Chelation of iron ions with synthetic melanin and melanins isolated from peel of Vicia-faba beans, black grapes and buckwheat seeds was studied by gamma-resonance spectroscopy (GRS) It is established that melanins effectively gelate iron ions in both its two and trivalent states. The main part of the coordinated ions Fe3+ ions forms part of the polynuclear (n³2) clusters and gives paramagnetic dublet GR-spectra due to the fast relaxation of the spin-spin interaction. The presence of magnetic relaxation spectra indicates that part of the coordination centers in melanin is isolated. The values of the parameters of the GR-spectra of the samples studied are characteristic of high-spin complex Fe2+ and Fe3+ ions with octahedral ligand environment. It is assumed that the ability of vegetable melanins to effectively bind prooxidant Fe2+ ions is one of the possible mechanisms of their oxidative and protective properties.
melanin, gamma-resonance spectroscopy, chelation, iron ions
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