The stable anhydrous form of alpha-lactose has been obtained by the dehydration of alpha-lactose monohydrate in methanol. An X-ray powder diffraction pattern was recorded at room temperature with a laboratory diffractometer equipped with an INEL curved sensitive detector CPS120. The starting structural model of this form was found by a Monte-Carlo simulated annealing method. The structure was obtained through Rietveld refinements and the minimization of crystalline energy for the localization of the H atoms of the hydroxyl groups. Soft restraints were applied to bond lengths and angles. Networks of O-H...O hydrogen bonds account for the crystalline cohesion. A comparison is made between the hydrogen-bond networks of this form and those of the monohydrate and hygroscopic anhydrous forms of alpha-lactose.
Hollow and solid whiskers are formed during the solvent exchange from the dimethyl sulfoxide or
dimethylformamide solvates of dexamethasone acetate to the sesquihydrate by immersion of the initial phase in
water. Detailed investigations using mainly optical and scanning electron microscopies lead us to propose a growth
mechanism of the hollow whiskers. Six criteria appear to be necessary for the formation of thin tubular crystals
during the solvent exchange. To reproduce the crystallization occurring at the surface of the initial crystal, an
experimental assembly was made with a syringe and a glass filter. When the six conditions are fulfilled, this technique
permits the production of 100% of hollow whiskers.
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