Gibbs Energy Of Solvation Research Articles

Thermodynamic quantities of solvation and dilution for some acetanilide derivatives in octanol and water mutually saturated

Based on published thermodynamic quantities for solution, partitioning and sublimation of acetanilide (ACN), acetaminophen (ACP) and Phenacetin (PNC), the thermodynamic quantities for drugs solvation in octanol-saturated water (W(ROH)) and water-saturated octanol (ROH(W)) as well as the drugs dilution in ROH(W) were calculated. The Gibbs energies of solvation were favourable in all cases. The respective enthalpies and entropies were negative indicating an enthalpy-driving for the solvation process in all cases. On the other hand, the Gibbs energies of dilution were favourable for ACP and PNC but unfavourable for ACN, whereas the respective enthalpies and entropies were negative for ACP and PNC but positive for ACN indicating enthalpy-driving for the dilution process in the case of the former drugs and entropy-driving for the latter. From the obtained values for the transfer processes, an interpretation based on solute-solvent interactions was developed.

Thermodynamic quantities of solvation and dilution for some acetanilide derivatives in octanol and water mutually saturateds

Based on published thermodynamic quantities for solution, partitioning and sublimation of acetanilide (ACN), acetaminophen (ACP) and Phenacetin (PNC), the thermodynamic quantities for drugs solvation in octanol-saturated water (W(ROH)) and water-saturated octanol (ROH(W)) as well as the drugs dilution in ROH(W) were calculated. The Gibbs energies of solvation were favourable in all cases. The respective enthalpies and entropies were negative indicating an enthalpy-driving for the sol- vation process in all cases. On the other hand, the Gibbs energies of dilution were favourable for ACP and PNC but unfavourable for ACN, whereas the respective enthalpies and entropies were negative for ACP and PNC but positive for ACN indicating enthalpy-driving for the dilution process in the case of the former drugs and entropy-driving for the latter. From the obtained values for the transfer process- es, an interpretation based on solute-solvent interactions was developed.

Nikolai Izmailov and the electrochemistry of solutions

The paper aims to pay tribute to scientific achievements of Nikolai Izmailov (1907–1961) to the solution chemistry. In the forties–fifties, Izmailov proposed the most detailed scheme of dissociation of electrolytes in solutions and considered the problem of the differentiating influence of non-aqueous solvents on the acids strength. He also generalized the concept of an unified acidity scale in different solvents, proposed several new methods for estimating Gibbs energy of ion solvation, and contributed a lot to the theory of physico-chemical analysis. Beginning from the thirties, Izmailov investigated the possibility to apply various indicator electrodes, especially glass electrodes, in organic solvents.

A method to determine the Gibbs energy of specific interactions in solutions. Hydrogen bonding of proton donating solutes in basic solvents

One of two fundamental types of solute–solvent intermolecular interactions are the specific interactions, such as hydrogen bonding complexation between solute and solvent. The Gibbs energy of specific interactions is an important quantity that determines rate and equilibrium constants in solutions, but it is difficult to obtain by direct measurement. We proposed equations allowing to determine the contribution of specific interactions to the Gibbs energy of solvation in nonelectrolyte solutions. Applying it for the case of proton donating solutes with one acidic hydrogen atom dissolved in basic solvents, we obtained the values of the Gibbs energies of 1:1 complexation in pure base. These values have been compared with the Gibbs energies of 1:1 complexation in tetrachloromethane. Most of the hydrogen bonds are found to have the same energy in pure base and in CCl 4, however, some weakly bound complexes seem to become even more weakened in pure base medium. Suggested method is applicable in a general situation when multiple associates of different stoichiometry and structure are formed.

The Ionic Work Function and its Role in Estimating Absolute Electrode Potentials

The experimental determination of the ionic work function is briefly described. Data for the proton, alkali metal ions, and halide ions in water, originally published by Randles (Randles, J. E. B. Trans Faraday Soc. 1956, 52, 1573) are recalculated on the basis of up-to-date thermodynamic tables. These calculations are extended to data for the same ions in four nonaqueous solvents, namely, methanol, ethanol, acetonitrile, and dimethyl sulfoxide. The ionic work function data are compared with estimates of the absolute Gibbs energy of solvation obtained by an extrathermodynamic route for the same ions. The work function data for the proton are used to estimate the absolute potential of the standard hydrogen electrode in each solvent. The results obtained here are compared with those published earlier by Trasatti (Trasatti, S. Electrochim. Acta 1987, 32, 843) and more recently by Kelly et al. (Kelly, C. P.; Cramer, C. J.; Truhlar, D. G. J. Phys. Chem. B 2006, 110, 16066. Kelly, C. P.; Cramer, C. J.; Truhlar, D. G. J. Phys. Chem. B 2007, 111, 408). A comparison of the ionic work function with the absolute Gibbs solvation energy permits an estimation of the surface potential of the solvent. The results show that the surface potential of water is small and positive whereas the surface potential of the nonaqueous solvents considered is negative. The sign of the surface potential is consistent with the known structure of each solvent.

Conformational preferences of 2-isopropylaminoethanol in aqueous solution using the CPCM continuum solvation model

All possible conformers of 2-Isopropylaminoethanol (2-IPAE) have been optimized in aqueous solution at the DFT level of theory [B3LYP/6-311++G(d,p)] using the conductor-like polarizable continuum model (CPCM). The Gibbs energies of solvation of all conformers, as well as their components, have been computed and discussed. The differences of Δ G solv between conformers are essentially determined by the electrostatic component. The conformers exhibiting an O–H···N intramolecular H-bond predominate in the gas phase equilibrium, but in aqueous solution their contribution is greatly reduced. On the contrary, conformers with a trans orientation around the OCCN dihedral and those with a gauche OCCN but without intramolecular H-bond increase significantly their population in solution. The effect of the OH group orientation on solvation has been deeply investigated by means of scans of the Gibbs energy of solvation around the HOCC dihedral for different backbone structures. Local solvation around the polar groups has also been investigated by calculating and comparing the interaction energies of the NH and OH groups with one water molecule. The optimized monohydrates, as well as the BSSE corrected interaction energies, were obtained at the B3LYP/6-311++G(d,p) level of theory.

A method for calculating the Gibbs energy of nonspecific solvation

A method for calculating the Gibbs energy of nonspecific solvation of nonelectrolytes was suggested. The new equation for the Gibbs energy of nonspecific solvation contains one solvent parameter that characterize nonspecific solvent-solute interactions and two experimental Gibbs energies of solvation in two standard solvents. The method is applicable to a wide range of solutes and solvents. It was successfully used to describe some 800 Gibbs energies of solvation for systems without specific solvent-solute interactions.

One-dimensional model for water and aqueous solutions. III. Solvation of hard rods in aqueous mixtures

A simple one-dimensional model for aqueous solution is applied to study the solvation thermodynamics of a simple solute (here, a hard-rod particle) in mixtures of waterlike particles and a cosolvent. Two kinds of cosolvents are considered, one that stabilizes and one that destabilizes the "structure of water." The results obtained for the Gibbs energy, entropy, enthalpy, and heat capacity of solvation are in qualitative agreement with experimental data on the solvation of argon and methane in mixtures of water and ethanol and of water and p-dioxane.

Calculations of the Gibbs Energy of Formation of Cavities in Water

The Gibbs energy Δcav G of formation of cavities in water was calculated by thermodynamic integration. The cavities corresponded to organic molecules of various volumes and shapes with characteristic radii of 3–7 A and spheres of radii 3–6 A. Statistical integrals were calculated by the Monte Carlo simulation of an ensemble of water molecules with periodic boundary conditions at 25°C and pressure 1 atm. Interaction between water molecules was described by the TIP4P four-point nonpolarizable model. It was found that the proportionality of Δcav G to cavity volume V obtained earlier for spheres with radii not exceeding 5 A remained valid for cavities corresponding to organic molecules of different volumes and shapes, including cavities with the characteristic radii exceeding 5 A. A possible explanation of the retention of the Δcav G ∞ V dependence at large characteristic radii was suggested in terms of the two-peak binomial model of the cavitation effect. The conclusion was drawn that the Δcav G = αV dependence could be used for calculating the nonpolar part of the Gibbs energy of solvation in implicit water models.

One-dimensional model for water and aqueous solutions. II. Solvation of inert solutes in water

The two one-dimensional models introduced in Part I are used to study the thermodynamics of solvation of inert solutes in water. It is shown that the anomalously large Gibbs energy of solvation of inert solutes in water, on one hand, and the large negative entropy of solvation, on the other hand, arise from different molecular sources. While the primitive model can give rise to a large positive solvation Gibbs energy, it fails to show large negative entropy and enthalpy of solvation. It is remarkable that the primitive cluster model can show both the large positive Gibbs energy and enthalpy of solvation.

Nikolai Izmailov (1907-1961): An appreciation

Nikolai Izmailov (1907-1961): An appreciation

Study of solute–solvent and solvent–solvent interactions in pure and mixed binary solvents

Solute–solvent and solvent–solvent interactions have been studied in fifteen pure solvents and seven binary aqueous mixtures by monitoring the solubility of a dye in the solvents. The standard Gibbs energy of solvation, as given by log s, where s is the solubility has been found to depend on various modes of solute–solvent interaction and also on the Hildebrand solubility parameter representing the cohesive energy density (solvent–solvent interaction) of solvent. In all the binary mixtures the value of log s has been found to deviate from the average of log s values in component pure solvents weighted with respect to their mole fractions. A dimensionless quantity has been defined to represent the deviation of the observed log s values from the mole fraction average. Results have been explained in terms of various modes of solvation interaction.

Theoretical Gas Phase Study of the Gauche and Trans Conformers of 1-Bromo-2-Iodoethane and Solvent Effects

This is a gas-phase study of the gauche and trans conformers of 1-bromo-2-iodoethane. The methods used are the second-order Moller-Plesset theory (MP2) and density functional theory (DFT). The functional used for the DFT method is B3LYP and the basis sets used are 6-311++G(d,p) for all atoms except that different basis sets, namely 3-21G, LANECP, CRENBL ECP, Stuttgart RLC ECP and 6-311G(d,p), have been explored for the iodine atom. The results indicate that the trans conformer is preferred. The energy difference between the gauche and trans conformers (ΔE g−t) and related thermodynamic parameters are reported. The ΔE g−t values are 12.50 kJ⋅mol−1 (B3LYP) and 10.00 kJ⋅mol−1 (MP2) with the basis sets being 6-311++G(d,p)[C,H,Br]/6-311G(d,p)[I]. The conformers of 1-bromo-2-iodoethane have also been subjected to vibrational analysis. The results from the two theoretical levels are in good agreement but they are not much affected by the basis set of the iodine atom. The study has been extended to explore solvent effects using Self-Consistent Reaction Field methods. The structural parameters of the conformers are little affected by the polarity of the solvent but ΔE g−t decreases and the solvation Gibbs energy increases with increasing polarity of the solvent.

Hydration of Cyclohexylamines: CPCM Calculation of Hydration Gibbs Energy of the Conformers

This work presents a theoretical study on the hydration of cyclohexylamine and isomers of cyclohexyldiamine. All possible conformers were fully optimized in solution using the conductor-like polarizable continuum model (CPCM) and density functional theory. Values of the Gibbs energy of solvation, its respective contributions (electrostatic, nonelectrostatic and conformational change), and the relative Gibbs energy of the conformers in aqueous solution and gas phase are reported. From these values and the Boltzmann populations of the conformers in both phases, the weighted mean values of DeltaG(solv) for the compounds are calculated. Three structural features were found to be important for the hydration of these compounds: the distance between the two NH2 groups (proximity disfavors hydration), their position relative to the ring (equatorial is preferred over axial), and the orientation of the nitrogen lone-pairs (gauche is more favorable to hydration than trans). In the particular case of vicinal cyclohexyldiamines, in addition to these two factors, the relative orientation of one group to the other should also be taken into account.

Solvation at keto-enol, acid-base and extraction equilibria and Meyer's equation

It is shown that the equation proposed by K. Meyer [K.H. Meyer, Berichte. 45(1912) 2843–2864] as empirical for constants of keto-enol equilibrium in various solvents is in fact a simple consequence of the additivity principle for Gibbs energies of molecules' solvation and hence is applicable to many types of chemical reactions. The examples of fulfillment of Meyer's equation in cases of keto-enol, acid-base and extraction equilibria are brought, and solvent parameters for each discussed example are determined. For the case of keto-enol equilibria with a possibility of intramolecular H-bond in enol form such parameters for 36 solvents are determined and compared with polarity parameters E T.

Thermodynamic properties of fullerene C60 solutions in a mixture of tetrachloromethane and toluene

The solubility of fullerene C60 in the tetrachloromethane-toluene system is measured over the entire range of compositions of the mixed solvent in the temperature range 298.15–338.15 K. An equation is proposed for describing the solubility of C60 as a function of the temperature and the composition of the mixed solvent. The equation is used for calculating the thermodynamic characteristics of solution of the fullerene. It is found that, in the investigated C60-CCl4/C6H5CH3 system, two types of solid solvates of the fullerene with the solvent are formed. The enthalpies and temperatures of incongruent melting of the crystalline solvates are determined by differential scanning calorimetry. The thermodynamic characteristics of solution and solvation of C60 in CCl4 and C6H5CH3 are obtained. It is shown that the entropy factor plays a decisive role in the temperature dependence of the Gibbs energy of solvation of the fullerene.

Extraction of Ce(III) with naphthenic acid from nitrate solutions

Extraction of Ce(III) with naphthenic acid from nitrate solutions was studied. The composition of solvation complexes, extraction constants, and Gibbs energies of extraction were found from the dependences of the distribution coefficients on pH and compositions of the aqueous and organic phases.

Temperature Dependence of the Solubility of Acetaminophen in Propylene Glycol + Ethanol Mixtures

The thermodynamic functions Gibbs energy, enthalpy and entropy of solution, mixing and solvation of acetaminophen in propylene glycol (PG) + ethanol (EtOH) cosolvent mixtures were evaluated from solubility data measured at several temperatures, using the van't Hoff and Gibbs equations. The solubility was greater at 50% m/m of PG at 20.0^C, while it was greater at 80% of PG at 40.0 ^C where m/m refers to mass percent. The solvation of this drug is appreciably greater in the mixtures than in the pure solvents. By means of an enthalpy–entropy compensation analysis, complex behavior was found for the solution. From 0 up to 20% of PG and from 60 up to 100% of PG the solution process is enthalpy driven, whereas from 20 up to 60% of PG it is entropy driven. These facts can be explained in terms of a decrease in the energy required for cavity formation in the solvent for mixtures containing 20–60% of PG.

Thermodynamic study of the solubility of acetaminophen in propylene glycol + water cosolvent mixtures

Based on van't Hoff and Gibbs equations the thermodynamic functions Gibbs energy, enthalpy, and entropy of solution, mixing and solvation of acetaminophen in propylene glycol + water (PG + W) cosolvent mixtures, were evaluated from solubility data determined at several temperatures. The solubility was greater at 100% of PG at all temperatures studied. The solvation of this drug in the mixtures increases as the PG proportion is also increased founding a maximum at 70% of PG. From 10% up to 20% of PG and from 70% up to 100% of PG, entropy driving was found, while from pure water up to 10% of PG and from 20% up to 70% of PG, enthalpy driving was found. These facts can be explained in terms of water-structure loss, and a diminishing in the energy required for cavity formation in the solvent, for mixtures from 30% up to 70% of PG.

Molecular Dynamics Simulation of Aqueous Solutions Using Interaction Energy Components: Application to the Solvation Gibbs Energy

Molecular dynamics simulations of aqueous solutions of the solutes acetamide (AcNH2), acetic acid (AcOH), and acetaldehyde (AcH) were made using Lennard–Jones 12-6-1 potentials to describe the solute–solvent interactions. The Morokuma decomposition scheme and the ESIE solute atomic charges were used to reproduce the exchange, polarization, and electrostatic components of the solute–water interaction energy. A nonlinear perturbation was incorporated into the “slow-growth” technique in order to improve the results for the solvation Gibbs energy that were found to be in agreement with the available experimental and theoretical values.