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Download fileSpontaneous Solid-State Cocrystallization of Caffeine and Urea
journal contribution
posted on 15.01.2020, 13:05 by Pól MacFhionnghaile, Clare M. Crowley, Patrick McArdle, Andrea ErxlebenThe
cocrystallization of caffeine and urea was monitored and analyzed
using infrared spectroscopy, Raman microscopy, scanning electron microscopy,
differential scanning calorimetry, and X-ray diffraction. The caffeine–urea
cocrystal was shown to form spontaneously over several weeks under
low energy mixing of the solids at room temperature and low relative
humidity (<30%). Premilling the two coformers separately accelerated
the process, and the cocrystal formation could be detected within
3 days. When caffeine and urea were milled together, the physical
mixture that was confirmed by X-ray powder diffraction immediately
after milling transformed to the cocrystal within hours of storage
at room temperature and 30% relative humidity. The scanning electron
microscopy images of the milled sample indicated the role of interparticle
surface contact in the spontaneous solid-state reaction. Multivariate
data analysis was used to find the optimum cooling crystallization
conditions for obtaining cocrystals suitable for single crystal X-ray
analysis.