Vanadium Chloroperoxidase as a Catalyst for Hydrogen Peroxide Disproportionation to Singlet Oxygen in Mildly Acidic Aqueous Environment

Abstract

Abstract Chemiluminescence studies show that the enzyme vanadium chloroperoxidase from the fungus Curvularia inaequalis is a highly efficient catalyst for the production of singlet oxygen from hydrogen peroxide in a mildly acidic aqueous environment, with a maximum turnover frequency of 100 s −1 with respect to H 2 O 2 consumption. The enzyme studied here can be regarded as a supplementary catalyst to inorganic molybdate, which operates in basic aqueous media. The enzyme system is 10 3 – 10 4 times faster than the molybdate system when compared at their optimal pH. The enzyme is very stable against singlet oxygen, in contrast to heme‐containing peroxidases which, due to inactivation by singlet oxygen, only produce a short burst, presumably by oxidation of the labile cofactor. The vanadium chloroperoxidase was compared with vanadium bromoperoxidase from the seaweed Ascophyllum nodosum and was found to be even more stable; it is stable towards a continuous flow of singlet oxygen for at least 1 hour and also it is not inactivated by 500 mM H 2 O 2 . An important difference with vanadium bromoperoxidase is that the vanadium chloroperoxidase is able to effectively use chloride as a cocatalyst (20 s −1 ) instead of bromide. This offers an important advantage from an application point of view; using chloride, no side products are observed when the chemical trap anthracene‐9,10‐bis(ethanesulphonate) is fully converted by singlet oxygen into its corresponding endoperoxide. By contrast, when bromide is used, 20% side product is formed. During the conversion the enzyme remains fully stable for 25,000 turnovers.