Electron Spin Resonance Study on Anionic Flavin Free Radicals.

Abstract
The anionic lumiflavin radical was studied in detail by ESR and nitrogen-15 as well as deuterium substitutions have been carried out. The free radicals of the flavin coenzymes and a number of isoalloxazine derivatives have also been investigated. A hyperfine coupling scheme of the lumiflavin radical is derived where N(9), N(10), CH3 (7), CH3(9), and H(5 or 8) are involved. The hyperfine couplings are interpreted in terms of spin densities and comparison is made with available quantum chemical calculations. The effect of the N(9)-substituted upon the resolution of the spectra is examined and discussed.