[Molecular descriptors of amino acids for the evaluation of the physicochemical parameters and biological activity of peptides].

Statistically significant correlation structure-activity relationships for two groups of oligopeptides (48 dipeptide fragments of analogues of inhibitors of the angiotensin-converting enzyme and 21 pentapeptide structural analogues of bradykinin) were obtained by the methods of regression analysis. Geometric, hydrophobic, and electron descriptors of the component amino acids were applied to the characteristics of the molecular structure of the peptides. The electron properties (electronegative charge, polarity of the molecules, and ability to form hydrogen bonds) were shown to have the greatest influence on the bioactivity of the studied compounds. A satisfactory fit between the calculated and experimental values of the bioactivity (IgA) of the peptides proved the validity of the four-parametrical equation for the evaluation of the unknown IgA values of oligopeptides on the basis of the physicochemical parameters of the participating amino acids.

[Influence of hydrophobicity of amino acid side chains on volume and viscosity properties of their aqueous solutions].

The standard partial molar volumes (V(0)(2),phi) and coefficients of viscosity (B eta) at 298.15 K for aqueous solutions of amino acids containing hydrophobic and hydrophilic groups have been calculated. Based on the transition state theory of Feakins, the partial molar free energies of activation of the viscous flow of amino acids in water have been obtained. Correlations between the delta mu(0)(2) values and the hydrophobic contribution (logP') of amino acid molecules and the "packing density" (Dh) of water molecules in their hydration shells have been established. It was shown that delta mu(0)(2) and V(0)(2),phi values reflect changes in the hydrophobicity of amino acid side chains and their hydrogen bonding ability.

[Peculiarities of electrostatic interactions between amino acids and salicylic acid in aqueous solution].

Based on calorimetric data, the enthalpy of the transfer of salicylic acid to aqueous buffer solutions with the addition of different amino acids at the constant acidity of medium pH 7.35 was determined. It was shown that the exothermicity of transfer and negative enthalpic coefficients for these pairwise interactions of salicylic acid with amino acids considerably increase with increasing charge of amino acid existing in the ionic form under these conditions. Weak interactions of salicylic acid with the anionic form of aspartic and glutamic acids are related to the repulsion between anion carboxyl groups. More intensive interactions are observed for zwitter-ions of glycine and alanine. The most intensive specific interactions with salicylic acid are observed for lysine and arginine, which exist in the solution as cations.

[Dissolution enthalpies of DL-alpha-alanine and dipeptides of aliphatic series in aqueous solutions of KCl].

The integrated enthalpies of dissolution DeltasolH(m) of DL-alpha-alanine, DL-alpha-alanyl-glycine, DL-alpha-alanyl-beta-alanine, DL-alpha-alanyl-DL-alpha-alanine and L-alpha-alanyl-L-alpha-alanine in mixtures of water with KCl have been measured at concentrations of electrolyte up to 4 mole/kg (T=298.15 K). On the basis of the data obtained, the standard enthalpies of dissolution (DeltasolH(0)) and transfer (DeltatrH(0)) of the amino acids and dipeptides from water to aqueous solutions with KCl were determined. It was found that the dependences DeltatrH(0) = f(X2) for all systems have extreme character, which indicates different mode of interactions between the components of the solution in different ranges of electrolyte concentration. Within the framework of the formalism of the McMillan-Mayers theory, the enthalpic pair coefficients of interaction of hxy biomolecules with KCl estimated. The coefficients are discussed in terms of the integral enthalpic effects of interactions between the components in aqueous solutions and the structural features of solutes.

[Hydration enthalpy characteristics of amino acids in solutions].

The enthalpies of solvation of 17 amino acids were evaluated by using the sublimation enthalpies of amino acids and the standard enthalpies of their solution in water. An equation was derived, which relates the volume-specific enthalpy of sublimation (deltaH(subl)/V(w)) to the sum of the common bond lengths in molecules (sigman(i)l(i)) of substances examined. The results obtained are interpreted in terms of the effect of hydrophobic and hydrophilic side chain on the interactions between the zwitterions of amino acids and water molecules.

[Thermochemistry of dissolving glycine, glycyl-glycine, and diglycyl-glycine in a mixed water-dimethylsulfoxide solvent at 298.15 K]. / Termokhimiia rastvoreniia glitsina, glitsil-glitsina i diglitsil-glitsina v smeshannom rastvoritele voda-dimetilsul'foksid pri 298.15 K.

The enthalpies of dissolving glycine, glycyl-glycine and diglycyl-glycine (deltaH(soln)0) in a mixed water-dimethylsulfoxide (DMSO) solvent was determined by the calorimetric method in the range of concentrations of the organic component 0 < X2 < 0.4 m.d. at 298.15 K. The enthalpies of solvation ((deltaH(solv)0) and transfer ((deltaH(tr)0) of these compounds from water to a mixed solvent were calculated. The dependencies deltaH(tr)0 =f(X2) were found to be extreme, indicating complex intermolecular interactions between the solution components. The influence of the structure and the properties of the substances dissolved and the composition of the mixture and the nature of organic solvent on their thermochemical characteristics was studied. The coefficients of enthalpy for pair interactions of glycine and its oligomers with DMSO molecules were calculated. These have positive values and increase in the order: glycyl-glycine < glycine < diglycyl-glycine. The changes in the thermochemical characteristics of dissolving, transfer, and solvation of glycine and its olygomers were shown to be determined by the energy of the mixed solvent formation, the nature of the organic solvents, and the structure of amino acids and peptides.

[Calorimetric study of the interaction between amino acids and sugars in water at 298.15 K]. / Kalorimetricheskoe issledovanie vzaimodeistvii mezhdu aminokislotami i sakharidami v vode pri 298.15 K.

The enthalpies of dissolving glycine and DL-alanine in water solutions of D-glucose, D-maltose, and sucrose at 298.15 K were determined by calorimetry. From the results obtained, the coefficients of enthalpy for pairwise interactions hxy of the amino acids and saccharides in water were calculated. It was found that the hxy values for glycine in solutions of all saccharides studied are negative; in the case of DL-alanine, the hxy values are positive for all saccharides except for sucrose solution. It was shown that the hxy values reflect the sum effect of interactions between the amino acids and saccharides in aqueous solutions and the contribution of hydration of the solutes.

[Thermodynamic and spectroscopic study of complex formation of dipeptides with dimethyl sulfoxide in their aqueous solutions]. / Termodinamicheskoe i spektroskopicheskoe issledovanie kompleksoobrazovaniia dipeptidov s dimetilsul'foksidom v ikh vodnykh rastvorakh.

Peculiarities of intermolecular interactions in water-dimethylsulfoxide solutions of dipeptides-glycyl-glycine, beta-alanyl-glycine, beta-alanyl-beta-alanine, DL-alpha-alanyl-DL-alpha-alanine, DL-alpha-alanyl-DL-valine-were analysed on the basis of thermodynamic characteristics and data on IR-spectra. Dimethylsulfoxide additions were shown to cause destruction of peptide associates present in aqueous solutions due to the formation of stronger bonds "peptide-DMSO". The existence of complexes between dimethylsulfoxide and beta-alanyl-glycine, beta-alanyl-beta-alanine, DL-alpha-alanyl-DL-alpha-alanine was found. The mechanism of their formation was determined by the dipeptide structure.

[Thermodynamic and spectroscopic study of intermolecular association in aqueous dipeptide solutions]. / Termodinamicheskoe i spektroskopicheskoe issledovanie mezhmolekuliarnoi assotsiatsii v vodnykh rastvorakh dipeptidov.

Peculiarities of the concentration dependences of apparent molar heat capacities and volumes of aqueous solutions of dipeptides were considered. Possible interpretation of the character of these dependences on the basis of Gibson and Sheraga's model of solvation shell were shown. Three concentration regions corresponding to the existence of various molecular forms of dipeptides in solution were marked out.