SOME ONE ELECTRON REDUCTION PRODUCTS OF FLAVIN ANALOGS: CYANOISOALLOXAZINES AND DEAZAISOALLOXAZINES

Abstract

Abstract— 8‐Cyanoisoalloxazines have been previously shown to form highly stable radical species at basic pH. We have measured the electron spin resonance (EPR) spectra of the radical forms of 8‐cyano‐10‐methyl‐3‐sulfopropylisoalloxazine (I) at both acidic and basic pH. In both cases. the EPR spectra are similar to those obtained from unsubstituted isoalloxazines. with no indication of hyperfine splitting due to the cyano nitrogen. Laser photolysis of I in the presence of EDTA at basic pH generates two radical species. One of these decays rapidly by a first‐order process to produce thc stable radical. The rate of this decay depends upon the initial flavin concentration, thus suggesting a reaction of the radical with oxidized isoalloxazine. The rates of reaction of the radical species with added oxidants (O2, ferricyanide), and the pH‐dependence of stable radical formation, indicate that the rapidly‐decaying species is the anion radical of I, and that the stable radical is formed by its reaction with oxidized flavin. Laser photolysis of I at acidic pH, as well as of 8‐cyano‐5‐deaza‐isoalloxazine at acidic or basic pH, does not generate stable radical species. I‐Deazaisoalloxazines do not give radical transients at all upon laser photolysis.