Small-angle X-ray scattering and electron microscopy of crude dispersions of swelling lipids and the influence of the morphology on the repeat distance (original) (raw)
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Physical Review E, 2009
The influence of cholesterol on lipid bilayer structure is significant and the effect of cholesterol on lipid sorting and phase separation in lipid-raft-forming model membrane systems has been well investigated by microscopy methods on giant vesicles. An important consideration however is the influence of fluorescence illumination on the phase state of these lipids and this effect must be carefully minimized. In this paper, we show that synchrotron x-ray scattering on solution lipid mixtures is an effective alternative technique for the identification and characterization of the l o ͑liquid ordered͒ and l d ͑liquid disordered͒ phases. The high intensity of synchrotron x rays allows the observation of up to 5 orders of diffraction from the l o phase, whereas only two are clearly visible when the l d phase alone is present. This data can be collected in ϳ1 min/ sample, allowing rapid generation of phase data. In this paper, we measure the lamellar spacing in both the liquidordered and liquid-disordered phases simultaneously, as a function of cholesterol concentration in two different ternary mixtures. We also observe evidence of a third gel-phaselike population at 10-12 mol % cholesterol and determine the thickness of the bilayer for this phase. Importantly we are able to look at phase coexistence in the membrane independent of photoeffects.
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.
Langmuir, 2000
The lipid membranes of the nervous system contain a large amount of glycolipids (mostly gangliosides) with bulky and charged headgroups made up of several sugar units. These headgroups have a large conformational flexibility and they are usually assumed to lie roughly parallel or perpendicular to the membrane surface, in connection with the well-known property of gangliosides to be involved in signal recognition and transduction. This paper deals with the study of the geometry of an array of planar lipid lamellae, containing flexible headgroups, confined in a rigid box and subject only to repulsive forces of steric and electrostatic origin. Under the assumption of constant conformational population of the heads we get, by Euler-Lagrange energy minimization, the expected result of a constant repeat distance dictated by the solvent-lipid volume ratio. By contrast, when the conformational population of the heads is allowed to vary in order to reduce the repulsion among the lamellae, the balance between repulsion and conformational energy makes the regular packing unstable, giving rise to periodic modulation of the repeat distance, with alternating domains of loosely and densely packed lamellae. In the case of strong dependence of the repulsion upon conformation, the fluctuations of the repeat distance are large and the domains wider, while in the opposite case of a weak modulation of the repulsion by the headgroup structure, the fluctuation amplitude is negligible and the domains are small. Although the periodic modulation of the repeat distance looks to be an ubiquitous effect, its magnitude seems to be small for most amphiphiles. However, in the case of flexible and very bulky headgroups, the phenomenon could be relevant. Our model differs from the classical picture of phase separation arising from the balance between attractive and repulsive (mixing entropy) forces, because, as suggested by force apparatus measurements, only repulsion energy among ganglioside lamellae is dominant. The model predictions have been confirmed by X-ray measurements in binary water-ganglioside mixtures which clearly show a modulation of the repeat distance in a rather large region of the phase diagram, while only a single repeat distance has been so far observed for the more common phospholipids lamellae. (1) Tettamanti, G.; Sonnino, S.; Ghidoni, R.; Masserini, M.; Venerando, B. Physics of Amphiphiles: Micelles, Vesicles and Microemulsions; (4) Cantú , L.; Corti, M.; Del Favero, E.; Muller, E.; Raudino, A.; Sonnino, S. Langmuir 1999, 15, 4975. (5) Cantú , L.; Corti, M.; Sonnino, S.; Tettamanti, G.
Estimations of lipid bilayer geometry in fluid lamellar phases
Biochimica et Biophysica Acta (BBA) - Biomembranes, 2000
The excess water bilayer thickness, d lY0 , and molecular area, A 0 , of lipid amphiphiles in the fluid lamellar phases of dioleoylphosphatidylcholine (DOPC) and dipalmitoleoylphosphatidylcholine (DPolPC) have been estimated between 15 and 50³C and for dimyristoylphosphatidylcholine (DMPC) between 25 and 50³C. These determinations have been made from X-ray measurements on samples of known water composition. With respect to temperature, T, d lY0 and A 0 are well fitted to a linear equation. We find d lY0 (A î) = (35.68 þ 0.02)3(0.0333 þ 0.0006)T (³C) and A 0 (A î 2) = (70.97 þ 0.05)+(0.136 þ 0.001)T (³C) for DOPC, d lY0 (A î) = (35.2 þ 0.1)3(0.068 þ 0.003)T (³C) and A 0 (A î 2) = (59.7 þ 0.2)+(0.210 þ 0.006)T (³C) for DMPC, and d lY0 (A î) = (34.54 þ 0.03)3(0.0531 þ 0.0009)T (³C) and A 0 (A î 2) = (67.12 þ 0.09)+(0.173 þ 0.003)T (³C) for DPolPC. The accuracy of these estimates depends largely on how accurately the excess water point is determined. Ideally, reliable X-ray and compositional data will be available around the excess water and it may be found by simple inspection, but this is the exception rather than the rule, since samples close to water excess normally sequester sizeable amounts of water in defects, which lead to an underestimate of d lY0. and overestimate of A 0. In this paper, we report a methodology for identifying and removing such data points and fitting the remaining data in order to determine the excess water point.
Cooperativity between Water and Lipids in Lamellar to Inverted-Hexagonal Phase Transition
Journal of the Physical Society of Japan, 2014
It has been unclear whether the role of water in the self-assembly of soft materials and biomolecules is influential or water is just a background medium. Here we investigate the correlation between hydration state of lipid membrane and structural phase transition of the membrane between lamellar and inverted-hexagonal phases, as an intermediate process of membrane fusion, by using the complementary techniques of X-ray scattering and terahertz (THz) spectroscopy. By comparing two lipid species, our results indicate that the structural changes of the lipid membrane depend on the behavior of the surrounding water, especially in the second hydration layer, in addition to the molecular shape of lipids. The water behaves differently at each membrane surface owing to the different hydrophilicities of the lipid head groups.
Lamellar and hexagonal lipid phases visualized by freeze-etching
Biochimica et Biophysica Acta (BBA) - Biomembranes, 1970
i. Rapid freezing of lipid-water preparations preserves the structure of the high temperature phases. Both lameUar and hexagonal phases can be readily demonstrated by electron microscopy and X-ray observations.
Dynamic molecular movements and aggregation structures of lipids in a liquid state
Current Opinion in Colloid & Interface Science, 2011
This paper discusses the molecular conformations and the liquid structures of triacylglycerols (TGs) and fatty acids in their melts. Three models for liquid state ordering have been proposed for TG melts to date: the smectic liquid crystal model, the nematic liquid crystal model, and the discotic model. To completely resolve the liquid structure of TGs, further research is required. However, some information on the molecular level has been obtained for fatty acids that are relatively simple compounds. The combination of various spectroscopic and thermodynamic measurements revealed that the hydrogen-bonded dimers of fatty acids are units of intermolecular and intramolecular movements in the liquids and in non-polar solvents. The dimers that construct the clusters resemble the smectic liquid crystal and determine the physicochemical properties of the liquid of the fatty acid. Cholesterol stabilizes the clusters, while ethanol destroys them. Selfdiffusion and neutron diffraction measurements revealed that two kinds of fatty acids exist in their binary liquid mixture exist as the homodimers composed of same species.
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.