Dextran sulfate-amphiphile interaction; Effect of polyelectrolyte charge density and amphiphile hydrophobicity

The interaction between dextran sulfate (DxS), of different charge density, and three cationic amphiphiles varying with respect, to hydrophobicity, wa s investigated by means of equilibrium dialysis and surface tension. The hy drophobicity of the amphiphilies studied increases in the order doxepin-HCl < amitriptyline-HCl < clomipramine-HCl, Dextran sulfate samples with five different charge densities, 0.07, 0.43, 0.7, 1.3, and 1.6 charges per monos achride, were used. The data from both methods clearly indicate that the po lyelectrolyte-amphiphile interaction shows a cooperativity that starts at a certain amphiphile concentration and which depends on both the hydrophobic ity of the amphiphile and the charge density of the dextran sulfate. A chan ge in the charge density of dextran sulfate and/or amphiphile hydrophobicit y affects both the onset of the cooperativity of the interaction and the de gree of the cooperativity. The results have also been compared with the dat a published on related systems.