IR spectroscopy of isolated neutral and protonated adenine and 9-methyladenine

Gydo C P van Zundert, Sander Jaeqx, Giel Berden, Joost M Bakker, Karl Kleinermanns, Jos Oomens, Anouk M Rijs

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IR spectroscopy is employed to study isolated adenine and its derivative 9-methyladenine in both their neutral and protonated forms. The IR spectra of neutral adenine and 9-methyladenine are measured in a molecular beam expansion via IR-UV ion-dip spectroscopy in the 525 to 1750 cm(-1) region. For adenine, UV excitation selects the 9H tautomer to give a conformer-selective IR spectrum. For 9-methyladenine, only one tautomer exists because of the methyl substitution at the N(9) position. The experimental spectra agree closely with spectra computed for these tautomers at the B3LYP/6-311++G(df,pd) level of theory. These spectra complement previous tautomer-specific IR spectra in the hydrogen stretching range. The 9H-adenine spectrum obtained is compared to a previously recorded FTIR spectrum of adenine at 280 °C, which shows close agreement, although the 7H tautomer cannot be excluded from contributing. Protonated adenine and 9-methyladenine are generated by electrospray ionization and studied via IR multiple-photon dissociation (IRMPD) spectroscopy. Comparison of the experimental spectra with computed spectra allows identification of the protonation site, which suggests that the 1-9 tautomer is the dominant contributor to the spectra.

Original languageEnglish
Pages (from-to)1921-7
Number of pages7
Issue number10
Publication statusPublished - 11 Jul 2011
Externally publishedYes


  • Adenine
  • Protons
  • Spectroscopy, Fourier Transform Infrared


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