Enthalpy and entropy interaction parameters of sodium chloride with some monosaccharides in water

Dilution enthalpies of sodium chloride and some monosaccharides (glucose, ga-lactose, xylose, arabinose, and fructose) in water and mixing enthalpies of aqueous sodium chloride and these monosaccharide solutions were measured by using an improved precision semimicro-titration calorimeter. Transfer enthalpies of sodium chloride from water to aqueous saccharide solutions were evaluated as well as enthalpy interaction parameters of sodium chloride with these monosaccharides in water. Combined with Gibbs energy interaction parameters, entropy interaction parameters were also obtained. The results show that interactions of the saccharides with sodium chloride depend on the stereochemistry of saccharide molecules. These interaction parameters can identify stereochemical structure of saccharide molecules.     

Solvation of Tetraethyl- and Tetrabutylammonium Bromides in Aqueous Acetone and Aqueous Hexamethyl Phosphoric Triamide Mixtures in the Water-Rich Region

The enthalpies of solutions of tetraethylammonium and tetrabutylammonium bromides in the water-rich region of the water–acetone and water–hexamethyl phosphoric triamide mixed solvents have been measured at 25°C using a precise calorimetry system. The enthalpies of electrolyte solutions at infinite dilution were calculated using the Debye–Hückel theory. The enthalpies of solute transfer from water to the mixtures with acetone and hexamethyl phosphoric triamide were calculated. The enthalpy coefficients of solute–pair interactions with hexamethyl phosphoric triamide and acetone in aqueous solution were obtained using the McMillan–Mayer formalism. The values obtained were compared with those for other organic cosolvents. It was found that in aqueous solution the solutes show a strong tendency for hydrophobic interaction with cosolvent molecules, particularly in the water–hexamethyl phosphoric triamide system.     

Enthalpic interactions of -alanine and -serine in aqueous urea solutions

The enthalpies of dilution of -alanine and -serine in various aqueous urea solutions have been determined by flow microcalorimetry at 298.15 K. The homogeneous enthalpic interaction coefficients over the whole range of aqueous urea solutions have been calculated according to the excess enthalpy concept. The results were interpreted from the point of view of solute–solute interactions moderated by solvent effects.     

Thermodynamic Study of the Solubility of Some Sulfonamides in Octanol, Water, and the Mutually Saturated Solvents

The free energy, enthalpy and entropy of solution, were evaluated from solubility data for a group of sulfonamides from 25 to 40°C in octanol, water, and the mutually saturated solvents. In aqueous media, the solubility was determined at the isoelectric point and ionic strength 0.15 mol-L^–1. The excess free energy and the activity coefficients of the solutes also were determined. The results are discussed in terms of solute–solvent interactions.     

Molecular Dynamics Simulation of Aqueous Solutions Using Interaction Energy Components: Application to the Solvation Gibbs Energy

Molecular dynamics simulations of aqueous solutions of the solutes acetamide (AcNH₂), acetic acid (AcOH), and acetaldehyde (AcH) were made using Lennard–Jones 12-6-1 potentials to describe the solute–solvent interactions. The Morokuma decomposition scheme and the ESIE solute atomic charges were used to reproduce the exchange, polarization, and electrostatic components of the solute–water interaction energy. A nonlinear perturbation was incorporated into the “slow-growth” technique in order to improve the results for the solvation Gibbs energy that were found to be in agreement with the available experimental and theoretical values.     

Heats of Mixing of Aqueous Solutions of Alkali Metal Salts of Substituted Benzenesulfonic Acids

The enthalpy change on mixing aqueous solutions of substituted benzene sulfonic acids and their salts, with salts having a common cation or anion, were measured at constant total ionic strength and at 25°C. The results are qualitatively interpreted in terms of solute–water structural properties and the ion size effect. The heat effects of mixing solutions having common anions obey the sign rule of Young and Smith. In anion–common cation mixings at concentration of 0.5 mol-kg^–1 only exothermic heat effects were observed, whose magnitude increase with the increasing difference in size of the mixed anions. The magnitude of the mixing effect increased with the salt concentration in cation–common anion mixing processes, In anion–common cation mixings the enthalpy of mixing changes sign from negative to positive, indicating a predominantly endothermic effect as concentration increases.     

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.     

Excess enthalpies of aqueous ternary solutions of urea and polyols at 25°C

The heats of dilution of nine ternary solutions of urea and polyols have been determined at 25°C. Excess enthalpies and their virial coefficients h _xy have been evaluated and compared with the data reported in the literature for mono- and polyfunctional alcohols and other oxygenated nonelectrolytes. The group additivity approach of Savage and Wood was applied and the contributions to the enthalpy coefficients, due to the water mediated interactions between urea and the functional groups –CH₂–, –OH, and –O– were determined. On the other hand, by using empirical combination rules among the cross- and self-enthalpic interaction coefficients it is possible to emphasize the large differences in the behavior (even in the presence of urea) of the polyols (and in particular of cyclitols) and of saccharides.     

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.     

Osmotic and activity coefficients of glycine, dl-α-alanine and dl-α-aminobutyric acid in aqueous solutions at temperatures between 288.15 and 303.15 K

The osmotic coefficients of glycine, dl-α-alanine and dl-α-aminobutyric acid in water were measured at 288.15, 293.15, 298.15 and 303.15 K using the isopiestic method. The activity coefficients were calculated for the amino acids and the pairwise free energy for solute–solute interactions were adjusted according to the McMillan–Mayer theory. The osmotic and activity coefficients of amino acids are compared with literature data when they are available and the results are discussed in terms of solute–solute interactions.     

水溶液中氯化铯与糖(D-葡萄糖、D-果糖和蔗糖)相互作用的热力学参数研究(298.15K)

用钾离子选择性电极为测量电极,氯离子选择性电极为参比电极,设计组成无液接电池,用于氯化铯-糖(葡萄糖、果糖及蔗糖)-水三元体系中组分之间弱相互作用的热力学性质研究.通过测量电池的电动势获得氯化铯在糖水溶液中的活度系数,根据Scatchard理论推测出糖在氯化铯水溶液中的活度系数.通过Mcmillan-Mayer理论将体系的过量热力学函数与溶液中溶质的相互作用参数相关联,获得氯化铯与糖在水溶液中相互作用的吉布斯自由能参数及盐效应常数.运用结构相互作用模型、糖的羟基水化效应及色散能理论,探讨体系中溶质-溶质、溶质-溶剂间的相互作用及糖的立体结构和金属离子体积对热力学参数的影响.     

The pH-dependence of preferential solvation as studied by intermolecular homo- and heteronuclear NOE measurements of adenosine in water–trifluoroethanol mixtures

A study of the state of solvation of the adenine ring in adenosine and adenosine 5-monophosphate disodium salt in water and in a (7.5:2.5) water–TFE mixture has been carried out by measurement of homo- and heteronuclear intermolecular NOE enhancements between water or TFE and the aromatic protons of these compounds. The results give evidence of site specificity in solute–solvent interaction for both solvent systems and preferential solvation of the solute by TFE in the water–TFE mixture. Significant pH dependence of these interactions has been discovered.     

Molecular dynamics simulation of acetamide solvation using interaction energy components: Application to structural and energy properties

Molecular dynamics simulation of an aqueous solution of acetamide was performed using Lennard–Jones 12-6-1 potentials to describe the solute–solvent interactions, and TIP3P to describe the water–water interactions. The Morokuma decomposition scheme and the ESIE solute atomic charges were used to reproduce the molecular parameters of the solute–water interaction potential. The results showed that the functions that use the EX-PL-DIS-ES interaction model lead to good values of the structural and energy properties (in particular, the hydration shell and the solvation energies) when they are compared with those from using AMBER-derived parameters, and with the available theoretical and experimental data.     

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.     

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.     

Spectral Studies on Some Pyrimidine Derivatives in Different Solvents

The electronic absorption spectra of 2-aminopyrimidine (compound I), 2-amino-4-methylpyrimidine (compound II), 2-amino-4,6-dimethylpyrimidine (compound III), 2-amino-4,6-dimethoxypyrimidine (compound IV), 4-amino-2,6-dimethylpyrimidine (compound V), and 4,5-diamopyrimidine (compound VI) have been measured in water and in a series of different organic solvents. The solvent effects on the spectra are discussed and the solvent induced spectral shifts are analyzed in terms of different solute–solvent interaction mechanisms, using the multiple linear regression technique.     

Apparent Molar Volumes of Sodium Methylbenzoates in N, N-Dimethyl Formamide–Water Mixtures at 298.15 K

Densities of sodium methylbenzoate (o-, m-, p-) have been measured in dimethyl formamide (DMF)–water mixtures at 298.15 K with an oscillating-tube densimeter. From these densities, apparent molar volumes of sodium methylbenzoates in DMF–H₂O mixtures have been calculated and partial molar volumes at infinite dilution have been evaluated. Substituent and solvent effects on the transfer volumes of each isomer from water to DMF–H₂O mixed solvents have also been obtained. The results are explained in terms of solvent–solvent and solute–solvent interactions.     

Enthalpic Interactions of Amino Acids with Glucose in Aqueous Solutions at 298.15 K

The enthalpies of mixing of aqueous glucose solutions and six kinds of aqueous amino acid solutions (glycine, L-alanine, L-serine, L-valine, L-proline, and L-threonine) and their respective enthalpies of dilution have been determined at 298.15 K using flow microcalorimetry. The experimental data have been analyzed in terms of the McMillan–Mayer model to obtain the heterotactic interaction coefficients. The results have been interpreted from the point of view of solute–solute interactions.     

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.