Complex Formation of Thorium(IV) Ion with Glycyl−Glycine and Glycyl−Valine

The protonation equilibria of glycyl−glycine and glycyl−valine and their complex formation with thorium(IV) ions in aqueous solution were studied over a wide range of pH values (2 to 12) using a combination of potentiometric, cyclic voltametric, and spectrophotometric methods at constant temperature (25 °C) and constant ionic strength (0.1 mol·dm−3 sodium perchlorate). The redox properties of the species obtained by the cyclic voltametry technique have confirmed the spectrophotometric results. Least-squares regression calculations are consistent with the formation of the ThL3+, ThHL23+, and ThL22+ species for the studied systems, where L represents each peptide. Finally, the species concentrations were plotted at different pH values and discussed.