Novel co-crystals of the nutraceutical sinapic acidElectronic supplementary information (ESI) available: Detailed list of co-formers, IR, PXRD, DSC, TGA, stability data, and additional figures. CCDC 1060811-1060815. For ESI and crystallographic data in CIF or other electronic format see DOI: 10.1039/c5ce00777a

Sinapic acid ( SA ) is a nutraceutical with known anti-oxidant, anti-microbial, anti-inflammatory, anti-cancer, and anti-anxiety properties. Novel co-crystals of SA were prepared with co-formers belonging to the category of GRAS [isonicotinic acid ( INC ), nicotinamide ( NIA )], non-GRAS [4-pyridinecarbonitrile ( PYC )], and active pharmaceutical ingredients (APIs) [6-propyl-2-thiouracil ( PTU )] list of compounds. Structural study based on the X-ray crystal structures revealed the intermolecular hydrogen-bonded interactions and molecular packing. The crystal structure of sinapic acid shows the anticipated acid-acid homodimer along with discrete hydrogen bonds between the acid carbonyl and the phenolic moiety. The robust acid-acid homodimer appears to be very stable and is retained in the structures of two co-crystals ( SA · NIA and SA · PYC ). In these cases, co-crystallization occurs via intermolecular phenol O-H N aromatic hydrogen bonds between the co-formers. In the SA · PTU · 2MeCN co-crystal the acid-acid homodimer gives way to the anticipated acid-amide heterodimer, with the phenolic moiety of SA hydrogen-bonded to acetonitrile. Attempts at obtaining the desolvated co-crystal led to lattice breakdown, thus highlighting the importance of acetonitrile in the formation of the co-crystal. Among the co-crystals examined, SA · INC (5 weeks), SA · NIA (8 weeks) and SA · PYC (5 weeks) were found to be stable under accelerated humidity conditions (40 °C, 75% RH), whereas SA · PTU · 2MeCN decomposed after one week into individual components due to solvent loss. Sinapic acid co-crystals display acid-acid homodimers, phenol O-H N hydrogen bonds and acid-amide heterodimers.