Gibbs Energies Of Transfer Research Articles

MicroITIES Detection of Adenosine Phosphates

AbstractThe complexation between a triamide ligand derived from tris‐2‐(aminoethyl)amine: N‐{2‐[bis‐(2‐(4‐tert‐butylbenzoyl)‐aminoethyl)‐amino]‐ethyl}4‐tert‐butylbenzamide, L, and the three adenosine‐containing nucleotides, ATP, ADP, and AMP, was investigated by facilitated ion transfer processes through a microhole array film. Differential pulse voltammetry (DPV) was used to measure the transfer currents for the respective nucleotides. The three nucleotides were found to have different transfer potentials with transfer currents proportional to their aqueous concentrations. Based on the differences of the transfer potentials, it is concluded that the host ligand, L, interacts with the phosphate moiety and the Gibbs transfer energy is dominated by the charge generated by the phosphate groups. The linear relationship between the current response and nucleotide concentration forms the basis of an anion sensor with a dynamic range from 0.1 mM to 5 mM.

Boron removal from produced water by facilitated ion transfer

This work aims to develop a novel technology to treat produced water with the intent to reuse it for crop irrigation. The concentration of boron in produced water is relatively high — 4–5 ppm, which gives rise to poisoning of the plants if used for irrigation. Therefore, boron concentration must be reduced to safe levels between 0.3 and 0.5 ppm. A process based on liquid-liquid electrochemistry has been investigated to transfer selectively borate anions present in produced water to an immiscible phase. Experiments have been carried out at laboratory scale under stationary conditions in an ITIES cell (Interface between Two Immiscible Electrolytic Solutions) to determine the suitability of borate receptors, which facilitate transfer from the aqueous phase to the immiscible phase. These measurements allow the determination of the equilibrium conditions for the system and important parameters such as Gibbs energy of transfer for the borate anion. Simulations have been carried out using a finite element method to validate experimental results. The simulations and experimental results are used as a basis for further model development in both static and continuous operation regimes.

Kinetics of facilitated proton transfer by hydrophobic aromatic amines across the water/1,2-dichloroethane interface

The kinetics of proton transfer facilitated by 4-octylaniline, 4-dodecylaniline and 4-hexadecylaniline across the water/1,2-dichloroethane interface has been investigated by cyclic voltammetry and ac impedance. It was found that their electrochemical behaviour is very similar and the three amines assist proton transfer from the aqueous to the organic phase. The formal Gibbs energy of proton transfer and the formal rate constant were evaluated. It is concluded that interfacial organisation of these molecules is an important factor in the kinetics of facilitated proton transfer and that the aromatic ring is able to penetrate the interface whilst the long hydrophobic chain contributes to the stability of the amine in the organic phase.

The partitioning of alkanediols into SDS and DTAB micelles from NMR-PRE experiments

The p-values of a number of α,ω-alkanediols, 1,2-alkanediols, and 1,5-hexanediol and 2,5-hexanediol between D2O and the micellar phases of anionic sodium dodecylsulfate (SDS) and cationic dodecyltrimethylammonium bromide (DTAB) have been determined using the using a NMR paramagnetic relaxation enhancement experiment (NMR-PRE). From the p-values, mole-fraction based partition coefficients and Gibbs energies of transfer for the alkanediols from the bulk D2O phase to the micellar phase have been calculated. Differences in the partition coefficients of the α,ω-alkanediols and the 1,2-alkanediols are discussed in terms of the smaller Gibbs transfer energy per CH2 group for α,ω-alkanediols. For the 1,5- and the 2,5-hexanediols, the p-values are substantially smaller than for the other hexanediols in both SDS and DTAB micelles. All of these results are consistent with the location of the two hydroxyl groups on the carbon backbone making a substantial contribution to the thermodynamics of transfer of solubilizates.

Solubilization of n-alkylbenzenes in aggregates of sodium dodecyl sulfate and a cationic polymer of high charge density (II).

The solubilization property of the aggregate composed of sodium dodecyl sulfate (SDS) and a cationic polymer (polydiallyldimethylammonium chloride, PDADMAC) was investigated. From the binding isotherm, the increasing free SDS concentration (Cf) above the critical aggregation concentration (cac) was clearly confirmed and used to calculate the Gibbs free energy change of solubilization. The maximum additive concentration of the alkylbenzene solubilizates remained almost constant around their aqueous solubilities below the cac and then increased with increasing SDS concentration above the cac and with decreasing alkyl chain length of the solubilizates. Also, their solubility increased with increasing temperature over the concentration range of the surfactant examined. Because the monomeric DS- concentration in the aqueous phase (Cf) increased with the SDS concentration above the cac in the SDS/PDADMAC system, Cf was evaluated from the binding isotherm to calculate the change in the Gibbs energies of transfer of the solubilizates using the phase separation model. The Gibbs energy change for the solubilizates decreased with increasing temperature and increasing alkyl chain length. The decrease in the Gibbs energy per CH2 group (DeltaGCH2 degrees) was favored by an increase of temperature, and it was larger in magnitude than that for micelles of single-surfactant systems. From the values of DeltaH degrees and TDeltaS degrees, the solubilization of alkylbenzenes into SDS/PDADMAC was found to be entropy-driven.

Determination of Solvation Descriptors for Ionic Species: Hydrogen Bond Acidity and Basicity

Literature values of Gibbs energies of transfer of ions from water to other solvents have been used in conjunction with our solvation equation to obtain descriptors for univalent ions. It is suggested that descriptors used for nonelectrolytes are not adequate to describe transfers of single ions, and that two specific ionic descriptors (J(+) and J(-)) for cations and anions, respectively, are required. The ions studied include the alkali metal and tetraalkylammonium cations, halide and other anions, and the tetraphenylarsonium, tetraphenylphosphonium, and tetraphenylborate ions. It is shown that simple cations such as Na(+) act as very strong hydrogen bond acids and that the R(4)N(+) ions are only weak hydrogen bond acids. The halide anions are very strong hydrogen bond bases, as is also the acetate anion. Other anions, such as azide, cyanide, and nitrate, are again very strong hydrogen bond bases. The tetraphenylarsonium, tetraphenylphosphonium, and tetraphenylborate ions have no hydrogen bond acidity but are quite strong hydrogen bond bases. It is suggested that this is due to the basic properties of the phenyl groups.

Mutational and structural-based analyses of the osmolyte effect on protein stability.

It is known that several naturally occurring substances known as osmolytes increase the conformational stability of proteins. Bolen and co-worker proposed the osmophobic theory, which asserts the osmolyte effect occurs because of an unfavorable interaction of osmolytes mainly with the protein backbone, based on the results on the transfer Gibbs energy of amino acids (Deltag) [Bolen and Baskakov (2001) J. Mol. Biol. 310, 955-963]. In this paper, we report the effect of sarcosine on the conformational stability (DeltaG) of RNase Sa (96 residues and one disulfide bond) and four mutant proteins. The thermal denaturation curves for RNase Sa in sarcosine fitted a two-state model on nonlinear least-squares analysis. All the RNase Sa proteins were stabilized by sarcosine. For example, the increase in stability of the wild-type protein in 4 M sarcosine due to the osmolyte effect (Delta(o)DeltaG) is 3.2 kcal/mol. Mutational analysis of the osmolyte effect indicated that the changed Delta(o)DeltaG values upon mutation (Delta(m)Delta(o)DeltaG), as estimated from the Deltag values, are similar to the experimental values. Structural-based analysis of the osmolyte effect was also performed using model denatured structures: (a) a fully extended model (single chain) with no disulfide bond, (b) two-part, unfolded models (two chains) with a disulfide bond constructed through molecular dynamic (MD) simulation, and (c) a two-part, folded model (two chains). The two-part, unfolded models were expected to be more suitable as denatured structures. The Delta(o)DeltaG values calculated using the two-part, unfolded models were more consistent with experimental values than those calculated using the fully extended and two-part, folded models. This suggests that MD simulation is useful for testing denatured structures. These results indicate that the osmophobic theory can explain the osmolyte effect on protein stability.

Investigation of surface properties of amino acids: polarity scale for amino acids as a means to predict surface exposed residues in films of proteins.

It is of great interest and importance to study how different amino acid residues contribute to and affect the properties of proteins coated as films on solid surface. This work shows that the solid/liquid interfacial energy of surface localized amino acid films and their Gibbs energies of transfer at the air/solution interface have the potential to be used as a rapid and simple method for studying the surface properties of proteins. Based on these results, a new polarity scale for amino acids has been proposed. This scale is compared with existing hydropathy scales in a benchmark test using some proteins with solved 3D structure. The proteins were characterized in terms of surface-exposed residues with a computer program, Graphical Representation and Analysis of Surface Properties (GRASP). It was also shown that each amino acid contribution is relative to the total protein surface and the other residues on the surface.

Investigation of surface properties of amino acids: polarity scale for amino acids as a means to predict surface exposed residues in films of proteins

It is of great interest and importance to study how different amino acid residues contribute to and affect the properties of proteins coated as films on solid surface. This work shows that the solid/liquid interfacial energy of surface localized amino acid films and their Gibbs energies of transfer at the air/solution interface have the potential to be used as a rapid and simple method for studying the surface properties of proteins. Based on these results, a new polarity scale for amino acids has been proposed. This scale is compared with existing hydropathy scales in a benchmark test using some proteins with solved 3D structure. The proteins were characterized in terms of surface-exposed residues with a computer program, Graphical Representation and Analysis of Surface Properties (GRASP). It was also shown that each amino acid contribution is relative to the total protein surface and the other residues on the surface.

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.

Thermodynamics of Resolvation of Sodium and Potassium Ions in Water–Dimethylformamide

The real primary medium effect of sodium and potassium ions and the real Gibbs energy of transfer of these ions from water into a mixed water–dimethylformamide (DMF) solvent are determined using the method of Volta potential differences at 298.15 K. For DMF, the surface potential at the solvent/gas interface is found to equal –0.434 V. Based on this value, chemical thermodynamic characteristics of the ions are calculated. The thermodynamic characteristics for resolvation of cations are compared with those for anions in the mixtures under investigation obtained earlier.

Transfer energetics of a series of homologous α-amino acids and hence of CH 2 group—a possible probe for the solvent effect on hydrophobic hydration and the three-dimensional-structuredness of aqueous cosolvents

Standard transfer Gibbs energies, Δ G t 0 and entropies, Δ S t 0 of a series of homologous α-amino acids (i) like glycine (gly), alanine (ala), α-amino butyric acid (aba) and nor-valine (n-val) from water to aqueous mixtures of three-dimensional-structure making (SM) 2-propanol (2-PrOH) and three-dimensional-structure breaking (SB) acetonitrile (ACN) have been determined from solubility measurements at five equidistant temperatures ranging from 15 to 35 °C by ‘formol titrimetry’. The chemical contributions ΔP t, ch 0 i as obtained by subtracting the cavity effect. ΔP t, cav 0 i and dipole–dipole interaction effect ΔP t, dd 0 i ( P= G or S), reflect that while ΔG t, ch 0 i are dictated by decreased hydrophobic hydration (H bH) and the superimposed increased basicity and dispersion effects. T ΔS t, ch 0 i are guided by superimposed structural interaction effect as well. These values also helped to compute the transfer energetics of the smallest hydrophobic moiety (CH 2), Δ P t,ch 0 (CH 2), by subtracting the values of lower homologues from those of immediately higher homologues and also those of Δ P t,H bH 0(CH 2) by subtracting the dispersion interaction effect of the (CH 2) group, Δ P t,disp 0 (CH 2), from the corresponding Δ P t,ch 0 (CH 2). These values are found to be additive in nature and are nearly equal to those obtained from the homologous series of RCOO − and RNH 3 + salts studied earlier. While Δ G t,H bH 0 (CH 2) are found to increase with cosolvent composition indicating the effect of decreased H bH, Δ S t,H bH 0 (CH 2) are found to pass through a characteristic maximum in the case of SM 2-PrOH, but a broad minimum in the case of SB ACN. The latter are indicative of the effect of three-dimensional-structuredness of solvents. This leads us to conclude that transfer energetics of the CH 2 group are not only an unambiguous reflector of the solvent effect of H bH, but also the best probe for the three-dimensional-structuredness of aquo-ionic and aquo-non-ionic cosolvents without being obscured by the effect of ‘buffer bonds’, as in the cases of HBz, pNA and R 4N + ions studied earlier.

Solvation and hydration characteristics of ibuprofen and acetylsalicylic acid.

Ibuprofen and acetylsalicylic acid were studied by thermoanalytical methods: sublimation calorimetry, solution calorimetry, and with respect to solubility. Upon measuring the temperature dependences of the saturated vapor pressure, enthalpies of sublimation, DeltaH(0) (sub), as well as the entropies of sublimation, DeltaS(0) (sub), and their respective relative fractions in the total process were calculated. The Gibbs energy of solvation in aliphatic alcohols as well as the enthalpic and entropic fractions thereof were also studied and compared with the respective properties of model substances and other nonsteroidal antiinflammatory drugs (benzoic acid, diflunisal, flurbiprofen, ketoprofen, and naproxen). In all cases, enthalpy was found to be the driving force of the solvation process. Correlations were derived between Gibbs energy of solvation in octanol, DeltaG(Oct) (solv), and the transfer Gibbs energy from water to octanol, DeltaG(0) (tr). Influence of mutual octanol and water solubilities on the driving force of partitioning is discussed. An enthalpy-entropy-compensation effect in octanol was observed, and consequences of deviation from the general trend are also discussed.

Systematic study of the transfer of amino acids across the water/1,2-dichloroethane interface facilitated by dibenzo-18-crown-6

Facilitated ion transfer reactions of 20 amino acids with dibenzo-18-crown-6 (DB18C6) at the water/1,2-dichloroethane (W/DCE) interfaces supported at the tips of micro- and nano-pipets were investigated systematically using cyclic voltammetry. It was found that there were only 10 amino acids, that is, Leu, Val, lie, Phe, Trp, Met, Ala, Gly, Cys, Gin (in brief), whose protonated forms as cations can give well-defined facilitated ion transfer voltammograms within the potential window, and the reaction pathway was proven to be consistent with the transfer by interfacial complexation/dissociation (TIC/TID) mechanisms. The association constants of DB 18C6 with different amino acids in the DCE (β0), and the kinetic parameters of reaction were evaluated based on the steady-state voltammetry of micro- or nano-pipets, respectively. The experimental results demonstrated that the selectivity of complexation of protonated amino acid by DB18C6 compared with that of alkali metal cations was low, which can be attributed to the vicinal effect arising from steric hindrance introduced by their side group and the steric bulk effect by lipophilic stabilization. Moreover, the association constants and the standard rate constants for different amino acids showed good correlations with their hydrophobicity (π), except Gly and Met, which inferred that the selectivity of such heterogeneous complex reaction for different amino acids with DB18C6, was not only affected by discrimination in binding these ions to the crown ether macro-cycle, but also significantly modified by the ion transfer Gibbs energy which was closely related to the structure of the transferred ions, protonated amino acids.

The determination of the standard Gibbs energies of ion transfer between water and heavy water by using the three-phase electrode approach

For the first time, the standard Gibbs energies of transfer of anions and cations across the nitrobenzene|heavy water interface are reported as measured by an electrochemical technique. The data have been obtained with the help of three-phase electrodes consisting of a nitrobenzene droplet that contains an electroactive compound (either decamethylferrocene to transfer anions or iron(III) tetraphenyl porphyrin chloride to transfer cations), a graphite electrode on the surface of which the droplet is attached, and a solution of the salts with the transferable ions in heavy water. The difference between these Gibbs energies of transfer and those of transfer between light water and nitrobenzene allows calculating the Gibbs energies of transfer between light water and heavy water. The latter vary in the interval from −0.50 to +0.50 kJ/mol with confidence intervals ranging from ±0.054 to ±0.117 kJ/mol.

Thermodynamics of Solutions IV: Solvation of Ketoprofen in Comparison with other NSAIDs

The present work discusses the characteristics of solvation (Gibbs energy, enthalpic and entropic terms of Gibbs energy) for ketoprofen together with other nonsteroidal antiinflammatory drugs (NSAIDs) in aliphatic alcohols. Ketoprofen was studied by classical thermoanalytical methods of sublimation calorimetry, solution calorimetry, and solubility. Temperature dependence of the saturated vapor pressure was determined, and the sublimation enthalpy, ΔHsub0, and sublimation entropy, ΔSsub0, as well as their respective relative fractions in the total process were calculated. The parameters yielded for ketoprofen were compared with the respective literature data of other benzophenone derivatives. The Gibbs energy of solvation as well as enthalpic and entropic terms thereof in aliphatic alcohols were also studied for ketoprofen and compared with the properties of model substances and other NSAIDs (benzoic acid, diflunisal, flurbiprofen, and naproxen). In all cases, the major driving force of the solvation process is enthalpy. Correlations were derived between Gibbs energy of solvation in octanol, ΔGsolvoct, and the transfer Gibbs energy from water to octanol, ΔGtr0. © 2003 Wiley‐Liss, Inc. and the American Pharmacists Association J Pharm Sci 92:2502–2511, 2003

Ion–Solvent Interactions and Determination of Single-Ion Gibbs Energies of Transfer from the Studies of the Solubility and Dissociation Constants of Oxalic Acid in Aquo + Methanolic Mixtures

Abstract The solvent effects on the dissociation of the simplest dibasic organic acid were examined from the determination of the first and second dissociation constants of oxalic acid conductometrically and pH-metrically in water + methanol mixtures (0–87 wt% of methanol). The solubility values of oxalic acid and potassium hydrogen oxalate were also determined in water + methanol mixtures. The dissociation constant and the solubility values were used to calculate the Gibbs energies of transfer ΔG 0 t of oxalic acid (H2OX), bioxalate (HOX−), oxalate (OX2−) and potassium (K+) ions from water to aquo-methanolic mixtures. These represent the quantitative measures of solute or ion–solvent interactions of the respective species in going from water to methanol + water mixtures. pK 1, pK 2 and the solubility values of oxalic acid increase continuously with increase in organic co-solvent. ΔG 0 t (H2OX) and ΔG 0 t (H+) are negative i.e. favourable but ΔG 0 t (H2OX), ΔG 0 t (OX2−) and ΔG 0 t (K+) are in general positive and hence unfavourable for the dissociation processes. The increase in basicity fecilitated the dissociation processes but decrease in dielectric constant and H-bonding capability enhance the association processes as the organic co-solvent increases. Attempts have been made to understand the solvation processes in terms of the structure of the aquo + organic mixtures and Walden products. The pK values can be suitably utilised to prepare buffer solutions in methanol + 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 methanol + water mixtures.

Studies of Activity Coefficients for Ternary Systems: Water + 18-Crown-6 + Alkali Chlorides at 298.15 K

Osmotic vapor pressure measurements have been carried out for three ternary systems, H2O + 0.2 m 18-crown-6 + LiCl, H2O + 0.2 m 18-crown-6 + NaCl and H2O + 0.2 m 18-crown-6 + KCl at 298.15 K using vapor pressure osmometry. Water activities for each ternary system were measured and used to calculate the activity coefficients of 18-crown-6 (18C6) and its salts following the methodology developed by Robinson and Stokes for isopiestic measurements. In the concentration range studied, it was found that (in NaCl and KCl solutions) there is considerable lowering of activity coefficients of one component in the presence of other solutes that has been attributed to the formation of the complexed 18C6:Na+ (or 18C6:K+) species in solution. The Gibbs energies of transfer of alkali chlorides from water to aqueous 18C6 solutions and that of 18C6 from water to aqueous electrolyte solutions have been calculated. These were further used to evaluate the pair and triplet interaction parameters. The calculation of thermodynamic equilibrium constants using the pair interaction parameter, gNE (i.e., the nonelectrolyte–electrolyte pair interaction) for the studied complexation of cations yields values which are in good agreement with those reported in literature obtained by using ion-selective potentiometry and calorimetry. The results are discussed in terms of water structural effects, complex formation, and hydrophobic interactions.

Studies of Electron-Transfer and Charge-Transfer Coupling Processes at a Liquid/Liquid Interface by Double-Barrel Micropipet Technique

Investigation of a heterogeneous electron-transfer (ET) reaction at the water/1,2-dichloroethane interface employing a double-barrel micropipet technique is reported. The chosen system was the reaction between Fe(CN)63- in the aqueous phase (W) and ferrocene in 1,2-dichloroethane (DCE). According to the generation and the collection currents as well as collection efficiency, the ET-ion-transfer (IT) coupling process at such an interface and competing reactions with the organic supporting electrolyte in the organic phase can be studied. In addition, this technique has been found to be an efficient method to distinguish and measure the charge-transfer coupling reaction between two ions (IT-IT) processes occurring simultaneously at a liquid/liquid interface. On this basis, the formal Gibbs energies of transfer of some ions across the W/DCE interface, such as NO3-, NO2-, Cl-, COO-, TBA+, TPAs+, Cs+, Rb+, K+, Na+, and Li+, for which their direct transfers are usually difficult to obtain because of the IT-IT coupling processes, were quantitatively evaluated.

Viscosity B-coefficients and activation parameters for viscous flow of a solution of heptanedioic acid in aqueous sucrose solution

Viscosity and density data for the system of heptanedioic acid dissolved in aqueous sucrose solution at temperature range from 288.15 to 313.15 K have been measured. The viscosity B-coefficients for heptanedioic acid in aqueous sucrose solution has been calculated. The effect of temperature and sucrose concentration on the B-coefficients is discussed. On the basis of the Feakins equation, the activation parameters (Δ μ 3 ≠, Δ H 3 ≠, Δ S 3 ≠, Δ G 12 0≠, Δ H 12 0≠ and Δ S 12 0≠) for viscous flow of the solution have been evaluated, together with the Gibbs energy of transfer for the solute from the ground state solvent to the hypothetical viscous transition state solvent (Δ G 3 ≠(1−1′)). The effect of sucrose concentration and temperature on the activation parameters has been discussed.