I. N. Mezhevoi

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.

Thermodynamic characteristics of the interaction between nicotinic acid and phenylalanine in an aqueous buffer solution at 298 K

The interaction between L-phenylalanine and nicotinic acid is studied by solution calorimetry in an aqueous buffer solution (pH 7.35) at different ratios of the reagents. Experimental data on the enthalpy of dissolution of amino acid in the buffer solution of nicotinic acid at 298.15 K are calculated. The values of thermodynamic parameters for the complexation of L-phenylalanine with nicotinic acid are calculated. It is shown that the formation of a 1: 2 molecular complex is stabilized by the entropy factor due to the dominant role of the dehydration effect of initial reagents.

Thermochemical characteristics of interactions of DL -alanine in aqueous solutions of glycerol, ethylene glycol, and 1,2-propylene glycol

The method of dissolution calorimetry was used to measure the integral enthalpy of dissolution ΔsolHm of DL-alanine in mixtures of water with glycerol, ethylene glycol, and 1,2-propylene glycol at a concentration of organic solvent up to 0.32 mole fraction. The standard dissolution enthalpy (ΔsolH0) and transport enthalpy of amino acids from water to mixed solvent (ΔtrH0) were calculated. The calculated enthalpy coefficients of pair interactions of the DL-alanine molecules with the polyol molecules are positive and less than these values for L-alanine. The effect of interactions of different types in solution and the structural features of biomolecules and co-solvents on the enthalpy of dissolution characteristics of amino acids were considered.

Thermochemical investigation of interaction of L-serin with glycerol, ethylene glycol, and 1,2-propylene glycol in aqueous solutions

By the method of dissolution calorimetry integral enthalpies of dissolution ΔsolHm of L-serine are measured in the mixtures of water with glycerol, ethylene glycol, and 1,2-propylene glycol at the concentration of the organic solvent up to 0.42 mole fraction. The standard values of enthalpies of dissolution (ΔsolH0) and transfer (ΔtrH0) of amino acids from water to mixed solvents are calculated. The calculated values of the enthalpy coefficients of pair interactions of L-serine with the molecules of co-solvents are positive. The data obtained are interpreted in terms of prevalence of different types of interactions in solutions and the influence of nature of co-solvents on the thermochemical characteristics of the dissolved amino acids.

Enthalpic parameters of interaction between diglycylglycine and polyatomic alcohols in aqueous solutions

Integral enthalpies of solution ΔsolHm of diglycylglycine in aqueous solutions of glycerol, ethylene glycol, and 1,2-propylene glycol are measured via solution calorimetry. The experimental data are used to calculate the standard enthalpies of solution (ΔsolH°) and transfer (ΔtrH°) of the tripeptide from water to aqueous solutions of polyatomic alcohols. The enthalpic pairwise coefficients hxy of interactions between the tripeptide and polyatomic alcohol molecules are calculated using the McMillan–Mayer solution theory and are found to have positive values. The findings are discussed using the theory of estimating various types of interactions in ternary systems and the effect the structural features of interacting biomolecules have on the thermochemical parameters of diglycylglycine dissolution.

Energetics of the molecular interactions of L-cysteine, L-serine, and L-asparagine in aqueous propylene glycol solutions at 298.15 K

Integral enthalpies of dissolution ΔsolHm of L-cysteine, L-serine, and L-asparagine in aqueous solutions of 1,3-propylene glycol at organic solvent concentrations of up to 0.26 mole fraction are measured via the thermochemistry of dissolution. Standard enthalpies of dissolution (ΔsolH○) and transfer (ΔtrH○) of amino acids from water to a mixed solvent are calculated. It is found that the calculated enthalpy coefficients of pair interactions of the amino acids with polyhydric alcohol molecules have positive values. The effect the arrangement of the hydroxyl group in the structure of polyhydric alcohols has on the enthalpy of interaction of amino acids in aqueous solutions is revealed. The effect of different types of interactions in solutions and the structural features of biomolecules and cosolvents on the enthalpy of dissolution of amino acids is analyzed.

Thermochemical analysis of intermolecular interaction of aliphatic amino acids with propanediol-1,3 in aqueous media

Integral enthalpy of dissolution of L-alanine, D,L-alanine, and D,L-valine in aqueous propanediol-1,3 (the diol molar fraction 0.26) has been determined. Standard enthalpies of the amino acids dissolution and transfer from water into the mixed solvent have been calculated. Influence of the interaction types and structural features of the amino acids and organic cosolvent on the enthalpies have been analyzed.

Enthalpy pair coefficients of interaction for DL-valine in aqueous solutions of polyatomic alcohols at 298 K

Integral enthalpies of dissolution ΔsolHm of DL-valine are measured via calorimetry of dissolution in aqueous solutions of glycerol, ethylene glycol, and 1,2-propylene glycol. Standard values of the enthalpies of dissolution (ΔsolH○) and transfer (ΔtrH○) of amino acid from water to mixed solvent are calculated from the resulting experimental data. The enthalpy coefficients for pair interactions hxy of amino acid with polyatomic alcohol molecules are calculated using the McMillan-Meyer theory and have positive values. The obtained results are discussed in light of the theory of the predomination of various types of interactions in mixed solutions and the effect of structural features of interacting biomolecules on the thermochemical parameters of the dissolution of amino acids.

Thermochemical characteristics of the interaction of L-cysteine with glycerol, ethylene glycol, and 1,2-propylene glycol in aqueous solutions

Integral enthalpies of dissolution ΔsolHm of L-cysteine in mixtures of water with glycerol, ethylene glycol, and 1,2-propylene glycol at concentrations of organic solvents of up to 0.37 mole fraction were measured by calorimetry of dissolution. The standard values of the dissolution enthalpies (ΔsolH°) and the transfer enthalpies (ΔtrH°) of amino acid from water to the mixed solvent were calculated. It was shown that the calculated enthalpic coefficients of the pair interactions of L-cysteine with cosolvent molecules have positive values. The obtained data are interpreted from the viewpoint of the prevalence of different types of interactions in the solutions and influence of the cosolvents nature on the thermochemical characteristics of amino acid dissolution.

Thermochemistry of glycyl-DL-α-alanine dissolution in water-alcohol solutions at 298.15 K

Integral enthalpies of glycyl-DL-α-alanine dissolution in aqueous solutions of ethanol, 1-propanol, and 2-propanol at concentrations of alcohols up to 0.4 mol fraction were measured by the calorimetry method. Standard values of the enthalpies of the peptide dissolution ΔsolH0 and transfer ΔtrH0 from water in mixed solvents were calculated. Dependences of the thermochemical characteristics of glycyl-DL-α-alanine dissolution on the concentration of cosolvents are of an extreme character. Within the limits of McMillan-Mayer’s theory enthalpy coefficients of pairwise interactions (hxy) of the studied compound with molecules of alcohols were calculated. They have positive values increasing in the series ethanol, 1-propanol, 2-propanol. The effect of the structure of dipeptides and composition of water-alcohol solvents on the dissolution enthalpy characteristics was considered on the basis of the obtained experimental and calculated data.