Vesicle Origami and the Influence of Cholesterol on Lipid Packing

• Published in: Langmuir Vol. 32; no. 19; pp. 4896 - 4903
• Main Authors: Tanasescu, Radu, Lanz, Martin A., Mueller, Dennis, Tassler, Stephanie, Ishikawa, Takashi, Reiter, Renate, Brezesinski, Gerald, Zumbuehl, Andreas
• Format: Journal Article
• Language: English
• Published: United States American Chemical Society 17.05.2016
• Subjects: Air; Cholesterol - chemistry; Cholesterol - metabolism; Interface Components: Nanops, Colloids, Emulsions, Surfactants, Proteins, Polymers; Models, Molecular; Molecular Conformation; Pressure; Surface Properties; Water - chemistry
• ISSN: 0743-7463; 1520-5827
• DOI: 10.1021/acs.langmuir.6b01143

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.