Oxidative Catalysis by TAMLs: Obtaining Rate Constants for Non‐Absorbing Targets by UV‐Vis Spectroscopy

Abstract

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 (kII′, 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 H2O2 in the presence of colorless substrates (S1) according to the rate law: −d[S]/dt=kIkII[H2O2][S][TAML]/(kI[H2O2]+kII[S]+kII′[S1]). The bleaching rate is thus a descending hyperbolic function of S1 : v=ab/(b+[S1]). Values of kII′ found from a and b for phenol and propranolol with commonly used TAML [FeIII{o,o′‐C6H4(NCONMe2CO)2CMe2}2(OH2)]+ are consistent with those for S1 (phenol, propranolol) obtained directly by UPLC. The study sends vital messages to enzymologists and environmentalists.

Predicting Properties of Iron(III) TAML Activators of Peroxides from Their III/IV and IV/V Reduction Potentials or a Lost Battle to Peroxidase

“…The general mechanism of catalysis by TAMLs in Equations (1) and (2) implies that the catalytic activity is determined by the values of rate constants k I and k II . The former is substrate independent in the absence of substrate inhibition, [20] though the latter is always a function of an electron donor substrate S. S are customarily classified as fast‐to‐oxidize and slow‐to‐oxidize substrates on the basis of their reactivities [21, 22] . The corresponding k II values are different as well.…”

“…Theg eneral mechanismo fc atalysis by TAMLsi nE quations (1) and( 2) impliest hatt he catalytica ctivityi sd eterminedb yt he values of rate constants k I and k II .T he former is substratei ndependenti nt he absenceo fs ubstrate inhibition, [20] though the latterisa lwaysafunctionofa nelectrondonor substrateS .Sare customarilyc lassifieda sf ast-to-oxidize ands low-to-oxidize substrates on theb asis of theirr eactivities. [21,22] Thec orresponding k II values ared ifferent as well.N eedlesst os ay,f or onep articular S, the k II values depend on thenatureofT AML,and this dependence is strong.S omeT AMLa ctivatorsa re inactivet oward slowto-oxidize substrates.I np articular, 1a does notc atalyzet he oxidation of propranololb yH 2 O 2 ,b ut 1b does; [20] 1b is inactive toward imidacloprid, though 2d is active. [23] Note that thesefour TAMLsc atalyzet he oxidationo ff ast-to-oxidize Orange II dye.…”

Transformative Catalysis Purifies Municipal Wastewater of Micropollutants

“…TAML catalysts − (Figure ) are bioinspired, miniaturized replicas (typically <1% by mass) of the peroxidase enzymes that faithfully mimic the efficient enzymatic catalytic cycle . The latest-generation TAMLs (e.g., 2 is the current best overall technical performer) outperform their predecessors (e.g., 1 ), which have been previously shown to activate peroxide to effectively degrade MPs, including pharmaceuticals, pesticides, natural and synthetic estrogens and testosterone, antimicrobials, bacterial spores, explosives, , dyes, , industrial chemicals including bisphenol A, and many more. , In a study on wastewater samples from a London Municipal Wastewater Treatment Plant (MWWTP), the highest-performance earlier-generation TAML system, 1 (40 and 80 nM) with H 2 O 2 (20 ppm), impressively degraded 11 priority MPs of the U.K. water industry present initially in parts per trillion to low parts per billion concentrations . However, 1 is an organofluorine catalyst.…”

Quantifying evolving toxicity in the TAML/peroxide mineralization of propranolol

“…In our execution of this study, propranolol is oxidized to near mineralization Our oxidation system is composed of hydrogen peroxide as the primary oxidant and an iron(III)-TAML peroxide activator (Figure 1), that closely replicates key steps of the catalytic cycles of peroxidase and cytochrome P450 enzymes (Collins, 2002;Collins et al, 2010, Collins andRyabov and Collins, 2009). In water, TAMLs catalyze the oxidation of a broad spectrum of molecules, including MPs (Kundu et al, 2013;Mills et al, 2015;Somasundar et al, 2020;Tang et al, 2016;Warner et al, 2020) according to Scheme 1. The mechanism in Scheme 1, when the oxidation is not complicated by extra phenomena , leads to the kinetic Equation 1.…”