Thermochemic properties of NaCl and KCl solutions in mixtures of water with N,N-dimethylacetamide at 25°

Enthalpies of solution of NaCl and KCl in water- N, N-dimethylacetamide (DMA) mixtures (containing 0–20 mol.% of DMA) were measured at 25 ° C. The standard dissolution enthalpies for both investigated salts increase with increase in DMA content in the mixed solvent, in contrast with the dissolution enthalpies for other inorganic salts in the same mixtures examined so far. The calculated single-ion transfer enthalpies from water to water-DMA mixtures exhibit the opposite course with a distinct minimum for anions and a maximum for cations. The extrema of the ionic transfer enthalpies observed in all water-organic mixtures investigated thus far seem to be a consequence of the shape of the solvation enthalpy curves for Ph₄P⁺ and BPh₄⁻ ions which are the basis for the calculation of individual ionic contributions and which are hydrophobically hydrated in water-organic solvents.     

苯甲酸在醇-水混合物中溶解和离解的焓和熵

羟基化合物水溶液,尤其是一元醇与水的混合物在许多领域都有重要应用.其溶液性质常常显示出异常的特征,如粘度-组成曲线出现极大值[1]等.单靠氢键的概念已不能很好解释所观察到的许多特异性质.一般认为这类特殊性质来源于溶液结构.但到目前为止,对这类体系的结构性质的认识仍然比较模糊.焓、熵等热力学性质可以验证诸如用ＮＭＲ谱[2]、近红外差示光谱[3]等实验手段所得到的结果.实际上,热力学性质提供了一个简单可靠的结构“探针”[4,5].本文选择苯甲酸作为研究对象,测定它在乙醇水和异丙醇水两种混合溶剂中的溶解焓和离解焓,并结合文献报导…     

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.     

Enthalpies of dissolution of propylene carbonate,acetonitrile, and 1,4-dioxane in mixtures of water with acetone or dimethyl sulfoxide

Enthalpies of dissolution of acetonitrile, propylene carbonate, and 1,4-dioxane in mixtures of water with acetone or DMSO were measured in the whole concentration range of the mixed solvents. Standard enthalpies of dissolution and enthalpies of transfer of solutes from water to its mixtures with acetone or DMSO were determined. In the region of small proportions of the nonaqueous component, the enthalpy of cavity formation in the mixed solvent makes the main contribution to the variation of the enthalpy of dissolution. An increase in the proportion of the nonaqueous component leads to competition between the contributions of cavity formation and specific interaction between the solute and the solvent during solvation.Translated fromIzvestiya Akademii Nauk. Seriya Khimicheskaya, No. 9, pp. 1747–1752, September, 1995.     

Standard enthalpies of dissolution of L-alanine in the water solutions of glycerol, ethylene glycol, and 1,2-propylene glycol at 298.15 K

The integral enthalpies of dissolution Δ_sol H ^m of L-alanine in mixtures of water with glycerol, ethylene glycol, and 1,2-propylene glycol under the concentration of organic solvents up to 0.32 mole fraction were measured by means of calorimetry. The standard values of the dissolution enthalpies (Δ_sol H ^o) and transfer enthalpies (Δ_tr H ^o) of amino acids from water to the mixed solvent were calculated. It was shown that the calculated enthalpic coefficients of pair interactions of L-alanine with cosolvent molecules have positive values. The data obtained are interpreted from the viewpoint of prevalence of different types of interactions in the solutions and influence of the cosolvents nature on the thermo-chemical characteristics of amino acid dissolution.     

Enthalpy characteristics of L-proline dissolution in certain water–organic mixtures at 298.15 K

A thermochemical study of the processes of L-proline dissolution in aqueous solutions of acetonitrile, 1,4-dioxane, acetone, dimethyl sulfoxide, nitromethane and tetrahydrofuran at Т = 298.15 K in the range of organic solvent concentrations x₂ = 0–0.25 mole fractions is performed. Standard values of the enthalpies of solution and transfer of L-proline from water to mixed solvent, and the enthalpy coefficients of pairwise interactions between L-proline and molecules of organic solvents, are calculated. The effect the composition of a water–organic mixture and the structure of organic solvents have on the enthalpy characteristics of L-proline dissolution and transfer is examined. The effect the energy properties of intermolecular interactions between components of a mixed solvent has on the intermolecular interactions between L-proline and molecules of cosolvent is estimated. The correlation between the enthalpy characteristics of L-proline dissolution and electron-donor properties of organic cosolvent in aqueous solutions is determined.     

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.     

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.     

Thermodynamic Parameters of the Dissolution of 4-Hydroxy-L-Proline and L-Phenylalanine in Mixed Aqueous Solvents at 298 K

The enthalpies of solution of 4-hydroxy-L-proline and L-phenylalanine in binary mixed aqueous solvents containing acetonitrile (AN), 1,4-dioxane (1,4-DO), or acetone (AC) at mole fractions of 0 to 0.25 are determined at T = 298.15 K via isothermal calorimetry. The standard enthalpies of solution (Δ_solH°) and transfer (Δ_trH°) of 4-hydroxy-L-proline and L-phenylalanine from water to mixed aqueous solvents are calculated using the experimental calorimetric data, as are the enthalpy coefficients of paired interactions (h _xy ) between the molecules of the investigated amino acids and the organic solvents. The effects the mixed aqueous solvent composition and the structure of the organic solvent molecules have on the enthalpies of solution and transfer for the investigated amino acids are considered. The correlation between the enthalpy of solution of the amino acids and the electron-donating properties of the organic solvents in the mixed aqueous solvent systems is established.     

Effect of Tryptophan and Asparagine Structure on the Enthalpic Characteristics of Their Dissolution in Aqueous Solutions of Sodium Dodecyl Sulfate

The integral enthalpies of dissolution of L-tryptophan and L-asparagine in aqueous solutions of sodium dodecyl sulfate (surfactant) at surfactant concentrations of up to 0.05 mol/kg of the solvent are determined and estimated calorimetrically. Standard values of the enthalpies of dissolution and transfer of amino acids from water to a mixed solvent are calculated. The calculated enthalpy coefficients of pair interactions between amino acids and surfactant molecules have positive values. Hydrophobic interactions between amino acids and surfactants have the dominant effect on the enthalpy characteristics of the interaction in a three-component solution.     

Thermochemistry of glycyl-<Emphasis Type="Italic">DL</Emphasis>-α-alanine dissolution in water-alcohol solutions at 298.15 K

Integral enthalpies of glycyl-DL-α-alanine dissolution in aqueous solutions of ethanol, 1-propanol, and 2-propanol at concentrations of alcohols up to 0.4 mol fraction were measured by the calorimetry method. Standard values of the enthalpies of the peptide dissolution Δ_sol H ⁰ and transfer Δ_tr H ⁰ from water in mixed solvents were calculated. Dependences of the thermochemical characteristics of glycyl-DL-α-alanine dissolution on the concentration of cosolvents are of an extreme character. Within the limits of McMillan-Mayer’s theory enthalpy coefficients of pairwise interactions (h _xy ) of the studied compound with molecules of alcohols were calculated. They have positive values increasing in the series ethanol, 1-propanol, 2-propanol. The effect of the structure of dipeptides and composition of water-alcohol solvents on the dissolution enthalpy characteristics was considered on the basis of the obtained experimental and calculated data.     

Enthalpies of glycylglycinate ion transfer from water to water-dimethyl sulfoxide solvent

The thermal effects of sodium glycylglycinate dissolution are determined calorimetrically at 298.15 K, and the enthalpies of glycylglycinate ion transfer from water to water-dimethyl sulfoxide solvent are calculated for compositions between 0.00 and 0.99 mole fractions of dimethyl sulfoxide. It is shown that when the concentration of the nonaqueous component is increased, the endothermicity of glycylglycinate ion transfer in the solution is considerably enhanced, weakening the solvation of anions.     

Enthalpies of solvation for dopamine hydrochloride in water-ethanol solutions

The enthalpies of dissolution of dopamine hydrochloride (H₂Dop · HCl) in water-ethanol solvents containing from 0 to 0.8 mole fraction of ethanol are measured by calorimetry at 298.15 K. Standard enthalpies of transfer (??_tr H ^°) for the molecular (H₂Dop) and cationic (H₃Dop⁺) forms of dopamine from water into binary solvents are calculated from the obtained data. The enthalpies of transfer of H₃Dop⁺ cation are determined from the enthalpies of dissolution of H₂Dop · HCl using the familiar method of separating the molar quantities into ionic contributions (Ph₄P⁺ = BPh ₄ ^? ), and by an original alternative procedure. The effect of the composition of the binary solvent on the solvation of dopamine is considered.     

Thermochemistry of Aniline Solution in Binary Mixtures Water-Aprotic Solvent

Enthalpies of aniline solution in mixed solvents water-1,4-dioxane, water-acetone, and waterdimethyl sulfoxide at 25°C were determined within entire ranges of their compositions. The enthalpies of its solvation and transfer from water into mixed solvents, and also contributions of hydrocarbon radicals and functional groups to these quantities were calculated. Effects of composition and properties of the mixtures on the aniline thermochemical characteristics in solutions were considered.     

The thermodynamic properties of solutions of L-ascorbic acid in dimethyl sulfoxide and water-dimethyl sulfoxide mixtures

Solutions of L-ascorbic acid (AA) in dimethyl sulfoxide (DMSO) and DMSO-water mixtures were studied by the densitometry, surface tension, and calorimetry methods. The apparent and partial molar volumes of AA in solutions at 298.15 K were calculated. Surface tension insignificantly increased as the concentration of AA in DMSO grew. The enthalpies of solution of AA in the solvents and the enthalpies of transfer of AA from water into DMSO and DMSO-water mixed solvents were calculated. The results obtained were explained by the existence of H-bonds between AA and DMSO molecules.     

Thermochemistry of electrolyte solutions

The results of calorimetric investigations of electrolyte solutions in the mixtures of water, methanol, N,N-dimethylformamide, and acetonitrile with numerous organic cosolvents are discussed with regard to the intermolecular interactions that occur in the solution. Particular attention is given to answer the questions how and to what extent the properties of the systems examined are modified by the cosolvent added and how much the properties of the cosolvent are revealed in the mixtures with the solvents mentioned above. To this goal, the analysis of the electrolyte dissolution enthalpies, single ionic transfer enthalpies, and enthalpic pair interaction coefficients as well as the preferential solvation (PS) model are applied. The analysis performed shows that in the case of the dissolution enthalpies of simple inorganic electrolytes in water–organic solvent mixtures, the shape of the dependence of the standard dissolution enthalpy on the mixed solvent composition reflects to a large extent the hydrophobic properties of the organic cosolvent. In the mixtures of methanol with organic cosolvents, the ions are preferentially solvated either by methanol molecules or by molecules of the cosolvent, depending on the properties of the mixed solvent components. The behavior of inorganic salts in the mixtures containing N,N-dimethylformamide is mostly influenced by the DMF which is a relatively strongly ion solvating solvent, whereas in acetonitrile mixtures, the thermochemical behavior of electrolyte solutions is influenced to a large extent by the properties of the cosolvent particularly due to the PS of cation by the cosolvent molecules.     

Enthalpies of transfer of N-methylformamide,formamide, and N,N-dimethylformamide from methanol to methanol+dimethylsulfoxide mixtures

The enthalpies of transfer of formamide, N-methylformamide and N,N-dimethylformamide from methanol to methanol+dimethylsulfoxide solvent systems have been measured. These data are analysed in terms of a recently developed model of solvation in mixed solvents. The results of the data analyses indicate that preferential solvation of the different functional groups of the amides differs, the carbonyl oxygen being preferentially solvated by methanol and the nitrogen protons are by dimethylsulfoxide.     

Thermochemistry of 1-bromoadamantane in binary mixtures of water-aprotic solvent

Solution enthalpies of 1-bromoadamantane in the mixed solvents water-N,N-dimetylformamide, water-N,N-dimethylacetamide and water-acetone were determined at 298.15 K, within the range of solubility of 1-bromoadamantane (1-BrAd) in the mixed solvents. The solution enthalpy of 1-bromoadamantane in water was determined based on extrapolation from the three mixtures. Enthalpies of transfer from the mixed solvents to cyclohexane were calculated. The effect of the composition of the mixtures on the thermochemical values obtained was also investigated.     

1,3,3-三硝基氮杂环丁烷在乙酸乙酯和N,N-二甲基甲酰胺中的溶解行为

在常压、298.15 K条件下, 用RD496-2000微热量仪分别测量了1,3,3-三硝基氮杂环丁烷(TNAZ)在乙酸乙酯(EA)和N,N-二甲基甲酰胺(DMF)中的溶解焓. 得到了TNAZ在不同溶剂中的微分溶解热和积分溶解热. 建立了热量与溶质的量之间的关系式. 对TNAZ, 得到了在乙酸乙酯中描述溶解过程的动力学方程为dα/dt=10-7.26(1-α)0.88; 在N,N-二甲基甲酰胺中, 描述溶解过程的动力学方程为dα/dt=10-7.21(1-α)0.66.     

Thermodynamic characteristics,structure, and interactions of L-proline in aqueous solutions of alcohols and urea

The enthalpies of dissolution of imino acid L-proline in aqueous solutions of methanol, 2-propanol, ethylene glycol, glycerin, and urea are measured by the calorimetric method at 313.15 K. Enthalpic parameters of the interaction of L-proline with nonaqueous components are calculated and compared with the data at 298.15 K. It is found that the sign of the heat capacity parameter of the pair and ternary interactions depends on whether the nonaqueous solvent component is a destroyer or stabilizer of the water structure. Partial molar heat capacities of proline in mixed solvents are obtained by the integral dissolution heat method. Temperature changes in the reduced enthalpy and entropy of the proline solution are determined at an increase in the temperature from 298 K to 313 K. It is shown that there is entropyenthalpy compensation at temperature changes in the characteristics during dissolution.