Volumetric properties, compressibilities and volume fluctuations in phospholipid-cholesterol bilayers

We conducted detailed measurements of the apparent specific volume of dipalmitoylphosphatidyleholine (DPPC)-cholesterol mixtures in excess water as a function of pressure up to 70MPa (700bar) at 20, 38 and 50degreesC. The volumetric properties and the isothermal compressibility kappa(T) of the lipid vesicles were determined at cholesterol concentrations, chi(chol), ranging up to 50 mol %. The thermodynamic data are compared with other physicochemical properties of phospholipid-cholesterol mixtures. Furthermore, the thermodynamic properties of the system are discussed in the light of the various T, chi(chol)-phase diagrams and computer simulation studies published in the literature.