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Kaufmann S.,ETH Zurich | Borisov O.,Institute Pluridisciplinaire Of Recherche Sur Lenvironnement Et Les Materiaux | Textor M.,ETH Zurich | Reimhult E.,University of Natural Resources and Life Sciences, Vienna
Soft Matter

Supported poly(ethylene glycol)-lipid bilayers (PEG-SLBs) are of interest as scaffolds in future generations of transmembrane protein sensor platforms and in their own right as model systems to investigate the behavior of glycosylated biological membranes. We investigate the effect of PEG-lipid concentration from the PEG dilute mushroom to brush regime in PEG-SLBs on lipid mobility and membrane behavior under locally applied compression force. Fluorescence recovery after photobleaching (FRAP) measurements demonstrated a gradual transition of the POPC lipid bilayer from liquid crystalline to gel phase for a PEG-lipid concentration below 10 mol% and PEG molecular weight of 2000 Da. The observed control of lipid phase behavior already at low interacting polymer lipid concentrations could have wider implications for the understanding of biological membrane systems. Further mechanical properties of the PEG-SLBs were probed by force-distance measurements with an atomic force microscope (AFM). Significant differences in the compression of mobile and immobile tethered polymer chains were observed. The results were interpreted through a model describing compression force profiles for polymers attached to mobile tethers, which reproduces a unique transition observed as mobile polymer tethers are locally depleted under compression. © 2011 The Royal Society of Chemistry. Source

Pedrero Z.,University of Pau and Pays de lAdour | Bridou R.,Institute Pluridisciplinaire Of Recherche Sur Lenvironnement Et Les Materiaux | Mounicou S.,University of Pau and Pays de lAdour | Guyoneaud R.,Institute Pluridisciplinaire Of Recherche Sur Lenvironnement Et Les Materiaux | And 2 more authors.
Environmental Science and Technology

Microbial activity is recognized to play an important role on Hg methylation in aquatic ecosystems. However, the mechanism at the cellular level is still poorly understood. In this work subcellular partitioning and transformation of Hg species in two strains: Desulfovibrio sp. BerOc1 and Desulfovibrio desulfuricans G200 (which exhibit different Hg methylation potential) are studied as an approach to the elucidation of Hg methylation/demethylation processes. The incubation with isotopically labeled Hg species (199Hgi and Me201Hg) not only allows the determination of methylation and demethylation rates simultaneously, but also the comparison of the localization of the originally added and resulting species of such metabolic processes. A dissimilar Hg species distribution was observed. In general terms, monomethylmercury (MeHg) is preferentially localized in the extracellular fraction; meanwhile inorganic mercury (Hgi) is associated to the cells. The investigation of Hg binding biomolecules on the cytoplasmatic and extracellular fractions (size exclusion chromatography coupled to ICP-MS) revealed noticeable differences in the pattern corresponding to the Hg methylating and nonmethylating strains. © 2012 American Chemical Society. Source

Bourhis K.,Institute Pluridisciplinaire Of Recherche Sur Lenvironnement Et Les Materiaux | Bourhis K.,Laboratoire Chimie Appliquee a lArt et a lArcheologie | Blanc S.,Institute Pluridisciplinaire Of Recherche Sur Lenvironnement Et Les Materiaux | Mathe C.,Laboratoire Chimie Appliquee a lArt et a lArcheologie | And 2 more authors.
Applied Clay Science

To better understand the interactions between organic (natural flavonol) and inorganic (alum) constituents of "Stil de grain", yellow lake model compounds based on quercetin as a chromophore were prepared and compared in terms of color and stability with those of historical, reconstituted samples. The extraction process of the natural dyes was optimized by varying the quantity of Rhamnus berries, the solvent, the temperature, the time and the extraction method in order to evaluate the role of the natural dye composition on the lake properties. The samples (chromophores and their Al(III) complexes embedded in an aluminum hydroxide matrix) were characterized by high performance liquid chromatography-photodiode array (HPLC-PDA), UV-Visible spectroscopy and X-ray photoelectron spectroscopy (XPS). The conditions of preparation (solvent, temperature, time, extraction method) were correlated to physico-chemical features. Extraction of quercetin from the lake was optimized by using acetic acid buffer and ultrasound. This procedure will enable an improved analysis to be made of current historical materials. © 2011 Elsevier B.V. Source

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