KINETICS AND MECHANISM OF A CHEMILUMINESCENT CLOCK REACTION BASED ON THE HORSERADISH-PEROXIDASE CATALYZED OXIDATION OF LUMINOL BY HYDROGEN-PEROXIDE

In the presence of limited amounts of urate the rapid onset of light emission from the horseradish peroxide catalysed oxidation of luminol by hydrogen peroxide is delayed, yielding a chemiluminescent clock reaction. Under appropriate conditions the rate of urate oxidation by hydrogen peroxide in the dark reaction is independent of the concentration of both reagents, reflecting a steady state in the catalytic system in which the enzyme intermediate, Compound (II), preferentially reacts with luminol to yield luminol radicals which rapidly oxidise urate. Luminol, therefore, acts as an electron-transfer mediator during the dark reaction and its concentration remains constant, yielding an overall zero-order process.