Adsorption of poly(rA) in duplex (A-motif) conformation on graphene oxide: spectroscopy and AFM study

The conformational diversity of nucleic acid structures, including the ability to self-assemble, such as an i/A-motif, significantly expands the horizon of possible applications of their hybrids with nanomaterials. In this work, the adsorption of polyriboadenylic acid (poly(rA) in the duplex (A-motif) conformation (at pH5) on graphene oxide (GO) was studied by UV absorption spectroscopy, thermal differential absorption spectroscopy, and atomic force microscopy. A new band with a maximum near 264 nm was revealed in the difference spectra of A-motif when GO was added to the solution. The appearance of this band is explained by the partial unzipping of the duplex and the disordering of stacked nitrogenous bases at adsorption on GO. Spectral changes in time show that the adsorption of a relatively long A-motif on GO takes a significant time (hours). Experiments with temperature heating (20→90 0C) of the A-motif adsorbed on GO showed that, upon adsorption its melting temperature and hyperchromic coefficient decrease, which indicates an imperfect duplex structure of the A-motif that is destabilized by GO. Possible physical reasons for the A-motif strong destabilization are discussed.