Observations of three "re-entrant" twisted structures in double-stranded DNA dispersion particles.

In this work we report on observations of new twisted (cholesteric-like) structures in liquid-crystalline dispersion particles with a hexagonal packing of double-stranded (ds) DNA molecules. Heating up to 80 °C of the DNA dispersion formed in a aqueous-salt solution with a high osmotic pressure (concentration) of poly(ethylene glycol) induces the formation of a new, optically active, spirally twisted structure of these molecules ("re-entrant" cholesteric structure (rest-A structure)). Cooling of this dispersion up to 22 °C is accompanied by the formation of an additional "re-entrant" cholesteric structure (rest-B).

Re-entrant cholesteric phase in DNA liquid-crystalline dispersion particles.

In this research, we observe and rationalize theoretically the transition from hexagonal to cholesteric packing of double-stranded (ds) DNA in dispersion particles. The samples were obtained by phase exclusion of linear ds DNA molecules from water-salt solutions of poly(ethylene glycol)-PEG-with concentrations ranging from 120 mg ml to 300 mg ml. In the range of PEG concentrations from 120 mg ml to 220 mg ml at room temperature, we find ds DNA molecule packing, typical of classical cholesterics.

[Ordering of double-stranded DNA molecules in a cholesteric liquid-crystalline phase and in dispersion particles of this phase].

The current notion of the organization of molecules in a cholesteric phase is fairly well substantiated in the case of low-molecular-weight compounds. However, this question is open to discussion in the case of double-stranded nucleic acids. In this work, an attempt to compare the well-known data on the structure of cholesteric phases formed by double-stranded DNA molecules and the results of experimental modeling obtained by the authors has been undertaken.

[About the Spatial Organization of Double-stranded DNA Molecules in the Cholesteric Liquid-crystalline Phase and Dispersion Particles of this Phase].

The answer to a question on the organization of molecules in a cholesteric phase is well enough proved in case of low molecular mass compounds. However, in case of double-stranded nucleic acids molecules the unequivocal answer to such question is a subject of discussions. In this work an attempt to generalize the well known literary data on the structure of the cholesteric phase formed by double-stranded DNA molecules was undertaken.

[Superparamagnetic Cobalt Ferrite Nanoparticles "Blow up" Spatial Ordering of Double-stranded DNA Molecules].

The formation of cholesteric liquid-crystalline dispersions formed by double-stranded DNA molecules, handled by positively charged superparamagnetic cobalt ferrite nanoparticles, as well as action of these nanoparticles on DNA dispersion, are considered. The binding of magnetic nanoparticles to the linear double-stranded DNA in solution of high ionic strength (0.3 M NaCl) and subsequent phase exclusion of these complexes from polyethylene glycol-containing solutions lead to their inability to form dispersions, whose particles do possess the spatially twisted arrangement of neighboring double-stranded DNA molecules.