Cysteine-based reversible-cyclic peptides for carbon nanotube functionalization

Single-walled carbon nanotubes (SWNTs) are interesting because of their unique electrical, mechanical and optical properties. These properties may be useful in applications such as small scale electronics, materials and medicine. A major drawback to working with SWNTs is their tendency to form aggregates in aqueous environments. To combat this problem, functionalization of the sidewalls allows hydrogen bonding with water molecules and lowers aggregation. Reversible cyclic peptides (RCPs) present a route to noncovalently functionalize the hydrophobic surfaces while preserving the optical properties of the SWNTs. These peptides have been shown to disperse a narrow range of SWNTs that is dependant upon the length of the amino acid (AA) sequence. When RCPs are oxidized around a SWNT, a very stable dispersion is produced. RCP-wrapped SWNT dispersions have been shown to be stable against dilution by dialysis without the formation of aggregates. These dispersions have been characterized using atomic force microscopy, Raman spectroscopy, UV/Vis/NIR, and transmission electron microscopy. The work in this thesis is centered around answering 6 questions: (1) Are cysteine-containing RCPs able to disperse SWNTs? (2) Is the placement of the disulfide important to disulfide formation? (3) Do Cysteine containing RCPs (RCP-Cys) selectively disperse SWNTs based on diameter? (4) Is the chirality of the disulfide important to diameter selection? (5) Is the alternating chirality of AAs important? (6) Can this RCP-Cys peptide system be used to decorate SWNTs with functional moieties to be utilized in various applications? It was found that cysteine-containing RCPs are able to disperse SWNTs, yet do not show diameter selection based on statistical comparisons of two limited SWNT populations dispersed and analyzed with atomic force microscopy. The chirality of cysteines on the N- and C-termini does not have a significant influence on the SWNT population observed with UV/Vis/NIR; however, there is a large decrease in the dispersability of RCPs when the alternating L/D-chiral pattern of AAs is not used. Finally, the RCP-Cys peptide design is capable of decorating SWNT side walls with functional moieties, as has been demonstrated with Au-labeled streptavidin and biotin-functionalized Lys sidechain imaged with transmission electron microscopy.