Splitting of infrared bands of mononucleotides in aqueous solution

We present in this paper a study based on the analysis of infrared spectra in aqueous solution of natural mononucleotides 5 ' -GMP, 5 ' -CMP, 5 ' -dAMP, 5 ' -TMP, and some analogues showing antitumoral/antiviral activity, 5 ' -ara-CMP and 5 ' -ara-AMP. Some of the IR bands in the spectra of these compounds in (H2O)-H-2 solution and pH 7-8 split clearly into, at least, two components, at medium-high concentration. These signals are those assigned to the phosphate group and several bands due to normal modes with high contribution of base stretch motions. The observed splitting increases with concentration, it is fairly symmetric and it is accompanied by an important increase of band width. The high contributions from groups or molecular fragments with significant dipole moments to the normal modes giving rise to these bands allow us to ascribe this effect to dipole coupling processes and/or interactions with the solvent. (C) 2001 Elsevier Science B.V. All rights reserved.