IR study of the symmetric νs(PO32–) mode of 5′-CMP in H2O solution. Relaxation of the phosphate group

Abstract

The IR v_s(PO₃^2–) band shape of cytidine 5′-monophosphate (5′-CMP) 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 the dynamics of the PO₃^2– 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 modulation speed, ca. 1, for the vibrational frequency is obtained. The full-width at half-height of the band in H₂O is ca. 3 cm^–1 wider than in ²H₂O. In the same way, the modulation speed is slightly higher and the decay of the correlation function is faster in H₂O than in ²H₂O. 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.