G. Nageswara Rao

Protonation Equilibria of L-Aspartic, Citric and Succinic Acids in Anionic Micellar Media

The impact of sodium lauryl sulphate (SLS) on the protonation equilibria of L-aspartic acid, citric acid and succinic acid has been studied in various concentrations (0.5-2.5% w/v) of SLS solution maintaining an ionic strength of 0.16 mol dm-3 at 303 K. The protonation constants have been calculated with the computer program MINIQUAD75 and the best fit models have been calculated based on statistical parameters. The trend of log values of step-wise protonation constants with mole fraction of the medium has been explained based on electrostatic and non-electrostatic forces operating on the protonation equilibria. The effects of errors on the protonation constants have also been presented.

Speciation Studies of L-Histidine Complexes of Pb(II), Cd(II), and Hg(II) in DMSO-Water Mixtures

Equilibrium study on complex formation of L-histidine with Pb(II), Cd(II), and Hg(II) has been investigated pH metrically in DMSO-water mixtures (0–60% v/v) at 303 K and 0.16 mol L−1 ionic strength. The predominant species detected for Pb(II) and Cd(II) are ML2H4, ML2H3, ML2H2, ML2H, and ML2 and those for Hg(II) are ML2H4, ML2H3, ML2, and ML. The appropriateness of experimental conditions is verified by introducing errors intentionally in the concentrations of ingredients. The models containing different numbers of species were refined by using the computer program MINIQUAD75. The best-fit chemical models were arrived at based on statistical parameters. The trend in variation of stability constants of the complexes with dielectric constant of the medium is attributed to the electrostatic and nonelectrostatic forces. The species distribution and the plausible equilibria for the formation of the species are also presented.

Chemical speciation of binary complexes of Pb(II), Cd(II) and Hg(II) with L-glutamic acid in dioxan-water mixtures

Abstract Binary complexes of L-glutamic acid with toxic metal ions such as Pb(II), Cd(II) and Hg(II) in 0.0-60.0% v/v 1,4 dioxan-water media at 303.0 K and an ionic strength of 0.16 mol dm-3 of sodium nitrate has been studied pH-metrically. The active forms of ligand are LH3, LH2 and LH. The best fit chemical models are chosen based on statistical parameters like crystallographic R-factor, χ2, skewness and kurtosis. The predominant species detected are ML2H4 ML2H3 ML2H2 ML2 and ML. Models containing different numbers of species were refined by using the computer program MINIQUAD75. The trend in variation of complex stability constants with changes in the dielectric constant of the medium is explained on the basis of electrostatic and non-electrostatic forces. The species distribution with pH at different compositions of dioxan–water mixture and plausible equilibria for the formation of species are also presented.

Mixed ligand complexes of toxic metal ions with L-glutamic acid and L-methionine in urea-water mixtures

Abstract Speciation of mixed ligand complexes of Pb(II), Cd(II) and Hg(II) with L-glutamic acid and L-methionine was studied in varying amounts (0.0-36.83%>w/v) of urea in aqueous solutions maintaining an ionic strength of 0.16 mol dm -3 (NaNO3) at 303 K. Titrations were carried out in the presence of 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) with sodium hydroxide. Stability constants of ternary complexes were refined with MINIQUAD75. The best-fit chemical models were selected based on statistical parameters and residual analysis. The species detected were MLXH for Pb(II), MLX and ML2X for Cd(II), and MLX and MLXH2 for Hg(II). Extra stability of ternary complexes compared to their binary complexes was believed to be due to electrostatic interactions of the side chains of ligands, charge neutralization, chelate effect, stacking interactions and hydrogen bonding. The species distribution with pH at different compositions of urea and plausible equilibria for the formation of species were also presented. The bioavailability of the toxic metal ions is explained based on the speciation.AbstractSpeciation of mixed ligand complexes of Pb(II), Cd(II) and Hg(II) with L-glutamic acid and L-methionine was studied in varying amounts (0.0-36.83%>w/v) of urea in aqueous solutions maintaining an ionic strength of 0.16 mol dm -3 (NaNO3) at 303 K. Titrations were carried out in the presence of 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) with sodium hydroxide. Stability constants of ternary complexes were refined with MINIQUAD75. The best-fit chemical models were selected based on statistical parameters and residual analysis. The species detected were MLXH for Pb(II), MLX and ML2X for Cd(II), and MLX and MLXH2 for Hg(II). Extra stability of ternary complexes compared to their binary complexes was believed to be due to electrostatic interactions of the side chains of ligands, charge neutralization, chelate effect, stacking interactions and hydrogen bonding. The species distribution with pH at different compositi...

Protonation equilibria of glycine, 1,10-phenanthroline and 2,2-bipyridyl in ethylene glycol–water mixtures

Abstract The solute–solvent interactions of glycine, 1,10-phenanthroline and 2,2-bipyridyl have been studied in 0–60% v/v ethylene glycol–water media by a pH metric method. The protonation constants were estimated with the computer program MINIQUAD75. Selection of the best fit chemical model of the protonation equilibria is based on the standard deviation in protonation constants and residual analysis using a sum of squares of residuals in all mass-balance equations. The observed linear variation of protonation constants with the inverse of dielectric constant of the solvent mixture can be attributed to the dominance of the electrostatic forces. The distribution of species, protonation equilibria and effects of influential parameters on the protonation constants are also presented.

Chemical speciation of oxalato complexes of indium(III)

Abstract Chemical speciation of binary complexes of indium(III) with oxalic acid has been investigated pH metrically at 303 K and at an ionic strength of 0.2 mol dm−3. The approximate formation constants have been calculated with the computer program SCPHD utilizing the experimental data obtained by monitoring H+ ion concentration. The formation constants thus obtained are refined with the computer program, MINIQUAD75 using primary alkalimetric data. The selection of the best-fit chemical model is based on the statistical parameters and residual analysis. The major complexes formed are In(C2O4)2−, In(C2O4)33−, [In(C2O4)2OH]2− and [In(C2O4)2 (OH)2]3−. The distribution patterns of the different species with the pH values showed that In(C2O4)2− is the predominant species.

Binary complexes of Mg(II) and Ca(II) in water–surfactant mixtures

Abstract Chemical speciation of Mg(II) and Ca(II) complexes of L-histidine in the presence of water–surfactant mixtures in the concentration range 0.0–2.5% w/v CTAB and SDS, 0.0–5.0% v/v TX-100 maintaining an ionic strength of 0.16 mol dm−3 at 303 K has been studied pH metrically. The active forms of the ligand are LH32+, LH2+, LH and L−. The models containing different numbers of species were refined by using the computer program, MINIQUAD75. The predominant species detected were ML2H44+, ML2H33+, ML2H22+, and ML2. The best fit chemical models were arrived at based on statistical parameters. The trend in variation of complex stability constants with change in the composition of the medium is explained on the basis of electrostatic and non-electrostatic forces. The effect of errors in the stability constants was also studied. Chemical speciation was also discussed based on the distribution diagrams.

Speciation of binary complexes of Co(II), Ni(II), Cu(II) and Zn(II) with L-aspartic acid in anionic, cationic and neutral micellar medium

Abstract Chemical speciation of binary complexes of Co(II), Ni(II), Cu(II) and Zn(II) with L-aspartic acid was investigated pH-metrically in (0.5–2.5%) anionic, cationic and neutral micellar media. The stability constants were calculated using the computer program MINIQUAD75. The best-fit chemical models were selected based on statistical parameters and residual analysis. The models for the binary species contained MLH, ML2 and ML2H for Co(II), ML, MLH, ML2 for Ni(II) and Cu(II), ML2,ML2H and ML2H2 for Zn(II) in anionic, cationic and nonionic micellar media The trend in variation of stability constants with change in the mole fraction of the medium was explained on the basis of electrostatic and non-electrostatic forces. Distributions of the species with pH at different composition of micellar media were also presented.

Speciation of complexes of Co (II), Ni (II) and Cu (II) with L-histidine in dioxan-water mixtures

Abstract L-Histidine complexes of Co (II), Ni (II) and Cu (II) metal ions were studied pH-metrically in 0–60% v/v dioxan–water mixtures at a temperature of 303K and at an ionic strength of 0.16mol L−1. Exhaustive modeling was performed to identify the species present in the present systems. The models contain MLH, ML2H4, ML2H2, ML2H and ML2 for Co (II), ML2H4, ML2H2, ML2H and ML2 for Ni (II), and MLH, ML2H2, ML2H and ML2 for Cu (II). The appropriate experimental conditions were verified by introducing errors intentionally in the concentrations of ingredients. The trend in the variation of stability constants with the dielectric constants of dioxan is explained on the basis of electrostatic and non-electrostatic forces. The bioavailability of metals and their transportation are explained based on the distribution diagrams.

Influence of co-solvent on chemical speciation of ternary complexes of bi- and tri- dentate ligands with essential metalions

AbstractChemical speciation of ternary complexes of Co(II), Ni(II), Cu(II) and Zn(II) ions with L-aspartic acid and ethylenediamine was studied pH-metrically in the concentration range of 0.0-60.0% v/v acetonitrile- and ethylene glycol-water mixtures maintaining an ionic strength of 0.16 mol L-1 at 303.0 K. Alkalimetric titrations were carried out in different relative concentrations (M:L:X = 1:2.5:2.5, 1:2.5:5.0, 1:5.0:2.5) of metal (M) to aspartic acid (L) to ethylenediamine (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 were MLX, ML2X, MLX2, MLX2H and MLX2H2 for Co(II), Ni(II), Cu(II) and Zn(II) in both media. The chemical speciation, metal bioavailability and transportation were explained based on the stability constants.Abstract Chemical speciation of ternary complexes of Co(II), Ni(II), Cu(II) and Zn(II) ions with L-aspartic acid and ethylenediamine was studied pH-metrically in the concentration range of 0.0-60.0% v/v acetonitrile- and ethylene glycol-water mixtures maintaining an ionic strength of 0.16 mol L-1 at 303.0 K. Alkalimetric titrations were carried out in different relative concentrations (M:L:X = 1:2.5:2.5, 1:2.5:5.0, 1:5.0:2.5) of metal (M) to aspartic acid (L) to ethylenediamine (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 were MLX, ML2X, MLX2, MLX2H and MLX2H2 for Co(II), Ni(II), Cu(II) and Zn(II) in both media. The chemical speciation, metal bioavailability and transportation were explained based on the stability constants.