THE EFFECT OF INCORPORATION OF PHOSPHONIC ACID DIBUTYL ESTER IN POPC MODEL MEMBRANES ON THE HYDRATION FORCE

The hydration and swelling properties of lipid model membranes formed by mixtures of 1-palmitoyl-2-oleoyl-glycerophosphatidyl-choline (POPC) and different molar ratios R(a/1) of dodecyl phosphonic acid dibutyl ester (PAB(12)) in water were studied at 25 degrees C. It is shown by X-ray diffraction and P-31 NMR spectroscopy that the system exists in a fluid lamellar phase at R(a/1) = 0.25 and 0.5 over a wide range of water concentration. Intermembrane forces were determined by the osmotic stress technique. The hydration repulsion was found to decrease exponentially with increasing intermembrane water layer thickness. The values of the pre-exponential factor of the hydration forces which slightly decrease with increasing R(a/1) were discussed according to the theory of water polarization near structured water/lipid interfaces (Cevc).