Effect of Ethylene Glycol on Chemical Speciation of Ternary Complexes of Phenylalanine and Maleic Acid with Ca(II), Mg(II) and Zn(II) Metal Ions

The stability constants of ternary complexes of Ca (II), Mg (II) and Zn (II) ions with Phenylalanine and Maleic acid were determined pH metrically in the presence of 0.060.0 % v/v ethylene glycol-water mixtures maintaining an ionic strength of 0.16 mol L-1 at 303.0 K. Alkali metric titrations were carried out in different relative concentrations [MLX=1.02.52.5, 1.02.55.0, 1.05.02.5 for Ca (II), Mg (II) and Zn (II) of metal (M) to Phenylalanine (L) to Maleic acid (X). Stability constants of ternary complexes were calculated and various models were refined with MINIQUAD75. The best fit chemical models were selected based on statistical parameters and residual analysis. The species detected are MLXH and ML2XH for Ca (II), Mg (II) and Zn (II). The relative stabilities of the mixed ligand complexes were compared with those of the binary complexes. The enhanced stability associated with the ternary complex is attributed to chelate effect, stacking interactions and hydrogen bonding.