S. G. Skuridin

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

Abstract 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.

Invited Article Liquid-crystalline dispersions of nucleic acids

Abstract The formation and properties of dispersions of double stranded natural and synthetic nucleic acids are described. Evidence is given for the liquid-crystalline state of the nucleic acid within the dispersed droplets in these phases. The exploitation of nucleic acid dispersions in biosensors is discussed.

Comparison of calculated and observed CD spectra of liquid crystalline dispersions formed from double-stranded DNA and from DNA complexes with coloured compounds

Abstract The CD spectra of dispersions of DNA, in the form of cholesteric liquid crystalline droplets, in an aqueous continuum have been studied. Calculated curves have been fitted to experimental spectra. The amplitude and the sign of the intense absorption band of the purine and pyrimidine bases vary with the droplet size, the pitch and the twist sense of the cholesteric phase. The CD spectra of dispersions of the complex formed by DNA and a coloured intercalating antibiotic have been similarly studied. A general satisfactory level of fitting between observed and calculated CD spectra was found.

A new approach for creating double-stranded DNA biosensors

The principle of sandwich-type biosensors based on liquid-crystalline dispersions formed from [DNA-polycation] complexes is outlined. These biosensors will find application in the determination of a range of compounds and physical factors that affect the ability of a given polycationic molecule to maintain intermolecular crosslinks between neighbouring DNA molecules. In the case of liquid-crystalline dispersions formed from [DNA-protamine] complexes, the lowest concentration of hydrolytic enzyme (trypsin) detectable was approximately 10-(14) M.

Two types of temperature induced transitions of poly(I) · poly(C) liquid crystals

Abstract Small-angle X-ray scattering curves, CD. spectra and textures of the liquid-crystalline phase formed from poly(I) · poly(C) in water-salt solutions containing poly(ethyleneglycol) have been obtained at different temperatures. It was found that heating the poly(I) · poly(C) liquid-crystalline phase is accompanied by two types of transitions, the first being cholesteric → compensated structure → cholesteric and the second being cholesteric → isotropic state transition. The latter transition takes place at a temperature which corresponds to that of separation of chains of a double-stranded poly(I) · poly(C) molecule. The temperature dependence of the abnormally high optical activity of poly(I) · poly(C) liquid crystals allows us to estimate the order parameter of poly(I) · poly(C) molecules in both the liquid-crystalline phase and the liquid-crystalline microphases.

Effect of platinum(II) chemotherapeutic agents on properties of DNA liquid crystals

We have investigated the X-ray and optical properties (CD spectra and polarization microscopy) of liquid-crystalline phases and dispersions formed on pretreatment of low molecular weight DNA with the platinum(II) coordination complexes, cis-diammine-dichloroplatinum(II) (DDP), 2,2-bipyridinedichloroplatinum(II) (1) and 2,2-bipyridineethylenediammineplatinum(II) (2). It is demonstrated that the platination of DNA leads to the ordering of neighbouring molecules of DNA in liquid-crystalline phases being diminished. The intense bands observed in the CD spectra of liquid-crystalline dispersions prepared from DNA pretreated with 1 or 2 can be used to determine the orientation of the latter compounds with respect to the helical axis of the DNA and to detect distortions in the secondary structure of DNA. The possible causes of the appearance of the intense bands in the CD spectra of liquid-crystalline phases and alterations in the manner of packing of the molecules of DNA within them are discussed.

Molecular Constructions (Superstructures) with Adjustable Properties Based on Double-Stranded Nucleic Acids

We describe formation of a molecular construction that consists of double-stranded molecules of nucleic acids (or synthetic polynucleotides) located at a distance of 30–50 Å in the spatial structure of particles of their cholesteric liquid-crystalline dispersion and crosslinked by polymeric chelate bridges. The resulting superstructure, which possesses peculiar physicochemical properties, can be used as an integral biosensor whose properties depend on temperature, the presence of chemical or biologically active compounds of different nature, etc.

Restructuring space ordering of (DNA-protamine) complexes in liquid crystalline dispersions under proteolytic enzyme treatment

Abstract Complexes of DNA with the protamines stellin A and stellin B, in polymer-containing solutions, form both liquid crystalline phases and liquid crystalline dispersions. The ‘non-specific’ organization of the (DNA-protamine) phase is determined by the presence of protamine ‘cross links’ between the DNA molecules and not by the inherent anisotropy (cholesteric) double-stranded DNA molecules. Elimination of these ‘cross links’ by proteolytic enzyme action causes an increase in the distance between the DNA molecules which results in the appearance of an intense band in the CD spectrum and a ‘fingerprint’ (cholesteric) texture.

Structural polymorphism of liquid-crystalline dispersions of double-stranded DNA complexed with synthetic polycations

Linear double-stranded DNA molecules interact with positively charged polyconidine molecules in aqueous salt solutions to yield liquid-crystalline dispersions (LCDs) with a mean particle diameter of ∼6000 Å. The packing density of (DNA-polycation) complexes differs among LCD particles formed at different ionic strengths. X-ray data on the liquid-crystalline phases of (DNA-polyconidine) complexes formed under different conditions were compared with a phase diagram, reflecting polymorphism of liquid crystals of linear double-stranded DNA. It was shown that LCD was hexagonal at 0.15 M ≤ CNaCl < 0.4 M and cholesteric at 0.4 M ≤ CNaCl < 0.55 M. Cholesteric LCD displayed abnormal optical activity in the circular dichroism spectrum. A similar situation was observed with poly(2,5-ionene), another polycation differing in chemical structure from polyconidine. The results demonstrated structural polymorphism of (DNA-polycation) LCDs. It was assumed that the packing mode of (DNA-polycation) complexes in LCD particles can be regulated by changing NaCl concentration. The mechanism generating the cholesteric liquid-crystalline state of DNA in a narrow range of NaCl concentrations is discussed.

General Principles of Creating Biosensing Units Based on Double-Stranded Nucleic Acid Liquid Crystals

The principles of creating biosensing units based on double-stranded nucleic acid liquid- crystalline dispersions are considered. These units are capable of ‘recognizing’ biologically active compounds (antitumor drugs, nucleases. etc.), reacting with the nitrogen bases of nucleic acids, as well as biologically active compounds splitting artificial ‘cross-links’ formed between DNA molecules.