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SOME ONE ELECTRON REDUCTION PRODUCTS OF FLAVIN ANALOGS: CYANOISOALLOXAZINES AND DEAZAISOALLOXAZINES
Author(s) -
Tollin Gordon,
Chan Rebecca L.,
Malefyt Thomas R.,
Bruice Thomas C.
Publication year - 1979
Publication title -
photochemistry and photobiology
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 0.818
H-Index - 131
eISSN - 1751-1097
pISSN - 0031-8655
DOI - 10.1111/j.1751-1097.1979.tb07044.x
Subject(s) - chemistry , electron paramagnetic resonance , flavin group , photochemistry , photodissociation , radical ion , radical , ferricyanide , hyperfine structure , hydroxyl radical , reaction rate constant , electron transfer , kinetics , ion , inorganic chemistry , organic chemistry , nuclear magnetic resonance , physics , quantum mechanics , enzyme
— 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 (O 2 , 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.