STRUCTURE OF THE SUBGEL (L(C')) AND GEL (L(BETA')) PHASES OF ORIENTED DIPALMITOYLPHOSPHATIDYLCHOLINE MULTIBILAYERS

An X-ray study of highly oriented films of 1,2-dipalmitoyl-sn-glycero-3-phosphatidylcholine (DPPC) in the L(c') phase is presented. The data describe the physical characteristics of the hydrophilic phosphorylcholine headgroups and hydrocarbon chains in the L(c') phase and show that the L(c') --> L(beta F) phase transition is characterized by a change in hydrocarbon chain packing, tilt angle and direction. Also, 1D electron density profiles indicate that L(c') and dry L(beta F) bilayers differ significantly in the bilayer interface region from those in the L(beta 1) (molecular tilt toward nearest neighbors) and hydrated L(beta F) (molecular tilt between nearest neighbors) phases.