Gibbs energy of cooperative hydrogen‐bonding interactions in aqueous solutions of amines and pyridines

Abstract

A method to determine the Gibbs energy of specific (hydrogen bonding) interactions of a solute with water is proposed. The energies of hydrogen bonding in bulk water are very difficult to determine by any method. The Gibbs energy of hydration of substances forming hydrogen bonds with water is considered as the sum of contributions due to non-specific interactions, the hydrophobic effect, and specific interactions. The first two terms were found to be rather accurately described by empirical equations. The Gibbs energies of hydrogen bonding of aliphatic amines and pyridines in bulk water are determined, and the results are compared with the energies of their complexes with one molecule of water. The cooperativity of hydrogen bonding is proved in aqueous solutions of amines and pyridines. To use our equations, experimental values of the Gibbs energies of solvation in 'standard' solvents need to be known. The Gibbs energies of solvation of ten amines and pyridines in dimethyl sulfoxide are determined experimentally using chromatographic head space analysis. The tendencies observed for the series of amines and pyridines are in agreement with other studies.

Solvophobic effects and relationships between the Gibbs energy and enthalpy for the solvation process

“…Here, Δ int(sp) G A / S is the contribution of specific interactions, that is, hydrogen bonding processes. In our previous work, we have applied this equation for the aqueous solutions of aliphatic amines and pyridines. The results of this current work allow to extend this approach to various associated solvents.…”

Relation between the characteristic molecular volume and hydrophobicity of nonpolar molecules

“…Now, if we consider, for instance, organic substances containing nitrogen or oxygen atoms, it is reasonable to suppose that the Gibbs free energy of hydration of non-hydrogen bonded form of these substances will be described by the same equations (2) and (3). In such cases, by subtracting the calculated value for non-bonded form from the experimental Gibbs free energy of hydration, one can find the Gibbs free energy of hydrogen bonding with water [24], which is not possible to determine using direct methods.…”

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

“…The enthalpies of specific interactions of proton acceptors with alcohols are less negative than the enthalpies of formation of corresponding 1 : 1 complexes in inert solvent . However, the Gibbs free energies of specific interactions of amines and pyridines with water were found to be more negative than those of 1 : 1 complexation in tetrachloromethane because of cooperative effects.…”

“…In our works we have shown that the Gibbs free energy of solvation in water and aliphatic alcohols can be represented as a sum of three contributions: because of nonspecific (van der Waals) solvation effects Δ solv(nonsp) G A/S , because of the solvophobic (or hydrophobic in the case of water) effect Δ s.e. G A , and the specific interactions term Δ int(sp) G A/S because of hydrogen bonding between solute A and solvent S (if a solute cannot form hydrogen bonds with a solvent, this term is zero) …”

“…G A using a number of experimental thermodynamic data and molecular parameters for Eqns –. In our previous works we have calculated the values of Δ int(sp) G A/ S for a number of proton acceptors in water. Here we extend the number of considered solutes and report their values of Δ int(sp) G A/S in several monohydric alcohols along with novel and previously published data for their aqueous solutions.…”