Degradation of Water-Insoluble Dyes by Microperoxidase-11, an Effective and Stable Peroxidative Catalyst in Hydrophilic Organic Media

Microperoxidase-ll (MP-11), a heme-containing undecapeptide, derived from horse heart cytochrome c was utilized as a peroxidative catalyst. Catalytic characteristics of MP-II in hydrophilic organic media were studied using 2,6-dimethoxyphenol as a reducing substrate in a series of organic solvents at various concentrations, indicating that MP-II was active in water-miscible organic solvents but at least 5% water was compulsory for the catalytic action. Thus, MP-II was not active in hydrophobic solvents. The pH of the water portion in the media affected the reaction rate. The optimal pH was found to be 9, where a release of protons from either an oxidizing or reducing substrate to the media was facilitated. The decolorization of water-insoluble synthetic dyes by MP-II in 90% methanol was attempted. MP-II showed effective decolorization activities against either azo or anthraquinone dyes. The degradation pathway for Solvent Orange 7 was investigated in detail, showing that MP-II catalyzed the oxidative cleavage of the azo linkage to generate 1,2-naphthoquinone and 2,4dimethylphenol as key intermediates.