Electrocatalytic Oxidation of L-Cysteine, L-Methionine, and Methionine-Glycine Using [Oxoiron(IV)-Salen] Ion Immobilized Glassy Carbon Electrode

The present work reports the selective oxidation of L-cysteine (L-Cys), L-methionine (L-Met), and methionine-glycine (Met-Gly) in phosphate buffer (PB) (pH = 7.2) using [oxoiron(IV)-salen] ion immobilized glassy carbon electrode (Fe-IV/Nf/GC electrode). The cyclic voltammogram (CV) of the modified GC electrode shows a clear oxidation peak at 1.18 (+/- 0.02) V, assigned to Fe-III/Fe-IV redox couple. The differential pulse voltammograms (DPV) show a well-defined oxidation peak at 1.32 (+/- 0.02) V for oxidation of L-Cys, 1.26 (+/- 0.02) V for L-Met and 1.51 (+/- 0.02) V for Met-Gly, respectively. Cyclic voltammetric (CV) response of oxidation peak current increases linearly with increase the concentration of L-Cys, L-Met, and Met-Gly in the concentration ranges about 0.4-20 mu M with the correlation coefficient value (R-2) of 0.99, and the detection limits are found to be 0.3 mu M (S/N = 3), 0.2 mu M (S/N = 3), and 0.3 mu M (S/N = 3), respectively. The present modified electrode exhibits good catalytic activity towards the oxidation of L-Cys, L-Met, and Met-Gly. The electrochemical oxidation of L-Cys, L-Met, and Met-Gly follows the electron transfer mechanism and provides L-cysteine (-S-S-, a disulfide), methionine sulfoxide (MetSO), and sulfone (MetSO(2)) as the major products. The present modified electrode is successfully applied to the medicinally important real samples and gets good recovery results.

Automated summary

This study reports the selective oxidation of L-cysteine, L-methionine, and methionine-glycine using the Fe-IV/Nf/GC electrode in phosphate buffer. The electrochemical detection shows a linear relationship between oxidation peak current and analyte concentration, and the oxidation mechanism follows the electron transfer principle.