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Nicolai B.,University of Paris Descartes | Rietveld I.B.,University of Paris Descartes | Barrio M.,Grup de Caracteritzacio de Materials GCM | Mahe N.,University of Paris Descartes | And 3 more authors.
Structural Chemistry | Year: 2013

The thermal expansion of tienoxolol has been investigated by X-ray powder diffraction up to its melting temperature. The data indicate that the expansion is anisotropic and even negative in one direction of the unit cell. The supramolecular structure formed by hydrogen-bonds reflects that of a trellis, which explains the observed behavior of tienoxolol crystals. © 2012 Springer Science+Business Media, LLC.

Allouchi H.,University of Tours | Nicolai B.,University of Paris Descartes | Barrio M.,Grup de Caracteritzacio de Materials GCM | Ceolin R.,Grup de Caracteritzacio de Materials GCM | And 4 more authors.
Crystal Growth and Design | Year: 2014

Solid-state properties of active pharmaceutical compounds are closely related to their dissolution behavior and bioavailability, and understanding their phase behavior leads to better control in the drug formulation process. l-Citrulline is an amino acid, which is known to exhibit polymorphism; however, only the structure of the α form is reported in the literature. The structure of the δ form has been elusive due to lack of good quality single crystals. It has been found to be orthorhombic P212 121 with the cell parameters a, b, and c respectively 14.895(5) Å, 9.852(2) Å, and 5.353(2) Å. The unit cell contains four molecules, and its volume is 785.5(4) Å3. Both the α form and the δ form possess uniaxial negative thermal expansion along the direction of the charge exchange of the l-citrulline zwitterions. In mixtures containing solid and saturated aqueous solution, the α form quickly transforms in a dihydrate, whereas the δ phase persists for over three weeks. Although the evidence is not conclusive, the δ phase is most likely the more stable form and most suitable for storage. © 2014 American Chemical Society.

Rietveld I.B.,University of Paris Descartes | Barrio M.,Grup de Caracteritzacio de Materials GCM | Espeau P.,University of Paris Descartes | Tamarit J.L.,Grup de Caracteritzacio de Materials GCM | Ceolin R.,University of Paris Descartes
Journal of Physical Chemistry B | Year: 2011

In 1981, Jacques, Collet, and Wilen already put forward the idea to use pressure to influence equilibria in binary enantiomer systems in analogy with temperature (Jacques et al. Enantiomers, Racemates and Resolutions; John Wiley & Sons: New York, 1981). Whereas temperature is used routinely to study phase equilibria, pressure is an all but forgotten parameter. This is therefore possibly the first paper on the influence of pressure on a binary enantiomer system: d- and l-camphor. The study consists of two parts, a topological approach, which uses data obtained from routine measurements (differential scanning calorimetry, X-ray diffraction), and the experimental determination of phase transitions as a function of pressure and temperature. This has resulted in two topological pressure-temperature phase diagrams of the pure enantiomer d-camphor and of the racemic mixture dl-camphor; both have been verified by the experiments as a function of pressure. In turn, these results have been used to construct part of the pressure-temperature-composition phase diagram of d- and l-camphor. A method to obtain the excess Gibbs energy from these binary phase diagrams as a function of pressure is proposed. © 2011 American Chemical Society.

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