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Moisture induced polymorphic transition of mannitol and its morphological transformation
Tomohiro Yoshinari1, Robert T Forbes, Peter York
1Drug Delivery Group, The School of Pharmacy, University of Bradford, Bradford BD7 1DP, UK.
International Journal of Pharmaceutics
|November 14, 2002
Summary
Moisture triggers a crystalline transformation in mannitol, shifting it from the delta to the beta form. This polymorphic transition, driven by water molecules, increases mannitol
Area of Science:
- Solid-state chemistry
- Materials science
- Crystallography
Background:
- Mannitol exists in three crystalline polymorphic forms: alpha, beta, and delta.
- Understanding polymorphic transitions is crucial for material properties and applications.
Purpose of the Study:
- To investigate the effect of moisture on the polymorphic transition of crystalline mannitol.
- To elucidate the mechanism of moisture-induced polymorphic transition from delta to beta form.
Main Methods:
- Controlled humidity storage (97% RH at 25°C).
- Powder X-ray diffraction (PXRD) for polymorphic identification.
- Scanning electron microscopy (SEM) for morphological analysis.
- Molecular modeling and solid-state NMR (CP/MAS) for mechanistic insights.
Main Results:
- The delta form of mannitol exhibited greater water uptake than the beta form at high relative humidity.
- PXRD confirmed a transition from the delta to the beta form upon exposure to moisture.
- Specific surface area increased from 0.4 to 2.3 m²/g for the delta sample after humidification.
- SEM revealed morphological changes associated with the transition.
Conclusions:
- Moisture induces a polymorphic transition from delta-mannitol to beta-mannitol.
- Water molecules act as a "molecular loosener," facilitating the delta to beta transition via multi-nucleation.
- The increased hygroscopicity of the beta form is attributed to the increased surface area resulting from the polymorphic transition.