From Form to Function: Crystal Engineering for Organic & Drug Molecules

Michael Doherty of UC Santa Barbara

Crystalline organic solids are ubiquitous as either final products or as intermediates in the fine chemical, pharmaceutical, organic electronics, and home & personal care industries.  In most cases the properties of the crystalline solid (e.g., structure, shape, size, etc.) have a major impact on the functionality of the product as well as the design and operation of the manufacturing process, and in most cases the two cannot considered separately.  Gibbs was the first to recognize that crystals rarely achieved their equilibrium (surface energy minimizing) shape but it took almost 100 years to discover how to identify their real growth shapes.  In this seminar I will describe a novel, (relatively) simple and accurate method for predicting the shape evolution and ultimate steady-state shape of 3-dimensional faceted crystals grown from solution.  The model is initialized from an arbitrary initial seed shape and size, but known polymorph. The growth model for the crystal faces is based on the pioneering screw dislocation model of Burton, Cabrera and Frank in which surface integration kinetics is the rate determining step.  The model has been successfully applied to a selection of complex molecular crystals of interest in pharmaceutical applications.