Cetylpyridinium (CP+) is a cationic surfactant that can be found in various effluents and known due its toxicity against aquatic organisms. The removal of this compound was investigated in water solutions by electrocoagulation, phosphate-assisted electrocoagulation and adsorption on electrogenerated adsorbents. Electrocoagulations were carried out with aluminum electrodes in CP+ synthetic solutions. After 2 h of electrolysis in 0.1 M NaCl solutions, CP+ was mainly removed by electroreduction at calculated rates of 0.024 and 0.0416 mu mol/C corresponding to abatements of 28% and 24% for starting concentrations of CP+ at 0.5 mM and 1:0 mM, respectively. The voltammetric study on steel or graphite electrodes confirmed a possible electroreduction of CP+ which may explain its removal during electrolysis. The change of the cathode from aluminum to carbon or steel did not change notably the removal efficiency of electrolysis in 0.1 M NaCl solution. However, after 2 h of electrolysis in 0.1 M NaCl in the presence of 0.1 M phosphate buffer, CP+ was mainly removed by adsorption on electrogenerated aluminum phosphate with rates of 0.0694 and 0.138 mu mol/C corresponding to abatements of 80% for 0.5 or 1 mM CP+ solutions. The key role of phosphate ions was proved by adsorption experiments. The electro-synthesized alumina adsorbed CP+ with a removal capacity of 10.2 mg/g. But on electro-synthesized and chemical-synthesized aluminum phosphate the removal capacities were 94.2 and 165.3 mg/g, respectively. (C) 2015 Elsevier B.V. All rights reserved.

Understanding the molecular mechanism of the interaction of amphipathic and antimicrobial peptides with membranes is of fundamental interest, especially because of the potential of amphipathic peptides as therapeutics. The most studied amphipathic peptides in this context are certainly melittin, magainin and alamethicin, of which melittin is the only one to exhibit a powerful hemolytic and therefore toxic action. Herein we study the effect of the antimicrobial but hemolytic peptide melittin on the bending elasticity of giant unilamellar vesicles (GUVs). The results are compared to the effects of non-hemolytic amphipathic peptides such as alamethicin. We found that monomeric melittin acts very differently on the membrane mechanical properties. Strikingly, the difference is the most pronounced for low peptide concentrations, relevant for the hemolytic action. This gives some insight into the subtle nature of this peptide-membrane interaction. Furthermore, the results show that bending elasticity measurements might be a sensitive way to distinguish between lytic and non-lytic antimicrobial peptides.

We investigated the influence of melittin on the organization of macroscopically oriented dipalmitoylphosphatidylcholine multilayers at 100% relative humidity as a function of temperature and peptide content by small-angle X-ray diffraction. Experiments were done under conditions known to lead to disk formation, a long-lived metastable state, below the transition temperature (T-m), of the pure lipid and in excess water. For T>T-m the system stays in a lamellar organization up to a lipid-to-peptide molar ratio, R-i, of 5, that is, the lowest R-i investigated herein. It was found that the macroscopically oriented system shows a rather complex behavior only below T-m. For T<T-m and for low peptide concentrations (R-i = 200) formation of the rippled phase was found to be abolished. At R-i = 100 melittin induces the formation of a rippled phase at relative low temperature (29 degrees C). At higher peptide content and T<T-m melittin induces the formation of a hexagonal phase, presumably metastable, in coexistence with a lamellar gel phase. A parallel is made with the well-known disk formation. An interpretation in terms of mismatch between the length of the peptide helix and the bilayer thickness is proposed.

A 92S6 glass with a composition in the ternary system SiO2–CaO–P2O5 was prepared by sol–gel method. Material was synthesized at temperatures ranging from 20 to 60°C for 24h using C16TMABr (C19H42BrN) as surfactant. Then properties of these synthesized glasses were investigated. The structure, morphology and textural properties were studied by means of X-ray powder diffraction (XRD), analysis of nitrogen adsorption/desorption isotherms (BET and BJH methods), and by scanning electronic microscopy (SEM) and energy dispersive spectroscopy (EDS). In vitro glasses bioactivity was evaluated by soaking them in simulated body fluid. The resulting solutions were analyzed by inductively coupled plasma optical emission spectrometry (ICP-OES). Results indicate that bioactivity increased with synthesis temperature. This result is principally related to differences in textural properties.

AbstractElectrolyses with aluminum electrodes were performed to control the removal of dodecyl sulfate (DS) from aqueous solutions. When electrolyses were conducted in 0.1 M HCl solution and in the presence of 6.9–13.8 mmol L−1 of DS the pH increased and electrogenerated Al3+ ions and DS anion led to the formation of a precipitate after an induction period. The abatement of DS anion was about 80% at a concentration of 13.8 mmol L−1, when the molar ratio DS/Al was near 3. For electrolyses carried out in 0.1 M NaCl solution, the pH increased from 5 to 9.4 and an alumina precipitate was formed. The removal of DS anion was less efficient than in acid solution. The abatement did not depend upon the DS concentration in the range 6.9–13.8 mmol L−1 and it slightly increased until 20% with the electrolysis time. These results were in agreement with a DS anion adsorption on electro-generated alumina which was investigated. The adsorption capacity was found at 0.865 mmol g−1 of alumina. This selective removal of DS ...

We present a brief review of over 30 years of research that led step-by-step to a reproductive method to determine bending elasticity, based on the analysis of thermal shape fluctuations of giant unilamellar vesicles.We also acknowledge the strong contribution of Marin D. Mitov and of a long-lasting French-Bulgarian cooperation in this research.The chapter starts with an introduction of the main theoretical notions necessary to understand this experimental method.Then we review the link between this physical model and the experimental measurable quantities, that is, the amplitudes of the vesicle thermal shape fluctuations.Further, we discuss the technical progress necessary to gradually overcome some principal technical limitations.Finally, we summarize what is currently the most accurate technique for bending elasticity measurements and briefly review published bending elasticity values obtained using thermally induced shape fluctuations of quasi-spherical giant unilamellar vesicles.

We show how to greatly improve precision when determining bending elasticity of giant unilamellar vesicles. Taking advantage of the well-known quasi-spherical model of liposome flickering, we analyze the full probability distributions of the configurational fluctuations instead of limiting the analysis to the second moment measurements only as usually done in previously published works. This leads to objective criteria to reject vesicles that do not behave according to the model. As a result, the confidence in the bending elasticity determination of individual vesicles that fit the model is improved and, consequently, the reproducibility of this measurement for a given membrane system. This approach uncovers new possibilities for bending elasticity studies like detection of minute influences by solutes in the buffer or into the membrane. In the same way, we are now able to detect the inhomogeneous behavior of giant vesicle systems such as the hazardous production of peroxide in bilayers containing fluorescent dyes.

Fluorescent probes are used in membrane biophysics studies to provide information about physical properties such as lipid packing, polarity and lipid diffusion or to visualize membrane domains. However, our understanding of the effects the dyes themselves may induce on the membrane structure and properties are sparse. As mechanical properties like bending elasticity were already shown to be highly sensitive to the addition of "impurities" into the membranes, we have investigated the impact of six different commonly used fluorescent membrane probes (LAURDAN, TR-DPPE, Rh-DPPE, DiIC18, Bodipy-PC and NBD-PC) on the bending elasticity of dye containing POPC GUVs as compared to single component POPC GUVs. Small changes in the membrane bending elasticity compared to single POPC bilayers are observed when 2 mol% of Rh-DPPE, Bodipy-PC or NBD-PC are added in POPC membranes. These binary membranes are showing non reproducible mechanical properties attributed to a photo-induced peroxidation processes that may be controlled by a reduction of the fluorescent dye concentration. For TR-DPPE, a measurable decrease of the bending elasticity is detected with reproducible bending elasticity measurements. This is a direct indication that this dye, when exposed to illumination by a microscope lamp and contrary to Rh-DPPE, does not induce chemical degradation. At last, LAURDAN and DiIC18 probes mixed with POPC do not significantly affect the bending elasticity of pure POPC bilayers, even at 2 mol%, suggesting these latter probes do not induce major perturbations on the structure of POPC bilayers.

Membranes mechanical properties are affected by solvent properties, i.e. the salt content. In this study, we use POPC GUVs (Giant Unilamellar Vesicles) as model membranes and we measure the membrane mechanical moduli by flickering analysis and micropipette technique for a series of alkali salt solutions. Salt concentration effects and ion specificity are investigated in these measurements. Membrane mechanical moduli are shown to display a complex dependence on the salt solution composition.

Lanthanide containing octahedral hexanuclear complexes with general chemical formula [Ln(60)(OH)(8)(NO3)(6)(H2O)(x)]2NO(3).yH(2)O where Ln = Ce-Lu (except Pm) or Y, x = 0, 6, 12, 14 or 16 and y = 0, 2, 4 or 5 constitute a great family of polymorphic compounds The synthesis and the crystal structures of all these compounds are overviewed. The hydration/ dehydration processes that allow the structural transitions from one compound to another are described The crystal structure of compounds with general chemical formula [Ln(6)O(OH)(8)(NO3)(6)(H2O)(6)]center dot 2NO(3) where Ln = Ce-Lu (except Pm) or Y is described It has been solved on the basis of a powder XRD diagram The use of such hexanuclear complexes as molecular precursors for new materials is also discussed (C) 2010 Academic des sciences. Published by Elsevier Masson SAS All rights reserved.

We report a small angle X-ray scattering study on the liquid phase of a series of room temperature ionic liquids and their binary mixtures. The ionic liquids studied belong to the tri-alkyl-methyl-ammonium family with bis(trifluoromethanesulfonyl)amide as the anion and were studied as a function of alkyl chain length. These ionic liquids were found to exhibit marked nanoscale ordering in their isotropic liquid state as judged from the small angle X-ray scattering. The observed structural ordering is of supramolecular order and depends strongly on the length of the cation hydrophobic side chain. Moreover, the data can be analyzed on the basis of a disordered smectic A phase, consisting of strongly interdigitated bilayers that sequester the ionic liquid into polar and hydrophobic regions. These findings were also found to be consistent with density data of these molten salts. Additionally, we demonstrate that this experimentally observed nanostructuring can further be fine-tuned using binary mixtures.

The Hofmeister series for salt solutions appears in many contexts of biophysics and physical chemistry, e.g. enzymatic activity, stability of biomolecules like the proteins, polymer folding and interfacial tension, while its effect on membrane mechanical properties has only been sparsely explored. With a newly established electroformation technique [1], we have been able to form GUVs (Giant Unilamellar Vesicles) in presence of high salt concentrations. In this study, we have explored the electroformation technique to form POPC GUVs in presence of different sodium halide solutions, and using the flickering technique, we have measured their effects on the bending elastic modulus of POPC bilayers. [1] Pott T., H. Bouvrais, P. Méléard, “Giant unilamellar vesicle under physiologically relevant conditions”, Chemistry and physics of lipids, Vol. 154, 2008, pp: 115-119.

Giant unilamellar vesicles (GUVs) are well-known model systems, especially because they are easily observable using optical microscopy. In this chapter, we revisit in detail the versatile GUV electroformation protocol. We demonstrate how GUV electroformation can be adapted to various membrane systems including synthetic lipid mixtures, natural lipid extracts, and bilayers containing membrane proteins. Further, we show how to adjust this protocol to a given aqueous environment and prove that GUVs can be obtained under physiologically relevant conditions, that is, in the presence of electrolytes. Finally, we provide firm evidence that electroformation is a method of choice to produce giant vesicles from native cell membranes. This is illustrated with the example of GUV electroformation from red blood cell ghosts in a physiologically pertinent buffer. GUVs obtained in this manner maintain the native membrane asymmetry, thereby validating the physiological relevance of GUV electroformation.

Magainin 2 belongs to the family of peptides, which interacts with the lipid membranes. The present work deals with the effect of this peptide on the mechanical properties of 1-palmitoyl-2-oleoyl-sn-glycerol-3-phosphocholine Giant Unilamellar Vesicle, characterized by the bending stiffness modulus. The bending elastic modulus is measured by Vesicle Fluctuation Analysis at biologically relevant pH and physiological buffer conditions and shows a dramatic decrease with increasing peptide concentration. The observed bilayer softening is interpreted in terms of a continuum model describing perturbations on the membrane organization. Our analysis suggests that the adsorbed peptides give rise to considerable local curvature disruptions of the membrane.

We present an upgrade to the giant unilamellar vesicle (GUV) electroformation method allowing easy GUV production in different buffers and with various membrane compositions. Our experimental results reveal that lipid deposits obtained from aqueous liposome or proteoliposome dispersions are highly efficient for GUV electroformation. This is related to the ability of such dispersions to produce readily well-oriented membrane stacks. Furthermore, we present a protocol for GUV electroformation in various aqueous media, including electrolyte-containing buffers at characteristic concentrations of biological fluids. This work unlocks historical barriers to GUV applications in scientific fields like biology, biochemistry, or biophysics where membrane composition, as well as its aqueous environment, should be adapted to biological significance.

We investigate the bending elasticity of lipid membranes with the increase of the alamethicin concentrations in the membrane via analysis of the thermally induced shape fluctuations of quasi-spherical giant vesicles. Our experimental results prove the strong influence of alamethicin molecules on the bending elasticity of diphytanoyl phosphatidylcholine and dilauroyl phosphatidylcholine membranes even in the range of very low peptide concentrations (less than 10(-3) mol/mol in the membrane). The results presented in this work, testify to the peripheral orientation of alamethicin molecules at low peptide concentrations in the membrane for both types of lipid bilayers. An upper limit of the concentration of the peptide in the membrane is determined below which the system behaves as an ideal two-dimensional solution and the peptide molecules have a planar orientation in the membrane.

A new experimental set-up for measuring the bending elastic modulus, kc, by the analysis of thermally induced shape fluctuations of quasi spherical giant vesicles is proposed. The stroboscopic video microscopy has better time resolution than the continuous illumination video microscopy. Consequently, it is no more necessary to use a “correction factor” to account for the artifact due to the finite video camera integration time. The experimental data so obtained can be completely interpreted using only two model parameters, kc, and the dimensionless membrane tension, σ̄. PACS number: 87.16.Dg

In this work we propose an improved experimental set-up for the measurement of the bending elastic modulus by the analysis of thermally induced shape fluctuations of quasi spherical GUVs using stroboscopic illumination. The stroboscopic video microscopy has better time resolution than the continuous illumination video microscopy. Consequently, it is no more necessary to use a "correction factor" to account for the artifact due to the finite video camera integration time. The experimental data, acquired under the stroboscopic illumination can be completely interpreted using only two model parameters, the bending elastic modulus and the dimensionless membrane tension.