Effect of (13)C-, (18)O- and (2)H-labeling on the infrared modes of UV-induced phenoxyl radicals

The structure and environment of redox active tyrosines present in several metalloenzymes can be studied by resonance Raman spectroscopy or Fourier transform infrared difference spectroscopy. Assignments of the vibrational modes in vivo often requires in vitro studies on model compounds. This approach is briefly reviewed. New results are shown on the influence of isotope-labeling on the infrared spectra of tyrosine, Formula: see text] and phenol radicals obtained in vitro by UV-irradiation. The infrared spectra of the radicals are dominated by the Formula: see text] mode at 1515-1504 cm(-1). The frequency shifts induced on this mode by (13)C- (2)H-, and (18)O-labeling are reported.