Evaluation of the Antioxidant Activity of New Coumarin Derivatives by Cyclic Voltammetry

Abstract

Free radicals, species with one or more unpaired electrons are produced in normal or pathological cell metabolism, from xenobiotics, or trough ionizing radiation. Electron acceptors such as molecular oxygen react easily with free radicals, to become radicals themselves. Oxygen free radicals or reactive oxygen species (ROS) such as superoxide anion radicals (O2 .-), hydrogen peroxide (H2O2), hydroxy radicals (.OH), and singlet oxygen (1O2) are continuously generated in cells exposed to an aerobic environment, and have been associated with the genesis of tumors as well as age-dependent diseases such atherosclerosis, arthritis, and neurodegenerative disorders. In this context, the chemopreventive role of antioxidants present in consumable fruits, vegetables, and beverages has received considerable attention and has been a growing interest in finding novel antioxidants in order to meet the requirements of pharmaceutical industries [1]. Several analytical methods have been used to evaluate the activity of antioxidant compounds, such as the cyclic voltammetry[2] and the 1,1-diphenyl-2-picrylhydrazyl radical (DPPH) assay[3]. In this work the antioxidant activity of two new synthetic coumarin derivatives, 3-bromo-6,7-dihydroxycoumarin and 6,7-dihydroxy-3-[(E)-2-phenylethenyl]coumarin, is evaluated by cyclic voltammetry. The anodic peak potentials were measured and compared to their antioxidant activities measured by the DPPH radical assay. The voltammetric experiments were carried out at pH 7.0 (phosphate buffer) in order to resemble the conditions of DPPH assays. Both voltammetric and DPPH assay data were compared with data obtained for 6,7-di-hydroxycoumarin and quercetin, with high antioxidant activity. The structure–activity relationships of the synthesized coumarins as potential antioxidants was investigated in order to understand how the different 3-substitutions affect the antioxidant activity of the 6,7-dihydroxycoumarin.