Specificity of phenolic disazo dyes in relation to transformation by laccase

Four novel disazo dyes were synthesized and characterized using FTIR and NMR spectroscopy. These water-soluble dyes had a hydroxyl group in the para position of the phenolic ring in relation to the azo bond, whereas the other substituents on the phenolic ring and/or between the two azo bonds varied. The transformation of the dyes was studied using purified fungal laccase. The rank order in which the dyes were transformed was IV > III ≫ I. Dye II was not a laccase substrate. As both dye I and II had a carboxylic substituent on the phenolic ring but the ring structures between the two azo linkages were different, we suggest that the latter also influenced laccase catalysis. Both of the redox mediators tested, violuric acid and N-hydroxybenzotriazole, enhanced the laccase reaction with violuric acid, being generally more effective. The results show that the chemical structure of both the phenolic ring as well as the ring distal to the phenolic moiety affect the reaction kinetics.