Self-assembly (SA) of peptides provides a flexible approach to developing novel materials with tailored morphologies and desired functions by modulating design and engineering of monomers. Natural amino acids have been frequently utilized in the design of sequences. Although promising, they still have some draw backs in terms of structural and metabolic stability as well as ease of functionalization. Using peptides consisting of only β-amino acids offers the means to overcome these limitations. Recently, our group reported that N-terminal acetylated β~3-peptides can self-assemble by head-to-tail into helical fibrils through a supramolecular three point H-bonding motif. We have also tuned the self-assembly of β~3-peptides to present a range of morphologies by the appropriate solvent medium. In order to further understand the control of self-assembly and engineer new architectures, here we show a new class of β~3-peptide amphiphiles consisting of alkyl chains of either C_(12), C_(14) or C_(16) that can self-assemble in a unique pattern. Self-assembly was investigated using atomic force microscopy and transmission electron microscopy. The alkyl chain was attached at different positions and β~3-peptide amphiphiles with identical composition but with a different sequence arrangement and position of alkyl chain self-assembled into different types of nanostructures under the same conditions. We found that β~3-peptide amphiphiles with the alkyl chain on the N-terminus or residue 1 self-assembled into twisted fibrous nanostructures. By comparison, when the alkyl chain is located at residue 2 or 3, self-assembly resulted in flat nanobelts. The results clearly demonstrate the significance of the position of an alkyl chain on the peptide backbone sequence in determining supramolecular architectures. These outcomes will give further insight into the design and control of β~3-peptide amphiphile self-assembly.
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