EPR Studies of DOPA–Melanin Complexes with Netilmicin and Cu(II) at Temperatures in the Range of 105–300 K

Magdalena Zdybel,Ewa Buszman,Dorota Wrześniok,Barbara Pilawa,Zdzisław Kruczyński,Ryszard Krzyminiewski

doi:10.1007/s00723-012-0340-y

Abstract

The application of electron paramagnetic resonance (EPR) spectroscopy in pharmacy of melanin complexes with netilmicin and Cu(II) was presented. The continuous microwave saturation of EPR spectra of DOPA–melanin and the complexes was performed. EPR spectra were measured on an X-band (9.3 GHz) spectrometer at temperatures in the range of 105–300 K. Paramagnetic copper ions decrease the intensity of the EPR lines of melanin’s free radicals. It was found that fast spin–lattice relaxation characterizes DOPA–melanin–Cu(II) complexes. Slow spin–lattice relaxation processes exist in melanin’s paramagnetic centers of DOPA–melanin and DOPA–melanin–netilmicin, [DOPA–melanin–netilmicin]–Cu(II), [DOPA–melanin–Cu(II)]–netilmicin complexes. Spin–lattice relaxation processes are faster at higher temperatures. The homogeneous broadening of EPR lines for melanin complexes was observed. The practical consequences of differences between paramagnetic properties of melanin complexes with netilmicin and the complexes with Cu(II) were discussed.

Highlights

Melanins are paramagnetic biopolymers with the high content of o-semiquinone free radicals [1,2,3,4,5], which play an important role during the formation of the polymer complexes with drugs [6, 7]
electron paramagnetic resonance (EPR) spectra of the studied samples change with increasing microwave power
Netilmicin]–Cu(II) and [DOPA–melanin–Cu(II)]–netilmicin complexes are shown in Fig. 4, respectively

Summary

Introduction

Melanins are paramagnetic biopolymers with the high content of o-semiquinone free radicals [1,2,3,4,5], which play an important role during the formation of the polymer complexes with drugs [6, 7]. It was shown that the free radical concentrations in melanin change after binding the drugs [6, 7, 11, 12]. The drug complexation by melanins causes their prolongated interactions in human organism during therapeutical application [13, 14]. These interactions depend on paramagnetic properties of the melanin polymer and they are modified by metal ions [11, 12]. Long-term medical treatment can lead to toxic concentrations of therapeutic substances in melanin and increased amounts of free radicals, which can lead to the tissue degeneration [13, 14]

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Conclusion