An update on solid-state characterization of the polyphenol pterostilbene

The aim of the study was to provide a complete and systematic characterization of the solid-state properties of the polyphenol pterostilbene (PTB) through an accurate screening of existing polymorphs. For this goal the commercial form of PTB was recrystallized from different hot solvent saturated solutions, also with a view to isolating any new solid forms.
The study is relevant from the point of view of preformulation, given the influence of crystal polymorphism on the physicochemical properties of biologically active compounds (aqueous solubility, dissolution rate, chemical stability, melting point and density).
The recrystallization of the commercial product from different solvents, e.g., acetone, chloroform diethyl ether, ethyl acetate, isopropanol alone and in mixture with water, methanol, dimethyl sulfoxide in equivolumetric solutions with ethanol and methanol and diethyl ether/ethanol, afforded the isolation of the more thermodynamically stable polymorph, form I.
The isolation of the metastable forms II, III and V was carried out by recrystallization of PTB from aqueous solutions of methanol and ethanol at different volumetric ratio. All the isolated phases were characterized using thermal analysis (differential scanning calorimetry, simultaneous thermogravimetric/differential scanning calorimetry analysis, hot stage microscopy) as well as Fourier transform infrared spectroscopy, powder X-ray diffraction and scanning electron microscopy.