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  • 1
    Electronic Resource
    Electronic Resource
    Molecular dynamics simulation of crystalline β-cyclodextrin dodecahydrate at 293 K and 120 K (1987)
    Springer
    European biophysics journal 15 (1987), S. 211-224 
    Details
    ISSN: 1432-1017
    Keywords: β-cyclodextrin dodecahydrate ; molecular dynamics simulation ; hydrogen bonds ; empirical force field ; water molecule diffusion ; positional disorder
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology , Physics
    Notes: Abstract Molecular dynamics (MD) simulations for crystalline β-cyclodextrin dodecahydrate (β-CD) at two different temperatures, 293 K and 120 K, have been performed using the GROMOS program package. The calculated structural properties are compared to those obtained from neutron diffraction studies of this system at the quoted temperatures. The simulation was carried out over a period of 20 ps on four unit cells containing 8 β-CD molecules and 96 water molecules, whereby all atoms were allowed to move. At room temperature, the experimental positions of the (non-hydrogen) glucose atoms are reproduced within 0.034 nm, a value which is smaller than the experimental (0.041 nm) or simulated (0.049 nm) overall root mean square (rms) positional fluctuation. The corresponding numbers for the low temperature study are 0.046 nm, 0.019 nm and 0.022 nm. At both temperatures the experimentally observed degree of anisotropy of the atomic motions is also found in the simulations. The comparison of a variety of structural properties leads to the conclusion that the molecular model and force field used are able to simulate the cyclodextrin system very well. Experimentally observed differences in properties as a function of number of glucose units in the CD molecule (α-CD, 6 versus β-CD, 7) and as a function of temperature are qualitatively reproduced by the simulations.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF00577069
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  • 2
    Electronic Resource
    Electronic Resource
    A molecular dynamics simulation of crystalline α-cyclodextrin hexahydrate (1987)
    Springer
    European biophysics journal 15 (1987), S. 197-210 
    Details
    ISSN: 1432-1017
    Keywords: α-cyclodextrin hexahydrate ; molecular dynamics simulation ; empirical force field ; hydrogen bonds
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology , Physics
    Notes: Abstract The structure of crystalline α-cyclodextrin (α-CD) hexahydrate, form I (C36H60O30·6H2O, space group P212121) is experimentally so well determined by X-ray and by neutron diffraction analyses that the positions of all the hydrogen atoms are available. This provides an opportunity for testing an empirical force field that is currently used in simulations of protein and nucleic acid structures by performing molecular dynamics studies employing the GROMOS program package on a system of 4 unit cells containing 16 α-CD molecules and 96 water molecules. A detailed comparison of the simulated and experimentally determined crystal structures shows that the experimental positions of the α-CD atoms are reproduced within 0.025 nm, well within the overall experimental accuracy of 0.036 nm; that the water molecules are on average within 0.072 nm from their experimental sites, with two thirds reproduced within experimental accuracy by the calculations; that high correlation is produced, between the occurrence of simulated and experimentally observed hydrogen bonds. The good agreement between simulated and experimental results suggests that the tested force field is reliable.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF00577068
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    Paper (German National Licenses)
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  • 3
    Electronic Resource
    Electronic Resource
    LiSmAlF6  -  das erste Fluoroaluminat mit zweiwertigem Samarium (1991)
    Weinheim : Wiley-Blackwell
    Zeitschrift für anorganische Chemie 606 (1991), S. 169-176 
    Details
    ISSN: 0044-2313
    Keywords: Lithium samarium hexafluoroaluminate ; preparation ; crystal structure ; Chemistry ; Inorganic Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Description / Table of Contents: LiSmAlF6  -  the First Fluoroaluminate with Divalent SamariumLiSmAlF6, the first quaternary fluoride with Sm2+ that has been obtained as red transparent single crystals, is formed while heating corresponding mixtures of the starting materials in niobium or tantalum crucibles under argon after 7-10 d at about 800°C. Orange-red, microcrystalline powder samples of LiSmAlF6 could be prepared at T ≤ 700°C after 1-2 d under the same conditions.LiSmAlF6, crystallizes as a new structure type in P6322 (Nr. 182) with a = 507.9(1), c = 1 040.5(1) pm and Z = 2 (CAD4, 2 512 Io, Rw = 2,3%). The crystal structure of LiSmAlF6 is related to the LiCaAlF6 structure type whereby the essential difference lies in the coordination of the M2+ ions. Ca2+, as well as Sr2+ in LiSrAlF6, exhibit octahedral coordination, whereas Sm2+ has, surprisingly, trigonal prismatic coordination to F-. The two triangles of the SmF6 prism are twisted by 8.3° with respect to each other.Measurements of the magnetic susceptibility show the temperature dependence typically found for Sm2+. The Madelung part of the lattice energy has been calculated and is discussed.
    Notes: LiSmAlF6, das erste in Form roter, transparenter Einkristalle erhaltene quaternäre Fluorid mit Sm2+, bildet sich beim Erhitzen geeigneter Ausgangsmenge in Niob- oder Tantaltiegln unter Ar nach 7-10 d bei ca. 800°C. Orangerote, mikrokristalline Pulverproben von LiSmAlF6 können bei T ≤ 700°C bereits nach 1-2 Tagen unter sonst gleichen Bedingungen dargestellt werden.LiSmAlF6 kristallisiert in einem neuen Strukturtyp in P6322 (Nr. 182) mit a = 507,9(1), c = 1 040,5(1) pm und Z = 2(CAD4, 2 512 Io, Rw = 2,3%). Die Kristallstruktur von LiSmAlF6 ist dem LiCaAlF6-Typ verwandt, zeigt aber den wesentlichen Unterschied in der Umgebung für M2+ : Ca2+, wie auch Sr2+ in LiSrAlF6, werden oktaedrisch, Sm2+ jedoch überraschenderweise trigonal-prismatisch von F- koordiniert. Die beiden Dreiecke des SmF6-Prismas sind um 8,3° gegeneinander verdreht.Messungen der magnetischen Suszeptibilität zeigen die für Sm2+ typische Temperaturabhängigkeit. Der Madelunganteil der Gitterenergie wurde berechnet und diskutiert.
    Additional Material: 5 Ill.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/zaac.19916060117
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  • 4
    Electronic Resource
    Electronic Resource
    SmAlF5  -  ein neues SmII-fluoroaluminat mit Al2F10-Oktaederdoppeln und [AlF2/2F4/1]-Ketten (1993)
    Weinheim : Wiley-Blackwell
    Zeitschrift für anorganische Chemie 619 (1993), S. 181-188 
    Details
    ISSN: 0044-2313
    Keywords: Samarium(II) fluoroaluminate ; preparation ; crystal structure ; Chemistry ; Inorganic Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Description / Table of Contents: SmAlF5  -  a New Samarium(II) Fluoroaluminate with Al2F10 Bioctahedra and [AlF2/2F4/1] Chains.SmAlF5 has been obtained as orange-red transparent single crystals while heating mixtures of SmF3, Sm-powder and AlF3 (2:1:3) in a niobium crucible under Ar after 7-10 d at about 750°C. SmAlF5 crystallises in I 4/m (Nr. 87) with a=1 414.4(4), c=722.2(3) pm and Z=8 (CAD4, 4 340 IO, Rw=1.7%).The crystal structure of SmAlF5 is isotypic to BaTiF5. Characteristic building units are linear chains of trans-corner sharing AlF6 octahedra, which are connected via corners to two further AlF6 octahedra. Isolated Al2F10 octahedra lie disordered between such chains. The Sm atoms connect the AlF6 octahedra to a three-dimensional network. Measurements of the magnetic susceptibility show the temperature dependence typically found for Sm2+. The Madelung part of the lattice energy has been calculated and is discussed.
    Notes: SmAlF5 wurde in Form orangeroter transparenter Einkristalle beim Erhitzen von SmF3, Sm-Pulver und AlF3 (2:1:3) im Niobtiegel unter Ar nach 7-10 d bei ca. 750°C erhalten. SmAlF5 kristallisiert in I4/m (Nr. 87) mit a=1 414,4(4), c=722,2(3) pm und Z=8 (CAD4, 4 340 IO, Rw=1,7%).Die Kristallstruktur von SmAlF5 ist isotyp zu BaTiF5. Charakteristische Baugruppen sind lineare Ketten trans-Spitzen verknüpfter AlF6-Oktaeder, die über Spitzen mit zwei weiteren AlF6-Oktaedern verknüpft sind. Isolierte Al2F10-Oktaederdoppel liegen fehlgeordnet zwischen solchen Ketten. Die Sm-Atome verknüpfen die AlF6-Oktaeder zum dreidimensionalen Gerüst. Messungen der magnetischen Suszeptibität zeigen die für Sm2+ typische Temperaturabhängigkeit. Der Madelunganteil der Gitterenergie wurde berechnet und diskutiert.
    Additional Material: 8 Ill.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/zaac.19936190130
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