Cholesterol in aqueous solution: hydrophobicity and self-association.

Free energies of transfer of cholesterol monomer from water to organic solvents show that the hydrophibicity of this sterol molecule is significantly less than predicted from hydrophobic surface area considerations. It is suggested that this phenomenon may arise from unusual orientation of water molecules at the surface of the solute. From the direct measruemtn of the hydrophobic free energy of transfer and comparison with thermodynamic data on micelle formation reported previously we calcuate specific attractive interactions between cholesterol monomers in the micelle of 2-4 kcal/mol, which suggests the possiblity of self-association (phase separation) in mixed micellar systems such as sterol-lipid complexes.