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 alfa-hydroxyl-beta-arylether model of lignin. The mechanism and extent of these mediated oxidations of Adlerol to Adlerone 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 alfa-hydroxyl-beta-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.