Low temperature Fourier transform infrared spectra and hydrogen bonding in polycrystalline uracil and thymine

M. Rozenberg*, G. Shoham, I. Reva, R. Fausto

*Corresponding author for this work

Research output: Contribution to journalArticlepeer-review

33 Scopus citations

Abstract

The FTIR spectra of pure NH and isotopically diluted (NH/ND and ND/NH) polycrystalline uracil and thymine were measured in the range 4000-400cm -1 at temperatures from 300 to 10K. For the first time, the essentially narrow bands corresponding to the uncoupled stretching (ν1) and out of plane bending (ν4) NH proton modes of uracil and thymine were observed in the solid phase. It was found that in the ν4 region the spectra reveal more details on the H-bond interactions present in both solids than in the ν1 range. The frequencies of the various bands observed in both spectral regions were used for estimation of the H-bond energy, using empirical correlations between this property and both the red shift of ν1 and the blue shift of ν4 that occur upon crystallization due to the establishment of the H-bonds. The results are compared with known thermodynamic, structural and theoretical data. The IR data also suggest that the H-bond networks of both crystals contain, besides the two NH⋯O-C bonds revealed by X-ray experiments, additional types of H-bonds, which do not show long range periodicity and, thus, cannot be detected by the conventional structural methods. The assignment of some other bands in the spectra of both substances was also reviewed.

Original languageAmerican English
Pages (from-to)2323-2336
Number of pages14
JournalSpectrochimica Acta - Part A: Molecular and Biomolecular Spectroscopy
Volume60
Issue number10
DOIs
StatePublished - Aug 2004

Bibliographical note

Funding Information:
M.R. gratefully acknowledges the financial support from the Israel Ministry for Immigrant Absorption; I.R. and R.F. acknowledge the financial support from Fundação para a Ciência e a Tecnologia, Lisbon (grant FCT #SFRH/BPD/1661/2000 and research project POCTI/43366/QUI/2001).

Keywords

  • H-bonding in solids
  • Isotopic dilution
  • Low temperature FTIR spectra
  • Thymine
  • Uracil

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