The impact of sodium lauryl sulphate (SLS) on the protonation equilibria ofL-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-3at 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 of Co(II), Ni(II), Cu(II) and Zn(II) with L-arginine as primary ligand (L) and succinic acid as secondary ligand (X) has been studied in various concentrations (0.0 -2.5% wyv) of the anionic surfactant solution maintaining an ionic strength of 0.16 mol dm À 3 (NaNO 3 ) at 303 K. Titrations have been carried out in the presence of different relative concentrations (M: L: X ¼ 1 : 2 : 2, 1 : 2 : 4, 1 : 4 : 2) of metal to L-arginine to succinic acid with sodium hydroxide as titrant. The trend of the variation in the stability constants with changing dielectric constant as well as mole fraction of the medium is explained based on the electrostatic interactions of the side chains of the ligands, charge neutralization, chelate effect, stacking interactions and hydrogen bonding. Distribution diagrams with pH at different compositions of surfactant and structures of plausible ternary complexes are presented.
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, ML 2 and ML 2 H for Co(II), ML, MLH, ML 2 for Ni(II) and Cu(II), ML 2 , ML 2 H and ML 2 H 2 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 nonelectrostatic forces. Distributions of the species with pH at different composition of micellar media were also presented.
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