Synergistic material-microbe interface toward deeper anaerobic defluorination.

Per- and polyfluoroalkyl substances (PFAS), particularly the perfluorinated ones, are recalcitrant to biodegradation. By integrating an enrichment culture of reductive defluorination with biocompatible electrodes for the electrochemical process, a deeper defluorination of a C6-perfluorinated unsaturated PFAS was achieved compared to the biological or electrochemical system alone. Two synergies in the bioelectrochemical system were identified: i) The in-series microbial-electrochemical defluorination and ii) the electrochemically enabled microbial defluorination of intermediates. These synergies at the material-microbe interfaces surpassed the limitation of microbial defluorination and further turned the biotransformation end products into less fluorinated products, which could be less toxic and more biodegradable in the environment. This material-microbe hybrid system brings opportunities in the bioremediation of PFAS driven by renewable electricity and warrants future research on mechanistic understanding of defluorinating and electroactive microorganisms at the material-microbe interface for system optimizations.

High-Level Disordered Metal-Organic Frameworks Synthesized by Interference-Oriented Attachment for Electrochemical Anion Sieve.

Disordered MOFs seamlessly amalgamate the robust stability and pore tunability inherent in crystalline MOFs with the advantages derived from abundant defects and active sites present in amorphous structures. This study pioneers the use of the interference-oriented attachment (IOA) mechanism to meticulously craft the morphology and crystal growth of MIL-101(Cr) (Cr-MOF), resulting in the successful synthesis of a high-level disordered Cr-MOF boasting an enhanced array of active sites and exceptional electrochemical properties. The correlation between disordered structures and the electrochemical properties of MOFs are elucidated using the lattice distortion index and fractal dimension. The high-level disordered MOF electrode showcases a remarkable fluoride sieving effect, outperforming conventional fluoride removal materials with a remarkable fluoride adsorption capacity of 41.04 mgNaF gelectrodes -1. First-principles calculations, in conjunction with relevant experiments, provided further validation that the disordered structure significantly enhances the defluorination performance of the material. This study introduces a novel approach for the direct bottom-up synthesis of high-level disordered MOFs, showcasing their potential for applications in electrochemical water treatment.

Toward the development of a molecular toolkit for the microbial remediation of per-and polyfluoroalkyl substances.

Per- and polyfluoroalkyl substances (PFAS) are highly fluorinated synthetic organic compounds that have been used extensively in various industries owing to their unique properties. The PFAS family encompasses diverse classes, with only a fraction being commercially relevant. These substances are found in the environment, including in water sources, soil, and wildlife, leading to human exposure and fueling concerns about potential human health impacts. Although PFAS degradation is challenging, biodegradation offers a promising, eco-friendly solution. Biodegradation has been effective for a variety of organic contaminants but is yet to be successful for PFAS due to a paucity of identified microbial species capable of transforming these compounds. Recent studies have investigated PFAS biotransformation and fluoride release; however, the number of specific microorganisms and enzymes with demonstrable activity with PFAS remains limited. This review discusses enzymes that could be used in PFAS metabolism, including haloacid dehalogenases, reductive dehalogenases, cytochromes P450, alkane and butane monooxygenases, peroxidases, laccases, desulfonases, and the mechanisms of microbial resistance to intracellular fluoride. Finally, we emphasize the potential of enzyme and microbial engineering to advance PFAS degradation strategies and provide insights for future research in this field.

Selective Mono-Defluorinative Cross-Coupling of Trifluoromethyl arenes via Multiphoton Photoredox Catalysis.

A new cross-coupling of trifluoromethyl arenes has been realized via multiphoton photoredox catalysis. Trifluoromethyl arenes were demonstrated to undergo selective mono-defluorinative alkylation under mild reaction conditions providing access to a series of valuable α,α-difluorobenzylic compounds. The reaction shows broad substrate scope and general functional group tolerance. In addition to the electron-deficient trifluoromethyl arenes that are easily reduced to the corresponding radical anion, more challenging electron-rich substrates were also successfully applied. Steady-State Stern-Volmer quenching studies indicated that the trifluoromethyl arenes were reduced by the multiphoton excited Ir-based photocatalyst.

Aerobic Microbial Transformation of Fluorinated Liquid Crystal Monomer: New Pathways and Mechanism.

Fluorinated liquid crystal monomers (FLCMs) have been suggested as emerging contaminants, raising global concern due to their frequent occurrence, potential toxic effects, and endurance capacity in the environment. However, the environmental fate of the FLCMs remains unknown. To fill this knowledge gap, we investigated the aerobic microbial transformation mechanisms of an important FLCM, 4-[difluoro(3,4,5-trifluorophenoxy)methyl]-3, 5-difluoro-4'-propylbiphenyl (DTMDPB), using an enrichment culture termed as BG1. Our findings revealed that 67.5 ± 2.1% of the initially added DTMDPB was transformed in 10 days under optimal conditions. A total of 14 microbial transformation products obtained due to a series of reactions (e.g., reductive defluorination, ether bond cleavage, demethylation, oxidative hydroxylation and aromatic ring opening, sulfonation, glucuronidation, O-methylation, and thiolation) were identified. Consortium BG1 harbored essential genes that could transform DTMDPB, such as dehalogenation-related genes [e.g., glutathione S-transferase gene (GST), 2-haloacid dehalogenase gene (2-HAD), nrdB, nuoC, and nuoD]; hydroxylating-related genes hcaC, ubiH, and COQ7; aromatic ring opening-related genes ligB and catE; and methyltransferase genes ubiE and ubiG. Two DTMDPB-degrading strains were isolated, which are affiliated with the genus Sphingopyxis and Agromyces. This study provides a novel insight into the microbial transformation of FLCMs. The findings of this study have important implications for the development of bioremediation strategies aimed at addressing sites contaminated with FLCMs.

Promotive Effects of Chloride and Sulfate on the Near-Complete Destruction of Perfluorocarboxylates (PFCAs) in Brine via Hydrogen-tuned 185-nm UV Photolysis: Mechanisms and Kinetics.

Hydrogen-tuned 185 nm vacuum ultraviolet (VUV/H2) photolysis is an emerging technology to destroy per- and polyfluoroalkyl substance (PFAS) in brine. This study discovered the promotive effects of two major brine anions, i.e., chloride and sulfate in VUV/H2 photolysis on the hydrated electron (eaq-) generation and perfluorocarboxylates (PFCAs) destruction and established a kinetics model to elucidate the promotive effects on the steady-state concentration of eaq- ([eaq-]ss). Results showed that VUV/H2 achieved near-complete defluorination of perfluorooctanoic acid (PFOA) in the presence of up to 1000 mM chloride or sulfate at pH 12. The defluorination rate constant (kdeF) of PFOA peaked with a chloride concentration at 100 mM and with a sulfate concentration at 500 mM. The promotive effects of chloride and sulfate were attributed to an enhanced generation of eaq- via their direct VUV photolysis and conversion of additionally generated hydroxyl radical to eaq- by H2, which was supported by a linear correlation between the predicted [eaq-]ss and experimentally observed kdeF. The kdeF value increased from pH 9 to 12, which was attributed to the speciation of the H·/eaq- pair. Furthermore, the VUV system achieved >95% defluorination and ≥99% parent compound degradation of a concentrated PFCAs mixture in a synthetic brine, without generating any toxic perchlorate or chlorate.

Dechlorination Helps Defluorination: Insights into the Defluorination Mechanism of Florfenicol by S-nZVI and DFT Calculations on the Reaction Pathways.

Defluorination is essential to eliminate the antibiotic resistance and detrimental effects of florfenicol (C12H14Cl2FNO4S, FF), which is achievable by sulfidated nanoscale zerovalent iron (S-nZVI), yet a comprehensive understanding of the mechanism is lacking. Herein, we used experimental data and density functional theory calculations to demonstrate four dechlorination-promoted defluorination pathways of FF, depending on S-nZVI or not. FF was defluorinated in a rapid and then slow but continuous manner, accompanying a consecutive dechlorination to deschloro (dFF) and dideschloro FF (ddFF). Unexpectedly, the predominant defluorination occurs by spontaneous hydrolysis of ddFF to form the hydrolyzed byproduct (HO-ddFF), i.e., independent of S-nZVI, which is initiated by intramolecular attack from carbonyl O to alkyl F and is thus limited for FF and dFF owing to the diminished nucleophilicity by electron-withdrawing Cl. The removal of Cl also makes the reductive defluorination of ddFF by S-nZVI amenable. The other two minor but more rapid defluorination pathways occur in synergy with the dechlorination of FF and dFF, which are mediated by the reactive carbanion intermediates and generate HO-dFF and HO-ddFF, respectively. The reliability of these dechlorination-facilitated defluorination pathways was verified by the consistency of theoretical calculations with experimental data, providing valuable insights into the degradation of fluorinated contaminants.

Novel Defluorination Pathways of Perfluoroether Compounds (GenX): α-Fe2O3 Nanoparticle Layer Retains Higher Concentrations of Effective Hydrated Electrons.

The development of efficient defluorination technology is an important issue because the kind of emerging pollutant of hexafluoropropylene oxide dimer acid (GenX) as an alternative to perfluorooctanoic acid (PFOA) has the higher environmental risks. In the UV/bisulfite system, we first developed a hydrophobic confined α-Fe2O3 nanoparticle layer rich in oxygen vacancies, which accelerated the enrichment of HSO3- and GenX on the surface and pores through electrostatic attraction and hydrophobic interaction, retaining more hydrated electrons (eaq-) and rapidly destroying GenX under UV excitation. Especially, under anaerobic and aerobic conditions, the degradation percentage of GenX obtain nearly 100%, defluorination of GenX to 88 and 57% respectively. It was amazed to find that the three parallel H/F exchange pathways triggered by the rapid reactions of eaq- and GenX, which were unique to anaerobic conditions, improved the efficiency of fluoride removal and weaken the interference of dissolved oxygen and H+. Therefore, this study provided an available material and mechanism for sustainable fluoride removal from wastewater in aerobic and anaerobic conditions.

Overlooked Activation Role of Sulfite in Accelerating Hydrated Electron Treatment of Perfluorosulfonates.

Photoexcitation of sulfite (SO32-) is often used to generate hydrated electrons (eaq-) in processes to degrade perfluoroalkyl and polyfluoroalkyl substances (PFASs). Conventional consensus discourages the utilization of SO32- concentrations exceeding 10 mM for effective defluorination. This has hindered our understanding of SO32- chemistry beyond its electron photogeneration properties. In contrast, the radiation-chemical study presented here, directly producing eaq- through water radiolysis, suggests that SO32- plays a previously overlooked activation role in the defluorination. Quantitative 60Co gamma irradiation experiments indicate that the increased SO32- concentration from 0.1 to 1 M enhances the defluorination rate by a remarkable 15-fold, especially for short-chain perfluoroalkyl sulfonate (PFSA). Furthermore, during the treatment of long-chain PFSA (C8F17-SO3-) with a higher concentration of SO32-, the intermediates of C8H17-SO3- and C3F7-COO- were observed, which are absent without SO32-. These observations highlight that a higher concentration of SO32- facilitates both reaction pathways: chain shortening and H/F exchange. Pulse radiolysis measurements show that elevated SO32- concentrations accelerate the bimolecular reaction between eaq- and PFSA by 2 orders of magnitude. 19F NMR measurements and theoretical simulations reveal the noncovalent interactions between SO32- and F atoms, which exceptionally reduce the C-F bond dissociation energy by nearly 40%. As a result, our study offers a more effective strategy for degrading highly persistent PFSA contaminants.

Hydrogen Peroxide-Assisted Alkaline Defluorination of the Fumigant and Potent Greenhouse Gas, Sulfuryl Fluoride: Hydrogen Peroxide as a Nucleophilic Reagent.

Sulfuryl fluoride (SO2F2, SF) is an effective and increasingly popular fumigant for treating buildings and commodities in international trade but has come under scrutiny as a potent greenhouse gas. Passage of vent gases through an alkaline spray has been proposed for scrubbing SF, but base hydrolysis is insufficiently fast and generates equal yields of fluoride and fluorosulfate, the latter of unknown environmental hazard. We report here that alkaline hydrogen peroxide (H2O2) markedly accelerates SF removal and gives nearly quantitative yield of fluoride, with fluorosulfate produced in less than 3.5% yield. The other major products are sulfate, peroxymonosulfate, and oxygen. The oxidation state of S was unchanged. Hydroxyl and superoxide radical scavengers had no effect on the rate. The reaction proceeds by sequential nucleophilic displacement of fluoride by hydroperoxide ion (HO2-) to form a transient diperoxysulfate species that rapidly undergoes intramolecular redox rearrangement to give sulfate and singlet oxygen. Peroxymonosulfate, produced through side reactions, can fully defluorinate SF as well, although more slowly. Two new peaks were detected in the 19F-NMR spectrum corresponding to intermediates. Fluoride can be removed conventionally, and the other products are innocuous or short-lived. Thus, H2O2-assisted alkaline defluorination promises to be an effective method for scrubbing spent SF fumes and preventing SF from reaching the atmosphere. This study highlights the benefits of H2O2 and peroxymonosulfate as nucleophiles in remediation chemistry.

Using Network Analysis and Predictive Functional Analysis to Explore the Fluorotelomer Biotransformation Potential of Soil Microbial Communities.

Microbial transformation of per- and polyfluoroalkyl substances (PFAS), including fluorotelomer-derived PFAS, by native microbial communities in the environment has been widely documented. However, few studies have identified the key microorganisms and their roles during the PFAS biotransformation processes. This study was undertaken to gain more insight into the structure and function of soil microbial communities that are relevant to PFAS biotransformation. We collected 16S rRNA gene sequencing data from 8:2 fluorotelomer alcohol and 6:2 fluorotelomer sulfonate biotransformation studies conducted in soil microcosms under various redox conditions. Through co-occurrence network analysis, several genera, including Variovorax, Rhodococcus, and Cupriavidus, were found to likely play important roles in the biotransformation of fluorotelomers. Additionally, a metagenomic prediction approach (PICRUSt2) identified functional genes, including 6-oxocyclohex-1-ene-carbonyl-CoA hydrolase, cyclohexa-1,5-dienecarbonyl-CoA hydratase, and a fluoride-proton antiporter gene, that may be involved in defluorination. This study pioneers the application of these bioinformatics tools in the analysis of PFAS biotransformation-related sequencing data. Our findings serve as a foundational reference for investigating enzymatic mechanisms of microbial defluorination that may facilitate the development of efficient microbial consortia and/or pure microbial strains for PFAS biotransformation.

Oxidative Transformation of Nafion-Related Fluorinated Ether Sulfonates: Comparison with Legacy PFAS Structures and Opportunities of Acidic Persulfate Digestion for PFAS Precursor Analysis.

The total oxidizable precursor (TOP) assay has been extensively used for detecting PFAS pollutants that do not have analytical standards. It uses hydroxyl radicals (HO•) from the heat activation of persulfate under alkaline pH to convert H-containing precursors to perfluoroalkyl carboxylates (PFCAs) for target analysis. However, the current TOP assay oxidation method does not apply to emerging PFAS because (i) many structures do not contain C-H bonds for HO• attack and (ii) the transformation products are not necessarily PFCAs. In this study, we explored the use of classic acidic persulfate digestion, which generates sulfate radicals (SO4-•), to extend the capability of the TOP assay. We examined the oxidation of Nafion-related ether sulfonates that contain C-H or -COO-, characterized the oxidation products, and quantified the F atom balance. The SO4-• oxidation greatly expanded the scope of oxidizable precursors. The transformation was initiated by decarboxylation, followed by various spontaneous steps, such as HF elimination and ester hydrolysis. We further compared the oxidation of legacy fluorotelomers using SO4-• versus HO•. The results suggest novel product distribution patterns, depending on the functional group and oxidant dose. The general trends and strategies were also validated by analyzing a mixture of 100000- or 10000-fold diluted aqueous film-forming foam (containing various fluorotelomer surfactants and organics) and a spiked Nafion precursor. Therefore, (1) the combined use of SO4-• and HO• oxidation, (2) the expanded list of standard chemicals, and (3) further elucidation of SO4-• oxidation mechanisms will provide more critical information to probe emerging PFAS pollutants.

Direct Defluorination and Amination of Polytetrafluoroethylene and Other Fluoropolymers by Lithium Alkylamides.

Polytetrafluoroethylene (PTFE) and, by extension, fluoropolymers are ubiquitous in science, life, and the environment as perfluoroalkyl pollutants (PFAS). In all cases, it is difficult to transform these materials due to their chemical inertness. Herein, we report a direct amination process of PTFE and some fluoropolymers such as polyvinylidene fluoride (PVDF) and Nafion by lithium alkylamide salts. Synthesizing these reactants extemporaneously between lithium metal and an aliphatic primary di- or triamine that also serves as a solvent leads to the rapid nucleophilic substitution of fluoride by an alkylamide moiety when in contact with the fluoropolymer. Moreover, lithium alkylamides dissolved in suitable solvents other than amines can react with fluoropolymers. This highly efficient one-pot process opens the way for further surface or bulk modification if needed, providing an easy, inexpensive, and fast experiment protocol on large scales.

Catalytic HF Shuttling between Fluoroalkanes and Alkynes.

In this paper, we report BF3 ⋅ OEt2 as a catalyst to shuttle equivalents of HF from a fluoroalkane to an alkyne. Reactions of terminal and internal aliphatic alkynes led to formation of difluoroalkane products, while diarylalkynes can be selectively converted into fluoroalkenes. The method tolerates numerous sensitive functional groups including halogen, protected amine, ester and thiophene substituents. Mechanistic studies (DFT, probe experiments) suggest the catalyst is involved in both the defluorination and fluorination steps, with BF3 acting as a Lewis acid and OEt2 a weak Lewis base that mediates proton transfer. In certain cases, the interconversion of fluoroalkene and difluoroalkane products was found to be reversible. The new catalytic system was applied to demonstrate proof-of-concept recycling of poly(vinylidene difluoride).

Defluorinative Alkylboration of Alkenes Enabled by Dual Photoredox and Copper Catalysis.

A regioselectivity reversed three-component defluorinative alkylboration of alkenes with trifluoromethyls and bis(pinacolato)diboron via dual photoredox/copper catalysis is reported. The mild conditions are compatible with a wide array of nonactivated trifluoromethyl aromatics bearing electron-donating or electron-neutral substituents, trifluoroacetamides, and various nonactivated terminal and internal alkenes, enabling straightforward access to synthetically valuable γ-gem-difluoroalkyl boronates with high efficiency. Furthermore, this protocol is applicable to alkene-tethered trifluoromethyl aromatics to furnish gem-difluoromethylene-containing cyclic compounds. Synthetic applications and preliminary mechanistic studies are also presented.

Selective Defluorination of Trifluoromethyl Substituents by Conformationally Induced Remote Substitution.

The selective reduction of an aromatic trifluoromethyl substituent to a difluoromethyl substituent may be achieved by base-promoted elimination to form a difluoro-p-quinomethide which is trapped by an intramolecular nucleophile. High yields are obtained when the nucleophilic trap entails the conformationally favoured cyclisation of an aminoisobutyric acid (Aib) derivative. The resulting cyclised difluoromethyl-substituted arylimidazolidinone products are readily converted to versatile difluoromethyl-substituted aldehydes by reduction and hydrolysis. Defluorination is successful on a range of benzenoid (both para and ortho CF3-substituted) and heterocyclic substrates. Double defluorination may likewise be achieved sequentially, or in a single step, from an Aib dipeptide derivative.

"Blockchain-Like" MIL-101(Cr)/Carbon Black Electrodes for Unprecedented Defluorination by Capacitive Deionization.

Metal-organic frameworks (MOF) have attracted extensive attention due to their ultra-high specific surface area and tunable structure, the mechanism of direct utilization for capacitive deionization (CDI) defluorination remains undefined. Here, MIL-101(Cr) with ultra-high specific surface area, high water stability, and open metal sites (OMSs) is prepared by a hydrothermal method for defluorination of CDI. Carbon black is used as a "chain" to connect F-stored in the holes of MIL-101(Cr) (Cr-MOF)as "blocks" to enhance the conductivity and ion storage capacity of MIL-101(Cr)/carbon black electrodes (Cr-MOF electrodes). This simple construction method avoids the process complexity of in situ synthesis and performs better. These easily constructed "blockchain-like" Cr-MOF electrodes exhibit excellent defluorination capacity (39.84 mgNaF gelectrodes -1 ), low energy consumption (1.2 kWh kgNaF -1 ), and good stability. The coupling of the electrochemical redox reaction of Cr3+ /Cr4+ with confined water is investigated using in situ and ex situ analysis methods combined with density functional theory (DFT), resulting in an unprecedented defluorination mechanism for Cr-MOF electrodes. This study opens up new ideas for the application of MOF in CDI, clarifies the removal mechanism of MOF, and lays a foundation for further promoting the application of raw materials with poor conductivity in the field of CDI.

Rapidly Constructing Sodium Fluoride-Rich Interface by Pressure and Diglyme-Induced Defluorination Reaction for Stable Sodium Metal Anode.

Sodium (Na) metal is able to directly use as a battery anode but have a highly reductive ability of unavoidably occurring side reactions with organic electrolytes, resulting in interfacial instability as a primary factor in performance decay. Therefore, building stable Na metal anode is of utmost significance for both identifying the electrochemical performance of laboratory half-cells employed for quantifying samples and securing the success of room-temperature Na metal batteries. In this work, we propose an NaF-rich interface rapidly prepared by pressure and diglyme-induced defluorination reaction for stable Na metal anode. Once the electrolyte is dropped into the coin-type cells followed by a slight squeeze, the Na metal surface immediately forms a protective layer consisting of amorphous carbon and NaF, effectively inhibiting the dendrite growth and dead Na. The resultant Na metal anode exhibits a long-term cycling lifespan over 1800 h even under the area capacity of 3.0 mAh cm-2 . Furthermore, such a universal and facile method is readily applied in daily battery assembly regarding Na metal anode.

Defluorinative 1,3-Dienylation of Fluoroalkyl N-Triftosylhydrazones with Homoallenols.

A silver-catalyzed regioselective defluorinative 1,3-dienylation of trifluoromethyl phenyl N-triftosylhydrazones using homoallenols as 1,3-dienyl sources provides a variety of α-(di)fluoro-ß-vinyl allyl ketones with excellent functional group tolerance in moderate to good yields. The reaction proceeds through a silver carbene-initiated sequential etherification and Claisen type [3,3]-sigmatropic rearrangement cascade. The synthetic utility of this protocol was demonstrated through the downstream synthetic elaboration toward diverse synthetically useful building blocks.

Defluorination of Fluorophenols by a Nonheme Iron(IV)-Oxo Species: Observation of a New Intermediate Along the Reaction.

High-valent iron(IV)-oxo intermediates are versatile oxidants in the biotransformation of various substrates by metalloenzymes and catalyze essential reactions for human health as well as in the biodegradation of toxic organic pollutants in the environment. Herein, we report a biomimetic system that efficiently reacts with halophenols through defluorination reactions and characterize various short-lived intermediates along the reaction mechanism. We study the reactivity pattern of a nonheme iron(IV)-oxo species with a series of trihalophenols (X=F, Cl, Br). A combined experimental and computational study reveals that the oxidative dehalogenation of 2,4,6-trifluorophenol is initiated with an H-atom abstraction from the phenolic group by the iron(IV)-oxo species resulting in the formation of a phenolate radical and an iron(III)-hydroxo species. This iron(III)-hydroxo species forms an adduct with the oxidized substrate with λmax at 558 nm which subsequently decays to give quinones as products.