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Effect of Cd(II) on free radicals in DOPA-melanin tested by EPR spectroscopy

Magdalena Zdybel 1Barbara Pilawa 1Ewa Chodurek 2

1. Department of Biophysics, Medical University of Silesia, Jedności 8, Sosnowiec 41-200, Poland
2. Department of Biopharmacy, Medical University of Silesia, Jedności 8, Sosnowiec 41-200, Poland


Melanins are the large organic compounds, which belong to natural pigments [1]. Melanin biopolymers bind major chemical compounds, especially metal ions, polycyclic aromatic hydrocarbons and drugs [1]. The binding of drugs by melanin biopolymers depends on the presence of free radicals and metal ions in their structure [1-3].
In this work effect of Cd(II) on free radicals in the model eumelanin as DOPA-melanin was examined. Electron paramagnetic resonance (EPR) spectroscopy was used as the experimental method. EPR spectra of DOPA-melanin, and DOPA-melanin-Cd(II) complexes were measured by an X-band (9.3 GHz) EPR spectrometer of Radiopan Firm (Poznań, Poland) and the Rapid Scan Unit of Jagmar Firm (Kraków, Poland). Synthetic DOPA-melanin was formed by the autooxidative polymerization of 3,4-dihydroxyphenylalanine (DOPA). The metal ions/DOPA molar ratios in the reaction mixtures were 2:1, 1:1 or 1:2. Free radical concentration in DOPA-melanin was high. Formation of melanin complexes with Cd(II) increased free radical concentration in DOPA-melanin. For the samples DOPA-melanin-Cd(II) (2:1) and DOPA-melanin-Cd(II) (1:1) free radical concentration increased with the increasing of Cd(II) in melanin. Free radical concentration in DOPA-melanin-Cd(II) (1:2) complexes were lower than for DOPA-melanin-Cd(II) (1:1) complexes. This effect was the result of free radical recombination during formation of these samples. g-Values characteristic for o-semiquinone free radicals were obtained. Broad EPR lines were measured. Linewidths increased after Cd(II) binding to DOPA-melanin. Changes of amplitudes and linewidths with microwave power shown the homogeneous broadening of EPR lines of DOPA-melanin complexes with Cd(II), independently on the metal ion concentration. Slow spin-lattice relaxation processes existed in all the tested samples, their EPR lines saturated at low microwave powers. Cd(II) caused fastening of spin-lattice relaxation processes in DOPA-melanin. The results are very important for evaluation of drugs binding to eumelanin in the presence of Cd(II).


1. Tran M.L., Powell B.J., Meredith P. (2006). Chemical and structural disorder in eumelanins: a possible explanation for broadband absorbance. Biophysical Journal, Vol. 90, pp. 743-752.
2. Buszman E., Pilawa B., Zdybel M., Wrześniok D., Grzegorczyk A., Wilczok T. (2005). EPR examination of Zn2+ and Cu2+ effect on free radicals in DOPA-melanin-netilmicin complexes. Chemical Physics Letters, Vol. 403, pp. 22-28.
3. Matuszczyk M., Buszman E., Pilawa B., Witoszyńska T., Wilczok T. (2004). Cd2+ effect on free radicals in Cladosporium cladosporioides-melanin tested by EPR spectroscopy. Chemical Physics Letters, Vol. 394, pp. 366-371.


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Presentation: Poster at IX Multidyscyplinarna Konferencja Nauki o Leku, by Magdalena Zdybel
See On-line Journal of IX Multidyscyplinarna Konferencja Nauki o Leku

Submitted: 2014-03-14 11:14
Revised:   2014-05-02 19:47