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High-Contrast and Fast Photorheological Switching of a Twist-Bend Nematic Liquid Crystal
Published on: October 31, 2019
Demonstration of a shear-based solid-state phase transformation in a small molecular organic system: chlorpropamide
Peter L D Wildfong1, Kenneth R Morris, Carl A Anderson
1Duquesne University Mylan School of Pharmacy, 600 Forbes Avenue, Pittsburgh, Pennsylvania 15282, USA. wildfongp@duq.edu
Journal of Pharmaceutical Sciences
|April 25, 2007
Summary
Mechanically induced solid-state transformations in chlorpropamide (API) enantiotropes were studied. Shear stress, not hydrostatic pressure, drives these phase changes during compaction, impacting drug formulation.
Area of Science:
- Solid-state chemistry
- Materials science
- Crystallography
Background:
- Understanding mechanically activated phase transformations of Active Pharmaceutical Ingredients (APIs) is crucial for materials and process development.
- Chlorpropamide, an anti-diabetic drug, exists in enantiotropic forms (A and C) with different solid-state properties.
Purpose of the Study:
- To investigate the mechanically induced solid-state transformation between the A and C enantiotropes of chlorpropamide.
- To elucidate the mechanisms governing pressure-induced phase interconversion in chlorpropamide polymorphs.
Main Methods:
- Powder X-ray diffraction (PXRD) was used to solve the crystal structure of the high-temperature stable phase (form C).
- In situ transmission PXRD and Raman spectroscopy quantified phase interconversion under applied pressure during compaction.
- Crystallographic structures of both enantiotropes were examined.
Main Results:
- Both chlorpropamide polymorphs underwent solid-state transitions that increased with applied pressure up to the powder consolidation limit.
- Phase interconversion was not observed under hydrostatic pressure, indicating a dependence on shear stress during compaction.
- Both crystal structures share a common slip system with preserved molecular positions.
Conclusions:
- Mechanically induced phase transformations in chlorpropamide are shear-dependent, occurring when resolved shear stresses initiate deformation.
- Lattice distortion under shear stress allows for simultaneous reconformation of molecules, facilitating the solid-state transformation between enantiotropes.
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