Faquan Yu

Preferred formation of the carboxylic acid–pyridine heterosynthon in 2-anilinonicotinic acids

The carboxylic acid–carboxylic acid homosynthon and carboxylic acid–pyridine heterosynthon are two competing supramolecular synthons in 2-anilinonicotinic acids that possess both carboxylic acid and pyridine functionalities. Previously we demonstrated that carboxylic acid–pyridine heterosynthons can be selectively formed in crystals by chemically introducing bulky functional groups to the aniline ring of the molecules. In this study we show that with the same philosophy, but a different strategy, i.e., adding substituent groups to the nitrogen bridging the two aromatic rings, we can also achieve the preferential formation of the carboxylic acid–pyridine heterosynthon over the carboxylic acid–carboxylic acid homosynthon. This is a new case of how molecular conformation can affect intermolecular interactions and consequent crystal packing.

sp2CH⋯Cl hydrogen bond in the conformational polymorphism of 4-chloro-phenylanthranilic acid

Chlorine can participate in numerous interactions such as halogen bonding, hydrogen bonding, and London dispersion in the solid state. In this work, we report the influence of a chlorine substituent on the polymorphism of a potential anticancer drug, 4-chloro-phenylanthranilic acid (CPAA). Three polymorphs have been discovered for this compound, and the three forms were characterized by single-crystal X-ray diffraction, power X-ray diffraction (PXRD), FT-IR, and Raman spectroscopy. Both conformational flexibility of the molecule and the sp2CH⋯Cl hydrogen bond seem to lead to the polymorphism of the system. The phase behavior was investigated by differential scanning calorimetry (DSC), with the conclusion that form II converts to III upon heating. A conformational scan shows the conformational minima corresponds to the conformers existing in the polymorphs. Lattice energy calculations show energies of −106.70, −104.72, and −194.42 kJ mol−1 for forms I to III, providing information on relative stability for each form. Hirshfeld analysis revealed that intermolecular interactions such as H⋯H, C⋯H, H⋯Cl, and H⋯O contribute to the stability of the crystal forms.

Solution growth and thermal treatment of crystals lead to two new forms of 2-((2,6-dimethylphenyl)amino)benzoic acid

We report the discovery of two new forms (II and III) of a potential non-steroidal anti-inflammatory and thyroid drug, 2-((2,6-dimethylphenyl)amino)benzoic acid (HDMPA) through solution growth and thermal treatment of crystals. Form II has been discovered through crystal growth in a variety of solvents, and characterized by single-crystal X-ray diffraction, powder X-ray diffraction (PXRD), FT-IR, and Raman spectroscopy. Form II converts into form III upon thermal treatment, as indicated by the phase behavior study of form II with differential scanning calorimetry (DSC). Form III has been characterized by IR, Raman and PXRD. Conformational flexibility of the molecule seems to lead to the polymorphism of the system. A conformational scan shows the conformational minima correspond to the conformers in the polymorphs. Lattice energy calculations show energies of −48.14 and −50.31 kcal mol−1 for forms I and II, providing information on the relative stability for each form. Hirshfeld analysis revealed that intermolecular interactions such as C⋯C, H⋯H, C⋯H, and H⋯O contribute to the stability of the crystal forms.

CCDC 1846857: Experimental Crystal Structure Determination

Related Article: Siqing Peng, Faquan Yu, Danrui Xu, Conggang Li, Sean R. Parkin, Tonglei Li, Mingtao Zhang, Sihui Long|2018|Cryst.Growth Des.|18|4849|doi:10.1021/acs.cgd.8b00840

Zwitterion formation and subsequent carboxylate–pyridinium NH synthon generation through isomerization of 2-anilinonicotinic acid

Through structural modification of 2-anilinonicotinic acid by isomerization, the ΔpKa between the carboxylic acid and pyridinium NH increased dramatically over the threshold to form zwitterions in the newly designed 4-anilinonicotinic acids. This in turn led to the formation of a hydrogen bond between carboxylate and pyridinium NH, and the absence of two commonly observed synthons, i.e., the acid–acid homosynthon and acid–pyridine heterosynthon. The new synthon has a stronger hydrogen bond than the acid–acid homosynthon and the acid–pyridine heterosynthon, as suggested by theoretical calculations. This, together with the much larger ΔpKa, explains its formation.