Reactivity and Mechanism of Laccase Mediators for Pulp Delignification, 1997 Biological Sciences Symposium Proceedings

Laccase-catalyzed oxygen delignification of kraft pulp occurs at low temperature and pressure, but requires the addition of chemical mediators such as 2,2’-azinobis-(3-ethylbenzthiazoline-6- sulfonate) (ABTS) and 1-hydroxybenzotriazole (HBT). We tested several other potential mediators with laccases from different sources. We found significant differences in reactivity between various fungal laccases for pulp delignification in the presence of the mediators ABTS and HBT. A comparison of T. versicolor lactase with various mediators, including ABTS, HBT, remazol blue, nitroso-naphthols and phenothiazines, has shown that HBT gave the most extensive delignification, but deactivated the enzyme and therefore required a higher enzyme dosage. Reaction products from lignin dimer oxidation by lactase were shown to be different in the presence of ABTS and HBT. From electrochemical analysis, new insights into the mechanism of interaction between mediators and lignin are presented. It is proposed that the dication of ABTS and the l-oxide radical of HBT, with redox potentials in the 0.8 to 0.9 V range, are required for pulp delignification.