Gibbs Energies Of Transfer Research Articles

Determination of Gibbs Energies of Transfer for Supporting Electrolytes of the Organic Phase in Liquid-Liquid Electrochemistry

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Thermodynamic Study of Partitioning and Solvation of (+)-Naproxen in Some Organic Solvent/Buffer and Liposome Systems

Naproxen (NAP) partitioning thermodynamics was studied in different solvent/buffer systems such as cyclohexane (CH/W), octanol (ROH/W), isopropyl myristate (IPM/W), and chloroform (CLF/W), as well as in dimyristoyl phosphatidylcholine (DMPC) and dipalmitoyl phosphatidylcholine (DPPC) liposome systems. In all cases, the mole fraction partition coefficients (K X o/w ) were greater than unity; therefore, the standard Gibbs energies of transfer were negative indicating a high affinity of NAP for all the organic media. K X o/w values were approximately 1000-fold higher in the ROH/W system with respect to the CH/W system, thus indicating a high degree of hydrogen-bonding contribution to partitioning, whereas in the case of the IPM/W and CLF/W systems, the K X o/w values were approximately only 2-fold or 5-fold lower than those observed in ROH/W. On the other hand, K X o/w values were approximately 55-fold or 39-fold higher in the liposomes compared to the ROH/W system, for DMPC and DPPC, respectively, thus indicating a high degree of bilayer immobilization and/or an electrostatic contribution to partitioning. In almost all cases, standard enthalpies of transfer of NAP from water to organic solvents were negative (except for CH), whereas the standard entropies of transfer were positive (except for IPM). For liposomes, the standard enthalpies and entropies of transfer were positive. These results indicate some degree of participation of the hydrophobic hydration on the NAP partitioning processes. By using the reported data for solvation of NAP in water, the associated thermodynamic functions for NAP solvation in all tested organic phases were also calculated. Finally, all the results obtained for NAP were compared with those presented previously for ketoprofen.

Studying ion transfers across a room temperature ionic liquid∣aqueous electrolyte interface driven by redox reactions of lutetium bis(tetra- tert-butylphthalocyaninato)

Ion transfer reactions across the interface between an aqueous electrolyte solution and the room temperature ionic liquid (RTIL) 1-hexyl-3-methylimidazolium tris(pentafluoroethyl)trifluorophosphate ([hmim][fap]) were studied with the help of three-phase electrodes. The electrode assembly comprised an edge plane pyrolytic graphite electrode modified with a thin layer of [hmim][fap] containing lutetium bis(tetra- tert-butylphthalocyaninato) (Lu[ tBu 4Pc] 2) as redox probe. Lu[ tBu 4Pc] 2 can be oxidized and reduced to a stable hydrophobic monovalent cation and anion, respectively, hence allowing investigation of the transfer of cations and anions in one and the same voltammetric experiment. In spite of the strong hydrophobicity of the salt [hmim][fap], the electrode reactions of the redox probe studied in contact with various inorganic aqueous electrolytes, were frequently accompanied by expulsion of ions constituting the RTIL into the aqueous phase. Using ion chromatography it was found that the distribution of ions in the aqueous electrolyte/RTIL biphasic system is strongly determined by ion exchange reactions. The affinity of the ions of the RTIL for the aqueous phase was assessed using the water–nitrobenzene (W–NB) system, and the following Gibbs energies of ion transfer were found: Δ W → NB G [ hmim ] + ⦵ = - 16.6 ± 0.9 kJ mol - 1 and Δ W → NB G [ fap ] - ⦵ = - 22.4 ± 0.3 kJ mol - 1 .

Cyclic voltammetry of ion transfer across a room temperature ionic liquid membrane supported by a microporous filter

Cyclic voltammetry is used to study the transfer of a series of cations and anions across a room-temperature ionic liquid (RTIL) membrane composed of tridodecylmethylammonium cation (TDMA +) and tetrakis(pentafluorophenyl)borate anion (TPFPB −), and supported by a thin (∼112 μm) microporous filter. Essential advantage of the thin membrane system is the substantial reduction of the ohmic potential drop, which is compensated in voltammetric measurements. Reversible partition of TPFPB − allows fixing the potential difference at one membrane interface and polarizing the other membrane interface in a defined way. It is shown that the polarized potential window for the interface between an aqueous electrolyte solution and RTIL attains the value of ca. 0.7 V at the ambient temperature of 25 ± 2 °C. Tetraphenylarsonium tetraphenylborate hypothesis is used for the first time to estimate the standard Gibbs energies of ion transfer from water to RTIL and to establish the scale of the absolute potential differences. A linear Gibbs energy relationship is found for the ion transfer from water to RTIL and o-dichlorobenzene.

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

A large number of quantitative studies have been made of the Gibbs energy of transfer (the solvent medium effect) for cations transferring from water into mixed aqueous−organic solvent systems, mainly at 25 °C. Nevertheless, no systematic effort appears to have been made to compile and analyze these data, particularly for multivalent cations. A critical review of this information and its presentation in a manner that permits comparison of different cations in a given solvent mixture and of a given cation transferring into different mixtures is therefore of value.

Basicities of Aquo + Alcoholic (Mono-ol) mixtures

Gibbs energies of transfer of H+ion [ΔG0t(w→s)(H+)] from water (w) to different aquo + alcoholic mixtures (s) were calculated using no extrathermodynamic assumptions. ΔG0t(w→s)(H+) values with and without interactions are given.ΔG0t(w→s)(H+) values (without interaction terms) compare well with the selected values of ΔG0t(w→s)(H+) in different aquo + alcoholic mixtures recommended by Marcus from compilations of data reported by various workers using different extrathermodynamic assumptions. Suitable conversion was made to bring the data into the range of the TATB scale.ΔG0t(w→s)(H+) values in binary mixtures (without interaction terms) are lower and qualitatively to some extent close to the values reported in the literature at least at low percentages.The results show that ΔG0solv(H+) and ΔG0t(w→s)(H+) values are increasingly positivei.e.less basic as the mass% of organic solvents increases and the sequence of basicities are in the orderi.e.the organic solvent and solvent mixtures are less basic than water contrary to the prevalent conceptions. The main factor appears to be the number of O-atoms with lone-pair of electrons responsible for H+acceptance, H-bonding and other structural modifications of the solvent mixtures. Obviously, the lower the molar mass of the organic solvent, the greater will be the basicity of the solvent and solvent mixtures.

Electrochemical study of the thermodynamics and kinetics of hydrophilic ion transfers across water | n-octanol interface

Thermodynamics and kinetics of hydrophilic ion transfers across water|n-octanol (W|OCT) interface have been electrochemically studied by means of novel three-phase and thin-film electrodes. Three-phase electrodes used for thermodynamics measurements comprise edge plane pyrolytic graphite, the surface of which was partly modified with an ultrathin film of OCT, containing hydrophobic lutetium bis(tetra-tert-butylphthalocyaninato) (Lu[tBu4Pc]2) as a redox probe. The transfers of anions and cations from W to OCT were electrochemically driven by reversible redox transformations of Lu[tBu4Pc]2 to chemically stable lipophilic monovalent cation \({\left( {{\text{Lu}}{\left[ {t{\text{Bu}}_{4} {\text{Pc}}} \right]}^{ + }_{2} } \right)}\) and anion \( {\left( {{\text{Lu}}{\left[ {t{\text{Bu}}_{{\text{4}}} {\text{Pc}}} \right]}^{{\,\, - }}_{2} } \right)} \), respectively. Upon reduction of Lu[tBu4Pc]2, the transfers of alkali metal cations from W to OCT have been studied for the first time, enabling estimation of their Gibbs transfer energies. For kinetic measurements, a thin-film electrode configuration has been used, consisting of the same electrode covered completely with a thin layer of OCT that contained the redox probe and a suitable electrolyte. Combining the fast and sensitive square-wave voltammetry with thin-film electrodes, the kinetics of \( {\text{ClO}}^{{\,\, - }}_{4} \), \( {\text{NO}}^{{\,\,{\text{ - }}}}_{{\text{3}}} \), and Cl− transfers have been estimated.

Voltammetry of microparticles of lutetium bisphthalocyanine

Oxidation of microparticles of lutetium (bis-tert-butylphthalocyaninato) complex immobilized on the surface of paraffin-impregnated graphite electrode and immersed into an aqueous electrolyte was investigated by cyclic voltammetry and square wave voltammetry. The electrode reaction exhibits the typical features of insertion electrochemistry where the anions of the aqueous electrolyte are transferred into the solid phase upon oxidation of the redox centers there in. The reaction is quasi-reversible and influenced by the ohmic resistance of the compound. The formal potentials of the electrode reaction involving the transfer of perchlorate, nitrate, and chloride ions follow the same order as the Gibbs energies of ion transfer in the systems water–nitrobenzenene and water–octanol. Bromide and thiocyanate ions are not intercalated.

Thermodynamics of Ethyl p-tert-Butylcalix[5]arene Pentanoate and Its Cation Complexes in Nonaqueous Media

The solution behavior of ethyl p-tert-butylcalix[5]arene pentanoate, EtCalix(5), in various protic and aprotic solvents has been assessed from the standard Gibbs energies of transfer of this ligand from acetonitrile to other solvents. These data were derived from solubility measurements of EtCalix(5) in different media. It is concluded that in solvents in which metal cation salts are predominant as ionic species in solution (within a low concentration range), the solvation of the ligand will not contribute significantly to the thermodynamics of cation complexation as a result of the medium effect. Various analytical techniques were used to identify the sites of ligand-cation interaction (1H NMR) and the composition (conductance and calorimetric measurements) of the metal-ion complexes in the various solvents. Titration calorimetry (direct and competitive) was used to thermodynamically characterize the cation binding ability of EtCalix(5) and gain quantitative information on the complex stability and the factors controlling it. Given the large bulk of data reported in the literature wrongly placed under the thermodynamic umbrella, particular emphasis is made about the need of identifying the process taking place in solution prior to proceeding with its thermodynamic characterization. The results are compared with those for the ethyl ester derivative of the cyclic tetramer, EtCalix(4). It is concluded that in moving from EtCalix(4) to EtCalix(5), (i) the selectivity of the latter for cations is swallowed toward the larger cations and (ii) although the number of binding sites increases, these are not able to exert the efficient control upon the ligand-cation binding ability as that found for the tetramer ester and these cations in these solvents.

Interactions between Gemini Surfactants and Polymers: Thermodynamic Studies

Aqueous mixtures containing a homopolymer, poly(vinylpyrrolidone) (PVP), or a hydrophobically modified graft copolymer, HM-pullulan, (PULAU9, where 9 stands for the nominal substitution degree), and different Gemini surfactants have been investigated at 25.0 degrees C. A wide variety of experimental conditions were addressed by changing the amount of polymer and of surfactant. The Gemini surfactants were synthesized, purified, and characterized by routine methods. They differ from each other in polar head groups (two sulfonate-, two quaternary ammonium-, or two arginine-based groups), in alkyl chain length (11 or 12 carbon atoms), and in the distance between the polar head groups. The spacers consist of 2, 3, and 6 methylene units or 3 oxyethylene units. Surface activity and solution calorimetry measurements yield some physicochemical features inherent to micelle formation and polymer-surfactant interactions. The data are supported by ionic conductivity, detecting the critical thresholds and quantifying the modifications in binding associated with critical association (CAC) and micelle formation (CMC*). The Gibbs energy of transfer from the micelles to a polymer-binding site, DeltaGtrans, was evaluated from the CAC/CMC* ratios versus the amount of added polymer. A similar procedure determined the enthalpy of transfer, DeltaHtrans. DeltaGtrans decreases with added polymer, whereas DeltaHtrans becomes more negative on increasing the amount of polymer in the medium. According to the selected data presented here, cationic Geminis do not interact with PVP, while significant interactions have been observed in other surfactants. In mixtures with PULAU9, the interaction is significant for all Geminis. This effect is due to interactions between the surfactants and the hydrophobic alkyl groups on the main polymer chain. The pendent groups facing away from the polysaccharide chain act as binding sites for aggregates onto such polymers.

Thermodynamic Equilibrium Constant Studies on Aqueous Electrolytic (Alkaline Earth Chlorides) Solutions Containing 18-Crown-6 at 298.15 K

Osmotic coefficient data have been obtained for the binary aqueous solutions of alkaline-earth chlorides (MgCl2, CaCl2 and BaCl2) at 298.15 K using a vapor pressure osmometer. The measurements are extended to aqueous ternary solutions (containing a fixed concentration of 0.1 mol⋅kg−1 18-Crown-6 (18C6) having various electrolyte concentrations (0.01–0.2 mol⋅kg−1). The mean activity coefficients of the ions and of 18C6 in binary and ternary solutions were obtained through calculations of activity and osmotic coefficient data. The lowering of activity coefficients of the ions and of 18C6 in ternary solutions is attributed to the presence of host-guest type equilibria due to complexation between them in the case of solutions containing Ca2+ and Ba2+ ions. The data are further subjected to scrutiny by applying the methodology developed by Patil and Dagade based on the McMillan-Mayer theory of solutions to obtain thermodynamic equilibrium constant values through transfer Gibbs energies. It is noted that the size of the crown cavity (diameter 0.266–0.32 nm), charge density of ions (i.e., coulombic interactions) as well as hydrophobic interaction play a major role in governing the occurrence and stability of the complexed species. The results are compared with those reported earlier for alkali-halides and 18C6 complexes and discussed further from the point of view of the importance of ion-pair formation equilibria in aqueous solutions.

Application of Volta chains to determine ionic components of real and chemical Gibbs energies of transfer of individual ions from water to aqueous-organic solvents

The state of individual ions in individual and mixed solvents was described from the thermodynamic point of view using the method of Volta potential differences. This methodology provides a way of solving the problem of determination of thermodynamic characteristics of individual ions in solutions. The possibility of using the method of Volta potential differences to determine the ionic components of the real and chemical thermodynamic properties of individual ions in solutions and the surface potentials at gas-solution interface is substantiated.

Study of the Mechanism of Enantioseparation. Part XII. Comparison Study of Thermodynamic Parameters on Separation of Phenylcarbamic Acid Derivatives by HPLC using Macrocyclic Glycopeptide Chiral Stationary Phases

Four macrocyclic glycopeptide chiral stationary phases (CSPs) based on native teicoplanin (Chirobiotic T), methylated teicoplanin aglycone (Chirobiotic m‐TAG), teicoplanin aglycone (Chirobiotic TAG), and vancomycin (Chirobiotic V) were compared for the high performance liquid chromatographic (HPLC) separation of enantiomers of 1‐methyl‐2‐piperidinoethylesters of 2‐, 3‐and 4‐ alkoxyphenylcarbamic acid (potential local anaesthetic drugs). The enthalpies (ΔH i ), entropies (ΔS i ), and Gibbs energies (ΔG i ) of transfer were evaluated for the separation of these compounds. The enantiomers were separated isothermally in the range of 0–50°C with 10°C increments, in the polar organic mode. The thermodynamic parameters were calculated in order to gain an understanding of the driving forces for retention in this chromatographic system. From these results, it is evident that the elongation of the alkoxy‐chain has major influence on the values of (ΔS i ) when using the vancomycin CSP and on the values of (ΔH i ) using the teicoplanin‐type CSPs.

Thermodynamics and temperature dependence of dissociation and solvation of alpha-alanine in H 2O-MeOH and of valine in H 2O-PrOH-2

Thermodynamic constants of amino acid dissociation with carboxylic, K 1, and amino groups, K 2, and standard thermodynamic functions of dissociation (Δ G 0 d,1, Δ G 0 d,2, Δ H 0 d,1, Δ H 0 d,2, Δ S 0 d,1, Δ S 0 d,2) of α-alanine in methanol–water solvent and of valine in propan-2-ol-water solvent (0, 20, 40, 60, 80 wt.%) have been determined by potentiometric method in galvanic cells without liquid junction at 278.15–328.15 K (with step of 10 K). The standard Gibbs energy of transfer of ionic forms of α-amino acids in MeOH-H 2O, PrOH-2-H 2O mixtures have been calculated. The short-range interaction part of dissociation Gibbs energy, Δ G 0 d,1,2 ⁎ have been obtained assuming the borders of ionic association area.

The gibbs energies of transfer of nicotinamide from water to water-ethanol mixtures and formation of the nicotinamide-silver(I) complex

The distribution coefficients of nicotinamide (NicNH2) and solubility products of nicotinamide-silver perchlorate were determined by the distribution and solubility methods over a wide range of water-ethanol (EtOH) solvent compositions. The Gibbs energies of transfer of NicNH2 and the AgNicNH2+ complex cation from water into water-ethanol mixtures were calculated. The influence of H2O-EtOH solvent compositions on the stability of the nicotinamide-Ag+ complex was studied potentiometrically at a 0.25 ionic strength of the medium (NaClO4) and 25.0 ± 0.1°C. The stability of complexes increased as the concentration of ethanol in mixtures grew. Reagent solvation contributions to complex formation equilibrium shifts were analyzed.

New Insights on Anion Recognition by Isomers of a Calix Pyrrole Derivative

Two isomeric structures of meso-tetramethyltetrakis(3-hydroxyphenyl)calix[4]pyrrole, 4-alphaalpha betabeta and 4-alphabeta alphabeta, have been isolated and characterized by 1H NMR in different solvents (CD3CN, CD3OD, and DMSO-d6) at 298 K. Standard Gibbs energies of solution derived from solubility data in various solvents were used to calculate the transfer Gibbs energy, delta(t)G(o), of these ligands using acetonitrile as the reference solvent. These results are consistent with the 1H NMR studies in different media that show chemical shift changes observed in the resonances of the NH and the OH protons of these ligands. Solvate formation was observed when these isomers were exposed to saturated atmosphere of N,N-dimethylformamide, dimethyl sulfoxide and propylene carbonate. Anion interaction involving 4-alphaalpha betabeta and 4-alphabeta alphabeta was investigated by 1H NMR in CD3CN while the complex composition was assessed through conductance measurements. Significant differences are observed in the affinity of these ligands for anions as well as in the composition of the fluoride complexes. Thus 4-alphaalpha betabeta shows selectivity for H2PO4(-) in acetonitrile while its isomer 4-alphabeta alphabeta is selective for the fluoride anion. Again the complex composition is altered for the fluoride anion when complexed with 4-alphaalpha betabeta in acetonitrile (1:1 complex) relative to 4-alphabeta alphabeta in the same solvent. The latter isomer shows an enhanced hosting ability for this anion. Thus two anions are taken up per unit of ligand. The thermodynamics of complexation of H2PO4(-) and these ligands in acetonitrile is discussed, and the results are compared with those involving calix[4]pyrrole and this anion in this solvent. It is shown that the isomers interact with two H2PO4(-) anions while one calix[4]pyrrole unit interacts with this anion. This paper demonstrates for the first time that the enthalpy parameter may be a suitable reporter of the number of hydrogen bonds formed when calix[4]pyrrole and its derivatives interact with the dihydrogen phosphate anion in acetonitrile. In moving from acetonitrile to N,N-dimethylformamide, 4-alphaalpha betabeta is unable to enter complexation with most anions, except fluoride, with which the formation of a 1:2 (ligand:anion) complex is demonstrated. The rather versatile behavior of these receptors for anions is explained on the basis of 1H NMR evidence and solvation effects. These investigations highlight the importance of the medium effect on the stability of the complex and reflect the inherent nature of the solvent and its highly significant involvement in the complexation process.

Photoinduced Electron Transfer to Triplet Flavins. Correlation between the Volume Change-Normalized Entropic Term and the Marcus Reorganization Energy

The data obtained through the application of nanosecond laser-induced optoacoustic spectroscopy (LIOAS) to several electron donor-acceptor pairs in aqueous solution were analyzed together with the respective experimentally determined Marcus reorganization energy. Acceptors were the flavin mononucleotide and flavin-adenine dinucleotide triplet states (3FMN and 3FAD) and donors were tryptophan, tyrosine, histidine, triethanolamine, and ethylenediaminetetraacetic acid. The respective calculated Gibbs energy for electron transfer, Delta(ET)G degrees , was used together with the enthalpy change for the formation of free radicals, Delta(FR)H, obtained from the LIOAS data, to derive the entropy change for the formation of the radicals, Delta(FR)S. In all cases, variation of the monovalent cations, i.e., [CH3(CH2)3]4N+, Li+, NH4+, K+, and Cs+, resulted in variation of the enthalpy change, Delta(FR)H, and in the structural volume change, Delta(FR)V, for the free-radical production, both derived from LIOAS. Delta(FR)H and Delta(FR)V linearly correlated with each other within the cation series. From this correlation the respective entropic term TDelta(FR)S was derived as well as the ratio X = TDelta(FR)S/Delta(FR)V for each of the pairs. X linearly correlated with the respective total Marcus reorganization energy, lambda, for all systems analyzed. This observation underlines the concept that both lambda and Delta(FR)V respond to the same phenomena. The correlation also offers an experimental approach for the understanding at a molecular level of the origin of the lambda values as well as for their evaluation.

One redox probe (dmfc) can drive the transfer of anions and cations across the aqueous electrolyte∣ionic liquid interface

Three-phase electrodes consisting of droplets of 1-hexyl-3-methylimidazolium tris(pentafluoroethyl)trifluorophosphate containing decamethylferrocenium (dmfc +) cations, immobilized on the surface of graphite electrodes and immersed in aqueous electrolyte solutions have been employed to study the redox driven transfer of anions and cations. Very surprisingly, it has been observed that anions as well as cations can be transferred with one redox probe (dmfc/dmfc +) because the Gibbs energies of ion transfer of the different ions are rather similar.

The gibbs energies of transfer of calcium ions from water into water-acetone mixtures

Volta potential differences measured at 298.15 K were used to determine the real primary effect of the medium of calcium ions and the real Gibbs energy of transfer of Ca2+ from water into a mixed water-acetone (Me2CO) solvent. The surface potential at the solvent/gas phase interface was found to be $$\Delta \chi ^{Me_2 CO} = - 0.337V$$ . This value was used to calculate the chemical thermodynamic characteristics of calcium ions. The thermodynamic characteristics of resolvation of the 2-1 electrolyte are compared with those obtained earlier for a 1-1 electrolyte.

Gibbs Energies of Transfer of Alkali Metal Cations between Mutually Saturated Water−Solvent Systems Determined from Extraction Experiments with Radiotracer 137Cs

Thermodynamic standard Gibbs energies of transfer of alkali metal cations related to Cs+ cation [DeltatG degrees*,(Cs+)-[DeltatG degrees*,(M+)] between several mutually saturated solvents of the type water-solvent were calculated from determined extraction exchange constants Kexch degrees,*(Cs+/M+). The used liquid-liquid extraction method with radioactive tracing by 137Cs permits attaining higher precision of the values as compared to the methods used up to now. The data for o-nitrophenyloctyl ether, 1,2-dichloroethane, and 1-octanol were compared with literature sources and recommended absolute values of DeltatG degrees,*M+) are reported. For dissociating solvents, the dependences of [DeltatG degrees,*(Cs+) - [DeltatG degrees,*(M+)] on Gibbs energy of hydration of an ion, DeltaGhydr degrees are straight lines either for four cations Cs+, Rb+, K+, and Na+ (nitrosolvents) or for three cations Cs+, Rb+, and K+ (1,2-dichloroethane and 1-octanol). The hydration of Na+ and still more of Li+ in the water-saturated organic phase is apparent from the results. This manifests for high-water-content equilibrium 1-octanol even in a reversal of the values [i.e., DeltatG degrees*,(Li+) being more negative than DeltatG degrees,*(Na+)], although for Cs+, Rb+, and K+, the general trend is conserved. Water-saturated 1-octanol is thus slightly less basic than water, but the overall selectivity is very low. For one studied nondissociating solvent, dioctyl sebacate, the trend of the dependences of log Kexch degrees,*(CsB/M+) on DeltaGhydr degrees is similar to that of Kexch degrees,*(Cs+/M+) for polar solvents, but different for different anions B, thus reflecting ion association in the organic phase.