Theoretical foundations of EPR spectroscopy and UV-Vis spectrophotometry – useful methods of plant antioxidant extracts from novel ecosystems

Abstract

This article reviews the application of the methods of electron paramagnetic resonance (EPR) spectroscopy and ultraviolet–visible (UV-Vis) spectrophotometry in the examination of plant antioxidants. It proposes their use in obtaining antioxidant raw materials from plants particularly those living in harsh environments exposed to extreme external factors. It presents the principles of the operation of the EPR spectrometer and UV-Vis spectrophotometer, as well as the role of spectroscopic parameters in analysing free radicals and antioxidants for medical purposes. In this article, an X-band (9.3 GHz) EPR spectroscopy is described as well as the role of DPPH (2,2-diphenyl-1-picrylhydrazyl) free radicals in the analysis of plant antioxidant properties. Antioxidants quench the EPR and UV-Vis spectra of DPPH. EPR and UV-Vis spectra decrease with increasing time of interaction of DPPH free radicals with the antioxidant plant extracts until the minimum is reached. After that the magnitude of the spectra remains constant. Extracts with stronger antioxidant properties characterise the lower minimum values of the EPR spectra amplitude and UV-Vis absorbance. The described spectroscopic methods are helpful in finding plant extracts with strong antioxidant properties for medical purposes. This work includes examples of quenching of the EPR and UV-Vis spectra of DPPH free radicals caused by their interactions with plant extracts, including examples of extracts obtained from the single raw plant materials and their combinations. We demonstrate the influence of habitat conditions on the antioxidant properties of the plant extracts. The importance of developing research into plant products obtained from disturbed environments was emphasised.