Gibbs Free Energies Of Transfer Research Articles

Molar gibbs (free) energies of transfer for barium(II) and mercury(II) from acetonitrile into nonaqueous solvents

Molar Gibbs energies of transfer for Ba 2+ and Hg 2+ were calculated from electrochemical data on the basis of the bis(biphenyl)chromium assumption for 21 solvents. The transfer data obtained for these cations could be separated into two groups according to the HSAB principle. One group consisted of systems, where both cation and solvent were capable of undergoing soft-soft interactions, the other group of systems where either the solvent or the cation or both lacked the ability for soft interactions. Within each of these two groups it was found that the Gibbs energies of transfer for Ba 2+ and Hg 2+ depended on each other as well as on the Gibbs energies of transfer of Ag +. A variety of solvent parameters were evaluated with respect to their ability to account for the Gibbs energies of transfer for Ba 2+ and Hg 2+ into hard and soft solvents. For solvent systems, which exclude soft-soft interactions, the Gibbs energies of transfer for Ba 2+ and Hg 2+ can be correlated with traditional solvent parameters such as the donor number, the B and the β parameter. Soft-soft interactions between cations and solvents can be represented by the SP parameter. A linear correlation between the Gibbs energies of transfer of the soft Hg 2+ ion and the shifts in the HgBr stretching frequencies ( D s parameter) was observed for all solvents.

Preferential solvation of ions in mixed solvents. Part 4.—Comparison of the Kirkwood–Buff and quasi-lattice quasi-chemical approaches

The relation of the Kirkwood–Buff integrals Gij=∫∞04πr2[gij(r)–1]dr where i is an ion solute and j one of two solvents in their mixture, to measurable quantitites is examined in the light of recent work of Ben-Naim and Newman. The derived local excess of one of the solvents δxij is compared with the same quantity calculated for the author's quasi-lattice quasi-chemical mode. The results for three aqueous solvent mixtures, involving a protic solvent (methanol), a strong donor aprotic solvent (dimethyl sulphoxide) and a weak donor aprotic solvent (acetonitrile) and several ions are compared and discussed. It is concluded that the need for the derivative of the standard Gibbs free energy of transfer of the ion with respect to the solvent composition limits the reliability of the Kirkwood–Buff approach.

Rate–equilibrium relationships based on the CH-acidity constants of oxocarbenium ions, for proton transfer from hydronium ion to α-methoxystyrenes: evidence for perfect synchronization between bond cleavage, bond formation, and positive-charge delocalization

The CH-acidity constants in water for the oxocarbenium ions derived from ring-substituted α-methoxystyrenes have been calculated from the following literature data. (i) Equilibrium constants for oxocarbenium-ion formation from the corresponding acetals; (ii) equilibrium constants for the acetalto-enol ether process in methanol; (iii) Gibbs free energies of transfer of acetals and enol ethers from methanol to water. The plot of the logarithms of hydronium-ion-catalytic rate constants against the pKa values of the intermediate ions exhibits a slightly curved relationship, with a mean slope βs= 0.58, which can be accounted for by the Marcus equation with an intrinsic barrier of ca. 15 kJ mol–1 and work terms Wr= 44 kJ mol–1 and Wp= 52 kJ mol–1. The agreement of all these parameters with those derived when the catalyst is changed indicates that C–H bond formation and O–H bond cleavage are synchronous concerted primitive changes. Separation of substituted-ring polar effects and direct resonance interactions from the overall substituent effects on rates and equilibria also shows that there is perfect synchronization between proton transfer and positive-charge delocalization.

Gibbs free energy of transfer of glycine and diglycine from water to alkylurea solutions: Measured vs. calculated values

Ternary systems comprising water (1), glycine (diglycine) (2) and alkylurea (3) have been investigated using vapor pressure osmometry. Equations were obtained in terms of the molalities of the solutes for the activity coefficients of glycine and diglycine in these systems. The alkylureas used were methyl-, ethyl- and N, N′-dimethylurea. Using the activity coefficients the Gibbs free energy of transfer at infinite dilution of component 2 from water to alkylurea solutions was determined. Since the enthalpies of transfer are known, the corresponding entropies could also be obtained. Calculation of the Gibbs free energy of transfer at infinite dilution of component 2 rests on the assumption that it can be divided into two parts: the difference between the Gibbs free energy of cavity formation and that of interaction in the alkylurea solution and water, respectively. The first part was calculated by scaled particle theory using experimental density and surface tension data. The second part was taken to be due mainly to the change in dipole-dipole interactions.

The solvation of fluoride ions. I. Free energies for transfer from water to aqueous alcohol and acetonitrile mixtures

The solubilities of NaF and LiF have been measured in mixtures of water with methanol, ethanol, ethylene glycol and acetonitrile over the whole composition range. Gibbs free energies of transfer of the fluoride ion from water to the mixed and pure solvents have been calculated from the solubility data via the tetraphenylarsonium tetraphenylborate assumption. The values so obtained indicate that the fluoride ion is preferentially solvated by water as a result of its strong hydrogen-bonding capabilities. Desolvation of the fluoride ion is especially marked in acetonitrile-rich solutions.

Preferential solvation of ions in mixed solvents. Part 2.—The solvent composition near the ion

The quasi-lattice quasi-chemical theory of preferential solvation that was related previously to the Gibbs free energy of transfer of an ion from a reference solvent to a mixture of solvents has now been extended to yield the actual amount of the preferential solvation of the ion. This is defined as δX1=xL1–x1, the excess (or deficiency) of the local mole fraction of the solvent S1 in the vicinity of the ion X over its mole fraction in the bulk, in a very dilute solution of X, in the mixture of solvents S1 and S2. The preferential solvation obtained for six cases as illustrations (sodium, silver and chloride ions in aqueous dimethyl sulphoxide and acetonitrile) is related to the equilibrium constants for solvent exchange.

Electrode kinetics of the Eu(III)—Eu(II) system at mercury electrodes in wateracetonitrile (AN) and waterDMSO mixtures

The electrode reaction of the Eu(III)—Eu(II) system on the mercury electrode in waterAN and waterDMSO mixtures has been studied. Charge transfer rate constants, and formal potentials at different mixed solvent compositions are determined. The standard rate constants of the process investigated passed through a minimum, as the concentration of AN in waterAN mixtures increased, while in waterDMSO mixtures it increased with increasing DMSO content. Formal potentials expressed in the ferrocene scale were used to calculate the difference between Gibbs free energies of transfer of the Eu(III) and Eu(II) ions from water to waterAN and waterDMSO mixtures.

Absolute electrode potentials in dioxane-water solvent mixtures and transfer free energies of individual ions

Standard e.m.f. values at 25 ° C for the cells Pt, H 2(g, 1 atm) ¦HI, solvent ¦AgI, Ag and M, Mx ¦solvent ¦AgX, Ag in nine solvent mixtures of dioxane with water, containing up to 80 wt.% dioxane, are reported. The e.m.f. data were used to determine standard absolute potentials of the hydrogen, the Ag, AgX (X  Cl, Br and I) and the M, M + (M  Li, Na, K, Rb and Cs) electrodes in these solvents by a new method reported recently. The radii of the solvated cations and their solvation extent in such media have been evaluated. The standard Gibbs free energies of transfer of individual ions from water to the respective solvents have also been computed. The results are interpreted and discussed in terms of the solvation characteristics of the solvents. The data obtained in the dioxane-water solvent system are compared with those in various aqueous protic and aprotic solvent systems.

Thermodynamic studies of the interactions of alkylureas with glycine, diglycine, and triglycine

The solubilities of glycine, diglycine, and triglycine have been measured in methyl‐, N,N '‐dimethyl‐, and ethylurea solutions. Gibbs free energies of transfer of glycine, the two oligoglycines, and the peptide group from water to alkylurea solutions have been calculated. Enthalpies of transfer for the same compounds and the peptide group have been determined from calorimetric measurements. The additivity principle is roughly obeyed for the contribution of the peptide group to the enthalpy of transfer. Comparison of the thermodynamic quantities of transfer to urea and alkylurea solutions reveals significant differences, those of the alkylureas clearly reflecting the hydrophobic interaction. Furthermore, Gibbs free energy of transfer of the peptide group to urea solutions is positive at lower urea concentrations but above 4 M it becomes negative and increases (i.e. becomes more negative) with increasing concentration. The interaction with the peptide group is thus an important factor in the denaturing activity of urea. For the alkylureas, on the other hand, the interaction with the peptide group is generally less favorable for unfolding.

ChemInform Abstract: Determination of Gibbs Free Energy of Transfer for Some Univalent Ions from Water to Methanol, Acetonitrile, Dimethylsulfoxide, Pyridine, Tetrahydrothiophene and Liquid Ammonia; Standard Electrode Potentials of Some Couples in These Solvents.

ChemInformVolume 18, Issue 26 Article ChemInform Abstract: Determination of Gibbs Free Energy of Transfer for Some Univalent Ions from Water to Methanol, Acetonitrile, Dimethylsulfoxide, Pyridine, Tetrahydrothiophene and Liquid Ammonia; Standard Electrode Potentials of Some Couples in These Solvents. M. JOHNSSON, M. JOHNSSON Lawrence Berkeley Lab., Univ. Calif., Berkeley, CA 94720, USASearch for more papers by this authorI. PERSSON, I. PERSSON Lawrence Berkeley Lab., Univ. Calif., Berkeley, CA 94720, USASearch for more papers by this author M. JOHNSSON, M. JOHNSSON Lawrence Berkeley Lab., Univ. Calif., Berkeley, CA 94720, USASearch for more papers by this authorI. PERSSON, I. PERSSON Lawrence Berkeley Lab., Univ. Calif., Berkeley, CA 94720, USASearch for more papers by this author First published: June 30, 1987 https://doi.org/10.1002/chin.198726058AboutPDF ToolsRequest permissionExport citationAdd to favoritesTrack citation ShareShare Give accessShare full text accessShare full-text accessPlease review our Terms and Conditions of Use and check box below to share full-text version of article.I have read and accept the Wiley Online Library Terms and Conditions of UseShareable LinkUse the link below to share a full-text version of this article with your friends and colleagues. Learn more.Copy URL Share a linkShare onFacebookTwitterLinked InRedditWechat No abstract is available for this article. Volume18, Issue26June 30, 1987 RelatedInformation

Redox equilibria in the Cu2+-Cu+-Cu system in water-dimethylsulphoxide (DMSO) mixtures

The redox equilibria in the Cu2+-Cu+-Cu system have been studied in water-DMSO mixtures using the potentiometric and coulometric techniques. The formal potentials of the Cu2+/Cu+, Cu2+/Cu and Cu+/Cu couples as well as the equilibrium constants of the reproportionation reaction Cu2++Cu=2 Cu+ were determined. Based on the potentials expressed in the ferrocene electrode scale,Gibbs free energies of transfer of Cu2+ and Cu+ from water to water-DMSO mixtures were calculated and discussed. A preferential solvation of Cu+ byDMSO was found.

Determination of Gibbs free energy of transfer for some univalent ions from water to methanol, acetonitrile, dimethylsulfoxide, pyridine, tetrahydrothiophene and liquid ammonia; standard electrode potentials of some couples in these solvents

The free energy of transfer, Δ G° tr, for 21 univalent ions are determined from water to methanol, acetonitrile, dimethylsulfoxide (DMSO), pyridine, tetrahydrothiophene and liquid ammonia. These solvents show a wide range of donor properties, whereby water and methanol are regarded as hard donors, dimethylsulfoxide and acetonitrile are on the borderline between hard and soft, and the remaining solvents are regarded as typical soft donors. The Δ G° tr values of ionic compounds are calculated from solubility product measurements of 1:1 salts. The extrathermodynamic tetraphenylarsonium tetraphenylborate (TATB) assumption has been applied in order to calculate the contributions from the single ions. The TATB assumption implies that the two large ions Ph 4As + and BPh 4 − are equally solvated, thus Δ G° tr(AsPh 4 +)=Δ G° tr(BPh 4 −), for all solvent pairs. Standard electrode potentials in non-aqueous solvents can be calculated from the standard electrode potentials in water and the Δ G° tr values. The standard electrode potentials calculated from the solubility product measurements, and the potentiometrically determined ones were found to be in excellent agreement. The extrathermodynamic assumption has thereby been experimentally shown to be close to the truth.

Standard Gibbs free energies of transfer of NaCl and KCl from water to mixtures of the four isomers of butyl alcohol with water. The use of ion-selective electrodes to study the thermodynamics of solutions

Measurements have been made on NaCl and KCl in water and in mixtures of water with the four isomers of butyl alcohol using the following cell, which has no liquid junction and which consists of ion-selective electrodes: cation(M); responsive glass or ion-selective electrode [graphic ommitted]. The standard Gibbs free energies of transfer of NaCl and KCl from water to mixtures of water with the four isomers of butyl alcohol were calculated from cell potentials. This paper compares measurements of ΔE°t and G°t using ion-selective electrodes with those obtained from amalgam cells. The results obtained using ion-selective electrodes are reliable, and the differences between ΔG°t of NaCl and KCl from water to butyl alcohol–water mixtures are very small. ΔG°t is proportional to the amount of butanol present over the experimental concentration range.

Non-ideal behaviour of benzene solutions of tri-n-octylammonium bromide and cyclohexanol

The practical osmotic coefficients for the benzene–tri-n-octylammonium bromide–cyclohexanol system have been determined by the cryoscopic method and expressions for the activity coefficients of both solutes in the ternary system have been deduced. The regression coefficients for these expressions have been obtained via the Gibbs–Duhem relation. The effects of different media on the solute activity coefficients have been elucidated by the total, primary and secondary medium effects. In addition, values of the partial molar Gibbs free energy of transfer at infinite dilution of tri-n-octylammonium bromide for various constant concentrations of cyclohexanol and vice versa have been determined, together with the limiting value of their derivatives.

Absolute electrode potentials in dimethyl sulphoxide-water mixtures and transfer free energies of individual ions

The standard potentials of H 2|H +, M|M + (M = Li, Na, K, Rb and Cs) and Ag¦AgX (X = Cl, Br and I) electrodes in seven aqueous solutions of dimethyl sulphoxide (DMSO), containing up to 60 wt.% DMSO, have been determined from EMF measurements of cells of the type: Ag¦AgX¦MX ( m), S¦M(Hg)¦MX ( m), W¦AgX¦Ag, or a variant of it, at 25°C by our recently reported procedure. The interest, validity and general applicability of this procedure in both aqueous protic and aprotic solvents have been demonstrated. The radii of solvated cations and their solvation extent in these media have been calculated. The standard Gibbs free energies of transfer of halogen acids and alkali metal halides as well as their constituent individual ions from water to each of the DMSO-water mixtures have been also computed. The results are interpreted and discussed.

Importance of the Debye interaction in organic solutions: Henry's law constants for polar liquids in nonpolar solvents and vice versa

Henry's law constants have been determined for γ-butyrolactone (BL), ethyl acetate (EA), and 2-methyl-3-pentanol (MEP) in mixtures of iso-octane (ISO) and toluene (TOL), for BL, EA, TOL, and ISO in cinnamaldehyde (CIN) and for TOL and ISO in each other and in BL. From these data and published vapor pressures, the activity coefficients at infinite dilution and the standard molar Gibbs free energy of transfer, ΔG20 of the solutes from dilute solution in ISO to dilute solution in each solvent medium have been calculated. The different behavior patterns of BL and EA are attributed to differences in their abilities to exist in different conformations possessing different dipole moments. For polar solutes, ΔG20 decreases with increasing polarizability of the solvent and with increasing dipole moment of the solute, suggesting increased contributions from dipole-induced dipole (Debye) interactions. The sigmoidal plot of ΔG20 against the change in pair potential energy calculated from the classical expressions suggests that ΔG20 seriously underestimates the strength of the Debye interactions in comparison with the London interactions.

Interactions of myoglobin with urea and some alkylureas: II. Calorimetric and circular dichroic studies

The interactions of myoglobin with urea, methyl-, N, N′-dimethyl- and ethylurea were studied by means of calorimetry and circular dichroism (CD). The enthalpies of transfer from water to aqueous denaturant solutions are positive for the alkylureas and negative for urea. The difference is due to the presence of hydrophobic groups in the alkylureas. Gibbs free energies of transfer for urea solutions were obtained from preferential binding data determined previously. An attempt is made to interpret the values of the thermodynamic quantities in terms of various interactions between protein and denaturant. Analysis of the far-ultraviolet CD spectra reveals some differences in the denaturing activity of urea and the alkylureas, the latter being stronger denaturants than urea. Myoglobin displays relatively high stability towards these denaturants since concentrations above 5 M are needed for achieving major conformational changes.

Studies of the interaction of methanol with pectin in aqueous solution

The interaction of methanol with pectin (degree of esterification 58%) in aqueous solution has been studied by conductivity measurements, circular dichroism, and equilibrium dialysis. Compared to other aliphatic alcohols methanol has a strong precipitating effect on pectin both in water and in 50% sucrose solutions at pH 7·0 and 3·4. The standard Gibbs free energy of methanol transfer from water into pectin solutions of concentration 0·024–0·032 g-equiv. of ester groups (kg of solvent) −1 is 4 kJ mole −1. The interaction of methanol with pectin gives a complex in which each ester group binds one molecule of alcohol. The reaction is assumed to be caused by the formation of a hydrogen bond involving the hydrogen atom of the hydroxyl group of methanol and the unshared electron pair of the carbonyl group. Methanol interacts strongly with pectin compared to other aliphatic alcohols because of its high acidity.

Molar gibbs (free) energies of transfer of silver(I), copper(I) and potassium(I)

Molar Gibbs energies of Ag+ for the transfer from acetonitrile into formamide, N-methylformamide, N,N-dimethylformamide, N,N-diethylformamide, N,N-dimethylacetamide, N,N-diethylacetamide, N-methyl-2-pyrrolidone, tetramethylurea, dimethyl sulphoxide, hexamethylphosphoric triamide, acetone, propylene carbonate, benzonitrile, N,N-dimethylthioformamide, N-methylthio-2-pyrrolidone and hexamethylthiophosphoric triamide have been calculated from the half-wave potentials of bis(biphenyl)chromium tetraphenylborate versus the silver, 0.01 mol dm–3 silver ion electrodes in the respective solvents as well as from polarographic half-wave potentials of Ag+vs. bis(biphenyl)chromium (I/O) in benzonitrile, N,N-dimethylthioformamide, N-methylthio-2-pyrrolidone and hexamethylthiophosphoric triamide. Molar Gibbs energies of transfer for K+ have also been calculated from polarographic half-wave potentials for the solvents mentioned, except for formamide and for hexamethylphosphoric triamide. Molar Gibbs energies of transfer for Cu+ from acetonitrile into benzonitrile, N,N-dimethylthioformamide, N-methylthio-2-pyrrolidone and hexamethylthiophosphoric triamide have been obtained from polarographic half-wave potentials employing the bis(biphenyl)chromium assumption. The data have been compared with molar Gibbs energies of transfer derived via the tetraphenylarsonium tetraphenylborate assumption and the assumption of negligible liquid junction potentials. A comparison of Gibbs energies of transfer for Ag+ with the data for K+ showed the difference in interactions between ‘hard’ and ‘soft’ solvents.

A study of the structure of water and its dependence on solutes, based on the isotope effects on solvation thermodynamics in water

The solvation of a particle in water, whether a ‘‘foreign’’ particle or a molecule of water, is expressed in terms of a non-hydrogen-bonding contribution to the pair potential and a contribution from hydrogen bonding. Only the latter depends on whether the water is H2O or D2O, since the hydrogen bond energy differs in these kinds of water. The effect of the isotopic constitution of the water on the solvation is examined for the cases of an inert solute, a water molecule, and a hydrogen-bond-forming solute. The average number of hydrogen bonds in which any water molecule in pure water participates is deduced from the Gibbs free energy and the enthalpy of condensation of H2O, D2O, and T2O molecules into the respective liquids. This number decreases from about 0.95 at 0 °C to about 0.35 at 100 °C, being a few percent higher in D2O than in H2O. The Gibbs free energies of transfer of gaseous solutes, nonelectrolytes, and ions from light to heavy water are interpreted in terms of the average number of hydrogen bonds broken or made in the water per particle of solute.