Total Asymmetric Transformations at Interfaces with Centrosymmetric Cristals: Role of Hydrophobic and Kinetic Effects in the Crystallization of the System Glycine/α-Amino Acids

Article abstract of DOI:10.1021/ja00210a041

A model of generation and amplification of optical activity, using the centrosymmetric crystals of glycine as substrates for total separation of occluded α-amino acids into enantiomeric territories, is described.The principle is based on the enantioselective occlusion of these additives through the enantiotopic (010) and (0<*>0) faces of glycine cristals.Such crystals, when floating at the air/solution interface, and if correctly oriented, may incorporate only one of the two enantiomeric additives present in solution.We demonstrate that complete (010) or (0<*>0) orientation may be induced by both kinetic and "hydrophobic" effects.The former is achieved through inhibition of nucleation and growth of the say (010) oriented crystals <(010) face toward air>, by (S) amino acids in solution, while the latter is due to induction of (0<*>0) orientation by (S) hydrophobic amino acids.By symmetry the enantiomers induce opposite orientation.The two effects are investigated separately, and possible mechanisms are proposed.Combimation of the two effects, which operate in the same direction, allows total orientation of glycin crystals and thus triggering of amplification starting with a solution containing leucine with an enantiomeric excess as low as 6percent.The relevance of such a mechanism to other systems and to nucleation in general is discussed.