Free Zn2+ determination in systems with Zn-Glutathione

Abstract

Zn-Glutathione speciation was studied applying the electrochemical technique AGNES (Absence of Gradients and Nernstian Equilibrium Stripping) to determine the free zinc concentration. In titrations varying either pH, total concentration of gluthatione (cT,GSH) or total concentration of Zn (cT,Zn), free Zn concentrations determined with AGNES were compared with the values predicted from previously reported complexation constants. The speciation of Zn was studied in a real sample of root extracts of Hordeum vulgare where the cT,Zn had been determined by ICP-MS and cT,GSH by HPLC. The free [Zn2+] was measured with AGNES using a special device where a mixture of N2/CO2 saturated in milliQ water controls the pH and avoids the evaporation of the sample. The lower free zinc concentration determined with AGNES, in comparison with the predicted one assuming the literature complexation constants and taking into account only the presence of Zn and GSH, indicates that it is necessary to include more ligands apart from GSH (as other phytochelatins) in the speciation model.

The authors gratefully acknowledge support of this research by the Spanish Ministry Spanish Ministry of Education and Science (Projects CTQ2009-07831, CTM2012-39183, CTQ2012-32863 and CTM2013-48967) and by the "Comissionat d'Universitats i Recerca de la Generalitat de Catalunya” (2014SGR269 and 2014SGR1132). ML acknowledges a FPI grant from the Spanish Ministry.