Phase Transition of Lipid Multilamellar Aqueous Suspension under High Pressure I. Investigation of Phase Diagram of Dipalmitoyl Phosphatidylcholine Bimembrane by High Pressure-DTA and -Dilatometry

Abstract

The pressure and temperature phase diagrams of DPPC bilayers have been obtained by DTA and dilatometry. Under atmospheric pressure DPPC shows three phase transitions at 42°C, 36°C and around 18°C, corresponding to the main-, pre- and sub-transitions respectively. Throughout our experiments we discovered very interesting phenomena in these transitions due to the effect of pressure and are as follows. First, the presence of a tricritical point on the pre-transition line has been found at about 2.5 kbar and 78°C, where the first order transition changes to a second order transition. Second, the sub-transition could be observed under high pressure without annealing procedure which required to stock DPPC at about 0°C for three or four days under atmospheric pressure. Third, a new fourth transition below the sub-transition temperature has been discovered.