Relation between peptide backbone solvation and the energetics of peptide hydrogen bonds.

The H-bond inventory approach is used commonly to interpret data involving changes in the number or types of protein hydrogen bonds. I point out here that this approach gives an incorrect answer either for the standard free energy or enthalpy of the reaction between simple amides and water. On the other hand, an electrostatic solvation approach fits almost within error the polar solvation free energies of small molecules, including amides. The electrostatic solvation approach is used here to discuss the relation between peptide backbone solvation and the enthalpy change for forming an alanine helix.