Solubilities of imidazolium-based ionic liquids in aqueous salt solutions at 298.15 K

The solubilities of ionic liquids in the ternary systems (ionic liquid + H₂O + inorganic salt) were reported at 298.15 K and atmospheric pressure. The examined ionic liquids are [C₄mim][PF₆] (1-n-butyl-3-methylimidazolium hexafluorophosphate), [C₈mim][PF₆] (1-n-octyl-3-methylimidazolium hexafluorophosphate), and [C₈mim][BF₄] (1-n-octyl-3-methylimidazolium tetrafluoroborate). The examined inorganic salts are the chloride-based salts (sodium chloride, lithium chloride, potassium chloride, and magnesium chloride) and the sodium-based salts (sodium thiocyanate, sodium nitrate, sodium trifluoroacetate, sodium bromide, sodium iodide, sodium perchlorate, sodium acetate, sodium hydroxide, sodium dihydrogen phosphate, sodium phosphate, sodium tetrafluoroborate, sodium sulfate, and sodium carbonate). The effects of the cations and the anions of the ionic liquids and of the inorganic salts on the solubility of the ionic liquids in the ternary solutions were systematically compared and discussed.     

Thermodynamic properties of ibuprofen sodium salt in aqueous/urea micellar solutions at 298.15 K

Thermodynamic, surface and micellar properties of anti-inflammatory drug sodium 2-(4-isobutylphenyl) propionate (sodium salt of ibuprofen (NaIBF)) in aqueous/urea solution were studied by surface tension measurements at 298.15 K in the presence of anionic surfactant sodium dodecylsulfate (SDS). Critical micelle concentration (cmc), surface tension at cmc (γcmc), maximum Gibbs surface excess (Γ_max), minimum surface area per surfactant molecule at the air/water interface (A _min) etc. were determined in pure water as well as in aqueous urea solution. The theories of Clint, Rosen and Rubingh have been applied to describe the interactions between these amphiphiles at the interface and in the micellar solution. Various thermodynamic parameters have been calculated and discussed in detail.     

Standard enthalpies of dissolution of L-tryptophan and the formation of its dissociation products in aqueous solutions at 298.15 K

The enthalpies of dissolution of crystalline L-tryptophan in water and in potassium hydroxide solutions at 298.15 K are determined via direct calorimetry. The standard enthalpies of formation of the amino acid and its dissociation products in aqueous solution are calculated.     

Dissociation constants of phosphoric acid in dimethylformamide-water mixtures at 298.15 K

The dissociation constants of phosphoric acid (pK ₁ and pK ₂) in water-dimethylformamide (DMFA) mixtures (0–0.65 mole fractions of DMFA) were determined at 298.15 K by potentiometric titration. The extrapolation of these data to pure DMFA and the comparative calculation method were used to estimate the dissociation constants of the acid in DMFA.     

水溶液中八种氨基酸与尿素的焓相互作用

用LKB-2277精密微热量计测定了298.15K时甘氨酸、L-丙氨酸、L-丝氨酸、L-脯氨酸、L-羟脯氨酸、L-蛋氨酸、L-苏氨酸和L-缬氨酸分别与尿素在水溶液中的混合过程焓变,根据McMillan-Mayer理论关联得到各组焓作用系数,并运用基团贡献法探讨了不同氨基酸与尿素分子的相互作用机制。结果表明,氨基酸的两性离子部分及α-碳上的非极性脂肪侧基、极性的羟基侧基和五元吡咯环侧基等对焓对作用系数具有不同的贡献。     

Density and activity of pertechnetic acid aqueous solutions at T = 298.15 K

The previous isopiestic investigations of HTcO₄ aqueous solutions at T = 298.15 K are believed to be unreliable, because of the formation of a ternary mixture at high molality. Consequently, published isopiestic molalities for aqueous HTcO₄ solutions at T = 298.15 K were completed and corrected. Binary data (variation of the osmotic coefficient and activity coefficient of the electrolyte in solution in the water) at T = 298.15 K for pertechnetic acid HTcO₄ were determined by direct water activity measurements. These measurements extend from molality m = 1.4 mol · kg⁻¹ to m = 8.32 mol · kg⁻¹. The variation of the osmotic coefficient of this acid in water is represented mathematically. Density variations at T = 298.15 K are also established and used to express the activity coefficient values on both the molar and molal concentration scale. The density law leads to the partial molar volume variations for aqueous HTcO₄ solutions at T = 298.15 K, which are compared with published data.     

Thermodynamic models of aqueous solutions containing inorganic electrolytes and dicarboxylic acids at 298.15 K. 2. Systems including dissociation equilibria

Atmospheric aerosols contain a significant fraction of water-soluble organic compounds, including dicarboxylic acids. Pitzer activity coefficient models are developed, using a wide range of data at 298.15 K, for the following systems containing succinic acid (H(2)Succ) and/or succinate salts: [H(+), Li(+), Na(+), K(+), Rb(+), Cs(+)]Cl(-)-H(2)Succ-H(2)O, HNO(3)-H(2)Succ-H(2)O, H(+)-NH(4)(+)-HSucc(-)-Succ(2-)-NH(3)-H(2)Succ-H(2)O, NH(4)Cl-(NH(4))(2)Succ-H(2)O, H(+)-Na(+)-HSucc(-)-Succ(2-)-Cl(-)-H(2)Succ-H(2)O, NH(4)NO(3)-H(2)Succ-H(2)O, and H(2)SO(4)-H(2)Succ-H(2)O. The above compositions are given in terms of ions in the cases where acid dissociation was considered. Pitzer models were also developed for the following systems containing malonic acid (H(2)Malo): H(+)-Na(+)-HMalo(-)-Malo(2-)-Cl(-)-H(2)Malo-H(2)O, and H(2)Malo-H(2)SO(4)-H(2)O. The models are used to evaluate the extended Zdanovskii-Stokes-Robinson (ZSR) model proposed by Clegg and Seinfeld (J. Phys. Chem. A 2004, 108, 1008-1017) for calculating water and solute activities in solutions in which dissociation equilibria occur. The ZSR model yields satisfactory results only for systems that contain moderate to high concentrations of (nondissociating) supporting electrolyte. A practical modeling scheme is proposed for aqueous atmospheric aerosols containing both electrolytes and dissociating (organic) nonelectrolytes.     

Enthalpies of interaction of glycine with some amides in aqueous solutions at 298.15 K

The dissolution enthalpies of glycine in aqueous solutions of acetamide, N-methylacetamide, N,N-dimethylacetamide, N-ethylformamide, N,N-diethylformamide and N,N-diethylacetamide were measured at 298.15 K. The enthalpic pair interaction coefficients of glycine zwitterion-amide molecules were determined by using standard solution enthalpies of glycine in water and aqueous solutions of amides. The additivity of groups concept of Savage and Wood was used to estimate the contribution of each of the functional groups of the studied amides.     

Enthalpies of dilution of mono-, di- and poly-alcohols in dilute aqueous solutions at 298.15 K

The enthalpies of dilution of aqueous solutions of methanol, ethanol, l-propanol, 2-propanol, 1-butanol, l-pentanol, 1-hexanol, cyclohexanol, 1,3-butanediol, 1,4-butanediol, 2,3-butanediol and poly-alcohol(cyclohexaamylose) have been determined at high dilution as a function of the mole fraction of alcohol at 298.15 K, by a rocking twin-microcalorimeter of the heat-conduction type. A smoothing equation of the enthalpies of dilution against the mole fractions of alcohols are given. The graphical comparison of experimental results with their smoothed values or literature ones, taking into account the dependence of the mole fractions, are also presented. It has been found for the aqueous solutions of shorter n-alcohols than hexanol that at very high dilution, exothermic values of molar enthalpies of dilution from a definite mole fraction of alcohols to infinite dilution with the change of mole fraction is proportional to carbon number of n-alcohols. The molar enthalpies of infinite dilution of aqueous butanediol isomers and 1-hexanol were very large. Molar enthalpies of infinite dilution of aqueous poly-alcohol (cyclohexaamylose) were endothermic. This revised version was published online in August 2006 with corrections to the Cover Date.     

Molar excess enthalpies for aqueous solutions of 2-chloroethanol and 2-bromoethanol at 298.15 K

Heats of mixing for two aqueous solutions of haloalcohols, 2-chloroethanol and 2-bromoethanol, have been measured for the whole composition range at 298.15 K with an LKB 2107 flow calorimeter. The mixing is endothermic for these solution, except for highly water-rich region. The enthalpic virial coefficient has been evaluated from the data in dilute aqueous solution.     

Viscosity of aqueous solutions of poly(ethylene glycol)s at 298.15 K

The viscosities of aqueous solutions of some poly(ethylene glycol)s (PEG) with nominal molecular weights ranging from 300 to 35 000 g mol⁻¹ were determined up to a concentration of 0.3 g cm⁻³ at 298.15 K. From these data the intrinsic viscosity and the viscosity average molecular weight of the solute were calculated. The viscosity coefficients B were evaluated and hence the partial molar Gibbs free energy of activation of viscous flow of solute at infinite dilution was calculated and interpreted in terms of the relative effects of solute on the ground and transition state solvent. The hydration numbers were determined and compared with available values in the literature.     

Dissociation constants of protolytic dissociation of glutamyl-glutamic and glycyl-glutamic acids in aqueous solution at 298 K

Protolytic dissociation constants of stepwise dissociation of glutamyl-glutamic and glycyl-glutamic acids in aqueous solutions at 298.15 K at ionic strengths of 0.1, 0.5, and 1.0 M on the NaCl background were measured by potentiometric titration. The thermodynamic dissociation constants were calculated. Using the obtained and published data, we discuss the effect of additional carboxy groups in the side chains of the molecule on the protolytic dissociation constants of peptides.     

Thermodynamic studies for aqueous solutions involving 18-crown-6 and alkali bromides at 298.15 K

Osmotic vapor pressure measurements have been carried out for three ternary systems, H₂O + 0.2 m 18-crown-6 + NaBr, H₂O + 0.2 m 18-crown-6 + KBr and H₂O + 0.2 m 18-crown-6 + CsBr at 298.15 K using vapor pressure osmometry. The concentration of salts was varied between 0.04 and 0.6 m. The measured water activities were used to calculate the activity coefficient of water, 18-crown-6 and mean molal activity coefficients of ions. The lowering of activity coefficients of one component in presence of other is attributed to the existence of host–guest type complex equilibria in solution phase. The Gibbs transfer free energies, which have been calculated using the activity data, were used to estimate the McMillan–Mayer pair and triplet interaction parameters and are compared with that of alkali chlorides reported recently by us using similar studies. The pair interaction parameters, g_NE (non-electrolyte–electrolyte interaction coefficient), are used to obtain the thermodynamic equilibrium constant values for 18-crown-6:M⁺ complexes, which on comparison with alkali chlorides indicate that the counter anions plays a definite role in stabilizing such complexes in solution phase. Sign and the magnitude of triplet interaction parameters (g_NNE or g_NEE) show that along with electrostatic interactions hydrophobic effects also play an important role in stabilizing the host–guest type complexes.     

Thermodynamics of aqueous solutions of orthophosphoric acid from the freezing point to 298.15°K

The osmotic coefficients of aqueous phosphoric acid have been determined at 298.15°K, at 273.15°K, and at the freezing point, and for concentrations from about 10^?4 m to 15 m. Phosphoric acid is incompletely dissociated even at very low concentrations, but it was possible to derived mean activity coefficients for the species H⁺ and H₂PO ₄ ^? by treating phosphoric acid as a 1-1 electrolyte.     

Stability of nickel(II) glycylglycinate complexes in aqueous solutions of dimethylsulfoxide at 298.15 K

Stability constants of nickel(II) glycylglycinate complexes in aqueous solutions of dimethylsulfoxide of variable composition (from 0.00 to 0.60 mole fractions DMSO) are determined according to potentiometry at 298.15 K and an ionic strength of 0.1 M (NaClO₄). It is determined that with a rise in the concentration of an organic cosolvent in solution, the stability of nickel(II) complexes with glycylglycinate ion on the whole increases, but the logK _stability = f(X _DMSO) dependences are of a critical character with a maximum of 0.3 mole fractions DMSO. It is demonstrated that the rise in the stability of complexes is related to the destabilization of ligands in the low concentration range of the organic component, while the presence of a maximum is due to the different dynamics of the solvation contributions from reagents during changes in the Gibbs energy of reaction.     

Diffusion of sodium alginate in aqueous solutions at T = 298.15 K

Taylor dispersion technique was used for measuring mutual diffusion coefficients of sodium alginate aqueous solutions at T = 298.15 K, by using as carrier stream solution both pure water and solutions of this polyelectrolyte at a slightly different concentration. The limiting values found at infinitesimal ionic strength, D⁰, were determined by extrapolating to c → 0. These studies were complemented by molecular mechanics calculations. From the experimental data, it was possible to estimate both the limiting conductivity and the tracer diffusion coefficient values for the alginate anion, and the hydrodynamic radius of the sodium alginate (NaC₆H₇O₆), as well as to discuss the influence of the kinetic, thermodynamic and viscosity factors on the diffusion of sodium alginate in aqueous solutions at finite concentrations. Thus, the aim of our innovative research is to contribute to a better understanding of the structure and the thermodynamic behavior of these polymeric systems in solution and supplying the scientific and technological communities with data on these important parameters in solution transport processes.     

Determination of acid dissociation constants by capillary electrophoresis

Capillary electrophoresis affords a simple, automated approach for the measurement of pKa values in the range 2-11 at a throughput of less than 1 h per sample per instrument. Agreement with literature values is usually within 0.20 log units with a precision better than 0.07 log units. The attractive features of capillary electrophoresis for pKa measurements are: (1) conventional instrumentation with a high level of automation are suitable for all measurements; (2) because it is a separation method samples need not be of high purity; (3) samples of low water solubility with suitable chromophores are easily handled (detection limits in the microM range); (4) sample consumption per measurement is in the microgram range; and (5) since only mobilities are measured, exact knowledge of concentrations is not needed. The general approach can be extended to pKa measurements in aqueous-organic solvent mixtures and non-aqueous solvents with suitable calibration. The widespread use of absorbance detection in capillary electrophoresis means that the sample must have a suitable chromophore for detection. The main source of controllable error is the accuracy of buffer standardization and their stability in use, and uncontrollable error, the retentive interactions of the sample with the column wall. The latter seems to be a rare problem in practice for typical operating conditions.     

Conductivity studies on some alkali metal iodides in aqueous N,N-dimethylformamide solutions at 298.15K

Summary Conductance measurements for NaI, KI, RbI, and CsI in water/N,N-dimethylformamide mixtures over the whole composition range at 298.15K are reported. The data were analyzed employing theFuoss-Justice equation in terms of limiting molar conductances (_o),Walden products (_o), and association constants (K _A). The results indicate that the salts are weakly associated in the above solvent mixture. Variation in theWalden products with solvent composition are briefly discussed. The results were also compared with values reported previously for some alkali metal chlorides and bromides.

---

Untersuchungen zur elektrischen Leitfähigkeit einiger Alkalimetalliodide in wäßrigen N,N-Dimethylformamidlösungen bei 298.15K

Zusammenfassung Die elektrische Leitfähigkeite von NaI, KI, RbI und CsI wurde in N,N-Dimethylformamid-Wasser-Mischungen verschiedener Zusammensetzung bei 298.15K gemessen. Die erhaltenen Daten wurden analysiert und bezüglich der Grenzäquivalenzleitfähigkeiten (_o), derWalden-Produkte (_o) und der Assoziationskonstanten (K _A) ausgewertet. Die Ergebnisse zeigen, daß diese Salze in den verwendeten Lösungsmittelgemischen nur schwach assoziiert sind. Die Änderungen derWalden-Produkte in Abhängigkeit der Lösungsmittelzusammensetzung werden kurz diskutiert. Abschließend werden die Resultate mit Ergebnissen früherer Messungen, in denen das Verhalten von Alkalimetallchloriden und Alkalimetallbromiden untersucht wurde, verglichen.

     

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.     

The chemical stability of L-isoleucine,L-threonine,and L-serine in aqueous solutions of KCl at 298.15 K

The experimental saturated solubilities of L-isoleucine, L-threonine, and L-serine in aqueous mixtures of a KCl solution at 298.15 K are presented in this article. The solubilities are measured by gravimetric method. In the present study the theoretical calculation of the standard transfer Gibbs free energy, cavity forming enthalpy of transfer, cavity forming transfer Gibbs free energy, dipole-dipole interaction effect have been computed. The chemical effects of the transfer Gibbs energies for the present amino acids have been obtained by subtracting the cavity effects and dipole-dipole interaction effects from the ΔG_t⁰(i). The stability of the experimental amino acids in aqueous KCl in terms of thermodynamic parameters is explained.