The resonance Raman spectra of three pharmacologically important sulfonamides, 4-sulfamyl-4′-dimethylaminoazobenzene (1), 4-sulfamyl-4′-hydroxyazobenzene (2), and 4-sulfamyl-4′-aminoazobenzene (3), are compared with those of analogues lacking the sulfonamide group. The —SO2NH2 moiety does not directly contribute intense or moderately intense bands to the resonance Raman spectra of 1, 2, and 3. However, —SO2NH2 ionization is reflected by frequency changes in a band near 1140 cm−1 and intensity changes in the 1420 cm−1 region. The normal Raman spectrum of 2 confirms that the intensity changes reflect —SO2NH2 ionization rather than unrelated changes in vibronic coupling. The effect of —OH ionization on the resonance Raman spectrum of 2 emphasizes that caution must be exercised when relating spectral perturbations to changes in contributions from valence bond type structures. Resonance Raman excitation profiles for the 1138, 1387, and 1416 cm−1 bands of 2 show that these bands gain intensity by coupling with the electronic transitions in the 240 to 450 nm region and that, more than 1000 cm−1 to the red of λmax, the wavelength dependence can be closely reproduced by the FB type terms of Albrecht and Hutley. The excitation profile for each band shows evidence for structure in the 470 nm region, although lack of sufficient excitation wavelengths prevents accurate estimation of the spacing. Under conditions of rigorous resonance the intense Raman lines all occur in the 1400 cm−1 region, i.e. they are 'bunched' in the region known to contain the —N=N— stretching vibration.
Heme-linked ionization of horseradish peroxidase compound II monitored by the resonance Raman Fe(IV)=O stretching vibration.