Applying vibrational spectroscopy to the study of nucleobases – adenine as a case-study

A full conformational study of solid-state anhydrous adenine is reported, using vibrational spectroscopy techniques coupled to DFT calculations, for the isolated molecule and the solid. In both cases, the N9H-amino tautomer was found to be the predominant species, followed by the N7H-amino form. An excellent agreement was achieved between experiment and theory, both for wavenumbers and intensities (without the need for scaling). A complete spectral assignment was performed, since all vibrational spectroscopic techniques were available to this study – FTIR, Raman and INS – allowing us to detect and interpret even the lowest frequency vibrational bands, not previously accessed. The quantum mechanical calculations presently carried out represent the highest theoretical level applied so far to the study of nucleobases.