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See detailCrystal chemistry of the hydrothermally synthesized Na-2(Mn1-xFex2+)(2)Fe3+(PO4)(3) alluaudite-type solid solution
Hatert, Frédéric ULg; Rebbouh, Leila; Hermann, Raphaël P. et al

in American Mineralogist (2005), 90(4), 653-662

Several compounds of the Na-2(Mn1-xFex2x)(2)Fe3+(PO4)(3) solid solition have been hydrothermally synthesized at 400 degrees C and 1 kbar; pure alluaudite-like compounds have been obtained for x = 0.00, 0 ... [more ▼]

Several compounds of the Na-2(Mn1-xFex2x)(2)Fe3+(PO4)(3) solid solition have been hydrothermally synthesized at 400 degrees C and 1 kbar; pure alluaudite-like compounds have been obtained for x = 0.00, 0.25, 0.50, 0.75, and 1.00. Rietveld refinements of the powder X-ray diffraction patterns indicate the presence of Na+ at the Al and A2' sites, Mn2+ and Fe2+ at the M1 site, and Mn2+, Fe2+, and Fe3+ at the M2 site. The presence of small amounts of Na+ at the M1 site and Mn2+ at the Al site indicates a partially disordered distribution of these cations. An excellent linear correlation has been established between the M1-M2 distance and the energy of the infrared band attributed to the M2+-O vibrations. The Mossbauer spectra, measured between 85 and 295 K, were analyzed in terms of a model which includes the next-nearest neighbor interactions at the M2 and M1 crystallographic sites. Fe2+ and Fe3+ isomer shifts are typical of the alluaudite structure and exhibit the expected second-order Doppler shift. The derived iron vibrating masses and Mossbauer lattice temperatures are within the range of values expected for iron cations in all octahedral environment. The Fe2+ and Fe3+ quadrupole splittings are typical of the alluaudite structure, and the temperature dependence of the Fe2+ quadrupole splitting was fit with the Ingalls model, which yielded a ground state orbital splitting of ca. 460 to 735 cm(-1) for the Fe2+ sites. The isomer shifts and quadrupole splittings of Fe2+ at the M1 site are larger than those of Fe2+ at M2, indicating that the M1 site is both larger and more distorted than the M2 site. [less ▲]

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See detailCrystal Growth, Transport, and the Structural and Magnetic Properties of Ln4FeGa12 with Ln = Y, Tb, Dy, Ho, and Er
Drake, B. L.; Grandjean, Fernande ULg; Okudzeto, E. K. et al

in Inorganic Chemistry (2010), 49

Ln4FeGa12, where Ln is Y, Tb, Dy, Ho, and Er, prepared by flux growth, crystallize with the cubic Y4PdGa12 structure with the space group and with a = 8.5650(4), 8.5610(4), 8.5350(3), 8.5080(3), and 8 ... [more ▼]

Ln4FeGa12, where Ln is Y, Tb, Dy, Ho, and Er, prepared by flux growth, crystallize with the cubic Y4PdGa12 structure with the space group and with a = 8.5650(4), 8.5610(4), 8.5350(3), 8.5080(3), and 8.4720(4) Å, respectively. The crystal structure consists of an iron-gallium octahedra and face sharing rare-earth cuboctahedra of the Au3Cu type. Y4FeGa12 exhibits weak itinerant ferromagnetism below 36 K. In contrast, Tb4FeGa12, Dy4FeGa12, Ho4FeGa12, and Er4FeGa12 order antiferromagnetically with maxima in the molar magnetic susceptibilities at 26, 18.5, 9, and 6 K. All the compounds exhibit metallic electric resistivity and their iron-57 Mössbauer spectra, obtained between 4.2 and 295 K, exhibit a single-line absorption with a 4.2 K isomer shift of ca. 0.50 mm/s, a shift that is characteristic of iron in an iron-gallium intermetallic compound. A small but significant broadening in the spectral absorption line width is observed for Y4FeGa12 below 40 K and results from the small hyperfine field arising from its spin-polarized itinerant electrons [less ▲]

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See detailA crystal of a typical EF-hand protein grown under microgravity diffracts X-rays beyond 0.9 Å resolution
Declercq, Jean-Paul; Evrard, Christine ULg; Carter, Daniel et al

in Journal of Crystal Growth (1999), 196

We report on our recent observation that crystals of a typical EF-hand protein (parvalbumin or Pa; Ca-loaded component from pike muscle with isoelectric point 4.10) grown under microgravity conditions ... [more ▼]

We report on our recent observation that crystals of a typical EF-hand protein (parvalbumin or Pa; Ca-loaded component from pike muscle with isoelectric point 4.10) grown under microgravity conditions diffract X-rays to a resolution better than 0.9 Å. The crystals were grown in the US space shuttle and characterized at 100 K, using an X-ray synchrotron beam. An effective atomic resolution has been achieved and substates in the conformation of the protein are observed. Large crystals up to 3 mm were also obtained. [less ▲]

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See detailCrystal Plasticity Modelling of Monotonic Shear Tests on Pure Titanium
Hammami, Walid ULg; Bouvier, S.; Duchene, Laurent ULg et al

in Oñate, E.; Owen, D. R. J. (Eds.) Computational plasticity X. Fundamentals and applications (2009, September)

This study consists in the modelling of shear tests performed on pure titanium using a polycrystalline model. Numerical and experimental results are presented.

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See detailCrystal plasticity prediction of Lankford coefficient using the MULTISITE model: influence of the critical resolved shear stresses
Hammami, Walid ULg; Delannay, Laurent; Duchene, Laurent ULg et al

in International Journal of Material Forming (2009, August), 2(Supplément 1), 65-68

The MULTISITE model [1] is based on polycrystalline plasticity and the underlying hypotheses of the model are (i) that the deformation of each grain is significantly influenced by the interaction with a ... [more ▼]

The MULTISITE model [1] is based on polycrystalline plasticity and the underlying hypotheses of the model are (i) that the deformation of each grain is significantly influenced by the interaction with a limited number of adjacent grains, and (ii) that local strains deviate from their macroscopic average according to specific “relaxation modes”. The LAMEL model [2] is reformulated into the more general elastic-viscoplastic MULTISITE model permitting various relaxation modes. This model has been validated for cubic materials but hexagonal close-packed (HCP) crystals usually demonstrate larger anisotropy than cubic crystals. The model was used to simulate uniaxial tensile tests performed on rolled sheets made of Ti-6Al-4V. The Lankford coefficients (r) calculated in various directions in the plane of the sheet were analysed. In this study, different grain interaction hypotheses were tested. Besides, it appeared that the value of the critical resolved shear stresses (CRSS) of the different slip system families of the HCP metal had significant effects on the results. Their influence as well as the influence of the strain rate sensitivity parameter was examined. [less ▲]

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See detailCrystal structure and activity of Bacillus subtilis YoaJ (EXLX1), a bacterial expansin that promotes root colonization.
Kerff, Frédéric ULg; Amoroso, Ana Maria ULg; Herman, Raphaël ULg et al

in Proceedings of the National Academy of Sciences of the United States of America (2008), 105(44), 16876-81

We solved the crystal structure of a secreted protein, EXLX1, encoded by the yoaJ gene of Bacillus subtilis. Its structure is remarkably similar to that of plant beta-expansins (group 1 grass pollen ... [more ▼]

We solved the crystal structure of a secreted protein, EXLX1, encoded by the yoaJ gene of Bacillus subtilis. Its structure is remarkably similar to that of plant beta-expansins (group 1 grass pollen allergens), consisting of 2 tightly packed domains (D1, D2) with a potential polysaccharide-binding surface spanning the 2 domains. Domain D1 has a double-psi beta-barrel fold with partial conservation of the catalytic site found in family 45 glycosyl hydrolases and in the MltA family of lytic transglycosylases. Domain D2 has an Ig-like fold similar to group 2/3 grass pollen allergens, with structural features similar to a type A carbohydrate-binding domain. EXLX1 bound to plant cell walls, cellulose, and peptidoglycan, but it lacked lytic activity against a variety of plant cell wall polysaccharides and peptidoglycan. EXLX1 promoted plant cell wall extension similar to, but 10 times weaker than, plant beta-expansins, which synergistically enhanced EXLX1 activity. Deletion of the gene encoding EXLX1 did not affect growth or peptidoglycan composition of B. subtilis in liquid medium, but slowed lysis upon osmotic shock and greatly reduced the ability of the bacterium to colonize maize roots. The presence of EXLX1 homologs in a small but diverse set of plant pathogens further supports a role in plant-bacterial interactions. Because plant expansins have proved difficult to express in active form in heterologous systems, the discovery of a bacterial homolog opens the door for detailed structural studies of expansin function. [less ▲]

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See detailCrystal Structure and Local Disorder in Modern and Ancient Prussian Blue Pigments
Samain, Louise ULg; Martinetto, Pauline; Bordet, Pierre et al

Poster (2012, June 06)

The necessity of understanding degradation and alteration processes in a painting's materials is well established for preservation and art history issues. The task is however complex because of the highly ... [more ▼]

The necessity of understanding degradation and alteration processes in a painting's materials is well established for preservation and art history issues. The task is however complex because of the highly heterogeneous character of a paint layer, which consists of a mixture of pigments and a binder on a support. In this context we focus on a particular pigment, Prussian blue. Prussian blue is a hydrated ferric ferrocyanide complex, first synthesized in 1704 in Berlin. It has been widely used by artists until the 1970's. However reports of discoloration had already appeared in eighteenth and nineteenth century books. To date, little attention has been devoted to the understanding of the degradation processes of Prussian blue in paint layers. The preparation methods of Prussian blue were rapidly recognized as a contributory factor in the fading of the pigment because they lead to the introduction of impurities in its structure. The crystal structure of Prussian blue is notoriously complex because of the presence of vacancies and local disorder. Unresolved questions about the crystal structure of the soluble variety of Prussian blue, i.e., Prussian blue containing alkali cations, are still found in the literature. We reproduced modern and ancient preparation methods of Prussian blue and analyzed the obtained pigments by high-energy powder diffraction at the beamline ID11, ESRF, Grenoble and at the beamline CRISTAL, Soleil, Paris. The crystal structure of soluble Prussian blue was reviewed by Rietveld refinement and appears to contain approximately a quart of iron(II) sites vacant, similarly to the well-known insoluble crystal structure. The refinement of the pair distribution function extracted from the total scattering signal revealed a local structure different from the average one. The local arrangements are best described by combining three different substructures with different numbers of vacancies and vary upon the type of synthesis. The PDF analysis also evidenced the formation of nanocrystalline ferrihydrite and alumina hydrate in Prussian blue pigments synthesized according to eighteenth-century recipes. The local disorder and the presence of an undesirable iron compound in Prussian blue can help to better understand the degradation mechanisms in paint layers containing this pigment. [less ▲]

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See detailCrystal structure of 7-chloro-3-isopropoxy-4H-1,2,4-benzothiadiazine 1,1-dioxide monohydrate, C10H13CIN2O4S H2O
Dupont, L.; Boverie, S.; Pirotte, Bernard ULg et al

in Zeitschrift für Kristallographie. New Crystal Structures (2005), NCS 220

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See detailCrystal structure of 7-chloro-3-isopropylamino-4H-1,2,4-benzothiadiazine 1,1-dioxide, C10H12CIN3O2S
Dupont, L.; Pirotte, Bernard ULg; De Tullio, Pascal ULg

in Zeitschrift für Kristallographie. New Crystal Structures (2005), NCS 220

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See detailCrystal structure of 7-chloro-3-isopropylsulfanyl-4H-1,2,4-benzothiadiazine 1,1-dioxide, C10H11CIN2O2S2
Dupont, L.; Boverie, S.; De Tullio, Pascal ULg et al

in Zeitschrift für Kristallographie. New Crystal Structures (2005), NCS 220

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See detailCrystal structure of a cold-adapted class C beta-lactamase.
Michaux, Catherine; Massant, Jan; Kerff, Frédéric ULg et al

in FEBS Journal (2008), 275(8), 1687-97

In this study, the crystal structure of a class C beta-lactamase from a psychrophilic organism, Pseudomonas fluorescens, has been refined to 2.2 A resolution. It is one of the few solved crystal ... [more ▼]

In this study, the crystal structure of a class C beta-lactamase from a psychrophilic organism, Pseudomonas fluorescens, has been refined to 2.2 A resolution. It is one of the few solved crystal structures of psychrophilic proteins. The structure was compared with those of homologous mesophilic enzymes and of another, modeled, psychrophilic protein. The elucidation of the 3D structure of this enzyme provides additional insights into the features involved in cold adaptation. Structure comparison of the psychrophilic and mesophilic beta-lactamases shows that electrostatics seems to play a major role in low-temperature adaptation, with a lower total number of ionic interactions for cold enzymes. The psychrophilic enzymes are also characterized by a decreased number of hydrogen bonds, a lower content of prolines, and a lower percentage of arginines in comparison with lysines. All these features make the structure more flexible so that the enzyme can behave as an efficient catalyst at low temperatures. [less ▲]

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