Thermodynamic study of interaction effects in aqueous solutions of purine and pyrimidine nucleobases ionic liquids at 298.15 K

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We report herewith experimental density and osmotic pressure measurements for aqueous 1-ethyl-3-methylimidazolium ([Emim]), and 1-n-butyl-3-metylimidazolium ([Bmim]) based nucleobases ionic liquids [NBILs] at 298.15 K to gain thermodynamic understanding of NBIL – water mixtures. Molar volumes Vm, standard entropies S0 and lattice potential energies UPOT are reported at 298.15 K using density data of pure state NBILs. Large values of S0 and small UPOT explains the existence of NBILs in liquid state at ambient conditions. Experimental density data of aqueous NBIL solutions were used to obtain apparent, partial and electrostricted volumes from which electrostricted hydration numbers were obtained. It was found that observed hydration numbers are solely due to anion hydration as cation shows negligibly small hydration. Negative magnitudes of excess molar volumes confirm the hydrophobic nature of NBILs. Using experimental osmotic coefficients, water activity (aW), mean molal activity coefficient γ± of NBILs, excess Gibbs free energy change ΔGE due to mixing etc. were obtained and found that these aqueous systems show negative deviation from limiting law. At low concentration hydrophobic hydration is dominant whereas hydrophobic ion-association occurs at higher concentration revealed from minimum in osmotic coefficients. Application of McMillan–Mayer theory of solutions yielded osmotic second virial coefficients which are found to be negative indicating attractive type of ion-ion – ion-pair interactions.