Interactions of Some Amino Acids with Aqueous N,N-Dimethylacetamide Solutions at 298.15 and 308.15 K: A Volumetric Approach

The apparent molar volumes, V _φ , of glycine, L-alanine and L-serine were obtained in aqueous 0 to ∼4 mol⋅kg⁻¹ N,N-dimethylacetamide (DMA) solutions from density measurements at 298.15 and 308.15 K. The standard partial molar volume, V _φ ^o, and standard partial molar volumes of transfer, Δ_tr V _φ ^o, were determined for these amino acids. It has been shown that hydrophilic-hydrophilic interactions between charged groups of the amino acids and the —CON= group of DMA are predominant in the case of glycine and L-serine, but for L-alanine the interactions between its side group (—CH₃) and DMA are predominant. An increase in temperature increases the standard partial molar volumes but decreases the transfer volumes of the amino acids. The results have been interpreted in terms of cosphere overlap model.     

Partial Molar Volumes of Some of α-Amino Acids in Binary Aqueous Solutions of MgSO4·7H2O at 298.15 K

The apparent molar volume, V ^o _{φ, 2}, of glycine, alanine, α-amino-n-butyric acid, valine and leucine have been determined in aqueous solutions of 0.25, 0.5 and 1.0 mol⋅dm⁻³ magnesium sulfate, and the partial specific volume from density measurements at 298.15 K. These data have been used to calculate the infinite dilution apparent molar volume, V ^o _2,m , group contribution of amino acids and partial molar volume of transfer, Δ_tr V _2,m ^o, from water to aqueous magnesium sulfate solutions. The linear correlation of V _2,m ^o for a homologous series of amino acids has been utilized to calculate the contributions of charged end groups (NH₃ ⁺, COO⁻), CH₂ - groups and other alkyl chains of amino acids to V _2,m ^o. The results for Δ_tr V _2,m ^o of amino acids from water to aqueous magnesium sulfate solutions have been interpreted in terms of ion-ion, ion-polar, hydrophilic-hydrophilic and hydrophobic-hydrophobic group interactions. The values of the standard partial molar volume of transfer for the amino acids with different hydrophobic contents, from water to aqueous MgSO₄ are in general positive, indicating the predominance of the interactions of zwitterionic/hydrophilic groups of amino acids with ions of the salt. The hydration number decreases with increasing concentration of salt. The number of water molecules hydrated to amino acids decreases, further strengthening the predominance of ionic/hydrophilic interactions in this system.     

Thermodynamics of the Interaction of a Homologous Series of Amino Acids with Sorbitol

The apparent molar volumes V _2,φ , apparent molar isentropic compressibilities K _S,2,φ , and enthalpies of dilution of aqueous glycine, alanine, α-amino butyric acid, valine, and leucine have been determined in aqueous 1.0 and 2.0 mol⋅dm⁻³ sorbitol solutions at 298.15 K. These data have been used to calculate the infinite dilution standard partial molar volumes V_2,m⁰V_{2,m}^{0}, partial molar isentropic compressibilities K_S,2,m⁰K_{S,2,m}^{0}, and enthalpies of dilution Δ_dil H ⁰ of the amino acids in aqueous sorbitol, along with the standard partial molar quantities of transfer of the amino acids from water to aqueous sorbitol. The linear correlation of V_2,m⁰V_{2,m}^{0} for this homologous series of amino acids has been utilized to calculate the contribution to V₂⁰V_{2}^{0} of the charged end groups (NH₃⁺\mathrm{NH}_{3}^{+}, COO⁻), the CH₂ group, and other alkyl chains of the amino acids. The results for the standard partial molar volumes of transfer, compressibilites and enthalpies of dilution from water to aqueous sorbitol solutions have been correlated and interpreted in terms of ion–polar, ion–hydrophobic, and hydrophobic–hydrophobic group interactions. A comparison of these thermodynamic properties of transfer suggest that an enhancement of the hydrophilic/polar group interactions is operating in ternary systems of amino acid, sorbitol, and water.     

D<Subscript>2</Subscript>O — H<Subscript>2</Subscript>O Solvent Isotope Effects on the Apparent Molar Volumes of Tetramethyl-<Emphasis Type="Italic">bis</Emphasis>-urea (Mebicarum) Solutions

Densities of solutions of tetramethyl-bis-urea (TMbU) or “Mebicarum” in H₂O and D₂O, with solute mole fraction concentrations (x ₂) ranging up to 3.2 × 10⁻³, have been measured at 288.15, 298.15, 308.15 and 318.15 K using a precision vibrating-tube densimeter. The limiting apparent molar volumes, V _φ,2 ^∞, and expansibilities, E _{p, φ, 2} ^∞, of the solute have been calculated. The isotope effect δ V _φ,2 ^∞(H₂O → D₂O;T) is negative, monotonously decreases in magnitude with temperature and reverses sign at T ≈ 318 K. Water (H₂O, D₂O) and TMbU molecules in infinitely- and highly-dilute aqueous solutions form H(D)-bonded hydration complexes with a high packing density. The hydration of TMbU should be treated as a superposition of two mechanisms, hydrophobic and hydrophilic, with the latter one predominating.     

Volumetric studies of some electrolytes in water and in aqueous sodium dodecylsulfate solutions at different temperatures

Abstract  

The apparent molar volumes (φ _v) of KCl, KNO₃, MgCl₂, and Mg(NO₃)₂ have been determined in water and in aqueous sodium dodecylsulfate solutions from density measurements at 303.15, 308.15, 313.15, 318.15, and 323.15 K. The limiting apparent molar volumes (j_v⁰ \varphi_{v}^{0} ) and experimental slopes (S _v) were derived from the Masson equation. The partial molar volume transfer (\Updelta [`(V)]<sub>\texttr</sub> ) (\Updelta {\bar{V}}_{\text{tr}} ) of the electrolytes were obtained from limiting apparent molar volume data from water to aqueous sodium dodecylsulfate solutions and have been interpreted in terms of ion–ion, hydrophilic–hydrophilic, and hydrophobic–hydrophobic interactions on the basis of a co-sphere overlap model. It is shown that the transfer volumes (\Updelta [`(V)]_\texttr ) (\Updelta {\bar{V}}_{\text{tr}} ) are positive and increase with increasing sodium dodecylsulfate concentration for all electrolytes. The structure making or breaking capacities of the electrolytes have been inferred from the sign of [∂² φ _v⁰/∂T ²]_p, i.e., the second derivative of the limiting apparent molar volume with respect to temperature at constant pressure. In water, KCl and KNO₃ exhibit structure breaking and MgCl₂ and Mg(NO₃)₂ exhibit structure making behavior. All the studied electrolytes were found to act as structure makers in aqueous sodium dodecylsulfate solutions.     

Solution Properties of Ternary D-Glucose + 1-Ethyl-3-methylimidazolium Ethyl Sulfate + Water Solutions at 298.15 K

The effect of an ionic liquid, 1-ethyl-3-methylimidazolium ethyl sulfate ([EMIm]ESO₄), on the thermophysical properties of aqueous D-glucose solutions including density, viscosity, and electrical conductivity have been investigated at 298.15 K. Using these properties, the apparent molar volumes, V _φ , the viscosity B-coefficients and the molar conductivities, Λ _m, have been computed for the ternary D-glucose + [EMIm]ESO₄+water solutions. The V _φ values were used to calculate the standard partial molar volumes, V_f⁰V_{\phi}^{0}, and transfer volumes, D_trV_f⁰\Delta_{\mathrm{tr}}V_{\phi}^{0}, of D-glucose from water to aqueous ionic liquid solutions. These volumetric parameters, for all the solutions studied, are positive and increase monotonically with increasing the concentration of [EMIm]ESO₄. These observations have been interpreted in terms of the interactions between D-glucose and ionic liquid in the aqueous solution. The viscosity data were analyzed in terms of the Jones-Dole equation to determine the values of the viscosity B-coefficients. The calculated conductometric parameters, the limiting molar conductivities, Λ ₀, the association constants, K _a, and the Walden products, Λ ₀ η, for [EMIm]ESO₄, decrease with increasing concentration of D-glucose. This trend suggests that the ions of an ionic liquid do not have the same hydrodynamic size in the presence of D-glucose molecules (ILs) and consequently provides evidence for the dehydration effect of the ionic liquid in aqueous D-glucose solutions.     

Apparent Molar Volume and Isentropic Compressibility for the Binary Systems {Methyltrioctylammonium Bis(trifluoromethylsulfonyl)imide + Methyl Acetate or Methanol} and (Methanol + Methyl Acetate) at <Emphasis Type="Italic">T</Emphasis>=298.15, 303.15, 308.15 and 313.15 K and Atmospheric Pressure

The densities and speeds of sound for binary mixtures containing the solute ionic liquid (IL) methyltrioctylammonium bis(trifluoromethylsulfonyl)imide ([MOA]⁺[Tf₂N]⁻), solute/solvent methanol, and solvent methyl acetate have been measured at 298.15, 303.15, 308.15 and 313.15 K at atmospheric pressure. The binary mixtures studied are ([MOA]⁺[Tf₂N]⁻ + methyl acetate or methanol), and (methanol + methyl acetate). The apparent molar volume, V _φ and the apparent molar isentropic compressibility, k _φ , have been evaluated from the experimental density and speed of sound data, respectively. The parameters of a Redlich–Mayer type equation were fitted to the apparent molar volume and apparent molar isentropic compressibility data. The apparent molar volume and apparent molar isentropic compressibility at infinite dilution, V_f⁰V_{\phi}^{0} and k_f⁰k_{\phi}^{0}, respectively, of the binary solutions have also been calculated at each temperature. The infinite dilution apparent molar volume indicates that intermolecular interactions for (IL + methyl acetate) mixtures are stronger than for (IL + methanol) mixtures at all temperatures except at 298.15 K, and that V_f⁰V_{\phi}^{0} for the (IL + methyl acetate or methanol) binary systems increases with an increase in temperature. For the (methanol + methyl acetate) system the intermolecular interaction are weaker and V_f⁰V_{\phi}^{0} also increases with an increase in temperature. Values of the infinite dilution apparent molar expansibility, E_f⁰E_{\phi}^{0}, indicate that the interaction between (IL + methyl acetate) is greater than for (IL + methanol) and (methanol + methyl acetate).     

Volumetric Properties of Some Aliphatic Mono- and Dicarboxylic Acids in Water at 298.15 K

The apparent molar volumes, V _φ , of two series of homologous aliphatic carboxylic acids, H(CH₂) _n COOH [n=0–5] and (CH₂) _n (COOH)₂ [n=0–5], were determined in dilute aqueous solutions by density measurements at T=298.15 K. Densities were measured using a vibrating-tube densimeter (DMA 5000, Anton Paar, Austria) at T=298.15 K. These results were used to calculate the apparent molar volumes of each solute over the concentration range 0.0050≤m/(mol⋅kg⁻¹)≤0.3000. Values of the apparent molar volumes of undissociated acids V_f(u)⁰V_{\phi (u)}^{0} were also calculated. The variation of V_f(u)⁰V_{\phi (u)}^{0} was determined as a function of the aliphatic chain length of the studied carboxylic acids.     

Study of the Volumetric Properties of the Aqueous Ionic Liquid 1-Methyl-3-pentylimidazolium Tetrafluoroborate

This paper reports the densities of aqueous solutions of the ionic liquid (IL) 1-methyl-3-pentylimidazolium tetrafluoroborate ([pmim][BF₄]) that were measured from 278.15 to 343.15 K, at intervals of 5 K, using an Anton Parr model DMA 4500 oscillating U-tube densitometer. The apparent molar volume, ^φ V _B, and the partial molar volume of [pmim][BF₄], , were calculated. The values of the apparent molar volume, ^φ V _B, were fitted to Pitzer’s model for volumetric properties by the method of least-squares, which allowed the partial molar volume of the IL at infinite dilution, , and Pitzer’s parameters, β _M,X ^(0)V and β _M,X ^(1)V , to be obtained. The small standard deviations of the fits show that Pitzer’s model is also appropriate for representing the volumetric properties of aqueous solutions of the ionic liquid [pmim][BF₄].     

Volumetric Properties of Amino Acids in Aqueous N-methylacetamide Solutions at 298.15 K

The apparent molar volumes (V _φ ) of glycine, L-alanine and L-serine in aqueous 0 to 4 mol⋅kg⁻¹ N-methylacetamide (NMA) solutions have been obtained by density measurement at 298.15 K. The standard partial molar volumes (V_f⁰)V_{\phi}^{0}) and standard partial molar volumes of transfer (D_trV_f⁰)\Delta_{\mathrm{tr}}V_{\phi}^{0}) have been determined for these amino acids. It has been show that hydrophilic-hydrophilic interactions between the charged groups of the amino acids and the –CONH– group of NMA predominate for glycine and L-serine, but for L-alanine the interactions between its side group (–CH₃) and NMA predominate. The –CH₃ group of L-alanine has much more influence on the value of D_trV_f⁰\Delta_{\mathrm{tr}}V_{\phi}^{0} than that of the –OH group of L-serine. The results have been interpreted in terms of a co-sphere overlap model.     

Volumetric properties of glucose in aqueous HCl solutions at temperatures from 278.15 to 318.15 K

Densities have been measured for Glucose + HCl +Water at 10-degree intervals from 278.15 to 318.15 K. The apparent molar volumes (V _Φ,G) and standard partial molar volumes (V _Φ,G ⁰ ) for Glucose in aqueous solution of 0.2, 0.4, 0.7, 1.1, 1.6, 2.1 mol·kg⁻¹ HCl have been calculated as well as volumetric interaction parameters (V _EG) for Glucose — HCl in water and standard partial molar expansion coefficients (∂V _Φ,G ⁰ / ∂T)_p. Results show that (1) the apparent molar volume for Glucose in aqueous HCl solutions increases lineally with increasing molality of Glucose and HCl; (2) V _Φ,G/0 for Glucose in aqueous HCl solutions increases lineally with increasing molality of HCl; (3) the volumetric interaction parameters for Glucose — HCl pair in water are small positive and vary slightly with temperature; (4) the relation between V _Φ,G ⁰ and temperature exists as V _Φ,G ⁰ = a ₀ + a ₁(T − 273.15 K)^2/3; (5) values of (∂V _Φ,G ⁰ / ∂T)_p are positive and increase as temperatures rise, and at given temperatures decrease slightly with increasing molalities of HCl, indicating that the hydration of glucose decreases with increasing temperature and molality of HCl. These phenomena are interpreted successfully by the structure interaction model. Translated from Acta Chimica Sinica, 2006, 64(16): 1635–1641 (in Chinese)     

Densities and apparent molar volumes for aqueous solutions of HNO3−UO2(NO3)2 at 298.15 K

In order to obtain the exact information of atomic number density in the ternary system of HNO₃−UO₂(NO₃)₂−H₂O, the densities were measured with an Anton-Paar DMA60/602 digital density meter thermostated at 298.15±0.01 K. The apparent molal volumes for the systems were calculated from the experimental data. The present measured apparent molar volumes have been fitted to the Pitzer ion-interaction model, which provides an adequate representation of the experimental data for mixed aqueous electrolyte solutions up to 6.2 mol/kg ionic strength. This fit yields θ ^V , and ψ ^V , which are the first derivatives with respect to pressure of the mixing interaction parameters for the excess free energy. With the mixing parameters θ ^V , and ψ ^V , the densities and apparent molar volumes of the ternary system studied in this work can be calculated with good accuracy, as shown by the standard deviations.     

Volumetric Properties and Refractive Indices for Binary Mixtures of 1-Propyronitrile-3-hexylimidazolium Bromide + Ethanol at Temperatures from 293.15 to 323.15 K

Densities and refractive indices have been measured for binary mixtures of 1-propyronitrile-3-hexylimidazolium bromide + ethanol in the temperature range 293.15–323.15 K. From the experimental data the excess molar volume V ^E, refractive index deviation Δn _D, and the coefficient of thermal expansion α were calculated and fitted to fifth- and third-order Redlich–Kister type equations, respectively. Using the measured densities, the apparent molar volumes (V _ϕ ), limiting apparent molar volumes (V_f⁰V_{\phi}^{0}) and limiting apparent molar expansivities (E_f ⁰E_{\phi} ^{0}) were also determined and the details are discussed.     

Aggregation Behavior of Pyridinium-Based Ionic Liquids in Aqueous Solution

Aggregation of the ionic liquids 1-butylpyridinium tetrafluoroborate, 1-butylpyridinium triflate, 1-butyl-2-methylpyridinium tetrafluoroborate, 1-butyl-3-methylpyridinium tetrafluoroborate, 1-butyl-4-methylpyridinium tetrafluoroborate, 1-butyl-3-methylpyridinium dicyanamide, and 1-octyl-3-methylpyridinium tetrafluoroborate in aqueous solution has been characterized at 298.15 K through density, ρ, speed of sound, u, and conductivity, σ, measurements. In addition, apparent molar volumes, V _φ , and isentropic compressibilities, κ _s , have been calculated from the experimental data. To characterize the formation of aggregates, the critical aggregation concentration of the ionic liquids, cac, the degree of ionization of the aggregates, β, and the standard Gibbs energy of aggregation, DG_m^°\Delta G_{\mathrm{m}}^{\circ}, have been obtained, with good agreement between results derived from the different methods. The dependence on the structural variation of these ions has been analyzed by comparing the results obtained for this series of ionic liquids.     

Volumetric and Viscometric Studies of <Emphasis Type="Italic">N</Emphasis>,<Emphasis Type="Italic">N</Emphasis>′-Bis(salicylaldehyde)-1,3-diaminopropane Schiff Base (Salpr) in Ionic Liquid + DMF solutions

The apparent molar volumes and viscosities of N,N′-bis(salicylaldehyde)-1,3-diaminopropane Schiff base (Salpr) have been determined in ionic liquid {1-pentyl-3-methylimidazolium bromide ([PnMIm]Br)} + N,N-dimethylformamide (DMF) solutions at 298.15 K from density and viscosity measurements using a vibrating tube densimeter and übbelohde type viscometer, respectively. These data have been used to calculate standard partial molar volumes, V_f ⁰V_{\phi} ^{0}, transfer partial molar volumes, Δ_tr V ⁰, and viscosity B-coefficients of the solutions. The transfer partial molar volumes are negative, and decrease with increasing the concentration of ionic liquid for all of the investigated solutions. It found that this ionic liquid interacts strongly with the Schiff base (Salpr) and has desolvation effect on the Schiff base molecules.     

Densities, Specific Heat Capacities, Apparent and Partial Molar Volumes and Heat Capacities of Glycine in?Aqueous Solutions of Formamide, Acetamide, and?N,N-Dimethylacetamide at T=298.15?K and?Ambient Pressure

Apparent molar volumes (V _2,φ ) and heat capacities (C _p2,φ ) of glycine in known concentrations (1.0, 2.0, 4.0, 6.0, and 8.0 mol⋅kg⁻¹) of aqueous formamide (FM), acetamide (AM), and N,N-dimethylacetamide (DMA) solutions at T=298.15 K have been calculated from relative density and specific heat capacity measurements. These measurements were completed using a vibrating-tube flow densimeter and a Picker flow microcalorimeter, respectively. The concentration dependences of the apparent molar data have been used to calculate standard partial molar properties. The latter values have been combined with previously published standard partial molar volumes and heat capacities for glycine in water to calculate volumes and heat capacities associated with the transfer of glycine from water to the investigated aqueous amide solutions, D[`(V)]<sub>2,tr</sub><sup>o</sup>\Delta\overline{V}_{\mathrm{2,tr}}^{\mathrm{o}} and D[`(C)]_p2,tr^o\Delta\overline{C}_{p\mathrm{2,tr}}^{\mathrm{o}} respectively. Calculated values for D[`(V)]<sub>2,tr</sub><sup>o</sup>\Delta\overline{V}_{\mathrm{2,tr}}^{\mathrm{o}} and D[`(C)]_p2,tr^o\Delta\overline{C}_{p\mathrm{2,tr}}^{\mathrm{o}} are positive for all investigated concentrations of aqueous FM and AM solutions. However, values for D[`(C)]_p2,tr^o\Delta\overline{C}_{p\mathrm{2,tr}}^{\mathrm{o}} associated with aqueous DMA solutions are found to be negative. The reported transfer properties increase with increasing co-solute (amide) concentration. This observation is discussed in terms of solute + co-solute interactions. The transfer properties have also been used to estimate interaction coefficients.     

Densities and Apparent Molar Volumes of NaOH(aq) to the Temperature 623 K and Pressure to 30 MPa

Densities of NaOH(aq) solutions with molalities between 0.033 and 6.047 mol⋅kg⁻¹ were measured with a vibrating-tube densitometer at temperatures between 373 K and 623 K and pressures from near the saturation vapor pressure of water to 30 MPa. Apparent molar volumes, V _φ, calculated from the measured densities in this work were well represented with the Pitzer ion-interaction treatment up to T = 523 K. Above that temperature the formation of ion pairs must be taken into account to describe correctly the molality dependence of V _φ and for the reliable extrapolation of V _φ to infinite dilution. Standard-state thermodynamic properties for the ion formation reaction were taken from recently published electrical conductivity measurements. A comparison with previous correlations of volumetric properties of NaOH(aq) is presented covering the full range of pressure and temperature.     

Hydrophobic Interactions of Methylureas in Aqueous Solutions Estimated with Density, Molal Volume, Viscosity and Surface Tension from 293.15 to 303.15 K

Density (ρ), viscosity (η), and surface tension (γ) for 0.005–0.25 mol ⋅ kg⁻¹ solutions of urea, 1-methylurea, and 1,3-dimethylurea solutions have been measured at intervals of 0.005 mol ⋅ kg⁻¹. Apparent molal volume (V _o, cm³ ⋅ mol⁻¹) and intrinsic viscosity coefficients (B and D) are calculated from the ρ and η values, respectively. Primary data were regressed and extrapolated to zero concentration for the limiting density (ρ ⁰), apparent molal volume (V _φ ⁰), viscosity (η ⁰), and surface tension (γ ⁰) values for solute–solvent interactions. The –CH₃ (methyl) groups of N-methylureas weaken hydrophilic interactions and enhance hydrophobic interactions, and the values of the ρ ⁰ and V _φ ^o reflect the intermolecular forces due to electrostatic charge, whereas the η ⁰ and γ ⁰ values reflect the frictional and surface forces. The B values depict the size of hydrodynamic sphere due to heteromolecular forces whereas D shows the effect of concentration. The molar surface energy (ΔE _m/sur) for dropwise flow was calculated from the γ values and decreases with concentration and temperature, but increases with –CH₃ weakening of the hydrophilic interactions and strengthening the hydrophobic interactions.