ORIENTED CRYSTALLIZATION AS A TOOL FOR DETECTING ORDERED AGGREGATES OF WATER-SOLUBLE HYDROPHOBIC ALPHA-AMINO-ACIDS AT THE AIR SOLUTION INTERFACE

The formation of two-dimensional ordered aggregates of water-soluble hydrophobic α-amino acids at the air-solution interface has been demonstrated through the induced epitaxial nucleation of α-glycine crystals at these interfaces. This crystallization method, albeit indirect, has been found to be very sensitive to small changes in the structure of the presumed aggregates. The hydrophobic-amino acids used were divided into two classes: The first, including valine, leucine, phenylalanine, norleucine, isoleucine, and n-aminooctanoic acid, induced fast oriented crystallization of α-glycine, at the solution surface, whereas the second class, tert-butylglycine, neopentylglycine, and hexafluorovaline, did not. The comparison between the packing arrangement of the α-glycine crystalline face attached at the interface and that of various hydrophobic α-amino acid crystals, complemented by surface tension measurements, brought evidence in favor of the formation of structured domains which must carry precise enantioselective information to generate the oriented crystallization process. These results may be relevant to any process involving structural self-aggregation. © 1990, American Chemical Society. All rights reserved.