Self-assembled nanomaterials based on beta (ß(3)) tetrapeptides.

ß(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 ß(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 ß(3)-tetrapeptides Ac-ß (3)Ala-ß(3)Leu-ß(3)Ile-ß(3)Ala (Ac-ß(3)[ALIA]), Ac-ß(3)Ser-ß(3)Leu-ß(3)Ile-ß(3)Ala (Ac-ß(3)[SLIA]) and Ac-ß (3)Lys-ß (3)Leu-ß(3)Ile-ß (3)Glu (Ac-ß(3)[KLIE]). ß(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-ß(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-ß(3)[SLIA] and Ac-ß(3)[KLIE] exhibit fibres in regular parallel alignment over surface areas in the order of 10 µm.