Oxygen Reduction on Iron−Melanin Granular Surfaces

We report the catalytic activity of iron−eumelanin granular deposits supported on graphite for the oxygen reduction in neutral and alkaline solutions. These deposits contain quinone groups and iron−melanin complexes as revealed by XPS, XANES, EXAFS, and IR spectroscopy. Voltammetric data show that the iron−eumelanin system exhibits higher electrocatalytic activity than quinone/hydroquinone films (Q/QH) on the same substrate. In contrast to Q/QH deposits, the iron-containing eumelanin system is able to reduce oxygen with transfer of four electrons, thus allowing the formation of reactive hydroxyl species. Our results can explain the physical chemistry basis of the oxygen-radical induced lipid peroxidation and consequent neurodegeneration of the melanin-containing dopaminergic neurons observed by several authors.