VOLUMETRIC STUDY ON DIOLEOYLPHOSPHATIDYLCHOLINE BILAYER BY PRESSURE PERTURBATION CALORIMETRY

Abstract

We investigated the thermotropic volume behavior of the bilayer membrane of dioleoylphospha-tidylcholine ( DOPC ), which is a typical unsaturated phospholipid, by means of pressure perturbation calorimetry (PPC) in the temperature range of 6.0-85.6 °C. The thermal expansion coefficient of DOPC in the bilayer membrane was found to monotonically increase from 0.65 × 10-3 K-1 to 1.07 × 10-3 K-1 with increasing temperature. This is slightly small compared to that of dipalmi-toylphosphatidylcholine ( DPPC ) in the same state at the same temperature. Further, we calculated the specific volume V sp , L and the specific volume of the hydrocarbon region V sp , HC for DOPC and DPPC to consider the difference in the packing state of these bilayer membranes. The V sp , HC value is smaller for DOPC than for DPPC at any temperature above ca. 42 °C, which indicates that the packing state of the DOPC bilayer membrane in the liquid crystalline state is denser than that of the DPPC bilayer membrane in the same state.