Control of secondary structure and morphology of peptide–guanidiniocarbonylpyrrole conjugates by variation of the chain length

Abstract

Peptide amphiphiles with well-organized secondary structure are an important family of molecules that are known to assemble into a variety of nanostructures. In this work, we present three guanidiniocarbonylpyrrole (GCP) containing peptide amphiphiles, which show versatile morphology and secondary structure changes as a result of different chain lengths and in different concentration regimes. The random coil conformation, α-helix, and β-sheet are obtained for peptide 1, peptide 2, and peptide 3, respectively under neutral aqueous conditions. Furthermore, all peptide amphiphiles can aggregate to form nanoparticles at low concentrations. However, at high concentrations, peptide 1 self-assembles into left-handed twisted helical fibers, while longer bamboo-like morphology can be observed exclusively for peptide 2. For peptide 3, freshly prepared samples show uniform spherical morphology, whereas an obvious morphological transition from original nanoparticles to disordered fibers was realized after incubating for one week. These fascinating morphology changes were determined by the combination of circular dichroism, dynamic light scattering, transmission electron microscopy, atomic force microscopy, and theoretical calculations.