Interaction between MnO₂ and Oxalate: Formation of a Natural and Abiotic Lignin Oxidizing System

Abstract

This paper reports for the first time the efficient modification/degradation of in situ lignin by manganese complexes formed by the association of MnO 2 , accumulated as black deposits during wood decay, and oxalic acid, produced 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 disruption of ray cell in oxidized wood and the formation of amorphous globular material not yet characterized. Thioacidolysis analysis of the oxidized lignin 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 phenylcoumarane dimers composing the polymer. Preferential oxidation of G moieties in all structures examined was observed during catalysis. The MnO 2 /oxalate system also appears to selectively oxidize the lignin macromolecule, as no xylose or glucose loss was observed in all treated samples. The oxidation process catalyzed by MnO 2 and oxalate may play an important role in the general pathway of lignin degradation and also in the transformation of the lignin polymer into humus and/or its precursors.

Lignin: Characterization of a Multifaceted Crop Component

“…Manganese (Mn) deficiency appears to be an exception, as it reduced the lignin concentration in wheat roots and shoots [ 75 , 76 ]. This exception can be explained by the fact that Mn is required for lignin biosynthesis as it activates several enzymes of the shikimate and phenylpropanoid pathway [ 159 , 160 ].…”

Induction and suppression of Dichomitus squalens and Ceriporiopsis subvermispora peroxidase activity by manganese sulphate in response to carbon and nitrogen sources

“…In the presence of excess Mn 3+ and low concentration of chelating compound such as oxalate, Mn 3+ disproportionates into MnO 2 which precipitates as black or brown deposits on the fungal mycelia. The MnO 2 deposits create a concentration gradient between the mycelia and liquid culture that further promotes the abstraction of Mn 2+ from the liquid culture . C. subvermispora lacks the ODC activity and this may contribute to the insignificant peroxidase activity suppression.…”

“…The MnO 2 deposits create a concentration gradient between the mycelia and liquid culture that further promotes the abstraction of Mn 2þ from the liquid culture. [29] C. subvermispora lacks the ODC activity and this may contribute to the insignificant peroxidase activity suppression.…”

Oxidation of Spruce Wood Sawdust by MnO2 plus Oxalate: A Biochemical Investigation

“…They also produce significant levels of oxalic acid during the process, which can acidify wood to pH 2 (Micales, 1995;Dutton et al, 1993). We therefore propose at this time that MnO 2 and related Mn(IV) species could indeed be actively involved in the degradation of lignocellulose when associated with oxalates (Lequart et al, 1998(Lequart et al, , 2000Hames et al, 1998). Still, such a mechanism is not demonstrated to occur in the natural environment, but all elements are in place within wood to promote this phenomenon.…”

“…We have recently shown that the solubilization of MnO 2 by oxalate at pH 2.5 leads to the production of Mn chelates capable of oxidizing lignin within wheat straw and poplar cell wall (Lequart et al, 1998(Lequart et al, , 2000Hames et al, 1998). Wood-destroying fungi accumulate large amounts of transition metals including manganese during decay (Illman et al, 1989;Jellison et al, 1997).…”