The Solubility of Four DNA and RNA Bases at Five Different Temperatures in Aqueous Mixtures of Dipolar Aprotic Acetonitrile and the Insights into the Solvation Phenomena

Standard transfer Gibbs free energies, \(\Delta G_\text{t}^{0} (i)\) and entropies, \(\Delta S_\text{t}^{0} (i)\) of four DNA and RNA bases, i.e., adenine (A), thymine (T), cytosine (C) and uracil (U) at 298.15 K from water to aqueous mixtures of acetonitrile (ACN) have been assessed using least square method from solubility quantifications at five equi-separated temperatures from 288.15 to 308.15 K under pressure 0.1 MPa. The observed variation of \(\Delta G_\text{t}^{0} (i)\) and \(T\Delta S_\text{t}^{0} (i)\) with composition of such protic and dipolar aprotic solvent mixtures are problematical to understand due to involvement of several interactions. Deduction of the cavity effect computed with Scaled Particle Theory and effects caused by dipole–dipole, dipole–induced dipole interactions agreed to the corresponding effects as controlled by chemical interactions between solutes and solvent molecules. Elimination of the associated dispersion interactions from chemical interactions generated the corresponding effects as directed by the hydrophilic and hydrophobic locations of the solutes with the components of the solvent mixtures compared to that in water. In the event of transfer entropies however, the corresponding interaction effects are also trickier than transfer Gibbs free energies due to the effect of the parallel structuredness of solvents. However, the complete behaviour of transfer Gibbs free energy, reflecting increased solvation of DNA-RNA bases, points us to conclude that acetonitrile as dipolar aprotic solvent accelerates denaturation of double-stranded nucleic acid helix.