title: Anomalous phase behavior of long chain saturated lecithin bilayers.
abstract: X-ray scattering has been performed on fully hydrated unoriented multilamellar vesicles of lecithins with even chain lengths n from 16 to 24 as a function of temperature in chain ordered phases. The longer chain lengths, n > or = 20, show anomalous behavior compared to the shorter chain lengths, n < 20. This report concentrates on n = 24. Although the history and time dependence shows that equilibrium was not always achieved, it appears that there is a second gel-like phase G2 below 40 degrees C. The G2 phase has a small tilt angle and opposite hexagonal symmetry breaking from the usual G1 gel phase. Also, as T is raised above 45 degrees C, the wide-angle data suggest the appearance of a phase with hexagonal chain packing and small chain tilt angle.
authors.affiliation: Department of Physics, Carnegie Mellon University, Pittsburgh, PA 15213, USA.
authors.forename: W J
authors.initials: WJ
authors.lastname: Sun
authors.forename: S
authors.initials: S
authors.lastname: Tristram-Nagle
authors.forename: R M
authors.initials: RM
authors.lastname: Suter
authors.forename: J F
authors.initials: JF
authors.lastname: Nagle
mesh_terms: D008051:Lipid Bilayers / Q000737:chemistry*; D010713:Phosphatidylcholines / Q000737:chemistry*; D012542:Scattering, Radiation; D013696:Temperature
chemical_list: D008051:Lipid Bilayers; D010713:Phosphatidylcholines