Adsorption of Poly(rA) on the Carbon Nanotube Surface and its Hybridization with Poly(rU)

Adsorption of poly(rA) on a single‐walled carbon nanotube surface in aqueous suspension and the subsequent hybridization of this polymer with free poly(rU) is studied. A comparison of the temperature dependence of the absorbance of free poly(rA) and poly(rA) adsorbed on the nanotube surface [poly(rA)NT] at νmax=38 500 cm−1 shows that the thermostability of the adsorbed polymer is higher. Molecular dynamics simulations demonstrate that more than half of the adenines are not stacked on the tube surface and some of them undergo self‐stacking. After addition of a complementary poly(rU) to the poly(rA)NT suspension, a double‐stranded polymer is formed as confirmed by the characteristic S‐like form of its melting curve. However, the melting temperature of this polymer is lower than that of the free poly(rA)⋅poly(rU) duplex. This result indicates that poly(rU) hybridization with poly(rA)NT occurs with defects along the whole length of the polymer because of π–π stacking between nitrogen bases and the nanotube surface, which hinders the usual hybridization process. Computer modeling demonstrates different possible structures of hybridized polymers on the nanotube surface. Nucleic acids on nanotubes: Strong adsorption of poly(rA) [blue line in picture] on a nanotube surface hinders hybridization of the polymer with complementary poly(rU) [brown line] because of π–π stacking between nitrogen bases and the nanotube surface. It leads to defects in the structure of the double‐stranded polymer. The number of the usual A–U Watson–Crick pairs with two H bonds is small.