Selective Oxidation of Halophenols Catalyzed by an Artificial Miniaturized Peroxidase.

The development of artificial enzymes for application in sustainable technologies, such as the transformation of environmental pollutants or biomass, is one of the most challenging goals in metalloenzyme design. In this work, we describe the oxidation of mono-, di-, tri- and penta-halogenated phenols catalyzed by the artificial metalloenzyme Fe-MC6*a. It promoted the dehalogenation of 4-fluorophenol into the corresponding 1,4-benzoquinone, while under the same experimental conditions, 4-chloro, 4-bromo and 4-iodophenol were selectively converted into higher molecular weight compounds. Analysis of the 4-chlorophenol oxidation products clarified that oligomers based on C-O bonds were exclusively formed in this case. All results show that Fe-MC6*a holds intriguing enzymatic properties, as it catalyzes halophenol oxidation with substrate-dependent chemoselectivity.

Synthesis of Polysubstituted Meta-Halophenols by Anion-Accelerated 2π-Electrocyclic Ring Opening.

Disrotatory - thermally allowed - 2π-electrocyclic ring-opening reactions require high temperatures to proceed. Herein, we report the first anion-accelerated 2π-electrocyclic ring opening of 6,6-dihalobicyclo[3.1.0]hexan-2-ones at low temperature to give the corresponding meta-halophenols in good to high yields (18 examples, 29-92 % yield, average: 65 %). Many of the phenols have unconventional substitution patterns and are reported here for the first time. Furthermore, the strength of the methodology was shown by the total synthesis of the densely functionalized phenolic natural product caramboxin (isolated as the lactam dehydrate). The reaction mechanism underlying the anion-acceleration was investigated in an ab initio study, which concluded that base-mediated proton abstraction anti to the concurrently departing endo-bromine was the initiating step in an overall concerted reaction mechanism leading directly to the meta-halophenol.

Corky off-flavor compounds in cork planks at different storage times before processing. Influence on the quality of the final stoppers.

BACKGROUND: Cork companies store cork planks before processing them for a minimum of 6 months to dry up and to stabilize their texture and chemical composition, although many companies extend this storage period up to 12 months. However, there is no information about the influence of this seasoning period on their 'corky' off flavors. For this reason, the main compounds responsible for the 'cork taint' of planks stored before processing from 6 to 12 months were investigated. RESULTS: Four haloanisoles and three halophenols were identified: 2,4,6-trichloroanisole (TCA), 2,3,4,6-tetrachloroanisole (TeCA), pentachloroanisole (PCA), 2,4,6-tribromoanisole (TBA), 2,4,6-trichlorophenol (TCP), 2,3,4,6-tetrachlorophenol (TeCP), and 2,4,6-tribromophenol (TBP). All of the planks presented some haloanisole or halophenol after 6 and 9 months of storage, which practically disappeared after a year of storage. These compounds were only detected in the cork stoppers made from planks with 6 and 9 months of storage. Of the alkylmethoxypyrazines, 2-methoxy-3,5-dimethylpyrazine (MDMP), 3-isopropyl-2-methoxypyrazine (IPMP), and 3-isobutyl-2-methoxypyrazine (IBMP) were identified. The MDMP was detected in a larger number of planks with 6 months of storage and at higher concentrations than IPMP and IBMP. However, MDMP was not detected in the cork stoppers made from planks at 6, 9, and 12 months of storage. CONCLUSION: A storage time of 6 months before processing of raw cork planks would be sufficient to obtain cork stoppers with low concentrations of corky off-flavor compounds. An increase in storage up to 9 or 12 months would result in practically 'cork taint'-free natural stoppers. © 2021 Society of Chemical Industry.

Simultaneous determination of haloanisoles and halophenols in water using in situ acylation combined with solid-phase microextraction with gas chromatography and mass spectrometry.

In this work, an in situ acylation combined with solid-phase microextraction coupled to gas chromatography and mass spectrometry method has been developed for simultaneously determining haloanisoles (2,4,6-trichloranisole, 2,4,6-tribromoanisole), and their direct precursors (2,4,6-trichlorophenol, 2,4,6-tribromophenol) and indirect precursors (2-chloropenol, 2,4-dichlorophenol, 2-bromophenol, 2,4-dibromophenol) in water. The key parameters for the solid-phase microextraction were determined by using Plackett-Burman screening and optimized by central composite optimization. Under optimal conditions, the eight compounds can be analyzed in a short time (33 min) with a strong linearity ranging from 2 to 200 ng/L (correlation coefficient greater than 0.996), showing good sensitivities with the limit of detection in a range of 0.23-0.91 ng/L and a limit of quantification of 0.77-3.03 ng/L, good repeatability (2.00-9.10%) and interday precision (1.67-11.3%). When environmental water samples were treated, the recoveries of target compounds were 75.5-127.3%, suggesting that the developed method could be applied in probing the origin of haloanisoles and monitoring halophenols and haloanisoles in natural waters at concentration levels of ng/L.

Environmental biodegradation of halophenols by activated sludge from two different sewage treatment plants.

Halophenols make a group of aromatic compounds that are resistible to biodegradation by environmental microorganisms. In this study, the biodegradation of 4-bromo-, 4-chloro- and 4-fluorophenols was studied with two types of activated sludges (from a small rural plant and from a bigger municipal plant) as an inoculum. Because of their wide use, surfactants are present in the wastewater and inhibitors enhance the biodegradation of different pollutants; the influence of natural surfactants on halophenols' biodegradation was also tested. Both types of activated sludge contained bacterial strains which were active in the halophenols' biodegradation process. The coexistence of surfactants and halophenols in the wastewater does not prevent microorganisms from effective halophenols' biodegradation. Moreover, surfactants can enhance the effectiveness of halophenols' removal from the environment. Different cell surface modifications of two isolated bacterial strains were observed in the same system of halophenols with or without surfactants. Halophenols and surfactants may also induce changes in bacteria cell surface properties.

Influence of saponins on the biodegradation of halogenated phenols.

Biotransformation of aromatic compounds is a challenge due to their low aqueous solubility and sorptive losses. The main obstacle in this process is binding of organic pollutants to the microbial cell surface. To overcome these, we applied saponins from plant extract to the microbial culture, to increase pollutants solubility and enhance diffusive massive transfer. This study investigated the efficiency of Quillaja saponaria and Sapindus mukorossi saponins-rich extracts on biodegradation of halogenated phenols by Raoultella planticola WS2 and Pseudomonas sp. OS2, as an effect of cell surface modification of tested strains. Both strains display changes in inner membrane permeability and cell surface hydrophobicity in the presence of saponins during the process of halogenated phenols biotransformation. This allows them to more efficient pollutants removal from the environment. However, only in case of the Pseudomonas sp. OS2 the addition of surfactants to the culture improved effectiveness of bromo-, chloro- and fluorophenols biodegradation. Also introduction of surfactant allowed higher biodegradability of halogenated phenols and can shorten the process. Therefore this suggests that usage of plant saponins can indicate more successful halogenated phenols biodegradation for selected strains.

Macrocyclic porphyrin photocatalysts without metal chelation: A novel pathway for complete degradation of tough halophenols with longwave visible LED light source.

Halophenols are toxic and persistent pollutants in water environments which poses harm to various organisms. Due to their high stability and long residence time, ultraviolet radiation, heavy metals and oxidizing agents have been largely adopted on treating these compounds. However, these treatment methods could pose toxicity or hazardous risks to the marine environment and plant operators. In this study, a water-soluble porphyrin photocatalyst was synthesized and introduced for halophenol treatment using UV-free LED white light. The porphyrin catalyst is a macrocyclic ring consisting of pyrroles linked with methine bridges, the highly conjugated ring provided the superior functionality of visible light absorption. Surprisingly, over 99 % degradation of halophenols and over 90 % dehalogenation have been achieved without metal chelation, even higher than those of transition metal porphyrins with inclusion of Fe3+, Zn2+, Cu2+, Co2+, Ni2+, and Mn2+. Ring-opening reactions were confirmed with the formation of carboxylic acids; dicarboxylic acids like acrylic acid, and malonic acid; while fumaric acid was the main product. Total organic carbon results indicated no CO2 produced during the reaction. Triplet absorbance and scavenger studies also indicated that singlet oxygen and conduction band electrons are the main radical species for halophenol degradation. The 100-fold singlet emission quenching over triplet absorption quenching indicated that the excited electrons tend to be transferred via singlet state. This concept brings along new approaches detoxifying halophenol-related wastewater without UV, metals and other additives, which is more environmentally-friendly and sheds light to the conversion of toxic materials into useful chemical precursors.

Determining high priority disinfection byproducts based on experimental aquatic toxicity data and predictive models: Virtual screening and in vivo study.

Only about 100 disinfection byproducts (DBPs) have been tested for their potential aquatic toxicity. It is not known which specific DBPs, DBP main groups, and DBP subgroups are more toxic due to the lack of experimental toxicity data. Herein, high priority specific DBPs, DBP main groups, DBP subgroups, most sensitive model aquatic species, potential PBT and PMT (persistent, bioaccumulative/mobile, and toxic) DBPs were virtually screened for 1187 updated DBPs inventory. Priority setting based on experimental and predicted acute and chronic aquatic toxicity data found that the aromatic and alicyclic DBPs in four DBPs main groups showed high priority because larger proportions of aromatic and alicyclic DBPs are in high hazard categories (i.e. Acute and/or Chronic Toxic-1 or Toxic-2) according to the criteria in GHS system compared to the aliphatic and heterocyclic DBPs. The halophenols, estrogen-DBPs, nonhalogenated esters, and nonhalogenated aldehydes were recognized as high priority DBPs subgroups. For specific DBPs, 19 and 31 DBPs should be highly concerned in the future study because both acute and chronic toxicity of those DBPs to all of the three aquatic life (algae, Daphnia magna, fish) were classified as Toxic-1 and Toxic-2, respectively. The Daphnia magna and algae were sensitive to the acute toxicity of DBPs, while the fish and Daphnia magna were sensitive to the chronic toxicity of DBPs. One potential PBT (Tetrachlorobisphenol A) and four potential PMT DBPs were identified. For verification, the acute toxicity of four DBPs on three aquatic organism were performed, and their tested acute toxicity data to three aquatic organisms were consistent with the predictions. Our results could be beneficial to government regulators to adopt effective measures to limit the discharge of high priority DBPs and help the scientific community to develop or improve disinfection processes to reduce the production of high priority DBPs.

Toxicity and underlying lipidomic alterations generated by a mixture of water disinfection byproducts in human lung cells.

Complex mixtures of disinfection by-products (DBPs) are present in disinfected waters, but their mixture toxicity has been rarely described. Apart from ingestion, DBP exposure can occur through inhalation, which may lead to respiratory effects in highly exposed individuals. However, the underlying biological mechanisms have yet to be elucidated. This study aimed to investigate the toxicity of a mixture of 10 DBPs, including haloacetic acids and haloaromatics, on human alveolar A549 cells by assessing their cytotoxicity, genotoxicity, and impact on the cell lipidome. A DBP mixture up to 50 µM slightly reduced cell viability, induced the generation of reactive oxygen species (ROS) up to 3.5-fold, and increased the frequency of micronuclei formation. Exposure to 50 µM DBP mixture led to a significant accumulation of triacylglycerides and a decrease of diacylglycerides and phosphatidylcholines in A549 cells. Lipidomic profiling of extracellular vesicles (EVs) released in the culture medium revealed a marked increase in cholesterol esters, sphingomyelins, and other membrane lipids. Overall, these alterations in the lipidome of cells and EVs may indicate a disruption of lipid homeostasis, and thus, potentially contribute to the respiratory effects associated with DBP exposure.

Comparative studies of transformation behaviors and mechanisms of halophenols in multiple chemical oxidative systems.

Due to wide applications, halophenols (HPs), especially bromophenols, chlorophenols, and fluorophenols, are commonly detected but resistant to biological removal in wastewater treatment plants (WWTPs). This study investigated the overall transformation behaviors of three representative HPs (2,4-dichlorophenol: 24-DCP, 2,4-dibromophenol: 24-DBP, 2,4-difluorophenol: 24-DFP) in six chemical oxidative systems (KMnO4, K2FeO4, NaClO, O3, UV, and persulfate (PS)). The results revealed fast removal of selected HPs by O3, PS and K2FeO4, while a large discrepancy in their removal efficiencies occurred under UV irradiation, KMnO4 oxidation and particularly chlorination. Based on the analysis of the identified intermediates and products, coupling among the five routes was the general route, and dimers were the main intermediates for HP oxidation. The effect of the halogen atom on the transformation pathways of HPs was highly reaction type dependent. Among the six chemical treatments, PS could induce HPs to yield relatively low-molecular-weight polymers and obtain the highest coupling degree. Transition state (TS) calculations showed that the H atom linked to the phenoxy group of HPs was the most easily abstracted by hydroxyl radicals to form the coupling precursor, i.e., phenoxy radicals. This high coupling behavior further resulted in the increased toxicity to green algae. Characterization revealed that HP reaction solutions treated with PS had a severely negative effect on algae growth, photosynthetic pigment synthesis, and the antioxidant enzyme system. These findings can shed light on the reaction mechanisms of advanced oxidation technologies and some risk management and control of PS technique may be considered when treating phenolic pollutants.

Dioxin-like compounds formation mediated by Fe3+-montmorillonite: The substituent effects of halophenols.

Toxic dioxin or/and dioxin-like compounds could be naturally formed from the reaction of halophenols on Fe3+-montmorillonite minerals under ambient conditions. Given that the toxicities and productions of dioxin or/and dioxin-like compounds are largely determined by the number, species, and position of the carried halogen atoms, it is necessary to explore the substituent effects on the reaction of halophenols with Fe3+-montmorillonite. Herein, Fe3+-montmorillonite catalyzed polymerizations of six halophenols were examined in a wide range of relative humidity (10%∼80%) using combinations of mass spectrometry identifications and density functional theory calculations. Results show that both the position and species of the substituents substantially impact the reaction rate, product species, and transformation pathways. In general, regardless of humidity ortho-substituted chlorophenols are more reactive than meta-substituted chlorophenols, which is also supported by the density functional theory calculations indicating that the ortho positions are more likely to be attacked. Regarding substituent species, bromophenols are slightly more reactive and also more easily affected by humidities than chlorophenols, which is due to the weaker electron absorbing ability of the bromine atom than the chlorine atom. Hydroxylated polyhalogenated diphenyl ethers are more frequently detected polymerization products, although hydroxylated polyhalogenated biphenyls are greater quantity of products. Overall, this study provides useful information for understanding the natural formation of dioxin or/and dioxin-like compounds mediated by clay minerals and underlying reaction mechanisms.

Investigation on detoxication effects of 2-hydroxypropyl-ß-cyclodextrin over two halogenated aromatic DBPs 2,4,6-trichlorophenol and 2,4,6-tribromophenol binding with human serum albumin.

The health effects of disinfection byproducts (DBPs) in drinking water drew great attention recently. Herein, by using in vitro (fluorescence quenching, UV absorbance, circular dichroism) and in silico (molecular docking) method, binding interactions of two halophenolic DBPs (2,4,6-trichlorophenol [TCP] and 2,4,6-tribromophenol [TBP]) with human serum albumin (HSA) and the influence of hydroxypropyl-beta-cyclodextrin (HPCD) on the interactions were investigated. TCP/TBP could form complexes with HSA mainly by hydrogen bonding, while changing its secondary structure, among which TBP showed more influential effect. Interestingly, the binding constants for halophenol-HSA complexes decreased obviously with the involvement of HPCD. Molecular docking results revealed that HPCD could include TCP/TBP into its cavity and change their original binding sites from subdomain IB to IIA, resulting in a more stable binding system. These findings are beneficial for understanding the toxicity of halophenols inside the human body and indicated that HPCD could be a promising detoxication agent for DBPs.

Development and validation of a method for the analysis of halophenols and haloanisoles in cork bark macerates by stir bar sorptive extraction heart-cutting two-dimensional gas chromatography negative chemical ionization mass spectrometry.

A method has been developed for the quantitative determination in cork bark macerates of 7 halophenols and 5 haloanisoles with demonstrated or suspected contribution to the cork taint off-flavour. Macerates were extracted with stirbar (20 mm polydimethylsiloxane-coated) sorptive extraction under optimized conditions (pH 3.5, 20% NaCl and 60 min). The bars were analysed by automated thermal desorption, heart-cutting two-dimensional gas chromatography and negative chemical ionization-mass spectrometry. Matrix effects were compensated for by a "matrix matched" calibration curve. Limits of detection were in the range 0.03-0.24 ng L-1, below the corresponding odor thresholds. Linearity (0.983 ≤ R2 ≤ 0.998), intra- and inter-day precision (5.4-14.3%) and accuracy (89-126%) were satisfactory. The analysis of 48 natural cork bark samples affected/not-affected bya cryptogamic disease (yellow spot) revealed compositional differences in 2,4,6-trichloroanisole (2,4,6-TCA), 2,4,6-trichlorophenol (2,4,6-TCP) and also in 2,6-dibromophenol, 2,3,4- and 2,4,5-TCP, 2,3,4-TCA and 2,3,4,6-tetrachlorophenol (2,3,4,6-TeCP). In addition, the contents of 2,4,6-TCP and 2,4,6-TCA, and 2,3,4,6-TeCP and some TCPs presented strong linear correlations.

Sustained production of superoxide radicals by manganese oxides under ambient dark conditions.

Manganese (Mn) oxides are ubiquitous in the environment and have strong reactivity to induce the transformation of various contaminants. However, whether reactive oxygen species contribute to their surface reactivity remains unclear. Here, sustainable production of superoxide radicals (O2•-) by various MnO2 polymorphs in the dark was quantified and the mechanisms involved were explored. The results confirm that O2•- was produced through one-electron transfer from surface Mn(III) to adsorbed O2. In contrast, no H2O2 was detected due to its decomposition by Mn oxides to form O2•- and Mn(III), leading to the sustained production of O2•- on Mn oxide surfaces. In addition, the production of O2•- was found to make a clear contribution (4 - 28%) to the transformation of a series of halophenols by MnO2, suggesting that the O2•--mediated surface reaction is an important supplement to the direct electron-transfer mechanism in the reactivity of Mn oxides. These findings advance our understanding of the surface reactivity of Mn oxides and also reveal an important but hitherto unrecognized abiotic source of O2•- in the natural environment.

Control of halophenol formation in seawater during chlorination using pre-ozonation treatment.

The reverse osmosis process is widely used for seawater desalination, whereas the pre-chlorination step for controlling membrane biofouling results in undesirable disinfection by-products, such as halophenols (HPs) which are not yet regulated but of increasing concerns. The formation and speciation of HPs during chlorination of three filtered seawater samples (SA, SB, and SC) with various phenol concentrations (0.25, 0.5, 1.0 mg/L) were evaluated. 4-Bromophenol (4-BrP), 2,4,6-trichlorophenol (2,4,6-TClP), 2,4-dibromophenol (2,4-DBrP), and 2,4,6-tribromophenol (2,4,6-TBrP) were identified during chlorination, with 2,4,6-TBrP as the predominant HP. Ozone as a common oxidant in water and wastewater treatment was subsequently applied to assess its effect in dissolved organic matter (DOM) and its ability of reducing HP precursors in the seawater samples. An initial ozone dose of 5 mg O3/L was capable of reducing dissolved organic carbon (DOC) in SA, and UV absorbance at 254 nm (UV254) in SB, whereas it induced an elevation of UV254 in SC. When ozone dose increased to 10 mg O3/L, the DOC and UV254 levels in all seawater samples were reduced. Ozone was more powerful on degrading DOM with molecular weight (MW) of near 1000 Da than those with MW of 20-100 Da, both of which composed the majority of DOM in the seawater samples. As determined by excitation emission matrix fluorescence spectroscopy, the most ozone-susceptible fraction of DOM was soluble microbial by-product-like substances, while the least was tryptophan-like aromatic proteins. Despite that the initial ozone of 5 mg O3/L was less effective in DOM degradation than the higher dose, it successfully degraded HP precursors. By pre-ozonation at 5 mg O3/L, no chlorophenol was detected during chlorination, and the mean reductions of the three bromophnols formed were above 92% in all seawater samples, with the reduction of 2,4,6-TBrP being the highest of 99.7, 99.6, and 99.1% in SA, SB, and SC, respectively.

Synthesis of 4H-Benzo[e][1,3]oxazin-4-ones by a Carbonylation-Cyclization Domino Reaction of ortho-Halophenols and Cyanamide.

A mild and convenient one-step preparation of 4H-1,3-benzoxazin-4-ones by a domino carbonylation-cyclization process is developed. Readily available ortho-iodophenols are subjected to palladium-catalyzed carbonylative coupling with Mo(CO)6 and cyanamide, followed by a spontaneous, intramolecular cyclization to afford 4H-1,3-benzoxazin-4-ones in moderate to excellent yields. Furthermore, the scope of the reaction is extended to include challenging ortho-bromophenols. Finally, to highlight the versatility of the developed method, Mo(CO)6 is successfully replaced with a wide array of CO-releasing reagents, such as oxalyl chloride, phenyl formate, 9-methylfluorene-9-carbonyl chloride, and formic acid, making this an appealing strategy for the synthesis of 4H-benzo[e][1,3]oxazin-4-ones.

Determination of trichloroanisole and trichlorophenol in wineries' ambient air by passive sampling and thermal desorption-gas chromatography coupled to tandem mass spectrometry.

The present paper describes the calibration of selected passive samplers used in the quantitation of trichlorophenol and trichloroanisole in wineries' ambient air, by calculating the corresponding sampling rates. The method is based on passive sampling with sorbent tubes and involves thermal desorption-gas chromatography-triple quadrupole mass spectrometry analysis. Three commercially available sorbents were tested using sampling cartridges with a radial design instead of axial ones. The best results were found for Tenax TA™. Sampling rates (R-values) for the selected sorbents were determined. Passive sampling was also used for accurately determining the amount of compounds present in the air. Adequate correlation coefficients between the mass of the target analytes and exposure time were obtained. The proposed validated method is a useful tool for the early detection of trichloroanisole and its precursor trichlorophenol in wineries' ambient air while avoiding contamination of wine or winery facilities.

A simple and sensitive vortex assisted liquid-liquid microextraction method for the simultaneous determination of haloanisoles and halophenols in wines.

A vortex assisted liquid-liquid microextraction (VALLME) method was developed and optimised for the determination of the main compounds that can cause cork taint in wines, 2,4,6-trichloroanisole (TCA), 2,3,4,6-tetrachloroanisole (TeCA), 2,4,6-tribromoanisole (TBA) and pentachloroanisole (PCA); and their corresponding halophenolic precursors. Target compounds were determined by gas chromatography combined with a micro-electron capture detector (GC-µECD) system. Halophenol extraction and derivatisation processes were performed at the same time. To optimise the VALLME method, the extraction solvent was selected. Then, the other parameters of influence, such as volume of extraction solvent and derivatisation agent, salt addition and vortex time were optimised using a central composite design combined with desirability functions. Once the optimal conditions had been determined, the method was validated, showing satisfactory linearity (with correlation coefficients over 0.983), repeatability (below 10.0%) and reproducibility (below 11.2%). Detection limits obtained were lower than the olfactory threshold of the studied compounds, being similar or even lower than previously reported with the advantage of reducing the extraction time. The analysis of real wine samples demonstrated the applicability of the method. To our knowledge, this is the first time that VALLME has been applied for the simultaneous determination of haloanisoles and halophenols in wine.

Development of a thermal desorption gas chromatography-mass spectrometry method for quantitative determination of haloanisoles and halophenols in wineries' ambient air.

An analytical method for the detection and quantification of haloanisoles and their corresponding halophenols in wineries' ambient air was developed. The target analytes were haloanisoles and halophenols, reported by previous scientific literature as responsible for wine taint. A calibrated pump and active tubes filled with Tenax GR™ were used for sampling. These tubes were thermally desorbed and analyzed using gas chromatography-triple quadrupole mass spectrometry in the selected reaction monitoring mode. The adsorption efficiencies of five commercial sampling tubes filled with different materials were evaluated. The efficiencies of the selected adsorbent were close to 100% for all sampled compounds. Desorption, chromatographic and mass spectrometric conditions were accurately optimized allowing very low limits of quantification and wide linear ranges. The limits of quantification in ambient air ranged from 0.8pgtube(-1) for 2,4,6-trichlorophenol, to 28pgtube(-1) for pentachlorophenol. These results are of great importance because human sensory threshold for haloanisoles is very low. The chromatographic method was also validated and the instrumental precision and trueness were established, a maximum RSD of 9% and a mean recovery of 91-106% were obtained. The proposed method involves an easy and sensitive technique for the early detection of haloanisoles and their precursor halophenols in ambient air avoiding contamination of wine or winery facilities.