Infrared-spectra and tautomerism of isocytosine - an ab-initio and matrix-isolation study
Vranken, H × Smets, J Maes, Guido Lapinski, L Nowak, Mj Adamowicz, L #
Pergamon-elsevier science ltd
Spectrochimica acta part a-molecular and biomolecular spectroscopy vol:50 issue:5 pages:875-889
Prototropic tautomerism of isocytosine has been investigated using both theoretical ab initio and experimental matrix isolation IR methods. The coexistence of the amino-hydroxy and amino-oxo N(3)H forms, with a clear predominance of the hydroxy form, was observed. The tautomerization constant [oxo]/[hydroxy] obtained from experimental and calculated IR intensities was 0.11 at the micro-oven temperature of 400 K. The ab initio prediction of the relative energies of the tautomers is in reasonable agreement with the experimental estimation. The change of the tautomeric form oxo --> hydroxy upon UV irradiation was used to separate the IR spectra of both tautomers. A theoretically assisted interpretation of the IR spectra of both observed tautomers is proposed.