Oxidative Functionalisation of Lignin by Layer-by-Layer Immobilised Laccases and Laccase Microcapsules

Laccase was either supported onto alumina particles or physically entrapped inside microcapsules. In both cases, the enzyme was protected by coating with oppositely charged polyelectrolytes by means of the layer-by-layer technique. The activities of these laccase particles andmicrocapsules were studied on softwood milled wood and kraft residual lignins, in the presence and absence of different mediators. Quantitative 31P NMR was used to determine the structural modifications induced in the lignin structures. Compared to the native enzyme, the laccase particles and microcapsules were found to be more reactive, showing higher conversions. Irrespective of the experimental conditions, the oxidation efficiency was enhanced by the presence of 1-hydroxybenzotriazole or violuric acid as the oxidation mediator. Differently immobilised laccases showed distinct reaction selectivities in the oxidative pattern of lignin.