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Hamburg, Germany

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. Source


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. Source


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. Source


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. Source


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. Source

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