MNO2 AND OXALATE - AN ABIOTIC ROUTE FOR THE OXIDATION OF AROMATIC COMPONENTS IN WHEAT-STRAW

Oxidants formed through the interaction between MnO2 and oxalate accum ulated in rotten wood have been evaluated as abiotic agents possibly i nvolved in wheat straw ligninolysis. The hemicellulose and cellulose c ontent of straw remained unchanged, and no release of free soluble mat erials from lignin or polysaccharides could be evidenced. Structural a nalysis of oxidized lignin in situ has revealed up to 30% and 10% decr ease of beta-O-4 linked Guaiacyl and Syringyl units, respectively. Lig nin phenolic moieties only were directly oxidized by MnO2/oxalate as n o structural alteration was observed within extensively permethylated wheat straw. Modifications were also evidenced at the level of the cel l wall linked cinnamic acids present in wheat straw. Esterified phenol ic acids were more readily oxidized by Mn complexes than ethers analog ues, and disappearance of ferulic moieties was always more pronounced than that of p-coumaric acids. The abietic Mn oxidants generated from MnO2 and oxalate may therefore significantly contribute to the decay a nd humification process of lignocellulosic material in Nature.