Ana Ion

Cathodic Stripping Voltammetry of Sulphur-Containing Amino Acids and Peptides in the Presence of Nickel Ion. Catalytic and Inhibiting Effects

Abstract The paper reviews recent studies on the effect of addition of Ni(II) in the cathodic stripping voltammetry of the following compounds: cysteine, penicillamine, cystine, glutathione (either reduced or oxidised) and N-acetylcysteine. With the exception of N-acetylcysteine, the above compounds give a cathodic stripping peak at -0.6 V (vs. Ag/AgCl, 3 M KCl electrode) which is due to the catalytic reduction of nickel ion. Even in the case of the disulphides the actual catalyst is the thiol produced by the cleavage of the -S-S- bond during the accumulation step. The catalytic peak enables the detection of the analyte with a better selectivity than is obtained with the stripping peak due to the reduction of mercury thiolates. In addition, Ni(II) suppresses the mercury thiolate peak of ligands such as cysteine or penicillamine, but does not modify the behaviour of thiols with low complexing properties (such as N-acetylcysteine). Consequently, compounds such as cysteine and its N-acyl derivatives can be d...

Electrochemistry of a carotenoid self-assembled monolayer

A carotenoid self-assembled monolayer was prepared by dipping a gold electrode into a solution of 4′-thioxo-β,β-caroten-4-one in acetonitrile. Electrochemistry of the surface layer was investigated by cyclic voltammetry in an aqueous solution. No electrochemical reaction was detected in the potential region between 0.5 and −0.6 V vs. SCE. The anodic reaction of adsorbed carotenoid occurs at 0.8 V, whereas the irreversible anodic desorption proceeds at 1.4 V in 0.01 M HClO4. Formation of the surface layer resulted in a decrease of the charging current as well as in a strong inhibition of the electron transfer reaction for species such as Fe(CN)63−, Ru(NH3)63+, and dissolved oxygen. Prolonged voltage cycling in the O2 reduction range induced some changes in the surface layer characteristics that were tentatively accounted for by the cross-linking of adsorbed molecules under the effect of transient oxygen radicals.