POLYMERIZATION-INDUCED EPITAXY OF POLYPEPTIDES ON GRAPHITE STUDIED BY SCANNING-TUNNELING-MICROSCOPY

Ultrathin, epitaxial films of homopolypeptides are directly grown on the basal plane of graphite by performing solution polymerization in the vicinity of the surface and are analyzed by scanning tunneling microscopy. Epitaxial films of poly(glycine) are obtained by a number of different synthetic methods, all forming hydrogen bonded networks resembling the beta-sheets commonly found in bulk with its chain orienting in <1010> of graphite. Polymerization of N-carboxy-gamma-benzyl-L-glutamate anhydrides yields a film of closely packed, highly aligned molecules of poly(gamma-benzyl-L-glutamate). Also, poly(L-phenylalanine) is shown to form crystalline film by polymerization of N-carboxy-L-phenylalanine anhydrides. As it has been difficult to crystallize this polypeptide by other methods, it demonstrates a wide applicability of this polymerization-induced epitaxy. The image patterns of these two polypeptides, however, cannot be explained by the known alpha- or omega-helices. This indicates a possibility of forming a unique structure by a flexibility offered by the noncovalent hydrogen bonding acting on the molecules that are constrained on an atomically flat surface.