Theoretical calculations and vibrational study of hypoxanthine in aqueous solution

The vibrational analysis of the two predominant tautomers of hypoxanthine (HX) in solution, the keto-N1–H/N7–H (HX/N7H) and N1–H/N9–H (HX/N9H) forms, have been carried out by means of DFT calculations, applying the B3LYP hybrid density functional and four basis sets namely 6-31G(d,p), 6-31++G(d,p), 6-11G(d,p) and 6-311++G(d,p). The influence of the solvent was considered using the Tomasiʹs Polarized Continuum Model (PCM). Comparison with experimental data provides support for the quality of results derived from theoretical computations. The assignment of the vibrational spectra of the hypoxanthine in aqueous solution has been performed in the light of information makes available from the previous experimental and theoretical studies, the observed isotopic shifts in the spectra of deuterated derivatives and from the theoretical normal modes computed from SCRF/DFT calculations. The interpretation of the vibrational spectra gives experimental evidences for the coexistence of the two tautomers, HX/N7H HX/N9H, in aqueous solution