Effect of solution speciation of impurities on α-glycine crystal habit: A molecular modeling study

In a recent work, we reported that solution speciation of certain “tailor-made” impurities (viz. aspartic and glutamic acids) controlled their stereoselective interactions at the α-glycine crystal interfaces [S.K. Poornachary, P.S. Chow, R.B.H. Tan, R.J. Davey, Cryst. Growth Des. 7(2) (2007) 254]. In this contribution, we rationalize this mechanism using molecular modeling and atom–atom potential energy calculations. The simulation results show preferential interaction of the impurity zwitterions on a flat (0 1 0) surface, and of the impurity anions either at the kink site on the (0 1 0) step, or on the (0 1 1) surface. We corroborate these results with the growth inhibition observed along b- and c-axes of α-glycine crystals in the presence of these impurities.