Gibbs Energies Of Transfer Research Articles

Correlation between the standard Gibbs energies of an anion transfer from water to highly hydrophobic ionic liquids and to 1,2-dichloroethane

Cyclic voltammetry is used to investigate the transfer of several semihydrophobic and hydrophilic anions (F−, Cl−, Br−, I−, NO3-, NO2-, SCN−, BF4-, ClO4-, PF6-) across the polarized interface between an aqueous electrolyte solution and a highly hydrophobic ionic liquid (IL) membrane. Three ILs are examined being composed of the trioctadecylmethylammonium (TOMA+), tridodecylmethylammonium (TDMA+) or tetradodecylammonium (TDA+) cation and the tetrakis[3,5-bis(trifluoromethyl)phenyl]borate (TFPB−) anion. The standard Gibbs energies of the anion transfer from water to IL, ΔGtr,i0,w→IL, are evaluated from the voltammetric measurements by applying the classical tetraphenylarsonium-tetraphenylborate hypothesis. Comparison of data for various ILs points to a small systematic effect of the cationic IL component, which is manifested by somewhat lower values of ΔGtr,i0,w→IL for most anions in the presence of TDMA+ or TDA+, indicating their stronger association with the anions. The capillary electrophoresis measurements suggest that the degree of interaction of anions with the IL cations in water could follow the order TDMA+ >TOMA+ >TDA+. It is shown that a linear correlation with the nearly unity slope between ΔGtr,i0,w→IL and the standard Gibbs energy of anion transfer from water to 1,2-dichloroethane (DCE), ΔGtr,i0,w→DCE, can be established for all three ILs studied. An extended correlation including both the present and the literature values of ΔGtr,i0,w→IL for the ion transfer from water to TDMATFPB reveals the consistency of data for the semihydrophobic cations and anions, and the presence of a weak solvation effect favoring the transfer of hydrophilic anions (F−, Cl−, Br−, I−) and disfavoring the transfer of hydrophilic cations (H+, Li+, Na+, K+, Rb+, Cs+).

Antioxidant activity, NMR, X-ray, ECD and UV/vis spectra of (+)-terrein: Experimental and theoretical approaches

Fungal metabolite terrein isolated from Aspergillus terreus is endowed with diverse biological and antioxidant activities. To determine the stereochemistry of the isolated terrein, we combined spectroscopic methods (CD and NMR spectra) and theoretical calculations (DFT and TD-DFT methods). Stereochemistry effects on the antioxidant activity of isolated terrein were evaluated by calculating bond dissociation enthalpies (BDEs), ionization potentials (IPs) and spin density delocalization of terrein and isoterrein stereoisomers with B3P86/6-31+G (d,p) method in gas and polarizable continuum model. The results showed a good agreement between experimental data and theoretical calculations which confirmed the (+)-terrein stereochemistry of isolated metabolite. Theoretical calculations showed that the antioxidant activity is relatively influenced by isomeric geometry of the terrein (a variation of 2kcal/mol between BDEs of terrein and isoterrein isomers), while chirality has no influence on the antioxidant activity [0.2kcal/mol difference between BDEs of (+)- and (–)-terrein]. The low antioxidant activity of (+)-terrein with respect to trolox and ascorbic acid was explained by the positive free Gibbs energy of the hydrogen atom transfer (HAT) mechanism and high BDE values of the 2-OH active site.

The Measurement of the Gibbs Energy of Transfer Between Oil and Water Using a Nano‐Carbon Paste Electrode

AbstractThe use of nano‐carbon paste electrodes for the measurement of Gibbs energies of transfer between oil and aqueous phases is reported. In this method the oil of interest is used as the binder for the nano‐carbon paste electrodes and the molecule of interest is dissolved in the organic or aqueous phase. Voltammetry is performed over a period of time and used to monitor the transfer of the molecule between the two phases. The method is illustrated for the transfer of ferrocenemethanol between water and oil using the ferrocenemethanol / ferroceniummethanol (FcCH2OH/FcCH2OH+) redox couple. Three pairs of voltammetric peaks were observed in a 0.1 M KCl solution when the nano‐carbon paste electrode was modified by dissolution of FcCH2OH in the binder oil: P1 [E=0.23 V, 0.17 V vs. Ag/AgCl (1 M KCl)], P2 [E=0.36 V, 0.32 V vs. Ag/AgCl (1 M KCl)] and P3 [E=0.55 V, 0.46 V vs. Ag/AgCl (1 M KCl)]. These are assigned to the FcCH2OH species existing in the aqueous solution [FcCH2OH(aq)/FcCH2OH+(aq)], originating in the oil (o) [FcCH2OH(o)/FcCH2OH+(aq)] and to oxidation of adsorbed (ads) material on the nano‐carbon [FcCH2OH(ads)] respectively. When supporting electrolyte containing the anions Cl−, NO3− or SCN− was used, an expulsion of the oxidised ferrocene occurred and the difference in midpoint potentials (Emid) between the peaks P1 and P2 observed in these experiments allowed the calculation of the Gibbs energy (ΔG°) of transfer of ferrocenemethanol from water to oil. The average ΔG° value thus obtained was (−12.7±0.2) kJ mol−1. For more hydrophobic anions (X−=PF6−, AsF6−), the electron transfer is coupled to the transfer of the anion into the oil and the ΔG° for the transfer of the ion pair of FcCH2OH+ and X− ions from water to oil was found to be −1.3 and −3.9 kJ mol−1 for PF6− and AsF6− respectively.

Chemical Transfer Energies of Some Homologous Amino Acids and the –CH2– Group in Aqueous DMF: Solvent Effect on Hydrophobic Hydration and Three Dimensional Solvent Structure

Standard transfer Gibbs energies, $$ \Updelta_{\text{tr}} G^{^\circ } $$ , of a series of homologues α-amino acids have been evaluated by determining the solubility of glycine, alanine, amino butyric acid and norvaline gravimetrically at 298.15 K. Standard entropies of transfer, $$ \Updelta_{\text{tr}} S^{^\circ } $$ , of the amino acids have also been evaluated by extending the solubility measurement to five equidistant temperatures ranging from 288.15 to 308.15 K. The chemical contributions $$ \Updelta_{\text{tr,ch}} G^{^\circ } (i) $$ of α-amino acids, as obtained by subtracting theoretically computed contributions to $$ \Updelta_{\text{tr}} G^{ \circ } $$ due to cavity and dipole–dipole interaction effects from the corresponding experimental $$ \Updelta_{\text{tr}} G^{ \circ } $$ , are indicative of the superimposed effect of increased basicity and dispersion and decreased hydrophobic hydration (hbh) in DMF–water solvent mixtures as compared to those in water, while, in addition, $$ T\Updelta_{\text{tr,ch}} S^{^\circ } (i) $$ is guided by structural effects. The computed chemical transfer energies of the –CH2– group, $$ \Updelta_{\text{tr,ch}} P^{^\circ } $$ (–CH2–) [P = G or S] as obtained by subtracting the value of lower homologue from that of immediately higher homologue, are found to change with composition indicating involvement of several opposing factors in the calculation of the chemical interactions. The $$ \Updelta_{\text{tr,ch}} G^{^\circ } $$ (–CH2–) values are found to be guided by the decreased hydrophobic effect in DMF–water mixtures, and are indicative of the nature of the three dimensional structure of the aquo-organic solvent system around each solute.

Aggregation properties and thermodynamics of micellization of gemini surfactants with diethyl ether spacer in water and water–organic solvent mixed media

The aggregation properties and thermodynamics of micellization of three cationic gemini surfactants (n–EO1–n) containing diethyl ether spacer group with varying carbon number (n=12, 14 and 16) in the hydrophobic tails have been studied in water and water–organic solvents mixed media over the range of temperature (298.15 to 328.15)K using the conductometric method. Ethylene glycol (EG) and 1,4-dioxane (DO) were used as organic co-solvents with three different volume percentages due to their unique nature than other solvents. With increasing tail length, the critical micellar concentration (cmc) of gemini surfactants decreased. The effect of the diethyl ether spacer group on aggregation behaviour has been compared with other reported spacer groups. The micellization process is delayed in the presence of organic co-solvents as compared to pure water giving a positive value for the Gibbs energy of transfer (ΔGtranso). The degree of counter ion dissociation (α) increases with increasing tail length of gemini surfactants. It also increases with increase in the percentage of organic co-solvents and it is more prominent in DO–WR than EG–WR mixed media. The standard Gibbs energy of micellization (ΔGmo) is found to increase with increasing volume percentage of an organic co-solvent and also with decrease in the chain length of gemini surfactants. The ΔGmo has been correlated with Gordon parameter. The ΔGmo increases with increasing temperature which is more prominent in the presence of high percentage of an organic co-solvent and also in the presence of an organic co-solvent with less polarity. The enthalpies of micellization in all cases are exothermic in nature. The compensation between the enthalpy and entropy for the formation of micellar aggregates has been observed.

Thermodynamic aspects of solubility and partitioning processes of some sulfonamides in the solvents modeling biological media

The thermodynamic aspects of solubility processes of sulfonamides (SAs) with the general structures 4-NH2–C6H4–SO2NH–C6H2(R1)(R2)-R3 (R1=2-CH3, 2-Cl; R2=4-CH3, 4-Cl; R35-H, 5-Cl), 4-NH2-2-Cl–C6H3–SO2NH–C6H3(R1)-R2 (R1=2-H, 2-Cl; R2=4-H, 4-Cl) and 4-NH2-2-CH3–C6H3–SO2NH–C6H3(R1)-R2 (R1=2-H, 2-Cl, 2-NO2; R2=4-H, 4-Cl) in water and 1-octanol (as phases modeling various drug delivery pathways) were studied using the isothermal saturation method. For the sulfonamides with various substituents in phenyl rings the processes of transfer from water to 1-octanol were studied by a diagram method combined with analysis of enthalpic and entropic terms. Distinguishing between enthalpy and entropy, as is possible through the present approach, leads to the insight that the contribution of these terms is different for different molecules (entropy- or enthalpy-determined). Thus, in contrast to the interpretation of only the Gibbs energy of transfer (extensively used for pharmaceuticals in the form of the partition coefficient, logP), the analysis of thermodynamic functions of the transfer process provides additional mechanistic information. This may be important for further evaluation of the physiological distribution of drug molecules and may provide a better understanding of biopharmaceutical properties of drugs.

Activity Coefficient Determination for the Ternary Systems CsCl in N-Methylformamide or Urea + Water Mixtures at T = 298.15 K

The mean activity coefficients for CsCl in N-methylformamide or urea (w) + H2O (1 − w) systems were determined in this work by potentiometry, using ion-selective electrodes at 298.15 K. The value of mass fraction w was varied between 0.00 and 0.40 in five unit-steps and the molality of CsCl was between 0.0020 and 1.4009 mol·kg−1. The experimental data have been correlated with the Pitzer, modified Pitzer and the extended Debye–Huckel equations. The resulting values of the mean activity coefficients, the osmotic coefficients and the standard Gibbs energy of transfer, together with the Pitzer ion-interaction parameters (β(0), β(1) and Cφ), extended Debye–Huckel parameters (a, c and d), and modified Pitzer parameters (b, BMX, CMX) are reported for the investigated systems.

Activity Coefficients in Quaternary Systems at 298.15 K: RbCl + MeOH + EtOH + H2O and CsCl + MeOH + EtOH + H2O Systems

Activity coefficients of RbCl or CsCl in methanol + ethanol + water were determined at 298.15 K by the cells containing ion-selective electrodes (ISEs). The molalities of RbCl and CsCl are up to approximately 1 mol·kg–1 in the mixed solvents, and the mass fractions of five aqueous MeOH/EtOH mixtures studied were (5/5, 10/5, 5/10, 10/10, and 15/15) %. The experimental data were optimized using the extended Debye–Huckel, the Pitzer, and the modified Pitzer equations. The results of the apparent standard electromotive force E0* of the three equations are in good agreement. The mean activity coefficients and the standard Gibbs energy of transfer of RbCl or CsCl from pure water to mixed solvents (MeOH + EtOH + water) were also calculated.

Thermodynamic Solvation of a Series of Homologous α-Amino Acids in Aqueous Mixtures of 1,2-Dimethoxyethane

The standard Gibbs energies $$ \left( {\Updelta {}_{\text{t}}G^\circ (i)} \right) $$ and entropies $$ \left( {\Updelta {}_{\text{t}}S^\circ } \right) $$ of transfer in aqueous mixtures of 1,2-dimethoxyethane (DME) containing 0, 20, 40, 60, 80, 100 wt-% DME have been determined from the solubility data of a series of homologous α-amino acids, evaluated by the formol titrimetric method. The observed result of Δt G°(i) and TΔt S°(i) against DME concentration profiles are complicated due to the various interaction effects. The chemical effects on the transfer Gibbs energies ( $$ \Updelta_{\text{t}} G_{\text {ch}}^{ \circ } (i) $$ ) and entropies of transfer $$ T\Updelta_{\text{t}} S_{\text {ch}}^{ \circ } (i) $$ have been obtained after elimination of the cavity effect, calculated by the scaled particle theory, and dipole–dipole interaction effects, estimated by the use of Keesom-orientation expression for total transfer Gibbs energies Δt G°(i) and entropies Δt S°, respectively. The chemical transfer energetics of the zwitterionic homologous α-amino acids are guided by the composite effects of increased dispersion interaction, basicity and decreased acidity, hydrogen bonding capacity and hydrophobic hydration of the DME mixed solvent as compared to that of reference solvent, water.

A revisit to the non-Bornian theory of the Gibbs energy of ion transfer between two immiscible liquids

Previously, Osakai and Ebina (1998) proposed a non-Bornian theory for the Gibbs energy (ΔGtr°,W→O) of ion transfer at the organic solvent/water interface. In a conventional manner, however, ΔGtr°,W→O was divided into ionic charge-dependent and -independent terms. The former was formulated based on non-Bornian, short-range interactions of an ion with primary solvent molecules, while the latter was evaluated as the energy of cavity formation by using the Uhlig formula. In this study, we have successfully shown that the above two terms can be brought together in the context of short-range ion–solvent interactions, and that the ΔGtr°,W→O scaled by the ionic surface area can be given by a quadratic function of the surface field strength of the ion. The obtained semiempirical equation of ΔGtr°,W→O is very simple, and would be useful for the prediction of ΔGtr°,W→O.

Thermal properties and interactions of l-proline in aqueous solutions of NaCl or KCl at different temperatures

The enthalpies of solution of l-proline in aqueous electrolyte solutions within the electrolyte molality range up to 4.9 mol kg−1 of NaCl and up to 4.0 mol kg−1 of KCl at 288, 298 and 313 K have been measured by the calorimetric method. Enthalpies of transfer of l-proline from water to aqueous electrolyte solutions up to saturation have been derived at 273–348 K. The enthalpic and heat capacity parameters of pair and triplet interaction of l-proline with electrolyte in water have been evaluated. Enthalpic parameters of pair interaction at 298 K have been compared to similar parameters for glycine and l-alanine. The temperature changes of reduced enthalpy, and also the change of entropy and reduced Gibbs energy of transfer of l-proline from water to aqueous electrolyte solution at temperature rise from 273 to 323 K have been determined. It has been shown that the entropy–enthalpy compensation takes place for transfer processes.

A PPy-B15C5 modified lanthanum (III) electrode in acetonitrile and its thermodynamic application

Polypyrrole modified electrode prepared by electropolymerization of pyrrole in the presence of a complexing ligand, benzo-15-crown-5 (B15C5), was prepared and investigated as a La3+-selective electrode in acetonitrile. The potentiometric response of the electrode was linear within the La3+ concentration range 1×10−4 to 1×10−1M with a Nernstian slope of 19.5mV decade−1 in AN. The electrode was applied to study the complexation of the lanthanum (III) ion in acetonitrile with other basic solvent molecules (D) such as dimethyl sulfoxide, N,N-dimethylformamide, propylene carbonate, N,N,Diethylaniline and methanol. The successive complex formation constant (βi) and Gibbs energies of transfer (ΔGtr) of La3+ in AN in relation to such D were obtained.

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

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

Thermodynamic Study of a Cationic Surfactant in Aqueous Solution Containing Ethylene Glycol and Its Oligomers: Effect of Number of Ethereal Oxygen Atoms in Glycols Molecule

Effect of glycols viz., ethylene glycol (EG), diethylene glycol (DEG), triethylene glycol (TEG) and tetraethylene glycol (TeEG) on micellization parameter of cationic surfactant tetradecyletrimethyl ammonium bromide (TTAB) was examined by means electrical conductivity measurements. The critical micelle concentration (CMC), degree of counterion dissociation (α) and Gibbs energy of micellization (ΔGm) as well as Gibbs energy of transfer (ΔG t ) of surfactant tail from bulk phase to micellar phase as a functions glycol concentration at 303.15 K were evaluated. In ordered to obtain enthalpy (ΔHm) and entropy (ΔSm) of micellization, CMCs were determined in 10.0% of glycols in temperature range from 303.15 K to 323.15 K. Thermodynamic parameters of the micellization reveal that effectiveness of glycols to reduce micellization increases with concentration and with number of ethereal oxygen, [-O-]n in glycol molecule.

Pitzer, Modified Pitzer, and Extended Debye–Hückel Modeling Approaches: Ternary RbF or CsF + Glycine + Water Electrolyte Systems at 298.15 K

This article deals with the mean activity coefficients of RbF or CsF in the glycine + water mixed systems. The Pitzer, the modified Pitzer, and the extended Debye–Huckel equations are used to describe the nonideal behavior of the electrolyte. The osmotic coefficients, the excess Gibbs free energy, and the standard Gibbs energies of transfer were calculated with the corresponding parameters.

Origin of the correlation between the standard Gibbs energies of ion transfer from water to a hydrophobic ionic liquid and to a molecular solvent

Cyclic voltammetry was used to evaluate the standard Gibbs energy of transfer of a series of semi-hydrophobic ions from water to the newly synthesized highly hydrophobic ionic liquid (IL) composed of the tridodecylmethylammonium (TDMA+) cation and the dicarbollylcobaltate (DCC−) anion. Results were compared with those reported for the ion transfer to 1,2-dichloroethane (DCE) and to ILs composed of the same cation but a structurally different anion: tetrakis(pentafluorophenyl)borate (TPFPB−) or tetrakis[3,5-bis(trifluoromethyl)phenyl]borate (TFPB−), and composed of the structurally different (ferrocenylmethyl)dodecyldimethylammonium+ cation (FcMDDA+) and the same anion (TFPB−). Dielectric relaxation spectroscopy (DRS) measurements of TDMADCC and TDMATPFPB provided the static (ɛs) and optical (ε∞) dielectric constants as the low- and high-frequency limits of the complex dielectric permittivity, respectively, as well as the corresponding relaxation times. The observed differences in the dielectric properties were clarified on the basis of the density functional theory (DFT) calculations of the ground state electronic structure, ion volume (ion radius) and dipole moment of the constituent IL ions. Contributions of the electrostatic and solvophobic interactions to the standard Gibbs energy of ion transfer were estimated using the advanced Born–Uhlig theory. The conclusion was made that the correlation established between the standard Gibbs energies of ion transfer from water to the studied ILs and to DCE has the origin in similar solvophobic contributions rather than in the comparable polarity of TDMADCC (ɛs=11.7) and TDMATPFPB (ɛs=7.1) and DCE (ɛs=10.5), as characterized by the static dielectric constant ɛs.

A Colorful Laboratory Investigation of Hydrophobic Interactions, the Partition Coefficient, Gibbs Energy of Transfer, and the Effect of Hofmeister Salts

Only a few pedagogical experiments have been published dealing specifically with the hydrophobic interaction though it plays a central role in biochemistry. A set of experiments is presented in which students partition a variety of colorful indicator dyes in biphasic water/organic solvent mixtures. Students monitor the partitioning visually and quantify it using inexpensive Spectronic 20 spectrophotometers. Through the experiments, the students explore the effects of charge, alkyl chain length, the presence of Hofmeister salts, and temperature on a variety of parameters related to hydrophobicity such as the partition coefficient, and the thermodynamic parameters of transfer of a molecule from the aqueous layer into the organic layer.

Investigation of the electrochemical processes related to IT coupling with ET by hydrophilic droplet electrodes

The electrochemical processes of ion transfer (IT) at a water/1,2-dichloroethane (W/DCE) interface coupling with electron transfer (ET) at an aqueous solution/Pt interface have been investigated systematically by hydrophilic droplet electrodes with cyclic voltammetry and Osteryoung square wave voltammetry. Here a disk Pt electrode is covered fully with an aqueous droplet containing redox couple of K3Fe(CN)6 and K4Fe(CN)6, and this assembly is immersed into the DCE phase. Based on this simple three-electrode setup, we can observe that the reduction of K3Fe(CN)6 and the oxidation of K4Fe(CN)6 on the Pt electrode are coupled with respective Cl− and K+ transfer processes at the W/DCE interface. The complicated mechanism of coupling processes has been discussed and evaluated by the analysis of several influence factors, such as, concentrations and ratios of redox couple in the aqueous droplet, and phase volume ratios. In addition, the Gibbs energies of different ions transfer at the W/DCE interface have been accurately determined by OSWV with K+ or Cl− as the internal reference ion. This method has also been demonstrated to be a useful tool to detect several ions simultaneously.

Partitioning behavior of amino acids in aqueous two-phase systems formed by imidazolium ionic liquid and dipotassium hydrogen phosphate

Partition coefficients of amino acids, including glycine, alanine, 2-aminobutyric acid, valine, leucine, threonine, methinoine, tryptophan and tyrosine, in [Cnmim]Br (n=4, 6, 8)+K2HPO4 aqueous two-phase systems (ATPSs) have been determined, and the relative hydrophobicity of the equilibrium phases in the ionic liquids-based aqueous two-phase systems has been characterized by the Gibbs energies of transfer for methylene group from the bottom salt-rich phase to the top ionic liquid-rich phase. Based on these results, factors affecting the partitioning behavior of the amino acids have been investigated. It is shown that partition coefficients of the amino acids increase with the increase of hydrophobicity of the amino acids and the ionic liquids, solution pH value, tie-line length of the ATPSs and temperature of the systems. The possible driving forces and the thermodynamic parameters for the partitioning of amino acids in the ionic liquids-based ATPSs have also been discussed.

The response behavior of PPy-DB18C6 electrode to terbium(III) in acetonitrile and its thermodynamic application

Polypyrrole modified electrode prepared by electropolymerization of pyrrole in the presence of a complexing ligand, dibenzo-18-crown-6(DB18C6), was prepared and investigated as a Tb3+-selective electrode in acetonitrile. The potentiometric response of the electrode was linear within the Tb3+ concentration range 1×10−5–1×10−2M with a Nernstian slope of 20.9mVdecade−1 in AN. The electrode was applied to study the complexation of the terbium(III) ion in acetonitrile with such other basic aprotic solvent molecules (D) as dimethyl sulfoxide, N,N-dimethyl formamide, propylene carbonate and pyridine. The successive complex formation constant (βi) and Gibbs energies of transfer (ΔGtr) of Tb3+ in AN in relation to such D were obtained.