B. B. V. Sailaja

Effect of non ionic micelles on the chemical speciation of binary complexes of Pb(II), Cd(II) and Hg(II) with L-phenylalanine

Abstract Complexes of Pb(II), Cd(II) and Hg(II) with L-phenylalanine in the presence of non-ionic surfactants, at an ionic strength of 0.16 mol dm-3 and temperature 303 K are investigated pH-metrically. The existence of different binary complex species is established from modelling studies using the computer program MINIQUAD75. The increased stability of the complexes with increasing micellar content is explained by electrostatic forces. The influence of the micelles on the chemical speciation is discussed based on the mole fraction of the medium. Distribution diagrams of various species of the complexes in relation to pH are presented.

Thermal decomposition of ammonium dioxodiaquaperoxyoxalatouranate(VI) hydrate

Abstract The chemical analysis and the thermal decomposition of the complex are consistent with the formation of an intermediate, which is a mixture of ammonium carbonate and uranium trioxide, subsequently decomposing to ammonium uranate. The ammonium uranate decomposes to uranium trioxide which is finally reduced to U3O8. Thermal decomposition, infrared absorption spectra, and X-ray diffraction patterns are used to characterize the complex and the intermediate products of the thermal decomposition. Based on this data, the complex salt may be represented as (NH4)2[UO2(O2)(C2O4)(H2O)2]·H2O.

Formation of binary complexes of Pb(II), Cd(II) and Hg(II) with maleic acid in CTAB-water mixtures

Abstract Complexation of toxic metal ions with maleic acid in (0.0–2.5% w/v) cetyltrimethylammonium bromide (CTAB)–water mixtures has been studied pH-metrically at ambient conditions and an ionic strength of 0.16 mol L-1. The existence of different binary species was established from modelling studies using the computer program MINIQUAD75. The best-fit chemical models were selected based on statistical parameters such as the crystallographic R factor and sum of the squares of residuals in mass-balance equations. The models for binary complex systems contain the chemical species ML2, ML2H and ML3 for Pb(II), Cd(II) and Hg(II) in CTAB–water mixtures. The trend in the variation of stability constants with change in the mole fraction of the medium was explained based on electrostatic and non-electrostatic forces. Distribution of the species with pH at different compositions of CTAB–water mixtures was also presented.

Influence of dielectric constant on protonation equilibria of maleic acid and L-asparagine in acetonitrile water-mixtures

Abstract The protonation constants of maleic acid and L-asparagine have been studied pH-metrically in various concentrations (0–50% v/v) of acetonitrile–water mixtures maintaining an ionic strength of 0.16 mol L-1 at 300C. The protonation constants have been calculated using the computer program MINIQUAD75 and are selected based on statistical parameters. Linear variation of step-wise protonation constants (log K) with the reciprocal of the dielectric constant of the solvent mixture has been attributed to the dominance of the electrostatic forces.

Protonation equilibria of L-phenylalanine and maleic acid in cationic micellar media

Abstract Solute-solvent interactions of L-phenylalanine and maleic acid have been studied in various concentrations (0.5-2.5% w/v) of cetyltrimethylammonium bromide solution maintaining an ionic strength of 0.16 mol dm-3 at 303 K. The protonation constants have been calculated using the computer program MINIQUAD75 and the best fit models are arrived at based on statistical grounds employing crystallographic R factor, x2, skewness and kurtosis. These protonation constants values have been found to shift in micellar media as compared to those in pure water. The differences in the values have been attributed to the solvent properties of the interfacial and bulk phases involving contribution from the micellar surface potential in the case of charged micelles. The trend of log values of step-wise protonation constants with mole fraction of the medium have been explained based on electrostatic and non-electrostatic forces operating on the protonation equilibria. Distributions of species, protonation equilibria and effect of influential parameters on the protonation constants have also been 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.

Protonation equilibria of glycylglycine and histamine in aqueous solution of an anionic surfactant

Abstract The protonation constants of glycylglycine and histamine are studied in sodium lauryl sulfate–water mixtures (0.5–2.5% w/v) at 303.0 ± 0.1 K at an ionic strength of 0.16 M using a pH-metric technique. The protonation constants are calculated with the computer program MINIQUAD75 and the best fit chemical model is based on the statistical parameters. The effect of solvent on protonation constants is discussed based on electrostatic and non-electrostatic forces operating on the protonation equilibria. Distribution of species, protonation equilibria and effect of influential parameters on the protonation constants are also presented.

Thermal decomposition of potassium dioxodiaquaperoxyoxalatouranate(VI)

Abstract Potassium dioxodiaquaperoxyoxalatouranate(VI) was obtained by reaction of uranyl nitrate with oxalic acid and then hydrogen peroxide in the presence of potassium ion. The complex was subjected to chemical analysis. The thermal decomposition behavior of the complex was studied using TG, DTA and DTG techniques. The solid complex salt and the intermediate product of its thermal decomposition were characterized using IR absorption and X-ray diffraction spectra. Based on the data from these physicochemical investigations, the structural formula of the complex was proposed as K 2 [UO 2 (O 2 )C 2 O 4 (H 2 O) 2 ].

Computer-augmented modeling studies of Pb(II) and Cd(II) complexes with maleic acid in ethylene glycol–water mixture

Abstract Chemical speciation of binary complexes of Pb(II) and Cd(II) ions with maleic acid have been studied pH metrically in the concentration range of 0–50% v/v ethylene glycol (EG)–water mixtures maintaining an ionic strength of 0.16 molL−1 at 303 K. Alkalimetric titrations were carried out in different relative concentrations of metal and maleic acid. Stability constants of various models of binary complexes were refined with MINIQUAD75. The best-fit chemical models were selected based on statistical parameters and residual analysis. The species detected are ML2, ML3, and ML2H for Pb(II) and Cd(II). The chemical speciation, metal bioavailability, and transportation are explained based on the distribution diagrams.

Speciation of binary complexes of Co(II), Ni(II), and Cu(II) with L-phenylalanine in anionic micellar medium

Abstract Speciation of binary complexes of Co(II), Ni(II), and Cu(II) with L-phenylalanine (Phe) in the presence of water–anionic surfactant mixtures in the concentration range of 0.0–2.5% w/v SLS has been studied pH-metrically at a temperature of 303 K and at an ionic strength of 0.16 mol L−1. The selection of best fit chemical models is based on statistical parameters and residual analysis. The predominant species detected were ML, ML2, and ML2H2 for Co(II), Ni(II), and Cu(II). The trend in the variation of stability constants with the mole fraction of SLS was explained on the basis of electrostatic and non-electrostatic forces. Distribution of the species with pH at different compositions of SLS–water media was also presented.