Over the last 20 years, the number of publications outlining the advances in design strategies, growing techniques, and characterization of cocrystals has continued to increase significantly within the crystal engineering field. However, only within the last decade have cocrystals found their place in pharmaceuticals, primarily due to their ability to alter physicochemical properties without compromising the structural integrity of the active pharmaceutical ingredient (API) and thus, possibly, the bioactivity. This review article will highlight and discuss the advances made over the last 10 years pertaining to physical and chemical property improvements through pharmaceutical cocrystalline materials and, hopefully, draw closer the fields of crystal engineering and pharmaceutical sciences.

The molecules presented here provide a test-bed for competitive supramolecular chemistry, and on the basis of five crystal structures a ranking of the relative structural importance and influence of competing weak/strong hydrogen bonds and weak/strong halogen bonds has been achieved.

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Image reproduced with permission from Abbie TrewinOther articles published in this issue include:Dipyrrin based homo-and hetero-metallic infinite architectures Stéphane A. Baudron, CrystEngComm, 2010,The nutraceutical compound pterostilbene is investigated for its propensity to form cocrystalline materials with active pharmaceutical ingredients. Three cocrystals of a 1 : 1 stoichiometric molar ratio of pterostilbene with caffeine (two polymorphs, Form I and Form II) and carbamazepine were prepared and characterized by crystallographic (XRPD, single-crystal) and thermoanalytical (TGA, DSC) techniques. Physical stability of the cocrystals with respect to relative humidity (RH) was examined and found to be dramatically improved in relationship to caffeine or carbamazepine. The carbamazepine : pterostilbene cocrystal was stable upon slurrying in water for 3 days; therefore, aqueous equilibrium solubility measurements were carried out, revealing that the cocrystal solubility was 7Â lower than carbamazepine dihydrate and 2.5Â lower than pterostilbene. Slurrying the caffeine : pterostilbene cocrystal (Form I) in water led to a solution that was supersaturated with respect to pterostilbene, resulting in the precipitation of pterostilbene after three days; therefore concentrations at specific time points were measured as opposed to equilibrium solubility. At five hours the concentration of the caffeine cocrystal was 33Â lower than the caffeine hydrate solubility, but was 27Â higher than the pterostilbene solubility.