Binding of polynucleotides with single-walled carbon nanotubes: Effect of temperature

The effect of the change of the temperature (in the range from 20 degrees C to 90 degrees C) on the light absorption intensity of water suspensions of nanohybrids formed with single-walled carbon nanotubes (SWNT) and single-stranded polyriboadenylic acids, poly(rA), and polyribocytidylic acids, poly(rC), was studied. Different degrees of the polymer coating of nanotube surfaces were found by atomic force microscopy (AFM). According to UV-vis absorption spectroscopy data, homopolymer adsorption onto the nanotube is followed with changes in optical characteristics of both, the polymer and SWNT, as a result of pi pi-stacking interaction of the polymer with the tube surface. Upon poly(rA) wrapping on the nanotubes, a significant part of its bases keeps self-stacking while upon adsorption of the more rigid poly(rC), it is almost completely disordered. Spectroscopic data can be explained by a polymer re-orientation on the nanotube with the heating that provides the optimal pi pi-stacking of nitrogen bases with the carbon surface. The increase of the temperature up to 90 degrees C does not result in the polymer slipping off the nanotube and in a noticeable nanotube precipitation.