Cocrystal of curcumin with 4,4′-bipyridine toward improved dissolution: Design, structure analysis, and solid-state characterization

The prime active ingredient of the herb curcuma longa, curcumin (CUR) has extensive pharmacological activities and high security. However, the low solubility severely restricts its investigation and application as a drug. In this paper, a new cocrystal, CUR–BPY, assembled by CUR and BPY (4,4′-bipyridine) has been synthesized and characterized by various analytical methods. Single-crystal X-ray diffraction reveals that CUR–BPY contains a pentameric BPY–CUR–BPY–CUR–BPY supramolecular architecture connected by OH⋯N hydrogen bonds and further extended to give a 1D loop-like chain through aromatic interactions. Powder dissolution experiment reveals that CUR–BPY exhibits obvious spring phenomenon and about 7 times higher apparent solubility than that of raw curcumin. The improved dissolution performance should be ascribed to the careful selection of BPY coformer and expected OH⋯N weak hydrogen bonding in CUR-BPY cocrystal.