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Structural Studies on Equimolar Suspensions of Palmitic Acid and 1-Lyso-Palmitoyl-Phosphatidylcholine

Published online by Cambridge University Press:  15 February 2011

J. Lemmich
Affiliation:
Condensed Matter Physics and Chemistry Department, Risø National Laboratory, DK-4000 Roskilde, Denmark Department of Chemistry, Technical University of Denmark, Building 206, DK-2800 Lyngby, Denmark, hoenger@emi.dtu.dk
F. Richter
Affiliation:
Department of Physics, E22, TU Mun̈chen, D-85748 Garching, Germany Present address: EMBL-Outstation at DESY, D-22603 Hamburg, Germany
T. H. Callisen
Affiliation:
Department of Chemistry, Technical University of Denmark, Building 206, DK-2800 Lyngby, Denmark, hoenger@emi.dtu.dk
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Abstract

An equimolar mixture of palmitic acid (PA) and 1-lyso-palmitoyl-phosphatidylcholine (Lyso-PPC) has been studied by time-resolved small angle and wide angle X-ray scattering during temperature cycles between room temperature and 53.5 °C. In addition to the X-ray experiments, differential scanning calorimetry (DSC) with a similar temperature vs. time course was performed. At room temperature we observe a coexistence of two different lamellar phases. Our results indicate that in one of these lamellar phases, Lyso-PPC and PA associate in lamellar structures resembling di-palmitoyl-phosphatidylcholine (DPPC) bilayers, whereas the other phase is an interdigitated lamellar phase, where the acyl chains of both Lyso-PPC and PA extend across the entire hydrocarbon width of the bilayer. Upon heating, the latter phase disappears at 42 °C, corresponding to the chain-melting temperature for DPPC bilayers. At a higher temperature the remaining lamellar phase undergoes a phase transition into an isotropic micellar phase. In the cooling scans a particular slow kinetics of the regeneration of the two lamellar phases is observed. Our experiments provide new information about this system where only the DPPC-like mesophase has been reported before.

Type
Research Article
Copyright
Copyright © Materials Research Society 1998

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