Model guaiacol compounds representing lignin monomers, as well as DHP-lignin and wood flour of controlled particle size were used to assess iron reduction at the pH of the natural wood cell wall. All compounds functioned as electron donors for ferric iron, with the lignin monomers demonstrating capacity for non-stochiometric reduction of iron with multiple moles of ferric ion reduced per mole of lignin monomer. Iron reduction was enhanced as pH decreased. The results provide a mechanism to explain how lignin may participate as part of a “moving radical front” after initial fragmentation of the lignocellulose cell wall by brown rot fungi. Further, relative to enzymatic action on wood, the data suggest a mechanism to generate electrons that would promote action by fungal enzymes that require an electron donor. The data also demonstrate how hydroxyl radicals would be generated to promote the generation of low levels of formaldehyde from lignin under conditions when lignin surfaces were exposed.

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