zinc
D005609:Free Radicals; D008652:Mesoporphyrins; D011166:Porphyrins; C083991:meso-tetrakis(1-benzylpyridinium-4-yl)porphyrin; C021096:tetra(4-N-methylpyridyl)porphine; D004295:Dihydroxyphenylalanine; C040616:DOPA melanin; D015032:Zinc; D010100:Oxygen