Understanding the Oxidation Electrochemistry of Adsorbed Eugenol on a Glassy Carbon Electrode Modified with Electrochemically Partially Reduced Graphene Oxide: A Theoretical and Experimental Approach

Abstract

The electro-oxidation of eugenol (EUG) natural antioxidant was studied by cyclic voltammetryin phosphate buffer solutions (PBS) of different pH at electrochemically partiallyreduced graphene oxide (GCE/ePRGO). The voltammetric responses were mainly controlledby adsorption at this modified electrode. Current values were higher at pH 2.0 PBS,therefore, this pH was chosen to perform all experiments. DFT calculations of pKa’s andstandard potentials defined the possible pathways of eugenol and its oxidation products.These pathways were evaluated through the comparison of voltammetric simulations ofadsorbed species with experiments at pH 2.0, which also allowed for the estimation ofthe values of the kinetic parameters involved in electrochemistry. Our findings suggest amulti-step redox process in which Eugenol is first oxidized to the radical species and thento a cationic product. At this stage, the pathways branch into to methylenquinone and a4-allyl-1,2-diquinone molecules. 4-allyl-1,2-diquinone is finally reduced in single or doublereversible electrochemical step to the hydroquinone species. The present physicochemicalwork allows for a deeper understanding of the eugenol oxidation mechanism, which wasonly partially proposed in previous studies.