title: Re-entrant cholesteric phase in DNA liquid-crystalline dispersion particles.
abstract: 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-1to 300 mg ml-1. In the range of PEG concentrations from 120 mg ml-1to 220 mg ml-1at room temperature, we find ds DNA molecule packing, typical of classical cholesterics. The corresponding parameters for dispersion particles obtained at concentrations greater than 220 mg ml-1indicate hexagonal packing of the ds DNA molecules. However, slightly counter-intuitively, the cholesteric-like packing reappears upon the heating of dispersions with hexagonal packing of ds DNA molecules. This transition occurs when the PEG concentration is larger than 220 mg ml-1. The obtained new cholesteric structure differs from the classical cholesterics observed in the PEG concentration range 120-220 mg ml-1(hence, the term 're-entrant'). Our conclusions are based on the measurements of circular dichroism spectra, X-ray scattering curves and textures of liquid-crystalline phases. We propose a qualitative (similar to the Lindemann criterion for melting of conventional crystals) explanation of this phenomenon in terms of partial melting of so-called quasinematic layers formed by the DNA molecules. The quasinematic layers change their spatial orientation as a result of the competition between the osmotic pressure of the solvent (favoring dense, unidirectional alignment of ds DNA molecules) and twist Frank orientation energy of adjacent layers (favoring cholesteric-like molecular packing).
authors.affiliation: Engelhardt Institute of Molecular Biology of the Russian Academy of Sciences, Vavilova St. 32, 119991, Moscow, Russia. yevdokim@eimb.ru.
authors.forename: Yuri M
authors.initials: YM
authors.lastname: Yevdokimov
authors.affiliation: Engelhardt Institute of Molecular Biology of the Russian Academy of Sciences, Vavilova St. 32, 119991, Moscow, Russia.
authors.forename: Sergey G
authors.initials: SG
authors.lastname: Skuridin
authors.affiliation: National Research Centre 'Kurchatov Institute', Kurchatova Sq. 1, 123182, Moscow, Russia.
authors.forename: Sergey V
authors.initials: SV
authors.lastname: Semenov
authors.affiliation: Shubnikov Institute of Crystallography of Federal Scientific Research Centre 'Crystallography and Photonics' of the Russian Academy of Sciences, Leninskii Ave. 59, 119333, Moscow, Russia.
authors.forename: Ljubov A
authors.initials: LA
authors.lastname: Dadinova
authors.affiliation: Engelhardt Institute of Molecular Biology of the Russian Academy of Sciences, Vavilova St. 32, 119991, Moscow, Russia.
authors.forename: Viktor I
authors.initials: VI
authors.lastname: Salyanov
authors.affiliation: Landau Institute for Theoretical Physics of the Russian Academy of Sciences, Kosygina St. 2, 119334, Moscow, Russia.
authors.forename: Efim I
authors.initials: EI
authors.lastname: Kats
mesh_terms: D004247:DNA / Q000737:chemistry*; D050866:Liquid Crystals / Q000737:chemistry*; D008958:Models, Molecular; D009690:Nucleic Acid Conformation; D055620:Optical Phenomena; D011092:Polyethylene Glycols / Q000737:chemistry; D013696:Temperature
chemical_list: D011092:Polyethylene Glycols; D004247:DNA
keywords: Abnormal optical activity; Cholesteric packing of ds DNA molecules in dispersion particles; Circular dichroism; Hexagonal packing of ds DNA molecules in dispersion particles; Hexagonal → cholesteric phase transition; Liquid-crystalline ds DNA dispersion particles; Quasinematic layers; Textures; X-ray scattering curves