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  • 1
    Electronic Resource
    Electronic Resource
    EXAFS and molecular dynamics studies of ionic solutions (2001)
    Chester : International Union of Crystallography (IUCr)
    Journal of synchrotron radiation 8 (2001), S. 173-177 
    Details
    ISSN: 1600-5775
    Source: Crystallography Journals Online : IUCR Backfile Archive 1948-2001
    Topics: Geosciences , Physics
    Notes: This paper focuses on recent advances in the X-ray absorption spectroscopy (XAS) analysis of ionic solutions. The asymmetry of radial distribution functions g(r) associated with the solvent molecules surrounding the ions has to be taken into account to perform a reliable structural analysis. Molecular dynamics (MD) simulations provide reliable g(r)'s which can be used as starting models in the XAS data analysis. The combined MD-XAS investigation reduces meaningfully the indetermination of the structural parameters, especially for coordination numbers and Debye–Waller factors. Double-electron excitation channels can be present in the XAS spectra of ionic solutions and they have to be accounted for in the background extraction. The ability of the XAS technique to probe three-body correlation functions in ionic solutions with the aid of MD g(r_1,r_2,\theta) has been shown. The analysis of the low-k region of the spectra allows the detection of a weak but significant hydrogen structural signal. The XAS technique is especially well suited to determine the detailed shape of the nearest-neighbor peak in the atom–atom pair correlation functions of disordered systems. The information that they contain about the short-range atom–atom pairwise interactions can be very helpful for specifying and properly modifying model potentials used in MD simulations.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1107/S0909049500016319
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    Paper (German National Licenses)
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  • 2
    Electronic Resource
    Electronic Resource
    K- and L-edge XAFS determination of the local structure of aqueous Nd(III) and Eu(III) (2001)
    Chester : International Union of Crystallography (IUCr)
    Journal of synchrotron radiation 8 (2001), S. 666-668 
    Details
    ISSN: 1600-5775
    Source: Crystallography Journals Online : IUCR Backfile Archive 1948-2001
    Topics: Geosciences , Physics
    Notes: The short-range coordination of Nd(III) and Eu(III) ions in aqueous solutions has been investigated by means of K-edge x-ray absorption spectroscopy. Experimental data are presented which demonstrate that an accurate determination of the Nd(III) and Eu(III) hydration structural parameters can be obtained from the analysis of the K-edge spectra. It is shown that the large widths of the core hole states do not appreciably reduce the potential structural information of the K-edge EXAFS data. In addition the available k-range of the K-edge spectra is much wider compared to that of the L3-edge which is affected by the presence of double-electron excitations in a more severe fashion.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1107/S0909049500016745
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    Paper (German National Licenses)
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  • 3
    Electronic Resource
    Electronic Resource
    Crystal structure of the 2:1 inclusion compound between deoxycholic acid and quadricyclane (1984)
    Springer
    Journal of inclusion phenomena and macrocyclic chemistry 1 (1984), S. 329-337 
    Details
    ISSN: 1573-1111
    Keywords: Inclusion compound ; deoxycholic acid ; quadricyclane ; photoreaction
    Source: Springer Online Journal Archives 1860-2000
    Topics: Chemistry and Pharmacology
    Notes: Abstract The 2:1 inclusion compound formed between deoxycholic acid (C24H40O4,M r=392.58) and quadricyclane (C7H8,M r=92.14) crystallizes in space groupP212121 witha=27.150(7),b=13.359(3),c=14.161(4) Å,Z=4. The structure was refined toR=0.086 andR w=0.088 for 2079 observed reflections withI〉2.5σ(I). The crystal packing is very similar to that found in the norbornadiene-deoxycholic acid inclusion compound and is characterized by an assembly of antiparallel pleated bilayers, formed by molecules of deoxycholic acid held together through hydrogen bonds. Quadricyclane occupies approximately the same position of norbornadiene and its atoms give rise to good van der Waals interactions with some methyl groups of deoxycholic acid.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF00665476
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    Paper (German National Licenses)
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