Thermodynamic and spectroscopic study of Al(3+) interaction with glycine, l-cysteine and tranexamic acid in aqueous solution.

In this paper a thermodynamic and spectroscopic study on the interaction between Al(3+) and glycine (Gly), l-cysteine (Cys), tranexamic acid (Tranex) is reported. Speciation models have been obtained by processing potentiometric titration data to determine stability constants of the species formed in aqueous solution at T=298.15K, 0.15≤I/molL(-1)≤1 in NaCl. Thermodynamic formation parameters have been obtained from calorimetric titration data, at T=298.15K, I=0.15molL(-1) using NaCl as ionic medium. Al(3+)-Cys system was also investigated by spectrophotometric and (1)H NMR measurements. (1)H NMR experiments were performed on Al(3+)-Tranex system as well. Different speciation models have been observed for the three systems. The results showed the formation of MLH, ML and M2L2(OH)2 species for Gly, ML, M2L and MLOH for Cys, MLH and MLOH for Tranex. The formed species are quite stable, i.e. for ML, logβ=7.18, 11.91 for Gly and Cys, respectively, at I=0.15molL(-1) and T=298.15K. For all the systems the dependence of formation constants on ionic strength over the range 0.1-1molL(-1) is reported. The sequestering ability of the ligands under study was also evaluated by pL0.5 empiric parameter. For Gly, Cys and Tranex, pL0.5=2.51, 3.74, 3.91 respectively, at pH=5, I=0.15molL(-1) and T=298.15K.