Beyond Mimicking Enzymes: NewTAML/Peroxide Abstracts sp3 C-H Bonds to Initiate Biotranscendent Water-Purifying Mineralization of Fluoroquinolone Antibiotics.

In neutral aqueous media under ambient temperature, the bis-amido-bis-sulfonamido-ligated [FeIII{4-NO2C6H3-1,2-(NCOCMe2NSO2)2CHMe}(OH2)]- NewTAML catalyst (2), activates hydrogen peroxide to mimic and greatly surpass enzymatic activity (biotranscendence) by sweeping fluoroquinolone antibiotics rapidly toward minerals. Stepwise identification of intermediates was paired with mechanistic examination of key steps. For ofloxacin, the 2/H2O2 activated catalyst (AC) first attacks ofloxacin's piperazine unit in two enzyme-mimicking parallel pathways, cleaving secondary (desaturation) and primary (N-demethylation) sp3 C-H bonds via H atom abstraction to form dehydro- and desmethyl-ofloxacin, respectively; desaturation is a novel expression of TAML peroxidase-like reactivity. Kinetic data obtained with selectively deuterated ofloxacin compounds revealed for desaturation and N-demethylation, respectively, kinetic isotope effects (kH/kD) of 8.6 and 3.8; ΔH‡ and ΔS‡ are presented. Dehydro- and desmethyl-ofloxacin are further oxidized through several identified intermediates toward minerals; ion chromatography revealed F-, CH3COO-, HCOO-, NO2-, and NO3- as final products. 2/H2O2 similarly oxidizes ciprofloxacin and norfloxacin. Desaturation by 2/H2O2 of 1-methyl-4-phenylpiperazine delivered a rate that is comprehensibly half that of ofloxacin. DFT calculations provided compelling evidence that the 2/H2O2 effective AC is oxidized by two-electrons above the ferric state producing ofloxacin desaturation via sequential hydrogen atom abstraction, single electron transfer and hydrolysis events. Iron(IV) compounds, once considered plausible as ACs in TAML/peroxide C-H bond activations, cannot oxidize ofloxacin sp3 C-H bonds. The temporal toxicity profile of ofloxacin's degradation intermediates based on in silico toxicities highlights that 2/H2O2 can serve as a powerful safe-and-sustainable-by-design (SSbD) fluoroquinolone detoxifying water treatment.