Decrease of carbon nanotube UV light absorption induced by π–π-stacking interaction with nucleotide bases

UV–vis absorption spectra of hybrids formed by carbon single-walled nanotubes (SWCNTs) and single-stranded DNA (ss-DNA), double-stranded DNA (ds-DNA), and synthetic homopolynucleotides (poly(rC) and poly(rG)) have been studied. In the 300–400 nm spectral range a decrease of SWCNT light absorption because of their interaction with polymers was observed. The revealed decrease of nanotube absorption is explained by SWCNT hypochromism that results from π–π-stacking interaction of polymer nitrogen bases with the tube surface. Molecular dynamic simulation demonstrates a spontaneous wrapping of polynucleotides around the nanotube. Simulation showed that pyrimidine oligonucleotide (d(C)25) manifests a higher rate of minimizing the hybrid structure with the wrapped polymer structure around the tube than the purine one (d(G)25). Such polymer behavior can be explained by the purine oligonucleotide property to form a stable ordering self-stacking structure which prevents structural re-orientation, in contrast to pyrimidine polynucleotides.