Modeling the crystal morphology of alpha-lactose monohydrate.

Molecular modeling techniques using attachment energy calculations have been applied, for the first time to our knowledge, to simulate the morphology of an organic hydrate: alpha-lactose monohydrate. Calculation of the strong intermolecular forces using the atom-atom approximation and the potential parameters of Nemethy et al. (Némethy, G.; Pottle, M. S.; Scheraga, H. A. J. Phys. Chem. 1983, 87, 1883-1887) reveals the crystallization to be dominated by intermolecular interactions between lactose molecules rather than lactose-water interactions, suggesting that water of hydration plays a space-filling role in the growth process. The simulated crystal shows a tomahawk-like morphology with the polar effect of the monoclinic space group P21 correctly reproduced by the occurrence of only one of the [010] forms. Confrontation of these results with experimental work of our own, involving crystals precipitated from aqueous solutions at various degrees of undercooling examined by scanning electron microscopy, and that of Visser and Bennema (Visser, R. A.; Bennema, P. Neth. Milk Dairy J. 1983, 37,109-137), who assigned faces to a crystal, gives good agreement, suggesting the suitability of the force field and atom-atom approaches to model the crystallization of organic hydrates.