THERMOTROPIC AND BAROTROPIC PHASE-BEHAVIOR OF DIHEXADECYLPHOSPHATIDYLCHOLINE BILAYER-MEMBRANE

The temperature (T)-pressure (P) phase diagram of the ether-linked dih exadecylphosphatidylcholine (DHPC) multilamellar vesicles was construc ted by the method of high-pressure optical density. The DHPC membrane at ambient pressure undergoes the pretransition (at 33.6 degrees C) fr om the interdigitated gel (L(beta)I) phase to the ripple gel (Pb) phas e, and succeedingly the main transition (at 44.4 degrees C) from the P '(beta) phase to the liquid crystal (L alpha) phase. Since the slope o f the T-P diagram for the pretransition, 0.316 K MPa(-1), is larger th an that fbr the main transition, 0.242 K MPa(-1), the phase boundary b etween P'(beta), and L(beta)I phases disappeared at high pressure abov e 130 MPa. A triple point among L(beta)I, P'(beta) and L(alpha) phases was found at 130 MPa and 74.5 degrees C. Difference in phase diagrams between the ether-linked and ester-linked phospholipid bilayer membra nes has been elucidated.