Small angle neutron scattering study of steroidal gels

Gels formed by a dilute solution of modified steroids in cyclohexane have been studied by Small Angle Neutron Scattering. The presence of very long objects associated with the gel network is clearly demonstrated. Contrast variation experiments show that these objects are essentially composed of steroid molecules. Absolute intensity measurements, and fits of the full scattering curves using models, suggest that these objects are chiral, possibly symmetrical double helices of diameter ca. 100 Å. It is suggested that the « contact points » in the network of the gel are achieved by coiling together two or more long objects over distances rather large compared to the diameter. The influence of the existence of such overlapping on the shape of the experimental scattering curves is discussed.Des gels formés à partir de solutions diluées dans le cyclohexane de stéroïdes modifiés, sont étudiés par diffusion de neutrons aux petits angles. La présence d'objets très longs associés avec le réseau du gel est mise clairement en évidence. Des experiences de variation de contraste montrent que ces objets sont essentiellement composés par des molécules stéroïdes. Des mesures d'intensités absolues et l'ajustement des courbes de diffusion à des modèles simples suggèrent que ces objets sont chiraux, probablement des doubles hélices symétriques de diamètre d'environ 100 Å. On suggère que les « points de contacts » entre objets sont formés en torsadant deux ou plusieurs de ces longs objets sur des distances relativement grandes par rapport au diamètre. L'influence de ce recouvrement des objets sur la forme des courbes de diffusion est discutée

Spin labeling of ion exchange membranes

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Molecular structure of a D-homoandrostanyl steroid derivative: single crystal and powder diffraction analyses.

International audienceThe knowledge of the structure of a molecular crystal is frequently a prerequisite for the understanding of its solid state properties. Even though single crystal diffractometry is the method of choice when it comes to crystal structure determination, methods using powder diffraction data become more and more competitive. There has been much recent interest in the development of a new generation of "direct-space" approaches that are particularly suited for molecular crystals. The crystallographic structure of a steroid derivative molecule (17,17-di-n-propyl-17a-aza-D-homo-5alpha-androstan-3beta-ol) was obtained in two independent ways: from a single crystal by laboratory X-rays and from a polycrystalline powder by high-resolution synchrotron powder diffraction. The molecule crystallizes in the orthorhombic space group P212121 (a = 6.5346, b = 17.6006 and c = 19.6978 Å). Hydrogen bonds form infinite chains of molecules parallel to the c axis