Self-assembled surfactant cyclic peptide nanostructures as stabilizing agents

A number of cyclic peptides including [FR](4), [FK](4), [WK](5), [CR](4), [AK](4), and [WR](n) (n = 3-5) containing L-amino acids were produced using solid-phase peptide synthesis. We hypothesized that an optimal balance of hydrophobicity and charge could generate self-assembled nanostructures in aqueous solution by intramolecular and/or intermolecular interactions. Among all the designed peptides, [WR](n) (n = 3-5) generated self-assembled vesicle-like nanostructures at room temperature as shown by transmission electron microscopy (TEM), scanning electron microscopy (SEM), and/or dynamic light scattering (DLS). This class of peptides represents the first report of surfactant-like cyclic peptides that self-assemble into nanostructures. A plausible mechanistic insight into the self-assembly of [WR](5) was obtained by molecular modeling studies. Modified [WR](5) analogues, such as [WMeR](5), [WR(Me)2](5), [WMeR(Me)2](5), and [WdR](5), exhibited different morphologies to [WR](5) as shown by TEM observations. [WR] 5 exhibited a significant stabilizing effect for generated silver nanoparticles and glyceraldehyde-3-phosphate dehydrogenase activity. These studies established a new class of surfactant-like cyclic peptides that self-assembled into nanostructures and could have potential applications for the stabilization of silver nanoparticles and protein biomolecules.