EPR Evidence for hydroxyl- and substrate-derived radicals in Fe(II)-oxalate/hydrogen peroxide reactions. The importance of the reduction of Fe(III)-oxalate by oxygen-conjugated radicals to regenerate Fe(II) in reactions of carbohydrates and model compounds

EPR spectroscopy has been employed for the direct detection of a variety of free radicals formed from reaction of Fe(II)-oxalate and H2O2 in the prese nce of carbohydrates and related compounds: this system has been designed t o model the proposed mode of action of brown rot fungi. The observed hyperf ine splittings allow characterization of individual radicals formed at diff erent positions in the carbohydrate rings. Relative signal intensities in s teady-state spectra indicate the rapid generation of the hydroxyl radical, followed by relatively unselective attack of (OH)-O-. on the substrates' C- H bonds: the rapidity of oxidation by Fe(III) of oxygen-conjugated carbon-c entred radicals (typically k 10(8) dm(3) mol(-1) s(-1)) is significantly re duced if there is an eclipsing beta-oxygen substituent. The relevance of th ese findings to cellulose-cleaving reactions of certain fungi is discussed.