Comparative electrochemical studies of kinetic and thermodynamic parameters of Quinoxaline and Brimonidine redox process

Abstract

The electrochemical response of two biologically important benzopyrazine derivative, Quinoxaline and Brimonidine (5-bromo-N-(4,5-dihydro-1H-imidazol-2-yl) quinoxaline-6-amine) was studied at glassy carbon electrode. Investigations were performed in acetate buffer at pH 3.6 where both compounds undergo complex electrode process which begins with quasi reversible redox process at pyrazine ring forming di-hydro derivative, which is further irreversible oxidized to hydroxyl-derivative. Cyclic voltammetry at different scan rates was employed for the determination of heterogeneous electron transfer rate constant and diffusion coefficient of the compounds. The values of electron transfer rate constant at different temperatures were used for the evaluation of thermodynamic parameters like enthalpy, entropy and Gibbs free energy changes, as well as apparent energy of activation. Computational study has been performed in order to evaluate some useful quantum chemical parameters with the aim to confirm and explain the difference in experimentally obtained kinetic and thermodynamic parameters of the investigated QUI and BRIM redox process. Results were compared with studies of similar compounds and pointed out the observed similarities and differences.