title: Vesicle Origami and the Influence of Cholesterol on Lipid Packing.
abstract: The artificial phospholipid Pad-PC-Pad was analyzed in 2D (monolayers at the air/water interface) and 3D (aqueous lipid dispersions) systems. In the gel phase, the two leaflets of a Pad-PC-Pad bilayer interdigitate completely, and the hydrophobic bilayer region has a thickness comparable to the length of a single phospholipid acyl chain. This leads to a stiff membrane with no spontaneous curvature. Forced into a vesicular structure, Pad-PC-Pad has faceted geometry, and in its extreme form, tetrahedral vesicles were found as predicted a decade ago. Above the main transition temperature, a noninterdigitated Lα phase with fluid chains has been observed. The addition of cholesterol leads to a slight decrease of the main transition temperature and a gradual decrease in the transition enthalpy until the transition vanishes at 40 mol % cholesterol in the mixture. Additionally, cholesterol pulls the chains apart, and a noninterdigitated gel phase is observed. In monolayers, cholesterol has an ordering effect on liquid-expanded phases and disorders condensed phases. The wavenumbers of the methylene stretching vibration indicate the formation of a liquid-ordered phase in mixtures with 40 mol % cholesterol.
authors.affiliation: Department of Chemistry, University of Fribourg , Chemin du Musée 9, 1700 Fribourg, Switzerland.
authors.forename: Radu
authors.initials: R
authors.lastname: Tanasescu
authors.affiliation: Department of Chemistry, University of Fribourg , Chemin du Musée 9, 1700 Fribourg, Switzerland.
authors.forename: Martin A
authors.initials: MA
authors.lastname: Lanz
authors.affiliation: Department of Chemistry, University of Fribourg , Chemin du Musée 9, 1700 Fribourg, Switzerland.
authors.forename: Dennis
authors.initials: D
authors.lastname: Mueller
authors.affiliation: Max Planck Institute of Colloids and Interfaces , Science Park Potsdam-Golm, 14476 Potsdam, Germany.
authors.forename: Stephanie
authors.initials: S
authors.lastname: Tassler
authors.affiliation: Paul Scherrer Institute (PSI), OFLB/010 5232 Villigen PSI, Switzerland.
authors.forename: Takashi
authors.initials: T
authors.lastname: Ishikawa
authors.affiliation: Experimental Polymer Physics, University of Freiburg , Hermann Herder Strasse 3, 79104 Freiburg, Germany.|Freiburg Centre for Interactive Materials and Bioinspired Technologies (FIT), 79110 Freiburg, Germany.
authors.forename: Renate
authors.initials: R
authors.lastname: Reiter
authors.affiliation: Max Planck Institute of Colloids and Interfaces , Science Park Potsdam-Golm, 14476 Potsdam, Germany.
authors.forename: Gerald
authors.initials: G
authors.lastname: Brezesinski
authors.affiliation: Department of Chemistry, University of Fribourg , Chemin du Musée 9, 1700 Fribourg, Switzerland.
authors.forename: Andreas
authors.initials: A
authors.lastname: Zumbuehl
mesh_terms: D000388:Air; D002784:Cholesterol / Q000737:chemistry* / Q000378:metabolism; D008958:Models, Molecular; D008968:Molecular Conformation; D011312:Pressure; D013499:Surface Properties; D014867:Water / Q000737:chemistry
chemical_list: D014867:Water; D002784:Cholesterol