3.2 Theoretical works related to thermal denaturation of DNA in solvent(s) presence O.Sinanoglu and S.Abdulnur show that the DNA double helix is stable in water but becomes denatured in some solvents. To reveal the role of water in keeping the helix together, the solvent contributions to the free energy difference between single strands and the helix are calculated for water, methyl alcohol, glycol, formamide, glycerol, ethanol, n-propanol, and n-butanol. The solvent's property crucial to denaturation is found to be mainly the enthalpy part of surface tension. Discussing the entropy contribution to the Gibbs free energy, the authors conclude that base (DNA) dipole orientation affects the solvent dipoles. They found also that this effect depends on the dielectric constant change with temperature. D. Macedo, I. Guedes, and E. Albuquerque 51 study solvent interaction effects on a DNA segment's nonlinear dynamical structure by using a time-independent perturbation approach.