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Solid-state characterization of two polymorphs of aspartame hemihydrate
S S Leung1, B E Padden, E J Munson
1Department of Pharmaceutics, College of Pharmacy, University of Minnesota, Minneapolis 55455-0343, USA.
Journal of Pharmaceutical Sciences
|April 21, 1998
Summary
Two aspartame hemihydrate polymorphs were identified: form I and form II. Form II, the commercial form, converts to form I under specific conditions, exhibiting distinct physical and chemical properties.
Area of Science:
- Solid-state chemistry
- Crystallography
- Pharmaceutical sciences
Background:
- Aspartame hemihydrate exists in different crystalline forms (polymorphs).
- Understanding these polymorphs is crucial for drug formulation and stability.
Purpose of the Study:
- To characterize and compare two polymorphs of aspartame hemihydrate.
- To investigate the transformation pathways and stability of these polymorphs.
Main Methods:
- Powder X-ray diffraction (PXRD) for crystal structure analysis.
- Differential scanning calorimetry (DSC) and thermogravimetric analysis (TGA) for thermal properties.
- Spectroscopic techniques (FTIR, 13C SSNMR) for molecular structure.
- Karl Fischer titration for water content.
- Microscopy and particle size analysis for morphology.
Main Results:
- A new polymorph, form II, was identified in commercial aspartame hemihydrate, differing from the known form I.
- Form II transforms to form I upon ball-milling or heating with steam.
- Both polymorphs dehydrate to an anhydrate, with form I dehydrating at a lower temperature.
- Both forms yield the same cyclized product (DKP) upon heating the anhydrate.
- Both forms hydrate to a 2.5-hydrate in contact with liquid water.
Conclusions:
- Aspartame hemihydrate exhibits polymorphism, with distinct forms having different properties.
- The commercial form (form II) is less stable and converts to form I.
- Understanding polymorph behavior is essential for controlling aspartame's solid-state properties.