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Tentative Assignment (tentative + assignment)

Distribution by Scientific Domains
Chemistry60%
Life Sciences40%

Selected Abstracts

Raman spectra of apatites: La10,x Si6,y (Al,Fe)y O26±,

JOURNAL OF RAMAN SPECTROSCOPY, Issue 1 2007
G. Lucazeau
Abstract Raman spectra of eight polycrystalline apatites of the general formula La10,xSi6,yM,yO26 ± , with M, = Al or Fe were obtained at 300 K. Raman spectra of La10Si4Fe2O26 and La9.83Si4.5Al1.5O26 were investigated in the range 80,1000 K and 80,623 K, respectively. Tentative assignments of bands to stretching and bending modes of SiO4 tetrahedra and to M'O vibrations are proposed. Except for the two new bands, which appear around 700 cm,1 when Al is replaced by Fe, only some band broadenings and relative intensity changes are observed as a function of the rate of O5 or La vacancies. Most of the bands soften and broaden continuously when raising the temperature. This is an indication that the Al- and Fe-substituted apatites do not undergo any structural change up to 1000 K. Above 1000 K, the broad and weak shoulder observed at 850 cm,1 for La10Si4Fe2O26 is replaced by a strong band at 868 cm,1, suggesting that SiO4 tetrahedra undergo a structural modification. All compounds show the same residual band broadening at 80 K. This suggests that there is a small rate of static disorder preferentially related to the solubility of Al and Fe in the Si sublattice rather than to other defects. Moreover, the observation of FeO modes indicates that the dynamics of the solid solution obeys the so-called two-mode behavior. The occurrence of FeO stretching vibrations 150 cm,1 lower than for those of SiO suggests that the coordination number of iron could be larger than 4, particularly for the Fe4+ species. Copyright © 2006 John Wiley & Sons, Ltd. [source]

Fore limb bones of late Pleistocene dwarf hippopotamuses (Mammalia, Cetartiodactyla) from Madagascar previously determined as belonging to the crocodylid Voay Brochu, 2007

FOSSIL RECORD-MITTEILUNGEN AUS DEM MUSEUM FUER NATURKUNDE, Issue 2 2010
Oliver Hampe
Abstract A humerus and two radii of juvenile dwarf hippopotamuses are redescribed. The subfossil bones from the collection of the Museum für Naturkunde Berlin were erroneously assigned to the horned crocodile Voay robustus (Grandidier & Vaillant, 1872) by Bickelmann & Klein (2009). All three limb bones presented here belong to immature animals. The epiphyses are not fused, except the proximal extremity of the right radius; and the radius and ulna are also unfused. The two radii are from individuals of different size, whereas the left radius and the humerus are from animals of similar size. Morphologically, the limb bones cannot be identified to species level. A tentative assignment to Hippopotamus madagascariensis is discussed based on the knowledge of the geographic origin on the island. (© 2010 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim) [source]

Re-investigation of the structure and crystal chemistry of the Bi2O3,W2O6 `type (Ib)' solid solution using single-crystal neutron and synchrotron X-ray diffraction

ACTA CRYSTALLOGRAPHICA SECTION B, Issue 2 2010
Neeraj Sharma
Single crystals of composition Bi35.66W4.34O66.51 (or Bi8.2WO15.3, bismuth tungsten oxide), within the type (Ib) solid-solution region of the Bi2O3,WO3 system, were synthesized using the floating-zone furnace method. Synchrotron X-ray and neutron single-crystal diffraction data were used to confirm the previously tentative assignment of the room-temperature space group as I41. Fourier analysis of the combined X-ray and neutron datasets was used to elucidate and refine fully the cation and anion arrays for the first time. The mixed cation site M1 is shown to be coordinated by eight O atoms in an irregular cube when M = Bi, and by six O atoms in an octahedron when M = W. The resulting disorder in the average structure around M1 is discussed in the context of experimentally observed oxide-ion conductivity. [source]

Characterization of reduced iso-,-acids derived from hops (Humulus lupulus) by NMR

MAGNETIC RESONANCE IN CHEMISTRY, Issue 9 2003
Lars I. Nord
Abstract Reduced forms of iso-,-acids (isohumulones), used in modern beer brewing were separated and characterized by 1H and 13C NMR spectroscopy. Components from mixtures of rho-iso-,-acids, tetrahydro-iso-,-acids, and hexahydro-iso-,-acids were isolated using high-performance liquid chromatography (HPLC) and analyzed by use of one- and two-dimensional NMR experiments. The data presented assign the identities of the main peaks in the HPLC traces for the reduced iso-,-acids. Previous tentative assignments regarding the cis and trans configurations and the structures of the acyl residues of the reduced iso-,-acids were confirmed and extensive NMR assignments were made. Furthermore, the previously unknown stereochemistry in the C-4 side-chain of the rho- and hexahydro-iso-,-acids was assigned. Copyright © 2003 John Wiley & Sons, Ltd. [source]

A mass spectrometric strategy for profiling glycoproteinoses, Pompe disease, and sialic acid storage diseases

PROTEOMICS - CLINICAL APPLICATIONS, Issue 4 2008
Valegh Faid
Abstract Glycoproteinoses, Pompe disease, and sialic acid storage diseases are characterized by a massive accumulation of unprocessed oligosaccharides and/or glycoconjugates in urine. The identification of these glycocompounds is essential for a proper diagnosis. In this study, we investigated the potential of MALDI-TOF-MS to identify glycocompounds present in urine from patients with different inborn errors of glycan metabolism. Urinary glycocompounds were permethylated, and analyzed using GC-MS and MALDI-TOF-MS. In order to confirm tentative assignments, a second aliquot of urine was purified on a C18 Sep-Pak cartridge and glycocompounds were desalted on a column of nonporous graphitized carbon. The glycocompounds were then sequentially on-plate digested using an array of exoglycosidases. A range of disease-specific oligosaccharides as well as glycopeptides was identified for all oligosacchariduria models. In addition, free sialic acid accumulated in urine from a patient suffering from French-type sialuria, has been detected by a GC-MS approach, which could be applied to other sialic acid storage diseases. This procedure is simple, and can be performed in few simple steps in less than 24,h. This current method can be applied for newborn screening for other inherited metabolic diseases as well as for assessing treatments in clinical trials. [source]