HIGH-PRESSURE VOLUMETRIC MEASUREMENTS ON PHOSPHOLIPID-BILAYERS

We report on a new apparatus which allows to perform high pressure vol umetric measurements on biochemical systems at temperatures ranging fr om 0 to 100-degrees-C and at pressures from ambient up to 2500 bar. As an example, we present PVT-data of dilute aqueous dispersions of the model biomembrane dimyristoylphosphatidylcholine. The thermal expansio n coefficient, isothermal compressibility and the lipid volume fluctua tions of the lipid bilayer in its various thermotropic and barotropic phases have been determined and an accurate temperature-pressure phase diagram of the liquid-crystalline to gel phase transition of the lipi d membrane could be obtained. The experimental results are compared wi th theoretical models for phospholipid bilayer phase transitions and f or the thermomechanical properties of the lipid in its various phases.