[Investigation of the thermal stability of nucleic acids and their structural components].

The thermal stability of homopolynucleotides (poly(A), poly(G), poly(C), poly(U)) and natural DNA, as well as their structural components: nucleoside (uridine), nucleotides (uridine-5'-monaphosphate, uridine-5'-diphosphate, and uridine-5'-triphosphate) and sugar (D-ribose) have been studied by the method of differential scanning microcalorimetry. The dependences of the heat flow on temperature have been obtained for the compounds having individual features in the temperature range from 20 to 400 degrees C. All samples showed exothermic peaks at temperatures higher than 200 degrees C (for DNA, this peak was found at a temperature of approximately 160 degrees C), which are related to processes of irreversible thermal destruction. The temperatures of thermal destruction and the effective energy of activation of this process for all compounds studied have been determined. The values of the effective heat of exothermal processes have been calculated for the polynucleotides. The experimental results indicate that there is a significant difference in the thermal stability between these homopolynucleotides and DNA, poly(G) being the most stable and DNA, the least stable. Based on the analysis of D-ribose, nucleoside, and nucleotides, it was concluded that the sugar ring is the most probable region of the destruction.

[Energetics of hydration of nucleic acids with various nucleotide composition]. / Energetika gidratatsii nukleinovykh kislot razlichnogo nukleotidnogo sostava.

The energetics of hydration of natural DNA of different AT/GC content and model double-helical polyribonucleotides was studied. The results obtained by a new approach, which is based on calorimetric measurements of hydration-dehydration energy of nucleic acid-water systems at different relative humidities are presented. A correlation between the dehydration energy and the nucleotide composition of native DNA was found. The energetic characteristics of systems containing deoxynucleoside monophosphates and water clusters of different dimensions were obtained by the Monte Carlo method. The results of computer simulation correlate with the experimental calorimetric data.

[Dynamic properties of water bound to matrices of natural DNA and model complexes]. / Dinamicheskie svoistva vody, sviazannoi na matritsakh prirodnykh DNK i model'nykh kompleksov.

From experimental data on the hydration energetics of nucleic acids obtained by differential scanning calorimetry under isothermal conditions, dielectric relaxation time tau d and "free volume" Vf occupied by water molecules in hydration shells of natural DNA and model polyribonucleotides were calculated. In addition, systems consisting of dinucleotides ApA, TpT, UpU, TpU, UpT and water clusters of various sizes (from 20 to 400 water molecules) were studied by Monte Carlo computer simulation. It was shown that, as water content in systems increases, the dynamic characteristics of bound water obtained with both methods approached the values for bulk water.

[Energetics of hydratation of nucleic acids with various nucleotide composition]. / Energetika gidratatsii nukleinovykh kislot razlichnogo nukleotidnogo sostava.

The hydration energetics of natural DNA with various AT/GC-composition and model double-helix polyribonucleotides was studied using a new approach which is based on calorimetric measurements of the dehydration energy of nucleic acid-water systems at various levels of relative humidity. A linear correlation between the dehydration energy and the nucleotide composition of natural DNA was found.

[Effect of water on the structural modification and stabilization of DNA from Clostridium perfringens]. / Vliianie vidy na strukturnye perekhody i stabil'nost' DNK iz Clostridium perfringens.

By the methods of infrared spectroscopy, piezogravimetry and microcalorimetry the process of forming of the structure and hydration environment of DNA from Clostridium perfringens in the wet films has been investigated. It were found three intervals of relative humidity (r.h.) in which three structural states of DNA: an unordered state (0-44% r.h.), the A-form (46-75% r.h.) and the B-form (80-86% r.h.) are realized. We measured the heat of water evaporation from the DNA-water samples with the differential scanning microcalorimeter. From these calorimetric data the distribution of the water molecules on the bond energy with DNA was determined. The contribution of the water molecules of hydration shell (73%) and hydrogen bonds in the Watson-Crick pairs (27%) to the total energy of stabilization of the helical B-form DNA from Cl. perfringens has been evaluated.

[Thermal restructuring and hydration of serum albumin]. / Termicheskie perestroiki i gidratsiia syvorotochnogo al'bumina.

Calorimetry and dielectrometry in the millimeter wave range have been applied to demonstrate a possibility for determination of heat capacity of bound water in biopolymer matrices in solution is shown. Variation of the hydration level of human serum albumin caused by the variation of temperature and protein concentration is described. Application of two methods based on comparison of calorimetric and dielectric data on protein solutions at different temperatures and concentrations have produced similar values of the heat capacity of bound water in the protein hydration shell (approximately 3 J/g.K).

[Physical properties of the DNA-water system]. / Fizicheskie svoistva sistemy DNK-voda.

The review of original and literary data obtained by the different physical methods on the structure, mechanical, electrostatic and energetic properties of DNA-ions-water system was done. On the basis of the examined results the main problem of DNA structure formation its dynamic and stability were discussed.

[Age-related thermodynamic and mechanical properties of the rat collagen]. / Zavisimost' termodinamicheskikh i mekhanicheskikh svoistv kollagena krys ot vozrasta.

The age peculiarities of cross-linking degree, thermodynamic and mechanic properties of rat tail tendon collagen fibres were investigated. It is shown that during the period from 1 to 3 months the melting temperature decreases and the enthalpy difference increases, from 3 to 24 months the melting temperature increases and the enthalpy difference decreases. The strength of fibres increases during the whole life. The maximal relative extension increases during the first 12 months and tends to decrease in after-life. The Young's module in the elastic deformation region decreases during the period from 1 to 3 months, then increases. It is shown tht those changes in fibre properties may be connected with the age dynamics of collagen cross-linking degree observed here: its decreasing during the period from 1 to 3 months and its following continuous increasing in after-life.