The Kinetic Story of Tailor-made Additives in Polymorphic Systems: New Data and Molecular Insights for <i>p-</i>Aminobenzoic Acid

Published on 2019-07-11T23:44:13Z (GMT) by
We report on the nucleation and growth kinetics of the α and β polymorphs of <i>p</i>-aminobenzoic acid (<i>p</i>ABA) in the presence of two additives: 4-amino-3-nitrobenzoic acid (ANBA) and 4-amino-3-methoxybenzoic acid (AMBA). While the presence of additives slowed down the nucleation kinetics of both forms, they had a much larger impact on the growth kinetics of the α-form than the β-form. This allowed the nucleation and growth, for the first time, of the β-form (a form much harder to crystallize) in conditions which would normally afford the α-form. Given our previous findings that the nucleation and growth of α <i>p</i>ABA is primarily controlled by aromatic stacking, our additive design strategy was based primarily on the idea that additives could be selected to attach strongly to <i>p</i>ABA stacks while at the same time disrupting adjacent molecules. Such a strategy was successful in selective polymorph inhibition of α; this was possible because the growth of β-form is controlled by interactions other than aromatic stacks. More generally, our study also confirms that additives designed to modify the growth of macroscopic crystals also inhibit their nucleation.

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Black, James. F. B.; Cruz-Cabeza, Aurora. J.; Davey, Roger. J.; Willacy, Robert. D.; Yeoh, Alvin (2019): The Kinetic Story of Tailor-made Additives in Polymorphic

Systems: New Data and Molecular Insights for p-Aminobenzoic

Acid. ACS Publications. Collection.