The Enthalpies of Solution of Tetraethyl- and Tetrabutylammonium Bromides in Aqueous Solutions of Hexamethylphosphorus Triamide at 328.15 K

The heats of solution of Et₄NBr and Bu₄NBr in water and aqueous solutions of hexamethylphosphorus triamide (HMPT) at 328.15 K were measured in a variable-temperature isothermic-shell calorimeter. The standard enthalpies of solution were calculated using the Debye-Hückel second-order theory. The enthalpy parameter of electrolyte—amide pair interactions was determined in terms of the McMillan-Mayer formalism. The processing of the data obtained in this work and previously led us to conclude that heat capacity changes caused by pair interactions of Et₄NBr and Bu₄NBr with HMPT were negative and independent of temperature over a wide temperature range. The methyl and methylene groups interacted with HMPT without heat capacity changes and, consequently, the enthalpies and entropies of their interactions with HMPT were constant over a wide temperature range.     

Solubility and Raman Spectroscopic Study of As(III) Speciation in Organic Compound-Water Solutions. A Hydration Approach for Aqueous Arsenic in Complex Solutions

Solubilities of arsenolite (As₂O₃, cub.) were measured from 22 to 90°C in water–acetone, water–acetic acid, and water—formic acid solutions of compositions ranging from the pure organic compound to pure water. Raman spectra were obtained at ambient temperature on As-containing water–acetic acid and water–acetone solutions. Results show that arsenic solvation by these organic compounds is negligible and hydroxide species dominate As speciation over a wide range of water activity (a_{H 2 O}> 0.01). The solubility data were analyzed using an approach based on stoichiometric hydration reactions. Results show that As₂O₃ solubility can be described as a function of water activity, independently of the nature of the organic compound, by involving two neutral As hydroxide complexes: As(OH)₃ and As(OH)₃·4H₂O. Stability constants derived for these species indicate that hydration weakens with increasing temperature. Calculations using these constants show that at low temperatures the tetrahydrate As(OH)₃·4H₂O is dominant in water-rich solutions; by contrast, in high-temperature crustal fluids, As(OH)₃ becomes the major As species. The proposed hydration model can be used to analyze solubility of arsenic-bearing minerals and arsenic transport in complex H₂O–CO₂—electrolyte solutions encountered in natural and industrial environments.     

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.     

Polymerization of Acrylamide and Copolymerization with Acrylonitrile with AIEt3-Hexamethyl Phosphoric Acid Triamide Complex

The polymerization of acrylamide and its copolymerization with acrylonitrile were investigated with AIEt₃ and AIET₃-hexamethyl phosphoric acid triamide. AIEt₃ initiates the polymerization of acrylamide. The addition of hexamethyl phosphoric acid triamide greatly influences the yields of methanol-insoluble polymer, η_sp/c, and the structure of polymer. Vinyl polymerization is dominant with AIET₃ in the presence of hexamethyl phosphoric acid triamide. On copolymerization of acrylamide with acrylonitrile, the acrylonitrile content in the copolymer increased with the addition of hexamethyl phosphoric acid triamide on AIEt₃.     

Peculiar properties of sodium lodide in alcohols,acetone, and alcohol-water mixtures at lower temperatures

The enthalpies of solution of sodium iodide in methanol, ethanol and acetone and in mixtures of methanol and ethanol with water were measured over wide ranges of electrolyte concentration and temperature. Standard enthalpies of solution, transfer enthalpies of NaI from alcohols to alcohol-water mixtures, and temperature coefficients of enthalpies of solution have been calculated. Thermodyanmic characteristics of solution and solvation of the Na⁺ and I^– ions in acetone and ethanol were determined at 243–298 K. It is noted that at lower temperatures the disruption of solvent structure by ions is a local effect. The presence of negative solvation of the Na⁺ and I^– ions in alcohol-water mixtures at lower temperatures is demonstrated.     

丝氨酸在醇-水溶液中的溶解焓

用RD-496III双热流精密微热量计测量了L-丝氨酸在纯水以及异丙醇、1,2-丙二醇和丙三醇水溶液中的溶解焓, 并计算了从水到醇-水溶液中的迁移焓. 实验发现, L-丝氨酸在水及醇-水溶液中的溶解焓都是正值, 它从水到醇-水溶液中的迁移焓也都是正值, 并且基本上随着醇浓度的增加而增加, 说明在溶解过程中, 溶质与混合溶剂分子的部分去水化吸热过程占主要地位. 另外, 实验还发现L-丝氨酸从水到异丙醇水溶液中的迁移焓大于在1,2-丙二醇水溶液中的, 更大于在丙三醇水溶液中的, 这是由于羟基的减少导致了疏水-亲水作用的增加和亲水-亲水作用的减弱.     

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.     

Formation Enthalpies of Water–n-octane–1-propanol–sodium Dodecyl Sulfate Microemulsions at 298.15 K

The solution enthalpies of water–n-octane–1-pentanol (PeⁿOH)–sodium dodecyl sulfate (SDS) microemulsions and their components in 2-propanol at 298.15 K were determined by the thermochemical method at fixed mass fractions of PeⁿOH (0.1450) and SDS (0.0775). The formation enthalpies of microemulsions were calculated using the thermochemical cycle, and it was shown that their values are positive. The results obtained indicate that the intercomponent interactions in the investigated systems are rather weak. The formation of thermodynamically stable microemulsions is determined by entropy changes associated with the disintegration of water and 1-pentanol homoassociates.     

甘氨酸从水到有机物水溶液的迁移焓研究

蛋白质是各种生物形态结构和生命活动所依赖的物质基础,在水溶液中蛋白质天然结构的稳定性归结于氨基酸残基之间以及与溶液中其它组分的相互作用．天然环境中存在的众多物质对蛋白质的溶解度、变性行为和解缔等都有很大的影响．为深入了解蛋白质折叠与解折叠过程中的物理化学现象,以氨基酸、肽、酰胺及其衍生物作为蛋白质模型分子的热力学研究引起了广泛重视．     

Calorimetric Investigations of Complex Formation of 2,3,4,5,6-Pentafluoroaniline with Proton Acceptors in CCl4

Abstract

Solution enthalpies of 2,3,4,5,6-pentafluoraniline in CCl₄ as well as in the solutions of tetrahydrofuran and hexamethylphosphoric triamide have been measured. From the obtained data and spectroscopically determined equilibrium constants the enthalpies of the complex formation of 2,3,4,5,6-pentafluoroaniline with one and two molecules of tetrahydrofuran and hexamethylphosphoric triamide have been calculated. The results yielded from the combination of calorimetric and spectroscopic data have been compared with those obtained using the i.r. method only.     

Enthalpies of solvation in cyclohexane and in water for homologous aliphatic ketones and esters

The standard enthalpies of solution at infinite dilution were determined for homologous aliphatic ketones and esters in water and in cyclohexane, using a rotating Calvet calorimeter, and solution concentrations about 5×10^–4 mole fraction. Vaporization enthalpies, obtained for each compound with an effusion calorimetric cell, were added to calculate the solvation enthalpies. Their dependence on the number of carbon atoms in the chain is discussed in terms of the Friedman and Krishnan treatment. The effect of polarization of the functional groups is evaluated, and separation from the influence of chain length and the hydrophobic interactions of the methylenes is attempted. For the aqueous solutions, the rearrangement in the structure of the solvent around solute molecules is also considered in relation to deviations from linearity. Comparisons are made with solvation enthalpies obtained for ketones and esters with branched or cyclic substitutes.     

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.     

Preferential Solvation in Mixed Solvents X. Completely Miscible Aqueous Co-Solvent Binary Mixtures at 298.15 K

Summary.  The Kirkwood-Buff integrals for 18 completely miscible aqueous co-solvent binary mixtures have been recalculated from thermodynamic data, and the volume-corrected preferential solvation parameters derived from them are presented. Also presented are these latter quantities for 15 additional such mixtures, for which the volume correction has not been applied previously. The self-interaction of the water, the mutual interaction of the water and the co-solvent, and the self-interaction of the co-solvent at infinite dilution derived from these integrals and parameters are then discussed. The systems studied include aqueous hydrogen peroxide, methanol, ethanol, 1- and 2-propanol, 2-methyl-2-propanol, 2,2,2-trifluoroethanol, 1,1,1,3,3,3-hexafluoro-2-propanol, ethane-1,2-diol, glycerol, 2-methoxyethanol (at 313 and 343 K), 2-ethoxyethanol, 2-butoxyethanol, 2-aminoethanol, N-methyl- and N,N-dimethyl-2-aminoethanol, tetrahydrofuran, 1,4-dioxane, acetone, formic, acetic, and propanoic acids, piperidine, pyridine, acetonitrile, formamide, N-methyl- and N,N-dimethylformamide, N-methylacetamide, N-methylpyrrolidin-2-one (at 303 K), hexamethyl phosphoric triamide, dimethylsulfoxide, and tetramethylenesulfone (at 303 K). Received January 10, 2001. Accepted (revised) February 20, 2001     

Solvation enthalpies of formamides and acetamides in a water—glycerol mixture. Additivity of thermochemical characteristics of solutions

The solution enthalpies of formamide and N,N-dimethyl- and diethylamides of formic and acetic acids in a water—glycerol mixed solvent were measured and the solvation enthalpies were calculated. The enthalpy coefficients of amide—glycerol pair interactions in aqueous solution were calculated. The effect of the mixture composition and the structure and properties of solutes on the enthalpic characteristics were considered. The contributions of structural fragments of the amide molecules to the enthalpic characteristics of solutions were calculated in the framework of the proposed additive scheme. This made it possible to analyze the role of nonspecific and specific solvations of the amides in solution and predict the vaporization, solution, and solvation enthalpies and enthalpy coefficients of pair interactions of experimentally unstudied N-methylformamide, N-ethylformamide, N-methyl-N-ethylformamide, N-methylacetamide, N-ethylacetamide, and N-methyl-N-ethylacetamide in a water—glycerol mixture, as well as donor numbers for these amides. Published in Russian in Izvestiya Akademii Nauk. Seriya Khimicheskaya, No. 6, pp. 1363–1370, June, 2005.     

Enthalpies of Dilution of Colchicine in Aqueous NaCl Solutions

The concentration effect on the dilution enthalpies (Δ_dil H _m) of colchicine (COL) in aqueous NaCl solutions has been investigated by isothermal titration microcalorimetry at 298.15 K. The corresponding homogeneous enthalpic interaction coefficients have been calculated according to the excess enthalpy concept. The results show that the dilution enthalpies of COL in aqueous NaCl solutions at different mass fractions are positive. The overall trend is that enthalpies of dilution become more positive with the increase of the salt mass fraction. The values of enthalpic pair-wise interaction coefficients, h ₂, have been obtained by fitting the data of the enthalpies of dilution with a viral expansion. The results can be interpreted from the view of solute-solute and solute-solvent interactions involved in the solvent effects.     

木糖醇在纯水和碱金属卤化物水溶液中的稀释焓

应用等温流动微量热法测定了298.15 K时木糖醇在纯水和碱金属卤化物水溶液中的稀释焓, 根据McMillan- Mayer理论计算了木糖醇在溶液中的二到四阶焓相互作用系数. 结果表明, 木糖醇在碱金属卤盐溶液中的焓对相互作用系数h₂均为正值, h₂值随着碱金属阳离子或卤素阴离子半径的增大皆依次增大. 根据木糖醇参与的溶质-溶质, 溶质-溶剂等弱相互作用, 对该种多元醇在碱金属卤盐水溶液中的焓相互作用系数的变化进行了解释.     

Complex Formation of Crown Ethers with Cations in Water–Organic Solvent Mixtures. III. Thermodynamics of Interaction Between Na+ Ion with 15-Crown-5 Ether in Water–Acetonitrile Mixtures at 25°C

Enthalpies of solution of 15-crown-5 ether in the acetonitrile–water–sodium iodide system have been measured at 25°C. The equilibrium constants of complex formation of 15C5 with sodium iodide have been determined by molar conductance at various mole ratios 15C5 to sodium iodide in mixtures of water with acetonitrile at 25°C. The thermodynamic functions for complexation of the crown ether with Na⁺ were calculated. From the result, the standard Gibbs energies of complex formation as a function of the normalized Lewis acidity parameters E ^N _T and enthalpy of solvation of 15C5 in the mixtures of water with acetonitrile have been analyzed. The enthalpies of transfer of the 15C5 complex with sodium iodide from pure acetonitrile to the mixtures studied were calculated and discussed.     

Aqueous solubilities and enthalpies of solution of adenine and guanine

A generator column—liquid chromatographic technique was used to determine the aqueous solubility of adenine from 20 to 30°C, and of guanine from 15 to 40°C. The 95% confidence limits of the solubilities and molar enthalpies of solution at 25°C are: 8.7±0.1×10^–3M and 33.5±0.5 kJ-mol^–1 for adenine; 3.9±0.1×10^–5M and 49.2±0.6 kJ-mol^–1 for guanine. the adenine enthalpy value includes a small correction for association in the saturated solutions. The previously undetermined molar enthalpy of the second ionization step of guanine (to form the doubly-charged guanine anion) is estimated from our data combined with other measurements to equal 33.8±2.9 kJ-mol^–1.     

Enthalpies of Dilution of Aqueous Solutions of NaOH, KOH, and CsOH at 300, 325, and 350°C

Dilution enthalpies, measured using isothermal flow calorimetry, are reported for aqueous solutions of KOH and CsOH at 300°C and 11.0 MPa, 325°C and 14.8 MPa, and for aqueous solutions of NaOH, KOH, and CsOH at 350°C and 17.6 MPa. Previously collected dilution enthalpies for aqueous solutions of NaOH at 300°C and 9.3 MPa and at 325°C and 12.4 MPa were included when fitting the Pitzer parameters. The concentration range of the hydroxide solutions was 0.5–0.02 molal. Parameters for the Pitzer excess Gibbs ion-interaction equation were determined from the fits of the experimental heat data. Equilibrium constants, enthalpy changes, entropy changes, and heat capacity changes for alkali metal ion association with hydroxide ion were estimated from the heat data. For all systems, the enthalpy changes and entropy changes were positive and had accelerating increases with temperature. The resulting equilibrium constants show significant, but smaller, increases with temperature.     

Flame Emission Spectroscopy of Aqueous and Nonaqueous Solutions in the Nitrous Oxide-Acetylene Flame

Abstract

The relative emission intensities and detection limits for 183 lines and bands of 52 elements in the nitrous oxide-acetylene flame have been determined. Linearity of the emission intensity with concentration was investigated and detection limits of the elements in 80 percent acetone were also obtained and compared with those of aqueous solutions. Emission was observed for all the elements in acetone solution, and only selenium did not give a measureable emission in aqueous solution.