TAML Catalysis for a Safer Environment: Oxidative Transformations of Natural and Anthropogenic Aqueous Micropollutants

Access to safe, clean drinking water remains a serious challenge across the modern world. The lack of access to clean water becomes even more widespread and dire upon taking into account the ubiquity of harmful micropollutants now found in waterways worldwide. These trace contaminants arise from sources ranging from the industrial (factory wastewater or agricultural run-off) to the personal (pharmaceuticals and personal care products in household wastewater). Thus, the development of safe, affordable, and effective treatments for these micropollutants is vital. Fe-TAML (TetraAmido Macrocylic Ligand) catalysts are a promising technology for water purification. Small molecule functional mimics of peroxidase enzymes, TAML catalysts work in conjunction with hydrogen peroxide to effectively remediate a wide variety of compounds of environmental interest. This work expands the scope of TAML chemistries by studying aspects of the activity, lifetime, and mechanisms of a bis-amido–bis-sulfonamido macrocycle catalyst, 2, with a focus on the treatment of natural and artificial micropollutants. Five issues are examined herein. (1) 2/H₂O₂ is found to rapidly oxidize the dangerous and widespread algal toxin microcystin-LR. Although the reaction is rapid, the extent of oxidation is limited. (2) Two model azole fungicides, propiconazole and flusilazole, were found to be highly resistant to oxidation by 2/H₂O₂ and 2/NaOCl, representing a “wall” which current TAML catalysts cannot surmount. The environmental and health effects of these widely used fungicides are reviewed. (3) The oxidative degradation of the benzimidazole fungicide carbendazim is characterized, and products of this reaction are identified. Here, current generation catalysts show significant improvements over previous generations. (4) The scope and mechanistic characteristics of catalytic nitration of phenolic compounds, including tyrosine, by 2 are examined in an initial study. (5) The phosphate catalyzed demetallation of 2 is explored, and the effect of pH on this process is examined.