cg8b01325_si_001.pdf (1.96 MB)
The Kinetic Story of Tailor-made Additives in Polymorphic Systems: New Data and Molecular Insights for p-Aminobenzoic Acid
journal contribution
posted on 2018-10-26, 00:00 authored by James. F. B. Black, Aurora. J. Cruz-Cabeza, Roger. J. Davey, Robert. D. Willacy, Alvin YeohWe
report on the nucleation and growth kinetics of the α and β
polymorphs of p-aminobenzoic acid (pABA) 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 pABA 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 pABA 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.