Density functional theory studies on conformational stability and vibrational spectra of 2′-deoxyinosine

Density functional theory (DFT) with B3LYP/6-311G (d) and B3LYP/6-31G (d) levels was applied to study the conformational stability and vibrational infrared (IR) and Raman spectra of 2′-deoxyinosine (2-dI) and its deuterated derivative. In this work, 14 conformers were found on the torsional potential energy map of the dihedral angles C8-N9-C1′-O4′ (χ) and O5′-C5′-C4′-O4′ (γ). It was shown that the dI_12 (χ = syn/γ = g−/2′-endo) conformer is the most stable form. For this lowest energy conformer, the harmonic force fields calculated by B3LYP/6-311G (d) and B3LYP/6-31G(d) methods were scaled with one scale factor of 0.9623 and a set of different scale factors determined from the other similar molecules, respectively. The predicted vibrational frequencies and isotopic shifts of IR bands of 2-dI were compared with the available observed IR spectra with a mean deviation of about 14.4 cm−1. The results made it possible to give reliable assignments of the IR and Raman spectra of the title molecule. This study shows that the scaled density functional force field approach enables, through the transferability of scale factors, good interpretation of vibrational spectra of large molecules.