One of the most powerful strategies for the preparation of nanotubes is based on the stacking of flat-shaped cyclic peptide components. This strategy allows precise control of the nanotube internal diameter, the external properties and, more recently, the structural characterisitics of the internal cavity. The recent advances in these technologies and the applications of the resulting materials are described.

Peptide nanotubes are novel supramolecular nanobiomaterials that have a tubular structure. The stacking of cyclic components is one of the most promising strategies amongst the methods described in recent years for the preparation of nanotubes. This strategy allows precise control of the nanotube surface properties and the dimensions of the tube diameter. In addition, the incorporation of 3- aminocycloalkanecarboxylic acid residues in the nanotube-forming peptides allows control of the internal properties of the supramolecular tube. The research aimed at the application of membrane-interacting self-assembled cyclic peptide nanotubes (SCPNs) is summarized in this review. The cyclic peptides are designed to interact with phospholipid bilayers to induce nanotube formation. The properties and orientation of the nanotube can be tuned by tailoring the peptide sequence. Hydrophobic peptides form transmembrane pores with a hydrophilic orifice, the nature of which has been exploited to transport ions and small molecules efficiently. These synthetic ion channels are selective for alkali metal ions (Na(+), K(+) or Cs(+)) over divalent cations (Ca(2+)) or anions (Cl(-)). Unfortunately, selectivity was not achieved within the series of alkali metal ions, for which ion transport rates followed the diffusion rates in water. Amphipathic peptides form nanotubes that lie parallel to the membrane. Interestingly, nanotube formation takes place preferentially on the surface of bacterial membranes, thus making these materials suitable for the development of new antimicrobial agents.

The design and synthesis of self-assembling cyclic peptides with tunable cavity properties is described, allowing the incorporation of guests with different features.