The volumetric and thermochemical properties of YCl3(aq), YbCl3(aq), DyCl3(aq), SmCl3(aq), and GdCl3(aq) at T=(288.15, 298.15, 313.15, and 328.15) K and p=0.1 MPa

Relative densities and massic heat capacities have been measured for acidified aqueous solutions of YCl₃(aq), YbCl₃(aq), DyCl₃(aq), SmCl₃(aq), and GdCl₃(aq) at T=(288.15, 298.15, 313.15, and 328.15) K and p=0.1 MPa. These measurements have been used to calculate experimental apparent molar volumes and heat capacities which, when used in conjunction with Young’s rule, were used to calculate the apparent molar properties of the aqueous chloride salt solutions. The latter calculations required the use of volumetric and thermochemical data for aqueous solutions of hydrochloric acid that have been previously reported in the literature. The concentration dependences of the apparent molar properties have been modeled using Pitzer ion interaction equations to yield apparent molar volumes and heat capacities at infinite dilution. The temperature and concentration dependences of the apparent molar volumes and heat capacities of each trivalent salt system were modeled using modified Pitzer ion interaction equations. These equations utilized the revised Helgeson, Kirkham, and Flowers equations of state to model the temperature dependences of apparent molar volumes and heat capacities at infinite dilution. Calculated apparent molar volumes and heat capacities at infinite dilution have been used to calculate single ion properties for the investigated trivalent metal cations. These values have been compared to those previously reported in the literature. The differences between single ion values calculated in this study and those values calculated from thermodynamic data for aqueous perchlorate salts are also discussed.     

Apparent molal volumes and heat capacities of some alkali halides and tetraalkylammonium bromides in aqueoustert-butanol solutions

The densities and volumetric specific heats of hydrochloric acid, alkali chlorides and bromides, and tetraalkylammonium bromides were measured in 0 to 40% by weighttert-butanol (t-BuOH) in water with a flow densimeter and a flow microcalorimeter. The effect of salt concentration was investigated in the case of NaCl. The apparent molal volumes and heat capacities and the derived transfer functions of the electrolytes from water tot-BuOH-water mixtures can be interpreted through solute-solute pair and triplet interactions by analogy with the transfer functions oft-BuOH from water to electrolyte solutions, with the salting-in and salting-out effects, and with the influence of electrolytes on the thermodynamics of micellization. At lowt-BuOH concentrations, the transfer functions seem to be reflecting primarily electrolyte-nonelectrolyte pair interactions. At intermediatet-BuOH concentration, wheret-BuOH associates, the hydrophobic bonding is enhanced by hydrophilic ions through a salting-out effect on monomers and by hydrophobic salts through triplet interaction (mixed association complexes). The Me ₄ NBr and Et ₄ NBr are intermediate electrolytes which do not have much effect on thet-BuOH hydrophobic bonding. At hight-BuOH concentrations the transfer functions tend to the values they would have in puret-BuOH.     

Enthalpies of the urea-tert-butanol-water system at 25°C

The enthalpies of solution of urea (U) in water (W)-tert-butanol (TBA) mixtures and of TBA in W-U mixtures, the enthalpies of dilution of TBA in W, and the enthalpies of mixing of U and TBA aqueous solutions were measured with a solution calorimeter and a flow microcalorimeter. Enthalpies of transfer of U and TBA to the mixed solvents were derived. Also, pair and triplet interaction parameters between the various solutes were derived from the mixing and dilution experiments. The enthalpic pair parameter h_U-TBA is positive, suggesting that the main contribution to this parameter is the decrease in hydrophobic hydration of TBA in the presence of U.     

Apparent molar heat capacities and apparent molar volumes of Pr(ClO4)3(aq), Gd(ClO4)3(aq), Ho(ClO4)3(aq), and Tm(ClO4)3(aq) at T=(288.15, 298.15, 313.15, and 328.15) K and p=0.1 MPa

Acidified aqueous solutions of Pr(ClO₄)₃(aq), Gd(ClO₄)₃(aq), Ho(ClO₄)₃(aq), and Tm(ClO₄)₃(aq) were prepared from the corresponding oxides by dissolution in dilute perchloric acid. Once characterized with respect to trivalent metal cation and acid content, the relative densities of the solutions were measured at T=(288.15, 298.15, 313.15, and 328.15) K and p=0.1 MPa using a Sodev O2D vibrating tube densimeter. The relative massic heat capacities of the aqueous systems were also determined, under the same temperature and pressure conditions, using a Picker Flow Microcalorimeter. All measurements were made on solutions containing rare earth salt in the concentration range 0.01 ⩽ m/(mol · kg⁻¹) ⩽ 0.2. Relative densities and relative massic heat capacities were used to calculate the apparent molar volumes and apparent molar heat capacities of the acidified salt solutions from which the apparent molar properties of the aqueous salt solutions were extracted by the application of Young's Rule. The concentration dependences of the isothermal apparent molar volumes and heat capacities of each aqueous salt solution were modelled using Pitzer ion-interaction equations. These models produced estimates of apparent molar volumes and apparent molar heat capacities at infinite dilution for each set of isothermal V_φ,2 and C_pφ,2 values. In addition, the temperature and concentration dependences of the apparent molar volumes and apparent molar heat capacities of the aqueous rare earth perchlorate salt solutions were modelled using modified Pitzer ion-interaction equations. The latter equations utilized the Helgeson, Kirkham, and Flowers equations of state to model the temperature dependences (at p=0.1 MPa) of apparent molar volumes and apparent molar heat capacities at infinite dilution. The results of the latter models were compared to those previously published in the literature.Apparent molar volumes and apparent heat capacities at infinite dilution for the trivalent metal cations Pr³⁺(aq), Gd³⁺(aq), Ho³⁺(aq), and Tm³⁺(aq) were calculated using the conventions V₂^∘(H⁺(aq)) ≡ 0 and C_p2^∘(H⁺(aq)) ≡ 0 and have been compared to other values reported in the literature.     

Hydrophobic nitroxide radicals as probes to investigate the hydrophobic interaction

The EPR spectrum of 2,2,6,6-tetramethylpiperidine-N-oxide (TEMPO) has been systematically investigated in several solvents and in aqueous solutions of glycerol,t-BuOH, Bu₄NBr,n-HexNH₃Br,n-OctNH₃Br, NaBPh₄, and Ph₄AsCl. Most of the results have been obtained at 25°C, though the temperature dependence of the linewidths has been examined in water and several organic solvents. Data on the spectrum of ditertiarybutylnitroxide in aqueous solutions of glycerol and Bu₄NBr are also presented. The spectrum was simulated to determine W_H, the linewidth after allowance for the unresolved proton hyperfine interaction, in each manifold of the triplet due to the nitrogen hyperfine interaction. The linewidth W_H is analyzed in terms of the reorientational correlation time Äθ and the angular velocity correlation time ÄJ. In most solutions Äθ is determined only by the bulk solution viscosity, except in situations where significant clustering of hydrophobic solute molecules occurs. In pure nonaqueous solvents the temperature dependence results are consistent with ÄJ being determined by the bulk viscosity, while in water or aqueous solutions, a very different behavior is found which is interpreted as a manifestation of clathrate-like hydration of the hydrophobic radical. This interpretation is incorporated in a two-state model developed to account for the W_H data of TEMPO in aqueous solutions of various hydrophobic solutes. The equilibrium parameters derived from the model, for the association of TEMPO with several hydrophobic solutes, support the concept of hydrophobic interactions as pictured from thermodynamic excess functions.     

Limiting Partial Molar Excess Heat Capacities and Volumes of Selected Organic Compounds in Water at 25°C

Well-known Picker flow microcalorimeters for the differential measurements of volumetric heat capacities have been employed in conjunction with vibrating tube densimeters to determine the molar heat capacity, volume, and the apparent properties in dilute aqueous solutions for 17 organic solutes of moderate hydrophobicity. The dependence on concentration of the apparent properties allowed the limiting partial molar quantities at infinite dilution to be extrapolated and the limiting partial molar excess quantities to be evaluated. Comparison with available literature data shows good agreement. The application of group contribution rules to the limiting partial properties has been tested using the original method and parameters proposed by Cabani et al. The predicted values of the partial molar volumes are in fair agreement with the present data except for some less common solutes. With partial molar heat capacities, the agreement is less satisfactory. To improve the performance of the method, missing parameters for some types of monofunctional and bifunctional molecules have been evaluated.     

Sublimation enthalpy of Ni(II) and Cu(II) diethyldithiocarbamate and diethylammonium diethyldithiocarbamate by the sublimation bulb technique

We have used a flow calorimeter and a flow densimeter for measurements leading to apparent molar heat capacities and apparent molar volumes of dilute aqueous solutions of NaIO₃, KMnO₄, and MnCl₂ at 25°C. These apparent molar quantities have been extrapolated to infinite dilution to obtain the corresponding standard state apparent and partial molar heat capacities and volumes. which have then been used for the calculation of conventional ionic heat capacities and volumes.     

Studies of Activity Coefficients for Ternary Systems: Water + 18-Crown-6 + Alkali Chlorides at 298.15 K

Osmotic vapor pressure measurements have been carried out for three ternary systems, H₂O + 0.2 m 18-crown-6 + LiCl, H₂O + 0.2 m 18-crown-6 + NaCl and H₂O + 0.2 m 18-crown-6 + KCl at 298.15 K using vapor pressure osmometry. Water activities for each ternary system were measured and used to calculate the activity coefficients of 18-crown-6 (18C6) and its salts following the methodology developed by Robinson and Stokes for isopiestic measurements. In the concentration range studied, it was found that (in NaCl and KCl solutions) there is considerable lowering of activity coefficients of one component in the presence of other solutes that has been attributed to the formation of the complexed 18C6:Na⁺ (or 18C6:K⁺) species in solution. The Gibbs energies of transfer of alkali chlorides from water to aqueous 18C6 solutions and that of 18C6 from water to aqueous electrolyte solutions have been calculated. These were further used to evaluate the pair and triplet interaction parameters. The calculation of thermodynamic equilibrium constants using the pair interaction parameter, g _NE (i.e., the nonelectrolyte–electrolyte pair interaction) for the studied complexation of cations yields values which are in good agreement with those reported in literature obtained by using ion-selective potentiometry and calorimetry. The results are discussed in terms of water structural effects, complex formation, and hydrophobic interactions.     

Magnetic field effects on the triplet exciplex dynamics in the duroquinone-N,N-dimethylaniline derivative systems

Magnetic field effects (MFEs) on the radical yield in the photoinduced electron transfer reaction from the p-halogen derivatives (4XDMA) of N,N-dimethylaniline to the excited triplet state of duroquinone (DQ) have been investigated in alcoholic solutions at room temperature. In 1-propanol and 1-butanol solutions, the radical yields decreased as the magnetic field increased and became nearly constant at 1-1.8 T in the DQ-4BrDMA and DQ-4IDMA systems, suggesting that the spin-orbit coupling interaction due to the heavy atoms governs the radical yield. On the other hand, in the methanol solution MFE due to a radical pair mechanism was observed. We concluded that the key intermediate to determine the radical yield is the triplet exciplex or contact radical ion pair in the 1-propanol and 1-butanol solutions, while it is the solvent-separated radical ion pair in the methanol solution.     

Volumetric Properties of Aqueous Binary Mixtures of 1-Butanol,Butanediols, 1,2,4-Butanetriol and Butanetetrol at 298.15 K

Excess molar volumes, V _m ^E, and partial molar volumes, ↕ ₂, have been determined for dilute aqueous solutions of 1-butanol, 1,2-butanediol, 2,3-butanediol, 1,3-butanediol, 1,4-butanediol, 1,2,4-butanetriol and 1,2,3,4-butanetetrol (erythritol) at 298.15 K, as a function of composition from density measurements. The limiting partial molar volumes, ↕ ₂∞, of alcohols in aqueous solution are evaluated through extrapolation. Interactions of the different solutes with water are discussed in terms of the relationship among polar and non-polar groups on water structure and the effect of the position of hydroxyl groups in the molecule.     

CIDEP and kinetics of 1,4-naphthosemiquinone radicals during photoreduction

Light modulated CIDEP experiments and T₁ measurements were performed on solutions of 1,4-naphthoquinone. Solvents were 2-propanol and 2-butanol and temperatures ?4 and ?21°C. Experiments with different concentrations of 1,4-naphthoquinone provided strong evidence for secondary polarization in 2-propanol. For 2-butanol the evidence was less convincing. The temperature dependence of the chemical decay rate constant confirmed the termination reaction as a diffusion controlled process. The experimental data for the initial polarization displayed no hyperfine dependency. They were readily accounted for the microscopic theory for the triplet mechanism considering the uncertaintly in the parameters characterizing the triplet state of 1,4-naphthoquinone. The experimental values for the radical pair polarization showed some scatter. However, their average values were found in satisfactory agreement with those calculated from the microscopic theory for bimolecular termination between 1,4-naphthosemiquinone radicals.     

Thermodynamic investigations on derivatives of pyrimidine nucleic acid bases: Joint use of calorimetric, volumetric and structural data for the description of properties of pyrimidine nucleic acid bases and their derivatives

The experimental enthalpies of solution Δ_solH_m^∞, van’t Hoff enthalpies of sublimation Δ_s^gH_m⁰ of solid compounds, partial molar volumes V₂⁰, and partial molar heat capacities C_p,2⁰ of aqueous solutions of pyrimidine nucleic acid bases and their derivatives, determined previously and collected here, are discussed in terms of calculated structural parameters. Relations have been established between the calorimetric and volumetric properties. Correlations have been developed to relate both the enthalpies of solvation and the partial molar heat capacities to the polar and apolar parts of the accessible molecular surface areas.     

Volumes and heat capacities of some watersurfactant-alcohol ternary systems

The densities and volumetric heat capacities of urea and alcohols were measured in aqueous solutions of octylammonium bromide (OABr) and of OABr in aqueous urea and alcohol solutions. The alcohols studies were methanol, ethanol, 1-propanol, 2-propanol, n-butanol, t-butanol, n-pentanol, n-hexanol and 2-butoxyethanol (BE). In most experiments, the concentration of the reference solute was kept low, and volumes and heat capacities of transfer from water to the mixed solvent were calculated. A more complete study was made with the system BE-OABr-H₂O where both solutes were systematically changed. The observed trends in the thermodynamic functions can be explained through three effects: interactions between the reference solute and the cosolvent in the premiceller region of the surfactant or pre-aggregation region of the alcohol, a distribution of the reference solute between water and the micelle or microphase and an equilibrium displacement of the system, monomer-aggregate, in the vicinity of the reference solute.     

Chemical models of the hydrophobic interaction: Apparent molal volumes and heat capacities of three symmetrical bolaform electrolytes and their homologous monomers in aqueous solution at 25°C

The densities and volumetric specific heats of aqueous solutions of Bu₃NHBr, Pent₃NHCl, and three diazonium salts, HN?Oct₃?NHBr₂, HN?Dec₃?NHCl₂, and Bu₃N?Oct?NBu₃Br₂, have been measured at 25°C. From these data, the apparent molal volumes φ _v and apparent molal heat capacities φ _c have been calculated and are reported here. In the series of compounds chosen, the diazonium (higher homologs) can be regarded as dimers of the alkyl-substituted ammonium ions (lower homologs), and these systems are examined as chemical models for the hydrophobic interaction. With the three homologous pairs studied here, the chemical model predicts that the strong interaction (limitingly, chemical binding) of two hydrocarbon chains in water leads to a major decrease in both φ _v and φ _c of the interacting solutes, ca.?22 cm³-mole^?1 and ?200 J-^oK^?1-mole^?1. These predictions constitute limiting behavior — useful, but not sufficient, to explain the observed concentration dependence of φ _v and φ _c in aqueous solutions of the lower homologs Bu₃NHBr, Pent₃NHCl, and Bu₄NBr. An explanation for the concentration dependence of φ _c is suggested with reference to ultrasonic relaxation data.     

Partial molar heat capacities and volumes of transfer of nucleic acid bases,nucleosides and nucleotides from water to aqueous solutions of sodium and calcium chloride at 25°C

Partial molar heat capacities and volumes of some nucleic acid bases, nucleosides and nucleotides have been measured in 1m aqueous NaCl and CaCl₂ solutions using Picker flow microcalorimeter and a vibrating tube digital densimeter. The partial molar heat capacities of transfer and volumes of transfer from water to the electrolyte solutions were calculated using earlier data for these compounds in water. The values of these transfer parameters are positive. The higher values for transfer to aqueous CaCl₂ solutions reflect the stronger interactions of the constituents of the nucleic acids with Ca⁺² ions than with the Na⁺ ions.     

Apparent molar heat capacities and volumes,van der Waals volumes and accessible surface areas of alkylated derivatives of cytosine and uracil in aqueous solutions at 25°C.

Densities and specific heat capacities of aqueous solutions: 1,3,5,6-tetramethyluracil, 1,6-dimethyl-3-ethyluracil, 1,6-dimethyl-3-propyluracil, 1,6-dimethyl-3-butyluracil, 1,N⁴-trimethylcytosine, 1,N⁴-dimethyl-5-ethylcytosine, 1,N⁴ dimethyl-5-propylcytosine, 1,N⁴-dimethyl-5-butylcytosine were determined using flow calorimetry and flow densimetry at 25°C. Apparent molar volumes and heat capacities, van der Waals volumes and accessible surface areas were determined. It was stated that for alkylcytosines and alkyluracils partial molar volumes and heat capacities correlate linearly with the number of substituted methylene groups-CH₂-as well as with the van der Waals volumes and accessible surface areas of the compounds studied; for cyclooligouracils the cyclization effect was discussed.     

Apparent molar volumes and apparent molar heat capacities of aqueous d-lactose · H2O at temperatures from (278.15 to 393.15) K and at the pressure 0.35 MPa

Apparent molar volumes V_φ and apparent molar heat capacities C_p,φ were determined for aqueous solutions of d-lactose · H₂O at molalities (0.01 to 0.34) mol · kg⁻¹ at temperatures (278.15 to 393.15) K, and at the pressure 0.35 MPa. Our V_φ values were calculated from densities obtained using a vibrating tube densimeter, and our C_p,φ values were obtained using a twin fixed-cell, power-compensation, differential-output, temperature-scanning calorimeter. Our results for d-lactose(aq) and for d-lactcose · H₂O were fitted to functions of m and T and compared with the literature results for aqueous d-glucose and d-galactose solutions. Infinite dilution partial molar volumes V₂^∘ and heat capacities C_p,2^∘ are given over the range of temperatures.     

Apparent molar heat capacities and volumes of aqueous electrolytes at 25°C: Cd(ClO4)2, Ca(ClO4)2, Co(ClO4)2, Mn(ClO4)2, Ni(ClO4)2, and Zn(ClO4)2

We have used a flow calorimeter and a flow densimeter for measurements leading to apparent molar heat capacities and apparent molar volumes of aqueous solutions of Cd(ClO₄)₂, Ca(ClO₄)₂, Co(ClO₄)₂, Mn(ClO₄)₂, Ni(ClO₄)₂, and Zn(ClO₄)₂. The resulting apparent molar quantities have been extrapolated to infinite dilution to obtain the corresponding standardstate apparent and partial molar heat capacities and volumes. These latter values have been used for calculation of conventional ionic heat capacities and volumes.     

Volumes,heat capacities and solubilities of amyl compounds in decyltrimethylammonium bromide aqueous solutions

Apparent molar heat capacities and volumes of amylamine (PentNH₂) 0.02m, capronitrile (PentCN) 0.02m and nitropentane (PentNO₂) 0.009m in decyltrimethylammonium bromide (DeTAB) micellar solutions, in water and in octane were measured at 25°C. By assuming that their concentration approaches the standard infinite dilution state, heat capacities and volumes were rationalized by means of previously reported equations following which the distribution constant between the aqueous and the micellar phase and heat capacity and volume of the additives in both phases are simultaneously derived. The present results are compared to those we have previously obtained for pentanol (PentOH). The thermodynamic properties of PentNH₂ in water and in micellar phase are substantially identical to those of PentOH but different from those of PentCN and PentNO₂ whereas the opposite behavior was observed in their pure liquid state and in octane. The nature of the solvent medium seems to affect the thermodynamic behavior of PentNH₂. Also, the study of the apparent molar heat capacities of the amyl compounds investigated here in micellar solutions as a function of surfactant concentration shows evidence of a maximum at about 0.4m DeTAB, which can be attributed to a micellar structural transition. Accordingly, the solubilities of PentCN and PentNO₂ as a function of the DeTAB concentration drop in the neighborhood of the concentration where heat capacities display the maximum.     

The apparent molar heat capacities and volumes of aqueous NaCl from 0.01 to 3 mol kg−1 in the temperature range 274.65 to 318.15 K

The heat capacities per unit volume of aqueous solutions of NaCl were measured with a flow microcalorimeter. The molality and temperature range covered were 0.01 to 3 mol kg^?1 and 274.65 to 318.15 K. The derived apparent molar heat capacities C₂, φ, when extrapolated to infinite dilution, give standard partial molar heat capacities C₂^o which are in excellent agreement with those of Criss and Cobble. The excess apparent molar heat capacities (C₂, φ - C₂^o) can be used to predict the temperature dependence of (H₂, φ - H₂^o), the excess apparent molar enthalpy. The calculated values of ΔH₂, φ agree within experimental uncertainty with the integral enthalpies of dilution of Ensor and Anderson and of Messikomer and Wood up to 323.15 K. Above this temperature significant differences are observed. The densities of the solutions were also remeasured in the same range of temperature and molality with a flow densimeter, and the derived apparent molar volumes agree with the literature values.