Catalytic Action and Destruction of Protohematin During Peroxide Dependent Luminol Chemiluminescence

The catalytic action of protohematin was studied during the H 2 O 2 ‐dependent chemiluminescent luminol reaction. In spite of the fact that the catalyst was ultimately inactivated, the average protohematin molecule catalyzed the consumption of about 10 3 molecules of luminol. The inactivation of catalyst and the initial consumption of luminol were studied during the luminescent reaction with different concentrations of reactants. A scheme accounting for the experimental observations is proposed. The formation of a primary protohematin‐H 2 O 2 complex is followed by binding of luminol, resulting in a ternary complex. A nucleophilic attack by a second molecule of H 2 O 2 on the luminol molecule results in light emission from excited aminophthalate via a hypothetical peroxide adduct. The destruction of protohematin occurs via the attack of H 2 O 2 on the porphyrin structure of the protohematin‐H 2 O 2 complex. Second order rate constants for the destruction of protohematin, the formation of the luminol complex and the nucleophilic attack of H 2 O 2 are presented.