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

Integral enthalpies of dissolution Δ_sol H ^m 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 (Δ_sol H ^○) and transfer (Δ_tr H ^○) of amino acid from water to mixed solvent are calculated from the resulting experimental data. The enthalpy coefficients for pair interactions h_xy 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.     

Energetics of the molecular interactions of L-alanine and L-serine with xylitol, D-sorbitol, and D-mannitol in aqueous solutions at 298.15 K

Integral enthalpies of dissolution Δ_sol H ^m of L-alanine and L-serine are measured via the calorimetry of dissolution in aqueous solutions of xylitol, D-sorbitol, and D-mannitol. Standard enthalpies of dissolution (Δ_sol H ^○) and the transfer (Δ_tr H ^○) of amino acids from water to binary solvent are calculated from the experimental data. Using the McMillan-Mayer theory, enthalpy coefficients of pairwise interactions h _xy of amino acids with molecules of polyols are calculated that are negative. The obtained results are discussed within the theory of the prevalence of different types of interactions in mixed solutions and the effect of the structural features of interacting biomolecules on the thermochemical parameters of dissolution of amino acids.     

Enthalpy characteristics of L-asparagine interaction with glycerol, ethylene glycol, and 1,2-propylene glycol in aqueous solutions

Integral dissolution enthalpies ??_sol H ^m of L-asparagine in the mixtures of water with glycerol, ethylene glycol, and 1,2-propylene glycol at the concentration of organic solvents up to 0.24 mole fraction were measured by the calorimetry method. The standard enthalpies of dissolution (??_sol H ⁰) and transport (??_tr H ⁰) of amino acids from water to the mixed solvents were derived. The calculated enthalpy coefficients of the molecule pair interactions of L-asparagine-cosolvent are positive, except for the amino acid-glycerol-water system. The data obtained are interpreted in terms of prevalence of different types of interactions in solution and effect of the cosolvent nature on the thermochemical characteristics of the L-asparagine dissolution.     

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

Integral enthalpies of dissolution Δ_sol H ^m 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 (Δ_sol H°) and the transfer enthalpies (Δ_tr H°) 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.     

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 Δ_sol H ^m 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 (Δ_sol H ⁰) and transfer (Δ_tr H ⁰) 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.     

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 ??_sol H ^m 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 (??_sol H ⁰) and transport enthalpy of amino acids from water to mixed solvent (??_tr H ⁰) 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 analysis of intermolecular interactions between <Emphasis Type="Italic">N</Emphasis>-acetylglycine and polyols in aqueous solutions

The integral enthalpies of dissolution Δ_sol H _m for N-acetylglycine in aqueous solutions of glycerol, ethylene glycol and 1,2-propylene glycol are measured via solution calorimetry. The standard enthalpies of dissolution (Δ_sol Н ⁰) and transfer (Δ_tr Н ⁰) for N-acetylglycine from water to aqueous solutions of polyhydric alcohols are calculated from experimental data. Positive values of enthalpy coefficients of pair interactions h _xy for amino acids and polyol molecules are calculated using the McMillan–Mayer theory. The results are discussed using an approach for evaluating different types of interactions in ternary systems and the effect the structural features of interacting biomolecules have on the thermochemical characteristics of N-acetylglycine dissolution.     

The thermochemical characteristics of solution of L-cysteine and L-asparagine in aqueous 1,4-dioxane and acetone

The integral heats of solution Δ_sol H ^m of L-cysteine and L-asparagine in mixtures of water with 1,4-dioxane and acetone were measured by solution calorimetry at organic solvent concentrations of up to 0.30 mole fractions. The standard enthalpies of solution (Δ_sol H ^o) and transfer (Δ_tr H ^o) of amino acids from water to mixed solvents were calculated. The calculated enthalpy coefficients of pair interactions of L-cysteine and L-asparagine with cosolvent molecules were positive. The results were interpreted from the point of view of the predominance of interactions of various types in solutions and the influence of the nature of cosolvents and amino acid side substituents on the thermochemical characteristics of solution.     

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

The enthalpies of solution (ΔH _sol ^o ) 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 x ₂=0–0.3 mole fractions. The enthalpies of glycine solvation (ΔH _solv ^o ) and transfer from water to mixed solvents (ΔH _tr ^o ) were calculated. The ΔH _sol ^o =f(x ₂) 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 solvation of L-serine in mixtures of water with some aprotic solvents at 298.15 K

The integral enthalpies of solution Δ_sol H ^m of L-serine in mixtures of water with acetonitrile, 1,4-dioxane, dimethylsulfoxide (DMSO), and acetone were measured by solution calorimetry at organic component concentrations up to 0.31 mole fractions. The standard enthalpies of solution (Δ_sol H°), transfer (Δ_tr H°), and solvation (Δ_solv H°) of L-serine from water into mixed solvents were calculated. The dependences of Δ_sol H°, Δ_solv H°, and Δ_tr H° on the composition of aqueous-organic solvents contained extrema. The calculated enthalpy coefficients of pair interactions of the amino acid with cosolvent molecules were positive and increased in the series acetonitrile, 1,4-dioxane, DMSO, acetone. The results obtained were interpreted from the point of view of various types of interactions in solutions and the influence of the nature of organic solvents on the thermochemical characteristics of solutions.     

Enthalpy characteristics of solution of L-cysteine and L-asparagine in water-alcohol mixtures at 298.15 K

The integral enthalpies of solution Δ_sol H ^m of L-cysteine and L-asparagine in mixtures of water with ethanol, n-propanol, and isopropanol at a mole fraction of alcohol of up to 0.32 were determined by calorimetry of solution. The standard enthalpies of solution (Δ_sol H ⁰) of L-serine and of its transfer (Δ_tr H ⁰) from water to a mixed solvent were calculated. The dependences of Δ_sol H ⁰ and Δ_tr H ⁰ on the composition of water-alcohol mixtures pass through a maximum. The calculated enthalpy coefficients of pair interaction of amino acids with alcohol molecules are positive and increase in the order ethanol, n-propanol, isopropanol. The data obtained were interpreted from the viewpoint of various types of interaction in solution and effect of the amino acid residue on the thermochemical characteristics of solution.     

Enthalpic characteristics of solution of amino acids and aliphatic dipeptides in aqueous solutions of KCl

The integral enthalpies of dissolution Δ_sol H ^m of L-α-serine and L-α-asparagine in mixtures of water with KCl were measured in electrolyte concentrations of up to 4 mol/kg at 298.15 K. The standard enthalpies of dissolution (Δ_sol H ^o) and transfer (Δ_tr H ^o) of amino acids from water to aqueous solutions of KCl were calculated. The enthalpic pair interaction coefficients h _xy of biomolecules with KCl were estimated within the McMillan-Mayer theory. The changing nature of the interaction between the components of the solution (depending on the structure of the dissolved biosubstance side substituents) is shown on the basis of data we obtained earlier for amino acids and dipeptides series. Estimates of the contributions from the electrostatic and other interactions of dipolar ions of amino acids and dipeptides with ions of electrolyte KCl in the enthalpic pair interaction coefficients h _xy are obtained using the Kirkwood approach.     

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 x ₂ = 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 Δ_sol H ^o, solvation Δ_solv H ^o, and transfer (Δ_tr H ^o) 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 Δ_sol H ^o, Δ_tr H ^o, and Δ_solv H ^o values as functions of x ₂ 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 (h _xy ) between DL-α-alanine and organic solvent molecules were calculated. The linear Kamlet-Taft equation was used to correlate the h _xy values with the properties of organic solvents.     

Effect of the composition of a water-alcohol solvent on the thermodynamics of dissolution of DL-α-alanyl-β-alanine at 298.15 K

Enthalpies of solution for DL-α-alanyl-β-alanine in H₂O-ethanol, H₂O-1-propanol, and H₂O-2-propanol mixed solvents with the alcohol mole fraction x ₂ = 0–0.3 are measured at 298.15 K. Standard enthalpies of solution (Δ_sol H ^°), standard enthalpies of transfer of DL-α-alanyl-β-alanine from water to binary solvent (Δ_tr H ^°), and coefficients of enthalpies of pair interactions with alcohol molecules (h _xy ) are calculated. The effect the structure and properties of alcohols and the composition of a water-alcohol mixture have on the enthalpy of dissolution for DL-α-alanyl-β-alanine are discussed. The h _xy values for dipeptides of the alanine series in water-alcohol binary solvents are compared.     

Enthalpy characteristics of dissolution of <Emphasis Type="SmallCaps">l</Emphasis>-cysteine and <Emphasis Type="SmallCaps">l</Emphasis>-asparagine in aqueous solutions of acetonitrile and dimethyl sulfoxide at 298.15 K

The integral enthalpies of dissolution Δ_sol H ^m of l-cysteine and l-asparagine in mixtures of water with acetonitrile and dimethyl sulfoxide at the concentration of organic solvent up to 0.32 molar fractions were measured by means of dissolution calorimetry. The standard enthalpies of dissolution (Δ_sol H°) and transfer (Δ_trans H°) of the amino acids from water to a mixed solvent were calculated. The enthalpy coefficients of pair interactions for L-cysteine and L-asparagine with cosolvent molecules are positive, except for the L-asparagine-water-acetonitrile system. The concepts on the prevailing effect of specific interactions in solutions and the influence of the nature of the cosolvents and lateral substituents of the amino acids on the thermochemical characteristics of dissolution were used to explain the data obtained.     

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 x ₂ = 0–0.4 molar parts and T = 298.15 K. Standard values of enthalpies of dissolution Δ_sol H ^o and Δ_tr H ^o of DL-α-alanyl-DL-norleucine transfer from water to binary solvent are calculated, along with the enthalpy coefficients of pair interactions h _xy 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.     

Measuring the enthalpies of interaction between glycine,L-cysteine,glycylglycine, and sodium dodecyl sulfate in aqueous solutions

Calorimetric measurements of enthalpies of solution Δ_sol H ^m for glycine, L-cysteine, and glycylglycine in aqueous solutions of sodium dodecyl sulfate (SDS) with concentrations of up to 0.05 mol kg^–1 are made. Standard enthalpy of solution Δ_sol H ⁰ and enthalpy of transfer Δ_tr H ⁰ of the dipeptide from water into mixed solvent are calculated. The calculated enthalpy coefficients of paired interactions of amino acids and dipeptide with SDS prove to be positive. Hydrophobic interactions between the biomolecules and SDS are found to have a major impact on the enthalpies of interaction in the three-component systems under study, within the indicated range of concentrations.     

Thermodynamic characteristics of the dissolution of glycine,glycylglycine, and glycylglycylglycine in aqueous solutions of sodium dodecyl sulfate at <Emphasis Type="Italic">Т</Emphasis> = 298.15 K

the enthalpies of dissolution of glycine (Gly), glycylglycine (GlyGly), and glycylglycylglycine (GlyGlyGly) are measured in aqueous solutions of sodium dodecyl sulfate (SDS) at SDS concentrations m = 0–0.7 mol kg^?1 and Т = 298.15 K by means of calorimetry. The obtained data are used to calculate the standard values of enthalpies of dissolution (Δ_sol H ^m ) and enthalpies of transfer (Δ_tr H ^m ) of glycine and its oligomers from water to SDS aqueous solutions. The dependences of Δ_sol H ^m and Δ_tr H ^m on SDS concentration in an aqueous solution at a constant concentration of glycine and its oligomers are determined. A comparative analysis of the thermodynamic characteristics of Gly, GlyGly, and GlyGlyGly transfer within the studied range of SDS concentrations is performed. The results are interpreted in terms of ion–ion, ion–polar, and hydrophobic interactions between SDS and molecules of glycine and its oligomers.     

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 x ₂ = 0–0.4 mole fractions were measured by calorimetry. The standard enthalpies of L-tryptophane solution (Δ_sol H ^°) and transfer (Δ_tr H ^°) 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 (h _xy ) 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 x ₂ = 0–0.3 mole fractions. The standard enthalpies of solution (Δ_sol H ^o) and transfer (Δ_tr H ^o) 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 h _xy 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 h _xy values and the properties of organic solvents.