Giant liposomes obtained by electroformation and observed by phase-contrast video microscopy show spontaneous deformations originating from Brownian motion that are characterized, in the case of quasispherical vesicles, by two parameters only, the membrane tension sigma and the bending elasticity k(c). For liposomes containing dimyristoyl phosphatidylcholine (DMPC) or a 10 mol% cholesterol/DMPC mixture, the mechanical property of the membrane, k(c), is shown to be temperature dependent on approaching the main (thermotropic) phase transition temperature T(m). In the case of DMPC/cholesterol bilayers, we also obtained evidence for a relation between the bending elasticity and the corresponding temperature/cholesterol molecular ratio phase diagram. Comparison of DMPC/cholesterol with DMPC/cholesterol sulfate bilayers at 30 degrees C containing 30% sterol ratio shows that k(c) is independent of the surface charge density of the bilayer. Finally, bending elasticities of red blood cell (RBC) total lipid extracts lead to a very low k(c) at 37 degrees C if we refer to DMPC/cholesterol bilayers. At 25 degrees C, the very low bending elasticity of a cholesterol-free RBC lipid extract seems to be related to a phase coexistence, as it can be observed by solid-state (31)P-NMR. At the same temperature, the cholesterol-containing RBC lipid extract membrane shows an increase in the bending constant comparable to the one observed for a high cholesterol ratio in DMPC membranes.
We report a small angle X-ray scattering study on the liquid phase of a series of room temperature ionic liquids and their binary mixtures. The ionic liquids studied belong to the tri-alkyl-methyl-ammonium family with bis(trifluoromethanesulfonyl)amide as the anion and were studied as a function of alkyl chain length. These ionic liquids were found to exhibit marked nanoscale ordering in their isotropic liquid state as judged from the small angle X-ray scattering. The observed structural ordering is of supramolecular order and depends strongly on the length of the cation hydrophobic side chain. Moreover, the data can be analyzed on the basis of a disordered smectic A phase, consisting of strongly interdigitated bilayers that sequester the ionic liquid into polar and hydrophobic regions. These findings were also found to be consistent with density data of these molten salts. Additionally, we demonstrate that this experimentally observed nanostructuring can further be fine-tuned using binary mixtures.
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