Resonance Raman spectra of flavin derivatives containing chemical modifications in positions 7 and 8 of the isoalloxazine ring.

The resonance Raman spectra of riboflavin, 7,8-dichlororiboflavin, 8-chlororiboflavin, 8-bromoriboflavin, 8-(methylmercapto)riboflavin, 7-chlorolumiflavin, 8-norlumiflavin, 7,8-norlumiflavin, and 3-CH2COOH-lumiflavin were measured in complex with riboflavin binding protein, which was used as a fluorescence quenching agent. Shifts in the positions of Raman bands in the vicinity of 1250, 1405, 1550, and 1585 cm-1 were observed in the spectra of many of these flavin derivatives. Comparable shifts were found in the IR spectra (solid KBr) of the uncomplexed flavins. The perturbed bands have been previously assigned to reasonably localized stretching modes in the isoalloxazine system, which are well removed from the 7 and 8 positions. Thus, a direct effect on these bands due to modification of the substitutents at positions 7 and 8 is precluded. These observations have led us to conclude that these Raman bands are associated with highly delocalized aromatic framework vibrations.