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). Modification of particles of the ds DNA dispersion (with rest-B structure) by replacing Na+ cations by multi-charged Gd3+ cations results in the third " re-entrant" structure (rest-C) despite a high density packing of ds nucleic acid molecules.