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A new cocrystal of baicalein, possessing three A-ring-hydroxyl groups and without B-ring-hydroxyl groups and 4,4′-bipyridine (BE·2BPY·H2O) has been prepared and characterized. The structural analyses and Hirshfeld surfaces show that baicalein is hydrogen-bonded to co-crystallized solvent water molecules featuring for example motifs that can be described with graph set R44(8) similar to those reported for the cocrystal of myricetin with 4,4′-bipyridine. A zipper-type architecture is observed in cocrystal BE·2BPY·H2O linking a baicalein, two 4,4′-bipyridine and a solvent water molecules via classical O–H⋯N and O–H⋯O and non-classical C–H⋯O hydrogen bonds into 2D sheets. Additionally, the cocrystal shows better solubility in 0.1 M HCl in comparison to pure baicalein. Cocrystal of baicalein with zipper-type architecture shows improved solubility compared to baicalein. [ABSTRACT FROM AUTHOR]

Abstract Based on analyzing intermolecular interaction in building unit of cocrystal of quercetin with 4,4′-bipyridine (QUE·BPY) reported by us on before, a new cocrystal of kaempferol with 4,4′-bipyridine (KAE·BPY) has been designed and synthesized. Within the reported QUE·BPY , 3′ OH was neither involved in the formation of the building unit nor played a big role in the 2D layer. Consequently, we boldly speculate kaempferol without 3′ OH might crystallize with 4,4′-bipyridine to form similar structure to QUE·BPY. Just as expected, structural analysis shows kaempferol molecules and 4,4′-bipyridine molecules alternate connect to form the building units through 7-OH and 4′ OH hydrogen bonds, the structure of KAE·BPY is similar to QUE·BPY. This work proves that new cocrystals could be designed and synthetized by analyzing the intermolecular interaction in building unit and seeking right structure of Active Pharmaceutical Ingredients (APIs). Additionally, the cocrystal of kaempferol with 4,4′-bipyridine shows advantages in terms of hygroscopic stability in comparison to pure kaempferol. Highlights • A kaempferol-4,4′-bipyridine cocrystal was prepared by solution evaporation. • The cocrystal was prepared by analyzing intermolecular interaction of building units. • The cocrystal shows improved hygroscopic stability in comparison to pure kaempferol. [ABSTRACT FROM AUTHOR]