Hierarchical assembly of collagen peptide triple helices into curved disks and metal ion-promoted hollow spheres.

A 27 amino acid collagen-based peptide (Hbyp3) was designed to radially display nine hydrophobic bipyridine moieties from a triple helical scaffold. Self-assembly of such functionalized triple helices led to the formation of micrometer-scaled disks with a curved morphology, presumably mediated by aromatic interactions, with a height that is in the range of the length of the triple helical peptide. Higher order assembly of these curved disks into micrometer-sized hollow spheres was accomplished through metal-ligand interactions between bipyridine groups of the disks and metal ions such as Fe(II), Co(II), Zn(II) and Cu(II). The thickness of the shell of these hollow spheres corresponds well with the thickness of the collagen peptide-based triple helix and the corresponding self-assembled disks. Addition of a metal ion chelator was found to reverse the assembly of the hollow spheres back to the curved disk structures. These data support the formation of the hollow spheres from the self-assembled disks of Hbyp3 upon addition of metal ions.