Thermodynamics of dipeptides in water. Calorimetric determination of enthalpy change values related to proton transfer processes of a series of dipeptides in water

Calorimetric measurements on a series of dipeptides having methionine as fi rst common term enabled us to determine the thermodynamic quantities relate d to the proton transfer processes at the free alpha -amino and alpha -carb oxyl groups of the dipeptides using methionyl-methionine (MetMet) as refere nce compound. The drawing forces were found to be the solvation processes of zwitterions, ions and undissociated molecules of dipeptides, hydrophobic effects of sid e-chains playing an important role. The results were interpreted in terms o f the reciprocal influence of the dipeptides components. Relative and absolute scales related to the enthalpic contribution to the a cidity and basicity of the dipeptides studied are supplied.