Introduction

Many current industrial products involve the direct formation of particles or at some point in the manufacturing process exist in the solid state. Consequently, consideration of solid-state properties is an integral component of any process to produce particles that will have desirable properties for optimum processing and end use. The application of molecular modeling techniques to the study of solid-state chemistry is playing an increasingly significant role in helping to predict and optimize such properties and also to alleviate many of the problems associated with particle formation and processing. An example where solid-state modeling is having a major impact on processing is crystallization, where the primary engineering concern has been to maximize process yields. Traditionally, little consideration has been given to particle property optimization. Typically, whatever crystal produced has been accepted and subsequently processed to improve materials handling and the property characteristics desired by the end user.

Crystallization of the same molecule under different process conditions can produce particles of radically different crystal structure, size, shape, and properties. In addition to properties that can influence downstream processing, particle characteristics can also influence chemical properties such as activity, reactivity, selectivity, rate of dissolution, and bioefficacy. Differences in the crystal structure can lead to the formation of enantiomorphs or polymorphs (materials with the same chemical structure, but different crystal structures), where one form may have undesirable properties. Changes in polymorphic form can be either problematic or beneficial.