An approach to the interpretation of the vibrational spectra of 20-deoxyinosine by means of DFT calculations

The FT-IR and FT-Raman spectra of 20-deoxyinosine (20-dI) are reported. This modified nucleoside of the four natural DNA bases binds with weak hydrogen bonds to any of them, feature used in PCR technique or in hybridisation essays [Howard Huge Medical Institute]. The FT-IR and FT-Raman spectra of its synthesized trideuterated derivative (20-dI-d3, deuteration at N1, and hydroxyl groups O30 and O50) have also been recorded. The observed isotopic shifts, the spectra of related molecules and theoretical calculations have been used to interpret the vibrational spectra of 20-dI. The accurate knowledge of the vibrational spectra is an important prerequisite for understanding its structure, conformation and possible behaviour in physiological conditions. Therefore, different optimised structures have been obtained, including variable number of water molecules (none, 1 or 2) surrounding the nucleoside. They have been situated close to the carbonyl group. The wavenumbers of the normal modes of vibration for each one have been calculated using Density Functional Theory methods, with the Becke’s Three Parameter Hybrid Functional and the LYP Correlation Functional (B3LYP) model, using 6-31G** basis set. An assignment of FT-IR and Raman spectra is proposed. The influence of the water molecules in the theoretical results is shown. q 2003 Elsevier B.V. All rights reserved.