Binding of Hg2+ by Cys, Cys-Gly and reduced glutathione: Study by differential pulse voltammetry on rotating Au-disk electrode, electrospray ionization mass-spectrometry and isothermal titration calorimetry

The study of Hg2+ binding with short-chain thiols as cysteine (Cys), dipeptide Cys-Gly and reduced glutathione (GSH) was performed by a recently proposed voltammetric method, using the rotating Au-disk electrode. For every thiol a similar complexation pattern was obtained. The highly stable Hg(thiol)2 complexes are formed with an excess (at least twofold) of the ligand, while at lower ligand-to-Hg ratios the Hg(thiol) species formation is observed. These results were deduced on basis of Multivariate Curve Resolution with Alternating Least Squares (MCR-ALS) data analysis. The electrochemical results were completed with electrospray ionization mass-spectrometry (ESI–MS) experiments that provided the stoichiometries of the complexes. For Cys and Cys-Gly several complexes were detected, depending on the Hg2+–ligand ratio, while for GSH only Hg(GSH) and Hg(GSH)2 species were observed. Isothermal titration calorimetry (ITC) was used to analyze some thermodynamic characteristic of the interactions between Hg2+ and GSH. This information is valuable because it confirms electroanalytical findings and gives deeper insight into the course of the interactions.