100,565 research outputs found
Structure and fluctuations of highly oriented phospholipid membranes
No full textHighly oriented lipid membranes deposited on solid substrates offer unique experimental possibilities to study self-assembly phenomena, fluctuations, and interactions in lipid bilayer systems, both with and without additional membrane-active molecules such as amphiphilic peptides or membrane proteins. In diffraction experiments, the high orientation allows for a precise distinction between the normal q(z), and lateral component q(parallel to) of the scattering vector (q) over right arrow, opening up a way to study biologically relevant questions associated with the lateral structure of the bilayers. Modern sources and instruments for neutron and X-ray scattering, in particular the advent of third-generation synchrotron sources enable studies even of weakly scattering and weakly ordered systems. (C) 2000 Elsevier Science Ltd. All rights reserved
Thermal fluctuations and stability of solid-supported lipid membranes
No full textIn this review article we discuss recent work on the thermal stability, thermal fluctuations and interaction forces in lipid membrane stacks. The lipid bilayers are deposited on solid surfaces for investigation by interface sensitive x-ray and neutron scattering on length scales ranging from the molecular to the mesoscopic scale. We discuss how the structure, composition, fluctuations, and interactions in lipid and biomimetic membranes can be studied in the fluid Lalpha phase. Results on the interaction potentials, height-height correlation functions, elasticity parameters, fluid lipid chain ordering, and collective lipid chain motions are discussed
Iterative micro-tomography of biopsy samples from truncated projections with quantitative gray values
No full textAbstractThree-dimensional reconstruction from truncated two-dimensional projections cannot be solved analytically without prior knowledge of the sample or access to the non-truncated projections. To suppress reconstruction artifacts in region of interest (ROI) or local tomography, an iterative algorithm has been devised based on back-projection and re-projection, assuming an approximately cylindrical shape of the entire sample of general homogeneity, which is especially applicable for micro-tomography of biopsy samples from biological tissue. Tomographic reconstruction is iteratively refined by minimizing the mismatch between an empty ROI and the reconstruction from the difference between measured sinogram and forward projected ROI reconstruction. By numerical simulation and experimental demonstration, it is shown that the algorithm is not only able to reconstruct quantitative gray values, but also to reduce artifacts of peripheral glow, and may lead to increased image sharpness. The method is particularly suitable for examination of biopsy/autopsy-samples of soft tissue by micro/nano-computed tomography.Bundesministerium für Bildung und Forschunghttp://dx.doi.org/10.13039/50110000234
Actin bundles cross-linked with α -actinin studied by nanobeam X-ray diffraction
No full textWe have performed scanning nano-beam small-angle X-ray scattering (nano-SAXS) experiments on in vitro-formed actin filaments cross-linked with -actinin. The experimental method combines a high resolution in reciprocal space with a real space resolution as given by the spot-size of the nano-focused X-ray beam, and opens up new opportunities to study local super-molecular structures of actin filaments. In this first proof-of-concept, we show that the local orientation of actin bundles formed by the cross-linking can be visualized by the X-ray darkfield maps. The filament bundles give rise to highly anisotropic diffraction patterns showing distinct streaks perpendicular to the bundle axes. Interestingly, some diffraction patterns exhibit a fine structure in the form of intensity modulations allowing for a more detailed analysis of the order within the bundles. A first empirical quantification of these modulations is included in the present work
Non-iterative coherent diffractive imaging using a phase-shifting reference frame
No full textLensless imaging is a high potential and currently intensely targeted research goal, in view of those fields of applications for which aberration-free high-resolution lenses are not available, for example for x-ray imaging. A recently proposed (direct inversion) variant of lensless imaging combines the advantages of two classical routes toward lensless imaging, the high-resolution characteristics of iterative object reconstruction, and the direct and deterministic nature of holographic reconstruction. Here, we use a simple standard optical setup using visible wavelength, a lithographic test object and a phase-shifting reference object to demonstrate the approach. Importantly, we show that a phase-shifting reference object, instead of the absorption mask proposed earlier, is sufficient for object reconstruction. This is relevant in view of the much easier implementation in future x-ray applications
How many photons are needed to reconstruct random objects in coherent X-ray diffractive imaging?
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Structure of magainin and alamethicin in model membranes studied by x-ray reflectivity
No full textAbstractWe have investigated the structure of lipid bilayers containing varied molar ratios of different lipids and the antimicrobial peptides magainin and alamethicin. For this structural study, we have used x-ray reflectivity on highly aligned solid-supported multilamellar lipid membranes. The reflectivity curves have been analyzed by semi-kinematical reflectivity theory modeling the bilayer density profile ρ(z). Model simulations of the reflectivity curves cover a large range of vertical momentum transfer qz, and yield excellent agreement between data and theory. The structural changes observed as a function of the molar peptide/lipid concentration P/L are discussed in a comparative way
Viral ion channel proteins in model membranes: a comparative study by x-ray reflectivity
No full textWe have investigated the effect of the transmembrane domain of three viral ion channel proteins on the lipid bilayer structure by X-ray reflectivity and scattering from oriented planar bilayers. The proteins show a similar effect on the lipid bilayer structural parameters: an increase in the lipid bilayer hydrophobic core, a decrease in the amplitude of the vertical density profile and a systematic change in the ordering of the acyl chains as a function of protein-to-lipid ratio. These results are discussed in a comparative view
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