A calorimetric study of the different thermal behaviour of DNA in the isotropic and liquid-crystalline states

A difference between the thermal behaviour of the isotropic and liquid-crystalline state of sonicated DNA in aqueous salt solution containing poly(ethyleneglycol)(PEG) has been demonstrated. On cooling, a different degree of renaturation of thermally denaturated DNA is observed between samples which form the isotropic state and more concentrated samples which on cooling form the cholesteric state.     

Hexagonal → cholesteric phase transition of DNA molecules in liquid-crystalline dispersion particles

To assess the character of packing of double-stranded (ds) DNA molecules in liquid-crystalline dispersion particles formed by phase exclusion of DNA molecules from aqueous salt solutions of poly(ethylene glycol), the circular dichroism spectra of these dispersions at different temperatures have been compared. It has been shown for the first time that heating dispersion particles with the hexagonal packing of ds-DNA molecules is accompanied by the hexagonal → cholesteric phase transition. This result can be described using the notion of quasi-nematic layers composed of orientationally ordered adjacent ds-DNA molecules in the structure of dispersion particles; these layers can be packed in two ways dictating their hexagonal or cholesteric spatial structure.     

Invite Article: The Liquid-Crystalline Phases of Double-Stranded Nucleic Acids in Vitro and in Vivo

This article describes the state of and progress in experimental studies of liquid crystals of naturally occurring nucleic acids and synthetic polynucleotides. The areas considered in this review include: (i) the liquid-crystalline phase of nucleic acids in aqueous salt solutions, (ii) the liquid-crystalline phase of nucleic acids in aqueous polymer solutions, (iii) the liquid-crystalline phase of nucleic acids in living systems. Some unsolved problems which are of interest from both a physicochemical and a biological point of view are discussed.     

Liquid crystalline dispersions of double-stranded nucleic acids and their complexes as a background for nanodesign: Review

Different strategies in design of nanoconstructions whose building blocks are both linear molecules of double-stranded nucleic acids and nucleic acid molecules fixed in the spatial structure of particles of liquid crystalline dispersions have been considered.     

Rare-earth-cation-induced change in the cholesteric twisting of neighboring nucleic acid molecules

Certain physicochemical characteristics of particles of the cholesteric liquid-crystal dispersions of complexes of double-stranded nucleic acids with rare earth elements have been determined. It is shown for the first time that the binding of the rare earth cations to linear nucleic acid molecules ordered in the structure of particles of the cholesteric liquid crystal dispersions is accompanied not only by amplification of the abnormal band in the circular dichroism spectrum, but also by the disappearance of the characteristic maximum on the X-ray scattering curves for small angles. The (cholesteric 1-cholesteric 2) transition induced by rare earth cations is an example of the operation of a microscopic machine consisting of spatially ordered nucleic acid molecules. Particles of the cholesteric liquid crystal dispersions of nucleic acid complexes with rare earth elements hold the abnormal optical properties for a long time.     

Liquid-crystalline phases of circular superhelical plasmid DNA and their modification by the action of nuclease enzymes

CD spectra of liquid-crystalline dispersions, X-ray diffraction patterns and optical textures of liquid crystals prepared from native superhelical DNA in poly(ethyleneglycol)-containing water-salt solutions before and after treatment of DNA with micrococcal nuclease have been obtained. It was found that condensation of native superhelical DNA is accompanied by the formation of liquid crystals with a non-specific optical texture. After treatment of the DNA, liquid-crystalline dispersions, with Micrococcal nuclease the DNA is able to form two similar types of liquid crystals with abnormal optical activity which differ in the peculiarities of their textures. The data obtained demonstrate the formation of multiple types of liquid crystals from high molar mass double-stranded optically active DNA molecules.     

Circular Dichroism Spectra of DNA Dispersions and Textures of DNA Phases

Optics and Spectroscopy - Circular dichroism (CD) spectra of liquid crystalline dispersions formed as a result of phase exclusion of double-stranded DNA molecules from aqueous-salt-poly(ethylene...     

The re-entrant cholesteric phase of DNA

The character of packing of double-stranded DNA molecules in particles of liquid-crystal dispersions formed as a result of the phase exclusion of DNA molecules from aqueous salt polyethylene glycol solutions has been estimated by comparing the circular dichroism (CD) spectra of these dispersions recorded at different osmotic pressures and temperatures. It is shown that the first cycle of heating of dispersion particles with hexagonally packed double-stranded DNA molecules leads to the occurrence of abnormal optical activity of these particles, which manifests itself in the form of a strong negative CD band, characteristic of DNA cholesterics. Moreover, subsequent cooling is accompanied by a further increase in the abnormal optical activity, which indicates the existence of the “hexagonal → cholesteric packing” phase transition, controlled by both the osmotic pressure of the solution and its temperature. The result obtained can be described in terms of “quasi-nematic” layers composed of orientationally ordered DNA molecules in the structure of dispersion particles. There are two possible ways of packing for these layers, which determine their hexagonal or cholesteric spatial structure. The second heating → cooling cycle confirms these results and is indicative of possible differences in the packing of double-stranded DNA molecules in the hexagonal phase, which depend on the osmotic pressure of the solution.     

On the possibility of determining anthracycline antibiotics in aqueous solutions using optical analytical system (biosensor)

We propose a version of the theory describing the circular dichroism spectra of cholesteric liquidcrystal dispersion particles of double-stranded DNA. The basis of the theory is the concept of absorption of electromagnetic waves by large molecular systems. The effect of physical parameters of dispersion particles on their circular dichroism is theoretically determined. It is experimentally demonstrated that circular dichroism can be used as a convenient tool for creating an optical analytical system for the determination of biologically active compounds that interact with DNA molecules.