title: Conformational and hydrational properties during the L(beta)- to L(alpha)- and L(alpha)- to H(II)-phase transition in phosphatidylethanolamine.
abstract: Differential scanning calorimetry (DSC) measurements have been carried out simultaneously with small- and wide-angle X-ray scattering recordings on liposomal dispersions of stearoyl-oleoyl-phosphatidylethanolamine (PE) in a temperature range from 20 to 80 degrees C. The main transition temperature, T(m), was determined at 30.9 degrees C with an enthalpy of 28.5 kJ/mol and the lamellar-to-inverse hexagonal phase transition temperature, T(hex), at 61.6 degrees C with an enthalpy of 3.8 kJ/mol. Additionally highly resolved small angle X-ray diffraction experiments performed at equilibrium conditions allowed a reliable decomposition of the lattice spacings into hydrophobic and hydrophilic structure elements as well as the determination of the lipid interface area of the lamellar gel-phase (L(beta)), the fluid lamellar phase (L(alpha)) and of the inverse hexagonal phase (H(II)). The rearrangement of the lipid matrix and the coincident change of free water per lipid is illustrated for both transitions. Last, possible transition mechanisms are discussed on a molecular level.
authors.affiliation: Institute of Biophysics and Nanosystems Research, Austrian Academy of Sciences, Graz, Austria. michael.rappolt@elettra.trieste.it
authors.forename: Michael
authors.initials: M
authors.lastname: Rappolt
authors.forename: Aden
authors.initials: A
authors.lastname: Hodzic
authors.forename: Barbara
authors.initials: B
authors.lastname: Sartori
authors.forename: Michel
authors.initials: M
authors.lastname: Ollivon
authors.forename: Peter
authors.initials: P
authors.lastname: Laggner
mesh_terms: D002152:Calorimetry, Differential Scanning; D008958:Models, Molecular; D044367:Phase Transition; D010714:Phosphatidylethanolamines / Q000737:chemistry*; D013696:Temperature; D014867:Water / Q000737:chemistry*; D014961:X-Ray Diffraction
chemical_list: D010714:Phosphatidylethanolamines; D014867:Water; C483858:phosphatidylethanolamine