Experimental and theoretical studies of electrochemical characteristics of 3,4-dihydroxyphenylacetic acid (DOPAC)

The electrochemical behavior of 3,4-dihydroxyphenylacetic acid (DOPAC) in aqueous solutions with different pHs and DOPAC concentrations was studied by cyclic voltammetry at various potential scan rates. The electro-oxidation of DOPAC involves a transfer of two electrons and two protons in solutions of pH < 8.0 and a transfer of two electrons and one proton in Solutions of pH > 8.0, in agreement with the one-step two-electron mechanism. The cyclic voltammetry indicated that the process of electro-oxidation of DOPAC follows an E(r)C(i) mechanism. The standard redox potential, E(0)', two-proton-two-electron and one-proton-two-electron processes of DOPAC were determined as 0.585 and 0.357 V versus saturated calomel electrode (SCE), respectively. The acidic dissociation constant of DOPAC was also obtained. Also, the diffusion coefficient of DOPAC was calculated as 9.2 x 10(-6) cm(2) s(-1) for the experimental conditions, using chronoamperometric results. The standard reduction potentials and the second acidic constant of DOPAC have been also calculated using standard ab initio calculations at the G3 level of theory in conjunction with a continuum solvation model. The theoretical values are in good agreement with experiment (C) 2009 Elsevier Ltd. All rights reserved.