Binding Of Ferrocyphen By Sds, Ctab And Triton X-100 In Water-Ethanol Co-Solvent

Abstract

The binding of Ferrocyphen [Fe(phen.)2(CN)2]2+ to sodium dodecylsulphate (SDS), cetyltrimethylammonium bromide (CTAB) and Triton X-100 surfactants was studied spectrophotometrically in water-ethanol medium. The equilibrium binding constant (Kb) and the number of binding sites (n) per surfactant monomer were obtained from Scatchard plots. The change in free energy of binding , and the change in free energy of dissociation of bound complex per binding site were calculated from Kb. It is proposed that ethanol stabilizes the surfactant monomers when compared with hydrophobic hydration and hence enhances hydrophobic binding. Kb values suggest that the binding is driven largely by favourable entropic contribution moderated primarily by hydrophobic and electrostatic interactions. The entropic, hydrophobic and hydrogen bond interaction effects are suggested to go through multiple equilibria steps. For CTAB the results indicate preferential electrostatic interaction between electron rich phenanthroline ligands of the metal complex and the cationic ammonium head group over hydrophobic interaction.

IFE Journal of Science Vol. 9 (1) 2007 pp. 137-144