Solvent Effect on the Hydrogen Bonds between Guanine and Cytosine and between Hypoxanthine and Cytosine

Abstract

Abstract The solvent effect on the hydrogen bonds between guanine and cytosine and between hypoxanthine and cytosine was studied by means of solution calorimetry and ab initio MO calculations. The experimental enthalpy changes for guanine–cytosine and hypoxanthine–cytosine systems in aqueous solution were estimated to be about −10 and −14 kJ mol−1, respectively. In order to explain these experimental results, the electronic structures of hydrated bases and hydrated base pairs were calculated, assuming two types of hydration schemes. In the first type, it was expected that the complementary base pairs were destabilized in aqueous solution. In the second type, the stabilization energies in aqueous solution were calculated to be −11.9 kJ mol−1 for the hydrated guanine–cytosine system and −18.5 kJ mol−1 for hypoxanthine–cytosine one, respectively, which agreed with the experimental results. This suggests that water molecules bound to base pairs contribute to the stabilization/destabilization of hydrogen bonds between bases. The present calculation showed the possibility of C–Hδ+···O hydrogen-bond formation between the complementary base pair and H2O.