Bond Hydroxylation Research Articles

A Thermostable Heme Protein Fold Adapted for Stereoselective C-H Bond Hydroxylation Using Peroxygenase Activity.

Thermostable protein folds of natural and synthetic origin are highly sought-after templates for biocatalyst generation due to their enhanced stability to elevated temperatures which overcomes one of the major limitations of applying enzymes for synthesis. Cytochrome P450 enzymes (CYPs) are a family of heme-thiolate monooxygenases that catalyse the oxidation of their substrates in a highly stereo- and regio-selective manner. The CYP enzyme (CYP107PQ1) from the thermophilic bacterium Meiothermus ruber binds the norisoprenoid β-ionone and was employed as a scaffold for catalyst design. The I-helix was modified to convert this enzyme from a monooxygenase into a peroxygenase (CYP107PQ1QE), enabling the enantioselective oxidation of β-ionone to (S)-4-hydroxy-β-ionone (94% e.e.). The enzyme was resistant to 20 mM H2O2, 20% (v/v) of organic solvent, supported over 1700 turnovers and was fully functional after incubation at 60 °C for 1 h and 30 °C for 365 days. The reaction was scaled-up to generate multi milligram quantities of the product for characterisation. Overall, we demonstrate that sourcing a CYP protein fold from an extremophile enabled the design of a highly stable enzyme for stereoselective C-H bond activation only using H2O2 as the oxidant, providing a viable strategy for future biocatalyst design.

Degradation of tris(1,3-dichloro-2-propyl) phosphate (TDCPP) by ultraviolet activated hydrogen peroxide: Mechanisms, pathways and toxicity assessments

The ubiquity and ecotoxicity of tri (1,3-dichloro-2-propyl) phosphate (TDCPP) in aquatic environments make it essential to develop efficient related treatment techniques. The present research aims to systematically explore the mechanisms and toxicity changes of TDCPP degradation through UV-driven hydrogen peroxide process (UV/H2O2). The results revealed degradation efficiency of TDCPP attained 95 % with 0.5 mM H2O2, corresponding to a reaction rate constant (k) of 0.04919 min−1. Furthermore, three typical chlorinated OPEs (Cl-OPEs) were simultaneously degraded by the UV/H2O2 process, with different degradation efficiencies, according to the following order: TCEP<TDCPP<TCPP. The degradation efficiency was restricted under alkaline condition and the presence of humic acid (HA), nitrate (NO3–), chloride (Cl-), sulfate (SO42-), and dihydrogen phosphate (H2PO4-). A total of 12 intermediates were identified, which were generated through different pathways, including bond breaking, hydroxylation, and oxidation reactions. The Toxicity Estimation Software Tool (T.E.S.T) results demonstrated stronger mutagenicity and developmental toxicity of the TDCPP intermediates than parent compound. According to RNA sequencing results, UV/H2O2-based TDCPP degradation for 20 min and 60 min still had negative effects on Escherichia coli (E. coli). Indeed, the Gene Ontology (GO) enrichment and Kyoto Encyclopedia of Genes and Genomes (KEGG) analysis results further suggested the stronger negative effect (e.g., damaging effects on the cell membrane, energy metabolism, and vitality) of the 20-min oxidation solution on E. coli, followed by those observed in without treatment and 60-min oxidation solution. Therefore, longer oxidation times are required in the UV/H2O2 process to decrease the toxicity of TDCPP.

Unraveling the fate of 6PPD-Q in aquatic environment: Insights into formation, dissipation, and transformation under natural conditions

The widespread occurrence of N-(1,3-Dimethylbutyl)-N′-phenyl-p-phenylenediamine-quinone (6PPD-Q) in aquatic environments and its hazards to aquatic species underscore the necessity of comprehending its environmental fate. Here, we investigated the transformation from 6PPD to 6PPD-Q and the attenuation of 6PPD-Q in surface water under natural conditions. Contrary to prior findings, this work revealed that 6PPD-Q and its precursor 6PPD-OH/6PPD-(OH)2, were not detected through target analysis and suspect screening during 6PPD transformation in the surface water under the natural conditions. 6PPD-Q predominantly accumulated in TWPs in ambient atmosphere with 1.28 % mass yield from the 6PPD dissipation. Subsequently, 6PPD-Q was eluted from TWPs and released to the water environment. The investigation on the natural attenuation of 6PPD-Q in the surface water demonstrated that direct and indirect photolysis facilitated the rapid dissipation of 6PPD-Q with a half-life of 2.57 h. Utilizing the liquid chromatography high resolution mass spectrometry (LC-HRMS), including both time of flight (TOF) MS and Orbitrap MS, twelve novel transformation products (TPs) of 6PPD-Q were identified by using a comprehensive non-targeted screening strategy. The results from two dimensions gas chromatography (GC×GC) TOF-MS revealed additional two TPs. Based on the molecular structure of TPs, four major pathways of 6PPD-Q attenuation were proposed, including bond cleavage, hydroxylation, quinone cleavage and rearrangement. All TPs were predicted to exhibit lower toxicity, indicating the natural attenuation of 6PPD-Q reduced its toxicity and potential environmental risks. This study provides crucial insights into the environmental fate of 6PPD-Q, highlighting the significance of understanding both its formation from 6PPD and its subsequent attenuation processes under natural conditions.

Rational Design of the Spatial Effect in a Fe(II)/α‐Ketoglutarate‐Dependent Dioxygenase Reverses the Regioselectivity of C(sp3)−H Bond Hydroxylation in Aliphatic Amino Acids

AbstractThe hydroxylation of remote C(sp3)−H bonds in aliphatic amino acids yields crucial precursors for the synthesis of high‐value compounds. However, accurate regulation of the regioselectivity of remote C(sp3)−H bonds hydroxylation in aliphatic amino acids continues to be a common challenge in chemosynthesis and biosynthesis. In this study, the Fe(II)/α‐ketoglutarate‐dependent dioxygenase from Bacillus subtilis (BlAH) was mined and found to catalyze hydroxylation at the γ and δ sites of aliphatic amino acids. Crystal structure analysis, molecular dynamics simulations, and quantum chemical calculations revealed that regioselectivity was regulated by the spatial effect of BlAH. Based on these results, the spatial effect of BlAH was reconstructed to stabilize the transition state at the δ site of aliphatic amino acids, thereby successfully reversing the γ site regioselectivity to the δ site. For example, the regioselectivity of L‐Homoleucine (5 a) was reversed from the γ site (1 : 12) to the δ site (&gt;99 : 1). The present study not only expands the toolbox of biocatalysts for the regioselective functionalization of remote C(sp3)−H bonds, but also provides a theoretical guidance for the precision‐driven modification of similarly remote C(sp3)−H bonds in complex molecules.

Rational Design of the Spatial Effect in a Fe(II)/α-Ketoglutarate-Dependent Dioxygenase Reverses the Regioselectivity of C(sp3)-H Bond Hydroxylation in Aliphatic Amino Acids.

The hydroxylation of remote C(sp3)-H bonds in aliphatic amino acids yields crucial precursors for the synthesis of high-value compounds. However, accurate regulation of the regioselectivity of remote C(sp3)-H bonds hydroxylation in aliphatic amino acids continues to be a common challenge in chemosynthesis and biosynthesis. In this study, the Fe(II)/α-ketoglutarate-dependent dioxygenase from Bacillus subtilis (BlAH) was mined and found to catalyze hydroxylation at the γ and δ sites of aliphatic amino acids. Crystal structure analysis, molecular dynamics simulations, and quantum chemical calculations revealed that regioselectivity was regulated by the spatial effect of BlAH. Based on these results, the spatial effect of BlAH was reconstructed to stabilize the transition state at the δ site of aliphatic amino acids, thereby successfully reversing the γ site regioselectivity to the δ site. For example, the regioselectivity of L-Homoleucine (5 a) was reversed from the γ site (1 : 12) to the δ site (>99 : 1). The present study not only expands the toolbox of biocatalysts for the regioselective functionalization of remote C(sp3)-H bonds, but also provides a theoretical guidance for the precision-driven modification of similarly remote C(sp3)-H bonds in complex molecules.

Effect of nitrogen oxides and sulfur oxides to triphenyl phosphate degradation and cytotoxicity on surface of different transition metal salts

Nitrogen oxides and sulfur oxides, as the dominant toxic gases in the atmosphere, can induce severe human health problems under the composite pollutant conditions. Currently the effect of nitrogen or sulfur oxides in atmospheric environment to the degradation and cytotoxicity of triphenyl phosphate (TPhP) on atmospheric particle surfaces still remain poorly understood. Hence, laboratory simulation methods were used in this study to investigate the effect and related mechanism. First, particle samples were prepared with the TPhP coated on MnSO4, CuSO4, FeSO4 and Fe2(SO4)3 surface. The results showed that, when nitrogen or sulfur oxides were present, more significant TPhP degradation on all samples can be observed under both light and dark conditions. The results proved nitrogen oxides and sulfur oxides were the vital influence factors to the degradation of TPhP, which mainly promoted the OH generation in the polluted atmosphere. The mechanism study indicated that diphenyl hydrogen phosphate (DPhP) and OH-DPhP were two main stable degradation products. These degradation products originated from the phenoxy bond cleavage and hydroxylation of TPhP caused by hydroxyl radicals. In addition, no TPhP related organosulfates (OSs) or organic nitrates (ON) formation were observed. Regarding the cytotoxicity, all the particles can induce more significant cellular injury and apoptosis of A549 cells, which may be relevant to the adsorbed nitrogen oxides or sulfur oxides on particles surfaces. The superfluous reactive oxygen species (ROS) generation was the possible reason of cytotoxicity. This research can supply a comprehensive understanding of the promoting effect of nitrogen and sulfur oxides to TPhP degradation and the composite cytotoxicity of atmospheric particles.

Photodegradation of the novel herbicide pyraclonil in aqueous solution: Kinetics, identification of photoproducts, mechanism, and toxicity assessment

Pyraclonil is a new type of pyrazole herbicide, whose photochemical fate in aqueous solution has not been reported yet. In this study, effects on the photolysis rate such as light source, pH, NO3−, Fe3+, fulvic acid (FA) and riboflavin (RF) were investigated. Pyraclonil photodegraded in pure water under both UV and simulated sunlight with half-lives of 32.29 min and 42.52 h, respectively. Under UV, the degradation rate of pyraclonil in pH 4 solution (0.0299 ± 0.0033 min−1) was about twice higher than that in pH 9 (0.0160 ± 0.0063 min−1). Under simulated sunlight, low concentration (0.1–1 mg/L) of FA, NO3−, Fe3+ and RF noticeably promoted the photodegradation of pyraclonil. Then, with the combination of experimental UPLC-Q-TOF/MS and computational calculation of density functional theory (DFT), fourteen transformation products (TPs) of pyraclonil were identified with possible mechanism of C–N bond cleavage, photorearrangement, demethylation, hydroxylation and oxidation. Additionally, acute toxicity assessment was conducted through ECOSAR prediction and laboratory bioassays. The prediction results indicated that toxicity of TP157 to daphnid and green algae was 1.3 and 1.4 times higher than that of the parent, respectively. The bioassay results indicated that toxicities of TP157 and TP263 to C. vulgaris were about 1.6 and 5.9 times higher than that of the parent, respectively. The results provided a reference for elucidating the potential hazards of pyraclonil to non-target organisms and promoting its rational use.

Degradation, transformation and cytotoxicity of triphenyl phosphate on surface of different transition metal salts in atmospheric environment

Triphenyl phosphate (TPhP) and transition metal elements have been ubiquitously detected in the atmosphere, which can participate in atmospheric chemical reactions and induce damage to human health. Currently the understanding of TPhP degradation, transformation and cytotoxicity on atmospheric particles surface are still limited. Therefore, this study used laboratory simulation methods to investigate the influence of irradiation time, transition metal salts, relative humidity (RH) to TPhP degradation, transformation and relative cytotoxicity. TPhP was coated on particle surfaces of four transition metal salts (MnSO4, CuSO4, FeSO4 and Fe2(SO4)3) in the experiment. Within 12 h irradiation, the significant TPhP photodegradation can be observed on all particles surface. Among these influence factors, the irradiation and RH were the crucial aspects to TPhP degradation, which primarily affect the OH concentration in the atmosphere. The transition metal elements only exhibited slightly catalytic effect to TPhP degradation. The mechanism study indicated that the major degradation products of TPhP are diphenyl hydrogen phosphate (DPhP) and OH-DPhP, which originated from the phenoxy bond cleavage and hydroxylation of TPhP induced by OH. As for the cytotoxicity to A549 cells, all the transition metal particles coated with TPhP can cause cellular injury, which was chiefly induced by the transition metal salt. The possible cytotoxicity mechanism of these particles to A549 cells can be attributed to the excessive reactive oxygen species (ROS) production. This study may provide a further understanding of TPhP degradation and related cytotoxicity with the coexistent transition metal salts in the atmosphere.

Uptake, biotransformation and physiological response of TBBPA derivatives in Helianthus annus

Tetrabromobisphenol A (TBBPA) and its derivatives are widely used as brominated flame retardants. Because of their high production and wide environment distribution, TBBPA derivatives have increased considerable concern. Previous studies have primarily focused on TBBPA, with limited information available on its derivative. In this study, we investigated the uptake, biotransformation and physiological response of two derivatives, Tetrabromobisphenol A bis(allyl ether) (TBBPA BAE) and Tetrabromobisphenol A bis(2,3-dibromopropylether) (TBBPA BDBPE), in Helianthus annus (H. annus) through a short-term hydroponic assay. The results revealed that H. annus could absorb TBBPA BAE and TBBPA BDBPE from solution, with removal efficiencies of 98.33 ± 0.5% and 98.49 ± 1.56% after 10 days, respectively, which followed first-order kinetics. TBBPA BAE was absorbed, translocated and accumulated while TBBPA BDBPE couldn't be translocated upward due to its high hydrophobicity and low solubility. The concentrations of TBBPA derivatives in plants peaked within 72 h, and then decreased. We identified twelve metabolites resulting from ether bond breakage, debromination, and hydroxylation in H. annus. The high-level TBBPA BAE suppressed the growth and increased malondialdehyde (MDA) content of H. annus, while TBBPA BDBPE didn't pose a negative effect on H. annus. TBBPA BAE and TBBPA BDBPE increased the activity of superoxide dismutase (SOD), peroxidase (POD), and catalase (CAT), with higher levels of these enzymes activity found in high concentration treatments. Contrastingly, TBBPA BAE exhibited higher toxicity than TBBPA BDBPE, as indicated by greater antioxidant enzyme activity. The findings of this study develop better understanding of biotransformation mechanisms of TBBPA derivatives in plants, contributing to the assessment of the environmental and human health impacts of these contaminants.

Degradation of ribavirin by Fe2+/PS oxidation technology: performance, mechanism and toxicity control

During the COVID-19 pandemic, the extensive use of ribavirin (RBV) raised concerns about its environmental residues and associated risks, necessitating remedial actions. This study investigates the degradation efficiency, mechanism, and biotoxicity of RBV using ferrous (Fe2+) activated persulfate (PS) advanced oxidation technology (Fe2+/PS oxidation). Experiments conducted under various conditions revealed that at pH = 3, PS concentration of 4 mM, PS/Fe2+ molar ratio of 2:1, and citric acid of 0.5 mM with Fe2+ added twice, the degradation rate of RBV reached 98.70 %. The degradation process of RBV by Fe2+/PS from 0 to 5 mins followed a first-order reaction kinetics model. The presence of halide ions (Cl-, Br-, I-) was found to inhibit the degradation efficiency. The active species involved were identified as SO4-·, ·OH, 1O2, and FeO2+, with SO4-· and ·OH being the most significant. Moreover, the products of ribavirin were determined and their degradation pathways were proposed. Dehydration, deamidation, C-N bond breaking and hydroxylation were the major pathways. Additionally, toxicity assessment showed that Fe2+/PS oxidation reduced the inhibition rate of bioluminescence in Vibrio fischeri from 31.58 % to 3.88 %, effectively controlling RBV toxicity during the reaction. This study provides insights into managing water environmental risks associated with pharmaceutical residues in the post-pandemic era.

Metabolite markers for three synthetic tryptamines N-ethyl-N-propyltryptamine, 4-hydroxy-N-ethyl-N-propyltryptamine, and 5-methoxy-N-ethyl-N-propyltryptamine.

N-Ethyl-N-propyltryptamine (EPT), 4-hydroxy-N-ethyl-N-propyltryptamine (4-OH-EPT), and 5-methoxy-N-ethyl-N-propyltryptamine (5-MeO-EPT) are new psychoactive substances classified as tryptamines, sold online. Many tryptamines metabolize rapidly, and identifying the appropriate metabolites to reveal intake is essential. While the metabolism of 4-OH-EPT and 5-MeO-EPT are not previously described, EPT is known to form metabolites by indole ring hydroxylation among others. Based on general knowledge of metabolic patterns, 5-MeO-EPT is also expected to form ring hydroxylated EPT (5-OH-EPT). In the present study, the aim was to characterize the major metabolites of EPT, 4-OH-EPT, and 5-MeO-EPT, to provide markers for substance identification in forensic casework. The tryptamines were incubated with pooled human liver microsomes at 37°C for up to 4 h. The generated metabolites were separated and detected by ultra-high performance liquid chromatography-quadrupole time-of-flight mass spectrometry analysis. The major in vitro EPT metabolites were formed by hydroxylation, N-dealkylation, and carbonylation. In comparison, 4-OH-EPT metabolism was dominated by double bond formation, N-dealkylation, hydroxylation, and carbonylation in vitro and hydroxylation or carbonylation combined with double bond loss, carbonylation, N-dealkylation, and hydroxylation in vivo. 5-MeO-EPT was metabolized by O-demethylation, hydroxylation, and N-dealkylation in vitro. The usefulness of the characterized metabolites in forensic casework was demonstrated by identification of unique metabolites for 4-OH-EPT in a human postmortem blood sample with suspected EPT or 4-OH-EPT intoxication.

Photodegradation of 2-chlorodibenzo-p-dioxin (2-CDD) on the surface of municipal solid waste incineration fly ash: Kinetics and product analysis

Considering that waste incineration fly ash is the main carrier of dioxins and can migrate over long distances in the atmosphere, it is of great significance to study the photochemical transformation behavior of dioxins on the surface of fly ash. In this work, 2-chlorodibenzo-p-dioxin (2-CDD) was selected to conduct a systematic photochemical study. The influence of various factors on the photodegradation of 2-CDD were first explored, and the results showed that small particle size of fly ash, low concentration of 2-CDD and appropriate level of humidity were more conducive to photodegradation, with the highest degradation percentage reaching 76%–84%. The components of fly ash (Zn (Ⅱ), Al (Ⅲ), Cu (Ⅱ) and SiO2) also had a certain promoting effect on the degradation of 2-CDD, which increases the degradation efficiency by 10%–20%, because they could act as effective photocatalysts to produce free radicals for reaction. With a higher total light exposure intensity, natural light environments led to a more complete degradation of 2-CDD than laboratory Xe lamp irradiation (90% degradation Vs. 79% degradation). Based on chemical probe and radical quenching experiment, hydroxyl radical also contributed to 2-CDD photodegradation on fly ash. A total of 16 intermediate products were detected by mass spectrometry analysis, and four initial reaction pathways of 2-CDD were speculated in the process, including dechlorination, ether bond cleavage, hydroxyl substitution, and hydroxyl addition. According to the results of density functional theory calculation, the reaction channels of ether bond cleavage and •OH attack were determined. The toxicity assessment software tool (TEST) was used to assess the toxicity and bioconcentration coefficient of reaction products, and it was found that the overall toxicity of the photodegradation products was reduced. This study would provide new insights into the environmental fate of dioxins during long-range atmospheric migration process.

Bioinformatic Discovery of a Cambialistic Monooxygenase.

Dinuclear monooxygenases mediate challenging C-H bond oxidation reactions throughout nature. Many of these enzymes are presumed to exclusively utilize diiron cofactors. Herein we report the bioinformatic discovery of an orphan dinuclear monooxygenase that preferentially utilizes a heterobimetallic manganese-iron (Mn/Fe) cofactor to mediate an O2-dependent C-H bond hydroxylation reaction. Unlike the structurally similar Mn/Fe-dependent monooxygenase AibH2, the diiron form of this enzyme (SfbO) exhibits a nascent enzymatic activity. This behavior raises the possibility that many other dinuclear monooxygenases may be endowed with the capacity to harness cofactors with a variable metal content.

UV-induced photodegradation of emerging para-phenylenediamine quinones in aqueous environment: Kinetics, products identification and toxicity assessments

Substituted para-phenylenediamine quinones (PPD-quinones) are a class of emerging contaminants frequently detected in the aqueous environment. One of them, N-(1,3-dimethylbutyl)-N′-phenyl-p-phenylenediamine quinone (6PPD-Q), was found to cause acute toxicities to aquatic species at extremely low environmental levels. The ubiquitousness and ecotoxicity of such pollutants underscore the importance of their transformation and elimination. In this work, we demonstrated effective removals of five PPD-quinones in aqueous environments under UV irradiation, with up to 94% of 6PPD-Q eliminated after a 40-min treatment. By applying high-resolution mass spectrometry (HRMS) non-targeted screening in combination with isotope labeling strategies, a total of 22 transformation products (TPs) were identified. Coupling with the time-based dynamic patterns, potential transformation mechanisms were identified as an •OH-induced photocatalysis reaction involving bond cleavage, hydroxylation, and oxidation. Computational toxicity assessment predicted lower aquatic toxicity of the TPs than their parent PPD-quinones. Our results in parallel evidenced an obvious reduction of PPD-quinones accompanied by the presence of their TPs in the effluent after UV disinfection in real municipal wastewater. This work builds a comprehensive understanding of the fate, transformation products, and related toxicological characteristics of emerging PPD-quinone contaminants in the aqueous environment.

A mechanistic study reveals the roles of the ligand and substrate in the Pd-catalyzed C–H bond hydroxylation of a carboxylic acid with molecular oxygen

DFT studies reveal critical factors influencing the reactivity of Pd-catalyzed C–H bond hydroxylation with O2: (1) substrate axial coordination; (2) proton shuttling by the ligand; and (3) dimeric palladium species formation.

Enantiocomplementary C–H bond hydroxylation through a dual-enzyme catalyzed one-pot two-step process

A one-pot, two-step C–H bond hydroxylation process that integrates HRP-catalyzed oxidation and carbonyl reductase-catalyzed reduction for the enantiocomplementary synthesis of benzyl alcohols.

Enhanced removal of sulfamethoxazole by Mn(II)/bisulfite in presence of nitrilotriacetic acid: Role of Mn(III)

Currently, the research on bisulfite (BS) activation by Mn(II) is very limited probably because of the low catalytic efficiency of Mn(II). Adding ligands to Mn(II)/BS system is likely to improve the BS activation, but the relative information is very rare. Therefore, the effect of nitrilotriacetic acid (NTA) on Mn(II)/BS system was investigated in this work using sulfamethoxazole (SMX) as the target contaminant. The results showed that the addition of NTA enhanced SMX removal in Mn(Ⅱ)/BS system through forming Mn(Ⅱ/III)-NTA complexes driving Mn(III)/Mn(II) cycle and stabilizing Mn(III). Alcohol scavenging experiments and competitive kinetic experiments indicated that sulfate radical (SO4•−) and hydroxyl radical (HO•) were not the main reactive species in Mn(II)/NTA/BS system. Mn(Ⅲ) was the primary oxidant for SMX elimination in this system and its existence was proved by UV-Vis absorption spectrum of reaction solution. Mn(Ⅱ)/NTA/BS system could greatly degrade SMX in near-neutral conditions, while nearly no SMX removal was observed at pH 3.0. The decrease of dissolved oxygen concentration significantly inhibited BS autocatalytic stage, thus suppressing the removal of SMX. Due to the competitive complexation of HCO3− and FA with NTA for Mn(II), their addition in Mn(Ⅱ)/NTA/BS system obviously inhibited SMX degradation. Four intermediates were detected during SMX degradation in Mn(Ⅱ)/NTA/BS system, and the possible SMX transformation pathways were speculated as N-S bond breaking, hydroxylation, amino oxidation and coupling reaction.

Bimetallic metal-organic framework as a high-performance peracetic acid activator for sulfamethoxazole degradation

A novel 3D bimetallic metal-organic framework (MOF(Fe–Co)) was successfully prepared and its performance on sulfamethoxazole (SMX) removal in advanced oxidation process (AOP) based on peracetic acid (PAA) was evaluated. MOF(Fe–Co) exhibited an efficient catalytic performance on PAA activation for SMX degradation under neutral condition. Increasing PAA concentration could enhance SMX removal, while the variation of MOF(Fe–Co) dosage from 0.05 to 0.2 g/L had an inappreciable effect on SMX removal. According to the results of inductively coupled plasma mass spectrometry analyses and X-ray photoelectron spectroscopy, catalytic reactions mainly occurred on the surface of MOF(Fe–Co). Organic radicals (i.e., CH3C(O)OO• and CH3C(O)O•) were demonstrated to be the predominant reactive radicals for SMX degradation by MOF(Fe–Co)/PAA through radical quenching experiments. The presence of Cl− could enhance the degradation of SMX by MOF(Fe–Co)/PAA, while HCO3− and natural organic matter inhibited SMX degradation severely. Five identified degradation products were detected in this system and four possible SMX transformation pathways were proposed, including amino oxidation, S–N bond cleavage, coupling reaction and hydroxylation.

106-fold faster C-H bond hydroxylation by a CoIII,IV2(µ-O)2 complex [via a CoIII2(µ-O)(µ-OH) intermediate] versus its FeIIIFeIV analog.

The hydroxylation of C-H bonds can be carried out by the high-valent CoIII,IV2(µ-O)2 complex 2a supported by the tetradentate tris(2-pyridylmethyl)amine ligand via a CoIII2(µ-O)(µ-OH) intermediate (3a). Complex 3a can be independently generated either by H-atom transfer (HAT) in the reaction of 2a with phenols as the H-atom donor or protonation of its conjugate base, the CoIII2(µ-O)2 complex 1a. Resonance Raman spectra of these three complexes reveal oxygen-isotope-sensitive vibrations at 560 to 590 cm-1 associated with the symmetric Co-O-Co stretching mode of the Co2O2 diamond core. Together with a Co•••Co distance of 2.78(2) Å previously identified for 1a and 2a by Extended X-ray Absorption Fine Structure (EXAFS) analysis, these results provide solid evidence for their "diamond core" structural assignments. The independent generation of 3a allows us to investigate HAT reactions of 2a with phenols in detail, measure the redox potential and pKa of the system, and calculate the O-H bond strength (DO-H) of 3a to shed light on the C-H bond activation reactivity of 2a. Complex 3a is found to be able to transfer its hydroxyl ligand onto the trityl radical to form the hydroxylated product, representing a direct experimental observation of such a reaction by a dinuclear cobalt complex. Surprisingly, reactivity comparisons reveal 2a to be 106-fold more reactive in oxidizing hydrocarbon C-H bonds than corresponding FeIII,IV2(µ-O)2 and MnIII,IV2(µ-O)2 analogs, an unexpected outcome that raises the prospects for using CoIII,IV2(µ-O)2 species to oxidize alkane C-H bonds.

Development of a heterogenous catalyst FeWO4/Cu2S as peroxymonosulfate activator for effective sulfachloropyridazine elimination

This work successfully synthesized magnetic FeWO4/Cu2S through a facile method with efficient peroxymonosulfate (PMS) activation to eliminate sulfachloropyridazine (SCP) in water, in which 97.56% of SCP was removed in 30 min with activating only 0.2 mM PMS. Factors such as calcination temperature, the addition amount of WS2 in FeWO4/Cu2S, molar ratio of Cu/Fe in FeWO4/Cu2S, catalyst dosage, solution pH, inorganic anions and natural organic matters（NOM）were investigated. It was found that in FeWO4/Cu2S at 1:2 possessed the best catalytic performance for PMS. FeWO4/Cu2S performed well in a wide pH range (3–9) and the effect was better under acidic conditions. A high catalyst dosage could supply more catalytic active sites for PMS activation and encourage the production of reactive oxygen species. Anions (HCO3−and HPO42−) and NOM significantly inhibited SCP degradation, whereas Cl− had only a tiny inhibitory impact. In addition, H2PO4− and NO3− demonstrated duality in the degradation of SCP. The oxidation process was dominated by non free radical oxidation by 1O2 rather than free radicals oxidation by HO⋅ and SO4•−. Three SCP degradation pathways—SO2 extrusion, S-N bond cleavage and hydroxylation were proposed according to intermediate products analysis. The mechanism was found that the introduction of W improved the dual metals cycles of Fe3+/Fe2+ and Cu+/Cu2+ which could efficiently promote PMS activation. In addition, the magnetic FeWO4/Cu2S was easy to separate after reaction, which had great application potential in the water treatment.