Total degradation of fenitrothion and other organophosphorus pesticides by catalytic oxidation employing Fe-TAML peroxide activators

Rapid analysis of dichlorvos via releasing the phosphate core

Monitoring the residual dichlorvos (O,O-dimethyl-O-2,2-dichlorovinylphosphate, DDVP) in food has received extensive attention owing to its large consumption in agriculture. However, the previous sensing methods are not time-efficient enough due to the long incubation time for enzyme inhibition (tens of minutes to hours) or bottlenecked by the complicated procedures for senor fabrication. Herein, a novel sensing strategy is proposed based on the hydrolysis of DDVP into PO43-. By using alkaline phosphatase for hydrolysis, a certain portion of DDVP was transformed to PO43- within only 8 min. Then, the released PO43- was detected by a fluorescent terbium metal-organic framework (Tb-MOF). The coordination of the naked P-O groups to the metal nodes of the Tb-MOF disturbed the antenna effects of its ligands. Thus, DDVP was quantified by the decrease of the fluorescence of Tb ions. Based on this method, DDVP residues on plum surfaces were collected by swabs and successfully detected. The recovery of DDVP was determined in the range from 105 % to 115 %, demonstrating the quantification accuracy of this method. The detection limit reached 4.7 μM, which was lower than the restricted amount in fruit set by the National Standard of China. The present method provides an efficient and user-friendly way for the detection of DDVP and many other organophosphorus pesticides in food.

Self-Assembled FeIII-TAML-Based Magnetic Nanostructures for Rapid and Sustainable Destruction of Bisphenol A

This study focused on constructing iron(III)-tetraamidomacrocyclic ligand (FeIII-TAML)-based magnetic nanostructures via a surfactant-assisted self-assembly (SAS) method to enhance the reactivity and recoverability of FeIII-TAML activators, which have been widely employed to degrade various organic contaminants. We have fabricated FeIII-TAML-based magnetic nanomaterials (FeIII-TAML/CTAB@Fe3O4, CTAB refers to cetyltrimethylammonium bromide) by adding a mixed solution of FeIII-TAML and NH3·H2O into another mixture containing CTAB, FeCl2 and FeCl3 solutions. The as-prepared FeIII-TAML/CTAB@Fe3O4 nanocomposite showed relative reactivity compared with free FeIII-TAML as indicated by decomposition of bisphenol A (BPA). Moreover, our results demonstrated that the FeIII-TAML/CTAB@Fe3O4 composite can be separated directly from reaction solutions by magnet adsorption and reused for at least four times. Therefore, the efficiency and recyclability of self-assembled FeIII-TAML/CTAB@Fe3O4 nanostructures will enable the application of FeIII-TAML-based materials with a lowered expense for environmental implication.

Boosted electrocatalytic oxidation of organophosphorus pesticides by a novel high-efficiency CeO2-Doped PbO2 anode: An electrochemical study, parameter optimization and degradation mechanisms

This article presents a novel and highly efficient electrocatalytic degradation method for two significant organophosphorus pesticides, fenitrothion (FEN), and methyl parathion (MPN), using a Ti/β-PbO2-CeO2 modified anode (indirect oxidation). A comprehensive electrochemical investigation was also carried out to gain new insight into the redox behavior and destruction pathway of these pesticides (direct oxidation). The study also explores the effects of various operating parameters, such as initial solution pH, applied current density, and initial pesticides concentration, on the conversion-paired electrocatalytic removal process. To further enhance the degradation efficiency, a new configuration of the electrochemical cell was designed, employing two types of electrodes and two independent power supply devices. The conversion paired electrocatalytic degradation process of these pesticides involves first the direct reduction of FEN (or MPN) on a graphite cathode and then the indirect oxidation of reduced FEN (or MPN) by hydroxyl radicals electro generated on the Ti/β-PbO2-CeO2 anode. The synergism of these two processes together will effectively lead to FEN (or MPN) degradation. The degradation percentages of 98% for FEN and 95% for MPN at the optimal conditions for the electrochemical degradation of these pesticides were achieved at pH = 7, initial concentration 50 mg L-1, with a current density of 90 mA cm-2 for direct reduction and 11 mA cm-2 for indirect oxidation. Overall, this study presents a promising and efficient approach for the remediation of organophosphorus pesticide-contaminated environments, offering valuable insights into the electrochemical degradation process and highlighting the potential for practical application in wastewater treatment and environmental protection.

Enhanced Direct Electron Transfer Mediated Contaminant Degradation by Fe(IV) Using a Carbon Black-Supported Fe(III)-TAML Suspension Electrode System

Iron complexes of tetra-amido macrocyclic ligands (Fe-TAML) are recognized to be effective catalysts for the degradation of a wide range of organic contaminants in homogeneous conditions with the high valent Fe(IV) and Fe(V) species generated on activation of the Fe-TAML complex by hydrogen peroxide (H₂O₂) recognized to be powerful oxidants. Electrochemical activation of Fe-TAML would appear an attractive alternative to H₂O₂ activation, especially if the Fe-TAML complex could be attached to the anode, as this would enable formation of high valent iron species at the anode and, importantly, retention of the valuable Fe-TAML complex within the reaction system. In this work, we affix Fe-TAML to the surface of carbon black particles and apply this "suspension anode" process to oxidize selected target compounds via generation of high valent iron species. We show that the overpotential for Fe(IV) formation is 0.17 V lower than the potential required to generate Fe(IV) electrochemically in homogeneous solution and also show that the stability of the Fe(IV) species is enhanced considerably compared to the homogeneous Fe-TAML case. Application of the carbon black-supported Fe-TAML suspension anode reactor to degradation of oxalate and hydroquinone with an initial pH value of 3 resulted in oxidation rate constants that were up to three times higher than could be achieved by anodic oxidation in the absence of Fe-TAML and at energy consumptions per order of removal substantially lower than could be achieved by alternate technologies.

Degradation of Organic Contaminants by Reactive Iron/Manganese Species: Progress and Challenges

Many iron(II, III, VI)- and manganese(II, IV, VII)-based oxidation processes can generate reactive iron/manganese species (RFeS/RMnS, i.e., Fe(IV)/Fe(V) and Mn(III)/Mn(V)/Mn(VI)), which have mild and selective reactivity toward a wide range of organic contaminants, and thus have drawn significant attention. The reaction mechanisms of these processes are rather complicated due to the simultaneous involvement of multiple radical and/or nonradical species. As a result, the ambiguity in the occurrence of RFeS/RMnS and divergence in the degradation mechanisms of trace organic contaminants in the presence of RFeS/RMnS exist in literature. In order to improve the critical understanding of the RFeS/RMnS-mediated oxidation processes, the detection methods of RFeS/RMnS and their roles in the destruction of trace organic contaminants are reviewed with special attention to some specific problems related to the scavenger and probe selection and experimental results analysis potentially resulting in some questionable conclusions. Moreover, the influence of background constituents, such as organic matter and halides, on oxidation efficiency of RFeS/RMnS-mediated oxidation processes and formation of byproducts are discussed through their comparison with those in free radicals-dominated oxidation processes. Finally, the prospects of the RFeS/RMnS-mediated oxidation processes and the challenges for future applications are presented.

A mechanistic switch in C−H bond activation by elusive FeV(O)(TAML) reaction intermediate: A theoretical study

The divergent behavior of C−H bond oxidations of aliphatic substrates compared to those of aromatic substrates shown in Gupta's experiment was mechanistically studied herein by means of density functional theory calculations. Our calculations reveal that such difference is caused by different reaction mechanisms between two kinds of substrates (the aliphatic cyclohexane, 2,3-dimethylbutane and the aromatic toluene, ethylbenzene and cumene). For the aliphatic substrates, C−H oxidation by the oxidant FeV(O)(TAML) is a hydrogen atom transfer process; whereas for the aromatic substrates, C−H oxidation is a proton-coupled electron transfer (PCET) process with a proton transfer character on the transition state, that is, a proton-coupled electron transfer process holding a proton transfer-like transition state (PCET(PT)). This difference is caused by the strong π− π interactions between the tetra-anionic TAML ring and the phenyl ring of the aromatic substrates, which has a “pull” effect to make the electron transfer from substrates to the Fe=O moiety inefficient.

An amplified fluorescence polarization assay for sensitive sensing of organophosphorus pesticides via MnO2 nanosheets

It is highly desirable to develop a simple, efficient and sensitive strategy for organophosphorus pesticides (OPs) in both environment pollution and human health. Herein, a novel amplified fluorescence polarization (FP) biosensor was established for highly sensitive detection of OPs using MnO₂ nanosheets as the signal enhancer. In this system, OPs can suppress the activity of acetylcholinesterase (AChE) efficiently, blocking the hydrolysis reaction of acetylthiocholine (ATCh) to generate thiocholine (TCh) by AChE. TCh can lead the decomposition of MnO₂ nanosheets to manganese ions. So, without the influence of TCh, MnO₂ nanosheets can maintain its original shape and form a stable complex with FAM-DNA, which greatly enhanced the FP signal. This method can tremendously improve the sensitivity of FP with a detection limit of 0.01 ng/mL for diazinon. In addition, it was also applicable to determine other four OPs and investigate the level of diazinon in real water samples. Consequently, the proposed approach provides a new promising platform for detection of OPs and is expected to be used in application of environmental monitoring.

Engineering the Oxidative Potency of Non-Heme Iron(IV) Oxo Complexes in Water for C-H Oxidation by a cis Donor and Variation of the Second Coordination Sphere

A series of iron(IV) oxo complexes, which differ in the donor (CH₂py or CH₂COO^-) cis to the oxo group, three with hemilabile pendant donor/second coordination sphere base/acid arms (pyH/py or ROH), have been prepared in water at pH 2 and 7. The ν_Fe═O values of 832 ± 2 cm^-1 indicate similar Fe^IV═O bond strengths; however, different reactivities toward C-H substrates in water are observed. HAT occurs at rates that differ by 1 order of magnitude with nonclassical KIEs (k_H/k_D = 30-66) consistent with hydrogen atom tunneling. Higher KIEs correlate with faster reaction rates as well as a greater thermodynamic stability of the iron(III) resting states. A doubling in rate from pH 7 to pH 2 for substrate C-H oxidation by the most potent complex, that with a cis-carboxylate donor, [Fe^IVO(Htpena)]²⁺, is observed. Supramolecular assistance by the first and second coordination spheres in activating the substrate is proposed. The lifetime of this complex in the absence of a C-H substrate is the shortest (at pH 2, 3 h vs up to 1.3 days for the most stable complex), implying that slow water oxidation is a competing background reaction. The iron(IV)═O complex bearing an alcohol moiety in the second coordination sphere displays significantly shorter lifetimes due to a competing selective intramolecular oxidation of the ligand.

Turn-on fluorescent probe towards glyphosate and Cr3+ based on Cd(ii)-metal organic framework with Lewis basic sites

Lewis basic site-functionalized porous Cd(ii)-MOF as a bi-functional fluorescent sensor of glyphosate and Cr³⁺ with exceptional LODs.

Application of FeIII-TAML/H2O2 system for treatment of fluoroquinolone antibiotics

Over the recent past, fluoroquinolone antibiotics (FQs) have raised extensive attention due to their potential to induce the formation of resistance genes and "superbugs", thus various advanced oxidation techniques have been developed to eliminate their release into the environment. In the present study, the prototype tetraamido macrocyclic ligand (Fe^III-TAML)/hydrogen peroxide (H₂O₂) system is employed to degrade FQs (i.e., norfloxacin and ciprofloxacin) over a wide pH range (i.e., pH 6-10), and the reaction rate increases with the increase in pH level. The effect of dosage of Fe^III-TAML and H₂O₂ on the degradation of FQs is evaluated, and the reaction rate is linearly correlated with the added amount of chemicals. Moreover, the impact of natural organic matters (NOM) on the removal of FQs is investigated, and the degradation kinetics show that both NOM type and experimental concentration exhibit negligible influence on the oxidative degradation of selected antibiotics. Based on the results of liquid chromatography-high resolution mass spectrometry and theoretical calculations, the reaction sites and pathways of FQs by Fe^III-TAML/H₂O₂ system are further predicted and elucidated.

Rapid destruction of triclosan by Iron(III)-Tetraamidomacrocyclic ligand/hydrogen peroxide system

Iron(III)-tetraamidomacrocyclic ligand (Fe(III)-TAML) activators can activate hydrogen peroxide to oxidize many kinds of organic pollutants. In this study, we investigated the degradation of triclosan, a widely used broad-spectrum bactericide, under the treatment of Fe(III)-TAML/H₂O₂ system at different pH conditions. We also studied the influence of natural organic matter (NOM) on the degradation process. Our results showed that complete removal of triclosan could be obtained within several minutes under the optimal conditions. The degradation of triclosan by Fe(III)-TAML/H₂O₂ system exhibited strong pH-dependence and the degradation rate increased with the increase in pH level from 7.0 to 10.0. When adding fulvic acid (FA) or humic acid (HA) in the reaction system, the degradation of triclosan could be suppressed slightly, and HA exhibited stronger inhibition than FA. Based on the analysis of reaction intermediates, phenoxyl radical reaction and ring open reaction were involved in the decomposition of triclosan. Significant inhibition of overall toxicity to Photobacterium phosphoreum further confirmed the high efficiency of Fe(III)-TAML/H₂O₂ system for the removal of antibiotic activities resulting from the parent triclosan molecule and its degradation products.

Designing Materials for Aqueous Catalysis: Ionic Liquid Gel and Silica Sphere Entrapped Iron-TAML Catalysts for Oxidative Degradation of Dyes

Materials have been developed that encapsulate a homogeneous catalyst and enable it to operate as a heterogeneous catalyst in water. A hydrophobic ionic liquid within the material was used to dissolve Fe-TAML and keep it from leaching into the aqueous phase. One-pot processes were used to entrap Fe-TAML in basic ionic liquid gels, and ionic liquid gel spheres structured via a modified Stöber synthesis forming SiO₂ particles of uniform size. Catalytic activity was demonstrated via the oxidative degradation of dyes. Fe-TAML entrapped in a basic ionic liquid gel exhibited consistent activity in five recycles. This discovery of heterogenized H₂O₂ activators prepared by sol-gel and Stöber processes opens new possibilities for the creation of engineered catalytic materials for water purification.

Self-assembly of FeIII-TAML-based microstructures for rapid degradation of bisphenols

Iron(III)-tetraamidomacrocyclic ligand (Fe^III-TAML) activators have drawn great attentions due to the high reactivity to degrade organic pollutants. However, previous studies showed that the reactivity and stability of Fe^III-TAML were both strongly pH-dependent, which dramatically decrease at lower pH levels. Herein, Fe^III-TAML/DODMA (dimethyldioctadecylammonium chloride) microspheres with diameters ranging from 100 to 2000 nm were synthesized via a surfactant-assisted self-assembly technique. The newly synthesized Fe^III-TAML/DODMA composite exhibits superior reactivity compared to free Fe^III-TAML as indicated by the degradation of bisphenols (i.e., bisphenol A and its analogues) over a wide pH range (i.e., pH 4.5-10.0). Based on the adsorption results and quantitative structure-activity relationship (QSAR) models, the enhanced reactivity of Fe^III-TAML/DODMA is mainly ascribed to the hydrophobic sorption of bisphenols. Moreover, the enhanced ionization of the axial water molecule associated with Fe^III-TAML could further enhance the reactivity of synthesized microcomposites, which was confirmed by the results of infrared and Raman spectra. Furthermore, Fe^III-TAML/DODMA shows distinct acid-resistance as explained by the protection of the hydrophobic alkyl chains of DODMA. This novel method would provide a simple and effective strategy to expand the application of Fe^III-TAML in a wide pH range and render Fe^III-TAML/DODMA microstructure as a potential catalyst for treatment of bisphenol compounds.

Zero-Order Catalysis in TAML-Catalyzed Oxidation of Imidacloprid, a Neonicotinoid Pesticide

Bis-sulfonamide bis-amide TAML activator [Fe{4-NO₂ C₆ H₃ -1,2-(NCOCMe₂ NSO₂ )₂ CHMe}]^- (2) catalyzes oxidative degradation of the oxidation-resistant neonicotinoid insecticide, imidacloprid (IMI), by H₂ O₂ at pH 7 and 25 °C, whereas the tetrakis-amide TAML [Fe{4-NO₂ C₆ H₃ -1,2-(NCOCMe₂ NCO)₂ CF₂ }]^- (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 [H₂ O₂ ]. 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 H₂ O₂ , catalyzed by the TAML analogue of 1 without a NO₂ -group in the aromatic ring.

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

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 H₂ O₂ in the presence of colorless substrates (S₁ ) according to the rate law: -d[S]/dt=k_I k_II [H₂ O₂ ][S][TAML]/(k_I [H₂ O₂ ]+k_II [S]+k_II '[S₁ ]). The bleaching rate is thus a descending hyperbolic function of S₁  : v=ab/(b+[S₁ ]). Values of k_II ' found from a and b for phenol and propranolol with commonly used TAML [Fe^III {o,o'-C₆ H₄ (NCONMe₂ CO)₂ CMe₂ }₂ (OH₂ )]⁺ are consistent with those for S₁ (phenol, propranolol) obtained directly by UPLC. The study sends vital messages to enzymologists and environmentalists.

2H and 13C isotope fractionation analysis of organophosphorus compounds for characterizing transformation reactions in biogas slurry: Potential for anaerobic treatment of contaminated biomass

The ability of anaerobic digestion (AD) to eliminate organophosphorus model compounds (OPs) with structural elements of phosphate, phosphorothioate and phosphorodithioate esters was studied. The enzymatic mechanism of the first irreversible degradation reaction was characterized using metabolite pattern and kinetic ²H/¹³C-isotope effect in original, cell-free and heat sterilized biogas slurry. The isotope fractionation study suggests different modes of degradation reactions. Representatives for phosphate ester, tris(2-chloroethyl) phosphate and tris(1,3-dichloro-2-propyl) phosphate, were hydrolyzed in biogas slurry without carbon or hydrogen isotope fractionation. Representatives for phosphorodithioate, Dimethoate and Malathion, were degraded in original slurry yielding carbon enrichment factor (ε_C) of -0.6 ± 0.1‰ and -5.5 ± 0.1‰ (-0.9 ± 0.1‰ and -7.2 ± 0.5‰ in cell-free slurry), without hydrogen isotope fractionation. Phosphorothioate degradation represented by Parathion and Parathion-methyl yielded surprisingly different ε_C (-0.7 ± 0.2 and -3.6 ± 0.4‰) and ε_H (-33 ± 5 and -5 ± 1‰) in original slurry compared to cell-free slurry (ε_C = -2.5 ± 0.5 and -8.6 ± 1.4‰; ε_H = -61 ± 10 and -10 ± 3‰) suggesting H-C bond cleavage. Degradation of Parathion and Parathion-methyl in sterilized slurry gave carbon but not hydrogen fractionation implying relative thermostable enzymatic activity with different mechanism. The correlation of ²H and ¹³C stable isotope fractionation of Parathion in biogas slurry showed distinct pattern (Λ_original = 31 ± 11, Λ_cell-free = 20 ± 2), indicating different mechanism from chemical hydrolysis. Overall, AD can be a potential treatment for OPs contaminated biomass or contaminated organic waste material.

Recent advances in metalloporphyrins for environmental and energy applications

Porphyrin-based chemistry has reached an unprecedented period of rapid development after decades of study. Due to attractive multifunctional properties, porphyrins and their analogues have emerged as multifunctional organometals for environmental and energy purposes. In particular, pioneer works have been conducted to explore their application in pollution abatement, energy conversion and storage and molecule recognition. This review summarizes recent advances of porphyrins chemistry, focusing on elucidating the nature of catalytic process. The Fenton-like redox chemistry and photo-excitability of porphyrins and their analogues are discussed, highlighting the generation of high-valent iron oxo porphyrin species. Finally, challenges in current research are identified and perspectives for future development in this area are presented.

Quantitative structure-activity relationship for the oxidation of aromatic organic contaminants in water by TAML/H2O2

Tetra-amido macrocyclic ligand (TAML) activator is a functional analog of peroxidase enzymes, which activates hydrogen peroxide (H₂O₂) to form high valence iron-oxo complexes that selectively degrade persistent aromatic organic contaminants (ACs) in water. Here, we develop quantitative structure-activity relationship (QSAR) models based on measured pseudo first-order kinetic rate coefficients (k_obs) of 29 ACs (e.g., phenols and pharmaceuticals) oxidized by TAML/H₂O₂ at neutral and basic pH values to gain mechanistic insight on the selectivity and pH dependence of TAML/H₂O₂ systems. These QSAR models infer that electron donating ability (E_HOMO) is the most important AC characteristic for TAML/H₂O₂ oxidation, pointing to a rate-limiting single-electron transfer (SET) mechanism. Oxidation rates at pH 7 also depend on AC reactive indices such as f_min^- and qH⁺, which respectively represent propensity for electrophilic attack and the most positive net atomic charge on hydrogen atoms. At pH 10, TAML/H₂O₂ is more reactive towards ACs with a lower hydrogen to carbon atoms ratio (#H:C), suggesting the significance of hydrogen atom abstraction. In addition, lnk_obs of 14 monosubstituted phenols is negatively correlated with Hammett constants (σ) and exhibits similar sensitivity to substituent effects as horseradish peroxidase. Although accurately predicting degradation rates of specific ACs in complex wastewater matrices could be difficult, these QSAR models are statistically robust and help predict both relative degradability and reaction mechanism for TAML/H₂O₂-based treatment processes.

Detection of Pesticide Residues (Fenitrothion) in Fruit Samples Based On Niobium Carbide@Molybdenum Nanocomposite: An Electrocatalytic Approach

We have reported an effective electrochemical sensor for assorted pesticide (i.e., Fenitrothion). Exact tracking of these pesticides has become more important for protecting the environment and food resources owing to their high toxicity. Hence, the development of compatible sensors for the real-time detection of pesticides is imperative to overcome practical limitations encountered in conventional methodologies. In this regard, the role of the novel, advanced functional materials such as niobium carbide (NbC) supported on molybdenum nanoparticles (NbC@Mo) has drawn great consideration in conventional sensory systems because of their numerous advantages over other nanomaterials. The nanocomposite was characterized by XRD, XPS, HR-TEM, and EIS. Under optimized working conditions, the modified electrode NbC@Mo/SPCE responds linearly as 0.01-1889 μM concentration range and the detection limit is 0.15 nM. Most importantly, the method was successfully demonstrated in fruit samples.

Characterization of the 3-methyl-4-nitrophenol degradation pathway and genes of Pseudomonas sp. strain TSN1

3-Methyl-4-nitrophenol (3M4NP) is formed in soil as a hydrolysis product of fenitrothion, one of the major organophosphorus pesticides. A Pseudomonas strain was isolated as a 3M4NP degrader from a crop soil and designated TSN1. This strain utilized 3M4NP as a sole carbon and energy source. To elucidate the biodegradation pathway, we performed transposon mutagenesis with pCro2a (mini-Tn5495) and obtained three mutants accumulating a dark pink compound(s) from 3M4NP. Rescue cloning and sequence analysis revealed that in all mutants, the transposon disrupted an identical aromatic compound meta-cleaving dioxygenase gene, and a monooxygenase gene was located just downstream of the dioxygenase gene. These two genes were designated mnpC and mnpB, respectively. The gene products showed high identity with the methylhydroquinone (MHQ) monooxygenase (58%) and the 3-methylcatechol 2,3-dioxygenase (54%) of a different 3M4NP degrader Burkholderia sp. NF100. The transposon mutants converted 3M4NP or MHQ into two identical metabolites, one of which was identified as 2-hydroxy-5-methyl-1,4-benzoquinone (2H5MBQ) by GC/MS analysis. Furthermore, two additional genes (named mnpA1 and mnpA2), almost identical to the p-nitrophenol monooxygenase and the p-benzoquinone reductase genes of Pseudomonas sp. WBC-3, were isolated from the total DNA of strain TSN1. Disruption of mnpA1 resulted in the complete loss of the 3M4NP degradation activity, demonstrating that mnpA1 encodes the initial monooxygenase for 3M4NP degradation. The purified mnpA2 gene product could efficiently reduce methyl p-benzoquinone (MBQ) into MHQ. These results suggest that strain TSN1 degrades 3M4NP via MBQ, MHQ, and 2H5MBQ in combination with mnpA1A2 and mnpCB, existing at different loci on the genome.

Metabolism of an Insecticide Fenitrothion by Cunninghamella elegans ATCC36112

In this study, the detailed metabolic pathways of fenitrothion (FNT), an organophosphorus insecticide by Cunninghamella elegans, were investigated. Approximately 81% of FNT was degraded within 5 days after treatment with concomitant accumulation of four metabolites (M1-M4). The four metabolites were separated by high-performance liquid chromatography, and their structures were identified by mass spectroscopy and/or nuclear magnetic resonance. M3 is confirmed to be an initial precursor of others and identified as fenitrothion-oxon. On the basis of their metabolic profiling, the possible metabolic pathways involved in phase I and II metabolism of FNT by C. elegans was proposed. We also found that C. elegans was able to efficiently and rapidly degrade other organophosphorus pesticides (OPs). Thus, these results will provide insight into understanding of the fungal degradation of FNT and the potential application for bioremediation of OPs. Furthermore, the ability of C. elegans to mimic mammalian metabolism would help us elucidate the metabolic fates of organic compounds occurring in mammalian liver cells and evaluate their toxicity and potential adverse effects.

Electrochemically Generated cis-Carboxylato-Coordinated Iron(IV) Oxo Acid-Base Congeners as Promiscuous Oxidants of Water Pollutants

The nonheme iron(IV) oxo complex [Fe^IV(O)(tpenaH)]²⁺ and its conjugate base [Fe^IV(O)(tpena)]⁺ [tpena^- = N,N,N'-tris(2-pyridylmethyl)ethylenediamine-N'-acetate] have been prepared electrochemically in water by bulk electrolysis of solutions prepared from [Fe^III₂(μ-O)(tpenaH)₂](ClO₄)₄ at potentials over 1.3 V (vs NHE) using inexpensive and commercially available carbon-based electrodes. Once generated, these iron(IV) oxo complexes persist at room temperature for minutes to half an hour over a wide range of pH values. They are capable of rapidly decomposing aliphatic and aromatic alcohols, alkanes, formic acid, phenols, and the xanthene dye rhodamine B. The oxidation of formic acid to carbon dioxide demonstrates the capacity for total mineralization of organic compounds. A radical hydrogen-atom-abstraction mechanism is proposed with a reactivity profile for the series that is reminiscent of oxidations by the hydroxyl radical. Facile regeneration of [Fe^IV(O)(tpenaH)]²⁺/ [Fe^IV(O)(tpena)]⁺ and catalytic turnover in the oxidation of cyclohexanol under continuous electrolysis demonstrates the potential of the application of [Fe^III(tpena)]²⁺ as an electrocatalyst. The promiscuity of the electrochemically generated iron(IV) oxo complexes, in terms of the broad range of substrates examined, represents an important step toward the goal of cost-effective electrocatalytic water purification.

Rapid Destruction of Tetrabromobisphenol A by Iron(III)-Tetraamidomacrocyclic Ligand/Layered Double Hydroxide Composite/H2O2 System

Iron(III)-tetraamidomacrocyclic ligand (Fe(III)-TAML) activators have received widespread attentions for their abilities to activate hydrogen peroxide to oxidize many organic pollutants. In this study, Fe(III)-TAML/layered double hydroxide (LDH) composite was developed by intercalating Fe(III)-TAML into the interlayer of LDH. Electrostatic interaction and hydrogen bonding might account for the adsorption of Fe(III)-TAML on LDH. The newly synthesized Fe(III)-TAML/LDH composite showed superior reactivity as indicated by efficient decomposition of tetrabromobisphenol A (TBBPA) in the presence of hydrogen peroxide, which can be fully degraded within 20 s and the degradation rate increased up to 8 times compared to free Fe(III)-TAML. In addition, the toxicity of the system was significantly reduced after the reaction. The higher reactivity of Fe(III)-TAML/LDH system is attributed to the enhanced adsorption of TBBPA on LDH, which could increase the contact possibility between Fe(III)-TAML and TBBPA. On the basis of the analysis of reaction intermediates, β-scission at the middle carbon atom and C-Br bond cleavage in phenyl ring of TBBPA were involved in the degradation process. Furthermore, our results demonstrated that the Fe(III)-TAML/LDH composite can be reused several times, which could lower the overall cost for environmental implication and render Fe(III)-TAML/LDH as the potential environmentally friendly catalyst for future wastewater treatment under mild reaction conditions.

TAML/H2O2 Oxidative Degradation of Metaldehyde: Pursuing Better Water Treatment for the Most Persistent Pollutants

The extremely persistent molluscicide, metaldehyde, widely used on farms and gardens, is often detected in drinking water sources of various countries at concentrations of regulatory concern. Metaldehyde contamination restricts treatment options. Conventional technologies for remediating dilute organics in drinking water, activated carbon, and ozone, are insufficiently effective against metaldehyde. Some treatment plants have resorted to effective, but more costly UV/H2O2. Here we have examined if TAML/H2O2 can decompose metaldehyde under laboratory conditions to guide development of a better real world option. TAML/H2O2 slowly degrades metaldehyde to acetaldehyde and acetic acid. Nuclear magnetic resonance spectroscopy ((1)H NMR) was used to monitor the degradation-the technique requires a high metaldehyde concentration (60 ppm). Within the pH range of 6.5-9, the reaction rate is greatest at pH 7. Under optimum conditions, one aliquot of TAML 1a (400 nM) catalyzed 5% degradation over 10 h with a turnover number of 40. Five sequential TAML aliquots (2 μM overall) effected a 31% removal over 60 h. TAML/H2O2 degraded metaldehyde steadily over many hours, highlighting an important long-service property. The observation of metaldehyde decomposition under mild conditions provides a further indication that TAML catalysis holds promise for advancing water treatment. These results have turned our attention to more aggressive TAML activators in development, which we expect will advance the observed technical performance.

Bimetallic synergistic degradation of chlorophenols by CuCoOx–LDH catalyst in bicarbonate-activated hydrogen peroxide system

A CuCoO_x–LDH-based catalyst demonstrated high activity for chlorophenol degradation with low leaching in a bicarbonate-activated hydrogen peroxide system.

Activation of Dioxygen by a TAML Activator in Reverse Micelles: Characterization of an Fe(III)Fe(IV) Dimer and Associated Catalytic Chemistry

Iron TAML activators of peroxides are functional catalase-peroxidase mimics. Switching from hydrogen peroxide (H2O2) to dioxygen (O2) as the primary oxidant was achieved by using a system of reverse micelles of Aerosol OT (AOT) in n-octane. Hydrophilic TAML activators are localized in the aqueous microreactors of reverse micelles where water is present in much lower abundance than in bulk water. n-Octane serves as a proximate reservoir supplying O2 to result in partial oxidation of Fe(III) to Fe(IV)-containing species, mostly the Fe(III)Fe(IV) (major) and Fe(IV)Fe(IV) (minor) dimers which coexist with the Fe(III) TAML monomeric species. The speciation depends on the pH and the degree of hydration w0, viz., the amount of water in the reverse micelles. The previously unknown Fe(III)Fe(IV) dimer has been characterized by UV-vis, EPR, and Mössbauer spectroscopies. Reactive electron donors such as NADH, pinacyanol chloride, and hydroquinone undergo the TAML-catalyzed oxidation by O2. The oxidation of NADH, studied in most detail, is much faster at the lowest degree of hydration w0 (in "drier micelles") and is accelerated by light through NADH photochemistry. Dyes that are more resistant to oxidation than pinacyanol chloride (Orange II, Safranine O) are not oxidized in the reverse micellar media. Despite the limitation of low reactivity, the new systems highlight an encouraging step in replacing TAML peroxidase-like chemistry with more attractive dioxygen-activation chemistry.

Removal of ecotoxicity of 17α-ethinylestradiol using TAML/peroxide water treatment

17α-ethinylestradiol (EE2), a synthetic oestrogen in oral contraceptives, is one of many pharmaceuticals found in inland waterways worldwide as a result of human consumption and excretion into wastewater treatment systems. At low parts per trillion (ppt), EE2 induces feminisation of male fish, diminishing reproductive success and causing fish population collapse. Intended water quality standards for EE2 set a much needed global precedent. Ozone and activated carbon provide effective wastewater treatments, but their energy intensities and capital/operating costs are formidable barriers to adoption. Here we describe the technical and environmental performance of a fast- developing contender for mitigation of EE2 contamination of wastewater based upon small- molecule, full-functional peroxidase enzyme replicas called "TAML activators". From neutral to basic pH, TAML activators with H2O2 efficiently degrade EE2 in pure lab water, municipal effluents and EE2-spiked synthetic urine. TAML/H2O2 treatment curtails estrogenicity in vitro and substantially diminishes fish feminization in vivo. Our results provide a starting point for a future process in which tens of thousands of tonnes of wastewater could be treated per kilogram of catalyst. We suggest TAML/H2O2 is a worthy candidate for exploration as an environmentally compatible, versatile, method for removing EE2 and other pharmaceuticals from municipal wastewaters.

Effective adsorption and enhanced removal of organophosphorus pesticides from aqueous solution by Zr-based MOFs of UiO-67

Though many efforts have been devoted to the adsorptive removal of hazardous materials of organophosphorus pesticides (OPs), it is still highly desirable to develop novel adsorbents with high adsorption capacities. In the current work, the removal of two representative OPs, glyphosate (GP) and glufosinate (GF), was investigated by the exceptionally stable Zr-based MOFs of UiO-67. The abundant Zr-OH groups, resulting from the missing-linker induced terminal hydroxyl groups and the inherent bridging ones in Zr-O clusters of UiO-67 particles, served as natural anchorages for efficient GP and GF capture in relation with their high affinity toward phosphoric groups in OPs. The correlation between the most significant parameters such as contact time, OPs concentration, adsorbent dose, pH, as well as ionic strength with the adsorption capacities was optimized, and the effects of these parameters on the removal efficiency of GP and GF from the polluted aqueous solution were investigated. The adsorption of GP on UiO-67 was faster than that of GF, and a pseudo-second-order rate equation effectively described the uptake kinetics. The Langmuir model exhibited a better fit to adsorption isotherm than the Freundlich model. Thanks to the strong affinity and adequate pore size, the adsorption capacities in UiO-67 approached as high as 3.18 mmol (537 mg) g(-1) for GP and 1.98 mmol (360 mg) g(-1) for GF, which were much higher than those of many other reported adsorbents. The excellent adsorption characteristics of the current adsorbents toward OPs were preserved in a wide pH window and high concentration of the background electrolytes. These prefigured the promising potentials of UiO-67 as novel adsorbent for the efficient removal of OPs from aqueous solution.

Rapid degradation of oxidation resistant nitrophenols by TAML activator and H2O2

TAML and H₂O₂remove toxic nitrophenol pollutants producing innocuous minerals. Mechanistic studies reveal the substrate inhibition due to the reversible binding of nitrophenolate to iron(iii) of the TAML resting state.

Rhodium-catalyzed oxidative C-H activation/cyclization for the synthesis of phosphaisocoumarins and phosphorous 2-pyrones

Rhodium-catalyzed cyclization of phosphinic acids and phosphonic monoesters with alkynes has been developed. The oxidative annulation proceeds with complete conversion of phosphinic acid derivatives and allowed the atom-economic preparation of useful phosphaisocoumarins with high yield and selectivity. The reaction is tolerant of extensive substitution on the phosphinic acid, phosphonic monoester and alkyne, including halides, ketone, and hydroxyl groups as substituents. Furthermore, we found that alkenylphosphonic monoesters proceed to give a wide range of phosphorus 2-pyrones through oxidative annulation with alkynes. Mechanistic studies revealed that C-H bond metalation was the rate-limiting step.

Robust iron coordination complexes with N-based neutral ligands as efficient Fenton-like catalysts at neutral pH

The homogeneous Fenton-like oxidation of organic substrates in water with hydrogen peroxide, catalyzed by six different metal coordination complexes with N-based neutral ligands, was studied at ambient conditions and initial pH 7, employing hydrogen peroxide as the terminal oxidant. At low catalyst concentration, the catalytic oxidative depletion of toluene achieved by selected catalysts was much more efficient than that obtained by the Fenton reagent at pH 3. The influence of pH, the water matrix and the catalyst/hydrogen peroxide concentration were investigated for the oxidation of toluene employing [FeCl2(bpmcn)] (1, bpmcn = N,N'-bis(2-pyridylmethyl)-N,N'-dimethyl-trans-1,2-diaminocyclohexane), the most efficient catalyst of the series. Moreover, the evolution of catalysts [FeCl2(bpmcn)] (1) and [Fe(OTf)2(Pytacn)] (3, Pytacn = 1-(2-pyridylmethyl)-4,7-dimethyl-1,4,7-triazacyclononane, OTf = trifluoromethanesulfonate anion) during the course of the reaction was also studied by electrospray ionization mass spectrometry (ESI-MS). The oxidation products derived from toluene oxidation were also analyzed. A plausible mechanism of toluene degradation using [FeCl2(bpmcn)] (1) and [Fe(OTf)2(Pytacn)] (3) as catalysts was proposed, which involves the coexistence of a metal-based path, analogous to that operating in organic media where substrate oxidation is executed by an iron(V)-oxo-hydroxo species, in parallel to a Fenton-type process where hydroxyl radicals are formed.

Zebrafish Assays as Developmental Toxicity Indicators in The Design of TAML Oxidation Catalysts

TAML activators promise a novel water treatment approach by efficiently catalysing peroxide-based degradation of chemicals of high concern at environmental concentrations. Green design ethics demands an exploration of TAML toxicity. Exposure to high concentrations of certain activators caused adverse effects in zebrafish. At typical TAML operational concentrations, development was not perturbed.

TAML activator/peroxide-catalyzed facile oxidative degradation of the persistent explosives trinitrotoluene and trinitrobenzene in micellar solutions

TAML activators are well-known for their ability to activate hydrogen peroxide to oxidize persistent pollutants in water. The trinitroaromatic explosives, 2,4,6-trinitrotoluene (TNT) and 1,3,5-trinitrobenzene (TNB), are often encountered together as persistent, toxic pollutants. Here we show that an aggressive TAML activator with peroxides boosts the effectiveness of the known surfactant/base promoted breakdown of TNT and transforms the surfactant induced nondestructive binding of base to TNB into an extensive multistep degradation process. Treatment of basic cationic surfactant solutions of either TNT or TNB with TAML/peroxide (hydrogen peroxide and tert-butylhydroperoxide, TBHP) gave complete pollutant removal for both in <1 h with >75% of the nitrogen and ≥20% of the carbon converted to nitrite/nitrate and formate, respectively. For TNT, the TAML advantage is to advance the process toward mineralization. Basic surfactant solutions of TNB gave the colored solutions typical of known Meisenheimer complexes which did not progress to degradation products over many hours. However with added TAML activator, the color was bleached quickly and the TNB starting compound was degraded extensively toward minerals within an hour. A slower surfactant-free TAML activator/peroxide process also degrades TNT/TNB effectively. Thus, TAML/peroxide amplification effectively advances TNT and TNB water treatment giving reason to explore the environmental applicability of the approach.