Solvent exchanges among molecular compounds |
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Authors: | Mallet F Petit S Lafont S Billot P Lemarchand D Coquerel G |
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Institution: | (1) Unité de Croissance Cristalline, de Chromatographie et de Modélisation Moléculaire (UC3M), Sciences et Méthodes Séparatives (SMS) UPRES EA 2659, IRCOF, Université de Rouen, rue Tesniére, F-76821 Mont Saint-Aignan Cedex, France;(2) Process Development 102, Aventis Pharma, route de Noisy, F-93235 Romainville Cedex, France;(3) Groupe de Physique des Matériaux UMR 6634, Université de Rouen, F-76801 Saint Etienne du Rouvray Cedex, France |
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Abstract: | Solid-solid transformations between solvates of pharmaceutical compounds are investigated under various conditions. In the
case of Roxithromycin, it is shown that starting from single crystals of the acetonitrile solvate, a transformation towards
the monohydrate occurs according to a cooperative mechanism. This smooth exchange of solvent probably involves a transport
of matter within channels, and the comparison of crystal structures is consistent with the persistence of the main features
of the 3D lattice. By contrast, starting from the DMSO solvate of Dexamethasone acetate, the transformation towards the sesquihydrated
form, induced by the immersion of the DMSO solvate in water, is fully destructive and reconstructive. This occurs far-from-equilibrium
and is therefore controlled by kinetic factors. The existence of an intermediate liquid phase within the particle is postulated
to account for the appearance of whisker-like crystals growing first on high-energy sites of the former particle. An extended
analysis of these transformations between solvates shows that they could be classified according to rules previously proposed
in the case of desolvation mechanisms.
This revised version was published online in July 2006 with corrections to the Cover Date. |
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Keywords: | whiskers solvent exchange solvates solid-solid transformation crystal structure |
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