Cholesterol solubility in mixed micellar solutions of ionic and non-ionic surfactants.

The solubility of cholesterol in mixed aqueous ionic and non-ionic micellar systems in the presence and absence of salts and ionic dyes has been studied. The mixed micellar system of cetyl trimethyl ammonium bromide and Triton X-100 solubilized more cholesterol than a system consisting of sodium dodecyl sulfate and Triton X-100. The influence of salts and dyes on these systems was moderate but different for each system. Sodium chloride, calcium chloride, and sodium citrate had mild effects on both the systems, whereas the effects of potassium hydrogen phthalate, sodium salicylate, and sodium acetyl salicylate were dramatic. The free energy, enthalpy, and entropy of solution were determined. On the basis of the energetics, the nature of the mixed systems is discussed. Solubility of cholesterol was found to bear a direct correlation with the total lipid content.