Interaction between MnO2 and oxalate: Formation of a natural and abiotic lignin oxidizing system

This paper reports for the first time the efficient modification/degradatio n of in situ lignin by manganese complexes formed by the association of MnO 2, accumulated as black deposits during wood decay, and oxalic acid, produc ed by fungi or resulting from oxidative degradation of cell wall components . The Mn oxidants formed are shown to modify both the chemical and physical properties of the wood cell wall. Microscopic analysis revealed the disrup tion of ray cell in oxidized wood and the formation of amorphous globular m aterial not yet characterized. Thioacidolysis analysis of the oxidized lign in showed a reduction up to 25-30% in the recovery of ether-linked guaiacyl (G) and syringyl monomers and up to 50-80% of Several diarylpropane and ph enylcoumarane dimers composing the polymer. Preferential oxidation of G moi eties in all structures examined was observed during catalysis. The MnO2/ox alate system also appears to selectively oxidize the lignin macromolecule, as no xylose or glucose loss was observed in all treated samples. The oxida tion process catalyzed by MnO2 and oxalate may play an important role in th e general pathway of lignin degradation and also in the transformation of t he lignin polymer into humus and/or its precursors.