Difference in self-assembling morphology of peptide nanorings

We synthesized the peptide nanorings of cyclo[-(D-Ala-L-Gln)(3)], cyclo[-(D-CyS-L-Gln)(3)], CyC10[-D-Cys-L-HiS-D-Ala-L-Asn-Gly-L-Gln-1 and Cyc1o[-(L-Gln)(5)], and studied the way in which the difference in the type and/or number of component amino acid residues changes the self-assembling morphology of the nanorings on gold substrates by atomic force microscopy. The study revealed that CyClo[-(D-Ala-L-Gln)(3)] formed nanotube bundles through inter-ring hydrogen bonds, while the nanorings of CyC10[-(D-CyS-L-Gln)3] adhered to the gold surface directly due to the high affinity of thiol to gold. In contrast, a random amino acid sequence of cyclo[-D-CyS-L-HiS-D-Ala-L-Asn-GlY-L-Gln-] resulted in many isolated nanotubes, which were first observed in the present study. While the D,L-peptide nanotubes have very straight forms, the homo-L-peptide of cyclo[-(L-Gln)(5)] formed interesting randomly branching nanotubes that were entwined and grew on the substrate. Scanning tunneling microscopy was also performed and high-resolution images of both the peptide nanotubes and the nanotube bundles were obtained.