Construction and Piezoelectric Properties of a Single-Peptide Nanotube Composed of Cyclic β-peptides with Helical Peptides on the Side Chains.

Abstract

To develop nanopiezoelectronics, it is necessary to investigate the relationship between the sizes and piezoelectric properties of the material. Peptide nanotubes (PNTs) composed of cyclic β-peptides have been studied as leading candidates for nanopiezoelectric materials. The current drawback of PNTs is aggregation to form a PNT bundle structure due to strong dipole-dipole interactions between PNTs. Here, we report the construction and piezoelectric properties of single PNTs without nonspecific aggregation by side-chain modification of helical peptides. A cyclic tri-β-peptide with a helical peptide was prepared by multiple-step liquid-phase peptide synthesis and assembled into PNTs by the vapor diffusion method. These nanotubes were characterized by polarized light microscopy and Fourier transform infrared (FTIR) spectroscopy. Additionally, atomic force microscopy (AFM) topographic images showed nanotubes with a height of 4 nm, which corresponds to the diameter of a PNT on a gold-coated mica substrate, indicating that a single PNT was prepared successfully. The converted piezoelectric response of a single PNT was determined to be 1.39 ± 0.12 pm/V. This value was consistent with that of a PNT bundle, which reveals that the piezoelectricity of PNTs is induced by deformation of their cyclic skeletons and is independent of the bundled structure. This finding not only demonstrates a new molecular design strategy to construct these smallest piezoelectric biomaterials by controlling the supramolecular hierarchical structures but also provides insights into the correlation between molecular assembly morphology and size-dependent piezoelectric properties.