Strucutural Changes of Dipalmitoyl Phosphatidylcholine Aqueous Solution Induced by Temperature, Pressure, and Adding Ethanol

Abstract

Temperature, pressure, and ethanol concentration dependences of the structure and dynamics of dipalmitoyl phosphatidylcholine (DPPC) aqueous solution were investigated by small-angle neutron scattering and neutron spin echo experiments. The effect of ethanol is almost the same as that of applying pressure to induce the interdigitated gel phase. A swollen phase, in which the mean repeat distance of lipid bilayers is larger than these of the other phases, is found between the liquid-crystalline phase and the interdigitated gel phase. The nature of the swollen phase is similar to the anomalous swelling observed above the transition point between the liquid-crystalline phase and the ripple gel phase. However, the temperature dependence of the mean repeat distance and the bending rigidity of lipid bilayers in the swollen phase are different from those of the anomalous swelling.