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Oxidative water purification of micropollutants (MPs) can proceed via toxic intermediates calling for procedures for connecting degrading chemical mixtures to evolving toxicity. Herein, we introduce a method for projecting evolving toxicity onto composite changing pollutant and intermediate concentrations illustrated through the TAML/H 2 O 2 mineralization of the common drug and MP, propranolol. The approach consists of identifying the key intermediates along the decomposition pathway (UPLC/GCMS/NMR/UV-Vis), determining for each by simulation and experiment the rate constants for both catalytic and noncatalytic oxidations and converting the resulting predicted concentration versus time profiles to evolving composite toxicity exemplified using zebrafish lethality data. For propranolol, toxicity grows substantially from the outset, even after propranolol is undetectable, echoing that intermediate chemical and toxicity behaviors are key elements of the environmental safety of MP degradation processes. As TAML/H 2 O 2 mimics mechanistically the main steps of peroxidase catalytic cycles, the findings may be relevant to propranolol degradation in environmental waters., Competing Interests: Y.S. and T.J.C. are coinventors on a patent for the latest generation TAML catalysts, allowed in the United States and pending elsewhere—the connection to this work is remote. T.J.C. is the Creator Founder and a Board member of Sudoc, LLC, formed to commercialize applications of the latest generation TAML catalysts. T.J.C.'s Irrevocable Family Trust is an owner of significant holdings in Sudoc, LLC—the vast majority of the Trust's future income is directed to supporting research and education in sustainability science, especially to advancing the rational handling of endocrine disrupting chemicals in our global civilization., (© 2020 The Author(s).)

A cyclic voltammetry study of a series of iron(III) TAML activators of peroxides of several generations in acetonitrile as solvent reveals reversible or quasireversible Fe III/IV and Fe IV/V anodic transitions, the formal reduction potentials (E°') for which are observed in the ranges 0.4-1.2 and 1.4-1.6 V, respectively, versus Ag/AgCl. The slope of 0.33 for a linear E°'(IV/V) against E°'(III/IV) plot suggests that the TAML ligand system plays a bigger role in the Fe III/IV transition, whereas the second electron transfer is to a larger extent an iron-centered phenomenon. The reduction potentials appear to be a convenient tool for analysis of various properties of iron TAML activators in terms of linear free energy relationships (LFERs). The values of E°'(III/IV) and E°'(IV V -1 ) correlate 1) with the pK a values of the axial aqua ligand of iron(III) TAMLs with slopes of 0.28 and 0.06 V, respectively; 2) with the Stern-Volmer constants K SV for the quenching of fluorescence of propranolol, a micropollutant of broad concern; 3) with the calculated ionization potentials of Fe III and Fe IV TAMLs; and 4) with rate constants k I and k II for the oxidation of the resting iron(III) TAML state by H 2 O 2 and reactions of the active forms of TAMLs formed with donors of electrons S, respectively. Interestingly, slopes of log k II versus E°'(III/IV) plots are lower for fast-to-oxidize S than for slow-to-oxidize S. The log k I versus E°'(III/IV) plot suggests that the manmade TAML catalyst can never be as reactive toward H 2 O 2 as a horseradish peroxidase enzyme., (© 2020 Wiley-VCH GmbH.)

Studies of the oxidative degradation of picric acid (2,4,6-trinitrophenol) by H 2 O 2 catalyzed by a fluorine-tailed tetraamido macrocyclic ligand (TAML) activator of peroxides [Fe III {4,5-Cl 2 C 6 H 2 -1,2-( N COCMe 2 N CO) 2 CF 2 }(OH 2 )] - ( 2 ) in neutral and mildly basic solutions revealed that oxidative degradation of this explosive demands components of phosphate or carbonate buffers and is not oxidized in their absence. The TAML- and buffer-catalyzed oxidation is subject to severe substrate inhibition, which results in at least 1000-fold retardation of the interaction between the iron(III) resting state of 2 and H 2 O 2 . The inhibition accounts for a unique pH profile for the TAML catalysis with the highest activity at pH 7. Less aggressive TAMLs such as [Fe III {C 6 H 4 -1,2-( N COCMe 2 N CO) 2 CMe 2 }(OH 2 )] - are catalytically inactive. The roles of buffer components in modulating catalysis have been clarified through detailed kinetic investigations of the degradation process, which is first order in the concentration of 2 and shows ascending hyperbolic dependencies in the concentrations of all three participants, i.e., H 2 O 2 , picrate, and phosphate/carbonate. The reactivity trends are consistent with a mechanism involving the formation of double ([LFe III -Q] 2- ) and triple ([LFe III -{Q-H 2 PO 4 }] 3- ) associates, which are unreactive and reactive toward H 2 O 2 , respectively. The binding of phosphate converts [LFe III -Q] 2- to the reactive triple associate. Density functional theory suggests that the stability of the double associate is achieved via both Fe-O phenol binding and π-π stacking. The triple associate is an outer-sphere complex where phosphate binding occurs noncovalently through hydrogen bonds. A linear free energy relationship analysis of the reactivity of the mono-, di-, and trinitro phenols suggests that the rate-limiting step involves an electron transfer from phenolate to an oxidized ironoxo intermediate, giving phenoxy radicals that undergo further rapid oxidation that lead to eventual mineralization.

Bis-sulfonamide bis-amide TAML activator [Fe{4-NO 2 C 6 H 3 -1,2-(NCOCMe 2 NSO 2 ) 2 CHMe}] - (2) catalyzes oxidative degradation of the oxidation-resistant neonicotinoid insecticide, imidacloprid (IMI), by H 2 O 2 at pH 7 and 25 °C, whereas the tetrakis-amide TAML [Fe{4-NO 2 C 6 H 3 -1,2-(NCOCMe 2 NCO) 2 CF 2 }] - (1), previously regarded as the most catalytically active TAML, is inactive under the same conditions. At ultra-low concentrations of both imidacloprid and 2, 62 % of the insecticide was oxidized in 2 h, at which time the catalyst is inactivated; oxidation resumes on addition of a succeeding aliquot of 2. Acetate and oxamate were detected by ion chromatography, suggesting deep oxidation of imidacloprid. Explored at concentrations [2]≥[IMI], the reaction kinetics revealed unusually low kinetic order in 2 (0.164±0.006), which is observed alongside the first order in imidacloprid and an ascending hyperbolic dependence in [H 2 O 2 ]. Actual independence of the reaction rate on the catalyst concentration is accounted for in terms of a reversible noncovalent binding between a substrate and a catalyst, which usually results in substrate inhibition when [catalyst]≪[substrate] but explains the zero order in the catalyst when [2]>[IMI]. A plausible mechanism of the TAML-catalyzed oxidations of imidacloprid is briefly discussed. Similar zero-order catalysis is presented for the oxidation of 3-methyl-4-nitrophenol by H 2 O 2 , catalyzed by the TAML analogue of 1 without a NO 2 -group in the aromatic ring., (© 2020 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim.)

Understanding the catalysis of oxidative reactions by TAML activators of peroxides, i. e. iron(III) complexes of tetraamide macrocyclic ligands, advocated a spectrophotometric procedure for quantifying the catalytic activity of TAMLs for colorless targets (k II ', M -1  s -1 ), which is incomparably more advantageous in terms of time, cost, energy, and ecology than NMR, HPLC, UPLC, GC-MS and other similar techniques. Dyes Orange II or Safranin O (S) are catalytically bleached by non-excessive amount of H 2 O 2 in the presence of colorless substrates (S 1 ) according to the rate law: -d[S]/dt=k I k II [H 2 O 2 ][S][TAML]/(k I [H 2 O 2 ]+k II [S]+k II '[S 1 ]). The bleaching rate is thus a descending hyperbolic function of S 1  : v=ab/(b+[S 1 ]). Values of k II ' found from a and b for phenol and propranolol with commonly used TAML [Fe III {o,o'-C 6 H 4 (NCONMe 2 CO) 2 CMe 2 } 2 (OH 2 )] + are consistent with those for S 1 (phenol, propranolol) obtained directly by UPLC. The study sends vital messages to enzymologists and environmentalists., (© 2020 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim.)

TAML activators enable unprecedented, rapid, ultradilute oxidation catalysis where substrate inhibitions might seem improbable. Nevertheless, while TAML/H 2 O 2 rapidly degrades the drug propranolol, a micropollutant (MP) of broad concern, propranolol is shown to inhibit its own destruction under concentration conditions amenable to kinetics studies ([propranolol] = 50 μM). Substrate inhibition manifests as a decrease in the second-order rate constant k I for H 2 O 2 oxidation of the resting Fe III -TAML (RC) to the activated catalyst (AC), while the second-order rate constant k II for attack of AC on propranolol is unaffected. This kinetics signature has been utilized to develop a general approach for quantifying substrate inhibitions. Fragile adducts [propranolol, TAML] have been isolated and subjected to ESI-MS, florescence, UV-vis, FTIR, 1 H NMR, and IC examination and DFT calculations. Propranolol binds to Fe III -TAMLs via combinations of noncovalent hydrophobic, coordinative, hydrogen bonding, and Coulombic interactions. Across four studied TAMLs under like conditions, propranolol reduced k I 4-32-fold (pH 7, 25 °C) indicating that substrate inhibition is controllable by TAML design. However, based on the measured k I and calculated equilibrium constant K for propranolol-TAML binding, it is possible to project the impact on k I of reducing [propranolol] from 50 μM to the ultradilute regime typical of MP contaminated waters (≤2 ppb, ≤7 nM for propranolol) where inhibition nearly vanishes. Projecting from 50 μM to higher concentrations, propranolol completely inhibits its own oxidation before reaching mM concentrations. This study is consistent with prior experimental findings that substrate inhibition does not impede TAML/H 2 O 2 destruction of propranolol in London wastewater while giving a substrate inhibition assessment tool for use in the new field of ultradilute oxidation catalysis.