X-Ray Microscopy of Fluid Lipid Membranes (original) (raw)
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The journal of physical chemistry. B, 2008
We fabricated a new class of supported membranes based on monolayers of artificial bola (transmembrane) lipids. The lipids used in this study are symmetric bola lipids with two phosphocholine head groups, which resemble natural archaea lipids. To prevent bending of the hydrocarbon chains, stiff triple bonds are inserted in the middle of the hydrocarbon cores. The formation of homogeneous "monolayers" of transmembrane lipids over macroscopic areas can be monitored with fluorescence microscopy. Structures of such supported monolayers in bulk water were characterized with specular X-ray reflectivity using high energy X-ray radiation, which guarantees a high transmission through bulk water. Here, the vertical structure of single monolayers could be resolved from reconstructed electron density profiles. To verify the structural model suggested by the specular reflectivity, we also performed small- and wide-angle X-ray scattering of transmembrane lipid suspensions. The wide-angl...
Volume constriction in a lipid-water liquid crystal using high-pressure x-ray diffraction
Physical Review A, 1990
We report a measurement of the change in the total volume of a biological lipid-water system when water molecules are removed from the fully hydrated lyotropic liquid-crystal phase, where the water molecules are near a polar interface, to the surrounding bulk water. The commonly used assumption of linear additions of constituent volumes predicts that the water mole fractions of these lipid-water phases should be independent of hydrostatic pressure. The discrepancy between this 0 prediction and our high-pressure x-ray-diffraction measurements is due to a decrease of 0.1 A in the total volume of the system per molecule of water incorporated into the fully hydrated lipidwater aggregate from the bulk water.
In situ X-ray and neutron diffraction study of lipid membrane swelling
The European Physical Journal Special Topics, 2007
Liposome suspensions comprising the synthetic cationic lipid DOTAP, the zwitterionic DPPC and the anti-cancer agent Paclitaxel were deposited on solid substrates and investigated by X-ray and neutron reflectivity measurements at ESRF and ILL. Well ordered multilamellar drug/lipid membranes were obtained, such as indicated by the several orders of Bragg reflections in the diffraction pattern. With an excess of Paclitaxel, additional Bragg peaks from the drug crystalline phase could be observed. Changes of the molecular organization in the drug-lipid system were investigated as a function of relative humidity using a custom-built controlled humidity chamber. For DOTAP multilayers the effects of bilayer swelling were much more pronounced than for DPPC under similar conditions, while the crystalline peaks of the drug were not affected. The pronounced swelling of DOTAP multilayers might be related to the electrostatic repulsion between the charged lipid headgroups.
Order Parameters and Areas in Fluid-Phase Oriented Lipid Membranes Using Wide Angle X-Ray Scattering
Biophysical Journal, 2008
We used wide angle x-ray scattering (WAXS) from stacks of oriented lipid bilayers to measure chain orientational order parameters and lipid areas in model membranes consisting of mixtures of 1,2-dioleoyl-sn-glycero-3-phosphocholine (DOPC)/cholesterol and 1,2-dipalmitoyl-sn-glycero-3-phosphocholine (DPPC)/cholesterol in fluid phases. The addition of 40% cholesterol to either DOPC or DPPC changes the WAXS pattern due to an increase in acyl chain orientational order, which is one of the main properties distinguishing the cholesterol-rich liquid-ordered (Lo) phase from the liquid-disordered (Ld) phase. In contrast, powder x-ray data from multilamellar vesicles does not yield information about orientational order, and the scattering from the Lo and Ld phases looks similar. An analytical model to describe the relationship between the chain orientational distribution and WAXS data was used to obtain an average orientational order parameter, S x-ray . When 40% cholesterol is added to either DOPC or DPPC, S x-ray more than doubles, consistent with previous NMR order parameter measurements. By combining information about the average chain orientation with the chain-chain correlation spacing, we extended a commonly used method for calculating areas for gel-phase lipids to fluid-phase lipids and obtained agreement to within 5% of literature values.
Chemistry and Physics of Lipids, 1988
From X-ray measurements in different lipid systems it is concluded that the repeat distance measured in lipids with limited swelling in the lamellar liquid crystalline state exhibits qualitatively the same dependence on the water concentration. Four regions of water concentrations with different structural and morphological changes can be distinguished. Their existence is qualitatively explained. The morphology of samples with water concentrations near the boundary between the single lamellar L phase and the two phase region L° + water has a drastic influence on the repeat distance measured. A procedure of how this boundary can be determined is proposed.
Direct imaging of rippled structures of lipid–cholesterol membranes using cryo-SEM and AFM
Bulletin of Materials Science, 2020
Cholesterol is a major component of many eukaryotic cell membranes and hence its effect on the structure of lipid membranes is of considerable interest. One major role of cholesterol is to stabilize the biologically relevant fluid phase over the crystalline gel phase. The suppression of the gel phase occurs above a threshold concentration of cholesterol. There have been reports on the formation of modulated phases at lower cholesterol concentrations, characterized by one-dimensional periodic rippling of the membranes. However, some of these structures have not been investigated in much detail. We have probed the structure of the gel phase of 1,2-dipalmitoyl-sn-glycero-3-phosphocholine (DPPC) membranes containing cholesterol using two direct-imaging techniques, cryogenic-scanning electron microscopy (cryo-SEM) and atomic force microscopy (AFM). In addition to confirming the results of earlier studies, we found evidence for the formation of two novel modulated structures in DPPC-cholesterol membranes. We also report the first direct observation of the cholesterol-induced modulated phase of DPPC membranes using AFM, which had so far been observed only using X-ray scattering.