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

## TL;DR

This study explores how eugenol, a natural antioxidant, undergoes oxidation on a modified electrode, revealing a detailed multi-step electrochemical process.

## Contribution

The paper provides a novel theoretical and experimental analysis of eugenol oxidation pathways using DFT and voltammetry.

## Key findings

- Eugenol oxidation involves a radical intermediate followed by formation of cationic products.
- Two oxidation pathways branch into methylenquinone and 4-allyl-1,2-diquinone.
- 4-allyl-1,2-diquinone is reversibly reduced to hydroquinone species.

## Abstract

The electro-oxidation of eugenol (EUG) natural antioxidant was studied by cyclic voltammetry in phosphate buffer solutions (PBS) of different pH at electrochemically partially reduced graphene oxide (GCE/ePRGO). The voltammetric responses were mainly controlled by 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 and standard potentials defined the possible pathways of eugenol and its oxidation products. These pathways were evaluated through the comparison of voltammetric simulations of adsorbed species with experiments at pH 2.0, which also allowed for the estimation of the values of the kinetic parameters involved in electrochemistry. Our findings suggest a multi-step redox process in which Eugenol is first oxidized to the radical species and then to a cationic product. At this stage, the pathways branch into to methylenquinone and a 4-allyl-1,2-diquinone molecules. 4-allyl-1,2-diquinone is finally reduced in single or double reversible electrochemical step to the hydroquinone species. The present physicochemical work allows for a deeper understanding of the eugenol oxidation mechanism, which was only partially proposed in previous studies.