Standard Partial Molal Properties Research Articles

Interactions of sodium salicylate and β-cyclodextrin in water: A volumetric, ultraacoustic and optical study

Present article reports the thermodynamic studies on standard transfer volumes and compressibilities of non-steroidal anti-inflammatory drug, sodium salicylate in 0.0005, 0.001, 0.004, 0.009, 0.0140 mol·kg−1 aqueous-β-cyclodextrin solutions at 303.15, 308.15 and 313.15 K. The transfer properties have been calculated from the standard partial molar volumes and compressibilities determined form the linear dependence of corresponding apparent molar properties over the drug concentration. Apparent molar properties have been calculated from measured density and ultrasonic velocity data. Further, the optical property, refractive index (n) of the studied drug solutions has been measured. In addition to this, the quantum mechanical calculations were performed using the DFT. The solvation energy (ΔESol), relative stabilization energy (ΔERel), complexation energy (ΔEComp) and change in the volume (ΔV) of the different complexes have been calculated. The results have been discussed in terms of the drug-solvent and drug-β-cyclodextrin interactions. The complex formation of sodium salicylate with β-cyclodextrin with dominating lateral interactions namely ion-hydrophilic/hydrophilic-hydrophilic or hydrogen bonding interactions has been confirmed from standard partial molar properties and computational studies.

The hydration properties of protein stabilizer, trimethylamine-N-oxide in aqueous solutions of N-methylacetamide—The volumetric and compressibility studies between 288.15 and 308.15 K

Apparent molar volumes, VΦ, and apparent molar isentropic compressions, KS,Φ, of the protein stabilizer, trimethylamine-N-oxide (TMAO) were determined from the densities and speed of sound measured at T = (288.15, 298.15 and 308.15) K in aqueous solutions of N-methylacetamide (NMA) at four different concentrations (2, 4, 6 and 8 mol/kg). The concentration dependencies of the calculated quantities extrapolated to the infinite dilution lead to the standard partial molar properties. The latter values were combined with the previously published data for TMAO in pure water, to obtain the partial molar properties of transfer from water to aqueous NMA solutions. From the transfer data the interaction parameters were determined according to the McMillan-Mayer theory formalism. The calculated parameters and their temperature characteristics are discussed in terms of solute-solvent, solute-solute and solute-cosolute interactions and compared with analogous data for protein denaturant, n-butylurea.

Thermodynamic Properties of Aqueous Species Calculated Using the HKF Model: How Do Different Thermodynamic and Electrostatic Models for Solvent Water Affect Calculated Aqueous Properties?

Thermodynamic properties of aqueous species are essential for modeling of fluid-rock interaction processes. The Helgeson-Kirkham-Flowers (HKF) model is widely used for calculating standard state thermodynamic properties of ions and complexes over a wide range of temperatures and pressures. To do this, the HKF model requires thermodynamic and electrostatic models of water solvent. In this study, we investigate and quantify the impact of choosing different models for calculating water solvent volumetric and dielectric properties, on the properties of aqueous species calculated using the HKF model. We identify temperature and pressure conditions at which the choice of different models can have a considerable effect on the properties of aqueous species and on fluid mineral equilibrium calculations. The investigated temperature and pressure intervals are 25–1000°C and 1–5 kbar, representative of upper to middle crustal levels, and of interest for modeling ore-forming processes. The thermodynamic and electrostatic models for water solvent considered are: Haar, Gallagher and Kell (1984), Wagner and Pruß (2002), and Zhang and Duan (2005), to calculate water volumetric properties, and Johnson and Norton (1991), Fernandez and others (1997), and Sverjensky and others (2014), to calculate water dielectric properties. We observe only small discrepancies in the calculated standard partial molal properties of aqueous species resulting from using different water thermodynamic models. However, large differences in the properties of charged species can be observed at higher temperatures (above 500°C) as a result of using different electrostatic models. Depending on the aqueous speciation and the reactions that control the chemical composition, the observed differences can vary. The discrepancy between various electrostatic models is attributed to the scarcity of experimental data at high temperatures. These discrepancies restrict the reliability of the geochemical modeling of hydrothermal and ore formation processes, and the retrieval of thermodynamic parameters from experimental data at elevated temperatures and pressures.

Data analysis and estimation of thermodynamic properties of aqueous monovalent metal-glycinate complexes

Recently, an aqueous glycine solution has been proposed as a non-toxic environmentally friendly lixiviant to leach precious metals such as gold. In confined spaces, gold can be leached effectively using cyanide as a lixiviant. However, in unconfined applications, cyanide poses detrimental environmental effects due to its high level of toxicity. In order to investigate the effectiveness of lixiviant systems containing glycine and examine their potential, it is essential to identify the thermodynamic properties and stability domains of metal-glycinate complexes. Numerous studies have been conducted on the thermodynamic equilibrium of divalent metal-glycinate formations but those of monovalent metal-glycinate are scarce in general and inexistent for most precious metals including gold. In this study, we use data analysis to relate the standard partial molal properties of metal-glycinate complexes to the standard partial molal properties of various metals and estimate the equilibrium constants of monovalent metal-glycinate formation at ambient conditions. Finally, the standard partial molal properties of the metal-glycinate complexes and their revised Helgeson-Kirkham-Flowers (HKF) equations of state have been estimated and used to deduce the equilibrium constants of metal-glycine systems at different temperatures. The proposed method has been tested using existing experimental data and showed excellent consistency.

Standard partial molar heat capacities and volumes of aqueous N-methylpiperidine and N-methylpiperidinium chloride from 283 K to 393 K

Densities and volumetric heat capacities for dilute solutions of N-methylpiperidine (N-MP, 0.2mol·kg−1) and N-methylpiperidinium chloride (N-MPH+Cl−, 0.1mol·kg−1) were measured relative to water at 0.1MPa using a vibrating-tube densimeter, and at 0.4MPa using a twin fixed-cell, power-compensation, differential temperature-scanning nano calorimeter, over the temperature ranges 283.15K≤T≤363.15K and 283.15K≤T≤393.15K, respectively. The resulting apparent molar volumes, Vϕ, and heat capacities, Cp,ϕ, were corrected for speciation effects using Young’s rule and extrapolated to infinite dilution using the Debye-Hückel limiting law, Yo≈Yϕ−AYIs1/2, to yield the standard partial molar properties, Yo, for N-MP(aq) and N-MPH+Cl−(aq). The standard partial molar volumes, Vo, and heat capacities, Cpo, were represented by a semi-empirical function of solvent density and temperature, Yo(ρw,T), the “density” model, which can be used to extrapolate these results, as well as other thermodynamic properties for the ionization of N-methylpiperidine, to higher temperatures.

Densities and Speeds of Sound of Glycine, l-Alanine, and l-Valine in Aqueous 1-Ethyl-3-methylimidazolium Chloride Solutions at Different Temperatures

The interactions of amino acids + water + 1-ethyl-3-methylimidazolium chloride [emim][Cl] solutions have been studied at different temperatures using volumetric and acoustic measurements. The density (ρ) and speed of sound (u) of glycine/l-alanine/l-valine + water + 1-ethyl-3-methylimidazolium chloride solutions have been measured at temperatures T = (288.15, 293.15, 298.15, 303.15, and 308.15) K and experimental pressure of 0.1 MPa. The apparent molar properties, standard partial molar properties, and partial molar properties of transfer have been determined from experimentally measured densities and speeds of sound. The resulting values of Vϕ0, ΔVϕ0, Kϕ,s0, and ΔKϕ,s0 have been used to discuss the nature of interactions present in the mixtures. The apparent molar expansivity ϕE0 and its temperature derivative (∂ϕE0/∂T) have also been calculated.

Partial molar volumes, expansibilities and compressibilities of glyglyglycine in aqueous sucrose and fructose solutions between 288.15 and 308.15 K

Apparent molar volumes ( V ϕ) and apparent molar adiabatic compressibilities ( K ϕ,s ) of triglycine (glyglyglycine) in aqueous and mixed aqueous solutions of fructose and sucrose (2, 4, and 6 mass%) have been determined at 288.15, 293.15, 298.15, 303.15, and 308.15 K. From these data, limiting partial molar volumes ( V ϕ 0 ) and limiting partial molar adiabatic compressibilities ( K ϕ , s 0 ) for glyglyglycine in aqueous sucrose and fructose solutions have been evaluated, together with the standard partial molar properties of transfer Δ tr Y of the glyglyglycine from water to aqueous saccharides solutions. Transfer parameters have been interpreted in terms of solute–cosolute interactions on the basis of a cosphere overlap model. Pair and triplet interaction coefficients have also been calculated from transfer parameter data. The partial molar volume at infinite dilution ( V ϕ 0 ) were used to obtain the partial molar expansion at infinite dilution, E 2 0 , for glyglyglycine to examine the temperature dependence of such interactions.

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, $\Delta\overline{V}_{\mathrm{2,tr}}^{\mathrm{o}}$ and $\Delta\overline{C}_{p\mathrm{2,tr}}^{\mathrm{o}}$ respectively. Calculated values for $\Delta\overline{V}_{\mathrm{2,tr}}^{\mathrm{o}}$ and $\Delta\overline{C}_{p\mathrm{2,tr}}^{\mathrm{o}}$ are positive for all investigated concentrations of aqueous FM and AM solutions. However, values for $\Delta\overline{C}_{p\mathrm{2,tr}}^{\mathrm{o}}$ 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.

Organic Sulfides in Hydrothermal Solution: Standard Partial Molal Properties and Role in Organic Geochemistry of Hydrothermal Environments

Thermodynamic properties for aqueous alkyl sulfides have been compiled and/or estimated through established methods. These properties are used to investigate reactions among various sulfur compounds in a variety of geological environments, ranging from sea floor hydrothermal systems to organic-rich sludge. Using thermodynamic data and the revised Helgeson-Kirkham-Flowers (HKF) equations of state, along with geochemical constraints imposed by the environment, it is possible to estimate the abiotic production of this class of organic sulfur compounds. For example, in hydrothermal systems in which H2 and H2S concentrations are buffered by the pyrite–pyrrhotite–magnetite (PPM) mineral assemblage, calculated equilibrium activities of dimethyl sulfide (DMS) are as high as 10−3 through formation reactions in which the environment contains millimolal concentrations of CO2. Higher activities are obtained when DMS formation from CO is considered and when more reducing mineral assemblages are present.

Standard partial molal properties of aqueous alkylphenols and alkylanilines over a wide range of temperatures and pressures

This article presents methods for predicting the standard partial molar Gibbs energy (standard chemical potential) and related derivative properties of aqueous hydroxy and aminoderivatives of (alkyl)benzenes over a wide range of temperatures and pressures. A thorough literature overview was conducted for collecting all available experimental data resulting from phase equilibrium, calorimetric and volumetric measurements that allow calculation of the thermodynamic properties of hydration. New experimental values are presented for solubility in water of isomeric toluidines and for the partial molal volume of phenol and cresols at high temperatures. Building upon the acquired database several prediction schemes were developed and tested for calculating the standard thermodynamic properties (and namely the Gibbs energy of hydration) of aqueous alkylphenols and alkylanilines as a function of temperature and pressure. First, a simple group contribution method was proposed for estimations at 298.15 K and 0.1 MPa using the simultaneous treatment of all available data on hydration properties at near ambient conditions. Second, this group contribution method allowed re-adjustment of the parameters of the Helgeson–Kirkham–Flowers model (HKF) using a new procedure proposed recently by Plyasunov and Shock [Plyasunov, A.V., Shock, E.L., 2001b. Correlation strategy for determining the parameters of the revised Helgeson–Kirkham–Flowers model for aqueous nonelectrolytes. Geochim. Cosmochim. Acta 65, 3879–3900]. Third, using the Sedlbauer–O’Connell–Wood equation of state for aqueous species (SOCW), group contributions were determined for predictions at high temperatures and pressures by simultaneous correlation of all available thermodynamic data on hydration properties. The latter method was constrained by the group contributions at 298.15 K and 0.1 MPa making both group contribution schemes consistent at near ambient conditions. The calculations from the HKF and SOCW equations of state and those from the simple thermodynamic integration of the data at 298.15 K and 0.1 MPa were compared for several alkylphenols and alkylanilines. Equilibrium constants for hydration reactions obtained from the three approaches are in very good agreement at temperatures to at least 400 K. At higher temperatures we assess the accuracy of different predictive schemes and their associated uncertainties. The reliable predictions of the standard chemical potentials to at least 573 K and 100 MPa are possible by the group contribution method using the SOCW equation of state.

Thermodynamics of aqueous methyldiethanolamine (MDEA) and methyldiethanolammonium chloride (MDEAH +Cl −) over a wide range of temperature and pressure: Apparent molar volumes, heat capacities, and isothermal compressibilities

Apparent molar volumes of aqueous methyldiethanolamine and its salt were determined with platinum vibrating tube densitometers over a range of temperatures from 283 K ⩽ T ⩽ 576 K and at pressures from 0.1 MPa to 20 MPa. Apparent molar heat capacities were obtained using a Sodev Picker flow microcalorimeter at a pressure of 0.1 MPa and within the temperature range of 283 K ⩽ T ⩽ 328 K. Apparent molar adiabatic and isothermal compressibilities at a pressure of 0.1 MPa were obtained at temperatures from 283 K ⩽ T ⩽ 313 K with speed of sound measurements. The experimental results were extrapolated to infinite dilution to obtain values for the standard partial molar volumes V ∘, heat capacities C p ∘ , and isothermal compressibilities κ T ∘ . The standard partial molar volumes V ∘ for the neutral amine and its salt show increasingly positive and negative values, respectively, at high temperatures and pressures, as predicted by corresponding states and group additivity arguments. The density model and the revised Helgeson–Kirkham–Flowers (HKF) model have been used to represent the temperature and pressure dependence of the standard partial molar properties to yield a full thermodynamic description of the system.

Standard Partial Molar Volumes of Aqueous Glycolic Acid and Tartaric Acid from 25 to 350 °C: Evidence of a Negative Krichevskii Parameter for a Neutral Organic Solute

Apparent molar volumes have been determined using a high-pressure vibrating-tube densimeter for aqueous solutions of glycolic acid (HGly = HOCH(2)COOH) and tartaric acid (H(2)Tar = HOOCCH(OH)CH(OH)COOH) at temperatures from 25 degrees C to 350 degrees C and pressures as high as 20 MPa. The resulting standard partial molar volumes (HGly,aq) are relatively independent of temperature until 315 degrees C, at which point (HGly,aq) deviates sharply toward negative values. This suggests that the Krichevskii parameter, A(Kr) = lim(x(2) --> 0) , which describes the discontinuities in standard partial molar properties at the critical point of water, is negative. Almost all aqueous nonelectrolytes are characterized by positive Krichevskii parameters. This is the first negative value reported for any organic molecule that is not an ion or zwitterion and only the third ever observed directly for a neutral species (the others are B(OH)(3) and H(3)PO(4)). The standard partial molar volumes for H(2)Tar(aq) are also relatively independent of temperature until 275 degrees C, suggesting a similar behavior. However, the onset of thermal decomposition prevented measurements at temperatures above 300 degrees C.

Ionization Constants of Aqueous Glycolic Acid at Temperatures up to 250 ∘C Using Hydrothermal pH Indicators and UV-Visible Spectroscopy

Chemical equilibrium constants for the ionization of aqueous glycolic acid (hydroxyacetic acid, HOCH2COOH) have been measured at temperatures 25–250 ∘C and pressure p = 4.5 MPa, using UV-visible spectroscopy with a high-pressure flow cell and thermally-stable colorimetric pH indicators. These are the first experimental values for the ionization constant of glycolic acid above 100 ∘C that have been reported. The results have been combined with recently determined values for the standard partial molar volumes of HOCH2COOH(aq) and HOCH2COO−(aq) under hydrothermal conditions to develop an “equation of state” that describes the temperature- and pressure-dependence of the equilibrium constant and standard partial molar properties of ionization from 25 to 325 ∘C.

Thiols in hydrothermal solution: standard partial molal properties and their role in the organic geochemistry of hydrothermal environments

In order to assess the potential role of organic sulfur compounds in hydrothermal systems, we use recent advances in theoretical geochemistry to estimate the standard partial molal thermodynamic properties and parameters for the revised Helgeson-Kirkham-Flowers equation of state for aqueous straight-chain alkyl thiols. Thermodynamic properties are used to determine the potential for thiol formation in both modern and Archean hydrothermal systems. We conclude that organic sulfur compounds may hold the key to the organic chemistry that led to the origin of life in hydrothermal settings. These results may also explain the presence of sulfur in a number of biomolecules present in ancient thermophilic microorganisms.

Sorption modelling by Gibbs energy minimisation: Towards a uniform thermodynamic database for surface complexes of radionuclides

Summary Radionuclide sorption on mineral-water interfaces can be thermodynamically modelled, similar to solid-solution aqueous-solution systems (only in chemical elemental stoichiometry), if definitions of the standard and reference states, surface activity terms (SAT), and elemental stoichiometries of surface-bound species are unequivocally established. A pre-requisite is that a unique common value of the reference (site) density (Γo) must be part of the definitions of standard and reference states, while the sample- and surface-specific maximum density parameters (Γmax) be included into the SAT corrections to reproduce saturation of physically available adsorption sites instead of introducing the additional mass balance constraints. Subsequently, the standard partial molal properties of surface complexes at multiple surface types on different sorbents can be found, comparable with the standard molar properties of solids, gases and aqueous species. Using surface complexation models (SCM) of U(VI) adsorption on quartz and amorphous silica (SiO2) phases in GEM (Gibbs energy minimization) implementation, a feasible way is shown how to construct a uniform, internally consistent thermodynamic dataset for surface species of radionuclides; to use standard partial molal Gibbs energies Go 298 of surface species in sorption modelling; how to convert Go 298 values from/to log K or intrinsic adsorption constants log Kint to use in the law-of-mass action (LMA) speciation codes, and finally, into “smart Kd” values for the applications related to waste repository performance assessment.

Aluminum speciation in crustal fluids revisited

Aluminum speciation in crustal fluids is assessed by means of standard thermodynamic properties at 25°C, 1 bar, and revised Helgeson-Kirkham-Flowers (HKF) (Tanger J. C. IV and Helgeson H. C., “Calculation of the thermodynamic and transport properties of aqueous species at high pressures and temperatures: Revised equations of state for the standard partial molal properties of ions and electrolytes,” Am. J. Sci. 288, 19–98, 1988) equations of state parameters for aqueous species in the system Al-O-H-Na-Si-Cl-F-SO4 derived from recent experimental data with the help of isocoulombic reactions and correlations among parameters in the HKF model. In acidic to neutral hydrothermal solutions and for fluorine concentrations in excess of 1 ppm, the fluoride complexes AlFn3−n dominate Al speciation at temperature (T) < 100°C, whereas the hydroxide fluoride species Al(OH)2F(aq)0 and AlOHF20(aq) are dominant up to ∼400°C. In high-temperature (T > 300°C) hydrothermal and metamorphic fluids, aluminum mobility is considerably enhanced by formation of NaAl(OH)3F(aq)0 and NaAl(OH)2F20(aq) ion paired mixed species. NaAl(OH)2F20(aq) controls Al transport in granite-derived fluids and during greisenization. At alkaline pH, Al(OH)4−, Al(OH)3H3SiO4−, and the NaAl(OH)40(aq) ion-pair are the dominant Al species. Thermodynamic calculations show that as a result of strong interactions of Al(aq) with NaOH, NaF, HF, and SiO2(aq) present in crustal fluids, the concentrations of aluminum in equilibrium with Al-bearing minerals can be several orders of magnitude higher than those calculated assuming that only Al hydroxyde complexes are formed. Interactions with these components are likely to be responsible for aluminum mobility during hydrothermal and metamorphic reactions.

Dissolution of primary minerals of basalt in natural waters: I. Calculation of mineral solubilities from 0°C to 350°C

The solubilities of forsterite, fayalite, enstatite, ferrosilite, hedenbergite, diopside, anorthite, high-albite, magnetite, hematite, ulvöspinel, ilmenite, F-apatite and OH-apatite and olivine, plagioclase, orthopyroxene, clinopyroxene and Fe–Ti oxide solid solutions of fixed composition were calculated in the temperature range 0–350°C at saturated water vapour pressure. The thermodynamic database used for end-member minerals was that of Robie and Hemingway [Robie, R.A., Hemingway, B.S., 1995. Thermodynamic properties of minerals and related substances at 298.15 K and 1 bar (105 Pascals) pressures and at higher temperatures. U.S. Geol. Surv. Bull. 2131, 461 pp.] except for plagioclases [Arnórsson, S., Stefánsson, A., 1999. Assessment of feldspar solubility constants in water in the range of 0° to 350°C at vapor saturation pressures. Am. J. Sci. 299, 173–209.] and that of Shock and Helgeson [Shock, E.L., Helgeson, H.C., 1988. Calculation of the thermodynamic and transport properties of aqueous species at high pressures and temperatures: correlation algorithms for ionic species and equation-of-state predictions to 5 kb and 1000°C. Geochim. Cosmochim. Acta 53, 2009–2036.] and Shock et al. [Shock, E.L., Oelkers, E.H., Johnson, J.W., Sverjensky, D.A., Helgeson, H.C., 1992. Calculation of the thermodynamic properties of aqueous species at high pressures and temperatures: effective electrostatic radii, dissociation constants, and standard partial molal properties to 1000°C and 5 kbar. J. Chem. Soc., Faraday Trans. 88, 803–826.] for most aqueous species. For aqueous Fe(OH) 4 − and Al(OH) 4 −, the thermodynamic properties reported by Diakonov et al. and Pokrovskii and Helgeson [Pokrovskii, V.A., Helgeson, H.C., 1995. Thermodynamic properties of aqueous species and the solubilities of minerals at high pressures and temperatures: the system Al 2O 3–H 2O–NaCl. Am. J. Sci. 295, 1255–1342], respectively, were used. In the present study, the standard partial molal properties and the HKF equation-of-state parameters for aqueous H 4SiO 4 0 were revised to better describe the recent experimental results at low temperatures. For H 4SiO 4 0, the new parameters are also consistent with quartz solubility experiments up to 900°C and 5 kbar. Further, the HKF equation-of-state parameters for aqueous Ti(OH) 4 0 were estimated from rutile solubility [Ziemniak, S.E., Jones, M.E., Combs, K.E.S., 1993. Solubility behaviour of titanium (IV) oxide in alkaline media at elevated temperatures. J. Sol. Chem. 22, 601–623.], which enables the calculations of the solubility of Ti-bearing minerals at elevated temperatures and pressures. Much higher solubilities were found for the silicate minerals below 100°C than previously reported, which is related to higher quartz solubility at low temperature and correspondingly new data on the thermodynamic properties of H 4SiO 4 0. The present results are particularly important for the stabilities of primary basaltic minerals of natural composition under weathering conditions. They are also of importance for the study of equilibrium/dis-equilibrium conditions in active geothermal systems.

Apparent Molar Volumes and Heat Capacities of Aqueous Trifluoromethanesulfonic Acid and Its Sodium Salt from 283 to 328 K

Apparent molar heat capacities $$C_{{\text{p}},\phi }$$ and volumes $$V_\phi$$ of aqueous trifluoromethanesulfonic (triflic) acid, HCF3SO3 (aq.) were determined with a Picker flow microcalorimeter and vibrating-tube densimeter at temperatures from 283 to 328 K and molalities from 0.05 to 9.5 mol-kg-1. Values of $$V_\phi$$ and $$C_{{\text{p}},\phi }$$ display a maximum near 0.8 mol-kg-1. $$V_\phi$$ also displays a shallow minimum at ∼5 mol-kg-1, while $$C_{{\text{p}},\phi }$$ continues to decrease smoothly up to the limit of our measurements at 9.5 mol-kg-1. We attribute this behavior to ion–ion interaction between triflate and the hydrated proton to form the aqueous complex H2n+1O n + CF3SO 3 - (aq.), n = 5. Standard partial molar properties C p o and Vo are consistent with results obtained from NaCF3SO3 (aq.) and yield values for the triflate anion CF3SO 3 - (aq.), over this range.

Thermodynamic properties of surface species at the mineral–water interface under hydrothermal conditions: a Gibbs energy minimization single-site 2p KA triple-layer model of rutile in NaCl electrolyte to 250°C

Standard partial molal thermodynamic properties of surface species in a single-site 2p K A triple-layer model (TLM) for rutile in NaCl electrolyte, consistent with the SUPCRT92-98 data, were estimated at temperatures T = 0 to 250°C and saturated vapor pressure P SAT using a Gibbs energy minimization (GEM) approach (Kulik, 1999) and hydrothermal potentiometric titration data (Machesky et al., 1998a). Evaluation strategy was based on conventional setting to zero of standard state entropy and heat capacity effects of the “surface hydronium desorption” reaction >O 0.5H 2 + = >O 0.5H 0 + H aq +, with one-term temperature extrapolation appropriate. The standard state properties of the “surface water dissociation” reaction >O 0.5H 0 = >O 0.5 − + H aq + in a three-term extrapolation, with Cp ° 298(>O 0.5 −) assumed equal to Cp ° 298(OH aq −) and Δ S ° 298 estimated from enthalpy of rutile surface protonation in water Δ H ° prot,298 , yielded a very good match of predicted pristine point of zero charge (pH PPZC) and measured point of zero charge (pH PZC) on rutile to T = 250°C. Correlation of Δ H ° prot,298 for various oxides versus pH PPZC suggests that the entropy Δ S ° prot,298 = 25 ± 4 J K −1 mol −1 may be constant for all oxide surfaces, pH PPZC( T) be hence a function of pH PPZC at T 0 = 25°C only: pH PPZC,T = −29.134 + T 0/ T(pH PPZC,T0 + 3.2385) + 4.545ln T. The standard partial molal properties of Na + and Cl − outer-sphere surface complexes on rutile were estimated from GEM TLM fits of potentiometric titration data at different T and m NaCl. Adjustable parameters were: standard partial molal Gibbs energy g 0(>O 0.5 −Na +), interdependent with inner capacitance density C 1 (increasing from 1.6 F · m −2 at 25°C to 2.3 F · m −2 at 250°C), and maximum site density Γ max (>O 0.5H 2 +Cl −). No surface activity term (SAT) ln Ξ = f(Γ max ) corrections were needed for >O 0.5 −Na + species, i.e., Na + adsorption on rutile occurs in the “TLM ideal region” up to 300°C and 1 m NaCl. From the GEM fits, parameters of three-term temperature extrapolations were found for a reaction >O 0.5H 0 + Na aq + = >O 0.5 −Na + + H aq +. Directly fitted g 0 (>O 0.5H 2 +Cl −) values were less certain because the SAT with low Γ max(>O 0.5H 2 +Cl −) = 0.9 ± 0.1 sites nm −2 had to be involved. Hence, symmetric electrolyte adsorption (pH PZSE = pH PPZC) has been assumed, from which the standard partial molal properties of >O 0.5H 2 +Cl − species were found using a zero-term extrapolation of an isocoulombic reaction >O 0.5H 2 +Cl − + >O 0.5 − + Na aq + = >O 0.5 −Na + + >O 0.5H 2 + + Cl aq −. This balanced like-charge reaction can serve as a very useful constraint reducing the set of adjustable TLM parameters at given T and pH PZC to C 1, p K Na and Γ max (>O 0.5H 2 +Cl −), optimal values of which could have been found from GEM fits of the rutile potentiometric titration data at different T and m NaCl.

Thermodynamic Properties of Sodium n-Perfluoroalkanoates in Water and in Water + Cyclodextrins Mixtures

Densities and heat capacities of water-substrate and water-substrate-cyclodextrin mixtures were determined at 298 K. The substrates studied are sodium n-perfluoroalkanoates, (CF) n COONa, (from sodium perfluoroacetate to sodium perfluorooctanoate) and the cyclodextrins are hydroxypropyl-a-cyclodextrin (HP-α-CD), hydroxypropyl-β-cyclodextrin (HP-β-CD), and hydroxypropyl-y-cyclodextrin (HP-γ-CD). From experimental data of (CF) n COONa in water, the standard partial molar properties were determined. Moreover, the properties of micellization of the surfactants were determined. HP-β-CD hardly affects the thermodynamic properties of CF 3 COONa while it strongly does those of the other substrates. From the experimental data the standard partial molar properties of the inclusion complex were calculated and compared to those of the sodium n-alkanoates + HP-β-CD we reported elsewhere (Langmuir 1998, 14, 6045). The larger hydrophobicity of the CF 2 group with respect to the CH 2 one is reflected in the properties of the inclusion complex. Studies extended to HP-α-CD and HP-γ-CD indicate that the size cavity of the cyclodextrin influences the thermodynamics of the inclusion complex formation more than that for the hydrogenated substrates. The presence of cyclodextrin affects the property of the surfactant in the aqueous phase while it scarcely does that in the micellar phase.