Homotactic enthalpic pairwise interactions of four deoxynucleosides (dU, dC, dG, dT) in dimethylformamide (DMF) + water mixtures at 298.15 K

The dilution enthalpies of four 2′-deoxynucleosides, namely 2′-deoxyuridine (dU), 2′-deoxycytidine (dC), 2′-deoxyguanosine (dG) and 2′-deoxythymidine (dT), in dimethylformamide (DMF) + water mixtures have been determined at 298.15 K respectively, using an isothermal titration calorimeter (ITC200 MicroCal). On the basis of the McMillan–Mayer theory, the homotactic enthalpic pairwise interaction coefficients (hXX) of the four 2′-deoxynucleosides in DMF + water mixtures of various mass fractions (wDMF = 0–0.30) have been calculated. It was found that the values of hXX of the four 2′-deoxynucleosides are all large negative and increase gradually across the whole studied composition range of the mixed solvent, though the variation degrees of them are somewhat different. The results are discussed from the point of view of solute–solute and solute–solvent interactions in solutions.