Transient kinetics studies of azo dye oxidation catalyzed by horseradish peroxidase

Abstract

The release of azo dyes into the environment is a continuing hazard resulting from industrial wastewater being released into the ecosystem. The industrial wastewater contains azo dye runoff that is used to color textiles, food, cosmetics, and other industrial products1-3. Oxidative decolorization is a potential method to remediate azo dye contamination1-3. Horseradish peroxidase (HRP) is an enzyme with a wide substrate range for organic compounds and strong oxidative power, making it a potential catalyst for azo dye decolorization. The oxidative strength of HRP is due to the Fe(III)-heme prosthetic group that reacts directly with hydrogen peroxide (H2O2) to form the high valent Fe-oxo species known as compound I (cpdI) and a subsequent intermediate, compound II (cpdII)4-8. These enzyme-bound high valent Feoxo species extract single electrons from a range of organic compounds via a collisional reaction, generating free radical species in solution. The radical species undergo radical quenching via different chemical routes, resulting in a wide range of products from a single organic substrate4-8. Previous research has shown that HRP catalyzes the oxidation of several azo dyes. The research described here focuses on the oxidation of the azo dye Orange IV (OIV). Initial research showed that OIV is oxidized to form a product, denoted as P-1, via a multistep process; however, further work showed that the reaction continued at a slower rate. The research described here utilized transient kinetic techniques to examine the slower reaction to elucidate a more complete mechanism for the oxidation of OIV and aid in future environmental remediation techniques.