Interaction of tyrosine-, tryptophan-, and lysine-containing polypeptides with single-wall carbon nanotubes and its relevance for the rational design of dispersing agents

The polypeptides poly-L-(Trp,Lys-HBr) (Trp/Lys center dot HBr = n/m) and poly-L(Tyr,Lys-HBr) (Tyr/Lys-HBr = n/m) were tested as dispersing agents for sinerle-wall carbon nanotubes (SWCNTs) for n/(n+m) values of 0, 0.2, and 1. Best results were obtained for the two copolymers, illustrating the importance of using amphiphilic dispersing agents. The dispersion effect is 3.5 times higher for the copolymer containing tryptophan, indicating a stronger interaction of the tryptophan residue with the SWCNTs compared to tyrosine. The degrees of debundling of the SWCNTs and the apparent binding of the polypeptides with the SWCNTs are analyzed by atomic force microscopy for the different dispersions. The interactions of the aromatic amino acid residues with the SWCNTs are further probed by using optical absorbance and fluorescence spectroscopy.