EPR examination of Zn2+ and Cu2+ effect on free radicals in DOPA–melanin–netilmicin complexes

DOPA–melanin and its complexes with netilmicin and metal ions (Zn2+,Cu2+) were examined by EPR spectroscopy. Broad EPR lines of o-semiquinone free radicals and paramagnetic Cu2+ were measured. Netilmicin slightly increased free radicals concentration in DOPA–melanin. Diamagnetic Zn2+ and paramagnetic Cu2+ ions increased and decreased, respectively, free radical concentrations in melanin–netilmicin complexes. Higher free radical concentrations were determined for (melanin–Zn2+)–netilmicin complexes than for (melanin–netilmicin)–Zn2+. Free radical concentrations were lower in (melanin–Cu2+)–netilmicin complexes than in (melanin–netilmicin)–Cu2+. Slow and fast spin–lattice relaxation processes were found for free radicals and Cu2+ systems in the samples. Netilmicin and Cu2+ increased spin–lattice relaxation time in melanin.