The binding of cetylpyridinium chloride (CPC) with some azo dyes (X6G, 3-BL, DY-42) has been extensively studied at various concentration of dyes, using cetylpyridinium-selective membrane electrode as a fast and accurate method. Klotz logarithmic plots have been constructed from EMF measurements. These plots indicated cooperativity in all of interactions. The accurate binding isotherms have been obtained and analyzed using Hill equation. The values of Hill equation parameters have been estimated and determined by considering this fact that saturation parameter of binding in the Hill equation (y) can be determined from the ratio of electromotive force (EMF) measurements in the presence and absence of dye. In all of the interactions Hill coefficients indicate cooperative binding in CPC-dye interactions due to the combination of both electrostatic and hydrophobic interactions. Intrinsic Gibbs energies of binding processes have been also calculated and interpreted on basis of interaction mechanism.
cetylpyridinium chloride; cooperative binding; binding isotherm; Hill equation; dye-surfactant
