1.10.11: Gibbs Energies- Solutions- Solute-Solute Interactions- Pairwise

Analysis of the thermodynamic properties of aqueous solutions was taken a step further by Savage and Wood who envisage two solute molecules A and B in aqueous solution [1]. The total pairwise interaction between these molecules is described in terms of pairwise group-group interaction parameters. Then, for example, the pairwise enthalpic solute-solute interaction parameter \(\mathrm{H}_{\mathrm{AB}\) is written as the sum of products, \(\mathrm{n}_{\mathrm{i}}^{\mathrm{A}} \, \mathrm{n}_{\mathrm{j}}^{\mathrm{B}} \, \mathrm{h}_{\mathrm{ij}}\) where \(\mathrm{n}_{\mathrm{i}}^{\mathrm{A}}\) is the number of A-groups in solute molecule \(\mathrm{i}\) and \(\mathrm{n}_{\mathrm{j}}^{\mathrm{B}}\) is the number of B-groups in solute molecule \(\mathrm{j}\) where \(\mathrm{h}_{\mathrm{ij}}\) is a pairwise enthalpic group interaction parameter. A similar analysis is carried out for interaction Gibbs energies leading to pairwise Gibbs energy parameters \(\mathrm{g}_{\mathrm{ij}}\). So, for example, \(\mathrm{g}(\mathrm{OH}-\mathrm{OH})\) is negative characteristic of a hydrophilic-hydrophilic interaction. Whereas \(\mathrm{g}\left(\mathrm{OH}-\mathrm{CH}_{2}\right)\) is positive indicating 'repulsion' within hydrophobic-hydrophilic pairs. Interestingly \(\mathrm{g}\left(\mathrm{CH}_{2}-\mathrm{CH}_{2}\right)\) is negative" which is indicative of a hydrophobic-hydrophobic attraction (cf. hydrophobic bonding); the corresponding enthalpic pairwise parameter is positive. Thus it is tempting to speculate that hydrophobic attraction is entropy driven [2]; for further comments see references [3-13].

The general approach is readily extended to a consideration of pairwise interactions between added solutes and both initial and transitions states for given chemical reactions in aqueous solution [14-18].

Footnotes

[1] J.J. Savage and R. H. Wood, J. Solution Chem.,1976,5,733.

[2] J.J. Spitzer, S. K. Suri and R. H. Wood, J. Solution Chem.,1985,14,5; and references therein.

[3] S. K. Suri and R. H. Wood, J. Solution Chem.,1986,15,705.

[4] S. K. Suri, J.J.Spitzer, R. H. Wood, E.G.Abel and P.T. Thompson, J. Solution Chem.,1986,14,781.

[5] A. L. Harris, P. T. Thompson and R. H. Wood, J. Solution Chem.,1980, 9,305.

[6] For the role of solute stereochemistry see F. Franks and M. D. Pedley, J. Chem. Soc. Faraday Trans. 1, 1983,79,2249.

[7] Amides in N,N-dimethvl formamide: M. Bloemendal and G. Somsen, J. Solution Chem.,1983,12,83.

[8] Solutions in DMF with a modification of the role of the solvent; M. Bloemendal and G. Somsen, J. Solution Chem.,1987,16,367

[9] Interaction between amides and urea in aqueous solution; P. J. Cheek and T. H. Lilley, J. Chem. Soc. Faraday Trans.1, 1988,84,1927.

[10]

1. Diols(aq); S. Andini, G. Castronuovo, V. Ella and L. Fasano, J. Chem. Soc. Faraday Trans.. 1990. 86, 3567.
2. Amino acids and peptides; T H. Lilley and R. P. Scott, J. Chem. Soc. Faraday Trans. 1, 1976,72,359.
3. Monosaccharides(aq); G. Barone, G. Castronuovo, D. Doucas, V.Elia and G. A. Mattia, J.Phys.Chem.,1983,87,1931.

[11] Urea and polyols(aq); G. Barone, V. Elia and E. Rizzo, J. Solution Chem.,1982,11,687.

[12] Volumes and heat capacities of aromatic solutes(aq); S. Cabani, P. Gianni,V. Mollica and L. Lepori, J. Solution Chem., 1981,10,563.

[13] Small peptides(aq); enthalpies; O. V. Kulikov, A. Zielenkiewicz, W. Zielenkiewicz. V. G. Badelin and A.Krestov , J. Solution Chem., 1993,22,59.

[14] M. J. Blandamer, J. Burgess, I . M. Horn, J. B. F. N. Engberts and P. Warrick Jr., Colloids and Surfaces, 1990,48,139.

[15] M. J. Blandamer, J. Burgess, J. B. F. N. Engberts and W. Blokzijl, Annu. Rep. Prog. Chem., Sect C, Phys. Chem.,1990,87,45.

[16] W. Blokzijl, J. B. F. N. Engberts, J. Jager and M. J. Blandamer, J. Phys. Chem.,1987, 91,6022.

[17] M. J. Blandamer, J. Burgess and J. B. F. N. Engberts, Chem. Soc Rev.,1985,14,237.

[18] M. J. Blandamer and J. Burgess, Pure Appl. Chem.,1982, 54,2285.