Concerning the crystal morphologies of the α and β polymorphs of p-aminobenzoic acid

Abstract

The definition of crystal morphologies in polymorphic systems is a fundamental area of crystal engineering with implications for down-stream processing and formulation, which make morphological studies highly relevant. There are few recent examples of such detailed studies in the literature and here we address the case of p-aminobenzoic acid (PABA), focusing on its two polymorphic forms, α and β. Using a combination of modelling techniques to create predicted morphologies, we interpret these in the light of experimental data recorded on crystals grown from a range of polar solvents. Preliminary discussion of the intermolecular interactions involved in crystal growth of both forms, allow us to explore the enhanced morphological importance of the (002) face in α PABA and of (10) and (01) faces for β PABA. It is suggested that desolvation plays a paramount role.