Interaction of Amino Acids and Single-Wall Carbon Nanotubes

In this article, we investigated the interactions between oxidized single-wall carbon nanotubes and three amino acids. A simple and environmental benign method to realize solubility of oxidized single-wall carbon nanotubes (OSWNT) in water was described. The amino acids used in this study include L-glycine (Gly), L-lysine (Lys), and L-phenylalanine (Phe). The OSWNT became soluble in water under ambient conditions and formed a stable suspension when amino acids (AA) were adsorbed on it. The interactions between OSWNT and three AA were characterized by transmission electron microscopy (TEM), scanning electron microscopy (SEM), Raman spectroscopy, Fourier transform infrared spectroscopy (FT-IR), and thermogravimetric analysis (TGA). The results indicate that there is an increasing in the diameter of OSWNT after AA adsorption. The OSWNT with different diameters were separated as a result of AA adsorption. The smaller the diameter of OSWNT, the more the AA adsorption amount is. The adsorbed amount of different AA on OSWNT follows the trend: Lys > Phe > Gly. The Pi-Pi stacking is an important factor to realizing adsorption of Phe zwitterions on the sidewall of OSWNT; but for Gly and Lys zwitterions, polar interaction is a determinant factor to realizing adsorption on the sidewall of OSWNT. The AA zwitterions were adsorbed on the surface of OSWNT by conjunct interaction of the Pi-Pi stacking, polar interaction, hydrogen bond, and covalent bonding. Hydrogen bond and covalent bond, formed with oxygen containing groups, is dominant at the end of OSWNT. The catalysis property of OSWNT makes a noticeable reduction of decomposition temperature for AA adsorbed on OSWNT.