Ions modulate stress-induced nano-texture in supported fluid lipid bilayers.

Most plasma membranes comprise a large number of different molecules including lipids and proteins. In the standard fluid mosaic model, the membrane function is effected by proteins whereas lipids are largely passive and serve solely in the membrane cohesion. Here we show, using supported 1,2-dioleoyl-sn-glycero-3-phosphocholine lipid bilayers in different saline solutions, that ions can locally induce ordering of the lipid molecules within the otherwise fluid bilayer when the latter is supported. This nanoordering exhibits a characteristic length scale of ∼20 nm, and manifests itself clearly when mechanical stress is applied to the membrane. Atomic force microscopy (AFM) measurements in aqueous solutions containing NaCl, KCl, CaCl2, and Tris buffer show that the magnitude of the effect is strongly ion-specific, with Ca2+ and Tris, respectively, promoting and reducing stress-induced nanotexturing of the membrane. The AFM results are complemented by fluorescence recovery after photobleaching experiments, which reveal an inverse correlation between the tendency for molecular nanoordering and the diffusion coefficient within the bilayer. Control AFM experiments on other lipids and at different temperatures support the hypothesis that the nanotexturing is induced by reversible, localized gel-like solidification of the membrane. These results suggest that supported fluid phospholipid bilayers are not homogenous at the nanoscale, but specific ions are able to locally alter molecular organization and mobility, and spatially modulate the membrane’s properties on a length scale of ∼20 nm. To illustrate this point, AFM was used to follow the adsorption of the membrane-penetrating antimicrobial peptide Temporin L in different solutions. The results confirm that the peptides do not absorb randomly, but follow the ion-induced spatial modulation of the membrane. Our results suggest that ionic effects have a significant impact for passively modulating the local properties of biological membranes, when in contact with a support such as the cytoskeleton

Robust superhydrophobic cellulose nanofiber aerogel for multifunctional environmental applications

The fabrication of superadsorbent for dye adsorption is a hot research area at present. However, the development of low-cost and highly efficient superadsorbents against toxic textile dyes is still a big challenge. Here, we fabricated hydrophobic cellulose nanofiber aerogels from cellulose nanofibers through an eco-friendly silanization reaction in liquid phase, which is an extremely efficient, rapid, cheap, and environmentally friendly procedure. Moreover, the demonstrated eco-friendly silanization technique is easy to commercialize at the industrial level. Most of the works that have reported on the hydrophobic cellulose nanofiber aerogels explored their use for the elimination of oil from water. The key novelty of the present work is that the demonstrated hydrophobic cellulose nanofibers aerogels could serve as superadsorbents against toxic textile dyes such as crystal violet dye from water and insulating materials for building applications. Here, we make use of the possible hydrophobic interactions between silane-modified cellulose nanofiber aerogel and crystal violet dye for the removal of the crystal violet dye from water. With a 10 mg/L of crystal violet (CV) aqueous solution, the silane-modified cellulose nanofiber aerogel showed a high adsorption capacity value of 150 mg/g of the aerogel. The reason for this adsorption value was due to the short-range hydrophobic interaction between the silane-modified cellulose nanofiber aerogel and the hydrophobic domains in crystal violet dye molecules. Additionally, the fabricated silane-modified cellulose nanofiber hydrophobic aerogels exhibited a lower thermal conductivity value of 0.037 W\ub7m -1 K -1 , which was comparable to and lower than the commercial insulators such as mineral wools (0.040 W\ub7m -1 K -1 ) and polystyrene foams (0.035 W\ub7m -1 K -1 ). We firmly believe that the demonstrated silane-modified cellulose nanofiber aerogel could yield an eco-friendly adsorbent that is agreeable to adsorbing toxic crystal violet dyes from water as well as active building thermal insulators

Influence of mono- and divalent ions on the formation of supported phospholipid bilayers via vesicle adsorption

We have used the quartz crystal microbalance with dissipation monitoring (QCM-D) technique to investigate how mono- and divalent cations influence the formation of supported (phospho)lipid bilayers (SPB, SLB), occurring via deposition of nanosized palmitoyloleoyl phosphatidylcholine (POPC) vesicles on a SiO2 support. This process is known to proceed via initial adsorption of intact vesicles until a critical surface coverage is reached, where the combination of vesicle-surface and vesicle-vesicle interaction causes the vesicles to rupture. New vesicles then rupture and the lipid fragments fuse until a final continuous bilayer is formed. We have explored how this process and the critical coverage are influenced by different mono- and divalent ions and ion concentrations, keeping the anions the same throughout the experiments. The same qualitative kinetics is observed for all cations. However, different ions cause quite different quantitative kinetics. When compared with monovalent ions, even very small added concentrations of divalent cations cause a strong reduction of the critical coverage, where conversion of intact, adsorbed vesicles to bilayer occurs. This bilayer promoting effect increases in the order Sr2+ <Ca2+ <Mg2+. Monovalent cations exhibit a much weaker but similar effect in the order Li+ >Na++ >K+. Theresultsareofpracticalvalueforpreparationoflipidbilayersandhelp shed light on the role of ions and on electrostatic effects at membrane surfaces/interfaces. © 2009 American Chemical Society

Formation et caractérisation d'empreintes moléculaires à la surface de bicouches lipidiques supportées

Ce travail explore une nouvelle méthode de création d'empreintes moléculaires sur surfaces basées sur la réorganisation de la surface induite par un template. Des bicouches lipidiques, concidérées comme un liquide bi-dimensionnel, sont utilisées pour induire une séparation locale et leur transition vers une phase gel pour stabiliser la structure imposée par le template. Ainsi, le processus réversible d'impression est basé sur la transition principale des lipides d'une phase fluide vers une phase gel. Des lipides seuls ou des mélanges de lipides, ayant une température de transition de phase (Tm) proche de la température ambiante, sont utilisés. La composition des membranes lipidiques est responsable de la reconnaissance structurale (têtes) et topologique (longueur des chaînes aliphatiques).Suite au peu de connaissances sur la préparation et les propriétés de ces systèmes, une étude de la formation de bicouches lipidiques supportées (SLBs) proche de leur Tm a été initiée. L'influence des paramètres expérimentaux, tels que la composition et le pH du tampon, la concentration des vésicules, la température et la structure chimique des lipides sur le mécanisme et la cinétique de formation des SLBs, a été étudiée par microbalance à cristal de quartz avec mesure de dissipation (QCM-D). Les résultats montrent en détail comment la formation des SLBs depend des paramètres et, ils permettent de spéculer sur un mécanisme de la formation des SLBs.Ensuite, la formation d'empreintes de deux protéines (un inhibiteur de la trypsine et l'annexine V) a été étudiée avec deux mélanges de lipides. Nous avons développé un protocole expérimental pour analyser leur interaction. Les résultats montrent la présence d'empreintes à la surface des SLBs, la reproductibilité et la réversibilité du processus d'impression. Cependant, les expériences préliminaires soulignent le fait que les empreintes ne sont pas encore hautement spécifiques et que le système lipidique doit être optimisé.This work explores the first step towards a new method for creating molecular imprints on surfaces based on template-induced surface reconstruction. Mixed lipid bilayers are used as a two-dimensional liquid for inducing local demixing and their transition to a gel phase for stabilizing the template-imposed structures. Thus the reversible imprinting process is based on the fluid to gel main transition of lipids, especially phospholipids. Single lipids or lipid mixtures having a phase transition temperature near the ambient temperature are used. The composition of lipid membrane is responsible for the structural fit (lipid headgroups) and a topological fit (legth of aliphatic chains).Since very little is known about the preparation and properties of such systems, a study of the formation of supported lipid bilayers (SLBs) close to their phase transition temperature was initiated. The influence of experimental parameters such as composition and pH of the buffer, the vesicle concentration, temperature and the chemical nature of the lipids on the mechanism and the kinetics of the SLB formation have been studied by dissipation enhenced quartz crystal microbalance (QCM-D), atomic force microscopy (AFM) and fluorescence microscopy. The results show in detail how the formation of SPBs depends on experimental parameters and allow to speculate on a more detailed mechanims of SPB formation.Then, the imprint formation of two proteins (trypsin inhibitor and annexin V) have been studied with two lipid mixtures. We have developed an experimental protocol to analyse their interaction. The results show the presence of molecular imprints at the surface of lipid membranes, the reproducibility and the reversibility of molecular imprinting process. However, the preliminary experiments exhibit the fact that the imprints are not yet highly specific and that the lipid system needs to be optimised further.STRASBOURG-Sc. et Techniques (674822102) / SudocSudocFranceF

The impact of molded pulp product process on the mechanical properties of molded Bleached Chemi-Thermo-Mechanical Pulp

AbstractThis study was carried out using bleached softwood Chemi-Thermo-Mechanical Pulp to evaluate the influence of Molded Pulp Products’ manufacturing process parameters on the finished products’ mechanical and hygroscopic properties. A Taguchi table was done to make 8 tests with specific process parameters such as moulds temperature, pulping time, drying time, and pressing time. The results of these tests were used to obtain an optimized manufacturing process with improved mechanical properties and a lower water uptake after sorption analysis and water immersion. The optimized process parameters allowed us to improve the Young’ Modulus after 30h immersion of 58% and a water uptake reduction of 78% with the first 8 tests done.</jats:p

Structure and rheology of cellulose nanofibrils suspensions and hydrogels: effect of volume fraction and ionic strength

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The impact of molded pulp product process on the mechanical properties of molded BCTMP

Abstract This study was carried out using bleached softwood Chemi-Thermo-Mechanical Pulp to evaluate the influence of Molded Pulp Products’ manufacturing process parameters on the finished products’ mechanical and hygroscopic properties. A Taguchi table was done to make 8 tests with specific process parameters such as moulds temperature, pulping time, drying time and pressing time. The results of these tests were used to obtain an optimized manufacturing process with improved mechanical properties and a lower water uptake after sorption analysis and water immersion. The optimized process parameters allowed us to improve the Young’ Modulus after 1h immersion of 58% and a water uptake reduction of 78% with the first 8 tests done.</jats:p

Propriétés rhéologiques et structurales de suspensions de NFC: effet de la fraction volumique et de la force ionique

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Propriétés structurales et thermomécaniques d’aérogels élaborés à partir d’hydrogels de NFC

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