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Mechanistic aspects of the reactions of copper complexes with lignin in the presence of hydrogen peroxide and lipid hydroperoxide model compounds as proposed for white rot fungi
2001 - IRG/WP 01-10399
The structural principles and the oxidative reactions of the catalytic system consisting of copper, hydroperoxides, and copper coordination compounds that contain aromatic nitrogen atoms are similar to those of catalytic centers of oxidative enzymes involved in delignification reactions of white rot fungi. The system is capable of selectively degrading lignin and its low molecular weight would allow to react oxidatively also at sites of the wood cell wall, where enzymes cannot penetrate. Understanding the mechanisms of white rot would offer perspectives to develop targeted wood preservatives to inhibit these enzymatic and non-enzymatic reactions of wood decay. Studies on the mechanism of the copper/pyridine and 4-aminopyridine resp./hydrogen peroxide system that were carried out with 14C-labeled lignin and cellulose model compounds demonstrated the selectivity of the copper system for lignin structures and the ability of the system to oxidise even non-phenolic lignin. Product profiles of the reactions supported by ESR measurements suggested a non-radical reaction pathway involved in that case. However, when a lipid hydroperoxide model (cumene hydroperoxide, CHP) was used as peroxide source, a variety of free radicals derived from this peroxide could be detected in ESR. Selective staining of treated wood sections with safranin and astra blue showed degradation of softwood and hardwood lignin in the middle lamella and secondary cell wall. Besides its importance for developing targeted wood preservatives, the coordinated copper system has great potential for application for selective lignin degradation in the pulp and paper industry and could therefore replace environmentally problematic chlorine and chlorine dioxide based pulp bleaching stages.
K Fackler, P Lamaipis, E Srebotnik, M Humar, C Tavzes, F Pohleven, M Sentjurc, T Watanabe, K Messner