Bibliothek

X
feed icon rss

Ihre E-Mail wurde erfolgreich gesendet. Bitte prüfen Sie Ihren Maileingang.

Leider ist ein Fehler beim E-Mail-Versand aufgetreten. Bitte versuchen Sie es erneut.

Vorgang fortführen?

Exportieren
  • 1
    Digitale Medien
    Digitale Medien
    A molecular dynamics simulation study of the effects of defects on the transformation pressure of polymorphic phase transformations (1996)
    College Park, Md. : American Institute of Physics (AIP)
    The Journal of Chemical Physics 105 (1996), S. 3215-3218 
    Details
    ISSN: 1089-7690
    Quelle: AIP Digital Archive
    Thema: Physik , Chemie und Pharmazie
    Notizen: The effect of defects (in the form of vacancies) on the transformation pressure of the Fm3m-Pm3m phase transition of KCl has been examined using molecular dynamics simulations. The simulated transformation has been found to be reversible, exhibiting a large hysteresis. Vacancy defects were systematically introduced into the crystal structure of the parent phase, and then a series of simulations using the Parrinello–Rahman method were performed to elucidate the transformation pressure. With an increase in the density of the defects, the hysteresis decreases. These results are entirely consistent with the observed behavior. © 1996 American Institute of Physics.
    Materialart: Digitale Medien
    URL: http://dx.doi.org/10.1063/1.471837
    Bibliothek Standort Signatur Band/Heft/Jahr Verfügbarkeit
    BibTip Andere fanden auch interessant ...
    Artikel (Nationallizenzen)
    Volltext
  • 2
    Digitale Medien
    Digitale Medien
    Ab initio structure determination of sulfathiazole polymorph V from synchrotron X-ray powder diffraction data (1999)
    Copenhagen : International Union of Crystallography (IUCr)
    Applied crystallography online 32 (1999), S. 436-441 
    Details
    ISSN: 1600-5767
    Quelle: Crystallography Journals Online : IUCR Backfile Archive 1948-2001
    Thema: Geologie und Paläontologie , Physik
    Notizen: The crystal structure of sulfathiazole [4-amino-N-(2,3-dihydro-2-thiazolylidene)benzenesulfonamide, C9H9N3O2S] polymorphic form V has been determined from high-resolution synchrotron X-ray powder diffraction data. The structure is monoclinic, space group P21/n, Z = 8, with two molecules in the asymmetric unit. The unit-cell dimensions are a = 14.3296 (3), b = 15.2733 (2), c = 10.4428 (2) Å and β = 91.052 (1)° with cell volume V = 2285.13 (8) Å3. The structure has been solved by direct methods without recourse to any computational modelling techniques for generating possible structures. The unrefined structure obtained from direct methods gave an Rwp value of 36.5%. Refinement of atomic and displacement parameters yielded a final Rwp of 12.54% (Rp = 9.37%). The conformations of the two molecules in the asymmetric unit are nearly identical and very similar to that found in other forms of sulfathiazole. The molecular packing is characterized by molecular sheets lying perpendicular to the a axis. Each sheet is two molecules thick, being integrated by hydrogen bonding. With 16 non-H atoms in the molecule and two molecules in the asymmetric unit, this structure represents a further advance in terms of the complexity of an organic structure solved from X-ray powder diffraction data.
    Materialart: Digitale Medien
    URL: http://dx.doi.org/10.1107/S0021889898017233
    Bibliothek Standort Signatur Band/Heft/Jahr Verfügbarkeit
    BibTip Andere fanden auch interessant ...
    Artikel (Nationallizenzen)
    Volltext
  • 3
    Digitale Medien
    Digitale Medien
    Computer Simulation of Crystal-liquid Interface: Application to Wettability of Solids (1996)
    Springer
    Pharmaceutical research 13 (1996), S. 1003-1007 
    Details
    ISSN: 1573-904X
    Schlagwort(e): molecular simulation ; interfacial energy ; wettability ; crystal structure ; Monte Carlo method ; potential energy calculations ; contact angle
    Quelle: Springer Online Journal Archives 1860-2000
    Thema: Chemie und Pharmazie
    Notizen: Abstract Purpose. This study describes the development and application of a molecular simulation technique for investigating the solid-liquid interface. It attempts to relate the molecular and crystal structure to the observed wettability of solids. Methods. Molecular simulations have been carried out for the crystal-water interface of a series of N-n-alkyl-D-gluconamide crystals using the Monte Carlo technique. The molecular system simulated consisted of a layer of water bounded by two crystal slabs. The interfacial potential energies were calculated for the crystal-water interactions and compared with experimental enthalpy values obtained from contact angle measurements. Results. The simulations clearly reveal the distinct hydrophilic and hydrophobic nature of the respective (010) and (010) faces of these compounds. The distribution of water at the interface observed in the simulations is in accord with the nature of the crystal faces. The calculated interfacial potential energies are in the right ball park, but consistently higher than the experimental values. The disparity, however, is justifiable, resulting from the highly simplified model simulated. Conclusions. Using the developed molecular simulation technique one can calculate the wettability of a solid given the crystal structure. This approach represents an important step towards the goal of engineering crystals with desired wettability characteristics.
    Materialart: Digitale Medien
    URL: http://dx.doi.org/10.1023/A:1016094204888
    Bibliothek Standort Signatur Band/Heft/Jahr Verfügbarkeit
    BibTip Andere fanden auch interessant ...
    Artikel (Nationallizenzen)
    Volltext
  • 4
    Digitale Medien
    Digitale Medien
    Dielectric Analysis of Phosphorylcholine Head Group Mobility in Egg Lecithin Liposomes (1996)
    Springer
    Pharmaceutical research 13 (1996), S. 1181-1185 
    Details
    ISSN: 1573-904X
    Schlagwort(e): lecithin ; phosphorylcholine ; polarization ; dielectric-relaxation ; activation-energy ; liposome
    Quelle: Springer Online Journal Archives 1860-2000
    Thema: Chemie und Pharmazie
    Notizen: Abstract Purpose. A knowledge of the interfacial properties of lecithin underpins our understanding of many of the physicochemical characteristics of drug delivery systems such as liposomes and lecithin stabilized microemulsions. In order to further this understanding, a high frequency dielectric study of the interfacial properties of egg lecithin liposomes was undertaken. Methods. The effect of temperature, lecithin concentration and probe sonication on the interfacial dielectric properties of liposomal suspensions was investigated by high frequency dielectric relaxation spectroscopy between 0.2–6 GHz. Results. The frequency dependent permittivity of each suspension exhibited a dielectric dispersion centred around 100 MHz, corresponding to the relaxation of zwitterionic head groups. The activation energy for head group reorientation was estimated as ΔH = 6.3 kJ mol−1. There was an increase in extent of inter-head group interactions on increasing the liposome volume fraction, whereas the effect of probe sonication showed that: (i) head groups in both the outer and inner lamellae contribute to the dielectric response; (ii) the head groups may be less restricted in liposomes of high surface curvature with few lamellae; (iii) the high frequency permittivity of the suspension increased on sonication, as a result of a reduction in the amount of (depolarized) interlamellar water following a reduction in the number of lamellae per liposome. Conclusions. Dielectric analysis of the zwitterionic head groups of lecithin therefore provides a means for investigating the surface of lecithin liposomes, and may be used to investigate the effect of drugs and other solutes on membranes.
    Materialart: Digitale Medien
    URL: http://dx.doi.org/10.1023/A:1016004001678
    Bibliothek Standort Signatur Band/Heft/Jahr Verfügbarkeit
    BibTip Andere fanden auch interessant ...
    Artikel (Nationallizenzen)
    Volltext
Schließen ⊗
Diese Webseite nutzt Cookies und das Analyse-Tool Matomo. Weitere Informationen finden Sie hier...