The oxidation of indole derivatives catalyzed by horseradish peroxidase is highly chemiluminescent.

The indole moeity is present in many substances of biological occurrence. Its metabolism, in most cases, involves an oxidative pathway. This study reports the oxidation of a series of indole derivatives, including several of biological origin, catalyzed by horseradish peroxidase in the presence of H2O2. Chemiluminescence emission was observed in most cases and its intensity and spectral characteristics were correlated with structural features of the substrates. The structures of the main products were determined. The participation of molecular oxygen and superoxide ion in the reaction was demonstrated and a general mechanism for product formation proposed. Since the oxidation of 2-methylindole proved to be highly chemiluminescent, its potentiality as a developing system for peroxidase-based assays was tested and showed to be very effective.