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Fisetin, a naturally occurring polyphenolic compound, has a proven record of in vitro demonstrated anti-carcinogenic, anti-inflammatory and antiviral properties, yet similarly to many promising APIs, its in vivo administration is complicated by low aqueous solubility and unfavourable pharmacokinetics. The presented study was focused on obtaining and characterizing cocrystals of fisetin, with the aim of improving its solubility. Solvent-drop grinding experiments, combined with FT-Raman and XRPD, were conducted to identify new cocrystalline phases, which were afterwards isolated as single-crystals and characterized structurally and in terms of thermal stability and solubility. Dissolution studies of pure fisetin and four cocrystals, namely fisetin-isonicotinamide 1 : 1 (FisInam), fisetin-nicotinamide 1 : 2 hemiethanolate (FisNam), fisetin-nicotinamide 1 : 1 (FisNam2) and fisetin-caffeine 1 : 2 (FisCaf), showed that a 2.5-fold increase of fisetin solubility was achieved for FisNam and to a smaller extent for FisCaf and FisInam (ca. 1.8-and 1.5-fold, respectively).

Water sorption isotherms at 27 degrees C have been measured for lysozyme and chymotrypsin in suspensions of toluene, di(n-butyl) ether, n-propanol, and a solution of 1M n-propanol in benzene. Sorption isotherms for the different suspensions are compared by converting solvent water content to the thermodynamic activity of water in each solvent. The sorption behavior is also compared to that for the two proteins hydrated from the vapor phase. At low water activities, all sorption isotherms are similar when compared on the basis of water activity. However, at higher activities, water sorption by the proteins in the organic suspensions is suppressed relative to the sorption of water vapor. The greatest suppression is observed for n-propanol, which suggests that the suppression may be due to a competition for water-binding sites on the protein by the organic solvent. Sorption isotherms at low water activities have also been predicted using a thermodynamic model in which it is assumed that water binds selectively to the ionizable residues on the surface of the protein. A comparison of predicted and measured sorption isotherms shows that the model can provide reasonable estimates of water sorption in nonpolar or moderately polar organic solvent suspensions at low levels of hydration.

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Cocrystallization of baicalein with nicotinamide yields a 1:1 cocrystal [systematic name: pyridine-3-carboxamide-5,6,7-trihydroxy-2-phenyl-4H-chromen-4-one (1/1)], C(6)H(6)N(2)O·C(15)H(10)O(5). The asymmetric unit contains one baicalein and one nicotinamide molecule, both in neutral forms. Molecules in the cocrystal form column motifs stabilized by an array of intermolecular hydrogen bonds.

Genistein, a naturally occurring polyphenolic compound, was combined with isonicotinamide, a pharmaceutically acceptable coformer, to yield a 1:2 cocrystal [systematic name: 5,7-dihydroxy-3-(4-hydroxyphenyl)chromen-4-one-pyridine-4-carboxamide (1/2)], C15H10O5·2C6H6N2O. The molecules in the cocrystalline phase are present in their neutral forms, and assemble a molecular layer by means of hydrogen bonding.

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