Determining the Gibbs energies of hydrogen-bonding interactions of proton-accepting solutes in aqueous solutions from thermodynamic data at 298 K with regard to the hydrophobic effect

Reaction rate and equilibrium constants in aqueous solutions are affected by the strength of hydrogen bonds formed between dissolved species and water molecules. Thermodynamic functions of hydrogen bonding with bulk water cannot be measured directly using spectroscopic methods, but the contribution of hydrogen-bonding processes to the thermodynamic functions of hydration may be determined using some model of aqueous solutions. We determined the Gibbs energies of hydrogen-bonding interactions in water for various simple proton-accepting organic molecules on the basis of two different models that allow the contributions of nonspecific van der Waals interactions and the hydrophobic effect to be quantified. It is shown that hydrogen bonding with bulk water may be stronger than with a single water molecule. The influence of solute structure on the Gibbs energy of hydrogen-bonding interactions is discussed. © 2011 American Chemical Society

Thermodynamic description of the solvophobic effect in ionic liquids

© 2016 Elsevier B.V.The solvophobic effect is a driving force for self-assembly processes that acts in protic molecular organic solvents as well as in both protic and aprotic ionic liquids. It is known to reduce the solubility of apolar compounds and influence the magnitudes of thermodynamic functions of solvation in molecular solvents. In ionic liquids, thermodynamic aspects of the solvophobic effects have not yet been carefully considered. By comparing the relations between the Gibbs free energy and enthalpy of solvation of different compounds, we show that the solvophobic effect in aprotic ionic liquids can be even stronger than in organic solvents forming a network of intermolecular hydrogen bonds, such as formamide and ethylene glycol. The strength of the solvophobic effect expressed in terms of energy contributions is correlated with the average number of ions per unit volume, which is inversely proportional to the molar volume of the liquid. It is shown that the solvophobic effects become stronger when we change the cation or anion of the ionic liquid with another of a smaller size, and can be extremely weak when the cation contains long alkyl chains, but they are a general phenomenon for all ionic liquids

Gibbs free energy of hydrogen bonding of aliphatic alcohols with liquid water at 298K

Thermodynamics of hydrogen bonding between water and molecules of aliphatic alcohols in dilute aqueous solutions is studied. The Gibbs free energies of hydrogen bonding of normal aliphatic alcohols from methanol to octanol with liquid water are determined from experimental data. The molar fractions of free unbonded molecules of alcohols and monomeric species of water are reported. Strong cooperative effects are observed when an alcohol molecule binds to an associate of water, leading to huge negative values of the Gibbs energies and an increased aqueous solubility. Formation of the second and third hydrogen bonds of an alcohol molecule with water is much less favorable, what can be described as an anti-cooperative effect. © 2011 Elsevier B.V

Solvophobic effects: Qualitative determination and quantitative description

Solvophobic effects strongly influence the thermodynamic properties of solutions and are one of the driving forces of self-assembly processes of supramolecular structures. However, the generally accepted definition and a quantitative measure of these effects have so far been absent. Based on the analysis of a large set of experimental data on the thermodynamic functions of solvation in various systems, we propose a qualitative criterion allowing us to judge about whether the solvophobic effects are manifested in the solution or not, and also a method to determine their contributions to the thermodynamic functions of solvation. A feature of the solvophobic effect is a violation of the linear relationship between the Gibbs free energy and the enthalpy of solvation, which is fulfilled for the solutions of different compounds in many non-associated solvents. It is shown that in self-associated solvents the solvophobic effect is observed for any dissolved compounds, including well soluble ones, resulting in an increase in the Gibbs energy of solvation. Previously proposed solvophobicity parameters are considered and compared with our results. © 2013 I. A. Sedov, B. N. Solomonov

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. © 2008 MAIK Nauka

The hydrophobic effect Gibbs energy

A new method of experimental determination of thermodynamic functions of the hydrophobic effect is proposed. It is based on regarding the thermodynamic functions of hydration as the sum of thermodynamic functions of nonspecific hydration, specific hydration and the hydrophobic effect. In addition to the previously developed method to determine the hydrophobic effect enthalpies, we present a new method to calculate the hydrophobic effect Gibbs energies. The hydrophobic effect Gibbs energies of noble and simple substance gases, alkanes, arenes, and their halogenated derivatives are determined. For all the compounds studied, the hydrophobic effect Gibbs energy is found to be positive. From the values of the Gibbs energies and the enthalpies of the hydrophobic effect, the entropies of the hydrophobic effect are calculated. They are found to be negative for all the compounds. An excellent linear correlation between the hydrophobic effect Gibbs energy and McGowan characteristic molecular volume of the solute is found. The method was applied to a large molecule of fullerene C60. The hydrophobic effect Gibbs energy of fullerene does not deviate from the linear dependence observed for small solutes. © 2007 Elsevier B.V. All rights reserved

Distinctive thermodynamic properties of solute-solvent hydrogen bonds in self-associated solvents

Solute-solvent hydrogen bonding affects reactivity and other properties of dissolved species. In self-associated media, because of cooperativity and solvent reorganization, the thermodynamic functions of solute bonding with bulk solvent can be different from those of bimolecular solute-solvent complexes. Using available experimental data on the Gibbs free energies of solvation in aliphatic alcohols and water, we have determined the energies of solute-solvent hydrogen bonding for various proton accepting solutes. We show that the increase in the strength of hydrogen bonds because of the cooperative effect is strong for bonding with bulk water and significantly less so with bulk aliphatic alcohols. The hydrogen bonding Gibbs free energies for the same solute with bulk water and alcohol are correlated, but they correlate poorly with the energies of formation of the corresponding bimolecular solute-solvent complexes. Thus, the traditional hydrogen bond basicity scales, based on data for bimolecular complexes, do not correctly describe the thermodynamics of hydrogen bonding with self-associated solvents. Our results may help to define a separate solute basicity scale for associated media. Copyright © 2012 John Wiley & Sons, Ltd

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 CCl4, 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. © 2008 Elsevier B.V. All rights reserved

A method for calculating the Gibbs energies of hydrophobic effects and specific interactions of nonelectrolytes in aqueous solutions

The thermodynamic characteristics of hydrophobic hydration, the Gibbs energies of hydrophobic effect, were calculated. The method for calculations was based on the division of the Gibbs energy of hydration into contributions of nonspecific interactions, specific interactions between solutes and solvents (if they exist), and hydrophobic effect. In the absence of specific interactions between solutes and water, the Gibbs energy of hydrophobic effect depended linearly on the characteristic molecular volume of the solute for substances with different structures and properties. The universality of this dependence allows the suggestion to be made that it remains valid also in the presence of specific interactions. This allows the Gibbs energy of specific interactions in water to be determined for a wide range of compounds, in particular, for aliphatic alcohols. © 2008 Pleiades Publishing, Ltd

Relation between the characteristic molecular volume and hydrophobicity of nonpolar molecules

Experimental values of the Gibbs free energies of hydration for a set of nonpolar or very slightly polar compounds are analyzed in order to investigate how does the hydrophobic effect depend on molecular structure and shape. The contribution due to the hydrophobic effect is evaluated using a method we suggested previously. A number of values of the Gibbs free energies of solvation in dimethyl sulfoxide and in hexadecane, which are required for calculation, were determined by gas chromatographic headspace analysis. It is found that the Gibbs hydrophobic effect energy is linearly dependent on characteristic molecular volume for a large variety of solutes with branched and unbranched carbon chains, different functional groups and atomic composition. Molecular structure and shape do not significantly affect the hydrophobicity of chemical species, and molecular volume is a main factor determining it. © 2010 Elsevier Ltd. All right reserved