Application of EPR spectroscopy in qualitative and quantitative examinations of paramagnetic centers in melanin

Abstract

Electron paramagnetic resonance (EPR) spectroscopy is a method useful in biology and medicine to examine paramagnetic substances, their role in disease processes and therapy. The aim of this review work is to present the physical foundations of EPR spectroscopy and to review the applications of the EPR method for the qualitative and quantitative research on paramagnetic centers in melanin. The possibilities of EPR spectroscopy and experimental procedures applied to determine the types of paramagnetic centers existing in synthetic melanin and in melanin biopolymers are discussed. A useful spectroscopic parameter to determine the type of paramagnetic centers is the spectroscopic cleavage coefficient g, which depends on the location of the unpaired electron in the molecule. o-Semiquinone free radicals with spin S = 1/2 and biradicals with spin S = 1, exist in melanin. Free radicals and biradicals can be distinguished spectroscopically by analysing the influence of temperature on the integral intensity of EPR lines. The concentration of paramagnetic centers in melanin is proportional to the intensity of the integral EPR spectrum. The influence of paramagnetic and diamagnetic metal ions, and oxygen on the concentration of paramagnetic centers in melanin is presented. The publications on the influence of medicinal substances on the concentration of paramagnetic centers in tumor cells were reviewed. The usefulness of EPR spectroscopy in identifying melanin in biological samples, among others, cancer cells, bacteria, and fungi, is presented.

Keywords

• melanin
• tumor cells
• paramagnetic centers
• free radicals
• biradicals
• epr spectroscopy