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

Standard free energies (DELTAG-degrees t) and entropies (DELTAS-degrees 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 urea (UH) and glycerol (GL) have been evaluated from solubility measurements at different temperatures. The observed DELTAG-degrees t and TDELTAS-degrees t vs composition profiles are complicated because of the interaction effects. Elimination of the cavity effect obtained by using scaled particle theory and effects due to dipole-dipole, dipole-induced dipole, and dispersion interactions yielded the corresponding effects as guided by the hydrophilic and hydrophobic sites of the solutes with the components of the solvent mixtures as compared to that in water. In the case of transfer entropies however, the corresponding interaction effects are further complicated by the effect of the relative structuredness of solvents. However, the overall DELTAG-degrees t behavior, reflecting increased stabilization of DNA-RNA bases, leads us to conclude that both UH and GL induce denaturation of double-stranded nucleic acid helices.