Chemical Speciation Of Complexes Of L-Valine And Lproline With Essential Metal Ions (Ca, Zn, Mn) In Sodium Lauryl Sulfate-Water Mixture

Abstract

The chemical speciation of an element, either essential or toxic is relevant, because the chemical form in which an element enters the body, mostly determines its absorption and transport properties, and hence its biological and physiological activities. In this study, Chemical speciation of Protonation equilibria of L-Proline and L-Valine, binary and ternary complexes of Ca(II), Zn(II) and Mn(II) with L-Proline and L-Valine have been studied pH-metrically in the varying concentrations (0.0–2.5% w/v) of SLS-water mixtures maintaining an ionic strength of 0.16 mol L– 1(NaCl) at 310K. The Protonation constant was calculated with the computer program SCPHD. Stability constants of binary and ternary have been calculated with MINIQUAD75. The best-fit chemical models were selected based on statistical parameters and residual analysis. In the present investigation, the protonation constants from the best fit models show the formation of LH2+, LH and L¯ for both L-proline and L-valine. The binary species that are refined are ML+, MLH2+ and ML2H+ for Ca(II), Zn(II) and Mn(II) with L-proline and L- valine. In mixed ligand speciation, alkalimetric titrations were carried out with 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 L-proline (L) to L-valine (X). The species detected for mixed ligand complexes are protonated and unprotonated ternary species like MLX, ML2XH and MLXH22+ for Ca(II), MLX, ML2X¯, MLXH22+ for Zn(II) and MLX, ML2XH and MLXH22+ for Mn(II). The trend in the variation of step -wise protonation constant and stability constants with change in mole fraction of the medium were explained on the basis of electrostatic and nonelectrostatic forces. The species distribution diagrams and the plausible equilibria for the formation of the species are also presented. The chemical speciation, metal bioavailability and transportation have been explained based on stability constant and distribution diagrams drawn using HYSS HYPERQUAD. The ternary complexes are more amenable for metal transport because of their extra stability while the binary complexes make the metal bioavailable due to their decreased stability.