Influence of Copper(II) Ions on Radicals in DOPA–Melanin

Abstract

DOPA–melanin (DOPA = 3,4-dihydroxyphenyl-alanine) complexes with Cu(II) cations were studied by electron paramagnetic resonance (EPR) spectroscopy. After the addition of metal cations to the melanin polymer, the EPR spectra parameters were measured. The axial g-factor values are g || = 2.20 and $$ g_{ \bot } = 2.0 5 $$ . Since $$ g_{||} > g_{ \bot } > 2 $$ , the ground state orbital of the unpaired electron of the Cu(II) complex is $$ \left| {{{x}}^{ 2} } \right. \, - \, \left. {{{y}}^{ 2} } \right\rangle $$ . Square coordination of these cations in melanin is proposed. The influence of the Cu(II) concentration in solution used during synthesis on the concentration of melanin radicals was investigated. Cu(II) cations causes the decrease in the paramagnetic center concentration in melanin. The Cu(II) EPR spectra are not saturated within the microwave power range of 0.7–70 mW used in our experiment.