Assignment of adenine ring in‐plane vibrations in adenosine on the basis of ¹⁵N and ¹³C isotopic frequency shifts and TUV resonance Raman enhancement

Abstract

Infrared, Raman and UV resonance Raman spectra of adenosine and its 1,3‐15N2, 2–13C, and 8–13C isotopic analogues were measured in neutral aqueous solution (Raman and UV Raman) and in the crystalline state (infrared and Raman). The observed isotopic wavenumber shifts are useful in distinguishing adenine ring vibrations from ribose vibrations. In‐plane modes of the adenine ring are selectively enhanced in UV resonance Raman spectra, which facilitates the assignment of the in‐plane vibrations. In addition to the in‐plane modes, a ribose vibration coupled with adenine in‐plane vibrations was identified in the UV resonance Raman spectra. The fundamental wavenumbers for 22 in‐plane normal modes of the 9‐substituted adenine ring of adenosine in the 1700–250 cm−1 region are proposed. Although the fundamental wavenumbers of adenosine correspond well with those of adenine above 1350 cm−l and below 800 cm−1 the vibrations in the 1350–800 cm−1, region are appreciably affected by the presence of the N‐9—C‐1′ glycosidic bond and the couplings between ribose and adenine ring vibrational motions. The adenosine fundamental wavenumbers and their isotopic shifts reported here may be useful in analysing vibrational spectra of adenine nucleosides and nucleotides and in improving the force field of the 9‐substituted adenine ring.

Normal coordinate analysis and vibrational spectra of adenosine

“…The latter is mainly due to out-of-plane mosubstitution (see supplementary information). This coincides with the observations made by Toytions of the base and the former to in-plane bends of the adenine moiety coupled with ribose vibraama et al 6 The intense band at 1330 cm 01 in the FT-IR and 1331 cm 01 in the Raman spectra of tions. The lack of intense neutron inelastic scattering bands in this region would support the proadenine 9,10 has been assigned to a pyrimidine ring vibration.…”

“…The important contribution of internal coordinates involving C8 to the 1420-cm 01 RaThe C2H, C8H, and NH 2 hydrogen wagging modes coupled to torsion modes give rise to sevman band agrees with the large shift observed on C8 isotopic substitution by Toyama et al 6 The IR eral strong to medium bands in the 769-to 639-cm 01 spectral region. The strong band at É 720 bands at É 1388, 1353, 1252, and 1224 cm 01 are assigned to ribose vibrations, and calculations cm 01 of adenine has been assigned to ring-breathing vibrations.…”

“…Observed empirical treatments to nucleosides. 23,24 The midand far-IR spectra of polycrystalline adenosine in isotopic wavenumber shifts on 1,3- In previously published Raman spectra of adenadi et al, 9 together with the calculated isotopic shifts (data not shown but available as suppleosine, 4,6 frequencies in the 3000-cm 01 region were not included. The fundamentals calculated with mentary information) are taken into account for the proposed assignments.…”

“…in the 1650-to 543-cm 01 region has been reported by Toyama and coworkers. 6 Because of the importance of adenine nucleosides in biochemistry, a greater understanding of their vibrational spectra is a useful basis in the study of both adenine-containing biopolymers and drug-enzyme interactions that would correlate antiviral and antitumoral action with the physicochemical properties of nucleoside analogues.…”

Structural features of the adenosine conjugate in means of vibrational spectroscopy and DFT

“…According to our calculations, the isolated modes are (IR only). However, Navarro and coworkers [11] and Toyama et al [43], assign a band at 1331 cm -1 also to a pyrimidine ring vibration. The isolated stretching mode of the single C-N bonds (in-phase vibration) is attributed to a weak-intensity IR band and a very strong Raman band at 1346 cm -1 that is supported by our calculations.…”