Basic studies on lignin degradation with biomimetic metalloporphyrin catalysts.

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The objectives of this investigation are basically to establish the enzyme model system for understanding of lignin bioegradation mechanisms with the biomimetic metallo-porphyrin complex and also to obtain the fundamental data for development of catalytic delignification processes.The reaction mechanism for C-C bond cleavage of -1 lignin model compound was investigated and the one-electron oxidation mechanism has been established on the basis of the following results. 1) The C-C bond cleavage of the model substrate yielded the aromatic aldehyde and phenylglycol products. 2) 0-18-labeled dioxygen was proved to be incorporated at the content of 83% into the hydroxyl group of the phenylglycol product. 3) D-label of the substrate was demonstrated in the clevage product.The reaction mechanism for the aromatic ring cleavage of a non-phenolic lignin model compound vertryl alcohol was also investigated. 0-18 tracer experiments clearly indicate that the unique regiospecific oxygenations with either water or dioxygen took place during the cleavage reaction catalyzed by the hemin catalyst.These results obtained clearly showed that the iron-porphyrin complex exhibts the the same features as expressed by ligninase enzyme., which also catalyzes the one electron oxidation of a wide variety of lignin model compounds. Various factors such as solvent, pH, ligand species such as glutathione, imidazol and tyrosine, substrate or catalyst concentrations etc. were also examined.