Compensation Between the Entropic and Enthalpic Changes Arising from Changes in Solvent–Solvent Interactions in Mixed Solvents

A theorem presented by Professor Ben-Naim (J Phys Chem 82:874–885, 1978) states that the standard state enthalpy and entropy changes arising from changes in the solvent structure that are induced by solvation of a solute cancel exactly in the standard state Gibbs energy. In this paper this is explored by consideration of the thermodynamics of transfer of electrolytes in mixed solvents, using previously developed models of the solvation process. Two cases are considered. One is random solvation, where curvatures in plots of the transfer enthalpies and entropies, which arise from changes in solvent–solvent interactions, exactly compensate in the transfer Gibbs (free) energies, which are sensibly linear with solvent composition. The second type of system are those with strong preferential solvation where it is found that the transfer Gibbs energies can be accounted for quantitatively in terms of changes in the solute–solvent interactions, with no contribution from changes in solvent–solvent interactions. The results are entirely consistent with the Ben-Naim theorem.     

Solvation enthalpy and the thermodynamics of hydration of trans-cyclohexyl-1,4-diamine and cis-cyclohexyl-1,2-diamine

The enthalpy of solution of trans-cyclohexyl-1,4-diamine and cis-cyclohexyl-1,2-diamine in water was determined by calorimetry. The enthalpy of hydration was determined from this quantity and from the enthalpy of sublimation/vaporization presented in another paper by the authors. Considering the solvation process resulting from cavity creation in the solvent and variation of solute conformation transfer steps, the enthalpy corresponding to solute–solvent interaction was estimated. The entropies of solvation and interaction were calculated from the values given for the enthalpies in the present paper and those available for the Gibbs free energies.     

The chemical stability of L-isoleucine,L-threonine,and L-serine in aqueous solutions of KCl at 298.15 K

The experimental saturated solubilities of L-isoleucine, L-threonine, and L-serine in aqueous mixtures of a KCl solution at 298.15 K are presented in this article. The solubilities are measured by gravimetric method. In the present study the theoretical calculation of the standard transfer Gibbs free energy, cavity forming enthalpy of transfer, cavity forming transfer Gibbs free energy, dipole-dipole interaction effect have been computed. The chemical effects of the transfer Gibbs energies for the present amino acids have been obtained by subtracting the cavity effects and dipole-dipole interaction effects from the ΔG_t⁰(i). The stability of the experimental amino acids in aqueous KCl in terms of thermodynamic parameters is explained.     

Improper matching of solvation energy components in G-based mixing rules

The physical significance of terms in two excess Gibbs free energy (G^ex)-based mixing rules, the modified Huron–Vidal (MHV1) and Wong–Sandler (WS) mixing rule, are examined through the use of solvation free energy. It is found that these mixing rules are in fact matching the charging contributions of solvation in an equation of state (EOS) to the complete solvation free energy in a liquid activity coefficient model (LM). The cavity contributions in the EOS are canceled as a result of the constant liquid molar volume to molecular volume ratio. The underlying idea of G^ex-based mixing rules that the EOS should behave like a LM at some limiting condition breaks down due to such an improper matching of solvation free energy components.     

Thermodynamics of Transfer of Atomic and Molecular Species into Binary Solvents

A method was suggested for separation of the Gibbs energy of transfer of atomic, molecularspecies from a solvent Solv1 into a binary solvent (Solv1 + Solv2) into the contribution from solvation of thereaction centers and that from nonspecific interactions, solvent reorganization, and cavity formation. The relationship for calculating the former contribution can be used for thermodynamically adequate comparative estimation of the stability of complex species in solution.     

Computational Analysis of Solute–Solvent Coupling Magnitude in the Z/E Isomerization Reaction of Nitroazobenzene and Benzylideneanilines

The dynamic solvent effect often arises in solution reactions, where coupling between chemical reaction and solvent fluctuation plays a decisive role in the reaction kinetics. In this study, the Z/E isomerization reaction of nitoroazobenzene and benzylideneanilines in the ground state was computationally studied by molecular dynamics simulations. The non-equilibrium solvation effect was analyzed using two approaches: (1) metadynamics Gibbs energy surface exploration and (2) solvation Gibbs energy evaluation using a frozen solvation droplet model. The solute–solvent coupling parameter (C_coupled) was estimated by the ratio of the solvent fluctuation Gibbs energy over the corresponding isomerization activation Gibbs energy. The results were discussed in comparison with the ones estimated by means of the analytical models based on a reaction–diffusion equation with a sink term. The second approach using a frozen solvation droplet reached qualitative agreement with the analytical models, while the first metadynamics approach failed. This is because the second approach explicitly considers the non-equilibrium solvation in the droplet, which consists of a solute at the reactant geometry immersed in the pre-organized solvents fitted with the solute at the transition state geometry.     

Thermodynamic studies of binary methanol and ethanol solutions of 1-dodecanol and 1-tetradecanol at 25°C

The osmotic coefficients of binary methanol and ethanol solutions of 1-dodecanol and 1-tetradecanol wer measured at 25°C up to 8 mol-kg^–1 in methanol and 5.5 mol-kg^–1 in ethanol. The activity coefficients of the solute were calculated from Bjerrum's relation. From the osmotic and activity coeficients the excess Gibbs energies of solution as well as the respective partial molar functions of solute and solvent and the virial pair interaction coefficients for the excess Gibbs energies were calculated. In addition, the difference in the Gibbs energy of solvation for the solvent in solution relative to the pure solvent was calculated, as well as the partial molar volumes and excess partial molar volumes of solutes at infinite dilution, and the coefficients of pairwise contributions to the excess volume were determined. The thermodynamic parameters obtained are discussed on the basis of solute-solvent and solute-solute interactions.     

Studies on silver(I) solvation in binary solvent mixtures containing dimethylsulfoxide. IV determination of solvent transference numbers for AgSCN and ionic coordination numbers of Ag+ in methanol-dimethylsulfoxide mixtures at 25°C

Solvent transport by AgSCN in the methanol (M)+dimethylsulfoxide (DMSO) system has been studied at 25°C by e.m.f. measurements. The solvent transference number of DMSO is positive as its concentration increases in the cathode compartment during electrolysis. The solubility of AgSCN has been determined in methanol, in DMSO and in methanol-DMSO mixtures. Using the known Gibbs free energy of solvation for the Ag⁺ ion, the corresponding energy for SCN, was found to be independent of the mole fraction. The experimental solvent transference numbers therefore only represent the contribution of Ag⁺, this is because it is preferentially solvated by DMSO. A coordination model has been applied to the Gibbs free energy of transfer of Ag⁺ in order to obtain coordination numbers thereby allowing calculation of solvent transference numbers. The experimental and the calculated solvent transference numbers are in good agreement at mole fractions of DMSO greater than 0.5. In highly methanolic solutions the assumption that the solvation of Ag⁺ in the solvent system studied is adequately represented by a total coordination number of four, proves to be too simple.     

On the influence of solvents on the rate of ion-transfer reactions

The literature data on the kinetics of cation electrodeposition on mercury in different solvents were analysed. For all cations considered in different solvents there was a linear decrease of the logarithm of the standard charge-transfer rate constant with increasing basicity of solvent and with more negative formal potential of the electrode reaction expressed in the scale of a solvent-independent electrode, as well as a linear dependence of the activation energy on the Gibbs energy of cation transfer. No dependence of the logarithm of the heterogeneous rate constant on the rate of exchange of solvent molecules from the first solvation sphere was observed. For the different electrode systems studied in one solvent, the dependences of the activation energy on (i) the cation solvation energy, (ii) the Gibbs energy of metal amalgamation, and (iii) metal solubility in mercury were analysed.     

The Gibbs energies of transfer of 2,2′-dipyridyl and pyridine from methanol into methanol-dimethylformamide mixed solvents

The distribution coefficients of 2,2′-dipyridyl and pyridine were determined by the method of distribution between two immiscible phases over the whole range of methanol-dimethylformamide solvent compositions at 298.15 K. The results were used to calculate the Gibbs energies of transfer of 2,2′-dipyridyl and pyridine from methanol into its mixtures with dimethylformamide. Changes in the solvation state of the amines were analyzed using the enthalpy and entropy components of the Gibbs energy of transfer.     

Thermodynamic quantities relative to solution processes of Naproxen in aqueous media at pH 1.2 and 7.4

Based on van’t Hoff and Gibbs equations, the thermodynamic functions Gibbs free energy, enthalpy, and entropy of solution, mixing and solvation of naproxen (NAP) in water at pH 1.2 and 7.4, were evaluated from solubility values determined at several temperatures. The solubility at pH 7.4 and 25.0°C was almost 150 times higher with respect to pH 1.2. The enthalpies of solution were positive and greater for pH 1.2, while the entropies of solution were both negative, thereby implying a greater molecular organization at pH 7.4. The results were discussed in terms of solute–solvent interactions.     

A method for calculating the Gibbs energy of nonspecific solvation

A method for calculating the Gibbs energy of nonspecific solvation of nonelectrolytes was suggested. The new equation for the Gibbs energy of nonspecific solvation contains one solvent parameter that characterize nonspecific solvent-solute interactions and two experimental Gibbs energies of solvation in two standard solvents. The method is applicable to a wide range of solutes and solvents. It was successfully used to describe some 800 Gibbs energies of solvation for systems without specific solvent-solute interactions.     

Thermodynamics of the Solvation and phase distributions of ethylenediamine in acetonitrile-dimethylsulfoxide-hexane systems

The enthalpies of dissolution and solvation of ethylenediamine over the range of compositions of a mixed acetonitrile-dimethylsulfoxide solvent at 298 K are determined calorimetrically. It is found that with an increase in the acetonitrile concentration, the solvation exothermicity of ethylenediamine declines, owing to the resolvation of amino groups. The Gibbs energies of transfer of ethylenediamine from dimethylsulfoxide into its mixtures with acetonitrile are determined from the distribution of a substance between immiscible phases. It is found that increasing the acetonitrile concentration in a binary solvent improves the stability of the ethylenediamine solvatocomplex, owing to a change in the entropy component of the Gibbs energy.     

Thermodynamics of the complex formation of copper(II) with L-phenylalanine in aqueous ethanol solutions

Constants of the acid dissociation and complexation of L-phenylalanine (HPhe) with copper(II) ions are determined by potentiometry in aqueous ethanol solutions containing 0 to 0.7 molar fraction of alcohol. Changes in the Gibbs energy for the transfer from water to a binary solvent of L-phenylalanine, Phe^? anion, and [CuPhe]⁺ complex are calculated. It is found that the weakening of solvation of the ligand donor groups in solvents with high ethanol contents is accompanied by an increase in the stability of [CuPhe]⁺ complex.     

Effect of water—ethanol solvent on the stability of copper(<Emphasis Type="SmallCaps">ii</Emphasis>) coordination compound with the nicotinate ion

The stability constants of copper(II) complexes with nicotinate ion in water—ethanol solvent were determined by the potentiometric method at 25.0±0.1 °C and ionic strength of 0.25 (NaClO₄) in the range X_EtOH = 0—0.7 mole fractions. The stability constant of copper(II) nicotinate complex considerably increases with increasing ethanol concentration in the solvent. The contributions of reactants to the Gibbs energy of the complex formation reaction on going from water to aqueous ethanol were analyzed. The results of thermodynamic analysis of solvation effects were used to evaluate the ratio of the ion and ligand transfer Gibbs energy contributions to the change in the reaction Gibbs energy in the water—ethanol system.     

Solvation and pairwise association in a 2D fluid

It is shown that it is possible: (a) to derive the 2D scaled particle theory formula of the reversible work of cavity creation using a geometric approach; (b) to obtain the solvation Gibbs energy in a 2D Lennard-Jones fluid; (c) to calculate the solvent contribution to the solvophobic interaction of two Lennard-Jones disks on the basis of geometric arguments. The solvent-excluded surface area associated with cavity creation decreases significantly upon pairwise association, leading to a marked increase in the configurational/translational entropy of solvent disks.     

Thermodynamics of solvation and solvophobic effect in formamide

Using semi-adiabatic calorimetry, we measured the enthalpies of solution for various low-polar compounds including alkanes, aromatic hydrocarbons and their halogenated derivatives in formamide at temperature of 298 K. For the same compounds, the values of limiting activity coefficients in formamide were determined using GC headspace analysis at 298 K, and Gibbs free energies of solution and solvation were calculated. Based on these data and the available literature values of the Gibbs free energy of solvation in formamide for a number of other low-polar solutes, a study of the solvophobic effect in this solvent is performed, and its resemblance to the hydrophobic effect in aqueous solutions is demonstrated. It is shown that the contribution of the solvophobic effect into the solvation Gibbs free energy in formamide is much higher than that in aliphatic alcohols, but lower than that in water. Like in water, the magnitude of this contribution for different solutes linearly increases with the solute molecular volume. Solvophobic effect also significantly affects the enthalpies of dissolution in formamide, causing them to be more negative in the case of alkanes and more positive in the case of arenes.     

Thermodynamics of Complexation of 18-Crown-6 with NH4+ Ion in Water-Dioxane Mixtures

The stability constants of 1 : 1 complexes of ammonium ion with 18-crown-6 in water and aqueous dioxane (dioxane weight fraction 0.2, 0.4, 0.6, and 0.8) in the range 283-318 K were determined electrometrically, and the thermodynamic parameters of the complexation were calculated. The stability of the complexes is determined by the enthalpy factor. The contributions from the Gibbs energy of solvation of NH₄ ⁺ ion, 18-crown-6·NH₄ ⁺ complex, and free 18-crown-6 to stabilization of the complex with increasing content of dioxane in the mixed solvent were estimated. The thermodynamics of complexation of ammonium, sodium, and potassium ions with 18-crown-6 in aqueous-organic solvents, such as water-2-propanol, water-acetone, and water-dioxane, were compared considering the effects of reactant solvation. The variations of the conformational component of the Gibbs energy of solvation of 18-crown-6 and the parameters of selective solvation of the reactants were evaluated. The influence of the dielectric permittivity and donor-acceptor properties of mixed aqueous-organic solvents on the Gibbs energy of complexation and solvation of the cations and 18-crown-6 was subjected to correlation analysis.     

KBPh4由水到系列水-醇混合溶剂的迁移自由能

由于四苯硼盐在分析化学、生物学、电化学等各领域中的广泛用途及其大阴离子在研究与计算单个离子迁移热力学函数中所具有的特殊作用,人们对四苯硼盐的溶液热力学性质进行了广泛研究,特别是对四苯硼钠和可作为参考电解质的四苯硼盐进行了深入细致的研究 [1, 2],得到了一些重要的的结论,为溶液理论的研究提供了有力的实验基础 .但是文献中对难溶碱金属四苯硼盐由单一到不同混合溶剂中的迁移热力学性质的系统研究较少 .在前文 [3]对 KBPh4由水到水-异丙醇和由甲醇到甲醇-异丙醇混合溶剂的迁移自由能进行研究的基础上,我们系统地对 KB…