Structural Characterization of Soft Interfaces by Standing-Wave Fluorescence with X-Rays and Neutrons

Abstract We present a review of standing-wave fluorescence techniques with x-rays and neutrons for the element-specific structural investigation of interfaces. The basic principles are introduced and typical measurement configurations with their advantages and limitations are compared. An overview of studies dealing with various types of interfaces is given. In particular, work on soft and biological matter in planar, interfacial geometries is discussed

The importance of ceramide headgroup for lipid localisation in skin lipid models

The stratum corneum's lipid matrix is a critical for the skin's barrier function and is primarily composed of ceramides (CERs), cholesterol (CHOL) and free fatty acids (FFAs). The lipids form a long periodicity phase (LPP), a unique trilayer unit cell structure. An enzyme driven pathway is implemented to synthesize these key lipids. If these enzymes are down- or upregulated as in inflammatory diseases, the final lipid composition is affected often altering the barrier function. In this study, we mimicked down regulation of enzymes involved in the synthesis of the sphingosine and CER amide bond. In a LPP lipid model, we substituted CER N-(tetracosanoyl)-sphingosine (CER NS) with either i) FFA C24 and free sphingosine, to simulate the loss of the CER amide bond, or ii) with FFA C24 and C18 to simulate the loss of the sphingosine headgroup. Our study shows the lipids in the LPP would not phase separate until at least 25% of the CER NS is substituted keeping the lateral packing and conformational ordering unaltered. Neutron diffraction studies showed that free sphingosine chains localized at the outer layers of the unit cell, while the remaining CER NS head group was concentrated in the inner headgroup layers. However, when FFA C18 was inserted, CER NS was dispersed throughout the LPP, resulting in an even distribution between the inner and outer water layers. The presented results highlight the importance of the CER NS headgroup structure and its interaction in combination with the carbon chain invariability for optimal lipid arrangement.Drug Delivery Technolog

The H5 guide system - the latest innovative guide system at the ILL

The H5 program with the complete rebuild of the guide system and the upgrade or renovation of all instruments leads to a tremendous increase of the instrument performances. The improvement was obtained both in terms of more useful flux and upgrade of the different instruments (e.g. higher field density for IN15). In addition, the industrial application instrument D50 offers an addition to the ILL instrument suite (see p. 27 in this issue). With the commissioning of the new spin echo spectrometer WASP in 2016, the H5 program will be completed and a considerable improvement for the ILL instrument park will be finalized

Simultaneous adsorption of toluene and water vapour on a high surface area carbon

Small angle neutron scattering is used to study the simultaneous adsorption of toluene and water vapour by a commercial high surface area carbon, oxidized to enhance its affinity for polar molecules. Owing to the smaller size of the molecule, water on its own penetrates the smallest defects in the carbon matrix more efficiently than does toluene, as revealed by the density of the carbon determined by contrast variation. Pore filling by water, however, is less complete. When water and toluene vapour are simultaneously present, they coexist in the pores, toluene being the dominant component and water accounting for about 12% of the total adsorbate. Phase separation is not observed. The carbon acts as a compatibilizer for the two different molecules

Evidence by neutron diffraction of molecular compounds in triarylamine tris-amide organogels and in their hybrid thermoreversible gels with PVC

International audienceWe report on neutron diffraction experiments performed on organogels prepared from triarylamine tris-amide (TATA), as well as on their ternary thermoreversible gels made up with poly[vinyl chloride] (PVC). Three different solvents together with their deuterated counterparts have been used; tetrachloroethane, wherein TATA fibrils display ohmic conductivity, bromobenzene and o-dichlorobenzene. The TATA crystal structure differs in the three solvents. Most importantly, the difference in the diffraction patterns whether hydrogenous solvents or deuterated solvents are used demonstrate the occurrence of molecular compounds. Tentative unit cells are presented. These results are also discussed in the light of the current views on the solvent role in the gelation process

Binding of actin filaments to charged lipid monolayers: Film balance experiments combined with neutron reflectivity

The binding of polymerised actin-a prototype of semi-flexible macromolecule-to lipid monolayers is studied by neutron reflectivity to deduce the average thickness, the interfacial roughness and the polymer volume fraction of the adsorbed film. Electrostatic interaction between actin filaments (F-actin) and the lipid monolayer is mediated through a cationic lipid (1,2-dimyristoyl-3-trimethylammonium-propane, DMTAP). The adsorbed F-actin forms a monolayer with an average thickness of 69 to 84 Å, depending on the ionic strength of the buffer and surface charge density of the monolayer. The volume fraction of F-actin in the adsorbed layer can be as high as 0.29. The thickness and high volume fraction of the actin layer suggest that actin filaments lie flat on the surface and form nematic ordering. The binding-unbinding equilibrium of F-actin is controlled by the ionic strength and exhibits a strong hysteresis. In contrast to the results obtained for filamentous actin, monomeric actin (G-actin) shows no detectable binding to the positively charged lipid layers