Self-Assembled Nanomaterials Based on Beta (β3) Tetrapeptides

β 3-amino acid based polypeptides offer a unique starting material for the design of self-assembled nanostructures such as fibres and hierarchical dendritic assemblies, due to their well-defined helical geometry in which the peptide side chains align at 120° due to the 3.0–3.1 residue pitch of the helix. In a previous work we have described the head-to-tail self-assembly of N-terminal acetylated β 3-peptides into infinite helical nanorods that was achieved by designing a bioinspired supramolecular self-assembly motif. Here we describe the effect of consecutively more polar side chains on the self-assembly characteristics of β 3-tetrapeptides Ac-β 3Ala-β 3Leu-β 3Ile-β 3Ala (Ac-β3[ALIA]), Ac-β3Ser-β 3Leu-β 3Ile-β 3Ala (Ac-β3[SLIA]) and Ac-β 3Lys-β 3Leu-β 3Ile-β 3Glu (Ac-β3[KLIE]). β 3-tetrapeptides complete 1 1/3 turns of the helix: thus in the oligomeric form the side chain positions shift 120° with each added monomer, forming a regular periodic pattern along the nanorod. Dynamic light scattering (DLS) measurements confirmed that these peptides self-assemble even in highly polar solvents such as water and DMSO, while diffusion-ordered NMR spectroscopy revealed the presence of a substantial monomeric population. Temperature dependence of the size distribution in DLS measurements suggests a dynamic equilibrium between monomers and oligomers. Solution casting produced distinct fibrillar deposits after evaporating the solvent. In the case of the apolar Ac-β 3[ALIA] the longitudinal helix morphology gives rise to geometrically defined (~70°) junctions between fibres, forming a mesh that opens up possibilities for applications e.g. in tissue scaffolding. The deposits of polar Ac-β 3[SLIA] and Ac-β 3[KLIE] exhibit fibres in regular parallel alignment over surface areas in the order of 10 μm

A two-dimensional metallosupramolecular framework design based on coordination crosslinking of helical oligoamide nanorods

Spontaneous formation of nanostructured materials of defined structure and morphology is a crucial milestone toward realizing true bottom-up nanofabrication. Supramolecular recognition offers unparalleled specificity, selectivity and geometric flexibility to design hierarchical nanostructures. However, competition between similar binding motifs and the dynamic nature of the attachment imposes a severe limitation on the complexity of the achievable structures. Here we outline a design based on two distinct binding motifs in a supramolecular fibrous assembly to realize a metallosupramolecular framework (MSF). Controlled geometries were achieved by one-dimensional supramolecular assembly of substituted oligoamide units. The assembly of the monomers yields nanorods of sub-nanometer diameter and lengths in the 100 μm range. Addition of Cu2+ led to the formation of well aligned two-dimensional arrays on mica surface. Vibrational spectroscopy confirmed that the backbone amide moieties are not affected by metal addition. XPS and NEXAFS results suggest that Cu(II) is reduced in the process to a mixture of Cu(I) and Cu(0), likely in an interaction with the amine moiety of the imidazole side chain. Our results indicate that the two dimensional superstructure is based on the formation of polynuclear metal complexes between the oligoamide nanorods, thus the structure is confirmed to be a metallosupramolecular framework