The Standard Partial Molar Volumes of Ions in Solution. Part 2. The Volumes in Two Binary Solvent Mixtures with No Preferential Solvation

Standard partial molar volumes of ions were obtained from literature data on 1:1 electrolytes in mixtures of propylene carbonate (PC) with acetonitrile (MeCN) and of water (W) with methanol (MeOH) at 298.15 K. The hypothesis was examined that when the solvents in the mixtures do not differ too much in their polarity and/or hydrogen-bonding ability, only negligible preferential solvation occurs in the solvent shell around the ion where electrostriction takes place. Given the solvent-independent intrinsic volume of an ion, the electrostriction, calculated by the shell-by-shell method, permits the examination of this proposition. This hypothesis was indeed validated by the calculated standard partial molar ionic volumes in the dipolar aprotic mixtures and in the protic aqueous methanol.     

用Pitzer理论预测混合电解质溶液的偏摩尔体积

用Pitzer理论研究了混合电解质溶液的偏摩尔体积,建立了偏摩尔体积的预测方法,并利用所得电解质溶液的表观摩尔体积的Pitzer参数预测了HNO₃-UO₂(NO₃)₂-H₂O、KCl-Na₂SO₄-H₂O、NaCl-Na₂SO₄-H₂O、NaCl-CaCl₂-H₂O、KCl-CaCl₂-H₂O、KCl-MgCl₂-H₂O和KCl-NaBr-H₂O共7个系统4种类型的混合溶液的偏摩尔体积。     

Partial Molar Volumes and Partial Molar Adiabatic Compressibilities of Fe(III) Tetrafluoroborate Complexes with DMSO, Pyridine, and Pyridine Derivatives

The apparent and limiting apparent molar volumes of dilute aqueous solutions of KBF₄, and the complexes [Fe(DMSO)₆](BF₄)₃, [Fe(Py)₄(H₂O)₂](BF₄)₃, [Fe(4-Mepy)₂(H₂O)₂](BF₄)₃, and [Fe(4-Etpy)₂(H₂O)₂](BF₄)₃ were determined from density data measured at 5, 15, and 25°C. The apparent and limiting apparent molar adiabatic compressibilities of these complexes were determined from ultrasonic sound velocities measured at the same temperatures in dilute aqueous solutions. The volume change associated with complex formation is discussed in terms of the nature of the coordinate bond and also the role of the central metal atom and ligands in the solvation behavior of these complexes.     

Partial Molar Volumes of Cobalt(III) Complexes. Part 3: Homologous Series of Aminopentaamminecobalt(III) Complexes

Partial molar volumes (V ₂°) have been determined at infinite dilution in aqueous solution at 20 °C for a series of octahedral N₆-coordinated cobalt(III) species having five-coordinated ammonia ligands along with an N-coordinated linear alkyl amine whose alkyl chain was varied from ethylamine to octylamine. The experimental values for V ₂° are consistent with the relative sizes of the ligands but show increasing deviations from those predicted by computer modeling, as the size of the cation increases, presumably due to the void space of the cation that increases with the size of the amine ligand. The value of the partial molar volume at infinite dilution increased by about 16 mL⋅mol⁻¹ with each added methylene group.     

The Partial Molar Volume and Heat Capacity of the Glycyl Group in Aqueous Solution at 25^C

The partial molar volumes, V₂ ^{^}, and the partial molar heat capacities, C_p,2 ^{^}, at infinite dilution have been determined for three new peptides of sequence seryl(glycyl)_xglycine, where x=0 to 2, in aqueous solution at 25^{^}C. Values for V₂ ^{^} at 25^°C have also been determined for two neutral peptide derivatives N-acetylglycylglycinamide and N-acetylglycylglycylglycinamide. These V₂ ^°; and C_p,2 ^°; results were used to estimate the partial molar volume and heat capacity of the backbone glycyl group, CH₂CONH, of proteins in aqueous solution at 25^°;C. The results obtained are compared with those calculated using partial molar data for alternative model compounds. The new glycyl group contributions are in excellent agreement with those currently used in our group additivity schemes for the calculation of the partial molar volumes and heat capacities of unfolded proteins.     

Partial Molar Volumes of Tetraalkylammonium Ions in N, N-Dimethylformamide

The densities of tetraalkylammonium bromide, R₄NBr (R = Et, Pr, Bu, Hex, Hep, Oct), solutions in dimethylformamide have been measured for the composition range (0.05–0.4) mol-kg⁻¹ at 25 ^∘C. Apparent molar V_φ and limiting partial molar volumes ⫫₂^o of the electrolytes have been evaluated. Using the extrapolation values, the limiting partial molar volumes of the tetraalkymammonium ions (⫫_i^o) have been calculated. Analysis of different contributions to the ionic ⫫_i^o indicated partial penetration of solvent molecules into the van der Waal’s volume of tetraalkylammonium (TAA) ions.     

Limiting Partial Molar Volumes of Electrolytes in 2-Methyl-2-Butanol <Emphasis Type="Bold">+</Emphasis> Water Mixtures at 298.15 K

Partial molar volumes at infinite dilution, V⁰₂, of alkali–metal halides (LiCl, NaCl KCl RbCl CsCl, NaBr, KBr, KI), tetra-n-alkylammonium bromides, R₄NBr (R=Me, Et, n-Pr, n-Bu, n-Pen), NaBPh₄, and Ph₄PCl have been determined in binary solvent mixtures of water with 2-methyl-2-butanol covering the water-rich region and the alcohol-rich region at 298.15 K. V⁰₂ for alkali–metal halides show relatively little dependence on the solvent composition. However, in the case of hydrophobic electrolytes the observed effects are more pronounced. A good linear dependence between V⁰₂(R₄NBr) and the molecular weight of the tetra-n-alkylammonium cation is found. Limiting single-ion volumes have been obtained using the assumption that V⁰(Ph₄P⁺)–V⁰(BPh^–₄)=2.0 cm³-mol^–1. The trends in the single-ion volumes are discussed in both solvent regions.     

超临界CO2-溶质二元系的密度及溶质的偏摩尔体积

在308．15和318．15K温度下，80－170bar压力范围内，测定了CO2-乙醇、CO2-丙酮和CO2-正庚烷混合物的密度，溶质的浓度范围是0－1．3mol·L－1．在此基础上，计算了溶质的偏摩尔体积，系统地研究了温度、压力和溶质浓度对二元混合物密度的影响，并从压力和溶质浓度对溶质偏摩尔体积影响的角度研究体系中的分子间相互作用．     

Effect of Structure on Excess Partial Volumes and Deviation in Molar Viscosity of Some Aqueous-Ethylene Glycols Mono Alkyl Ether

The data obtained for density, viscosity, and dielectric constant are used for the study of the physical properties of 2-ethoxy ethanol-water mixtures. Density measurements showed the presence of contraction in the volume of the mixture and also in the partial molal volume of the components. Viscosity data provided supporting evidence of interaction between the two solvents. The dielectric data for the system were studied in terms of a deviation fraction, δD, representing the deviation from an ideal volume mixture. The results are also compared with the data obtained in the literature for water-2-methoxy ethanol and water-ethylene glycol mixtures.     

Partial Molar Volumes and Refractions of Cobalt(III) Complexes, Part 2: Homologous Series of Nitrilopentaamminecobalt(III) Complexes

Both the partial molar volumes (V° _2m refractions (R° _2m ) of the solutes at infinite dilution have been determined at 20 °C for a series of six octahedral N₆-coordinated cobalt(III) species featuring five coordinated ammonia ligands along with a sixth N-coordinated organonitrile of increasing ligand size (from acetonitrile to sebaconitrile). The experimental values for V° _2m are consistent with the relative sizes of the ligands but show larger values than those generated by computer modeling as the size of the cation increases, presumably due to the void space of the cation which increases with the size of the nitrile ligand.     

Molar Volumes and Heat Capacities of Electrolytes and Ions in Nonaqueous Solvents: 1. Formamide

Apparent molar volumes and heat capacities of 27 electrolytes have been measured as a function of concentration in formamide at 25°C using a series-connected flow densimeter and Picker calorimeter system. These data were extrapolated to infinite dilution using the appropriate Debye–Hückel limiting slopes to give the corresponding standard partial molar quantities. Ionic volumes and heat capacities at infinite dilution were obtained by an appropriate assumption based on the reference electrolyte Ph₄PBPh₄ (TPTB). The ionic volumes, but not the heat capacities, agree reasonably well with previously published statistically based predictions. The values obtained are discussed in terms of simple models of electrolyte solution behavior and a number of interesting features are noted, including, possible dependencies of ionic volumes on solvent isothermal compressibility and of ionic heat capacities on solvent electron acceptor abilities.     

Thermodynamic properties of peptide solutions 3. Partial molar volumes and partial molar heat capacities of some tripeptides in aqueous solution

Partial molar volumes, V ₂ ^o , and partial molar heat capacities, C _p,2 ^o , of the tripeptides glycylglycylglycine, glycylglycylalanine, glycylalanylglycine and alanylglycylglycine have been determined in aqueous solution at 25°C. For the three alanyl-containing tripeptides, the data indicate that the tripeptide-water interaction is influenced by the side chain position within the molecule. The results have been rationalized in terms of likely solutesolvent interactions. The V ₂ ^o and C _p.2 ^o data have also been used to calculate the contribution to these properties of a-CH₃ side chain.     

Thermodynamic properties of peptide solutions: 7. Partial molar isentropic pressure coefficients of some dipeptides in aqueous solution

The partial molar isentropic pressure coefficients at infinite dilution, K _S,2 ^o , have been determined for a number of dipeptides in aqueous solution at 25°C. For a series of dipeptides of sequence gly-X, where X is an amino acid with a neutral side chain, the K _S,2 ^o values are all more negative than that for diglycine. The results are discussed in terms of the hydration of the side chains. There are significant differences in the K _S,2 ^o values for sequence isomeric dipeptides. These differences can be rationalized in terms of the mutual interactions between the side chain and the ionic end groups in the dipeptides. Possible relationships between K _S,2 ^o and V ₂ ^o , the partial molar volume at infinite dilution, were investigated. For the dipeptides of sequence gly-X there is an interesting linear relationship between K _S,2 ^o /V ₂ ^o and V ₂ ^o .     

Thermodynamic properties of peptide solutions 4. Partial molar volumes and heat capacities of aqueous solutions of some glycyl dipeptides

Partial molar volumes, V ₂ ^o and partial molar heat capacities C _p,2 ^o have been determined in aqueous solution at 25°C for the dipeptides glycyl-L-asparagine, glycyl-DL-threonine, glycyl-DL-serine and glycyl-DL-phenylalanine. These results, along with those for some other dipeptides of sequence Gly-X, were used to estimate side chain contributions to V ₂ ^o and C _p,2 ^o . For these dipeptides both V ₂ ^o and C _p,2 ^o were found to be a linear function of the respective thermodynamic property for the amino acid X. The contributions of the glycyl units to V ₂ ^o and C _p,2 ^o of the dipeptide are discussed.     

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.     

Thermodynamic properties of peptide solutions. Part 15. Partial molar isentropic compressibilities of some glycyl dipeptides in aqueous solution at 15 and 35°C

The partial molar isentropic compressibilities at infinite dilution,K _s,2 ^o , have been obtained for eight glycyl dipeptides of sequence gly-X (X is an amino acid) in aqueous solution at the temperatures 15 and 35°C. The results have been combined with those obtained at 25°C, that were reported earlier, to evaluate the temperature dependences ofK _s,2 ^o for the dipeptides in the temperature range 15 to 35°C. TheK _s,2 ^o values for all the dipeptides are negative and increase (become more positive) with an increase in temperature. The slopes of the temperature dependences ofK _s,2 ^o for the dipeptides with typically hydrophobic side-chains are significantly larger than those for dipeptides with hydrophilic side-chains.     

Densities and Excess Molar Volumes of Binary and Ternary Mixtures of Aqueous Solutions of 2,2,2-Trifluoroethanol with Acetone and Alcohols at the Temperature of 298.15 K and Pressure of 101 kPa

Excess molar volumes V_m^E of the binary mixtures of (trifluoroethanol + 1-propanol), (trifluoroethanol + 2-propanol), (acetone + water), (methanol + water), (ethanol + water), (1-propanol + water), (2-propanol + water), and the ternary mixtures of (trifluoroethanol + methanol + water), (trifluoroethanol + ethanol + water), (trifluoroethanol~+ 1-propanol + water), (trifluoroethanol + 2-propanol + water) and (trifluoroethanol + acetone + water) were measured with a vibrating tube densimeter at the temperature of 298.15 K and the pressure 101 kPa. The extrema in V_m^E of trifluoroethanol mixtures occur at –0.690 cm³-mol^–1 for (trifluoroethanol + 1-propanol), at –0.990~cm³-mol^–1 for (trifluoroethanol + 2-propanol); at 0.562 and –0.973 cm³-mol^–1 for (trifluoroethanol + methanol + water), at 0.629 and –0.973 cm³-mol^–1 for (trifluoroethanol + ethanol + water), at 1.082 and –0.659 cm³-mol^–1 for (trifluoroethanol~+ 1-propanol + water), at 0.998 and –0.991 cm³-mol^–1 for (trifluoroethanol~+ 2-propanol + water), and at 0.515 and –1.472 cm³-mol^–1 for (trifluoroethanol + acetone + water). The experimental ternary V_m^E values were predicted by empirical expressions using binary solution data.     

Thermodynamic properties of peptide solutions: 14. Partial molar expansibilities and isothermal compressibilities of some glycyl dipeptides in aqueous solution

The partial molar volumes at infinite dilution have been obtained for a series of glycyl dipeptides in aqueous solution at 15, 30, and 35°C. These results have been combined with data obtained at 25°C, that were reported earlier, to evaluate the partial molar expansibilities at infinite dilution for the dipeptides at 25°C. These quantities, along with the partial molar heat capacities and isentropic compressibilities at infinite dilution that were reported in previous studies, were used to derive the partial molar isothermal compressibilities at infinite dilution for the glycyl dipeptides at 25°C. The results obtained are rationalized in terms of the hydration of the constituent groups of the dipeptides.     

Solvation Effect of Li+ on the Voltammetric Properties of [PMo12O40]3−. Part 2: Comparative Studies on the Preferential Solvation in Acetonitrile+S and Acetone+S Mixtures

For [PMo₁₂O₄₀]^3?, the presence of Li⁺ produced a two‐electron wave at nearly the same potential as the first one‐electron wave in acetonitrile or acetone. The voltammetric behavior of [PMo₁₂O₄₀]^3? in a binary mixture of acetonitrile and solvent S was compared with those in a mixture of acetone and S. When the donor number (DN) of S>20, the first two‐electron wave was converted into one‐electron waves in such binary mixtures. The conversion occurred at lower mole fractions of S in an acetonitrile+S mixture than in an acetone+S mixture. The ⁷Li NMR results showed that the preferential solvating ability of Li⁺ with S was greater in the former mixture. A linear relationship was found between the iso‐solvation point x_iso(S) and the reciprocal of the difference between the DNs of S and acetonitrile, which gave the basis to explain the anomalies observed for a mixture of acetonitrile and H₂O.