Speciation of Ternary Complexes of Some Essential Metal Ions with L-Glutamic Acid and L-Methionine in 1, 2-Propanediol – Water Mixtures
Muddapu Padma Latha, Vegi Maheswara Rao, Tirukkovalluri Siva Rao and Gollapalli Nageswara Rao*
School of Chemistry, Andhra University, Visakhapatnam-530 003, India
* Corresponding author: E-mail: gollapallinr@yahoo.com
Abstract
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.
Keywords: Chemical speciation; ternary complexes; L-glutamic acid; L-methionine; 1,2-propanediol