Nanoparticles to Control Stranded Packing of DNAs

Abstract

We report here on new optic and small-angle X-ray scattering (SAXS) measurements concerning the formation of the dispersions from double-stranded (ds) DNA molecules, doped with negatively charged gold nanoparticles (nano-Au). The nano-Au fixation nearby the surfaces of linear ds DNA in solution of high ionic strength (0.3 M NaCl) and subsequent phase exclusion of (ds DNA-nano-Au) complexes from solution containing poly(ethylene glycol) results in decrease in the amplitude of abnormal negative band in the circular dichroism spectra of the formed cholesteric liquid-crystalline dispersions (CLCD). Besides, doping of linear ds DNA with nano-Au and phase exclusion of the formed (ds DNA-nano-Au) complexes does not accompanied by alteration in the standard structural parameters obtained from SAXS data which reflect local ordering of ds DNA molecules, but results in the decrease in the amplitude of the characteristic Bragg maximum. Our experimental data, supplemented by a simple model numeric computations of screened (in the water-salt solution of high ionic strength) electrostatic energy for ds DNA molecules and negatively charged but polarizable nano-Au, suggest that doping of ds DNA with negative charged nano-Au results in an appearance of a population of "modified" by nano-Au ds DNA molecules. These molecules, in contrast to the free ds DNA molecules, lose an ability to form spatially twisted structure at phase exclusion and instead of ordered spatial structure of ds DNA CLCD only random disordered aggregates are obtained. Keywords: Circular Dichroism, Liquid-crystalline Dispersions, Negatively charged Gold Nanoparticles, Phase Exclusion of Linear DNA, Small-angle X-ray Scattering