The connection of the orientation and induction effects to the polar cohesion parameter has been discussed in the articles of , 88 , 89 . The presence of the dispersion forces term in the polar cohesion parameter has historical roots. The polar-nonpolar solvent interaction had been studied mainly by Prauznitz and co-workers 13,75-77 during the development of an expression for the two-component cohesion parameter (before Hansen developed his three- Overall, we can conclude that experimental data for DNA chemical denaturation has confirmed the theory developed in the present article and is based on the combination of Gibbs and Hildebrand's expanded thermodynamic approaches. This theory allows the calculation of both the enthalpy and the entropy at 50% DNA denaturation. The expression for the entropy of this process at DNA melting temperature can be obtained by the combination of equations 17 and 26 :