Chemical Speciation Of Complexes Of L-Histidine And L- Glutamic Acid With Toxic Metal Ions In Dimethylformamide-Water Mixture

Abstract

The protonation equilibria of complexes of Pb (II), Cd (II), and Hg (II) with L-Histidine and L-Glutamic were investigated pH metrically in Dimethylformamide-water mixtures (0-50%v/v) at 310 K and ionic strength of 0.16 moldm-3. The protonation constants have been calculated using the computer program MINIQUAD75. The protonation constants from the best fit models show the formation of LH32+, LH2+, LH and L- in the case of L-histidine and XH3+, XH2, XH- and X2- in the case of L-glutamic acid. The present investigation binary chemical speciation of Pb (II), Cd(II)and Hg(II) complexes of L-Histidine and L-Glutamic acid in 0.0-50 % v/v Dimethylformamide-water mixtures the dominant species detected L-Histidine with metal were ML2H4, ML2H3, ML2H2, ML2H and ML2 for Pb(II) and Cd(II) and Hg(II) forms ML2H4, ML2H3, ML2 and ML. for L-Glutamic acid MX2H4, MX2H3, MX2H2, MX and MX2 for Pb(II), Cd(II) and Hg(II) in DMF-water mixtures. Distributions of species, formation equilibria and effect of influential parameters on the stability constants have been presented. Possible structures of the various species present in solution are also indicated based on the analysis of the pH metric data. Speciation of mixed ligand complexes of Pb(II), Cd(II) and Hg(II) with L-Histidine and Lglutamic acid were studied in Dimethylformamide-Water mixture. Titrations were carried out in the presence of different relative concentrations (M: L: X=1.0:2.5:2.5, 1.0:2.5:5.0, 1.0:5.0:2.5 in the case of Pb (II) and Cd(II) and 1.0:5.0:5.0, 1.0:5.0:10.0, 1.0:10.0:5.0 in the case of Hg(II)) were carried out with 0.4 mol dm-3 NaOH as titrant in Dimethylformamide- water mixture. Stability constants of ternary complexes were refined with MINIQUAD75. The species detected were MLXH3, MLXH2, MLXH and ML2X for Pb(II), MLX2H2 and ML2X for Cd(II) and MLXH3 and MLXH2 for Hg(II). The species distribution diagrams drawn using HYSS HYPERQUAD with pH at different compositions of Dimethylformamide and plausible equilibria for the formation of species were presente