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, Theophylline and methyl gallate can form a 1 : 1 co-crystal. Their tableting performance follows the order of theophylline > co-crystal [ methyl gallate. While co-crystallization profoundly improves the tabletability of methyl gallate, it significantly deteriorates that of theophylline. This difference in bulk compaction behaviour originates from the dissimilar crystal plasticity and elasticity, which results from unique molecular packing features in the respective crystal lattices. The presence of a three-dimensional hydrogen bonded network gives rise to very low plasticity in the methyl gallate crystal, which leads to its poor tabletability. In contrast, the layers of two-dimensional rigid, hydrogen bonded molecules in the co-crystal improve the crystal plasticity, by facilitating slip with shear that, in turn, enhances tabletability. However, theophylline undergoes plastic deformation more readily when compared to the co-crystal, because the slip layers in theophylline are composed of hydrogen bonded columns, which provide additional flexibility for slip. As a consequence, theophylline crystals have significantly enhanced tabletability.

Phase behaviors of 1:1 profen-nicotinamide cocrystal systems were delineated by constructing their temperature-composition phase diagrams. Cocrystallization with nicotinamide can simultaneously improve tableting behavior, hygroscopicity, and dissolution performance of ibuprofen and flurbiprofen. This could pave the way for further development of such cocrystal systems into consistent, stable, efficacious and readily manufacturable drug products.

Tuning mechanical performance of molecular materials is currently attractive owing to their practical applications in pharmaceutical, food, and fine chemical industries and optoelectronics. Here we employed a crystal engineering approach to transform four food flavouring agents, vanillin isomers, from brittle to soft solids by forming co-crystals with 6-chloro-2,4dinitroaniline (cda). The series includes vanillin (van), ethylvanillin (evan), iso-vanillin (ivan), as well as a Schiff base of orthovanillin (ovan) with ethylene diamine (sb-ovan). All the co-crystals adopt flat two-dimensional (2D) layer packing, except the sb-ovan:cda, which adopts a corrugated layer packing with the presence of slip planes. The mechanical properties of the cocrystals were studied by (1) a qualitative method, (2) nanoindentation, and (3) powder compaction techniques, which allowed for successfully establishing the relationship among crystal structure, mechanical properties, and tablet tensile strength. The simple qualitative mechanical (deformation) tests confirmed plastic shearing deformation behavior in the cda co-crystals with van, evan, and ivan, while the co-crystal of sb-ovan:cda showed plastic bending due to the presence of slip planes formed by van der Waals interactions in the structure. The measured tensile strengths of the vanillin isomers and their respective co-crystals, which followed the order: sb-ovan:cda > evan > van > ivan:cda > evan:cda > van:cda > sb-ovan > ivan, confirmed that the plastically bendable co-crystal, sb-ovan:cda, shows a significant improvement in the compaction properties compared to any other form studied. In contrast to the initial brittle forms with isotropic structures, the new co-crystal solids show improved plasticity due to their anisotropic 2D-layer structures with active slip planes that facilitate the plastic deformation, which enhances tabletability, particularly in the plastic bendable solid. The study also suggests that the bending type crystals are potentially far better suitable for tabletability than the shearing and brittle type crystals.

The existence of a cocrystal between curcumin (CUR) and phloroglucinol (PHL) was suspected but could not be demonstrated in a recent systematic effort to synthesize novel curcumin cocrystals. We hypothesize that the elusive CUR–PHL cocrystal is a kinetically stable form that can be prepared by trapping it using a fast solvent removal crystallization process. The polarity of crystallization solvent and relative solubility of cocrystal formers in the solvent appear to be critical parameters governing the phase purity of the resulting cocrystal. Organic solvents of higher polarity and in which the cocrystal formers exhibited congruent solubility tended to afford a purer cocrystal phase. Essentially phase-pure CUR–PHL cocrystals were successfully obtained from acetone, and their 1:1 stoichiometry was confirmed by differential scanning calorimetry and solid state nuclear magnetic resonance spectroscopy. Compared with the individual component phases, the cocrystal displayed reduced hygroscopicity and improved tabletability. However, the intrinsic dissolution rate of the cocrystal showed no significant improvement compared with the pure CUR crystal due to the instantaneous conversion of the cocrystal to CUR at its surface upon contact with the dissolution medium.

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Fluorescence-based technologies have revolutionized in vivo monitoring of biomolecules. However, significant technical hurdles in both probe chemistry and complex cellular environments have limited the accuracy of quantifying these biomolecules. Herein, we report a generalizable engineering strategy for dual-emission anti-Kasha-active fluorophores, which combine an integrated fluorescein with chromene (IFC) building block with donor-π-acceptor structural modification. These fluorophores exhibit an invariant near-infrared Kasha emission from the S 1 state, while their anti-Kasha emission from the S 2 state at around 520 nm can be finely regulated via a spirolactone open/closed switch. We introduce bio-recognition moieties to IFC structures, and demonstrate ratiometric quantification of cysteine and glutathione in living cells and animals, using the ratio (S 2 /S 1) with the S 1 emission as a reliable internal reference signal. This de novo strategy of tuning anti-Kasha-active properties expands the in vivo ratiometric quantification toolbox for highly accurate analysis in both basic life science research and clinical applications.

The 1:1 cocrystal between piroxicam and saccharin exhibits significantly deteriorated powder compaction properties compared to both coformers. The molecular origin of this effect is revealed by a systematic investigation of crystal mechanical properties, probed with nanoindentation, and crystal structure analysis. The order of bulk powder tabletability of the three materials is identical to that of single crystal plasticity (saccharin > piroxicam > cocrystal). The lowest plasticity of the cocrystal is confirmed by its highest crystal hardness and the highest yield strength. The low plasticity of the cocrystal is attributed to structural packing features that discourage plastic deformation. This work demonstrates that cocrystallization, even though it may be useful to improve pharmaceutically relevant properties, must be carefully evaluated to avoid unexpected problems in formulation and drug product manufacturing due to compromised mechanical properties.

The effect of preparation method on MnO x -CeO 2 mixed oxide catalysts for methane combustion at low temperature was investigated by means of BET, XRD, XPS, H 2 -TPR techniques and methane oxidation reaction. The catalysts were prepared by the conventional coprecipitation, plasma and modified coprecipitation methods, respectively. It was found that the catalyst prepared by modified coprecipitation was the most active, over which methane conversion reached 90% at a temperature as low as 390°C. The XRD results showed the preparation methods had no effect on the solid solution structure of MnO x -CeO 2 catalysts. More Mn 4+ and richer lattice oxygen were found on the surface of the modified coprecipitation prepared catalyst with the help of XPS analysis, and its reduction and BET surface area were remarkably promoted. These factors could be responsible for its higher activity for methane combustion at low temperature.