Evaluation and Correlation of Solubility and Solvation Thermodynamics of Some DNA and RNA Bases in Aqueous Mixtures of Dipolar Aprotic N,N-Dimethyl Formamide

In this article we report the solubilities of some DNA and RNA bases, viz., uracil (U), thymine (T), cytosine (C) and adenine (A) at five equidistant temperatures from 288.15 to 308.15 K under the experimental pressure p = 0.1 MPa, in aqueous mixtures of dipolar aprotic N,N-dimethyl formamide (DMF) and, hence, standard Gibbs energies and entropies of transfer (∆\( S_{\text{t}}^{0} \)) from water to aqueous mixtures of DMF have been evaluated at 298.15 K. The chemical effects of the transfer Gibbs energies \( \Delta G_{\text{t,chem}}^{ 0} (i) \) and entropies of transfer (\( \Delta S_{\text{t,chem}}^{ 0} (i) \)) have been obtained after elimination of the cavity effect, dipole–dipole interaction and dipole–induced-dipole interactions. The cavity effect has been estimated by the scaled particle theory; on the other hand dipole–dipole interaction and dipole–induced-dipole interactions have been computed from the Keesom orientation expressions. The observed \( \Delta G_{\text{t}}^{ 0} (i) \) and \( T\Delta S_{\text{t}}^{ 0} (i) \) versus composition profiles are non-uniform because of the various interaction effects. Elimination of the effect due to dispersion interaction from the total chemical interaction yields the corresponding effects of the hydrophilic and hydrophobic sites of the solutes with the components of the solvent mixtures as compared to those present in water. In the case of transfer entropies, the relative structuredness of solvents is a guiding factor. However, the overall \( \Delta G_{\text{t}}^{ 0} \) behavior reflects increased stabilization of the DNA-RNA bases, which leads us to conclude that DMF induces denaturation of the double-stranded nucleic acid helix.