A differential method is described for measuring dielectric constants and losses in aqueous protein solutions at millimetrerange wavelengths. Employment of the method allows to improve the accuracy of determining the degree of hydratation. A method has also been suggested for taking into account the contribution of ions to the dielectric constant of solutions. The differential method was used to study hydratation of nine globular proteins. The data obtained are compared with the corresponding values provided by other experimental techniques and with theoretical predictions based on some models of hydratation. Good agreement is obtained with results provided by the isopiestic and NMR techniques. The discrepancy shown for hemoglobin is discussed in the paper. As has been shown, the dielectric method registers a monomolecular surface layer of water only. With pH varying between 4.0 and 3.2, a significant increase is observed in the hydratation of serum albumin. Presumably, this effect is connected with a N--F conformational transition.

Electrochemistry↗

PubMedDate not supplied

[Hydration and structure of hemiprotonated polycytidylic acid in films].

Structural transitions of poly(rC)-Ka+ in humid films with different water content were studied by infrared spectroscopy and piezogravimetry. From analysis of the hydration isotherms and the dependence of spectral parameters (frequencies and intensities of the main bands) on n the hydration sites of the polynucleotide were determined (C2O, O4', N4H2, N1, PO2-, C2'OH). It was found that the transition of the polynucleotide from the unordered state to a double-stranded complex poly(rC+).poly(rC) occurs in the interval of n from 2 to 8. The value n = 8 corresponds to the total hydration of poly(rC). A model of hydration of poly(rC+).poly(rC) based on the experimental results and known X-ray parameters of this double helix complex is proposed. The most important feature of the model is the presence of single water bridges between PO2(-)-groups in the first hydration shell of each chain and triple water bridges between O4', N4H2 and C2'OH- atomic groups of opposite chains. The experimental results obtained and the proposed structure of hydration environment of poly(rC+).poly(rC) suggest that the stabilization of this complex is stabilized by the intra- and inter-chain water bridges and hydrogen bonds between pairs of cytosine bases.

Hydrogen-Ion Concentration↗

PubMedDate not supplied

[Energetics of hydratation of nucleic acids with various nucleotide composition].

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.

Algorithms↗

PubMedDate not supplied

[Dynamic properties of water bound to matrices of natural DNA and model complexes].

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.

Algorithms↗

PubMedDate not supplied

[Energetics of hydration of nucleic acids with various nucleotide composition].

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.

Calorimetry↗

PubMedDate not supplied

[Study of effect of water on the interaction of DNA and actinocin derivatives with various aminoalkyl chain length by infrared spectrophotometry and computer modeling].

A comparative study of the effect of water on the interaction of DNA with actinocin derivatives having different numbers of methylene groups in side chains was performed by IR spectroscopy. It was found that, as relative humidity increases, water molecules simultaneously bind to hydrate-active sites of DNA and ligands. The absorption band at v = 1137 cm-1, caused by oscillations of the C-O and P-O groups of atoms in the DNA-ligand complex having two methylene groups, is due to the interactions between the cationic groups of the ligand and the sugar-phosphate backbone of DNA, which may be one of the reasons for the high stability of this complex. Using computer simulation of interaction of DNA fragments and actinocin derivatives in water environment, molecular models of the formation of their complexes for two ways of binding were constructed.

Computer Simulation↗

PubMedDate not supplied

[The use of the spectrophotometric analysis for the calculation of the thermodynamic parameters in actinocin derivative-DNA systems].

The spectral properties of the actinocin derivative ActII in complexes with DNA were studied by UV visible spectrophotometry. Two binding models with one and two binding sites for competitive binding with different values of parameters were considered. To choose an optimal model of complexation, the optimization program of spectrophotometric concentration dependencies DALSMOD was used. Using this program, it was concluded that at least three complexes with different absorption spectra are present in the system ActII-DNA. The logarithms of K2 and K3 for DNA-ActII mixtures, calculated for models I and II at different sodium ion concentrations, were in good agreement with predictions of the counterion condensation theory. The analysis of the absorption spectra of ActII-DNA mixtures at different temperatures made it possible to obtain the values of deltaH and deltaS for each type of complexes. The values of entropy deltaS were positive in the 0.02 M NaCl solution and negative in the 0.15 M NaCI solution.

Algorithms↗

PubMedDate not supplied

[Age-related thermodynamic and mechanical properties of the rat collagen].

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.

Aging↗

PubMedDate not supplied

[Concentration and temperature effects in interactions of the dye pyronine G with polynucleotides].

The interaction of poly(A) and poly(A).poly(U) with pyronine G dye depending on the concentration of components and temperature was studied spectrophotometrically in the visible and UV ranges at pH (6.86). It was found that the interaction of pyronine G with poly(A) and poly(A).poly(U) results in the formation of two types of complexes. The relation of the equilibrium concentrations of these complexes depends on the initial concentrations of the components in solution. The formation of complex I results in shifting the spectrum towards the short wave range with regard to the monomer band and reflects the aggregation of the dye cations. Complex II is characterized by the shift towards the long wave range. Complex II is formed in considerable amounts for poly(A).pyronine G system at large P/D and for poly(A).poly(U).pyronine G system at P/D = 5-6 and is probably due to the interaction between the dye and polynucleotides of the intercalation type or reflects the interaction between the dye and two negatively charged phosphate groups. Analysis of temperature measurements of spectra confirms the formation of various types of complexes in the system studied.

In Vitro Techniques↗

PubMedDate not supplied

[Study of the hydratation of the double-helical poly A-poly U complex by IR-spectroscopy and piezogravimetry methods].

IR-spectra of a double-helical poly A-poly U complex and coiled poly U were studied at various r.h. in a 900-3800 cm-1 region. By the method of piezomicrobalance hydration isotherms for these polynucleotides were obtained. It is concluded that, as in the DNA case, simultaneous hydration of nucleic bases the backbone of polynucleotides occurs at lower r.h., and that the poly A-poly U hydration level is higher than poly A and poly U ones separately. Drastic changes in spectral parameters of poly A poly U uracil and adenine in-ring and out-of-ring absorption bands observed in 44-76% r.h. region were interpreted as a transition to helical conformation of the complex. Calculation of resonance frequencies for these normal vibrations in the dipole-dipole approximation agrees with the experimental data.

Adenine↗

PubMedDate not supplied

[IR-spectroscopic study of the temperature anomaly of water sorbed onto DNA].

IR-spectra of liquid water and that sorbed on native and denaturated DNA at different relative humidity (RH) are obtained in the region of valent OH-(OD)-oscillations within the temperature range 0--100 degrees C. An S-shape decrease of absorption intensity was observed for water sorbed on DNA at 94% RH in two temperature regions (25--45 and 75--95 degrees C). Proceeding from the assumption that individual absorption bands are described by equal symmetrical functions, development of complex absorption contour of D2O in the region 3000--2000 cm-1 into constituents was performed. It enabled to determine band parameters of underphase vuf and synphase vsf valent and overtone of deformation oscillations of OD-groups in liquid and sorbed water and to reveal at higher temperatures the bands of "free" OD-groups (v = 2668 cm-1). Relative contribution of integral intensity of the latter at 96 degrees C in sorbed water is about 4 times lower than in the liquid one.

Chemical Phenomena↗

PubMedDate not supplied

[Study of structural transformations of the sugar-phosphate chain and nitrogen bases of DNA hydrate by IR-spectroscopy].

The IR-spectra (900-1800 cm-1) of films of native and denatured DNA were studied within the temperature range 4-100 degrees C at different relative humidity (r.h.). Two temperature intervals of S-like change of spectral parameters of absorption bands of sugar-phosphate chain of double-helical DNA are found on temperature relationships at high humidity. These two intervals point to two types of cooperative transitions of sugar-phosphate pattern. The band parameters of nitrous bases are changed only under high temperature transition. In the region of structural transitions of different subsystems of DNA hydrate hyperchromism was wound for the bands of sugar-phosphate chain and hydrate cover unlike hyperchromism specific of most nitrous bases bands. From the data obtained it is proposed to use the basic characteristics of temperature relationship of spectral parameters of the absorption bands of sugar-phosphate pattern and hydrate envelope in the region of low-temperature transition for the "in vivo" analysis of the DNA structure in complex biological systems.

Chemical Phenomena↗