The low frequency vibrations of the nucleosides: Uridine,cytidine and inosine. Determination of vibrations associated with the ribose ring

The room temperature far i.r. spectra of the nucleoside cytidine and its deuterated analog cytidine- d₃ have been measured from 200 to 100 cm⁻¹. Several spectral features involving hydroxyl deformations have been identified. Between 200 and 400 cm⁻¹ the spectra of the nucleosides cytidine, uridine and inosine have been compared to those of the respective bases cytosine, uracil and hypoxanthine thereby allowing the identification of several bands associated with deformations of the furanose ribose unit. These frequencies are common among the nucleosides investigated and have been compared to calculated frequencies for “ribose” modes in polynucleotides. Upon cooling to 7 K the cytidine and cytidine-d₃ spectra below 200 cm⁻¹ exhibit a remarkable narrowing resembling a “gas-like” spectra, revealing more spectral features than expected from a group theoretical analysis of the unit cell. The low temperature spectra also exhibit an apparent periodicity. Two equally possible explanations are given; one accounts for the observed periodicity via a vibrational exciton-like theory, while the alternative explanation treats the periodicity as accidental.