L-Cysteine oxidation studied by rotating ring disk electrodes: Verification of reaction intermediates

Abstract

l-Cysteine (l-Cys) is an amino acid of high interest in the electrochemical field since it is one of the five electrochemically active amino acids. Due to the S atom on its side chain, this molecule presents the highest amount of possible oxidation states. The rotating ring disk electrode (RRDE) technique is a very useful method for the investigation of complex mechanisms, such as l-Cys oxidation, as it allows the identification of some intermediates. By rotating disk electrode (RDE), it was possible to observe that the adsorption of l-Cys onto Pt electrodes is influenced by mass transport. The chemical reaction was found to be reversible, while the charge transfer irreversible. The RRDE study facilitated the proposal of an electrochemical-chemical-electrochemical mechanism. The ring current was observed to be dependent on the quadratic of the potential applied to the disk electrode combined with the value of the rotation rate in a soft-model algorithm. The product of this chemical step was oxidized in two steps on the ring, with the first one including the generation of an adsorbed intermediate as the rate-limiting step.