Phloretin (PHL) is an abundant dietary flavonoid possessing
several
pharmacological activities but with poor aqueous solubility and low
bioavailability. Herein, two new cocrystals of phloretin-nicotinamide
(PHL-NIC) and phloretin-isonicotinamide (PHL-INM) have been synthesized
and characterized by various analytical methods. Two cocrystals exhibited
different crystal packing and intermolecular interactions. Strong
photoluminescence was observed in the PHL-NIC cocrystal while not
in the PHL-INM cocrystal and pure PHL. Density functional theory (DFT)
calculations were conducted to interpret the distinct photoluminescent
behavior between the cocrystals. Both cocrystals exhibited enhanced
dissolution performance in comparison with the pure PHL. This study
demonstrates that cocrystallization is a powerful strategy to tune
the physical properties of functional organic solids.
Crystal habit is a key physical attribute
that impacts the processing
and performance of organic crystalline materials, especially pharmaceuticals
and organic electronics. Here, we report that the presence of a solvent
creates the highly unusual triangular habit of an organic crystal,
biochanin A (BCA), a natural product with multiple pharmacological
activities. From the vapor phase, BCA grows as needles with equal
rates along the opposite directions of the polar c axis. In contrast, crystal growth from a toluene solution is observed
only along the –c direction, leading to a
triangular plate. This rare growth morphology is attributed to the
polar crystal structure of BCA and differences in solvent–surface
interactions. Molecular dynamics simulations show that toluene molecules
bind to the hydroxyl exposing face more strongly than the methoxy
exposing face, leading to inhibition of growth along the +c axis. This study contributes in-depth understanding regarding
the solvent effect on the habit modification of polar crystals.
Pharmaceutical cocrystals,
a type of multicomponent crystalline
material incorporating two or more molecular and/or ionic compounds
connected by noncovalent interactions (such as hydrogen bonds, π–π
interactions, and halogen bonds), are attracting increasing attention
in crystal engineering. Sulfaguanidine (SGD), one of the most frequently
used sulfonamide compounds, was chosen as a model compound in this
work to further investigate the hydrogen bond interactions in cocrystals,
since it possesses various hydrogen bond donor and acceptor sites.
Five cocrystals of SGD, synthesized successfully by slurry and slow
evaporation methods, were fully characterized by thermal analysis,
X-ray techniques, and Fourier transform infrared spectroscopy. To
gain insight into the nature of hydrogen-bonding interactions, theoretical
calculations including the analysis of Hirshfeld surface, MEPS (molecular
electrostatic potential surface), and QTAIM (quantum theory of atoms
in molecules) were conducted. The results are a part of a systematic
study of cocrystals of sulfonamides that aims to establish synthon
hierarchies in cocrystals containing molecules with multiple hydrogen-bonding
functional groups.
Piroxicam (PRM) and meloxicam (MEL) are two nonsteroidal anti-inflammatory drugs, belonging to the Biopharmaceutics Classification System Class II drugs. In this study, six novel pharmaceutical salts of PRM and MEL with three basic organic counterions, that is, 4-aminopyridine (4AP), 4-dimethylaminopyridine (4DMP), and piperazine (PPZ), were prepared by both slurrying and slow evaporation. These salts were characterized by single-crystal and powder X-ray diffraction, thermal analysis, and Fourier transform infrared spectroscopy. All six salts, especially MEL-4DMP and MEL-4AP, showed a significantly improved apparent solubility and dissolution rate in sodium phosphate solution compared with the pure APIs. Notably, PRM-4AP and PRM-4DMP salts exhibited enhanced fluorescence, and the PRM-PPZ salt showed weaker fluorescence compared with that of pure PRM due to different luminescence mechanisms.
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