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

## TL;DR

A new catalyst surpasses enzyme-like activity to break down fluoroquinolone antibiotics in water, safely converting them into harmless minerals.

## Contribution

The study introduces a novel TAML/peroxide catalyst that achieves biotranscendence by efficiently mineralizing fluoroquinolones.

## Key findings

- The NewTAML catalyst activates hydrogen peroxide to rapidly oxidize fluoroquinolones like ofloxacin through unique desaturation and N-demethylation pathways.
- Kinetic isotope effects of 8.6 and 3.8 were observed for desaturation and N-demethylation, respectively.
- Final mineralization products include F–, CH3COO–, HCOO–, NO2–, and NO3–, indicating complete detoxification.

## Abstract

In neutral aqueous
media under ambient temperature, the bis-amido-bis-sulfonamido-ligated
[FeIII{4-NO2C6H3-1,2-(NCOCMe2
NSO2)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 (k
H/k
D) 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.