Gibbs Energies Of Transfer Research Articles

Kinetic and Thermodynamic Studies of Uncatalysed and Hg(Ii)-Catalysed Solvolysis of a Chlorocobalt(Iii) Complex in Binary Aqueous Media

The kinetics of solvolysis of trans — [Co(py)4Cl2]ClO4 have been investigated in aquo-organic solvent media such as water + ethanol (0-60% v/v) and water -+ urea (0-40% w/w) in the temperature range 40-60°C. The first-order rate constant varies nonlinearly with the reciprocal of the relative permittivity ∊r. The solvolysis of these types of complex involves a rate-determining dissociative step corresponding closely to 100% separation of Co3+ … Cl in the transition state. The Gibbs energy cycle relating the Gibbs energy of activation in water and in the mixtures to the Gibbs energies of transfer of individual ionic species between water and the mixtures Δ G°t(Cl) can be applied. Moreover, more than one extrema in the enthalpies and entropies of activation are found with both binary aqueous solvent mixtures. The solvolysis of trans — [Co(py)4Cl2]ClO4 has also been studied in the presence of Hg(II) and the ionic strength dependence of the reaction rate has been analysed.

Activity coefficients of NaCl in PEG 4000 + water mixtures at 288.15, 298.15 and 308.15 K

The electromotive force of the cell containing two ion-selective electrodes (ISE), Na-ISE | NaCl ( m ) , PEG 4000 ( Y ) , H 2 O ( 100 − Y ) | Cl-ISE has been measured at temperatures of 288.15, 298.15, and 308.15 K as a function of the weight percentage Y of PEG 4000 in a mixed solvent. Y was varied between 0 and 25% in five-unit steps and the molality of the electrolyte ( m) was between ca. 0.003 and 5 mol kg −1. The values of the standard electromotive force were determined using routine methods of extrapolation, together with Debye–Hückel and Pitzer equations. The results obtained produced good internal consistency for all the temperatures studied. Once the standard electromotive force was determined, the mean ionic activity coefficients for NaCl, the Gibbs energy of transfer from the water to the PEG 4000–water mixture and the primary NaCl hydration number were calculated.

Thermodynamic studies on corrosion inhibition of aqueous solutions of amino/carboxylic acids toward copper by EMF measurement

Electromotive force ( E) measurements were made on an electrochemical cell [Cu x Hg|CuCl 2( m) in a solvent S|AgCl–Ag] (where S is a dilute aqueous solution (0.01 m) of amino acid (glycine, alanine, methionine and glutamic acid) or aliphatic carboxylic acid (formic acid, acetic acid, n-butyric acid and glutaric acid)) at 30 °C. These measured E values were used to compute the dissociation constants ( K 1 and K 2) and the degree of dissociation ( α 1 and α 2) by iterative procedures. The standard cell potential ( E°) and the mean activity coefficient ( γ ±) of CuCl 2 were also determined. The E° data were next used to evaluate the Gibbs energy of transfer ( Δ G tr ∘ ) of CuCl 2 from water to dilute aqueous solutions of the amino/carboxylic acids. The negative Δ G tr ∘ values suggested that these acids act as potential corrosion inhibitors. The magnitudes of Δ G tr ∘ values show that the amino acids act as better corrosion inhibitors towards copper than the aliphatic carboxylic acids.

Ionic Recognition by 7-Nitro-1,3,5-triaza Adamantane: First Thermodynamic Study

A thermodynamic study involving 7-nitro-1,3,5-triaza adamantane, 1, and its interaction with metal cations in nonaqueous media is first reported. Solubility data of 1 in various solvents were used to derive the standard Gibbs energies of solution, DeltaG(s)o in these solvents. The effect of solvation in the different media was assessed from the Gibbs energy of transfer taking acetonitrile as a reference solvent. 1H NMR studies of the interaction of 1 and metal cations were carried out in CD3CN and CD3OD and the data are reported. Conductance measurements revealed that this ligand forms lead(II) or zinc complexes of 1:1 stoichiometry in acetonitrile. It also revealed a stoichiometry of two molecules of 1 per mercury(II) and two cadmium (II) ions per molecule of 1. The addition of silver salt to 1 led to the precipitation of the silver-1 complex which was isolated and characterized by X-ray crystallography. At variance with conductance measurements in solution, in the solid state the X-ray structure shows a 1:1 stoichiometry in the Hg(II) complex. The thermodynamics of complexation of 1 and these cations provide a quantitative assessment of the selective behavior of this ligand for ions of environmental relevance.

Salt addition effect on partition coefficient of some phenolic compounds constituents of olive mill wastewater in 1-octanol-water system at 298.15 K

The 1-octanol-water partition coefficient is an important property to measure the hydrophobicity of organic compounds, which has been demonstrated to be a parameter in studying the conformation of biomolecules in aqueous solutions. For biological systems, electrolytes play an important role in thermodynamic properties. The salt addition effect on the distribution of phenolic compounds between water and 1-octanol at 298.15 K has been studied. The phenolic compounds used were vanillic acid, protocatechuic acid, vanillin, tyrosol, cathecol, caffeic acid and syringic acid, and the considered salts were potassium chloride, sodium chloride and lithium chloride. The influence of both the concentration and size of the added salt on the partition coefficient (Kow) have been considered. This study shows a salting in with the following decreasing order: LiCl > NaCl > KCl. The Gibbs energies of transfer of phenolic compounds (168–1) form chloride solutions to organic phase have been calculated using experimental 1-octanol-water partition coefficients.

Solvent effects and ion-solvent interactions from the studies of the solubility and dissociation constants of oxalic acid in aquo + 2-propanol mixtures and determination of single-ion Gibbs energies of transfer from water to 2-propanol + H2O mixtures

The solvent effects on the dissociation of the simplest dibasic organic acid were examined from the determination of the first and second dissociation constants ot oxalic acid conductometrically ana pH-metrically in water + 2-propanol mixtures (0-87 wt% of 2-propanol). The solubility values of oxalic acid and potassium hydrogen oxalate were also determined. The dissociation constants and the solubility values were used to calculate the Gibbs energies of transfer ΔG 0 t of oxalic acid (H 2 OX), bioxalate (HOX-), oxalate (OX 2- ) and potassium (K + ) ions from water to aquo-propanolic mixtures. These represent the 'medium effects' or quantitative measures of solute or ion-solvent interactions of the respective species in going from water to 2-propanol + water mixtures. pK 1 , pK 2 and the solubility values of oxalic acid increase continuously with increase in organic co-solvent. AG 0 t (H 2 OX) and AG 0 t (H + ) are negative i.e. favourable but AG 0 t (H 2 OX), ΔG 0 t (OX 2- ) and AG 0 t (K + ) are in general positive and hence unfavourable for the dissociation processes. The increase in basicity facilitated the dissociation processes but decrease in dielectric constant and H-bonding capability enhances the association processes as the organic co-solvent increases. The pK-values can be suitably utilised to prepare buffer solutions in 2-propanol + water mixtures. The solvent effect and solvation phenomena can be better understood from the collection of single-ion values of transfer. These may be utilised to calculate the solubilities of electrolytes in 2-propanol + water mixtures. Attempts have been made to understand the solvation processes in terms of the structure of the aquo-organic mixtures and Walden products.

The thermodynamic characteristics of formation of nickel(II) complexes with L-tyrosine in aqueous-ethanolic solvents

Acid dissociation constants of L-tyrosine (H2Tyr) and the constants of complex formation between L-tyrosine and nickel(II) ions in water-ethanol mixtures were determined potentiometrically. The Gibbs energies of transfer of tyrosine, HTyr− tyrosinate anion, and [NiHTyr]+ complex from water into binary solvents were calculated. An increase in the stability constants of the [NiHTyr]+ and [Ni(HTyr)2] complexes in solvents with a high content of ethanol was caused by weakening of the solvation of amino ligand donor groups.

Interaction of monovalent cations with acetonitrile

AbstractSolvation of monovalent cations (Me+) of alkali metalsNa+, K+, Rb+, and Cs+, coinage metalsCu+, Ag+, Au+, and p‐block elements Ga+, In+, and Tl+ with acetonitrile was studied by means of ab initio calculations and time‐of‐flight secondary ion mass spectrometry (TOF‐SIMS). The intermolecular interactions in the complexes Me+···CH3CN were investigated using the coupled clusters theory including single, double, and noniterative triple substitutions (CCSD(T)) in conjunction with the Pol and Pol‐dk basis sets. The binding energies of these donor‐acceptor complexes were estimated; taking into account the basis set superposition error, zero‐point vibrations, correlation contribution, and scalar relativistic corrections. The theoretical ΔG0298 K values based on CCSD(T)/Pol and/or CCSD(T)/Pol‐dk binding energies correlated well with experimental transfer Gibbs energies (from water to acetonitrile) for the series of cations. In the case of Au monocation, relativistic correction turned out to be extremely important. Composition of the complex of Ag+ and Na+ with acetonitrile was determined by using SIMS supporting both theoretical and experimental transfer Gibbs energies. © 2009 Wiley Periodicals, Inc. Int J Quantum Chem, 2009

Thermodynamics of Partitioning of Propranolol in Some Organic Solvent/Buffer Systems

Propranolol (PPN) partitioning thermodynamics was studied at five temperatures in several solvent/buffer systems, namely, cyclohexane (CH/W), octanol (ROH/W), isopropyl myristate (IPM/W), and chloroform (CLF/W). In all cases, the mole fraction partition coefficients (Ko/wX) were greater than unity; therefore, the standard Gibbs energies of transfer are negative, indicating a high affinity of PPN for all organic media evaluated. Ko/wX values were approximately 57 times higher in the ROH/W system with respect to CH/W, thus indicating a high degree of hydrogen bonding contribution to partitioning, whereas in the case of the IPM/W and CLF/W systems, the Ko/wX values were similar to those observed in ROH/W. In all cases, standard enthalpies and entropies of transfer of PPN from water to organic solvents were positive. These results indicate some degree of participation of the hydrophobic hydration in the PPN partitioning processes.

Activity coefficients of NaCl in aqueous mixtures with ɛ-increasing co-solvent: Formamide–water mixtures at 298.15 K

The electromotive force of the cell containing two ion-selective electrodes (ISE), Na-ISE|NaCl( m), formamide ( Y), H 2O(100 − Y)|Cl-ISE has been measured at a temperature of 298.15 K as a function of the weight percentage Y of formamide in a mixed solvent. Y was varied between 0 and 100% in ten-unit steps and the molality of the electrolyte ( m) was between ca. 0.01 and saturation. The values of the standard electromotive force, E 0 (molal scale), were determined using routine methods of extrapolation together with Debye-Hückel, Pitzer and Scatchard equations. The results obtained produced good internal consistency, within the normal limits of experimental error encountered in these types of measurement. Once E 0 was determined, the mean ionic activity coefficients for NaCl, the Gibbs energy of transfer from the water to the formamide–water mixture, the standard solubility product and the primary NaCl hydration number were calculated. The variation of these magnitudes with the composition of this mixture with ɛ-increasing co-solvent is discussed in comparison with those previously obtained with ɛ-decreasing methanol–water and ethanol–water systems in terms of the ion–solvent and ion–ion interactions and their changes with the properties of the medium.

Mutual Solubility of Hydrophobic Ionic Liquids and Water in Liquid-Liquid Two-phase Systems for Analytical Chemistry

Liquid-liquid two-phase systems formed by a hydrophobic ionic liquid and water find several useful ways of application in analytical chemistry. One of the most important properties of such two-phase systems is the mutual solubility of the IL and water. Recent advancements on this subject have been reviewed. The solubility of ionic liquids in water is related to the standard Gibbs energies of the transfer of ions constituting the ionic liquid from the ionic liquid phase to water. Although this single ionic property cannot be measured thermodynamically and also varies from one ionic liquid to another, the standard Gibbs energy of the ion transfer from a polar aprotic solvent, such as nitrobenzene and 1,2-dichloroethane, to water is a convenient measure for it. The solubility of an ionic liquid in water and the electrochemical properties at the interface between the two phases are intimately related with each other.

The thermodynamic characteristics of dissolution and solvation of cetyltrimethylammonium perchlorate in the water-propan-2-ol system

The solubility of cetyltrimethylammonium perchlorate (CTAP) in propan-2-ol and its mixtures with water was determined by the isothermal saturation method over the whole composition range at 278.15–308.15 K. The solubility products and total standard Gibbs energies of transfer of the n-C16H33N(CH3)3+ and ClO4− ions were calculated. The solubility of CTAP in the mixed solvent specified was substantially influenced by solvophilic effects and the heterosolvation of ions caused by them.

Effect of Solvents on the Corrosion Inhibition of Copper by 1,2,3-Benzotriazole

Electromotive force (E) measurements have been made at 303.15 K on the cell, CuxHg/CuCl2 (m) in solvent S′ [S′=W or FD or DMF each containing 15 ppm of 1,2,3-benzotriazole (BTA)] /AgCl/Ag (where W, FD and DMF represent the solvents water, formamide and N,N-dimethylformamide, respectively). The Emf data have been compared with the corresponding data under the same conditions in pure W, FD and DMF; the Emf values change from negative to very positive in the presence of BTA in these solutions and suggest the possibility that the presence of BTA in W, FD and DMF helps to bind copper ions with solvent molecules through formation of new complex structures of the film formed on the metal surface. We have suggested the probable mechanism of formation of a protective film through complex formation. The higher Emf values in the presence of BTA indicate strong ion-solvent interactions and the order of interactions was found to be as: FD≥DMF>W. Further iterative procedures were employed to evaluate K1,K2 (dissociation constants), α1,α2 (degrees of dissociation), γ± (mean activity coefficient) and Eo (standard cell potential) making use of the measured E values. The standard molar Gibbs energy of transfer, ΔGtro, of CuCl2 from the pure S to S′ were calculated using the computed standard cell potentials. The calculated ΔGtro values were found to be negative which was indicative of strong ion-solvent interactions and reasonably supported the trend of ion-solvent interactions. From these studies we concluded that BTA acts as a better corrosion inhibitor towards copper in FD and DMF than water.

Solvent Effect on Deprotonation Equilibria of Acids of Various Charge Types in Non-aqueous Isodielectric Mixtures of Protic Ethylene Glycol and Dipolar Aprotic N,N-Dimethylformamide at 298.15 K

Deprotonation constants of phthalic (H2A) and biphthalic (HA−) acids and of mono-protonated (BH+) and di-protonated (BH 2 2+ ) piperazine acids have been determined at 25 °C by measuring the Emf of galvanic cells comprising H+-sensitive glass GE(H+) and Ag,AgCl electrodes in non-aqueous isodielectric mixtures of protic ethylene glycol (EG) and dipolar aprotic N,N-dimethylformamide (DMF). Solvent effects on deprotonation of the acids: ∂(ΔG diss o )=2.303RT[p(s K a)−p(R K a)], have been dissected into transfer Gibbs energies, ΔG t o , of the species involved by evaluating ΔG t o of the uncharged phthalic acid and base piperazine (B) from the measured solubilities of the acid and base, respectively, and using ΔG t o of H+ based on the TATB reference electrolyte assumptions, as evaluated earlier. The contributions of the different species involved in the protolytic equilibria i.e., H+,H2A,HA−,BH 2 2+ and BH+ and their respective conjugate bases HA−,A2−,BH+ and B have been discussed in terms of their solvation behavior as guided by the ‘acid-base’, dispersion, structural and electronic characteristics of the acid-base species and of the co-solvent molecules and binary mixtures, ignoring the Born-type electrostatic interactions on the ionic species as the solvent system is quasi isodielectric.

Investigation of the Lipophilicity of 2-Benzoylpyridine-Thiosemicarbazone Based on the Ion Transfer across the Liquid/Liquid Interface

The ion transfer reaction of 2-benzoylpyridine-thiosemicarbazone (HL), which has antimicrobial and antifungal properties and anticancer activity, has been studied to determine its lipophilicity by cyclic voltammetry at the water/1,2-dichloroethane (1,2-DCE) interface. The physicochemical parameters such as standard partition coefficient (lg P I) and the standard Gibbs energy of transfer ( Δ G tr , I 0 , w → o ) of the protonated form of the ligand were measured as a function of pH in aqueous phase. The protonated form of the ligand exhibited reversible or quasi-reversible voltammograms at the 1,2-DCE in the range of pH 1–5. The protonation constants of the ligand, p K a1 and p K a2, were determined spectrophotometrically and were found to be 12.14 and 3.24, respectively. The standard Gibbs energy of transfer ( Δ G tr , N 0 , w → o ) and the partition coefficient of neutral species (lg P N) were also determined by the shake-flask method. The standard Gibbs energy of transfer of this compound across the water/1,2-DCE interface was evaluated as the quantitative measure of its lipophilicity. The difference between lg P I and lg P N was related to the degree of charge delocalization and was used to evaluate qualitatively the lipophilicity of the ligand.

A Partially Substituted Calix[4]resorcarene Receptor and Its Selective Recognition for Soft Metal Cations (Silver and Mercury)

A partially substituted calix[4]resorcarene receptor, namely, 5,17-ethylthiomethylated calix[4]resorcarene, 1, has been synthesized and characterized by 1H NMR in CD3OD, CDCl3, and CD3CN and 13C NMR in CD3OD, as well as by 2D NMR. Partition data in the methanol-hexane and acetonitrile-hexane solvent systems show that the monomeric species are predominant in these solvents. The solubility of 1 in various solvents was determined at 298.15 K. These data were used to calculate the standard solution Gibbs energy of 1 in these solvents. Taking hexane as the reference solvent, the standard transfer Gibbs energy of 1 to various solvents was calculated. Good agreement is found between the DeltatG(o) values in the hexane-methanol and hexane-acetonitrile and the DeltapG(o) values of this ligand in these solvent systems. The higher partition constant of 1 in the hexane-methanol relative to the hexane-acetonitrile solvent system contrasts with corresponding data for the fully functionalized receptor, 2. This is explained in terms of the solvation differences of these receptors in these solvents as reflected in the DeltatG(o) values. The cation complexing properties of this receptor were investigated through 1H NMR, conductance, calorimetric, and potentiometric methods. Among the metal cations (alkali, alkaline earth, heavy, and transition), 1 interacts only with Ag+ in methanol and Hg2+ in propylene carbonate, acetonitrile, methanol, and N,N-dimethylformamide. While 1 forms a 1:1 complex with Ag+ in methanol, the hosting ability of the receptor for the mercury cation is enhanced in methanol, acetonitrile, and N,N-diethylformamide. Thus, Hg2+ complexes of 1:2 (ligand:metal cation) stoichiometry are found in these solvents. In moving to propylene carbonate, the composition of the mercury complex is altered from 1:2 to 1:1. The results are compared with corresponding data for 2 and these metal cations in the appropriate solvents. The lack of stability observed for 2 and Hg2+ in acetonitrile resulting from the departure of pendant arms from the resorcarene backbone greatly contrasts with the high stability observed for 1 and this metal cation in the various solvents. Preliminary results on the extraction of silver picrate by this ligand in the water-dichloromethane solvent system are reported. Final conclusions are given.

Statistical evaluations of single-ion Gibbs energies of transfer

A statistical approach for the evaluation of single-ion Gibbs energies of transfer of the cations Li+, Na+, K+, Rb+, Cs+, Ba2+, Ag+, Tl+, Cu+, Zn2+, Cu2+, Cd2+, Hg2+ and Pb2+ into 40 solvents based on the principal component analysis is presented. It is shown that the Gibbs energies of transfer depend both on the nature of the cation and on the donor site of the respective solvent molecule. Correlation of the data for the investigated cations required separating the solvents into subgroups according to their donor atoms in the solvent molecule. Gibbs energies of transfer into oxygen donor solvents could be correlated with the Born term [N L(z i e 0)2/(8πe0 r i )]. Several cation parameters were investigated with respect to the transfer data into nitrogen and sulfur donor solvents. No correlations were found. Thus the use of cation parameters derived from the statistical analysis are proposed to account for the Gibbs energies of transfer into nitrogen and sulfur donor solvents.

Studies on the solubilities and dissociation constants of substituted benzoic acids in 2-propanol-water mixtures and ion-solvent interactions

The solvational behaviour of 2- and 3-substituted bromo- and iodo-benzoic acids have been examined from the solubility of the acids and the dissociation constants for the reaction HA = H + + A- (where HA is substituted benzoic acid) determined conductometrically using Fuoss-Kraus method in 2-propanol + water mixtures (0-87 mass% of 2-propanol). The changes in the solubility values depend on the hydrophobic character and the dielectric constant of the solvent medium. The Gibbs energy of transfer for anions have been determined from the relation ΔG° t , (dissn.) = ΔG° t (H + ) + ΔG° t (A - ) - ΔG° t (HA) using the previously determined values of ΔG° t (H + ). ΔG° t (A - ) values have been found to be increasingly positive in aquo-organic mixtures and the ΔG° t (A - ) values of the 3-compounds are considerably different from those of 2-compounds. The results are discussed in the light of solute-solvent Interactions. The effects of substitution on the interaction energies of anions have been determined.

Probing carboxylate Gibbs transfer energies via liquid|liquid transfer at triple phase boundary electrodes: ion-transfer voltammetry versus COSMO-RS predictions

Understanding liquid|liquid ion transfer processes is important in particular for naturally occurring species such as carboxylates. In this study electrochemically driven mono-, di-, and tri-carboxylate anion transfer at the 4-(3-phenylpropyl)pyridine|aqueous electrolyte interface is investigated experimentally for a triple phase boundary system at graphite electrodes. The tetraphenylporphyrinato-Mn(III/II) redox system (Mn(III/II)TPP) dissolved in the water-immiscible organic phase (4-(3-phenylpropyl)pyridine) is employed for the quantitative study of the structure-Gibbs transfer energy correlation and the effects of the solution pH on the carboxylate transfer process. For di- and tri-carboxylates the partially protonated anions are always transferred preferentially even at a pH higher than the corresponding pK(a). COSMO-RS computer simulations are shown to provide a quantitative rationalisation as well as a powerful tool for predicting Gibbs free energy of transfer data for more complex functionalised carboxylate anions. It is shown that the presence of water in the organic phase has a major effect on the calculated Gibbs free energies.

Gibbs Energies of Transfer of Anions from Water to Mixed Aqueous Organic Solvents

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