Enthalpic Pairwise Interaction Coefficients Research Articles

Enthalpies of dilution of formamide in aqueous alcohol solutions at 298.15 K

Enthalpies of dilution of formamide in aqueous n-propanol, 1,2-propanediol and glycerol solutions have been determined by isothermal calorimetry at 298.15 K. The values of dilution enthalpy were used to determine homogeneous enthalpic interaction coefficients which characterize the interactions of formamide in alcohol solutions. The variations of the enthalpic pairwise interaction coefficients with the mass fraction of alcohol in mixtures are interpreted in terms of solute–solute and solute–solvent interactions.

The Heterotactic Enthalpic Interaction Coefficients of α-Amino Acids with Maltose in Aqueous Solution at T=298.15 K

The mixing enthalpies of maltose with several typical α-amino acids (glycine, L-alanine, L-serine, L-valine, L-threonine and L-proline) and dilution enthalpies of each compound have been determined in aqueous solutions at T=298.15 K by a flow-mixing microcalorimeter. The heterotactic enthalpic pairwise interaction coefficients, h xy , of each amino acid with maltose have been calculated by the McMillan–Mayer formalism, and are discussed in terms of intermolecular interactions of the hydrated solute species.

Enthalpic Pairwise Interactions between Some Amino Acids and 2-Butanone in Aqueous Solutions at 298.15 K

The enthalpies of dilution of aqueous solutions of six kinds of amino acids (glycine, l-α-alanine, l-γ-aminobutyric acid, l-α-valine, l-α-serine, and l-α-threonine) with 2-butanone and enthalpies of mixing were measured at 298.15 K, using a mixing-flow microcalorimeter. The experimental data were treated according to the McMillan−Mayer theory, to obtain the enthalpic interaction coefficients. Combining the enthalpic pairwise interaction coefficients (hxy) of amino acids with cyclohexanone from the literature, the experimental results have been discussed from the point of view of solute−solute and solute−solvent interactions.

Concentration effect of sodium chloride on enthalpic interaction coefficients of D-mannitol and D-sorbitol in aqueous solution

The dilution enthalpies of D-mannitol and D-sorbitol in aqueous sodium chloride solution at various concentrations have been determined by isothermal microcalorimetry at 298.15 K. The homogeneous enthalpic interaction coefficients over a quite large range of concentration of aqueous sodium chloride solutions have been calculated according to the excess enthalpy concept. The results show that enthalpic pairwise interaction coefficients (h2) of D-mannitol and D-sorbitol are positive in aqueous sodium chloride solution and become more positive with increase of the concentration of sodium chloride. The results are interpreted in terms of the different conformations of the two polyols, solute-solute and solute-solvent interactions involved by solvent effects.

Studies on the Enthalpic Interactions of Formamide and N,N-Dimethylformamide with myo-Inositol in Aqueous Sodium Chloride Solutions at 298.15 K

The mixing enthalpies of formamide and N,N-dimethylformamide with myo-inositol and their respective enthalpies of dilution in aqueous sodium chloride solution have been determined by using flow-mix isothermal microcalorimetry at 298.15 K. These experimental results have been used to determine the heterotactic enthalpic interaction coefficients (hxy, hxxy, and hxyy) according to the McMillan−Mayer theory. It has been found that the heterotactic enthalpic pairwise interaction coefficients (hxy) between formamide and myo-inositol in aqueous sodium chloride solution are negative and become less negative with an increase in the concentration of sodium chloride. In contrast, the values of hxy between N,N-dimethylformamide and myo-inositol are positive and become more positive with increasing concentration of sodium chloride solutions. The results are discussed in terms of solute−solute interaction and solute−solvent interaction.

Enthalpies of Dilution for myo-Inositol in Aqueous Alkali Metal Salt and Alkaline Earth Metal Salt Solutions

The enthalpies of dilution of myo-inositol in aqueous solutions of alkali metal salts and alkaline earth metal salts have been determined with flow-mix isothermal microcalorimetry at 298.15 K. The enthalpic interaction coefficients in the range of salt solutions have been calculated according to the McMillan−Mayer theory. The results show that enthalpic pairwise interaction coefficients h2 of myo-inositol are negative in aqueous alkali metal salt and alkaline earth metal salt solutions. The absolute value of h2 becomes small with an elongation of the radius of the alkali metal cation while it becomes large with an elongation of the radius of the alkaline earth metal cation. The results are discussed in terms of the different metallic ions, interactions of solute with solute and solute with solvent.

Studies on the Interactions of l-Valine and l-Threonine with Saccharides in Aqueous Solutions at 298.15 K

Mixing enthalpies of aqueous l-valine and l-threonine solutions with aqueous sorbose solution and aqueous fructose solution and their dilution enthalpies have been determined with a Thermometric-2277 thermal activity monitor at 298.15 K. The experimental data have been analyzed in terms of McMillan−Mayer formalism to obtain the enthalpic virial coefficients for heterotactic interaction. The enthalpic pairwise interaction coefficients hxy of l-valine with saccharides are positive and those of lthreonine are negative. The variations of the enthalpic pairwise interaction coefficients are interpreted in terms of solute−solute interactions.

Enthalpic interaction coefficients of glycine in aqueous sodium halide solutions at 298.15 K

The enthalpies of dilution have been measured for glycine in aqueous NaCl and NaBr solutions at 298.15 K using a flow microcalorimetry. The enthalpic interaction coefficients of glycine in the studied aqueous sodium halide solutions have been calculated according to the McMillan–Mayer model. Combining the previous studies for other sodium halides, the effect of the anions on enthalpic pairwise interaction coefficients between the glycine molecules has been rationalized in terms of the concepts of electrostatic interaction and structural interaction. The experimental data of the present work and those of the literature are combined, to put forward the general chemical principal, namely the more strongly solutes are solvated the less will be their tendency to interact with other solutes.

Enthalpic interactions of some α-amino acids with 1,2-ethanediol in aqueous solutions at 298.15 K

The enthalpies of mixing of six kinds of aqueous amino acid solutions (glycine, l-alanine, l-valine, l-serine, l-threonine and l-proline) and aqueous 1,2-ethanediol solution and their respective enthalpies of dilution have been measured at 298.15 K using flow microcalorimetry. The experimental data have been analyzed in terms of the McMillan–Mayer formalism to obtain the heterotactic enthalpic interaction coefficients. The heterotactic enthalpic pairwise interaction coefficients, h xy , have been discussed from the points of view of solute–solute interactions.

Enthalpies of Interaction of N,N-Dimethylformamide with Polyalcohols in Aqueous Solutions at 298.15 K

Enthalpies of mixing of aqueous DMF solutions with aqueous polyalcohols (glycol, 1,2-propanediol, 1,3-propanediol, and glycerol) solutions and their respective enthalpies of dilution have been determined at 298.15 K using flow microcalorimetry. The experimental results obtained have been analyzed to give the heterotactic enthalpic interaction (or virial) coefficients of the solutes in terms of the McMillan−Mayer model. The enthalpic pairwise interaction coefficients hxy have been discussed from the points of view of solute−solute interactions. In addition, using the additivity groups approach by Savage and Wood (SWAG), contributions of each of the functional group of DMF and the polyalcohol studied have been estimated.

Enthalpy changes of salting processes of hen-egg white lysozyme in various electrolyte solutions

The enthalpy changes of salting process of hen-egg white lysozyme in buffer acetate solutions (pH=4.25) as a function of concentration of following electrolytes: LiCl, KCl, K2SO4, Li2 SO4 and (NH4)2SO4 are determined. Obtained data according to McMillan and Mayer’s approach, has been analyzed in the terms of the enthalpic pairwise interaction coefficients: lysozyme – lysozyme hxx, and lysozyme – salt hxy. The ability of cations to precipitate lysozyme solution in relation to the concentration of cations can be seen from the series as follows: Li+> Na+>K+>NH4++

The enthalpies of dilution of pyridine and methylpyridine at 298.15 K

The enthalpies of dilution of aqueous solutions for pyridine and methylpyridine isomers have been determined with a 2277-Thermal Activity Monitor at 298.15 K. The results have been treated using the excess function concept and homotactic interaction coefficients have been obtained. The homotactic enthalpic pairwise interaction coefficients are discussed qualitatively in terms of substitution effects of methyl group introduced into the pyridine ring.

Studies on the interactions between some [formula omitted]-amino acids with a non-polar side chain and two saturated cyclic ethers at 298.15 K: enthalpic measurement and computer simulation

Mixing enthalpies of heterocyclic compounds (THF and 1 , 4 -dioxane) and α -amino acids with a non-polar side chain (glycine, L-alanine, L-aminobutyric acid and L-valine), and dilution enthalpies of each compound have been determined in aqueous solutions at 298.15 K by a flow-mixing microcalorimeter. The heterotactic enthalpic pairwise interaction coefficients, h xy , of each amino acid with THF and 1 , 4 -dioxane have been calculated by the McMillan–Mayer formalism, and discussed in terms of intermolecular interactions between the hydrated solute species. Using the additivity groups concept by Savage and Wood (SWAG), contributions of each functional group of studied solutes have been estimated. In addition, the mixing energies and Huggins parameters of amino acid-heterocyclic compound systems have been obtained by computer simulation. The results of computer simulation are consistent with enthalpic measurements.

Enthalpies of dilution of glycine and l-alanine in aqueous 1-propanol solutions at T = 298.15 K

The dilution enthalpies of glycine and l-alanine in aqueous 1-propanol solutions have been measured by a mixing-flow microcalorimeter at T = 298.15 K. The homogeneous enthalpic interaction coefficients of the two zwitterions have been calculated according to the analysis of the excess enthalpy suggested by Friedman [J. Solution Chem. 1 (1972) 387–390]. The enthalpic pairwise interaction coefficients h 2 of glycine are negative and pass through a minimum with increasing 1-propanol content in mixed solvents, while those of l-alanine decrease from positive to negative. The variations of the enthalpic pairwise interaction coefficients are interpreted in terms of solute − solute and solute − solvent interactions.

Enthalpic Interaction of Amino Acids with 2-Chloroethanol in Aqueous Solutions at 298.15 K

The enthalpies of mixing have been determined for five kinds of aqueous amino acids solutions (glycine, L-alanine, L-valine, L-serine, and L-proline) with 2-chloroethanol by an LKB-2277 Bio Activity Monitor at 298.15 K. In addition, the enthalpies of dilution at 298.15 K of aqueous solutions containing the five kinds of amino acids and 2-chloroethanol have been obtained. The heterotactic enthalpic pairwise interaction coefficients of the virial expansion of excess enthalpy were evaluated and interpreted from the point of view of solute–solute interactions. In comparison with ethanol, 2-chloroethanol shows a stronger exothermic interaction with amino acids because of its hydrophilic Cl atom and a more acidic −OH group. Using the additivity groups concept by Savage and Wood (SWAG), contributions of each of functional group of the amino acids and ethanol and 2-chloroethanol have been estimated.

Enthalpic interaction between α-amino acids and pyridine and methylpyridine in aqueous solutions

Enthalpies of dilution of aqueous L-serine, pyridine and methylpyridine solutions and their enthalpies of mixing have been determined by a mixing-flow microcalorimeter at 298.15 K. The data have been analyzed in terms of McMillan-Mayer formalism to fit to virial polynomials from which the heterotactic enthalpic pairwise interaction coefficients, hxy, betweenL-serine and pyridine and methylpyridine isomers have been evaluated. The results obtained in the present paper are compared with those reported in the earlier paper about glycine and L-alanine in the same organic solvent aqueous solutions, giving a global insight of the interaction mechanism between the a-amino acids and pyridine and methylpyridine from the point of view of solute-solute interactions and substituent effects of methyl groups introduced into the pyridine ring.

Enthalpies of Interaction of l-Valine and l-Threonine with Pyridine and Methylpyridine in Aqueous Solutions at 298.15 K

Enthalpies of mixing in aqueous solutions of l-valine and l-threonine with pyridine and methylpyridine isomers and their enthalpies of dilution have been determined by flow microcalorimetry at 298.15 K. The results have been analyzed using the excess function concept, and heterotactic enthalpic pairwise interaction coefficients, hxy, of the virial expansion of the excess enthalpy have been obtained. These are briefly discussed in terms of intermolecular interactions between the hydrated solute species. In addition, the results obtained in the present paper along with literature data have been treated in terms of the Savage−Wood additivity group (SWAG), and values of the functional group interaction parameters for α-amino acids + pyridine and α-amino acids + methylpyridine systems have been estimated. The SWAG approach has been appraised in terms of the results obtained.

Enthalpies of Dilution and Enthalpies of Mixing of α-Amino Acids + Pyridine and α-Amino Acids + Methylpyridine in Aqueous Solutions at 298.15 K

The enthalpies of mixing of aqueous solutions have been determined for glycine and l-alanine with pyridine and methylpyridine by flow microcalorimetry at 298.15 K. In addition, the enthalpies of dilution at 298.15 K of aqueous solutions containing glycine, l-alanine, pyridine, and methylpyridine have been obtained, respectively. These data have been analyzed using the McMillan−Mayer theory, and heterotactic interaction coefficients are given for the interaction of glycine and l-alanine with pyridine and methylpyridine, among which the enthalpic pairwise interaction coefficients, hxy, are discussed in terms of solute−solute interaction and substituent effects.

Enthalpic interactions of glycine in aqueous sodium halide solutions

Dilution enthalpies of glycine in aqueous NaF and NaI solutions of various molalities at 298.15 K have been determined, respectively, by mixing flow microcalorimetry. The results have been analyzed according to the modified McMillan–Mayer model to obtain homogeneous enthalpic interaction coefficients. The effect of the anions on enthalpic pair-wise interaction coefficients has been discussed from the point of view of electrostatic interaction and structural interaction.

Enthalpies of dilution of glycine, l-alanine and l-serine in aqueous ethylene glycol solutions at 298.15 K

Enthalpies of dilution of glycine, l-alanine and l-serine in aqueous ethylene glycol solutions have been measured at 298.15 K by a mixing-flow microcalorimeter. The homogeneous enthalpic interaction coefficients of the three zwitterions have been computed by least-squares fitting on the basis of the McMillan–Mayer theory. The variations of the enthalpic pairwise interaction coefficients with the mass fraction of ethylene glycol in mixtures are interpreted in terms of solute–solute and solute–solvent interactions.