Three flexible peptides (P1: (C(17)H(35)CO-NH-GRGDG)(2)KG; P2: (Fmoc-GRGDG)(2)KG; P3: (CH(3)CO-NH-GRGDG)(2)KG) self-assembled to form a variety of morphologically distinct assemblies at different pHs. P1 formed nanofibers at pH 3, then self-assembled into nanospheres with pH up to 6 and further changed to lamellar structures when the pH value was further increased to 10. P2 aggregated into an entwined network structure at pH 3, and then self-assembled into well-defined nanospheres, lamellar structures, and vesicles via adjusting the pH value. However, P3 did not self-assemble into well-ordered nanostructures, presumably due to the absence of a large hydrophobic group. The varying self-assembly behaviors of the peptides at different pHs are attributed to molecular conformational changes. These self-assembled supramolecular materials might contribute to the development of new peptide-based biomaterials.

Peptide self-assembling materials have recently emerged as one of the most promising biomaterials. In this study, we synthesized three amphipathic cyclopeptides (CPs1-3) with systematically modified side chains to control the morphologies of self-assembly. Owing to the varying modifications of the side chains, various micro/nanostructures were achieved because of different driving forces. The obtained morphologies were characterized by transmission electron microscopy (TEM) and scanning electron microscope (SEM). Apart from hydrogen bond interactions for CPs, CP1 self-assembles into spindlelike aggregates with an average diameter of 70 nm and a length of 300 nm owing to the salt-bridge interactions in a neutral medium. CP2 can form micro/nanotubes with the diameters ranging from 750 nm to 2 mm via the hydrophilic and hydrophobic interactions between the cyclopeptide ring and the alkyl chain. While CP3 forms solid nanospheres with an average diameter of 516 nm through aromaticaromatic p-p interactions. This approach can lead to the fabrication of new functional supramolecular assemblies and materials and broaden the insights for the mechanism of the self-assembly.