Dual Electrocatalytic Behavior of Oxovanadium(IV) Salen Immobilized Carbon Materials Towards Cysteine Oxidation and Cystine Reduction: Graphene Versus Single Walled Carbon Nanotubes

Abstract

Oxovanadium(IV) salen (VO(salen)) (where salen=N,N’-bis(salicylidene)ethylenediamine) is embedded onto reduced graphene oxide (rGO) and single walled carbon nanotubes (SWCNTs). The resulting materials, VO(salen) embedded rGO (rGO-VO(salen)) and VO(salen) embedded SWCNTs (SWCNTs-VO(salen)) show remarkable electrocatalytic activity for cysteine oxidation and cystine (the oxidized product of cysteine) reduction as demonstrated by cyclic voltammetry (CV). The materials, rGO-VO(salen) and SWCNTs-VO(salen) are characterized through spectroscopic and microscopic techniques. Transmission electron microscopy exhibits nanocrystalline view of VO(salen) on rGO-VO(salen) while it appears like aggregated nodules in the SWCNTs-VO(salen) revealing the nano-structures excellently. Electrochemical cysteine oxidation is studied using rGO-VO(salen) coated glassy carbon (GC) electrode (GC/rGO-VO(salen)) and SWCNTs-VO(salen) coated GC electrode (GC/SWCNTs-VO(salen)). The efficiency of the catalytic platforms is compared. Overall number of electrons and electron transfer rate constant are obtained using rotating disc electrode for cysteine oxidation at GC/rGO-VO(salen) and GC/SWCNTs-VO(salen). Calibration curves for the determination of cysteine at GC/rGO-VO(salen) and GC/SWCNTs-VO(salen) exhibit linear range from 1.0 μM to 5.0 mM and 1.0 μM to 4.0 mM, respectively. GC/rGO-VO(salen) and GC/SWCNTs-VO(salen) are successfully applied for the real samples analysis with remarkable recovery. © 2016 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim