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

Abstract

The bis-sulfonamide TAML activator of peroxides [Fe{4-NO₂C₆H₃-1,2-(NCOCMe₂NSO₂)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.

Graphical Abstract

Keywords:

• Iron(III)
• TAML activators
• hydrogen peroxide
• microcystin-LR
• oxidation
• kinetics

Acknowledgement

The assistance from Liam Dugan (Center for Molecular Analysis of Carnegie Mellon University) is gratefully acknowledged.

Disclosure statement

There are no competing interests.

Additional information

Funding

The research was funded primarily through EPA grant SU83946101. The instrumentation used at the Center for Molecular Analysis at Carnegie Mellon University is funded by NSF grant number DBI-9729351. TJC thanks the Heinz Endowments and Heinz Family Foundation.