FREE-RADICALS IN MELANIN-CATIONIC PORPHYRINS 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)-porphy rin (TBzPyP), and their respectives complexes ZnTMPyP and ZnTBzPyP. By monitoring signal intensities and progressive microwave power saturat ion it was shown that the interaction increases the equilibrium concen tration 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 t ype 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 inc rease in the number of photoinduced free radicals in L-Dopa melanin du ring illumination with visible light.