The enthalpic interaction coefficients of N,N′-hexamethylenebisacetamide and N-methylformamide with four types of amino acids in aqueous sucrose solutions at 298.15 K

The mixing enthalpies of N,N′-hexamethylenebisacetamide (HMBA) and N-methylformamide (NMF) with glycine, l-alanine, l-serine, and l-valine in aqueous sucrose solutions have been determined by using mixing-flow isothermal microcalorimetry at the temperature of 298.15 K along with their dilution enthalpies, respectively. Based on the obtained results, the heterotactic enthalpic interaction coefficients (h_xy, h_xxy, and h_xyy) have been obtained according to McMillan–Mayer’s theory with the sucrose molality from 0 to 1.5 mol · kg⁻¹. The fitted results indicate that the values of h_xy between HMBA or NMF and the four investigated amino acids in aqueous sucrose solutions are all positive. Meanwhile, the values of h_xy reach the corresponding maximum at different sucrose molalities except that the values of h_xy between NMF and glycine decrease monotonically with the increasing molality of sucrose. Furthermore, the order for the value of h_xy of the four amino acids with HMBA or NMF are h_xy (l-valine) > h_xy (l-alanine) > h_xy (l-serine) > h_xy (glycine) in pure water or in aqueous solution with the same molality of sucrose. The values of h_xy between HMBA and the four amino acids are much larger than that between NMF and the same amino acids with the same molality of sucrose. All the variations of the heterotactic enthalpic pairwise interaction coefficients in the quaternary systems can be interpreted with the help of the solute–solute and solute–solvent interactions theory.     

The Mixing Enthalpy Interaction Coefficients of N,N′-Hexamethylenebisacetamide with l-Alanine and l-Serine in Aqueous Glucose Solutions at 298.15 K

The mixing enthalpies of N,N??-hexamethylenebisacetamide (HMBA) with l-alanine and l-serine in aqueous glucose solutions have been determined by using mixing-flow isothermal microcalorimetry along with their dilution enthalpies at the temperature of 298.15?K. These results can be used to obtain the heterotactic enthalpic interaction coefficients (h _xy , h _xxy , and h _xyy ) in the range of the glucose molality, (0 to 1.5) mol?kg^?1, according to the McMillan?CMayer theory. Combining our previous research results for glycine (see Liu et al. in J. Chem. Eng. Data 55, 5258?C5263, 2010), we find that the heterotactic enthalpic pairwise interaction coefficients h _xy between HMBA and the investigated amino acids in aqueous glucose solutions are all positive and reach maximum values at about 0.3 mol?kg^?1 glucose. In addition, the order for the value of h _xy of the three amino acids in pure water and aqueous solution of the same glucose molality is h _xy (l-alanine)>h _xy (l-serine)>h _xy (glycine). All variations of the heterotactic enthalpic pairwise interaction coefficients with the molalities of glucose in the quaternary systems are discussed in terms of solute?Csolute and solute?Csolvent interactions.     

Enthalpic interactions between some amino acids and cyclohexanone in aqueous solutions at 298.15 K

The enthalpies of mixing of glycine, l-α-alanine, l-γ-aminobutyric acid, l-α-valine, l-α-serine and l-α-threonine with cyclohexanone in aqueous solutions and their respective enthalpies of dilution have been measured by calorimetry at 298.15 K. Experimental enthalpies of dilution and mixing have been correlated with the virial expansion equation that was obtained with the McMillan-Mayer theory. The enthalpic interaction parameters h_xy, h_xxy and h_xyy of the amino acids studied with cyclohexanone in aqueous solutions have been evaluated, and the heterotactic enthalpic pair interaction coefficients (h_xy) are discussed in terms of solute-solute interactions.     

Viscometric studies on saccharides in aqueous magnesium chloride solutions at T = (288.15 to 318.15) K

The viscosity B-coefficients of mono-, di-, tri-saccharides and the derivatives (methyl glycosides) in m_B = (0.5, 1.0, 2.0, and 3.0) mol · kg⁻¹ aqueous solutions of magnesium chloride have been determined from viscosity data using the Jones–Dole equation at T = (288.15, 298.15, 308.15, and 318.15) K. The viscosity B-coefficients of transfer (Δ_tB), the temperature derivatives of B-coefficients (dB/dT), pair and triplet viscometric interaction coefficients (η_AB, η_ABB) have been determined. The viscosity B-coefficients data of systems studied in water have been reported earlier. The results have been interpreted in light of the solute–solute and solute–solvent interactions occurring in these systems. The comparison of results has been made with those reported in the presence of potassium chloride, ammonium sulphate, and sodium sulphate.     

Enthalpic interactions of some α-amino acids with glycol 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 glycol solution and their respective enthalpies of dilution have been determined at 298.15 K using flow microcalorimetry. The experimental data have been analyzed according to the McMillan–Mayer formalism to obtain the heterotactic enthalpic interaction coefficients (h_xy). h_xy coefficients have been discussed from the points of view of solute–solute interactions.     

The dilution enthalpies of l-prolinol in N,N-dimethylformamide aqueous solutions at T = 298.15 K

Values of the enthalpy of dilution were measured for l-prolinol in pure water and N,N-dimethylformamide (DMF) aqueous solutions with various mass fractions of DMF at T = 298.15 K using a flow-mixing microcalorimeter. A pseudo phase equilibrium model was proposed to simplify the complex aggregation equilibrium and interpret the abnormality in the dilution enthalpy, which together with the McMillan–Mayer approach was used to fit the experimental data to obtain the enthalpic pairwise interaction coefficients and the molar aggregation enthalpies of l-prolinol in DMF aqueous solutions. The results are discussed in terms of the hydrophobic interaction and the interactions between the solvated solutes.     

The Heterotactic Enthalpic Interaction Coefficients of <Emphasis Type="Italic">α</Emphasis>-Amino Acids with Maltose in Aqueous Solution at <Emphasis Type="Italic">T</Emphasis>=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 interactions of anti-tumor drug matrine in aqueous sodium chloride solutions

The enthalpies of dilution of matrine (MAT) in pure water and aqueous sodium chloride solutions were determined by isothermal titration microcalorimetry at 298.15 K, and the corresponding homogeneous enthalpic interaction coefficients were calculated according to the modified McMillan–Mayer model. The values of enthalpic pair-wise interaction coefficients, h ₂, are all positive and become more positive with increasing concentration of sodium chloride.     

Rheological behaviour of some saccharides in aqueous potassium chloride solutions over temperature range (288.15 to 318.15) K

The viscosities, η of mono-, di-, tri-saccharides and methylglycosides, viz., d(+)-xylose (XYL), d(?)-arabinose (ARA), d(?)-ribose (RIB), d(?)-fructose (FRU), d(+)-galactose (GAL), d(+)-mannose (MAN), d(+)-glucose (GLU), d(+)-melibiose (MEL), d(+)-cellobiose (CEL), d(+)-lactose monohydrate (LAC), d(+)-maltose monohydrate (MAL), d(+)-trehalose dihydrate (TRE), sucrose (SUC), d(+)-raffinose pentahydrate (RAF), α-methyl-d(+)-glucoside (α-Me-GLU), methyl-α-d-xylopyranoside (Me-α-XYL), and methyl-β-d-xylopyranoside (Me-β-XYL) in water and in (0.5, 1.0, 2.0, and 3.0) mol · kg^?1 aqueous solutions of potassium chloride (KCl) have been determined at T = (288.15, 298.15, 308.15, and 318.15) K from efflux time measurements by using a capillary viscometer. Densities used to determine viscosities have been reported earlier. The viscosity data have been utilized to determine the viscosity B-coefficients employing the Jones–Dole equation at different temperatures. From these data, the viscosity B-coefficients of transfer, Δ_tB have been estimated for the transfer of various saccharides/methylglycosides from water to aqueous potassium chloride solutions. The Δ_tB values have been found to be positive, whose magnitude increases with the increase in concentration of potassium chloride in all cases. The dB/dT coefficients, pair, η_AB and triplet, η_ABB viscometric interaction coefficients have also been determined. Gibbs free energies of activation and related thermodynamic parameters of activation of viscous flow have been determined employing Feakin’s transition-state theory. The signs and magnitudes of various parameters have been discussed in terms of solute–solute and solute–solvent interactions occurring in these solutions. The effect of substitution of –OH by methoxy group, –OCH₃ has also been discussed.     

Solubility of proline–leucine dipeptide in water and in aqueous sodium chloride solutions from T = (288.15 to 313.15) K

Solubility of proline–leucine dipeptide, in water and in aqueous sodium chloride solutions, was measured at T = (288.15, 298.15, 308.15 and 313.15) K as a function of electrolyte concentration m = (0.1, 0.25, 0.5, 0.75 and 1) mol · kg⁻¹ of water. Solubility data has been evaluated from density measurements using a vibrating tube densimeter. It has been observed that sodium chloride renders the dipeptide proline–leucine more soluble in water. Salting-in coefficients and standard free energies of transfer of proline–leucine, from water to aqueous sodium chloride solutions, have been calculated from the solubility data. Standard enthalpies and entropies of transfer have also been estimated and interpreted in terms of electrostatic and hydrophobic perturbed domains in the hydration shells of the dipeptide and of the cation and anion of the salt, as a function of temperature and salt concentration.     

Effect of potassium chloride on diffusion of theophylline at T = 298.15 K

Ternary mutual diffusion coefficients measured by Taylor dispersion method (D₁₁, D₂₂, D₁₂, and D₂₁) are reported for aqueous solutions of KCl + theophylline (THP) at T = 298.15 K at carrier concentrations from (0.000 to 0.010) mol · dm^?3, for each solute. These diffusion coefficients have been measured having in mind a better understanding of the structure of these systems and the thermodynamic behavior of potassium chloride and theophylline in solution. For example, from these data it will be possible to make conclusions about the influence of this electrolyte in diffusion of THP and to estimate some parameters, such as the diffusion coefficient of the aggregate between KCl and THP.     

Dependence of enthalpic pairwise self-interactions on ionic strength: Some 2-deoxy and N-acetyl monosaccharides in aqueous NaCl solutions at T = 298.15 K

The dilution enthalpies of four derivatives of monosaccharides, namely 2-deoxy-d-glucose (2-DGlu), N-acetyl-d-glucosamine (GluNAc), 2-deoxy-d-galactose (2-DGal) and N-acetyl-d-galactosamine (GalNAc), in aqueous NaCl solutions of various molalities (b = 0–3.0 mol · kg⁻¹) have been determined respectively at T = 298.15 K by isothermal titration calorimetry (MicroCal ITC200). The corresponding values of enthalpic pairwise self-interaction coefficients (h₂) have been calculated according to the McMillan–Mayer theory. It was found that across the range studied of ionic strength (I) or molality (b = I), the h₂ coefficients are all positive, in the order h₂ (GluNAc) > h₂ (GalNAc) > h₂ (2-DGlu) > h₂ (2-DGal), and decrease gradually after increasing first up to a maximum at b ≈ 1.5 mol · kg⁻¹. The effects of ionic strength (I) on the trends of h₂ have been discussed from the point of view of complex (solute + solute) and (solute + solvent) interactions in solutions.     

(Vapour + liquid) equilibria,volumetric and compressibility behaviour of binary and ternary aqueous solutions of 1-hexyl-3-methylimidazolium chloride,methyl potassium malonate,and ethyl potassium malonate

(Vapour + liquid) equilibrium data (water activity, vapour pressure, osmotic coefficient, and activity coefficient) of binary aqueous solutions of 1-hexyl-3-methylimidazolium chloride ([C₆mim][Cl]), methyl potassium malonate, and ethyl potassium malonate and ternary {[C₆mim][Cl] + methyl potassium malonate} and {[C₆mim][Cl] + ethyl potassium malonate} aqueous solutions were obtained through the isopiestic method at T = 298.15 K. These results reveal that the ionic liquid behaves as surfactant-like and aggregates in aqueous solutions at molality about 0.4 mol · kg⁻¹. The constant water activity lines of all the ternary systems investigated show small negative deviations from the linear isopiestic relation (Zdanovskii–Stokes–Robinson rule) derived using the semi-ideal hydration model. The density and speed of sound measurements were carried out on solutions of methyl potassium malonate and ethyl potassium malonate in water and of [C₆mim][Cl] in aqueous solutions of 0.25 mol · kg⁻¹ methyl potassium malonate and ethyl potassium malonate at T = (288.15 to 308.15) K at atmospheric pressure. From the experimental density and speed of sound data, the values of the apparent molar volume, apparent molar isentropic compressibility and excess molar volume were evaluated and from which the infinite dilution apparent molar volume and infinite dilution apparent molar isentropic compressibility were calculated at each temperature. Although, there are no clear differences between the values of the apparent molar volume of [C₆mim][Cl] in pure water and in methyl potassium malonate or ethyl potassium malonate aqueous solutions, however, the results show a positive transfer isentropic compressibility of [C₆mim][Cl] from pure water to the methyl potassium malonate or ethyl potassium malonate aqueous solutions. The results have been interpreted in terms of the solute–water and solute–solute interactions.     

Activity coefficients of electrolyte and amino acid in the systems (water + potassium chloride + dl -valine) at T = 298.15 K and (water + sodium chloride + l -valine) at T = 308.15 K

The activity coefficient data were reported for (water  +  potassium chloride  + dl -valine) at T =  298.15 K and (water  +  sodium chloride  + l -valine) at T =  308.15 K. The measurements were performed in an electrochemical cell using ion-selective electrodes. The maximum concentrations of the electrolytes and the amino acids studied were 1.0 molality and 0.4 molality, respectively. The results of the activity coefficients of dl -valine are compared with the activity coefficients of dl -valine in (water  +  sodium chloride  + dl -valine) system obtained from the previous study. The results show that the presence of an electrolyte and the nature of its cation have a significant effect on the activity coefficient of dl -valine in aqueous electrolyte solutions.     

Enthalpies of solvation of ethylene oxide oligomers CH3O(CH2CH2O)nCH3 (n = 1 to 4) in different H-bonding solvents: Methanol,chloroform, and water. Group contribution method as applied to the polar oligomers

The enthalpies of solution and solvation of ethylene oxide oligomers CH₃O(CH₂CH₂O)_nCH₃ (n = 1 to 4) in methanol and chloroform have been determined from calorimetric measurements at T = 298.15 K. The enthalpic coefficients of pairwise solute–solute interaction for methanol solutions have been calculated. The enthalpic characteristics of the oligomers in methanol, chloroform, water and tetrachloromethane have been compared. The hydrogen bonding of the oligomers with chloroform and water molecules is exhibited in the values of solvation enthalpy and coefficient of solute–solute interaction. This effect is not observed for methanol solvent. The thermochemical data evidence an existence of multi-centred hydrogen bonds in associates of polyethers with the solvent molecules. Enthalpies of hydrogen bonding of the oligomers with chloroform and water have been estimated. The additivity scheme has been developed to describe the enthalpies of solvation of ethylene oxide oligomers, unbranched monoethers and n-alkanes in chloroform, methanol, water, and tetrachloromethane. The correction parameters for contribution of repeated polar groups and correction term for methoxy-compounds have been introduced. The obtained group contributions permit to describe the enthalpies of solvation of unbranched monoethers and ethylene oxide oligomers in the solvents with standard deviation up to 0.6 kJ · mol⁻¹. The values of group contributions and corrections are strongly influenced by solvent properties.     

Effect of sodium acetate on the rheological behaviour of some mono-, di-, and tri-saccharides in aqueous solutions over the temperature range (288.15 to 318.15) K

The Jones–Dole viscosity B-coefficients for various mono-, di-, and tri-saccharides in water and in (0.5, 1.0, 2.0, and 3.0) mol · kg^?1 aqueous solutions of sodium acetate have been determined at different temperatures, T = (288.15, 298.15, 308.15, and 318.15) K from viscosity data. Densities used to determine viscosities have been reported earlier. The viscosity B-coefficients of transfer, Δ_tB, has been estimated for the transfer of saccharides from water to aqueous sodium acetate solutions. The positive Δ_tB values were obtained in all cases and their magnitudes increase with the increase in concentration of sodium acetate. Pair, η_AB and higher order, η_ABB viscometric interaction coefficients (using McMillan–Mayer theory), and dB/dT coefficients have also been determined. Activation Gibbs free energies and other related thermodynamic activation parameters of viscous flow have been determined using Feakin’s transition-state theory. These parameters have been discussed in terms of solute–solute and solute–solvent interactions occurring in these solutions.     

Effect of the reference solution in the measurement of ion activity coefficients using cells with transference at T = 298.15 K

This work reports individual activity coefficients of ions at T = 298.15 K in aqueous solutions obtained from voltage values of the respective half-cell ion-selective-electrode and a single-junction Ag–AgCl reference electrode, filled with different reference solutions at different concentrations. For potassium and chloride ions in KCl aqueous solutions, reference solutions of KCl, NaCl, or CsCl were used. For sodium and chloride ions in aqueous NaCl solutions, reference solutions of CsCl were used. Experimental runs were performed at molalities (1, 2, and 3) m of the reference solution. The concentration of the sample solution was increased, starting from around 1 · 10^?3 m, up to the molality of the reference solution. The values of activity coefficients are calculated using the Henderson equation to estimate the liquid-junction potential. Results show that the ionic activity coefficients are independent of the nature and concentration of reference solution.     

Enthalpies of solution of dl-α-alanyl-dl-α-asparagine in aqueous alcohols at 298.15 K

The enthalpies of solution of dl-α-alanyl-dl-α-asparagine (AlaAsn) were measured in aqueous methanol, ethanol, 1-propanol and 2-propanol with an alcohol mole-fraction content x₂ (from 0 to 0.4) at 298.15 K. The experimental results were used to calculate the enthalpies of transfer of AlaAsn from water to these mixtures as well as the enthalpy coefficients of pair-wise interactions (h_xy) between AlaAsn and alcohol molecules in water, according to the McMillan–Mayer's model. The h_xy values were found to be positive and increasing in a series methanol < ethanol < 1-propanol < 2-propanol.     

Isopiestic study of (calcium chloride + water) and (calcium chloride + magnesium chloride + water) atT = 313.15 K

The osmotic coefficients of aqueous calcium chloride solutions were experimentally determined atT =  313.15 K by the isopiestic method. Magnesium chloride served as the isopiestic standard for the calculation of osmotic coefficients. The molality range covered in this study correspond to about 0.1mol · kg ^− 1to 3.0mol · kg ^− 1. In addition, the osmotic coefficients of aqueous mixtures of calcium chloride and magnesium chloride were determined over the range of ionic strength levels of about 0.1mol · kg ^− 1to 9mol · kg ^− 1and at various mole fractions. The results obtained were correlated by the Pitzer equation.     

Hygrometric determination of the water activities and the osmotic and activity coefficients of (ammonium chloride + sodium chloride + water) atT = 298.15 K

The mixed aqueous electrolyte system of ammonium and sodium chlorides has been studied by the hygrometric method at the temperature 298.15 K. The relative humidities of this system were measured at total molalities from 0.3mol · kg ^− 1 to 6 mol · kg ^− 1for different ionic-strength fractions of NH ₄Cl with y =  (0.33, 0.50, and 0.67). The data obtained allow the deduction of new water activities and osmotic coefficients. The experimental results are compared with the predictions of the extended composed additivity model proposed in our previous work, the Robinson–Stokes, Reilly–Wood–Robinson, and Lietzke–Stoughton models. From these measurements, the new Pitzer mixing ionic parameters were determined and used to predict the solute activity coefficients in the mixture.