Understanding and Designing Tailor-Made Additives for Controlling Nucleation: Case Study of <i>p</i>-Aminobenzoic Acid Crystallizing from Ethanolic Solutions
Peter L. Kaskiewicz, Ian Rosbottom, Robert B. Hammond, Nicholas J. Warren, Colin Morton, Peter J. Dowding, Neil George, Kevin J. Roberts
Abstract
A workflow for tailor-made additive screening and crystallization control using a combination of molecular modeling and experimental techniques is presented. The impact of seven structurally analogous additives, the majority of which contain a carboxylic acid group, on the nucleation of α-para-aminobenzoic acid is assessed. Intermolecular grid search modeling is used to determine dimer interaction energies. Of these, three tailor-made additives are found to form stronger carboxylic group dimer interactions with the compound. Solvation energy calculations demonstrate the stability of these dimers in solution. Subsequent intermolecular interaction assessment demonstrates an ability of one of the tailor-made additives to interfere with the molecular preassembly route to nucleation, with molecular charge distributions providing an insight into this effect. Polythermal crystallization experimental screening confirms the effectiveness of these tailor-made additives to inhibit nucleation. Interestingly, the nucleation mechanism is found to change from instantaneous to progressive nucleation in the absence and presence of the tailor-made additives in solution, respectively, together with an increase in the effective interfacial tension.