Selective Suspension of Single-Walled Carbon Nanotubes Using β‑Sheet Polypeptides

Individual single-walled carbon nanotubes (SWNTs) were suspended in water using amphipathic β-sheet peptides of the general sequence Ac-(XKXE)2-NH2. By substituting natural and nonnatural amino acids of varying aromatic and hydrophobic character in the X position, the interactions between the peptide and the nanotube sidewall could be systematically varied. Surprisingly, enhancing the degree of favorable π–π and hydrophobic interactions, which strongly influence the self-assembly properties of these peptides, did not correlate with an improvement in nanotube dispersion efficiency. We found that substituents in the X-position of the peptides play a significant role in SWNT interaction and contributes to (n,m) structure specificity.