Anionic Surfactant Influence On Binary Complexes Of Ca(II), Mg(II) And Zn(II) Ions With Glycylglycine

Abstract

A pH metric  titration study has been undertaken to determine the anionic surfactant influence on mixed  binary  systems consisting of calcium (II), magnesium (II) and zinc (II) with glycylglycine (GG)  at various concentrations (0.0–2.5% w/v) of the SLS  (Sodium Lauryl Sulphate) surfactant solution while maintaining an ionic strength of 0.16 mol L^-1 (NaCl) at 30 °C. Titrations were performed in the presence of different ratios (M:L = 1:2.50, 1:3.75, and 1:5.00) of metal (M) and glycylglycine (L)  using sodium hydroxide. Model systems were developed based on statistical parameters and residual analysis. For Ca(II), Mg(II) and Zn(II), the species detected were ML₂, ML₂H, and ML₂H₂. The electrostatic relationship of the ligands' side chains, charge neutralization, chelate effect and stacking interactions are used to explain the trend in the variation of logarithm of stability constants (log β) values with changing dielectric constant and mole fraction of the surfactant. The variation in species distribution as a function of pH and surfactant composition is also presented and discussed, as are plausible equilibria for the formation of the species and structures of the ternary complexes are also presented and discussed.