Growth mechanism and morphology of phenytoin and their relationship with crystallographic structure

Abstract

Phenytoin crystal growth kinetics have been measured in phosphate buffer as a function of pH, supersaturation, and temperature. Incorporation of growth units into the crystal lattice is controlled by surface integration and follows a screw-dislocation mechanism. This mechanism explains the observed dependence of growth rate on supersaturation and pH. A prediction of phenytoin crystal morphology was made by two methods: the Bravais-Friedel-Donnay-Harker (BFDH) model and attachment energy calculations. The results from both methods compare well with observed phenytoin morphology resulting from growth in certain supersaturation ranges. Observed phenytoin crystal morphology is dominated by the (020) and (011) faces. Both faces were predicted to be morphologically important with the BFDH and attachment energy models. The (002) and (200) faces were also predicted to be morphologically important. However, the (002) was not observed and the (200) was only observed on crystals grown at low supersaturation ( sigma <or=0.4). Solvent-solvent interaction at the growing crystal faces and the types of intermolecular bond formed are proposed as the source of deviation between predicted and observed morphology.