Molecular modeling of crystal-crystal interactions between the α- and β-polymorphic forms of L-glutamic acid using grid-based methods

Grid-based search methods, employing interatomic potential force fields and appropriate distance constraints, were applied to model interparticle interactions between faceted nanosized molecular clusters of L-glutamic acid having a polyhedral shape as predicted using molecularly based, morphological modeling. Calculations revealed that an interparticle central distance of ca. 30 angstrom was sufficient for satisfactory energy convergence, reflecting the dominance of short-range van der Waals interactions for this material. The modeling indicated that preferential binding takes place where the interacting crystal surfaces on two separate particles form a relatively large number of hydrogen bonds per unit area of the interacting surfaces. In particular, binding is preferred between the (111) and (101) faces of the alpha- and beta-polymorphic forms, respectively, in excellent agreement with experimental data. Potential development of the methodology is reviewed.