Evidence of transient amorphization during the polymorphic transformation of sorbitol induced by milling.

In this paper, we show that the polymorphic transformation γ â†’ α of sorbitol upon milling involves a transient amorphization of the material. This could be done by comilling sorbitol with a high Tg amorphous material (Hydrochlorothiazide, Tg = 115 °C) to stabilize any transient amorphous fractions of sorbitol through the formation of a molecular alloy. The results indicate that for large sorbitol concentration (50%), the comilling leads to a heterogeneous mixture made of sorbitol crystallites in the form α embedded into an amorphous molecular alloy sorbitol / HCT. Interestingly, the kinetic investigation of this transformation reveals that these two components are not produced simultaneously. On the contrary, they are produced one after the other, during two distinct consecutive stages. The first stage concerns the formation of the amorphous alloy while the second one concerns the polymorphic transformation γ â†’ α of the fraction of crystalline sorbitol not involved in the alloy. These results clearly indicate that the polymorphic transformation of sorbitol upon milling results from the recrystallization of a transient amorphous state generated by the mechanical shocks. The investigations were mainly performed by calorimetry and powder X-ray diffraction.

Polymorphism and stability of ibuprofen/nicotinamide cocrystal: The effect of the crystalline synthesis method.

The development over the past decade of design strategies for cocrystal preparation have led to numerous methods for the synthesis of cocrystal without take care of their influence on the precise structure and stability of cocrystalline states. On the other hand the mechanism of cocrystal formation remains widely unclear, especially the identification of the type of interactions mostly responsible for the cocrystalline stability. The present study focuses on the influence of the crystalline synthesis method on the polymorphism of cocrystals was analyzed from the preparation of S-ibuprofen/nicotinamide and RS-ibuprofen/nicotinamide cocrystals by co-milling, slow solvent evaporation and crystallization from the melt. X-ray diffraction and Raman spectroscopy experiments have shown that the polymorphic form of the cocrystals obtained by recrystallization from the melt (Form A) is different from that prepared by milling and by slow evaporation in solution (Form B). It was shown that both isothermal and non-isothermal recrystallizations from the melt blending are observed via a transient metastable micro/nano structure of form A. Additionally, it was observed that form A transforms into Form B upon heating via very weak changes in the hydrogen bond network. The crystallization in form A from the melt, instead of form B by other methods, was explained by the difficulty to form a supramolecular organization too far energetically from that existing in the melt. This study shows the crucial role of supramolecular H-bonding on the formation mechanism of cocrystals and how does the synthesis method of cocrystals change the supramolecular organization and the related structure of cocrystals.

Interest of molecular/crystalline dispersions for the determination of solubility curves of drugs into polymers.

We present here a method to increase the dissolution rate of drugs into polymers in order to make easier and faster the determination of the solubility curves of these mixtures. The idea is to prepare molecular/crystalline dispersions (MCD) where the drug is dispersed into the polymer, partly at the molecular level and partly in the form of small crystallites. We show that this particular microstructure greatly increases the dissolution rate of crystallites since: (1) The molecular dispersion has a plasticizing effect which greatly increases the molecular mobility in the amorphous matrix. (2) The fine crystallite dispersion in the matrix strongly reduces the distances over which the drug molecules have to diffuse to invade homogeneously the polymer by dissolution. MCD are here obtained by combining solid-state co-amorphization by high energy mechanical milling and then recrystallization by annealing under a plasticizing atmosphere. We have used MCD to determine the solubility lines of the two polymorphic forms (I and II) of sulindac into PVP. The investigations have been performed mainly by DSC and powder x-ray diffraction.