Solid−Liquid Interfacial Free Energy of Water: A Molecular Dynamics Simulation Study

Pressure Dependence of the Crystallization Rate for the S-Enantiomer and a Racemic Mixture of Ibuprofen

This paper examines the pressure effect on the crystallization rate of the pharmaceutically active enantiomerically pure S-enantiomer and the racemic mixture of the well-known drug ibuprofen. Performed experimental studies revealed that at ambient pressure S-ibuprofen crystallizes faster than the racemic mixture. When the pressure increases, the crystallization rate slows down for both systems, but interestingly it is more apparent in the case of the S-enantiomer. It is found that this experimentally observed trend can be understood based on the predictions of the classical nucleation theory. We suggest that the solid-liquid interfacial free energy is the main reason for the observed variations in S- and RS-ibuprofen's stability behaviors. Employing a special method of computational studies, i.e., the capillary fluctuation method, we show that the increase in pressure affects the solid-liquid interfacial free energy for S- and RS-ibuprofen in an entirely different way. Importantly, the detected differences correspond to the experimentally observed variations in the overall crystallization rates.

Direct calculation of solid-liquid interfacial free energy for molecular systems: TIP4P ice-water interface

By extending the cleaving method to molecular systems, we perform direct calculations of the ice Ih-water interfacial free energy for the TIP4P model. The values for the basal, prism, and {112[over]0} faces are 23.3+/-0.8 mJ m{-2}, 23.6+/-1.0 mJ m{-2}, and 24.7+/-0.8 mJ m{-2}, respectively. The closeness of these values implies a minimal role of thermodynamic factors in the anisotropic growth of ice crystals. These results are about 20% lower than the best experimental estimates. However, the Turnbull coefficient is about 50% higher than for real water, indicating a possible limitation of the TIP4P model in describing freezing.