Thermodynamic studies on the interaction between some amino acids with some rare earth metal ions in aqueous solutions

The interactions between the amino acids (glycine and l-threonine) with some rare earth metal ions (Pr3+, Nd3+, Eu3+, Gd3+, Dy3+, Ho3+ and Yb3+) were studied at a wide range from ionic strengths (0.07–0.32 M KNO3) and temperatures (25–45 °C) in aqueous solutions by using Bjerrum potentiometric method. The stoichiometric and thermodynamic stability constants were calculated as well as the standard thermodynamic parameters (ΔG°, ΔH° and ΔS°) for all possible reactions that occur. The degree of formation (n̄) for all studied systems was determined and discussed. The thermodynamic parameters differences (ΔΔG°, ΔΔH° and ΔΔS°) were calculated and discussed to determine the factors which control these complexation processes from the thermodynamic point of view.