IR STUDY OF THE SYMMETRICAL V(S)(PO32-) MODE OF 5'-CMP IN H2O SOLUTION - RELAXATION OF THE PHOSPHATE GROUP

The IR upsilon(s)(PO32-) band shape of cytidine 5'-monophosphate (5'-C MP) in H2O solution at different concentrations, 0.009-0.3 mol dm(-3), has been studied and the results have been interpreted in terms of th e dynamics of the PO32- group. The relaxation of this mode in aqueous solution seems to be predominantly vibrational. A reasonably good fit was obtained applying theories for vibrational dephasing to the decay of the IR time correlation functions up to 3 ps. An intermediate modul ation speed, ca. 1, for the vibrational frequency is obtained. The ful l-width at half-height of the band in H2O is ca. 3 cm(-1) wider than i n (H2O)-H-2. In the same way, the modulation speed is slightly higher and the decay of the correlation function is faster in H2O than in (H2 O)-H-2. These effects could be associated with the smaller mass of the solvent molecules. Similar trends have been observed when increasing the concentration of the mononucleotide.