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Paineau E.,University of Lorraine | Bihannic I.,University of Lorraine | Baravian C.,CNRS Mechanical Energy, Theories, and Applications Laboratory | Philippe A.-M.,CNRS Mechanical Energy, Theories, and Applications Laboratory | And 5 more authors.
Langmuir | Year: 2011

In this article, we present a general overview of the organization of colloidal charged clay particles in aqueous suspension by studying different natural samples with different structural charges and charge locations. Small-angle X-ray scattering experiments (SAXS) are first used to derive swelling laws that demonstrate the almost perfect exfoliation of clay sheets in suspension. Using a simple approach based on geometrical constraints, we show that these swelling laws can be fully modeled on the basis of morphological parameters only. The validity of this approach was further extended to other clay data from the literature, in particular, synthetic Laponite. For all of the investigated samples, experimental osmotic pressures can be properly described by a Poisson-Boltzmann approach for ionic strength up to 10-3 M, which reveals that these systems are dominated by repulsive electrostatic interactions. However, a detailed analysis of the Poisson-Boltzmann treatment shows differences in the repulsive potential strength that are not directly linked to the structural charge of the minerals but rather to the charge location in the structure for tetrahedrally charged clays (beidellite and nontronites) undergoing stronger electrostatic repulsions than octahedrally charged samples (montmorillonites, laponite). Only minerals subjected to the strongest electrostatic repulsions present a true isotropic to nematic phase transition in their phase diagrams. The influence of ionic repulsions on the local order of clay platelets was then analyzed through a detailed investigation of the structure factors of the various clay samples. It appears that stronger electrostatic repulsions improve the liquidlike positional local order. © 2011 American Chemical Society.

Fischer B.,HASYLAB | Autenrieth T.,European Plastics Converters EUPC | Wagner J.,University of Rostock
Langmuir | Year: 2010

Highly defined, hybrid inorganic-organic colloidal core-shell particles consisting of a silica core and a shell of fluorinated acrylate are prepared in a two-step route. The core-shell structure of the particles is investigated by means of small-angle X-ray scattering (SAXS). Because of highly acidic sulfonic acid surface groups resulting from the radical initiator sodium peroxodisulfate at the organic shell, long-range electrostatic interactions lead to the formation of liquidlike mesostructures. Increasing the effective interaction by reducing the next-neighbor distances induces a freezing of the liquidlike structures, i.e., a transition to crystalline and glassy structures. Because of the high electron density in the core and the fluorinated polymer shell, these particles are strong X-ray scatterers. In combination with the large number of effective charges and the outstanding monodispersity, these core-shell particles are a promising model system for the investigation of the glass transition by photon correlation spectroscopy employing coherent X-rays. © 2010 American Chemical Society.

Markert C.,Saarland University | Fischer B.,HASYLAB | Wagner J.,University of Rostock
Journal of Applied Crystallography | Year: 2011

In the presence of phosphate anions, spindle-shaped mesoscale hematite particles can be prepared via controlled precipitation of iron(III) chloride. The aspect ratio of the particles is determined by the concentration of phosphate anions selectively covering specific crystal surfaces and thus enabling anisotropic growth of the particles. The scattering function for suspensions of polydisperse spindles is derived and used to analyse the small-angle scattering resulting from these particles. In the presence of an external magnetic field, the particles align perpendicular to the field direction as a result of the negative anisotropy of their magnetic susceptibility . Hereby, an isotropic-nematic phase transition can be induced in external magnetic fields. © 2011 International Union of Crystallography Printed in Singapore - all rights reserved.

Passow C.,University of Rostock | Fischer B.,HASYLAB | Sprung M.,HASYLAB | Kockerling M.,University of Rostock | Wagner J.,University of Rostock
Langmuir | Year: 2014

The dynamic behavior of an inverse ferrofluid consisting of diamagnetic, spherical silica particles suspended in the paramagnetic ionic liquid (EMIm)2[Co(NCS)4] is investigated by means of x-ray photon correlation spectroscopy in the presence of an external magnetic field. Dipole-dipole interactions between the diamagnetic holes in the paramagnetic continuum of the suspending medium induce a direction-dependence of the diffusive motion of the colloidal particles: due to a magnetic repulsion perpendicular to the direction of an external field the diffusive motion of the colloidal particles is selectively frozen in this direction. © 2014 American Chemical Society.

More R.,Max Planck Institute for Chemistry | Busse G.,Max Planck Institute for Chemistry | Hallmann J.,Max Planck Institute for Chemistry | Paulmann C.,Hasylab | And 3 more authors.
Journal of Physical Chemistry C | Year: 2010

This work discusses the photoreaction of crystalline β-9- anthracenecarboxylic acid (C15H10O2, 9AC). The thermally Reversible [4 + 4] photodimerization of crystalline 9AC was investigated with electronic and vibrational spectroscopy and with photocrystallographic techniques. The photocrystallographic studies and their interpretation lead to a complex picture of the mechanism of this photoreaction. The increase of the peak widths during photoreaction is interpreted as a disorder increase in the crystalline lattice. Quantum chemical calculations suggest that this disorder is caused by the formation of various product configurations during photoreaction. At least three possible configurations have been found. Different tautomeric sites lead to an additional disorder parameter adding another complexity in the observed photodimerization reaction. For the overall photodimerization a maximum conversion rate of 75% has been determined. Application of the Johnson, Mehl, Avrami, and Kolmogorov (JMAK) model leads to an extraordinary Avrami parameter suggesting unusual transformation kinetics of the bulk during photoreaction. The unusual Avrami parameter is discussed as an autocatalytic step during photoreaction through an excimer state. It is created by one photoexcited 9AC molecule and a ground state 9AC molecule. Taking into account this additional kinetical pathway, out of statistical reasons additional lattice disordering mechanisms are possible. © 2010 American Chemical Society.

Cordomi A.,University of Barcelona | Prades J.,University of the Balearic Islands | Frau J.,University of the Balearic Islands | Vogler O.,University of the Balearic Islands | And 4 more authors.
Journal of Lipid Research | Year: 2010

An experimental and theoretical study on 1,2-dielaidoyl-sn-glycero-3- phosphoethanolamine (DEPE) membranes containing fatty acids (FAs) was performed by means of X-ray diffraction analysis and molecular dynamics (MD) simulations. The study was aimed at understanding the interactions of several structurally related FAs with biomembranes, which is necessary for further rational lipid drug design in membrane-lipid therapy. The main effect of FAs was to promote the formation of a HII phase, despite a stabilization of the coexisting Lα + HII phases. Derivatives of OA exhibited a specific density profile in the direction perpendicular to the bilayer that reflects differences in the relative localization of the carboxylate group within the polar region of the membrane as well as in the degree of membrane penetration of the FA acyl chain. Hydroxyl and methyl substituents at carbon-2 in the FA acyl chain were identified as effective modulators of the position of carboxylate group in the lipid bilayer. Our data highlight the specific potential of each FA in modulating the membrane structure properties. Copyright © 2010 by the American Society for Biochemistry and Molecular Biology, Inc.

Sharifi S.,University of Sistan and Baluchestan | Marti O.,University of Ulm | Funari S.S.,HASYLAB | Amirkhani M.,University of Ulm
Physics and Chemistry of Liquids | Year: 2013

We study the effect of polyethylene glycol (PEG) on the dynamic and structure of water droplets at the reverse sodium bis-(2-ethylhexyl) sulfosuccinate (AOT) microemulsion. The mixture of water and oil with anionic surfactant AOT can form microemulsion. The dynamic of microemulsion in the presence of PEG is investigated by photon correlation spectroscopy technique. We mainly focus on the variation of the translational diffusion behaviour as a function of the polymer concentration and polymer length scale. By increasing the content of the lowest PEG length scale (Mn = 285), the dynamic of microemulsion slows down. In addition, one relaxation process is distinguished for all polymer concentration. However, for the two higher polymer length scale (Mn = 2200 and 6000), two relaxations are observed and the dynamic of microemulsion speeds up. We used the small angle X-ray scattering technique to monitor the size and the polydispersity of the mixture system (AOT microemulsion/PEG). © 2013 Taylor and Francis Group, LLC.

Andreozzi P.,University of Rome La Sapienza | Funari S.S.,HASYLAB | La Mesa C.,University of Rome La Sapienza | Mariani P.,Marche Polytechnic University | And 3 more authors.
Journal of Physical Chemistry B | Year: 2010

Sodium dodecylsulfate (SDS) and cetyltrimethylammonium bromide (CTAB) dispersed in aqueous solution form catanionic vesicles. Depending on composition, such vesicles show different net charge, stability, and interaction capability, indicative of the strong impact that catanionic systems may have in gene therapy and drug delivery technologies. To reveal the interplay among composition, net charge, sensitivity to temperature changes, vesicle size, and inner structure, a series of experiments on catanionic vesicles prepared at different SDS/CTAB mole ratios was performed. Dynamic light scattering, small-angle X-ray scattering, and ζ-potential experiments allow one to characterize an unexpected critical phenomenon at the nanoscale level. On heating, vesicles increase in size, but at a critical temperature an abrupt vesicle size reduction has been observed, together with a transition from multi- to a unilamellar state. The critical temperature regularly depends on the SDS/CTAB mole ratio. The unilamellar state obtained upon heating is retained for weeks. These phenomena suggest a new way to produce stable unilamellar vesicles with tunable size and charge. © 2010 American Chemical Society.

Prades J.,University of the Balearic Islands | Funari S.S.,HASYLAB | Gomez-Florit M.,University of the Balearic Islands | Vogler O.,University of the Balearic Islands | Barcelo F.,University of the Balearic Islands
Molecular Membrane Biology | Year: 2012

2-Hydroxyoleic acid (2OHOA) is a synthetic fatty acid with antihypertensive properties that is able to alter structural membranes properties. The main purpose of this study was to analyze the effect of 2OHOA on the membrane architecture in cholesterol (Cho)-rich domains. For this purpose, model membranes mimicking the composition of lipid rafts and PC- or PE-Cho-rich domains were examined in the absence and presence of 2OHOA by synchrotron X-ray diffraction, atomic force microscopy (AFM) and microcalorimetry (DSC) techniques. Our results demonstrate that 2OHOA phase separates from lipid raft domains and affects the lateral organization of lipids in the membrane. In model raft membranes, 2OHOA interacted with the sphingomyelin (SM) gel phase increasing the thickness of the water layer, which should lead to increased bilayer fluidity. The hydrogen binding competition between 2OHOA and Cho could favour the enrichment of 2OHOA in SM domains separated from the SM-Cho domains, resulting in an enhanced phase separation into SM-2OHOA-rich liquid-disordered (non-raft) and SM-Cho-rich liquid-ordered (raft) domains. The segregation into 2OHOA-rich/Cho-poor and 2OHOA-poor/Cho-rich domains was also observed in PC bilayers. © 2012 Informa UK, Ltd.

Prades J.,University of the Balearic Islands | Vogler O.,University of the Balearic Islands | Alemany R.,University of the Balearic Islands | Gomez-Florit M.,University of the Balearic Islands | And 3 more authors.
Biochimica et Biophysica Acta - Biomembranes | Year: 2011

Free triterpenic acids (TTPs) present in plants are bioactive compounds exhibiting multiple nutriceutical activities. The underlying molecular mechanisms have only been examined in part and mainly focused on anti-inflammatory properties, cancer and cardiovascular diseases, in all of which TTPs frequently affect membrane-related proteins. Based on the structural characteristics of TTPs, we assume that their effect on biophysical properties of cell membranes could play a role for their biological activity. In this context, our study is focused on the compounds, oleanolic (3β-hydroxy-12- oleanen-28-oic acid, OLA), maslinic (2α,3β-dihydroxy-12-oleanen-28- oic acid, MSL) and ursolic ((3β)-3-hydroxyurs-12-en-28-oic acid, URL) as the most important TTPs present in orujo olive oil. X-ray diffraction, differential scanning calorimetry, 31P nuclear magnetic resonance and Laurdan fluorescence data provide experimental evidence that OLA, MSL and URL altered the structural properties of 1,2-dipalmitoyl-sn-glycero-3- phosphatidylcholine (DPPC) and DPPC-Cholesterol (Cho) rich membranes, being located into the polar-hydrophobic interphase. Specifically, in DPPC membranes, TTPs altered the structural order of the Lβ′, phase without destabilizing the lipid bilayer. The existence of a nonbilayer isotropic phase in coexistence with the liquid crystalline Lα phase, as observed in DPPC:URL samples, indicated the presence of lipid structures with high curvature (probably inverted micelles). In DPPC:Cho membranes, TTPs affected the membrane phase properties increasing the Laurdan GP values above 40 °C. MSL and URL induced segregation of Cho within the bilayer, in contrast to OLA, that reduced the structural organization of the membrane. These results strengthen the relevance of TTP interactions with cell membranes as a molecular mechanism underlying their broad spectrum of biological effects. © 2010 Elsevier B.V. All rights reserved.

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