Basic studies on lignin degradation with biomimetic metalloporphyrin catalysts.

本研究的主要目的是建立仿生金属卟啉配合物催化木质素生物降解的酶模型体系，为进一步研究木质素生物降解机理提供基础数据。电子氧化机理已建立在以下结果的基础上。1)模型底物的C-C键断裂产生芳香醛和苯乙二醇产物。2)证明0-18-标记的双氧以83%的含量掺入到苯乙二醇产物的羟基中。3)在裂解产物中证实了底物的D-标记，并对非酚类木质素模型化合物异丙基醇的芳环裂解反应机理进行了探讨。0-18示踪实验清楚地表明，在氯化血红素催化剂催化的裂解反应过程中，发生了独特的区域特异性氧化反应，无论是与水还是与分子氧的氧化反应。这些结果清楚地表明，铁-卟啉络合物具有与木质素酶相同的特征。其还催化多种木质素模型化合物的单电子氧化。还检查了各种因素，如溶剂、pH、配体物质如谷胱甘肽、咪唑和酪氨酸、底物或催化剂浓度等。

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.