Relationship between the unbinding and main transition temperatures of phospholipid bilayers under pressure

The anomalous swelling regime in dimyristoyl- (DMPC) and dilauroyl-phosphatidylcholine bilayers (DLPC) was studied as a function of pressure using neutron diffraction and a specially constructed high pressure cell suitable for aligned multibilayer systems. The power law behavior describing anomalous swelling was observed to be preserved in all PC bilayers up to a hydrostatic pressure of 240 MPa. There was a concomitant decrease in the anomalous swelling of DMPC layers with increasing pressure. The theoretical unbinding transition temperature was found to be coupled to the main gel-to-liquid transition temperature for PC lipids with hydrocarbon chains≥13.