[What is the damage gamma-irradiation on solutions-cryoconservants at 77 K?].

Originating under the gamma-radiation action at 77 K on glassy phosphate solutions (6 mol/l) of glycerol and glycero-1-phosphate, H-atoms have motility by virtue of tunneling effect and react with the stabilized radicals of a matrix (OH /H2O+) and with solutes: at storage them in liquid nitrogen the radicals of separation H from carbon atoms C1 and C2 will be derived. According to the assessment maximal radiation "damage" is plotted to the investigated system for year, approximately 1 mol/l.

[Free-radical mechanism of chitosan radiation degradation and problems of the chemical antiradiation protection].

An analysis of published data on the radiolytic properties of chitosan and of some modelling its fragments substances was performed. The main process of radiation chitosan degradation is connected with the formation and conversion of free radicals. The mechanisms of the primary radicals C2, C1 and C3 (of the NH2 and H removal radicals) conversion up to the formation of some terminal products of chitosan radiolysis were offered in the form of the generalized schemes.

[About the "double" radioprotecting mechanism of some sulfur-containing substances].

The hypothesis about the double-acting mechanism of some radioprotectors during the irradiation of the DNA solutions is expressed in literature: the water radicals interception and the formation up to the irradiation of the additional intermolecular bonds "protector-DNA" (stabilization of the double helix). The realization conditions of this hypothesis were obtained by the molecular mechanics methods and the free radical mechanism appearance of the intrastrand cross-links "protector-DNA" during the irradiation of the polymer is given.

[On control of radioactive-chemical protection and point mutations by inhibitors of free radical reactions].

An opportunity to control the DNA protection against radiation in cells and the formation of 2-desoxyribose residue epimers (sites of potential point mutations) by using a set of free radical scavengers differing by parameters of availability (molecular mask and access window) is discussed. The values of steric probability (efficiency) of formation of a chemical bond between atoms Cn of a 2-desoxyribosyl radical (n from 1 to 5) and H-atom of a scavenger donor group were determined. It was shown that the maximum effect of radioprotection determined, for example, by transformations of C2 radical reached 25% (4-oxy-3,5-di-tert-butyl-alpha-methylbenzylamine) and maximum yield of C4-epimer was 15.

[The role of adsorbed water in polysaccharide radiation destruction].

The role of water in the potato starch destruction during gamma-irradiation of native starch preparations with various equilibrium humidity (5-45%) and starch jellies (systems with different quantity of polymer structured water) has been studied. The scheme reactions of the formation of primary radicals and molecular products of radiolysis in the system "structured starch--water" is also given.

[Efficacy of radioprotectors and gene mutations following 2-deoxyribosyl damage. Computer modeling].

The fundamental new universal method of evaluation of the interaction between macroradical and radioprotector (the access window method) is presented here. It's based on the modelling phenomenon of molecule penetration to the active centre of macromolecule structure through the functional groups free "window". The steric modelling of the B-DNA structure fragments allowed to measure the conformation parameters of the intermediate stereocomplex between interacting substancies.

[Radiochemistry of polysaccharides (review)].

Data on the radiolysis of polysaccharides (in the form of aqueous solutions in liquid or frozen states, and native "dry" preparations) is surveyed to explore the possibility of participation of free radicals in formation of ruptures in macromolecules, low-molecular products of polysaccharides decomposition, carbonyl, carboxyl, and peroxide groups in the macromolecules. The reaction schemes for principal transformation pathways of polysaccharides free radicals account for ultimate molecular products of the radiolysis. Effects of the adsorbed structured water on formation and conversions of free radicals, of postradiation polymer decomposition, and radiation protection of polysaccharides are discussed.

[Interactions of inhibitor of free radical reactions and 2-deoxyribosyl macroradicals].

By steric computer modelling of five types of 2-deoxyribosyl radicals and their molecular products generated in DNA by radiation as a result of R + InH = RH + In reaction the displacement of DNA bases (maximum--for C'1 atoms and minimum for C'3 ones) has been determined. Literature data on the DNA decay in the irradiated cells, and in DNA frozen solutions as well as the data on radiolysis of compounds modelling separate DNA fragments allowed to offer a general scheme of the every 2-deoxyribosyl radical transformation and to calculate a balance between the intermediate and final molecular products (processes) of the 2-deoxyribosyl radiolysis. The DNA conformation change due to the 2-deoxyribosyl stereoisomers formation at C'3 and C'4 atoms is discussed as one of the suggested reasons for genetic radiation mutation.

[Free radical mechanisms of radiation modification of DNA sugar fragment].

Analysis of the DNA and modeling its certain fragments substances radiolysis data allows to attribute the cardinal role to the primary 2-deoxyribosyl radicals in the processes of the breaks (C'3, C'5) and alkali-labile sites (C'1, C'2, C'4) in DNA strands, of the free bases appearance (C'3, C'5). The higher yield of bases destruction in DNA is explained by the transferring of a damage (unpaired electron) from 2-deoxyribosyl to a base within one nucleotide.

[The radiation modification of the sugar fragment in DNA: the formation of breaks, a change in polymer conformation and the transfer of the damage to the base].

Comparative analysis of the author's own data and data reported in the literature on the nature of the intermediate and end molecular products of radiolysis of DNA, its precursors and substances stimulating certain DNA fragments, allows to attribute the formation of breaks and alkaline-labile sites in DNA strands and changes in the polymer conformation, to the formation and transformations of some types of primary radicals of the sugar fragment. In order to explain certain effects induced by irradiation of DNA and its precursors (a balance of basic products of radiation destruction of DNA and ESR data concerning low temperature radiolysis of bases, nucleotides and nucleosides) the author proposes a model of the transfer of a damage (free valence) from 2-deoxyribosyl to a base within one nucleotide.

[The yields of the processes of DNA radiation-chemical destruction in the chromatin].

The methods of gel electrophoresis and spectrophotometry were used to study DNA destruction in the chromatin (a nucleosome set of 1 to 8 units) irradiated with 60Co-gamma quanta in water solutions at doses ranging from 1 to 40 kGy, depending on the chromatin concentration, the nature of gas that saturated the solution (Ar, N2O), and the protein/DNA ratio in the chromatin samples. In conditions of a complete involvement of water radiolysis products, OH and eaq, in the reaction with the chromatin (the chromatin concentrations in the solution exceeding 0.04 weight % when calculated per DNA) determined were G ("DNA-protein") cross-links = 6.

[Mechanism of the formation of DNA-protein cross-links during the gamma irradiation of chromatin in aqueous solutions].

The method of gel electrophoresis was used to study DNA-protein cross-link formation in fragmentized chromatin gamma-irradiated in water solutions (0.03%). By introducing changes into irradiation conditions (for instance, the use of different gases saturating the solution and the administration of radical acceptors) and by the subsequent electrophoretic analysis (treatment of the exposed chromatin by dissociating mixtures and enzymes) the authors showed a covalent nature of the cross-links in a radiation-induced DNA-protein complex and found the value of G (a cross-link) to be 0.

[Computer analysis of anisotropic ESR spectra and the structure of radical H and OH adducts of nucleic acid components in frozen aqueous solutions].

Computer analysis of ESR spectra recorded under gamma-irradiation of polycrystal and glass-like solutions of nucleotides and nitrous bases was carried out to determine the localization sites of free valency (damage) in DNA macromolecule when interacting with water radiolysis products (OH and H). The analysis was performed on a mini-computer with the program of reconstruction of ESR anisotropic spectra in the variation search regime. When calculating the theoretical spectra anisotropic width of the lines, g-factors and HHS constants on X and Z axes were taken into account.

[Mechanisms of induced processes in aqueous hemoglobin solutions at 77 K].

ESR spectra of gamma-irradiated and frozen at 77 K human oxyhemoglobin and partially denaturated methemoglobin solutions were analysed. The quartet signal ascribed to the anion-radical of proximal histidine was shown to dominate in the spectra of both solutions. The spectra of methemoglobin solution irradiated with relatively small doses have an intensive singlet ascribed to the stabilized electron.

[The role of structural factors in radiolytic damage of human hemoglobin].

A significant difference was discovered in low temperature (77 K) gamma-radiolytic behavior of 20% aqueous solutions of human oxyhemoglobin and partly denaturated methemoglobin. In the latter case twice as high yield of the sum of free radicals and OH radicals was observed, as well as presence in the ESR spectrum of a narrow singlet line at g 2.00 (absent for irradiated solutions of oxyhemoglobin) ascribed to the stabilized electron.

[Molecular mechanisms of the radiation destruction and formation of cross links in chromatin in aqueous solutions].

The modified gel-electrophoresis techniques were used to study DNA destruction in oligonucleosomes of the chromatin and the formation of DNA-protein cross-links under the effect of 60Co-gamma-rays. The yields of DNA destruction were evaluated in different conditions of chromatin irradiation: they were comparable with the yields of single-strand breaks. The bonds in the DNA-protein polymer formed were found to be covalent.

[Radiation destruction of DNA and histone in the composition of the chromatin].

A study was made of the radiolysis of low-molecular-weight chromatin in water solution (0.037%) at 273 K in the absence of O2. It was demonstrated by the gel-electrophoresis method that both fragments of the complex are destructed and polymers formed involving DNA and protein.