V.S. Leontiev

RNA-Wrapped Carbon Nanotubes Aggregation Induced by Polymer Hybridization

The aggregation of poly(rA)-wrapped single-walled carbon nanotubes (SWNTs) induced by hybridization of the adsorbed polymer with free poly(rU) has been studied by differential UV absorption spectroscopy, NIR luminescence, and AFM. After the addition of poly(rU) into a poly(rA):SWNTs suspension, the double-stranded poly(rA)·poly(rU) was formed, which is evident from the characteristic S-like form of the melting curve for the polymer created. Hybridization of free poly(rU) with two complementary poly(rA), one of which was adsorbed to different individual nanotubes, links them together and causes the appearance of aggregates. The aggregation of nanotubes is accompanied with light scattering and can be monitored in an AFM image after the deposition of the suspension on a mica substrate. Molecular dynamic simulation demonstrates a possible structure of the SWNTs aggregate.

Nanohybrid Structures Formed by Carbon Nanotubes with Long Polynucleotide

Adsorption of poly(rA) on the single-walled carbon nanotubes (SWNTs) surface have been studied by AFM and computer modeling. It follows from AFM images that relatively long fragments of polymers attached to two individual nanotubes in aqueous suspension form branched structures. The size of these structures increases after the addition of a complementary poly(rU) to the aqueous suspension of nanotubes with adsorbed poly(rA), which is induced by hybridization of the adsorbed and free polymer. Molecular dynamic simulation demonstrates different possible structures of these nanohybrids.

Raman spectroscopy and SEM study of SWNTs in aqueous solution and films with surfactant or polymer surroundings

Abstract Raman spectra of single‐walled carbon nanotubes (SWNTs) in aqueous solutions with sodium dodecylsulfate (SDS) or fragmented single‐stranded DNA (ss‐DNA) and films obtained from these solutions have been studied. Scanning electron microscope (SEM) film study shows that micelles formed by SDS molecules around SWNT in solution do not keep individual nanotubes from sticking together in bundles during drying out the film. DNA wrapped around SWNT precludes the full nanotubes sticking in the film that facilitates the following splitting of these bundles.

Spectroscopy Study of SWNT in Aqueous Solution With Different Surfactants

Aqueous solutions of HiPCO SWNT with different surfactants (anionic (SDS), cationic (CTAB) and non‐ionic (Triton X‐100)) have been studied by Raman and Near‐infra‐red (NIR) absorption spectroscopy. The nanotube interaction with surfactant leads to the spectral shift of lines and its intensity redistribution, compared with the spectrum of SWNT in KBr pellet. The most essential spectral changes are observed for nanotube aqueous solution with the surfactant containing a charge group. Two possible models of micelle formation around the nanotube are discussed.

Enhancement of single-walled nanotubes luminescence intensity upon dithiothreitol doping

In the present work the influence of reducing agent dithiothreitol doping on photoluminescence spectra of nanotubes with adsorbed biopolymers (single-stranded DNA and polyC) in aqueous suspensions and films was studied. It is revealed that greater intensity enhancement at 10−3 mol/L dithiothreitol concentration is observed for (7,5) and (6,5) nanotubes in suspension with single-stranded DNA (by more than 150% of initial intensity) comparing to polyC suspension (less than 60%) while for (6,4) and (9,1) nanotubes enhancement is less than 50% for both suspensions. Photoluminescence intensity increasing for nanotube film with DNA is less than 50% without noticeable dependence on nanotube chirality. It is assumed, that different influence of biopolymers on nanotube luminescence intensity enhancement is due to their different coverage of nanotube surface.

Hybridization of poly(rI) with poly(rC) adsorbed to the carbon nanotube surface

Hybridization of homopolynucleotide poly(rC) adsorbed to the carbon nanotube surface with poly(rI) free in solution has been studied by absorption spectroscopy and molecular dynamics method. It was found that hybridization on the nanotube surface has a slow kinetics, the behavior of which differs essentially from fast hybridization of free polymers. The duplex obtained is characterized with the reduced thermostability and a lower hyperchromic coefficient than it was observed when the duplex was formed in the absence of the nanotube. These features point to the imperfectness in the structure of the duplex hybridized on the nanotube surface. Computer simulation showed that the strong interaction of nitrogen bases with the nanotube surface weakens significantly hybridization of two complementary oligomers, as the surface prevents the necessary conformational mobility of the polymer to be hybridized.

SWNTs with DNA in Aqueous Solution and Film

Raman and luminescence spectra of SWNTs in aqueous solutions with fragmented single‐stranded DNA and films prepared from these solutions have been obtained. SEM film study shows that nanotubes aggregate in bundles after film drying. In Raman spectra it leads to the enhancement of the intensity of the low‐frequency component of the tangential mode (G−), to the shift and broadening of the high‐frequency component of this mode (G +). It was shown that the ratio of areas of the high‐frequency component of the G mode to the low‐frequency component (SG+/SG−) can serve as an indicator of nanotube aggregation into bundles for SWNTs suspended in solution. The film yields luminescence which indicates the presence of individual tubes or small bundles in the films. The luminescence bands of SWNTs in the film become wider and are attributed to the interaction of DNA with the nanotube surface in the solid state.