The ion transfer of the basic dye rhodamine B across the liquid-liquid interface of two immiscible solvents

The ion transfer of the basic dye rhodamine B at the interface between water and nitrobenzene, water and 1, 2-dichloroethane, as well as water and nitrobenzene - chlorobenzene mixtures has been studied by cyclic voltammetry and chronopotentiometry with linear current scanning. A transfer mechanism of rhodamine B is proposed in terms of its electrochemical behavior, dissociation and distribution equilibria, and is ascribed as diffusion-controlled reversible process of rhodamine B. The experimental data obtained for the relationship between interracial half-wave potential Δ^W_oφ° and pH are in agreement with the theoretical equation based on the mechanism, and the standard interfacial potential differences Δ^W_oφ° and standard Gibbs energies Δ^W_oG° are calculated by extrapolation. The effect of the nature of solvent on the transfer behavior and the stability of the interface have been discussed.     

The double layer at the interface between two immiscible electrolyte solutions: Part II. Structure of the water/nitrobenzene interface in the presence of 1:1 and 2:2 electrolytes

From fast galvanostatic pulse measurements at 25°C the capacitance of the water/nitrobenzene interface was evaluated as a function of the interfacial potential difference Δ_o^w? for systems consisting of NaBr, LiCl or MgSO₄ in water and tetrabutylammonium tetraphenylborate, tetraphenylarsonium tetraphenylborate or tetraphenylarsonium dicarbollylcobaltate in nitrobenzene. The modified Verwey—Niessen model, in which an inner layer of solvent molecules separates two space-charge regions (the diffuse double layer), describes the structure of the water/nitrobenzene interface well at electrolyte concentrations above ca. 0.02 mol dm^?3, provided that the ions are allowed to penetrate into the inner layer over some distance. For all the systems studied the zero-charge potential difference was found at Δ^w_o?_pzc ≈ 0 on the basis of the standard potential difference Δ^w_o?⁰_TMA + = 0.035 V for tetramethylammonium cation which was used as a reference ion. At zero surface charge a comparison was made with the theoretical capacitance calculated using the mean spherical approximation for a model consisting of two ion and dipole mixtures facing each other. The effect of ion penetration on the interfacial capacitance was estimated from the solution of the linearized Poisson-Boltzmann equation for a triple dielectric model with a continuous distribution of the point ions. The concentration-independent inner layer potential difference and capacitance can only be inferred from the capacitance data if the ion size effect is taken into account. A non-iterative procedure based on the hypernetted-chain equation was used for the evaluation of the potential drop across the diffuse double layer. The extend of the penetration into the inner layer appears to be a function of ion solvation, e.g. the more hydrated ion the less extensive ion penetration is likely.     

Evaluation of Gibbs free energy for the transfer of a highly hydrophilic ion from an acidic aqueous solution to an organic solution based on ion pair extraction

A method to determine the standard Gibbs free energy for the transfer, ΔG°_tr, of a highly hydrophilic metal ion from an aqueous solution, W, in the presence of high concentration of H⁺ to an organic solution, O, was proposed based on the theoretical consideration of the distribution process of ions between W and O. The usefulness of the proposed method was verified experimentally by comparing ΔG°_tr of Mg²⁺ determined by the method with that obtained by voltammetry for the ion transfer at the W|O interface. The O examined were nitrobenzene (NB) and 1,2-dichloroethane (DCE). By applying the proposed method, ΔG°_tr of NpO₂⁺, UO₂²⁺, NpO₂²⁺ and PuO₂²⁺ from an acidic W to NB were determined.     

Interactions of Peptides and Lysozyme with Aqueous Tetraethylammonium Bromide at 298.15 K

The apparent molar volumes, V _{ø, 2}, of gly-leu, gly-gly-leu and the partial specific volume ν^° of hen-egg-white lysozyme have been determined in aqueous of TEAB solutions by density measurements at 298.15 K. These data have been used to calculate the infinite dilution apparent molar volumes V _2,m ^o for the peptides in aqueous TEAB solutions and the standard partial molar volumes of transfer Δ_tr V _2,m ^o of the peptides from water to aqueous TEAB solutions. The results on Δ_tr V _2,m ^o of peptides from water to aqueous TEAB solutions have been interpreted in terms of ion-ion, ion-polar, hydrophilic-hydrophilic and hydrophobic-hydrophobic group interactions. In order to supplement this information, enthalpies of transfer of aqueous peptides from water to TEAB solution have been determined at 298.15 K using a VP-ITC titration calorimeter. The data on partial molar volumes and enthalpies of transfer have been discussed in light of various interactions operating in the ternary system of peptides, water and TEAB. The partial specific volume of transfer of lysozyme from water to aqueous TEAB solutions also indicates the predominance of hydrophobic interactions.     

Solvent extraction of lead using a nitrobenzene solution of strontium dicarbollylcobaltate in the presence of polyethylene glycol PEG 400

Summary From extraction experiments and γ-activity measurements, the extraction constant corresponding to the equilibrium Pb²⁺(aq)+SrL²⁺ (nb)↔PbL²⁺ (nb)+Sr²⁺ (aq) taking place in the two-phase water-nitrobenzene system (L=PEG 400; aq = aqueous phase, nb = nitrobenzene phase) was evaluated as logK_ex(Pb²⁺, SrL²⁺)=2.0±0.1. Further, the stability constant of the PEG 400 - lead complex in nitrobenzene saturated with water was calculated for a temperature of 25 °C: log β_nb(PbL²⁺)=12.9±0.1.     

Ion transfer of bromophenol blue across liquid-liquid interfaces

The ion transfer of the acidic dye bromophenol blue (BPB) at the interfaces of water/nitrobenzene (W/NB), water/1,2-dichloroethane (W/1,2-DCE) and water/(nitrobenzene+chlorobenzene) (W/(NB +CB)) was studied in detail by cyclic voltammetry (CV), chronopotentiometry with linear current scanning (CLC), controlled potential electrolysis and UV spectroscopic methods. Using controlled potential electrolysis, we observed successfully the transfer process of BPB across the W/NB interface from the colour changes of BPB in two different phases. The proposed transfer mechanism for BPB is proved to be reasonable using UV spectroscopy of the product of the electrolysis. The standard potential differences Δ^o_w^o and the standard Gibbs energies of the BPB transfer from water to some organic solvents were calculated. The dissociation constants of BPB obtained were quite close to the literature values.     

Ionic solvation in water + co-solvent mixtures. Part 8. Total free energies of transfer and free energies of transfer with the “neutral” component removed of single ions from water into water + acetone

The acid dissociation constants of a wide range of acids in water+acetone mixtures have been combined with values for the free energy of transfer of the proton. ΔG⁰_t(H⁺ to calculate values for the free energy of transfer of ions which derive only from the charge on the ion. ΔG⁰_t(i)_c. As the values of ΔG⁰_t(H⁺) have been revised, revised values for the total free energies of transfer of cations and anions, ΔG⁰_t(M⁺) and ΔG^o_t(X^-), are given. New data for ΔG^o_t(MX_n) is also split into values for ΔG⁰_t(Mⁿ⁺) (where n=1 and 2) and ΔG⁰_t(X^?). These free energies of transfer, both total and those deriving from the charge alone, are compared with similar free energies in other mixtures water+co-solvent. Values for ΔG^o_t(i)_c do not conform to a Born-type relationship and show the importance of structural effects in the solvent even when only the transfer of the charge is involved.     

Electron transfer reactions between the superoxide ion and quinones

The electron transfer reactions of the superoxide ion with benzoquinone, trimethylbenzoquinone, and menadione in dimethylformamide were studied. A procedure of the determination of the relative rate constants of these reactions was developed; the reaction of O? ₂ with butyl bromide was chosen as a standard one. The relative rate constants measured at 20,°, 35°, and 50°C were slightly dependent on the quinone structure. The relationship between the free energy ΔF*of the electron transfer reactions and the standard free energy ΔF^o was discussed. This relationship is proposed as ΔF* = αΔF^o + β, where the proportionality coefficient α is equal to 0.04–0.11 for exothermal reactions and to 0.90–0.96 for endothermal reactions.     

Thermal and Some other Properties of 2,4′-Bipyridyl Complexes with Various Salts of Lead(II)

New complexes of lead(II) with 2,4′-bipyridyl (L), with the general formulae PbL₂X₂ (where X ^?1=Cl, Br, I, NCS) and PbL₃X₂ (where (X]^?1=NO₃, ClO₄), have been prepared. Analysis of the IR spectra indicates that the 2,4′-bipyridyl is bonded to the Pb(II) ion through the least hindering N(4′). The thermal decompositions of the complexes were studied under non-isothermal conditions in air. The intermediates of decomposition at different temperatures were characterized by thermal analysis (TG and DTG), chemical analysis and X-ray diffraction. Upon heating, the complexes undergo full or partial deamination. The complexes PbL₂Cl₂ and PbL₂Br₂ decompose to volatile lead(II) halide. PbO is the final product of decomposition for the other complexes.     

Thermodynamic transfer functions for urea and thiourea from water to water-tetrahydrofuran mixtures from precise vapor-pressure measurements

The rate of change of the standard chemical potential with solvent composition, \(\partial \bar G_0 /\partial Z\) , has been calculated from precise vapor-pressure measurements for urea at three temperatures and for thiourea at 298.15°K in water-tetrahydrofuran (THF) mixtures. From these results the standard free energy of transfer ΔG _t ^o of the solutes from water to various water-THF mixtures has been obtained together with the standard molar entropy ΔS _t ^o and the standard molar enthalpy ΔH _t ^o of transfer at 298.15°K in the case of urea. The quantity ΔG _t ^o for urea is negative in the water-rich region and positive for mole fractions THF>0.2. There is a nearly complete compensation between ΔH _t ^o andTΔS _t ^o at 298.15°K up to mole fraction THF=0.5. These phenomena can be partly related to the structure in H₂O-THF mixtures.     

Extraction of lead with nitrobenzene solution of strontium bis-1,2-dicarbollylcobaltate in the presence of 15-crown-5

From extraction experiments and γ-activity measurements, the extraction constant corresponding to the equilibrium Pb²⁺(aq)+SrL₂ ²⁺(nb)⇆PbL₂ ²⁺(nb)+Sr²⁺(aq) taking place in the two-phase water-nitrobenzene system (L=15-crown-5; aq = aqueous phase, nb = nitrobenzene phase) was evaluated: logK _ex (Pb²⁺,SrL₂ ²⁺)=3.0. Further, the stability constant of the PbL₂ ²⁺ complex in nitrobenzene saturated with water was calculated: log β_nb(PbL ₂ ²⁺ )=17.8     

The thermodynamic characteristics of formation of organic molecule complexes with the magnesium ion in water: The results of quantum-chemical modeling

The Gibbs energy ΔG _b of formation of organic molecule complexes with the Mg²⁺ ion in water was calculated on the basis of a two-stage scheme for the complex formation reaction. The first stage is ligand transfer from infinity into the second coordination sphere of the Mg²⁺ ion, and the second stage is the dissociation of bonds between water molecules and the Mg²⁺ ion and the formation of bonds between the ligand and Mg²⁺. The contribution of the first reaction stage to ΔG _b was calculated on the assumption that the ligand was a solid body with a charge or dipole moment (if the ligand was neutral). The contribution of the second stage to ΔG _b was calculated using quantum-chemical modeling. The major contribution to ΔG _b was made by a change in the internal energy of the complex as a result of the dissociation/formation of coordination bonds and a change in the electric component of the Gibbs energy of interaction between the magnesium ion and molecule with water when they formed a complex. The contribution of the nonpolar component of complex interaction with water was comparatively small. Accurate calculations of the contribution of vibrational degrees of freedom to ΔG _b were also of importance.     

The Heats of Mixing of Aqueous Solutions of Dipeptides with Solutions of Nitric Acid and Potassium Hydroxide over the Temperature Range 288.15–308.15 K

The heats of interaction of D,L-α-alanyl-D,L-valine, β-alanyl-β-alanine, and α-alanyl-β-alanine with solutions of nitric acid and potassium hydroxide were determined calorimetrically at 288.15, 298.15, and 308.15 K and solution ion strengths of 0.5, 1.0, and 1.5 in the presence of KNO₃ and LiNO₃. The heat effects of step dissociation of the dipeptides were calculated using the RRSU universal program. The standard thermodynamic characteristics (Δ_r H ^o, Δ_r G ^o, Δ_r S ^o, and ΔC _p ^o) of proton interaction with the ligands specified were determined. The data obtained were analyzed in terms of Herny concepts. The thermodynamic characteristics of ionization correlated with the structural features of the dipeptides.     

Ionization of aqueous benzoic acid: Conductance and thermodynamics

Molar conductances of dilute aqueous benzoic acid solutions are presented for temperatures from 5 to 80°C. The data have been analyzed to give acid dissociation constants as well as ΔH ^o, ΔS ^o, and ΔC _p ^o for the ionization process and the limiting conductance of the benzoate ion. The conductance-viscosity product changes less than 4% over the temperature range, indicating that the interaction of the benzoate ion with the solvent changes little if at all with increasing temperature. The pK _a(m) vs.T data show that ΔH ^o decreases quadratically while ΔC _p ^o increases linearly withT although, over the 75°C range, ΔC _p ^o increases only about 6 cal-mole^?1 deg^?1 around an average of ?37 cal-mole^?1deg^?1. The acid dissociation constants as derived from the conductance-molal concentration analysis show an average uncertainty of about 0.1% and are fitted to within about 0.01% by the equation $$p{\text{K}}_{\text{a}} (m) = - 75.5422 + 3136.34/T + 28.7965 log T - 6.8139 {\text{x}} 10^{ - 3{\text{T}}} $$ whereT is the absolute temperature.     

An electrochemical method for determination of the standard Gibbs energy of anion transfer between water and n-octanol

The transfer of the ions Cl⁻, Br⁻, I⁻, ClO₄⁻, SCN⁻, NO₃⁻, BF₄⁻, and (C₆H₅)₄B⁻ across the water|n-octanol (W|OC) liquid interface was studied and the standard Gibbs energies of ion transfer were determined. The ion transfer was achieved by oxidation of decamethylferrocene dissolved in a droplet of n-octanol that was attached to a graphite electrode immersed in the aqueous solutions of the respective alkali salts of the anions. The electrode reaction can be described by the equation: dmfc_(OC)+X_(W)⁻⇄dmfc⁺_(OC)+X⁻_(OC)+e⁻, where X⁻ is the transferred anion. Square-wave voltammetry at this three-phase arrangement was utilised to determine the formal potential of the decamethylferrocene/decamethylferrocenium (dmfc/dmfc⁺) couple under the condition of ion transfer across the water|n-octanol interface. For calibration the standard Gibbs energies of ion transfer have been extrapolated to octanol from the series of known data for methanol, ethanol, n-propanol, and n-butanol. All these data are consistent and the experimental dependence of the formal potentials on the standard Gibbs energies is as predicted by theory. The validity of data is further supported by calculations of Gibbs energies of ion transfer using the Born theory. Until now it was not possible to perform electrochemical measurements at the water|n-octanol interface because in the conventional four-electrode cells this interface cannot be polarised. With the new method it is now for the first time possible to determine the Gibbs energies of transfer of ions across the water|n-octanol interface. These values are of very wide use for assessing the lipophilicity of compounds in chemistry, medicine, and pharmacology.     

The enthalpies of solution of DL-α-alanine in water-organic solvent mixtures at 298.15 K

The integral enthalpies of solution (298.15 K) of DL-α-alanine in water-organic solvent mixtures were measured at organic component concentrations x ₂ = 0–0.4 mole fractions. The organic solvents used were acetonitrile (ACN), formamide (FA), N,N-dimethylformamide (DMFA), and N,N-dimethylsulfoxide (DMSO). The standard enthalpies of solution Δ_sol H ^o, solvation Δ_solv H ^o, and transfer (Δ_tr H ^o) of DL-α-alanine from water to mixed solvents were calculated. The influence of the structure and properties of solutes and mixture composition on solute thermochemical characteristics was considered. The solution of DL-α-alanine in the mixtures studied was endothermic over the whole range of organic component concentrations. The Δ_sol H ^o, Δ_tr H ^o, and Δ_solv H ^o values as functions of x ₂ can pass extrema (DMSO and DMFA), be almost independent of mixed solvent composition (FA), or be exothermic and monotonic functions (ACN). The enthalpy coefficients of pair interactions (h _xy ) between DL-α-alanine and organic solvent molecules were calculated. The linear Kamlet-Taft equation was used to correlate the h _xy values with the properties of organic solvents.     

The association of hexacyanoferrate(II) ions and group IIA cations

A thermodynamic study has been made of the equilibrium $$M^{2 + } {\text{ + }}Fe(CN)_6^{4 - } {\text{ }} \rightleftharpoons {\text{ }}MFe(CN)_6^{2 - } $$ in dilute aqueous solution by a potentiometric method using a divalent-cation electrode where, M²⁺ is a group IIA cation. Ion pairing was found to be quite extensive: Thus, at 25°C, the association constants extrapolated to zero ionic strength were 5840, 4730, 4560, and 6080M ^?1 for M²⁺=Mg²⁺, Ca²⁺, Sr²⁺, and Ba²⁺, respectively. In each case, ion pairing is slightly endothermic, the corresponding ΔH ^o values being 18.0, 13.0, 7.8, and 17.5 kJ-mole^?1. However, the values of ΔS ^o are larger and positive, thus favoring ion pairing: the values are 133, 115, 96, and 131 J^o-K^?1-mole^?1 for the same series of cations. There was also some indication of a small amount of ion triplet formation, M₂Fe(CN)₆. Comparisons were made with the predictions of the Fuoss theory, and these support the view that the bonding in the ion is largely electrostatic and not covalent.     

The standard enthalpies of formation of alkoxy-NNO-azoxy compounds

The standard enthalpies of combustion Δ_c H ^o and formation Δ_f H ^o of seven alkoxy-NNO-azoxy compounds containing the-N⁺(O^?)=NO-characteristic group were determined by combustion in a calorimetric bomb in the atmosphere of oxygen. The contribution of this group to the Δ_f H ^o enthalpies of the substances studied was calculated. The Δ_f H ^o enthalpies found by the method of group contributions were in satisfactory agreement with experimental data.     

A physicochemical study of the sorption of lead: Correlations in a series of chelating polymer sorbents

The sorption properties of chelating polymer sorbents (CPSs), the derivatives of poly(styrene-2-oxy-azo-2′-oxybenzene), with respect to the lead ion are studied. The parameters of the sorption processes—optimum conditions of sorption (acidity, temperature, and time), the sorption capacities of sorbents, the possibility of desorption, and the stability constants of the chelated polymers—are determined. Quantitative correlations between p K′_OH of the functional analytical group (FAG) of the sorbent and σ _{o + p(p)} for ortho-and para-substituents, between p K′_OH and pH₅₀ for the formation of chelate complexes of lead, between p K′_OH and the stability of lead complexes (logβ), and between σ _{o + p(p)} and pH₅₀ for the formation of chelate complexes of lead are established with the aim of studying regularities of the influence of the structure and acid-base properties of FAGs on parameters of chemisorption of Pb²⁺. It is shown that the established correlations provide a means for quantitatively predicting physicochemical parameters of sorbents and the process of sorption of lead with the aim of targeted synthesis of CPSs and their use in the chemistry of polymer compounds and in the process of concentrating.     

The thermodynamic characteristics of dissolution of tetraethylammonium bromide and interparticle interactions in the water-formamide-Et4NBr and methanol-formamide-Et4NBr systems

The heat effects of dissolution of tetraethylammonium bromide in water-formamide (FA) and methanol-formamide mixtures were measured at 298.15 and 313.15 K. The second approximation of the Debye-Hückel theory was used to calculate the standard enthalpies of solution Δ_sol H ^o. The mean standard heat capacities of solution ΔC _p ^o and temperature-induced changes in the standard entropies of solution were determined over the temperature range studied. The electrolyte-FA pair interaction parameters in water and methanol were calculated. In the region of low FA concentrations in water and methanol, the Δ_sol H ^o = f(x ₂) and ΔC _p ^o = f(x ₂) dependences were substantially different in character. Some common features of the behavior of tetraethylammonium bromide were only observed in the region of high FA contents, where the intrinsic structure of water virtually disappeared.