The change in Gibbs free energy for hydrophobic association. Derivation and evaluation by means of inverse temperature transitions
The change in Gibbs free energy resulting from changes in the temperature ( Tt) and heat (∆ Ht) of an inverse temperature transition (ITT) of hydrophobic association is derived and utilized to develop a hydrophobicity scale for amino acid residues within an elastic model protein, (GVGVP) n. On raising the temperature, hydrophobic residues go from water to hydrophobic association. Using Tt and ∆ Ht of the ITT, the change in Gibbs free energy for hydrophobic association, ∆GHA0, in kcal/mol-(GXGVP) where X is the guest amino acid residue, was calculated for the naturally occurring amino acid residues in PBS. ∆GHA0 varies by more than 10 kcal/mol-(GXGVP) from the most hydrophobic tryptophan residue to the most hydrophilic glutamate residue.