Speciation of Ternary Complexes of Some Essential Metal Ions with L-Glutamic Acid and L-Methionine in 1, 2-Propanediol – Water Mixtures

Chemical speciation of ternary complexes of Co(II), Ni(II), Cu(II), and Zn(II) ions with L-glutamic acid and L-methionine have been studied pH metrically in the concentration range of 0–60% volume/volume 1,2-propanediol-water mixtures maintaining an ionic strength of 0.16 mol dm–3 at 303 K. Alkalimetric titrations were carried out in different relative concentrations (M: L: X = 1:2:2, 1:2:4, 1:4:2) of metal (M) to L-glutamic acid (L) to L-methionine (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 MLX and MLX2 for Co(II); MLX, ML2X and MLXH for Ni(II); MLX, MLXH and MLXH2 for Cu(II); MLX and MLXH for Zn(II). The chemical speciation, metal bioavailability and transportation are explained based on the stability constants.