Emiko Komatsu

Reaction Selectivity on Decoloration of Azo Dyes Catalyzed by Peroxidase

An investigation was conducted into the reaction selectivity of azo dye decoloration by peroxidase (POD). The effects of pH and the addition of p-iodophenol on decoloration rate were investigated using 3 types of dye in single-dye and mixed-dye systems. The addition of p-iodophenol accelerated decoloration. In the mixed-dye system, a pH of 8.0 resulted in the highest decoloration rate. HPLC was used to determine the decoloration rate of individual dyes in the mixed-dye system. The decoloration reaction of Orange I proceeded swiftly, decoloration of Orange II was slowed, and decoloration of Orange G was accelerated. The reaction mechanism in the mixed-dye system is considered to be as follows. Orange I reacts much faster than the other dyes, producing radicals immediately after the reaction commences and then decomposing. Meanwhile, since Orange II has a higher oxidation potential than Orange I, the reaction between Orange II and POD begins after completion of the Orange I reaction. The reaction with Orange G, which has a higher oxidation potential than Orange II, commences even later. Some of the Orange II radicals produced undergo radical reactions with Orange G, transferring electrons to Orange G and reverting to Orange II. As a result, the Orange II reaction is inhibited more than in an Orange II-only system. Conversely, when p-iodophenol was introduced into the mixed-dye system, the reaction selectivity was lost as p-iodophenol radicals reacted simultaneously with all 3 dyes.