V. I. Smirnov

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.

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.

The enthalpy of solution of DL-α-alanyl-DL-α-valine depending on the composition of water-alcohol binary solvents at 298.15 K

The integral enthalpies of solution of DL-α-alanyl-DL-α-valine in water-ethanol, water-n-propanol, and water-isopropanol mixtures at alcohol concentrations x2 = 0–0.4 mole fractions were measured calorimetrically. The enthalpies of solution of the peptide ΔsolH° and transfer from water to a mixed solvent ΔtrH° were calculated. The effect of the structure and properties of the peptide and mixture composition on the enthalpy characteristics of the peptide are discussed. The enthalpy coefficients of pair interactions hxy of DL-α-alanyl-DL-α-valine with alcohol molecules were calculated. It was found that they were positive and increased in the series ethanol, n-propanol, isopropanol. An analysis of the results allows the general features of changes in the thermodynamic parameters of solution of peptides of the DL-α-alanine series with different amino acid residues in water-alcohol mixtures to be established.

Dependence of the solution and transfer enthalpies of DL-α-alanyl-DL-α-asparagine on the composition of water-amide binary solvents at 298.15 K

Solution enthalpies of DL-α-alanyl-DL-α-asparagine (AlaAsn) in water-formamide, water-N-methylformamide, water-N,N-dimethylformamide, and water-N,N-dimethylacetamide mixtures were measured in the range of amide mole fractions x2 = 0–0.3. The standard enthalpies of solution (ΔsolH°) and transfer (ΔtrH°) of AlaAsn from water to the binary solvent and enthalpy coefficients of pair-wise interactions (hxy) of AlaAsn with amide molecules were calculated. The influence of the composition of the water-organic mixture on the enthalpy characteristics of AlaAsn is discussed. It is shown that the enthalpy characteristics of solution and transfer of AlaAsn are related to the structure of amides.

Thermochemistry of the dissolution of DL-α-alanyl-DL-norleucine in aqueous solutions of amides at 298.15 K

Enthalpies of the dissolution of DL-α-alanyl-DL-norleucine are determined by calorimetry in aqueous solutions of formamide (FA), N-methylformamide (MFA), N,N-dimethylformamide (DMF), and N,N-dimethylacetamide (DMA) at a concentration of amides of x2 = 0–0.4 molar parts and T = 298.15 K. Standard values of enthalpies of dissolution ΔsolHo and ΔtrHo of DL-α-alanyl-DL-norleucine transfer from water to binary solvent are calculated, along with the enthalpy coefficients of pair interactions hxy of DL-α-alanyl-DL-norleucine with amide molecules. The effect of the composition of water-organic mixtures and the structure of amides on the enthalpy characteristics of dissolution and transition of DL-α-alanyl-DL-norleucine is considered. Quantitative estimates of the contributions to energy from DL-α-alanyl-DL-norleucine-amides pair interactions determined by the polarity, polarizability, and electron acceptor and electron donor ability of organic cosolvents are given using the Kamlet-Taft correlation equation.