TRANSFER ENERGETICS OF SOME DNA AND RNA BASES IN AQUEOUS MIXTURES OF UREA AND GLYCEROL

Standard free energies (DELTAG-degrees t) and entropies (DELTAS-degree s t) of transfer of some DNA and RNA bases, viz., uracil (U), thymine (T), cytosine (C), and adenine (A) from water to aqueous mixtures of u rea (UH) and glycerol (GL) have been evaluated from solubility measure ments at different temperatures. The observed DELTAG-degrees t and TDE LTAS-degrees t vs composition profiles are complicated because of the interaction effects. Elimination of the cavity effect obtained by usin g scaled particle theory and effects due to dipole-dipole, dipole-indu ced dipole, and dispersion interactions yielded the corresponding effe cts as guided by the hydrophilic and hydrophobic sites of the solutes with the components of the solvent mixtures as compared to that in wat er. In the case of transfer entropies however, the corresponding inter action effects are further complicated by the effect of the relative s tructuredness of solvents. However, the overall DELTAG-degrees t behav ior, reflecting increased stabilization of DNA-RNA bases, leads us to conclude that both UH and GL induce denaturation of double-stranded nu cleic acid helices.