Synthesis and atomic force microscopy observations of the single-peptide nanotubes and their micro-order assemblies

Hexa-peptide nanotubes $\left(cyclo\right[-(L-\mathrm{Gln}-D-\mathrm{Ala}{)}_3])$ and octa-peptide nanotubes $\left(cyclo\right[-(L-\mathrm{Gln}-D-\mathrm{Ala}{)}_4])$ were synthesized by a solid-phase method using Fmoc chemistry. We investigated their morphology by atomic force microscopy (AFM) and observed the single straight nanotube forms. We also obtained AFM images of the nano-order and/or micro-order assemblies on the same substrates. The assembled forms were rather different between the hexa-peptide nanotubes and the octa-peptide nanotubes. While the former produce nanobundles or microbundles, the latter form micro-order aggregated bundles.