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The response of ejaculated bovine spermatozoa to gold nanoparticles was studied by the standard method of nuclear chromatin decondensation in vitro. After the treatment of semen samples with a hydrosol containing gold nanoparticles with an average diameter of 3.0 nm and a concentration of 1 x 10(15) particles/mL, the ability of sperm nuclei to decondense in the presence of sodium dodecyl sulfate (SDS) and dithiothreitol (DTT) dramatically changed compared to the control. The frequencies of gametes with nondecondensed ("intact"), partially decondensed, and completely decondensed nuclei correlated as 40 : 32 : 28% and 0 : 36 : 64% in the experiment and the control, respectively. Moreover, the appearance of a sufficiently large number of gametes with destructed and almost completely destroyed nuclei was noticed in the spermatozoa treated with gold nanoparticles. This article suggests the putative mechanisms of action of ultrasmall gold nanoparticles on the structural and functional integrity of the deoxyribonucleoprotein (DNP) complex of mature male gametes.

The properties of the particles of cholesteric liquid-crystalline dispersions formed by double-stranded DNA molecules obtained as a result of phase exclusion of these molecules from water-salt polymer-containing solutions are briefly described. Physicochemical properties of quasinematic layers of dispersion particles and double-stranded DNA molecules in their content are taken into account in the course of developing fundamental background of the liquid-crystalline approach to the DNA structural nanotechnology. According to different versions of this approach, which is based on intraparticle gelation of cholesteric liquid-crystalline dispersions, spatial structures (DNA nanoconstructions, "rigid" DNA particles) with unique properties, are created. By means of atomic force microscopy images of "rigid" DNA particles of different type are registered. Specific properties of metallic nanoparticles (in particular, gold nanoparticles) are considered while developing the other approach to DNA structural nanotechnology, which provides the basis for "metallized" DNA nanoconstructions.

Currently, neutron capture therapy is a promising cancer treatment. This method is based on the reaction of the thermal neutron capture by some non-radioactive elements (e.g., Gds57), which results in subsequent emission of electrons and gamma rays. An effective instrument for delivery of gadolinium into the tumor tissue are the particles of the "rigid" nanostructures (NS) based on double-stranded DNA complexes with gadolinium (NS-Gd). The local concentration of Gd in such nanostructures may reach 40%. To optimize the process of neutron capture therapy it is very important to investigate possible penetration mechanisms of NS-Gd particles into the tumor cells. In this work, the dynamics of interaction NS-Gd with cultivated chinese hamster ovary cells (CHO) was studied by confocal and electron microscopy. It is shown that NS-Gd are able to enter CHO cells. This process begins in about 1 hour after the start ofincubation. After 6 h NS-Gd particles were detected in almost all cells. A further increase of the incubation time does not lead to significant changes in cell morphology, although the number NS-Gd inside the cells increases. The plasma membrane of the cells remains intact. The NS-Gd particles, which entered the cells, remain inside the cells for a long time. The data obtained show that NS-Gd are relatively low-toxic and suggest that the presence of NS-Gd in the tumor cells does not prevent their division. The data obtained are important for improving the efficiency of the neutron capture therapy method.

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.

The response of the mouse male germ cells exposed to gold nanoparticles (approximately 2.5 nm) was studied. Our investigation demonstrates that treatment with Au nanoparticles for four days does not impair the architecture of the spermatogenic epithelium. Cytogenetic evaluation using micronucleus assay showed that gold nanoparticles can affect the chromosomes of early primary spermatocytes. However, gold nanoparticles did not induce chromosome abnormalities in spermatogonial stem cells. Further, the cauda epididymal sperm was isolated on the 14th day after treatment and was incubated in SDS solution (Na sodium dodecyl) and then in a solution containing DTT (dithiothreitol) to induce nuclear chromatin decondensation. Observations showed that after four days of treatment of spermiogenic (postmeiotic) cells with gold nanoparticles the decondensation process had no differences from the control. On the contrary, in the experiment with the same cells and period of fixation but with a single exposure to gold nanoparticles, the number of mature gametes with totally decondensed nuclei reached 100% as opposed to 44% in the controls.

The formation of liquid-crystalline dispersions as a result of interaction of linear, double-stranded DNA molecules with poly(propyleneimine) dendrimers in water-salt solutions was studied. It was shown, that this process does not depend on the ionic strength of solution and molecular structure of dendrimer. By means of the atomic force microscopy, it was established, that in the case of the dendrimer molecules of the 4th generation (G4), the mean size of particles of (DNA-dendrimer G4) liquid-crystalline dispersion is equal to 300-400 nm. The "boundary" conditions (ionic strength of solutionand molecular mass of dendrimer) of formation of optically active (cholesteric) and optically inactive of the (DNA-dendrimer) dispersions were determined using circular dichroism spectroscopy. The interaction of dendrimers of 1st, 2nd, 3rd and 5th generations with DNA molecules results in the obtaining of the optically inactive dispersions. Dendrimer molecules of 4th generation induce the formation of two types dispersions: in solutions of high ionic strength (micro > 0.4) they induce the formation of cholesteric liquid-crystalline dispersions, and in solutions of low or intermediate ionic strength (micro < 0.4) they can form the optically inactive one. The "molecular crowding" affects both the efficiency of binding of dendrimer molecules of 4th generation to DNA, and the mode of spatial packing of (DNA-dendrimer G4) complexes in particles of liquid-crystalline dispersion. The possible reasons capable of explaining the structural polymorphism of (DNA-dendrimer) liquid-crystalline dispersions are discussed.

This paper reviews data obtained in our Laboratory in the field of the liquid-crystalline dispersions of the double-stranded nucleic acids (DNA, RNA) and results of the analysis of behavior of these biopolymeric molecules in the quasinematic layers. The fundamental data obtained in this area were used as a background for creation of the DNA nanoconstructions, containing different "guest" (biologically active or/and chemical substances) molecules. Two theoretically possible ways for creation of the DNA nanoconstructions were compared. The unique properties of the nanoconstructions dictating the scope of their practical application are described.

The binding of chitosan molecules to DNA in solutions of different ionic strength has been studied. The data were analyzed in terms of the model of ion condensation and the thermodynamic theory of the binding of protracted ligands to DNA. Combining these approaches made it possible to estimate the sterical and energetic characteristics of chitosan-DNA binding and establish the dependence of the chitosan-DNA binding constant on the ionic strength of solution.

The binding of Gd3+ ions to linear double-stranded DNA molecules in water-salt solutions or in liquid-crystalline dispersions is accompanied by sharp changes in their optical and X-ray characteristics. Depending on the initial conditions of complex formation, the binding of Gd3+ ions either to DNA bases or phosphate groups occurs, which leads to changes in the properties of the liquid-crystalline dispersions. The packing of neighboring DNA molecules in particles of the liquid-crystalline dispersion of the complex DNA-Gd3+ depends strongly on the concentration of Gd3+ ions. This process is accompanied by a decrease in the amplitude of Bragg's reflection maximum. The unique properties of the developed material open the possibilities for its practical use.

The double-stranded, linear DNA molecules form the liquid-crystalline dispersions (LCD) in water-salt solutions containing positively charged polyconidin molecules. It was established from the analysis of the absorption spectra of the LCDs formed from (DNA-polyconidin) complexes, that the mean size of the particles of these dispersions is equal to -6000 angstroms. The small-angle X-ray data show, that in the LCD particles different density of packing of the (DNA-polycation) complexes is realized. The comparison of the X-ray data of the liquid-crystalline phases of (DNA-polyconidin) complexes formed under various conditions with the phase diagram, that reflects the polymorphism of the linear double-stranded DNA liquid crystals, demonstrates that the hexagonal mode of the LCD packing is existing in 0.15-0.4 M NaCl solutions, whereas in 0.4-0.55 M NaCl solutions-- the cholesteric one. As a result of specific spatial organization the cholesteric LCD possesses of an abnormal optical activity in the CD spectrum. The similar situation takes place in the case of another synthetic polycation--poly(2,5-ionen), whose chemical structure differs from that of polyconidin. Thus, the structural polymorphism of the (DNA-polyconidine) LCDs was evidenced. It means that change of NaCl concentration opens a gate to control the spatial packing of the molecules of (DNA-polycation) complexes in the particles of LCDs. The supposition about mechanism of formation of the DNA cholesteric liquid-crystalline state in the narrow interval of NaCl concentrations was suggested.

The temperature stability of nanoconstructions formed by double-stranded DNA molecules fixed in the structure of their liquid crystalline dispersions and cross-linked by nanobridges was determined. It was shown that the heating of nanoconstructions is accompanied by a decrease in the amplitude of the negative bands in the CD spectrum both at lambda approximately 310 and lambda approximately 505 nm. Temperature "melting curves" were derived and characterzed by T(M) values. The T(M) values at lambda approximately 310 and lambda approximately 505 nm coincided with each other but differed from the T(M) value characteristic of the DNA cholesteric liquid crystalline dispersion.

A problem on the electrostatic interaction of two homogeneously charged macromolecular rods of a finite length, submerged into an electrolyte solution was considered. An explicit expression for the energy of interaction and rotational moment as a function of the angle of rotation between the long axes of the molecules was obtained. At small angles of rotation, the expression for energy turns into the corresponding formula for parallel rods, and the rotational moment tends to zero, as it follows from geometrical considerations. The possibility is discussed whether the study is applicable to real biological systems, including liquid-crystalline dispersions of DNA.

The data on the morphology, structural parameters, and abnormal optical properties of particles of cholesteric liquid-crystalline dispersions of double-stranded DNA are reviewed. The general principles of the creation and operation of biosensing units based on particles of these suspensions, including dispersed particles immobilized in hydrogels, are described. Examples demonstrating the analytical potentialities of liquid-crystalline biosensing units are given. A method for constructing "sandwich"-type biosensing units based on the particles of liquid-crystalline dispersion formed from molecules of DNA-polycation complexes is described.

Due to noncooperative binding of ligands to DNA molecules, DNA molecules are in equilibrium with different numbers of adsorbed ligands. This equilibrium for a given concentration of the free ligand in the solution is characterized by the distribution function, which describes the probability of revealing the DNA molecule with a definite number of adsorbed ligands. If polycations act as ligands, DNA molecules with the number of ligands sufficient for neutralizing the charges on phosphates may undergo a phase transition. One example of this transition is the formation of liquid-crystalline dispersions during the binding of DNA to chitosan. We analyzed the binding of chitosan to DNA on the assumption that this binding is due to equilibrium adsorption. At a definite concentration of chitosan in solution, DNA molecules are in equilibrium with different numbers of adsorbed molecules of chitosan. If the number of adsorbed ligands exceeds some critical value, the DNA molecule covered with chitosan becomes capable of interacting with other DNA molecules. As a result of this interaction (attraction), liquid-crystalline dispersions can form. Equations describing the dependence of the concentration of DNA molecules on the concentration of the ligand in solution were derived. It was shown that, at given parameters of the model, it is possible to describe experimental data characterizing the formation of cholesteric liquid-crystalline dispersions. The analysis of the data makes it possible to reconstitute both the size of the binding site occupied by chitosan on the DNA and the energy of interaction of chitosan with DNA.

Three variants of the model for the formation of "bridges" between the nucleic acid molecules fixed in the structure of particles of liquid-crystalline dispersions were considered. What the three variants have in common is that the bridges represent polymeric chelate cross-links consisting of alternating molecules of daunomycin and copper ions. The differences between the three variants are that in the first variant, the bridges begin and end with daunomycin molecules that form a complex by the mechanism of external binding with nucleic acids; in the second variant, the bridges begin and end with copper ions coupled with the pairs of bases of nucleic acids; and in the third variant, the bridges begin with the daunomycin molecule and end with the copper ion. For each variant, a mathematical model was constructed, which describes the formation of bridges, and equations of binding were derived. The results of calculations were compared with the experimental data. Within the framework of each variant, the values of the energy of interaction between the daunomycin molecule and the copper ion in the bridge, the energy of interaction of the daunomycin molecule with the nucleic acid, and the length of the bridge were varied. For all variants, those values of the parameters were chosen that fit best the experimental data. The theoretical curves obtained using the three variants of the model agree rather well with the family of experimental curves. The best agreement between the theoretical and experimental data was obtained when the polymeric chelate bridge includes more than two daunomycin molecules.

Formation of molecular construction that consists of double-stranded molecules of nucleic acids (or synthetic polynucleotides) located at the distance 30-50 A in the spatial structure of particles of their cholesteric liquidcrystalline dispersion and crosslinked by polymeric chelate bridges is described. The resulting superstructure, which possesses peculiar physicochemical properties, could be used as integral biosensor whose properties depend on temperature, the presence of chemical or biologically active compounds of different nature, etc.

The binding of daunomycin and copper ions to poly(I).poly(C) molecules fixed in a particle of a liquid-crystalline dispersion was studied. A thermodynamic model of adsorption was developed, which makes it possible to describe the formation of complexes of a particular kind, "bridges" that connect adjacent nucleic acid molecules fixed in a liquid crystal. The bridges represent chelate complexes, which incorporate the molecules of the antibiotic daunomycin and copper ions. Equations describing the dependence of the concentration of these bridges in solution on the concentration of their constituents were derived. The family of dependences of experimental amplitudes of bands in CD spectra typical of "bridge" structures on the concentration of copper ions represents a set of S-shaped curves, and, as the concentration of daunomycin in solution increases, the level of saturation of these curves increases. The analysis of experimental data with the use of this model suggests that the structures of this type compete with daunomycin molecules for the binding sites on poly(I).poly(C). By using this model, the energies of formation of bridge structures were calculated.

Liquid-crystalline dispersions of nucleic acid-chitosan complexes (NA-chitosan) possess optical and X-ray diffraction properties different from those of "classical" cholesterics. It is possible that positive charge distribution (distance between charges, chitosan conformation, etc.) in the polymeric chain of chitosan molecule combining with NA molecule is the factor that affects the spatial structure of resulting dispersions.

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.

Right-handed helical double-stranded DNA molecules were shown to interact with chitosans to form under certain conditions (chitosan molecular weight, content of amino groups, distance between amino groups, ionic strength and pH of solution) cholesteric liquid-crystalline dispersions characterized by abnormal positive band in CD spectrum in the absorption region of DNA nitrogen bases. Conditions were found for the appearance of intense negative band in CD spectrum upon dispersion formation. In some cases, no intense band appeared in CD spectrum in spite of dispersion formation. These results indicate not only the multiple forms of liquid-crystalline dispersions of DNA-chitosan complexes but also a possibility to control the spatial properties of these complexes. The multiplicity of liquid-crystalline forms of DNA-chitosan complexes was attempted to explain by the effect of character of dipoles distribution over the surface of DNA molecules on the sense of spatial twist of cholesteric liquid crystals resulting from molecules of the complexes.

A thermodynamic model of the formation of bridges consisting of alternating daunomycin molecules and copper ions and connecting neighboring nucleic acid molecules in a particle of a liquid crystalline dispersion was constructed. The model is based on the conception that ligands are adsorbed on lattices of reaction centers which are formed in a liquid crystal at a particular spatial arrangement of adjacent nucleic acid molecules (phasing). Equations were derived that describe typical experimentally obtained S-shaped dependences of bridge concentration on the concentration of copper ions and daunomycin molecules in an initial solution. It was shown that dependences of this kind take place in two variants of the adsorption model: when the binding of daunomycin with adjacent nucleic acid molecules is considered to be independent on the formation of bridges and when bridges compete with single daunomycin molecules for the sites on adjacent nucleic acid molecules.

Abnormal optical properties of liquid-crystalline dispersions (phases) formed as a result of phase exclusion of double-stranded DNA and RNA from water-salt poly(ethylene glycol) solutions and X-ray parameters of these phases are compared. It is shown that the cholesteric packing of nucleic acid molecules is realized at the certain osmotic pressure of a solvent only. A comparison of the optical properties of liquid-crystalline phases (dispersions) to their X-ray parameters allows one to put forward a suggestion on various hydratation (fluctuation) regimes of the nucleic acid behaviour under the condensed phases formation and factors, influencing the mode of packing of these molecules in phases formed. It is shown as well, that immobilization of DNA cholesteric liquid-crystalline particles in the content of polymeric matrix is accompanied by the stabilization of these particles and, hence, their specific abnormal optical activity as well as by formation of particles having a structure, which corresponds to the "optically isotropic ordered liquid" without abnormal optical activity. Data on stabilization of the cholesteric structure of liquid-crystalline DNA dispersions by creation of polymeric chelate bridges between the neighbouring DNA molecules, fixed in the structure of liquid-crystalline dispersions, are shown.

The circular dichroism spectra of liquid-crystalline dispersions formed of double-stranded DNA molecules were calculated. It was found that the amplitude and sing of the anomalous band in these spectra in the region of absorption of nitrous bases depend on the size of dispersed particles, the pitch of their cholesterol helix and the sign of its spatial winding. The theoretical calculations are compared with experimental data characterizing the anomalous optical properties of liquid-crystalline DNA dispersions and synthetic polynucleotides formed as a result of phase elimination in aqueous salt solutions of polyethyleneglycol. The theoretically calculated circular dichroism spectra of liquid-crystalline DNA dispersions agree with the circular dichroism spectra of these dispersions observed experimentally.

The X-ray and optical properties as well as the textures of liquid crystals formed of DNA molecules bound in complex with an anthracycline antibiotic daunomycin were investigated. It was shown that DNA.daunomycin complexes, depending on the extent of alteration of the DNA secondary structure by daunomycin, could yield two types of cholesterics differing in the direction of their spatial twisting as well as nematics. Liquid-crystalline dispersions of DNA.daunomycin complexes have CD spectra with "mirror" bands depending on daunomycin concentration. "Testing" of the orientation of daunomycin molecules on the DNA in liquid-crystalline particles suggested two types of binding.

The change in the spatial structure of superhelical and nicked DNA molecules in liquid-crystalline dispersions under micrococcal nuclease treatment was studied. Micrococcal nuclease digestion leads to restructuring from the "nonspecific" packing of circular DNA in dispersion particles to the cholesteric one. The transition is described by the Kolmogorov-Avramy equation; however, the parameters of the equation are essentially different for the different topological forms of circular DNA. The liquid-crystalline state of DNA expands the range of the solvent properties (ionic conditions etc.) under which the micrococcal nuclease action remain highly efficient.

The optical properties (circular and linear dichroism) of the 11 anthraquinone antibiotics complexed with DNA molecules under conditions giving rise to cholesteric liquid-crystalline dispersions were investigated. Complexes of compounds A911 and A912 with double-stranded linear or circular DNA molecules differ strongly in their properties from those of other anthraquinones. The possible reasons of these differences and their possible correlation with the biological activity of the A911 and A912 are discussed.

Superhelical pBR322 DNA molecules form liquid-crystalline dispersions in water-salt solutions containing poly(ethyleneglycol). The formation of the liquid-crystalline dispersions from superhelical DNA molecules results in the appearance of two sites inside the DNA molecules that are split by Micrococcal nuclease. The first site of digestion does not differ from the standard site split by this enzyme in water-salt solutions, whereas the second one represents a new site specific only for the DNA molecules forming liquid-crystalline dispersions. Splitting of the DNA molecule through the first site is accompanied by formation of its linear form; splitting of a new site results in the formation of two linear DNA fragments with molecular masses equal to half of the initial DNA molecules. Enzyme digestion of superhelical DNA molecules forming liquid-crystalline dispersions induces a reformation of the "nonspecific" space organization of dispersions to the cholesteric one. A hypothetic model for packing of the superhelical DNA molecules inside liquid-crystalline dispersions and its transformation under enzyme action is suggested.

A comparative study of polyconidin effects in the replicative and transcription activity of hepatocyte DNA in intact animals, and on peculiarities of spatial organization DNA in the DNA complex with oligomer-25 conidin was carried out. It was shown that polyconidin binding to DNA results in "cross-linking". This process is accompanied by formation of liquid-crystalline dispersion without abnormal optical activity. Liquid crystals possess high density packing of DNA molecules complexed with quaternary ammonium salt of oligomer-25 conidin. The addition of heparin to liquid-crystalline dispersions or phases, destroys the structure of the DNA complex with quaternary ammonium salt of oligomer-25 conidin. As a result "free" DNA molecules appear, they form the cholesteric liquid-crystalline phase. An increase in transcription activity and synchronization of DNA synthesis in hepatocyte was demonstrated. A correlation between chromatin modification and biological activity of chromatin after formation of the DNA--oligomer-25 conidin complex is proposed.

A brief concept of biosensors is presented. Structural peculiarities and properties of single- and double-stranded nucleic acids that are to be taken into account when creating sensing units for biosensors using different principles of molecular recognition are considered. General schemes of sensing units based on liquid-crystalline dispersions formed from low-molecular mass DNA, its complexes with "cross-linking" agents and from circular superhelical DNA molecules are described.

The effect of anthrachinone and anthracene derivatives on linear and circular superstranded molecules of DNA in conditions of their condensation was studied. It was shown that the compounds formed strong intercalation complexes with the molecules of the linear and circular superstranded DNA when the DNA molecules were in the condensed condition. The optical properties of the disperse liquid crystal phases formed of the complexes of the investigated compounds with the molecules of linear double-chain DNA differed. Moreover, the optical properties of the condensed phases formed of the complexes of the compounds with the molecules of linear and circular superstranded DNA also differed. The causes of the differences are discussed.

The optical properties of the DNA complexes with the compounds of bivalent platinum were studied. The compounds differed by the nature of the anionic and neutral ligands and their spatial arrangement about the platinum atom. It was shown that the same as cis-[Pt (NH3)2Cl2] the platinum compounds with the biological activity, i.e. [Pt (en) Cl2], cis-[PtNH3 (Bz) Cl2] and cis-[Pt (NH3)2NO2Cl] induced at low values of r (a ratio of the number of the platinum moles added to the number of the DNA nucleotide moles in the solution) an increase in the amplitude of the positive band in the spectrum of the circular dichroism (CD) of the linear DNA and a marked decrease in the amplitude of the negative band in the spectrum of the CD of the liquid crystalline microphase of DNA formed in the presence of polyethyleneglycol. By the character of the action on the CD spectrum of the linear and condensed DNA [Pt (tetrameen)Cl2] which had no selective antimitotic effect might be referred to the above platinum compounds. Trans-[Pt (NH3)2NO2Cl], [PtNH3PyCl2], cis-[Pt (NH3)2(NO2)2] and [Pt (NH3)3Cl]Cl having no biological activity either induced only a decrease in the amplitude of the positive band in the CD spectrum of the linear DNA or had no effect on the CD spectrum. The effect of these compounds on the CD spectrum of the liquid crystalline microphase of DNA was slightly pronounced or not observed.

The conditions (mol. weight of PEG, ionic strength) of formation of double-stranded RNA (dsRNA) compact particles in water-salt solutions, containing poly(ethylene glycol) (PEG) have been determined. It has been shown, that in solutions of mild ionic strength (approximately 0,3) the compact particles of dsRNA are characterized by an intense positive CD-band (lambda 270 nm), but in solutions of high ionic strength (1,0-1,5)--by intense positive or negative CD-bands (lambda 270 nm). The heating of the solutions of a high ionic strength, containing the compact particles with negative CD-bands is accompanied by the change of sign of CD-band. The same effect is observed in the case of decrease of the ionic strength of the solutions. "Melting" of compact particles as revealed by the CD-method occurs prior to the melting of the secondary structure of dsRNA. These data show, that the intense CD-bands reflect the ordered arrangement of the chromophores of polynucleotide chain in compact particles. The reasons of change of the sign of the CD-bands are discussed.

A comparative X-ray study of DNA compact particles, formed in PEG-containing solution from native DNA and from DNA molecules with altered secondary structure was carried out. Low-angle reflections, present in X-ray patterns of compact particles (in powder form) from native DNA, correspond to spacings of 84, 42 and 35 A, while wide-angle reflections correspond to spacings of 12.8; 8.4, 6.0, 4.5, 3.4 A. Low-angle reflections at 84 and 42 A are present also in X-ray patterns of compact particles, formed from DNA molecules with altered secondary structures. These two reflections are believed to be the results of an ordering of DNA molecules within the compact particles. The main features of this ordering appear in the first approximation to be independent on DNA secondary structure. The CD spectra of all types of compact particles, mentioned above, were also studied. It has been shown that the intense negative band (lambda approximately 270 nm) in a CD spectrum appeared only in the case of compact particles, formed from native DNA molecules. The nature of the revealed correlation between the 35 A reflection and the CD negative band is discussed. Data presented in the paper allow one to suppose that the 35 A reflection in X-ray patterns and the CD negative band result from specific interactions between double-stranded DNA fragments spatially brought together in compact particles. Such type of interaction is believed to be characteristic only of native DNA molecules.

The data showing the features of the DNA compactization process in PEG-containing solutions of chlorides of different alkaline metals (LiCl, KCl, RbCl and CsCl) and an ammonium salt (CH3-(CH2)17-N-(CH3)3Br) are presented. The data indicate that the formation of a compact form of the double-stranded DNA in PEG-containing water-salt solutions depends not only on the PEG concentration and ionic strength but on tha cation nature as well. The compactization occurs most easily in the presence of Na+-ions. This indicates a specific character of interaction between Na+-ions and DNA phosphate groups which may be due to an optimum structural fit between the hydrated Na+-ions and orientation of the phosphate groups in the DNA molecule. The nature of forces involved in the processes of the intramolecular compactization and intermolecular aggregation of double-stranded DNA molecules in water-salt solution is discussed. The difference between the effect of Na+ and that of K+-ions on the compactization process at the ionic strengths close to physiological values makes it possible to suggest that the changes of the tertiary structure of double-stranded DNA which accompany its function in vivo may take place under conditions of a decreased water activity at the expense of relatively slight changes in ion composition of the water surrounding DNA.

Influence of pH on absorbance and CD-spectra of DNA in PEG-containing water-salt solutions has been studied. The changes in the spectra appeared due to disturbance of the DNA secondary structure upon acidification of the medium proir to or after DNA compactization. If acidification preceeds DNA compactization an intense negative band in the CD spectrum inherent to the compact particles is observed at pH values 7-4. The intensity of the band decreases with an increase of the acidity. The size of the compact particles as evaluated from the dependence of the apparent optical density on the wavelength value remains unchanged (about 1200 A). If the solution is strongly acidified (pH 4.0-2.8) and a considerable disturbance in the DNA secondary structure takes place a negative band in the CD spectrum completely disappears. If one acidifies a solution containing preformed DNA compact particles a decrease of the intensity of the CD negative band starts at lower pH values (less than 2.8). This process is accompanied by an increase of the size of the particles. Acidic "denaturation" of DNA within the compact particles (pH approximately 2.5) is followed by a dissappearance of the CD negative band and a considerable increase of the particle size. The data obtained indicate that the specific arrangement of DNA strands manifested in a CD negative band depends on the defects in the DNA secondary structure.

Here we present a brief conception of biosensors. Structural peculiarities and properties of single- and double-stranded nucleic acids that are to be taken into account when creating biosensors on the basis of these biomolecules are considered. On the example of two biologically active compounds a possibility is shown for constructing biosensors on the basis of liquid-crystalline dispersions of low molecular mass DNA and on the basis of liquid-crystalline DNA dispersions immobilized due to their inclusion into the synthetic polymeric matrix.