Kinetics of catalytic oxidation of the potent aquatic toxin microcystin-LR by latest generation TAML activators

The bis-sulfonamide TAML activator of peroxides [Fe{4-NO₂C₆H₃-1,2-(NCOCMe₂ NSO₂)₂CHMe}]^- (2) catalyzes the H₂O₂ oxidation of microcystin-LR (m-LR), a common surface water contaminant produced by cyanobacteria that is toxic at very low concentrations. The major reaction product is by 16 Da heavier than m-LR, suggesting that the first oxidative step involves addition of oxygen to one of m-LRs three C = C units to form an epoxide. The kinetic data suggest that the m-LR → m + 16 conversion occurs without any kinetically meaningful intermediate with the catalytic rate constant k _II of 2.5 × 10⁵ M⁻¹ s⁻¹, which characterizes the interaction of m-LR with the oxidized, active form of the catalyst. The primary m + 16 product undergoes much slower further catalytic oxidation in the aqueous reaction medium. This communication describes a potential utility of TAML/H₂O₂ catalysis for microcystin detoxification that calls for further research.