Liquid-crystalline Dispersion Particles Research Articles

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.

Anomalous behavior of the DNA liquid-crystalline dispersion particles and their phases

The dispersions were obtained as a result of phase exclusion of the DNA molecules from aqueous-salt-PEG-containing solutions. The CD spectra have shown cholesteric and hexagonal packing of the DNA in single dispersion particles at room temperature. The phase transition of the hexagonal → the “re-entrant” cholesteric packing of DNA takes place at elevated temperature. The texture of the “re-entrant” phase does not demonstrate attributes of DNA cholesteric phase. Alternative reasons of such discrepancy are discussed in the presented Letter.

Double-Stranded DNA Packing in Particles of Liquid-Crystalline Dispersions and Liquid-Crystalline Phases Obtained from These Particles

Double-Stranded DNA Packing in Particles of Liquid-Crystalline Dispersions and Liquid-Crystalline Phases Obtained from These Particles

DNA Liquid-Crystalline Dispersion Particles as a Platform for Creation of “RIGID” Spatial Structures

DNA Liquid-Crystalline Dispersion Particles as a Platform for Creation of “RIGID” Spatial Structures

Spatial ordering and abnormal optical activity of DNA liquid-crystalline dispersion particles

In our work, we investigate physicochemical and optical properties of double-strand DNA dispersions. The study of these properties is of biological interest, because it allows one to describe the characteristics of certain classes of chromosomes and DNA containing viruses. The package pattern of DNA molecules in the dispersions particles (DP) is examined. The consideration of the DNA liquid-crystalline DP optical activity based on the theory of electromagnetic wave absorption by large molecular aggregates has been performed. The investigation is also focused on various effects induced by the interaction between biological active compounds and DNA in the content of liquid-crystalline DP.

Temperature-induced changes of the packing of double-stranded linear DNA molecules in particles of liquid-crystalline dispersions

The circular dichroism spectra of liquid-crystalline dispersions obtained by phase exclusion of linear double-stranded DNA molecules from aqueous saline solutions of polyethylene glycol (120 ≤ C PEG ≤ 300 mg/mL) have been investigated. The formation of liquid-crystalline dispersions at polyethylene glycol concentrations ranging from 120 to 200 mg/mL was accompanied by the emergence of an abnormal negative band in the spectrum of circular dichroism; this is indicative of cholesteric packing of the double stranded DNA molecules in the particles of the dispersion. Liquid-crystalline dispersions formed at PEG concentrations higher than 220 mg/mL and room temperature did not show any abnormal bands in the circular dichroism spectra; this is indicative of hexagonal packing of double-stranded DNA molecules in the particles of the dispersions. Heating of optically inactive liquid crystal dispersions induced a transition of the dispersions into a different state accompanied by the emergence of an abnormal negative band in the spectrum of circular dichroism. This transition is considered within the concept of the transformation of a hexagonal packing of DNA molecules into a cholesteric packing. A qualitative mechanism of such a transition is proposed that is formulated in the terms of the “quasinematic” layers of double-stranded DNA molecules that change their spatial orientation under the competing influences of the osmotic pressure of the solvent, orientational elasticity of the cholesteric packing, and thermal fluctuations.

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.

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. The comparison brings leads to assumption regarding the high probability of the existence of both short-range (positional) and long-range (orientational) order in the arrangement of double-stranded DNA molecules in the liquid crystalline phase. The presence of the orientational order, i.e., the rotation of quasinematic layers of double-stranded DNA molecules through a small angle, determines the formation of a spatially twisted (cholesteric) structure with specific physical and chemical properties. In addition, these results prompt a suggestion on the mode of the ordering of dsDNA molecules in liquid-crystalline dispersion particles and allow these particles to be considered candidate biosensing units.

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. Besides the experimental results of authors describing the packing of these molecules in the cholesteric liquid-crystalline dispersion particles are added to these data. Comparison of the results obtained offers the possibility to come out with an assumption of high probability of the existence of both the short-range positional and long-range orientational order in arrangement of double-stranded DNA molecules in a liquid-crystalline phase, and in the particles of dispersions of this phase generated under certain conditions. The occurrence of the orientational order, i.e. rotation of 'quasinematic' layers of double-stranded DNA molecules by a small angle, defines the formation of spatially twisted (cholesteric) structure with characteristic for it physical and chemical properties.

Superparamagnetic cobalt ferrite nanoparticles “blow up” the 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. The action of magnetic nanoparticles on DNA dispersion (one magnetic nanoparticle per one double-stranded DNA molecule) results in such "perturbation" of DNA structure at sites of magnetic nanoparticles binding that the regular spatial structure of DNA dispersion particles "blows up"; this process is accompanied by disappearance of both abnormal optical activity and characteristic Bragg maximum on the small-angle X-ray scattering curve. Allowing with the fact that the physicochemical properties of the DNA liquid-crystalline dispersion particles reflect features of spatial organization of these molecules in chromosomes of primitive organisms, it is possible, that the found effect can have the relevant biological consequences.

Linear clusters of gold nanoparticles in quasinematic layers of DNA liquid-crystalline dispersion particles

The effects of small size (approximately 2 nm) gold nanoparticles on the properties of particles of cholesteric liquid-crystalline dispersions formed by double-stranded DNA molecules were analyzed. It has been shown that gold nanoparticles induce two different processes. First, they facilitate reorganization of the spatial cholesteric structure of dispersion particles to nematic one. This process is accompanied by the fast decrease in the amplitude of abnormal band in the CD spectrum. Second, they can form ensembles consisting of gold nanoparticles. This process is accompanied by the development and displacement of surface plasmon resonance band in the visible region of the absorption spectrum. The appearance of this band is analyzed by considering two different models of the formation of ensembles consisting of gold nanoparticles. By small-angle X-ray scattering we performed structural analysis of phases formed by DNA cholesteric liquid-crystalline dispersion particles treated with gold nanoparticles. As a result of this study it was possible to prove the formation of linear clusters of gold nanoparticles in the "free space" between the adjacent DNA molecules fixed in the quasinematic layers of liquid-crystalline particles. It has been hypothesized that the formation of linear clusters of gold nanoparticles is most likely related to DNA molecules, ordered in the spatial structure of quasinematic layers, and the toxicity of these nanoparticles in biological systems hypothesized.

Gold Nanoparticle Clusters in Quasinematic Layers of Liquid-Crystalline Dispersion Particles of Double-Stranded Nucleic Acids

The interaction between gold nanoparticles and particles of cholesteric liquid-crystalline dispersions formed by double-stranded DNA and poly(I)×poly(C) molecules is considered. It is shown that small-sized (~ 2 nm) gold nanoparticles induce two different structural processes. First, they facilitate the reorganization of the spatial cholesteric structure of the particles into a nematic one. This process is accompanied by a fast decrease in the amplitude of an abnormal band in the CD spectrum. Second, they induce cluster formation in a "free space" between neighboring nucleic acid molecules fixed in the structure of the quasinematic layers of liquid-crystalline particles. This process is accompanied by slow development of the surface plasmon resonance band in the visible region of the absorption spectrum. Various factors influencing these processes are outlined. Some assumptions concerning the possible mechanism(s) of fixation of gold nanoparticles between the neighboring double-stranded nucleic acid molecules in quasinematic layers are formulated.

Retention of gold nanoparticles in the structure of quasinematic layers formed by DNA molecules

Gold nanoparticles are shown to get incorporated into double-stranded DNA molecules forming quasinematic layers in the cholesteric liquid-crystalline dispersion particles. The process of nanoparticle incorporation results in distortion in an ordered arrangement of the neighboring dsDNA molecules in a layer and in global spatial structure of particles of the dispersion, which may be one of the possible causes of the genotoxicity of gold nanoparticles.

Regulation of the spatial organization of DNA molecules in particles of liquid-crystalline dispersions by means of biologically active compounds

Using the “structural conflict” method based on differences in the spatial organization of a liquid-crystalline dispersion (LCD) of DNA-polycation complexes and the DNA cholesteric LCD, it was shown that in a solvent with specific properties, the spatial structure of the LCD of DNA-polycation complexes can be controlled by biologically active compounds (BAC) that cause either dissociation of the DNA-polycation complex or destruction of the polycation molecules. In both cases, the cholesteric structure of LCD typical of the initial uncomplexed DNA molecules is recovered. The recovery of cholesteric LCD of DNA was proved by circular dichroism spectroscopy and confirmed by X-ray diffraction and polarization microscopy. The fact that spatial restructuring of LCD of the DNA-polycation complexes is induced by BAC in low concentrations opens up the possibility for using particles of these dispersions as sensing elements (sandwich-type biosensing units) of biosensor devices. A new method for determination of heparin based on the use of LCD of the DNA-polyconidine complexes was developed. The minimum heparin concentration determined in the sample equals ∼ 0.4–0.5 µg mL−1.

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.

Effect of intercalators on the properties of liquid-crystalline dispersions of nucleic acid-chitosan complex

Molecules of deoxyribonucleic acid and synthetic polydeoxyribonucleotides (NA) in the particles of liquid-crystalline dispersions resulting from interaction with chitosan are accessible to interaction with intercalators. The intercalation is accompanied by alteration in the direction of spatial twist of cholesterics of NA-chitosan complexes. This effect is absent in the case of "classical" cholesterics produced from NA molecules via phase exclusion, i.e., the cholesteric structure of NA-chitosan complex is very "labile" as distinct from "classical" cholesteric NA.

Molecular design based on polyribonucleotides fixed in the structure of liquid-crystalline dispersion and cross-linked via polymeric chelate bridges

A method of molecular design based on cross-linking of polyribonucleotide molecules with polymeric chelate bridges (anthracycline-Cu2+-…-Cu2+-anthracycline) was developed. The formation of polymeric chelate cross-bridges between neighboring polyribonucleotide molecules in the particles of liquid-crystalline dispersions was shown to require the formation of external complex (anthracycline-polyribonucleotide). The properties (shape, size, optical activity, etc.) of molecular constructions composed of different polyribonucleotides were studied and compared. Molecular constructions on the basis of polyribonucleotides could be used as sensing elements with adjustable properties in biosensor technology, nanobiotechnology, and molecular pharmacology.