科研之友
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摘要
The effect of grinding at ambient temperature and at 77 K (CryoMill Retsch) on the polymorphic transitions in alpha- and epsilon-chlorpropamide has been compared. The result of grinding of alpha-chlorpropamide at room temperature could not be interpreted as a mere formation of traces of the epsilon-polymorph. The diffraction patterns suggested the presence of small amounts of some unknown polymorph, possibly in a mixture with other polymorph(s). Possibly, mechanical treatment gave a defect nanostructured phase with alternating domains. Cryogrinding of alpha-chlorpropamide did not result in polymorphic transitions. In contrast, cryogrinding of the epsilon-polymorph was much more efficient than grinding at ambient temperature: almost no changes could be observed at ambient temperature, whereas cryogrinding gave the alpha-form. The observed phenomena could be interpreted taking into account that at low temperatures the epsilon-polymorph undergoes a polymorphic transition into another polymorph-the epsilon'-form. Without grinding, the epsilon'-form transforms back to the epsilon-polymorph when heated back to ambient temperature. If grinding takes place in the temperature range of the epsilon-to epsilon'-polymorphic transition, the transformation to the alpha-form occurs. One phase transition, induced by low temperature, facilitates another one, induced by mechanical treatment. The reason for this interesting phenomenon is to be sought in the similarity of the crystal packing of molecules with different molecular conformations in the epsilon- and epsilon'-forms, and of the similarity of the molecular conformations despite different crystal packing in the epsilon'-and alpha-forms.
- 出版日期2011-7
