Laccase/mediated oxidation of a lignin model for improved delignification procedures

Laccase oxidises the phenolic but not the non-phenolic subunits of lignin. Redox mediators drive laccase towards the oxidation of non-phenolic subunits, particularly the benzyl alcohol groups. In search for non-polluting delignification strategies of wood pulp for paper making, oxidations by laccase/mediator systems have been performed on Adlerol, a non-phenolic -hydroxyl--arylether model of lignin. The mechanism and extent of these mediated oxidations of Adlerol to Adlerone (-carbonyl) have been investigated and compared with chemical oxidations. The more valuable mediator of laccase results to be violuric acid, which performs a radical oxidation of Adlerol. Earlier studies had revealed that Adlerone is efficiently degraded under, for example, kraft cooking conditions, whereas Adlerol resists degradation. Thus, a pre-oxidation of the -hydroxyl--arylether subunits in wood pulp by the laccase/VLA system appears promising for weakening the network of lignin, thereby activating it towards subsequent oxydelignification treatments.