Role of synthetic surfaces and container topography on the crystal growth of carbamazepine and theophylline

The effects of interfacial interactions, packed and dispersed microspheres, and the topography of crystallization vessels are explored in the crystal growth of two polymorphic pharmaceutical drugs; carbamazepine and theophylline. Three distinct results have emerged from this work: (1) Thiol self-assembled monolayers (SAMs) bearing carboxy functionalities at the interface selectively nucleate the (011) face of the P-monoclinic form of carbamazepine. Geometrical and chemical complementarities at the interface are analyzed to establish the epitaxial relationship between the SAM surface and the crystal faces. (2) Glass vials coated with perfluorinated (PF) silane SAMs led to larger, better formed crystals due to reduced interfacial interactions between SAM and crystal nuclei. Consequently, better control over polymorph selection is achieved by modification of other factors such as temperature, humidity, and rate of evaporation. (3) It was observed that sites of crystallization of concomitant polymorphs of carbamazepine are related to the topography of the crystallization vessel. Such site selectivity is rationalized on the basis of kinetic to thermodynamic phase transition and Ostwald ripening