Freezing temperatures of aqueous solutions of mixtures of amides and polyols. Gibbs energy of interaction of the amide group with the hydroxyl group in aqueous solution

Freezing temperatures of dilute aqueous mixtures of: formamide with myo-inositol, d-mannitol, and cyclohexanol; N,N-dimethylformamide with inositol, mannitol, and cyclohexanol; and acetamide with inositol and mannitol have been measured. These data have been analyzed to yield the pairwise molecular Gibbs energies of interaction between the molecules in an aqueous solution. Using the group additivity principle, the results yield the pairwise functional group Gibbs energies of interaction of the amide group with the hydroxyl group, G _OH,CONH =–31 J-kg-mol^–2.     

Freezing temperatures of aqueous solutions of hexamethylenetetramine with polyols,amides, and ethers

Freezing temperatures of dilute aqueous solutions of hexamethylenetetramine and mixtures of hexamethylenetetramine with myo-inositol, d-mannitol, cyclohexanol, formamide, acetamide, 1,4-dioxane, and 1,3,5-trioxane have been measured. These data yield pairwise molecular Gibbs energies of interaction between the molecules in an aqueous solution. Using the additivity principle, the results also yield the pairwise functional group Gibbs energies of interaction in an aqueous solution for the amine nitrogen with itself and with the hydroxyl, amide, ether, and methylene groups.     

Freezing temperatures of aqueous solutions of methyl formate and ethyl acetate with a variety of nonelectrolytes. Gibbs energy of interaction of the ester group with other functional groups

Freezing temperatures of dilute aqueous solutions of ethyl acetate and mixtures with myo-inositol, D-mannitol, formamide, 1,3,5-trioxane, 1,4-dioxane, acetamide, hexamethylenetetramine, and methyl formate have been measured. In addition, freezing temperatures of dilute aqueous solutions of methyl formate and mixtures with the above solutes have been measured. From these data, the pairwise molecular Gibbs energies of interaction between the molecules were calculated. Using the additivity principle, the pairwise functional group Gibbs energies of interaction were calculated for ester group interactions with a variety of other functional groups.     

Interactions of ether groups with saccharides. Enthalpy of dilution of aqueous systems containing S-trioxane and inositol,mannitol, or cyclohexanol

Enthalpies of dilution of aqueous systems containing trioxane, and trioxane with each of mannitol, inositol and cyclohexanol have been determined at 25°C. The data have been treated in terms of the Savage-Wood additivity principle and, in conjunction with literature data on ether compounds a revised estimate of the pairwise group-interaction enthalpy for CH₂/–O– and a first estimate for CHOH/–O– are presented. Systems of saccharides and saccharides with alcohols do not conform to the Savage-Wood principle and an explanation in terms of the specific hydration properties of saccharides is offered.     

Gibbs energies of interaction of the CH2 and CHOH groups from freezing point data for aqueous binary mixtures of D-mannitol,myo-inositol,and cyclohexanol

Freezing temperatures of dilute aqueous solutions of D-mannitol, myo-inositol, D-mannitol + myo-inositol, D-mannitol + cyclohexanol, and myo-inositol + cyclohexanol have been measured over the concentration range 0.1 to 1.0 mol-kg^–1. These data yield pairwise molecular Gibbs energies of interaction which have been corrected to 25°C and treated according to the Savage-Wood additivity principle to give pairwise functional group Gibbs energies of interaction for CH₂/CH₂, CH₂/COOH, and CHOH/CHOH. Anomalous behavior of some systems is discussed in terms of the interactions.     

Enthalpies of dilution of aqueous systems containing hexamethylenetetramine and other nonelectrolytes

Enthalpies of dilution of aqueous systems containing hexamethylenetetramine, alone and in ternary system with each of mannitol, myoinositol, cyclohexanol, formamide, dimethylformamide, and trioxane have been determined. The data have been treated in terms of the Savage-Wood additivity principle and first estimates for the pairwise groups interaction enthalpies of N/N, CH₂/N, CHOH/N, COHN/N and –O–/N have been made. The results are discussed in light of all other known group interaction enthalpies. The limitations and utilities of the Savage-Wood principle are reviewed.     

Enthalpies of dilution of aqueous solutions of amides and alcohols

Enthalpies of dilution of aqueous systems containing formamide, dimethyl-formamide, the mixture of these amides, and each amide separately with mannitol, inositol, and cyclohexanol have been determined at 25°C. The data have been treated in terms of the Savage-Wood additivity principle and in combination with literature data. New values for the methylene-amide, carbinol-amide, and amide-amide group interaction enthalpies are presented. These may be used with data on a wider variety of solute systems to obtain interaction enthalpies for new groups.     

Freezing temperatures and enthalpies of dilution of aqueous solutions of amides. Gibbs energies and enthalpies of interaction of the N,N-dimethylamide group in aqueous solutions

Enthalpies of dilution, freezing temperatures, and densities of aqueous solutions of N,N-dimethylacetamide and N,N-dimethylpropionamide have been measured. Freezing temperatures of dilute aqueous solutions of formamide and N,N-dimethylformamide have also been measured. These data yield the pairwise molecular Gibbs energies and enthalpies of interaction: these have been treated according to a group additivity principle to give pairwise functional group Gibbs energies and enthalpies of interaction. The results indicate that substitution on the amide nitrogen may increase the Gibbs energy and enthalpy of interaction of the amide group with itself in an aqueous environment but the effect if present is small.     

Freezing points and enthalpies of dilute aqueous solutions of tetrahydropyran, 1,3-dioxane, 1,4-dioxane,and 1,3,5-trioxane. Free energies and enthalpies of solute-solute interactions

The enthalpies of dilute aqueous solutions of tetrahydropyran, 1,3-dioxane, 1,4-dioxane, 1,2,5-trioxane, and an equimolal mixture of tetrahydropyran and 1,3,5-trioxane were measured at 25°C and at molalities from about 0.1 to 1.0 mol kg¹. The freezing points of the same aqueous solutions (except for 1,3-dioxane) were measured over a similar molality range. The results were used to calculate the enthalpies and Gibbs free energies of the pair-wise interactions of the above solutes in dilute aqueous solutions at 25°C. From these results, the additivity principle proposed by Savage and Wood was used to get the Gibbs free energy and enthalpies of interaction for the ether-ether and ether-methylene groups. Because of the limited number of measurements, the interaction parameters were not determined with great precision. Nevertheless, the standard errors for the predicted enthalpies and Gibbs free energies are quite reasonable. The signs and magnitudes are similiar to those determined for other polar groups.     

Enthalpy of dilution of aqueous systems containing S-trioxane and some amides. Analysis of the interaction of saccharides with amides in aqueous media

Enthalpies of dilution of aqueous systems of trioxane+formamide and trioxane+dimethylformamide have been determined at 25°C. The data have been treated in terms of the Savage-Wood additivity principle, and a first estimate of the pairwise group interaction enthalpy for-O-/CONH is presented. Systems of saccharides and amides are not amenable to the Savage-Wood treatment used in recent works. However, when treated in conjunction with all available data to yield a different set of group interaction parameters, saccharides behave more predictably. Implications of this state of affairs are considered.     

Interaction of water with poly(vinyl methyl ether) in aqueous solution

Near-infrared, viscometric, and calorimetric measurements were made on aqueous poly(vinyl methyl ether) (PVME) solutions at temperatures between 15 and 43°C. We found a hydrogen-bonded structure of water around the polymer chain (a polymer-water complex), which is characterized by two distinct hydration numbers (i.e., 2.7 and 5.0 water molecules on each monomer unit of the chain) by analyzing the concentration dependence of endothermic enthalpies at a cloud point temperature, ca. 35°C. In particular, the 2.7 water-polymer complex has been suggested to be cooperatively formed by using data of the near-infrared (nir) absorption spectrum around 1930 nm. Furthermore, the peak-wavelength of the nir spectrum has been observed to change drastically at the cloud point when the temperature is raised. This can be interpreted as a cooperative collapse of the hydrogen-bonded water structure to free water, resulting in the aggregation of the polymer chains due to the exposure of their hydrophobic groups at the cloud point. © 1994 John Wiley & Sons, Inc.     

Group contributions to the partial molar volume of ionic organic solutes in aqueous solution

Partial molar volumes at infinite dilution in water at 25°C for more than 400 organic electrolytes (carboxylic acid and amine salts, sulfates, sulfonates, selected polyelectrolyes, aminoacids and derivatives) are described through a simple additivity scheme already adopted for non-electrolytes. Twenty-five charged groups are assigned a contribution and the partial molar volumes of more than 150 monofunctional organic ions are reproduced with a standard deviation of 0.8 cm³-mol^–1. The different volumetric behavior of hydrophobic and hydrophilic centers, either charged or uncharged, is discussed. Deviations from additivity for mono-and polyfunctional ions are analyzed in terms of (i) extension of the hydration cosphere of different polar centres; (ii) intramolecular interactions and their dependence on the nature, number and mutual separation of interacting groups.     

New intermolecular interaction potential for simulation of water and aqueous solutions in a wide range of state parameters

A new semiempirical method for derivation of additive effective potentials is proposed. Local features of the shape of the potential energy surface of water dimers are approximated by Gaussian functions. Optimum geometric parameters of nonlinear bifurcated and inverted dimers, obtained from quantum-chemical calculations are constants of the new BMW potential. Free parameters of the potential were chosen based on the results of Monte Carlo simulation of the structural and thermodynamic functions of water in a wide range of state parameters (268 K T 673 K, 0.1 MPa p 400 MPa). Calculations revealed rather high concentrations of the bifurcated and inverted dimers in the systems of H-bonds of water models. Clustering of non-tetrahedral fragments of the network of H-bonds is responsible for a microheterogeneous structure of water on the microscopic level.     

Studies of the reaction of the hydroxyl radical with the oxalate ion in an acidic aqueous solution by pulse radiolysis

The reaction of the · OH radical with the oxalate ion in an acidic aqueous solution was studied by pulse radiolysis. The rate constant for the reaction of formation of the radical HOOC-COO·(λ_max = 250 nm, ɛ = 1800 L mol⁻¹ cm⁻¹) is (5.0±0.5)·107 L mol⁻¹ s⁻¹. In the reaction with the hydrogen ion (k = 1.1·10⁷ L mol⁻¹ s⁻¹), the radical HOOC-COO· is transformed into a nonidentified radical designated arbitrarily as H⁺(HOOC-COO)· (λ_max = 260 nm, ɛ = 4000 L mol⁻¹ cm⁻¹). Published in Russian in Izvestiya Akademii Nauk. Seriya Khimicheskaya, No. 6, pp. 1165–1167, June, 2008.     

Interactions of La(III) with anions in aqueous solutions. A139La NMR study

The interactions of the La(III) cations with three anions (X), nitrate, chloride and perchlorate, in aqueous solutions in the pH range 4.0–6.5, were studied by¹³⁹La NMR spectroscopy. A single model, involving the formation of the contact ion-pair (inner-sphere complex) (LaX)²⁺ was successfully and quantitatively applied to the chemical shift and the transverse relaxation rate data. Both measurements gave values for the thermodynamic equilibrium constants of formation of (LaX)²⁺ (K _th ) in good agreement (average K _th =0.45±0.05; 0.15±0.09; 0.03±0.01, respectively for nitrate, chloride and perchlorate). The complexes are characterized by chemical shifts of –25, 22 and –3.1 ppm and by transverse relaxation rates of 11.2, 5 and 1.65 kHz respectively for nitrate, chloride and perchlorate. The¹³⁹La quadrupolar relaxation rate is not controlled by the reorientational correlation time. This finding is discussed, and it is suggested that the very fast exchange of water molecules in the first coordination sphere of La(III) is responsible for the time fluctuation of the electric field gradient at the¹³⁹La nucleus site.     

Parameters of the interaction between components; structural and hydrophobic effects in systems water-ethylene glycol-n-butyl alcohol and water-ethanol-xenon at 248–348 K

At 298.15 K the interaction parameters have been determined in six ternary systems: water-alcohol (MeOH, EtOH, EG (ethylene-glycol))-the dissolved substance (PrOH, BuOH, Xe). It is found for the coefficients of pair interactions that h ₂₃(EG-BuOH) = h ₂₃(MeOH-BuOH), c ₂₃(EG-BuOH) ? c ₂₃(MeOH-BuOH) < 0. Interactions become more hydrophobic in a series: EG-BuOH ≈ EG-Xe < MeOH-PrOH < MeOH-BuOH≤EtOH-Xe < EtOH-PrOH. For two systems the interaction parameters are defined in an interval 248–348 K. Temperature dependence of enthalpy and heat capacity coefficients of pair interactions, thermal capacity of transfer, an excess heat capacity and their constituents is discussed.     

Enthalpy of dilution of aqueous mixtures of amides,sugars, urea,ethylene glycol,and pentaerythritol at 25°C: Enthalpy of interaction of the hydrocarbon,amide, and hydroxyl functional groups in dilute aqueous solutions

The enthalpy of dilution of all one-and two-solute aqueous mixtures of a series of compounds were measured from about 0.2 to 2.0 mole-kg^–1 at 25°C. The compounds included in the study wereN-methylformamide,N-methylacetamide,N-methylpropionamide,N-butylacetamide, urea, ethylene glycol, pentaerythritol, glucose, and sucrose. The results of the enthalpy measurements were used to calculate the pairwise enthalpy of interaction for each compound with all the other compounds. A simple additivity principle is used to correlate the data. The principle assumes that each functional group on one molecule interacts with every functional group on the other molecule and that each of these interactions has a characteristic effect on the enthalpy that is independent of the positions of the functional groups in the two molecules. The resulting equation gives a rough but useful correlation of the results. Of the six interactions between the CH₂, CONH, and CHOH functional groups, the CONH–CONH interaction is the strongest, the CHOH–CHOH interaction is the weakest, and the CH₂–CH₂ interaction is about equal in magnitude to the rest of the interactions. Thus, the CH₂–CH₂ and CONH–CONH are not the only interactions making important contributions to the enthalpy of a wide variety of systems.     

Interactions of D-Maltose and Sucrose with Some Amino Acids in Aqueous Solutions

Calorimetric titrations have been performed at 298.15 K in aqueous solutions to derive the stability constants and thermodynamic parameters of the interactions of D-maltose and sucrose with some amino acids (glycine, DL-alanine, DL-leucine, and L-serine). The apparent molal volumes of the disaccharides in dilute aqueous solutions of the amino acids have been determined from density measurements at 298.15 K. In contrast to D-maltose, sucrose was found to associate with the amino acids and these associated species are preferentially entropy stabilized. These results are interpreted in terms of the influence of the nature of the solutes, their specific conformations, and hydration, on the ability of the disaccharides to form associated complexes with the amino acids.     

Activity coefficients of DL-valine in aqueous solutions of KCl at 25°C. Measurement with ion selective electrodes and modelling

Electrochemical cells with two ion selective electrodes, a cation and an anion ion selective electrode, versus a double junction reference electrode were used to measure the activity coefficients of DL-valine at 298.15 K, up to 0.5 molality, in aqueous solutions of KCl up to 1.0 molality. The results obtained in this work are compared with those reported before for the activity coefficients of DL-valine in aqueous solutions of NaCl. The experimental data were correlated using the model proposed previously by Khoshkbarchi and Vera for the activity coefficients of amino acids in aqueous electrolytes solutions.