Vibrational mode analysis of 2-aminoadenine and its deuterated species from Raman and ultraviolet resonance Raman data

Abstract

Resonance Raman spectroscopy data of 2-aminoadenine and its deuterated species (C8-deuterated, N-deuterated and C8-, N-deuterated derivatives) in aqueous solution have been collected in the spectral region between 400 and 1800 cm−1, by using ultraviolet excitation wavelengths (λexc = 222, 257 and 281 nm) located in the three main UV absorption bands corresponding to the strongly allowed electronic transitions of the molecule of interest. Moreover, a Raman spectrum has been recorded under off-resonance conditions with a visible excitation (λexc= 488 nm). In order to assign the 2-aminoadenine in-plane vibrational bands displayed in the RRS spectra, a normal coordinate analysis has been performed by means of an empirical internal valence force field. These calculations are based on our recent normal mode analysis of adenine and guanine nucleic bases and their deuterated species, which was based on the joint use of resonance Raman spectroscopy and neutron inelastic scattering data. In the 2-aminoadenine force field proposed here, the diagonal force constants have been directly transferred from those recently obtained for adenine (and from guanine as concerns the 2-amino group), the interaction force constants (off-diagonal) then being adjusted on the basis of the actual experimental data from 2-aminoadenine and its deuterated species. The current force field is also able to assign infrared and Raman data obtained by other authors from polycrystalline samples of the pure species.