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

TLDR: Using neutron diffraction and a specially constructed high pressure cell suitable for aligned multibilayer systems, the much observed anomalous swelling regime in dimyristoyl- and dilauroyl-phosphatidylcholine bilayers, DMPC and DLPC is studied.

Abstract: Using neutron diffraction and a specially constructed high pressure cell suitable for aligned multibilayer systems, we have studied, as a function of pressure, the much observed anomalous swelling regime in dimyristoyl- and dilauroyl-phosphatidylcholine bilayers, DMPC and DLPC, respectively. We have also reanalyzed data from a number of previously published experiments and have arrived at the following conclusions. ~a! The power law behavior describing anomalous swelling is preserved in all PC bilayers up to a hydrostatic pressure of 240 MPa. ~b! As a function of increasing pressure there is a concomitant decrease in the anomalous swelling of DMPC bilayers. ~c! For PC lipids with hydrocarbon chains >13 carbons the theoretical unbinding transition temperature T ! is coupled to the main gel-to-liquid crystalline transition temperature TM . ~d! DLPC is intrinsically different from the other lipids studied in that its T ! is not coupled to TM . ~e! For DLPC bilayers we predict a hydrostatic pressure ( .290 MPa) where unbinding may occur.