V. G. Badelin

Calorimetric study of dissolution of amino carboxylic acids in water at 298.15 K

The enthalpies of solution of glycine, DL-alanine, D-valine, and L-serine in water at 298.15 K were measured on a special ampule calorimeter equipped with an isothermal shell. The enthalpies of hydration of 12 α-amino acids differing in the steric configurations of the side radical were estimated using the measured values and the published data on the heats of solution and sublimation for biologically active substances. The influence of hydrophobicity of the substances on their dissolution and hydration was considered.

The thermochemical characteristics of solution of DL-α-alanylglycine and DL-α-alanyl-DL-α-alanine in water-organic solvent mixtures at 298.15 K

The integral enthalpies of solution of DL-α-alanylglycine and DL-α-alanyl-DL-α-alanine in water-organic solvent (acetonitrile, 1,4-dioxane, acetone, N,N-dimethylformamide, and N,N-dimethylsulfoxide) mixtures were measured at organic component concentrations x2 = 0–0.4 mole fractions and T = 298.15 K. The standard enthalpies of solution (ΔsolH°) and transfer (ΔtrH°) of the peptides from water into mixed solvents were calculated. The influence of the structure and properties of solutes and mixture composition on the thermochemical characteristics of the peptides was considered. The enthalpy coefficients of pair interactions (hxy) of DL-α-alanylglycine and DL-α-alanyl-DL-α-alanine with organic solvent molecules were calculated. The hxy values were correlated with the properties of organic solvents using the Kamlet-Taft equation.

The enthalpies of solution of DL-α-alanine in water-organic solvent mixtures at 298.15 K

The integral enthalpies of solution (298.15 K) of DL-α-alanine in water-organic solvent mixtures were measured at organic component concentrations x2 = 0–0.4 mole fractions. The organic solvents used were acetonitrile (ACN), formamide (FA), N,N-dimethylformamide (DMFA), and N,N-dimethylsulfoxide (DMSO). The standard enthalpies of solution ΔsolHo, solvation ΔsolvHo, and transfer (ΔtrHo) of DL-α-alanine from water to mixed solvents were calculated. The influence of the structure and properties of solutes and mixture composition on solute thermochemical characteristics was considered. The solution of DL-α-alanine in the mixtures studied was endothermic over the whole range of organic component concentrations. The ΔsolHo, ΔtrHo, and ΔsolvHo values as functions of x2 can pass extrema (DMSO and DMFA), be almost independent of mixed solvent composition (FA), or be exothermic and monotonic functions (ACN). The enthalpy coefficients of pair interactions (hxy) between DL-α-alanine and organic solvent molecules were calculated. The linear Kamlet-Taft equation was used to correlate the hxy values with the properties of organic solvents.

The enthalpies of solution and solvation of glycine in mixed water-formamide solvents at 298.15 K

The enthalpies of solution (ΔHsolo) of glycine in aqueous formamide, N-methylformamide, N,N-dimethylformamide, and N,N-diethylformamide were determined by calorimetry at 298.15 K over the concentration range x2=0–0.3 mole fractions. The enthalpies of glycine solvation (ΔHsolvo) and transfer from water to mixed solvents (ΔHtro) were calculated. The ΔHsolo=f(x2) dependences for glycine in water-N-and water-N,N-substituted amide mixtures had extrema and, in water-formamide mixtures, this dependence was a smooth function, whose values changed in the opposite direction. The enthalpy coefficients of pair glycine-amide interactions were calculated. The interrelation between the enthalpy characteristics of solution, transfer, and solvation of glycine and the structure and physicochemical characteristics of solvents, on the one hand, and the composition of mixtures, on the other, was revealed.

The dependence of the enthalpy of solution of L-methionine on the composition of water-alcohol binary solvents at 298.15 K

The integral enthalpies of solution of L-methionine in water-methanol, water-ethanol, water-n-propanol, and water-iso-propanol mixtures were measured calorimetrically at alcohol concentrations x2 = 0–0.4 mole fractions. The standard enthalpies of solution (ΔsolHo) and transfer of L-methionine (ΔtrHo) from water to a binary solvent were calculated. The influence of the structure and properties of L-methionine and the composition of aqueous-organic mixtures on its enthalpy characteristics was considered. The enthalpic pair interaction coefficients (hxy) between L-methionine and alcohol molecules were calculated; they were positive and increased in the series methanol (MeOH), ethanol (EtOH), n-propanol (n-PrOH), iso-propanol (i-PrOH). The enthalpy characteristics of solution and transfer of L-methionine were compared with those of glycine, L-threonine, L-alanine, and L-valine in similar binary solvents.

Effects of water-alcohol binary solvents on the thermochemical characteristics of L-tryptophane dissolution at 298.15 K

The enthalpies of L-tryptophane solution in water-methanol, water-ethanol, water-1-propanol, and water-2-propanol mixtures at alcohol concentrations of x2 = 0–0.4 mole fractions were measured by calorimetry. The standard enthalpies of L-tryptophane solution (ΔsolH∘) and transfer (ΔtrH∘) from water to the binary solvent were calculated. The influence of the composition of the water-alcohol mixture and the structure and properties of L-tryptophane on the enthalpy characteristics of the latter was considered. The enthalpy coefficients of pair interactions (hxy) of L-tryptophane with alcohol molecules were calculated. The coefficients were positive and increased in the series: methanol (MeOH), ethanol (EtOH), 1-propanol (1-PrOH), and 2-propanol (2-PrOH). The solution and transfer enthalpies of L-tryptophane were compared with those of aliphatic amino acids (glycine, L-threonine, DL-alanine, L-valine, and L-phenylalanine) in similar binary solvents.

The enthalpies of solution of L-α-alanyl-L-α-alanine in water-organic solvent mixtures at 298.15 K

The integral enthalpies of solution (T = 298.15 K) of L-α-alanyl-L-α-alanine in aqueous-organic solvents (acetonitrile, 1,4-dioxane, acetone, formamide, N-methylformamide, N,N-dimethylformamide, N,N-diethylformamide, and N,N-dimethylsulfoxide) were measured at organic component concentrations x2 = 0–0.3 mole fractions. The standard enthalpies of solution (ΔsolHo) and transfer (ΔtrHo) of the peptide from water into mixed solvents were calculated. The influence of the structure and properties of solutes and mixture composition on solute thermochemical characteristics is considered. The enthalpy pair interaction coefficients hxy between L-α-alanyl-L-α-alanine and organic solvent molecules were calculated. The linear Kamlet-Taft four-parameter equation was used to reveal correlation between the hxy values and the properties of organic solvents.

Thermodynamic characteristics of solution and viscous flow of amino acids in water at 298.15 K

Thermodynamic and transport properties of aqueous solutions of 13 amino acids at 298.15 K are analyzed in relation to the structure of the side chains of the biomolecules on the basis of the newly obtained and published data. The standard enthalpies of solution (ΔsolH0), partial molar volumes (V2,φ0), and partial molar contributions to the molar Gibbs free energy of activation of the viscous flow (Δμ20≠) were determined for the amino acids in water. Correlation equations were suggested to describe the relationship between the enthalpy characteristics of hydration of amino acids, viscous flow parameters, and bulk properties of their aqueous solutions.

The thermochemical characteristics of solution of DL-α-alanylglycine and DL-α-alanylalanine in water-alcohol mixtures at 298.15 K

The integral enthalpies of solution of DL-α-alanylglycine and DL-α-alanylalanine in water-ethanol, water-n-propanol, and water-isopropanol mixtures were measured calorimetrically at alcohol concentrations x2 = 0−0.4 mole fractions. The standard enthalpies of solution (ΔsolH°) of the peptides and their transfer (ΔtrH°) from water into the mixed solvents were calculated. The influence of the structure and properties of the solutes and mixture composition on the enthalpy characteristics were considered. The ΔsolH° = f(x2) and ΔtrH° = f(x2) dependences were found to have extrema. The enthalpy coefficients of pair interactions (hxy) between the peptide and alcohol molecules were calculated. The coefficients were positive and increased in the series ethanol, n-propanol, isopropanol.

Mass spectrometry study of the sublimation of aliphatic dipeptides

The sublimation of glycyl-L-α-alanine (Gly-Ala), L-α-alanyl-L-α-alanine (Ala-Ala), and DL-α-alanyl-DL-α-valine (Ala-Val) aliphatic dipeptides is studied by electron ionization mass spectrometry in combination with Knudsen effusion. The temperature range in which substances sublime as monomer molecular forms is determined. Enthalpies of sublimation ΔsH°(T) are determined for Gly-Ala, Ala-Ala, and Ala-Val. It is shown that the enthalpy of sublimation of dipeptides increases with an increase in the side hydrocarbon radical. The unknown ΔsH°(298) values for 17 amino acids and nine dipeptides are estimated using the proposed “structure-property” correlation model, in which the geometry and electron characteristics of molecules are used as structural descriptors.