2008 Annual Meeting
(744d) Mechanistic Model for the Effect of Molecular Imposters on the Shape of Molecular Organic Crystals
Models of crystal growth shape have moved away from those depending only on crystal geometry or thermodynamics to incorporate mechanistic ideas such as the incorporation of solute at kink sites. In particular, there exists a class of kinetic models based on step flow and the spiral growth of crystal surfaces which are founded on the work of Burton, Cabrera, and Frank (1951) and Chernov (1961); solvent effects in these models have been accounted for by Winn and Doherty (1998).
We furnish an extension of these crystal growth models to capture the effect of structurally-related by-products (here termed imposters) based on a mechanistic description of the way a molecular imposter impacts a growing crystal surface. We argue that the imposter has no net effect on these growth spirals except at the point where the first turn of a spiral occurs. The model is applied to alpha-glycine growing from water in the presence of L-alanine, and our shape predictions are compared to experimental results (Weissbuch et al., 1983).
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Chernov, A.A. The Spiral Growth of Crystals. Soviet Physics Uspekhi, 4: 117145, 1961.
Weissbuch, I., L. Addadi, Z. Berkovitch-Yellin, E. Gati, S. Weinstein, M. Lahav, and L. Leiserowitz. Centrosymmetric crystals for the direct assignment of the absolute configuration of chiral molecules: Application to the alpha-amino acids by their effect on glycine crystals. J. Am. Chem. Soc., 105: 66156621, 1983.