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The methods of UV (DUV) spectroscopy and thermal denaturation were used to study the effect of Cd2+ ions on the conformational equilibrium of three-stranded (A21, A2U) and single-stranded (poly U, poly A and poly I) polynucleotides in aqueous solutions containing 0.1 M Na+ (pH 7). An analysis of the form and intensities of DUV-spectra of poly A, poly I and A2I revealed the presence of two types of complexes: interaction with N7 of purines, resulting in the formation of macrochelates and binding to N1 of poly A and poly I. Cd2+ ions do not bind to heteroatoms of A2U nitrogen bases, and, therefore, the conformation of its structure remains unchanged up to a concentration of Cd2+ 0.01 M. A "critical" concentration (1.5x10(-4) M) of Cd2+ ions exists above which A2I transits cooperatively into a new helical conformation, which has a lower thermostability. It is supposed that, during the formation of metallized A2I, Cd2+ ions form bridges between the adenine and hypoxanthine of its homopolynucleotide circuits, being arranged inside the triple helix.

Interaction of Mg2+, Ca2+, Cu2+ ions with the four-stranded poly(I) was studied using differential UV and visible spectroscopies. It was shown that, up to concentrations of approximately 0.1 M, Mg2+ and Ca2+ ions do not bind to heteroatoms of hypoxanthine of the four-stranded poly(I). Cu2+ ions interact with N7 (and/or N1) and O6 (through the water molecule of the hydrate shell of the ion). The latter seems to induce the enolization of hypoxanthine the deprotonation of N1, and, as a result, the transition of the four-stranded helix to single-stranded coils. Single-stranded chains form compact particles with an effective radius of about 100 A.

The interaction of Ag+ ions with ribonucleotides of canonical bases in aqueous solution was studied by differential UV spectroscopy. Atoms coordinating silver ions (N7, O6 of guanosine 5'-monophosphate, N3, O2 of cytidine 5'-monophosphate, N7, N1, N3 of adenosine 5'-monophosphate and N3 of uridine 5'-monophosphate) and the binding constants characterizing the formation of appropriate complexes were determined. The differences in the relative affinity of Ag+ ions for the atoms of nucleotide bases correlate with the potential on them.

Using the method of differential scanning calorimetry, the DNA helix-coil transition was studied in solutions (10(-3) M Na+, 10(-3) M tris HCl, pH 7.0) containing divalent copper ions at relative metal ion concentrations (Mt2+/PDNA) ranging from 0.2 to 20. Dependences of the melting temperature and enthalpy on relative ion concentration were determined. An aggregation of Cu(2+) + DNA complexes in the range of average ion concentration was established. It is shown that the melting enthalpy of "units" increases with copper ion concentration. The data obtained were compared with values determined by UV-spectroscopy. Association constants for Cu2+ binding to DNA were defined by the ligand theory.

Using the method of differential scanning calorimetry, the DNA helix-coil transition studied in solutions (10(-3) M Na+, 10(-3) M tris HCl, pH 7.0) containing divalent metal ions (Mn2+ and Ca2+) at relative metal ion concentrations (Me/PDNA) ranging from 0.2 to 20. Dependences of the melting temperature and enthalpy on the ion relative concentration were stated. The fine structure of melting curves in DNA+Me complexes was observed. The resolution degree of this structure was shown to increase in the range of moderate ion concentrations. The data obtained were compared with values determined by UV-spectroscopy. Association constants were defined for Mn2+ and Ca2+ binding to DNA by the ligand theory.

Experimental data on DNA melting in the presence of magnesium and calcium ions are compared with the calculated results by the "ligand" theory and "condensation" theory developed by de Marky and Manning (TMM). The maximum is observed in TMM dependences of DNA melting temperature change (delta Tm) on the ion concentration (D), absent in the experimental dependences and the "ligand" theory. The main cause of the discrepancy of calculated and experimental dependences delta Tm (D) is the fact that TMM neglects Na+ ion effects on Me2+ ion binding ("condensation") to DNA. The results obtained show that in comparison with TMM the "ligand" theory describes more adequately DNA helix-coil transition in the presence of divalent metal ions in the region of both low and high ionic strengths of solution.

DNA complexes with Ca2+ ions formed in films at various relative humidities were studied by IR-spectroscopy for molar concentration ratio of calcium ions and DNA phosphate groups [Ca2+]/[P] = 0.4-20. It is shown that the transition of DNA complexed with Ca2+ ions into B-form occurs at higher average numbers (n) of water molecules absorbed per nucleotide: n18 at the ratio [Ca2+]/[P] = 10, n24 at [Ca2+]/[P] = 20 and n12 in the absence of Ca2+ ions. This shows stronger binding of water molecules in the hydrate shell of DNA-Ca2+ if compared with free DNA. The results confirm a model proposed earlier. Ca2+ ions interact with phosphate oxygens of DNA and with N(7) nitrogens of guanine forming chelated complexes.

The properties of animal DNAs exposed to prolonged irradiation in the Chernobyl zone, have been studied by the methods of viscometry, thermal denaturation, IR-spectroscopy, and electrophoresis. High content of low-molecular fractions have been observed in the preparations of DNA from liver and spleen, their quantities increasing with age and generation of animals. This effect is especially strong in DNA from liver. Low-molecular fraction of DNA is shown to be enriched with G-C pairs and to consist of the following four fractions: 1) approximately 500 base pairs (B.p.), 2) approximately 1.5 divided by 2 thousand B.p., 3) approximately 4 divided by 5 thousand B.p. and 4) a mixture of approximately 20 thousand B.p. fragments. Further, it has been observed that the DNA preparations from the tissues of experimental animals contain about ten times higher contents of Fe, Zn, Se and other elements as compared to the control preparations.

DNA with Cu2+ ions in solution and films is studied by IR and Raman spectroscopy at different relative humidities (R.H. = 51 divided by 98%). DNA complexed with Cu2+ ions is shown to transit to the double-helix conformation, passing A-form, the water content per nucleotide (n) being essentially larger: 12 for Cu2+/P = 0.4 (n = 8 for DNA without ions). Cu2+ decrease the biopolymer hydration at R.H. 50-76% interactions with Cu2+ are stated to depend on the hydration degree of macromolecules. The analysis of the absorption band shifts of Raman spectra evidences the changes in the base torsion angle around the glycoside bond to the values characteristic of the syn-conformation and the interaction both with phosphates and nitrogen bases.

DNA complexed with Mn2+ ions in films is studied at different relative humidities and ion contents ([Mn2+]/[P] = 0.4-1) by IR spectroscopy. It is shown that substantially more sorbed water molecules are necessary for the transition of DNA complexed with Mn2+ ions into the double helical conformation (preferentially B-form) that for macromolecules in the absence of ions. DNA-Mn2+ complexes ([Mn2+]/[P] = 1) are able to absorb more water molecules than DNA. The results of the work evidence Mn2+ ion interaction with phosphates and nitrogen bases of the macromolecule: N7G, O6G.

The interaction between the native DNA macromolecules and Ca2+, Mn2+, Cu2+ ions in solutions of low ionic strength (10(-3) M Na+) is studied using the methods of differential UV spectroscopy and CD spectroscopy. It is shown that the transition metal ions Mn2+ exercise binding to the nitrogen bases of DNA at concentrations approximately 5 x 10(-6) M and form chelates with guanine of N7-Me(2+)-O6 type. Only at high concentrations in solution (5 x 10(-3) M) do Ca2+ ions interact with the nitrogen bases of native DNA. In the process of binding to Ca2+ and Mn2+ the DNA conformation experiences some changes under which the secondary structure of the biopolymer is within the B-form family. The DNA transition to the new conformation is revealed by its binding to Cu2+ ions.

The interaction of effective antibacterial drug decametoxyn with natural DNA was studied by UV-spectroscopy. Decametoxyn shows a specificity to nucleotides: it decreases the cooperativity of melting and the thermal stability of DNA parts enriched by AT pairs. The characteristics of the helix-coil transition on the DNA parts enriched by GC-pairs are invariable. Interaction with AT-pairs results in their partial or complete melting at room temperature, followed by intermolecule aggregation. Interacting with phosphates decametoxyn manifests itself not as a dication but as two single-charged ions.

The dependence of animal DNA denaturation on magnesium ion concentration has been studied in the range (10(-6)--10(-1) M with sodium ion content of 10(-3) and 10(-2) M. Special attention has been given to the effect of multivalent metallic impurities bound to DNA. An increase of DNA thermal stability has been shown to occur in the magnesium concentration rage of 10(-6)--10(-4) M. At concentrations exceeding 10(-3) M the T M begins to decrease. The dependence of the DNA melting range on magnesium ion concentration has a maximum at approximately 10(-5) M Mg2+. At low magnesium and sodium ion concentrations a strong asymmetry of the melting curves has been observed. This effect can be described in terms of the melting theory for DNA complexed with small molecules and is explained by magnesium ion redistribution from the denatured portions of DNA to native ones. The method for calculation of melting curves in the DNA-ligand system has been proposed. Studies of thermal denaturation parameters have been shown to be an effective method for the estimation of binding constants of ligands to native and denatured DNA.

Using the thermal denaturation method the effect of bivalent copper of (4-10(-6)-10(-3)) M concentrations on the helix-coil transition of DNA was studied in the solution of Na+ concentrations 10(-3)-10(-1) M. Unlike the previous studies, this paper makes allowance for the effect of impurity ions present in DNA and deionized water. It has been shown that in the region of low Cu2+ and Na+ concentrations, thermal stability increases, the melting range extends and the denaturation curves become asymmetric. At concentrations more than approximately 3-10(-5) M Cu2+, melting temperature starts to fall, and the range reduces to 1-1.5 degrees at [Cu2+] greater than or equal to 2-10(-4) M. As [Cu2+] reaches these values, the denaturation curve asymmetry and melting range increase again, which is due to the inversion of the relative stability of AT- and GC-pairs. Employing experimental and phase-transition-theory data for homopolymers, the constants of Cu2+ binding with phosphates and DNA bases were calculated. The concentration dependence of the DNA denaturation parameters was shown to be governed by the superposition of binding Cu2+ with phosphates and nucleic acid bases.

Ultraviolet differential spectra (UDS) and CD-spectra of poly (A) in the presence of Cu2+ ions are studied at different degrees of phosphate groups screening. The binding of cu2+ ions with bases of phosphates is shown to lead to disordering or to ordering respectively, of the mutual orientation of nucleotides. The UDS components due to conformation variations in poly (A) and association between Cu2+ ions and its bases are calculated. Comparison of the latter UDS-component with the differential spectrum of a protonated adenosine-monophosphate permits to assume that Cu2+ ions are in a coordination bond with N (1) adenine. The calculation of the concentration dependence of the binding constants indicates binding cooperativity and weak dependence on the screening degree of poly (A) phosphate groups.

High-resolution IR spectra of uracil, thymine, methyl-derivatives of uracil and 5,6-dihydrouracil are obtained using the matrix isolation method.

The spectral characteristics of interacting pyrimidine bases of nucleic acids--cytosine, 1-methylcytosine, uracil in autoassociates and hydrates--are investigated using the high-resolution infrared spectroscopy in argon matrices. Shifts of vibration frequencies in simple complexes are stated to be from 10 to 30 cm-1 in the 4000-400 cm-1 region observed. The isolated state-solid phase transition is followed by the absorption maximum shift, the latter being some hundreds of cm-1 in the 4000-2000 cm-1 region and some tens of cm-1 in the 1800-400 cm-1 region.

UV-differential spectra and CD spectra of poly(A) were studied in the presence of manganese ions at 10(-3) and 0.1 M Na+ in solution. It was shown that at at both low and high ionic strengths Mn2+ ions in low concentrations form bindings with phosphates of the polymer, increasing the degree of its helicity. At higher concentrations Mn2+ ions start to bind with poly(A) bases leading to a conformational helix-random coil transition. With manganese contents exceeding 10(-3) M, aggregates are formed, in which the mutual orientation of bases is characterized by a high degree of order. The calculation of concentration dependences of Mn2+ - poly(A) base binding constants shows that the process is cooperative. As the ionic strength increases from 10(-3) to 0.1 M Na+, the constant of the poly(A) - Mn2+ complex formation decreases by about an order of magnitude.

Using an Cphi-4A spectrophotometer (USSR), denaturation of DNA containing approximately 2% residual protein has been studied in the presence of catecholamines and their precursors: epinephrine, beta-3,4-dioxyphenylalanine, norepinephrine, 3,4-dimethoxyphenylethylamine, tyrosine, and phenylalanine. All these substances, excluding phenylalanine, induce positive excessive hyperchromicity (as compared to initial DNA). The correlation between this effect and molecular structures of the substances studied has been shown to exist. An increase of DNA hyperchromicity in the presence of catecholamines has been found to result from the oxygen presence in the aromatic rings of the catecholamines molecules. It is assumed that the interaction between the negative O-atoms in catecholamines and bivalent metal cations in the nucleoprotein complex weakens the DNA-protein binding. This leads to an additional disorientation due to the heat of nucleic acid bases, which were previously bound by the residual protein.

The influence of cuprum ions on the interaction between the antimalarial drug quinacrine (QA) and DNA is studied by polarized laser luminescence spectroscopy and fluorescence microscopy at molecular and cellular levels. An alteration of quinacrine luminescence intensity in complex with DNA caused by cuprum ions is explained in terms of redistribution of QA molecules from quenching GC- to fluorescent AT-DNA binding sites due to the competition of Cu2+ with the dye. Mechanisms of component interactions in the triplex "DNA-QA-Cu2+" in model and cellular systems are shown to be in qualitative agreement. QA photodynamic activity change caused by Cu2+ action is explained on the basis of the ideas being developed.

Anti-tumour antibiotic carminomycin interaction with chicken erythrocyte DNA is studied in aqueous-salt solutions by the laser polarized fluorescence method. Fluorescence quenches almost equally effectively during the antibiotic absorption on native (nDNA) and denatured (dDNA) DNAs, but the polarization degree of residual fluorescence differs about two times. Carminomycin binding to dDNA is characterized by one interaction type with a large density of occupancy sites - one antibiotic molecule per base pair. Carminomycin forms two types of complexes with nDNA, differing significantly with binding constants. Strong binding, intercalation, is saturated at one carminomycin molecule per 3 base pairs independently on the solution ionic strength. The weaker, external, interaction is characterized by the binding constant being by two orders of magnitude lower than that for intercalation, and the external interaction contribution is negligible.

The light scattering method for investigation of structural and aggregate stability is proposed, based on the comparison between angle and time dependence of total intensity of scattering light and its depolarized component. The structural evolution of liposome is observed by the anisotropic light scattering method. It is shown that the sols aggregate stability violation follows the appearance and increase of small-scale defects of vesicules. The interpretation of light scattering data is confirmed by electron micrographs.

Differential spectra (DS) of native and denaturated DNA in the presence of magnesium and calcium ions of 10(-3)--10(-1) M concentrations have been studied. DS of denaturated DNA unlike those of native DNA have pronounced maxima at 290 and approximately nm and approximately 247 nm minimum. Denaturated DNA with the ions studied forms light scattering molecular aggregates precipitating in the course of time. The aggregate dimensions were estimated. The kinetics of spectral variations with temperature and ion or DNA concentration was studied. Comparison of experimental DS with spectra of protonized nucleotides and DNA in the presence of transition metals allows to predict the existence of a binding between megnesium or calcium ions and the N(3) cytosine of single stranded DNA. The constants of ion association with these groups of nucleotides were calculated. The binding of calcium or magnesium with denaturated DNA is shown to be cooperative. This is due to the ion-induced transition of coil DNA strands to an ordered shape.

By the methods of heat denaturation and luminescence the interaction between an antitumor drug prospidine and DNA in aqueous solutions at two ionic strengths (0.1 and 0.001 M NaCl) and at various prospidine concentrations was studied. For the first time it has been demonstrated that the interaction occurs at 0.1 M NaCl and therapeutic prospidine concentrations. In the framework of Frank-Kamenetsky's theory of melting of a polymer with stabilizing ligands the size of the binding site and binding constants (K) with the decrease of ionic strength, the lack of alterations in the DNA UV absorption spectrum on complex formation and the data on the competitive binding of ethydium bromide suggest that at the first stage of the reaction an external complex is formed due to electrostatic interactions between quaternary nitrogen atoms of prospidine and DNA phosphate groups. Incubation of the complex at 37 0 C leads to a decrease of the DNA melting temperature and hyperchromic effect. Presumably this is due to the relatively slow formation of chemical bonds between alkylating groups of prospidine and nucleophilic groups of DNA bases, which results in the destabilization and denaturation of DNA. It is concluded that the interaction between prospidine and DNA must be taken into consideration when studying the molecular mechanism of prospidine antitumour activity.

Study is presented of the effect of noradrenaline on thermic denaturation of DNA-total histone complexes within the range of protein concentrations which corresponds to c1/c2 0-1.7 in solutions of 10(-3) M Na+ ionic strength (c1 and c2 being the weight concentrations of protein and nucleic acid, respectively). Denaturation of these systems has been found to be strongly affected by bivalent metals contained in DNA samples. Their presence accounts for the high temperature and wide melting range of DNA and diminution of the latter with an increase of the protein concentration in DNA-histone complexes. The denaturation parametres obtained for the studied systems are in fair agreement with predictions from the clip thermodynamic theory. Noradrenaline is shown to be capable of destabilizing DNA-total histon complexes. This is due to the inactivation of bivalent metals bound with DNA by noradrenaline. It is also suggested that noradrenaline does not weaken the histone binding with a nucleic acid.

The studies on the oscillatory structure of adsorption spectra of pyrimidine bases of nucleic acids isolated in Ar matrix at 11 K are described. To clear up the importance of molecule isolation in the matrix, amorphous films of the materials studied were investigated experimentally at 11 and 77 K. The work was carried out using the low temperature optic attachment developed by the authors. The long wavelength band of cytosine and deuterocytosine in the matrix is shown to consist of two bands: 1) lambda max = 267 nm with oscillatory progressions of 500 and 400 cm-1, respectively, and 2) lambda max = 280 nm with progression approximately 800 cm-1. The first pi pi*-absorption band of 1-methylcytosine has a single oscillatory progression 470 cm-1. Thymine and uracil in Ar matrices form diffuse structural spectra of 630 and 660 cm-1, respectively. The oscillatory progressions are attributed to the oscillatory frequencies of the pyrimidine molecule ring oscillations in the excited state. The annealing of the matrix results for all the materials in smearing the oscillatory molecule structure up to its complete vanishing. In film samples the oscillatory structure is not seen at low temperatures.

The interaction of DNA with Cu2+ and Mn2+ ions in low ionic strength solutions (10(-3) M NaCl) has been studied by the viscosimetry method. The DNA characteristic viscosity [eta] decreases sharply at low ion concentrations (addition of 10(-5) M Cu2+ leads to [eta] reduction by a factor of 1.4) and attains certain saturation at high concentrations, the saturation magnitude slightly depending on the ion type. The reduction is much lower in solutions containing bivalent ions, in concentration 2 X 10(-2) M NaCl. The experimental data for bivalent and monovalent (Na+) ions have been compared. The results are discussed in terms of equilibrium ion-DNA binding and compared with the Fixman theory. It is discussed if ion binding constants can be determined by visosimetry. It is shown that the cause of the viscosity reduction with time observed by some authors may be the action of DNAases activated by metal ions.