Enantioselective Environmental Toxicology of Chiral Pesticides

Toxic effect and mechanism of β-cypermethrin and its chiral isomers on HTR-8/SVneo cells

Beta-cypermethrin (β-CYP) consists of four chiral isomers, acting as an environmental estrogen and causing reproductive toxicity, neurotoxicity, and dysfunctions in multiple organ systems. This study investigated the toxic effects of β-CYP, its isomers, metabolite 3-phenoxybenzoic acid (3-PBA), and 17β-estradiol (E2) on HTR-8/SVneo cells. We focused on the toxic mechanisms of β-CYP and its specific isomers. Our results showed that β-CYP and its isomers inhibit HTR-8/SVneo cell proliferation similarly to E2, with 100 μM 1S-trans-αR displaying significant toxicity after 48 h. Notably, 1S-trans-αR, 1R-trans-αS, and β-CYP were more potent in inducing apoptosis and cell cycle arrest than 1R-cis-αS and 1S-cis-αR at 48 h. AO/EB staining and flow cytometry indicated dose-dependent apoptosis in HTR-8/SVneo cells, particularly at 100 μM 1R-trans-αS. Scratch assays revealed that β-CYP and its isomers variably reduced cell migration. Receptor inhibition assays demonstrated that post-ICI 182780 treatment, which inhibits estrogen receptor α (ERα) or estrogen receptor β (ERβ), β-CYP, its isomers, and E2 reduced HTR-8/SVneo cell viability, whereas milrinone, a phosphodiesterase 3 A (PDE3A) inhibitor, increased viability. Molecular docking studies indicated a higher affinity of β-CYP, its isomers, and E2 for PDE3A than for ERα or ERβ. Consequently, β-CYP, its isomers, and E2 consistently led to decreased cell viability. Transcriptomics and RT-qPCR analyses showed differential expression in treated cells: up-regulation of Il24 and Ptgs2, and down-regulation of Myo7a and Pdgfrb, suggesting the PI3K-AKT signaling pathway as a potential route for toxicity. This study aims to provide a comprehensive evaluation of the cytotoxicity of chiral pesticides and their mechanisms.

Chiral Flipping in Viedma Deracemization

Understanding deracemization is crucial for progress in chiral chemistry, especially for improving separation techniques. Here, we first report the phenomenon of chiral flipping (or reverse deracemization) in a chiral material (i.e., sodium chlorate crystals) during Viedma deracemization, employing a small-volume reactor system for precise analysis. We observe considerable chiral flipping, influenced by the initial imbalance in the numbers of L- and D-form particles. We developed a simple probabilistic model to further elucidate this behavior. We find that the fluctuation in the populations of chiral crystal particles resulting from their random dissolution and regeneration is the key factor behind chiral flipping. This study not only brings to light this intriguing observation of chiral flipping but also contributes to the enhancement of deracemization techniques.

Enantioselective analysis of the pesticide imazamox after in vitro permeability study in Caco-2 cells

Imazamox (IMX), a chiral herbicide used in cereals and oilseed crops to control weeds, is commonly sold as a racemic mixture. Its enantiomers, being chiral compounds, may exhibit unique properties when exposed to chiral environments. While IMX enantiomers have been reported to degrade differently in soil and be toxic to some species, their effects on human systems remain poorly understood. This study utilized Caco-2 (human colon adenocarcinoma cell line) cells to assess the in vitro permeability of a racemic mixture of IMX and its isolated enantiomers. Additionally, the study aimed to evaluate whether the metabolite imazamox-O-desmethyl (IMX-D) forms during the permeability process. An enantioselective chromatographic method was developed, fully validated, and the apparent permeability values were obtained. The apparent permeability of rac-IMX, (+)-IMX, and (-)-IMX was determined to be 4.15 × 10-5 , 5.78 × 10-5 , and 7.33 × 10-5  cm s-1 , respectively. These findings suggest that IMX exhibits high intestinal permeability, with an enantioselective absorption for (-)-IMX as compared to (+)-IMX. Finally, the permeability study in Caco-2 cells revealed that the metabolite IMX-D was not generated.

Enantioselective metabolism of fenpropathrin enantiomers by carboxyl/choline esterase 6 in Tetranychus cinnabarinus

BACKGROUND

Tetranychus cinnabarinus is a polyphagous pest mite commonly found in agriculture. As an excellent acaricide, fenpropathrin (FEN) is frequently used to control T. cinnabarinus in agriculture. However, commercial FEN is a racemate with two enantiomers, R-FEN and S-FEN. Considering that investigations on the metabolism of FEN by T. cinnabarinus are based on racemate FEN, it is important to investigate the enantioselective metabolism of FEN in T. cinnabarinus.

RESULTS

S-FEN was more toxic to T. cinnabarinus than R-FEN by more than 68.8-fold. Moreover, the synergist bioassay revealed that carboxylesterase and cytochrome P450 were the primary enzymes engaged in the detoxification of FEN in T. cinnabarinus, with carboxylesterase playing a leading role. Seven genes were substantially different after the induction of S-FEN and R-FEN. TcCCE06 was screened and selected as a key gene that related to FEN metabolism in T. cinnabarinus. The metabolic results showed that the recombinant TcCCE06 effectively metabolized 32.1% of the R-FEN and 13.8% of the S-FEN within 4 h of incubation. Moreover, R-FEN was demonstrated to have a higher affinity for the TcCCE06 protein than S-FEN based on molecular docking.

CONCLUSION

Our results indicated that TcCCE06 mediates the enantioselective metabolism of FEN in T. cinnabarinus. Our findings will contribute to a more comprehensive understanding of the mechanisms underlying the differential toxicity of the FEN enantiomers against T. cinnabarinus. Furthermore, they also provide a new perspective for the development of enantiomer-enriched acaricides with higher activity and lower pesticide dosage and pollution risks. © 2023 Society of Chemical Industry.

Investigation of the miRNA levels changes to acceptable daily intake dose pesticide mixture exposure on rat mesentery and pancreas

Consumers are constantly exposed to a variety of chemical mixtures as part of their everyday activities and lifestyle. Food, water and commercial products are only some examples of the possible ways people get exposed to these mixtures. However, following federal and local guidelines for risk assessment related to chemical exposure, risk analysis focuses on a single substance exposure scenario and not on a mixture, as in real life. Realizing the pronounced gap of this methodology, the real-life risk simulation scenario approach tries to address this problem by investigating the possible effect of long-term exposure to chemical mixtures closely resembling the actual circumstances of modern life. As part of this effort, this study aimed to identify the cumulative effects of pesticides belonging to different classes and commonly used commercial products on long-term exposure with realistic doses. Sprague Dawley rats were given a pesticide mix of active ingredients and formulation chemicals in a daily acceptable dose (ADI) and 10xADI for 90 days. Following thorough everyday documentation of possible side-effects, after 90 days all animals were sacrificed and their organs were examined. Exposure to pesticides particularly affects the miRNA levels at that point will provide us with more information about whether they can be potential biomarkers.

Enantioseparation of agrochemicals by gas chromatography. Exploring columns based on cyclodextrin derivatives dissolved into polysiloxanes

The main goal of this work is to expand the availability of chiral columns for the analysis of agrochemicals by gas chromatography. A broader offer of chiral stationary phases would allow shifting toward enantioselective analytical techniques environmentally more friendly for those compounds. We prepared seven chiral capillary columns based on derivatives of either, β-cyclodextrin or γ-cyclodextrins dissolved at high concentrations, in two typical polysiloxanes with different polarities, demonstrating not only the significance of the chiral selector but also of the polymer solvent for achieving adequate enantioseparation of some agrochemicals. The enantiorecognition ability of each column was evaluated with 20 volatile and semivolatile agrochemicals, possessing one or two chiral centers. Besides, to elute more polar agrochemicals, as well as to enhance enantioselectivity, three derivatization procedures targeting the carboxyl and/or amine group were evaluated. The results revealed that the prepared column consisting of octakis(2,3-di-O-acetyl-6-O-tertbutyldimethylsilyl)-γ-cyclodextrin dissolved in (14%-cyanopropyl-phenyl)-86%-methyl-polysiloxane provides the broadest enantiorecognition capacity. This column allowed the enantioseparation of seventeen chiral agrochemicals, including metalaxyl, furalaxyl, and four imidazolinones, which were not enantioseparated in the remaining columns. To the best of our knowledge, glufosinate, fluorochloridone, fenarimol, furalaxyl, and four imidazolinones were enantioseparated by gas chromatography for the first time.

Effect of Extra-Framework Anion Substitution on the Properties of a Chiral Crystalline Sponge

Chiral metal-organic materials, CMOMs, are of interest as they can offer selective binding sites for chiral guests. Such binding sites can enable CMOMs to serve as chiral crystalline sponges (CCSs) to determine molecular structure and/or purify enantiomers. We recently reported on the chiral recognition properties of a homochiral cationic diamondoid, dia, network {[Ni(S-IDEC)(bipy)(H2O)][NO3]}n (S-IDEC = S-indoline-2-carboxylicate, bipy = 4,4'-bipyridine), CMOM-5[NO3]. The modularity of CMOM-5[NO3] means there are five feasible approaches to fine-tune structures and properties via substitution of one or more of the following components: metal cation (Ni2+); bridging ligand (S-IDEC); linker (bipy); extra-framework anion (NO3-); and terminal ligand (H2O). Herein, we report the effect of anion substitution on the CCS properties of CMOM-5[NO3] by preparing and characterizing {[Ni(S-IDEC)(bipy)(H2O)][BF4]}n, CMOM-5[BF4]. The chiral channels in CMOM-5[BF4] enabled it to function as a CCS for determination of the absolute crystal structures of both enantiomers of three chiral compounds: 1-phenyl-1-butanol (1P1B); methyl mandelate (MM); ethyl mandelate (EM). Chiral resolution experiments revealed CMOM-5[BF4] to be highly selective toward the S-isomers of MM and EM with enantiomeric excess, ee, values of 82.6 and 78.4%, respectively. The ee measured for S-EM surpasses the 64.3% exhibited by [DyNaL(H2O)4] 6H2O and far exceeds that of CMOM-5[NO3] (6.0%). Structural studies of the binding sites in CMOM-5[BF4] provide insight into their high enantioselectivity.

Structure-Dependent Mechanism of Organophosphate Release from Albumin and Butyrylcholinesterase Adducts When Exposed to Fluoride Ion: A Comprehensive In Silico Study

The most favorable targets for retrospectively determining human exposure to organophosphorus pesticides, insecticides, retardants, and other industrial organophosphates (OPs) are adducts of OPs with blood plasma butyrylcholinesterase (BChE) and human serum albumin (HSA). One of the methods for determining OP exposure is the reactivation of modified BChE using a concentrated solution of KF in an acidic medium. It is known that under the action of fluoride ion, OPs or their fluoroanhydrides can be released not only from BChE adducts but also from the adducts with albumin; however, the contribution of albumin to the total pool of released OPs after plasma treatment with KF has not yet been studied. The efficiency of OP release can be affected by many factors associated with the experimental technique, but first, the structure of the adduct must be taken into account. We report a comparative analysis of the structure and conformation of organophosphorus adducts on HSA and BChE using molecular modeling methods and the mechanism of OP release after fluoride ion exposure. The conformational analysis of the organophosphorus adducts on HSA and BChE was performed, and the interaction of fluoride ions with modified proteins was studied by molecular dynamics simulation. The geometric and energy characteristics of the studied adducts and their complexes with fluoride ion were calculated using molecular mechanics and semiempirical approaches. The structural features of modified HSA and BChE that can affect the efficiency of OP release after fluoride ion exposure were revealed. Using the proposed approach, the expediency of using KF for establishing exposure to different OPs, depending on their structure, can be assessed.

Enantioselective metabolism of novel chiral insecticide Paichongding by human cytochrome P450 3A4: A computational insight

As a novel chiral neonicotinoid insecticide, Paichongding (IPP) has been widely applied in agriculture due to its excellent insecticidal activity. However, the enantioselective metabolism of IPP stereoisomers (5R7R-IPP, 5S7S-IPP, 5R7S-IPP, and 5S7R-IPP) mediated by enzymes in non-target organisms, especially the cytochrome P450s (CYPs), remains unknown. To address this knowledge gap, we developed an integrated computational framework to elucidate the binding interactions and enantioselective metabolism of IPP stereoisomers in human CYP3A4. The results reveal that 5R7R-IPP shows much stronger binding affinity to CYP3A4 than 5S7S-IPP, while enantiomers 5R7S-IPP and 5S7R-IPP have no essential difference in their binding potential, owing to their specific interactions with key CYP3A4 residues. Although enantiomers 5R7R-IPP and 5S7S-IPP feature distinct binding modes resulting from the chiral differences, their transformation activities are slightly different, with C5 and C13 being the primary metabolic sites, respectively. In contrast, CYP3A4 preferably metabolizes 5R7S-IPP over 5S7R-IPP. The metabolism of epimers 5R7R-IPP and 5R7S-IPP share C5-hydroxylation routes due to the conserved 5R-conformaitons, but differ with the transformation routes at C11/C13 and C3 sites. The 7R-chirality of 5S7R-IPP significantly reduces the metabolic potency compared to 5S7S-IPP. CYP3A4-catalyzed hydroxylation and desaturation of IPP stereoisomers generate various chiral metabolites, with C5- and C13-hydroxyIPPs further transforming into depropylated products. Furthermore, the toxicity assessment reveals that IPP, along with the majority of its hydroxylated, desaturated, and depropylated metabolites, can potentially induce adverse effects on human health, specifically hepatotoxicity, respiratory toxicity, and carcinogenicity. This study provides valuable insights into the enantioselective fate of chiral IPP metabolism by CYP3A4, and the identified metabolites can serve as potential biomarkers for monitoring IPP exposure and associated health risk in human body.

Tefluthrin induced toxicities in zebrafish: Focusing on enantioselectivity

Tefluthrin is one of widely used chiral pyrethroid pesticides. The potential enantioselective risk posed by tefluthrin to the aquatic ecosystem is still unclear. In this study, the toxicity differences and corresponding mechanism of tefluthrin on zebrafish were investigated at the enantiomeric level. The results indicated that two tefluthrin enantiomers showed different acute toxicity, developmental toxicity and oxidative stress to zebrafish. The acute toxicity of (1R,3R)-tefluthrin was 130-176 fold as that of (1S,3S)-tefluthrin on zebrafish embryos, larvae and adults. (1R,3R)-Tefluthrin presented approximately 10, 3 and 2 times inhibition effect on the deformity rate, hatching rate and spontaneous movements on embryos as that of (1S,3S)-tefluthrin. Meanwhile, (1R,3R)-tefluthrin caused stronger oxidative stress on zebrafish embryo than (1S,3S)-tefluthrin. The molecular docking results revealed that there were stereospecific binding affinities between tefluthrin enantimers and sodium channel protein (Nav1.6), which may lead to acute toxicity differences. Transcriptome analysis showed that the two tefluthrin enantiomers markedly disturbed differential embryonic genes expression, thereby potentially causing the chronic enantioselective toxicity. The findings of the study reveal the toxicity differences and potential mechanism of tefluthrin enantiomers on zebrafish. These results also provides a foundation for a systematic evaluation of tefluthrin at enantiomer level.

Enantioseparation/Recognition based on nano techniques/materials

Enantiomers show different behaviors in interaction with the chiral environment. Due to their identical chemical structure and their wide application in various industries, such as agriculture, medicine, pesticide, food, and so forth, their separation is of great importance. Today, the term "nano" is frequently encountered in all fields. Technology and measuring devices are moving towards miniaturization, and the usage of nanomaterials in all sectors is expanding substantially. Given that scientists have recently attempted to apply miniaturized techniques known as nano-liquid chromatography/capillary-liquid chromatography, which were originally accomplished in 1988, as well as the widespread usage of nanomaterials for chiral resolution (back in 1989), this comprehensive study was developed. Searching the terms "nano" and "enantiomer separation" on scientific websites such as Scopus, Google Scholar, and Web of Science yields articles that either use miniaturized instruments or apply nanomaterials as chiral selectors with a variety of chemical and electrochemical detection techniques, which are discussed in this article.

Comprehensive evaluation of novel fungicide benzovindiflupyr at the enantiomeric level: Bioactivity, toxicity, mechanism, and dissipation behavior

Racemates in the environment can lead to inaccurate risk assessment. To obtain the enantiomeric level information of benzovindiflupyr for accurate risk assessment, the absolute configuration of benzovindiflupyr was first confirmed, and the enantioseparation method was developed by supercritical fluid chromatography tandem mass spectrometry. The enantioselectivity for bioactivity and toxicity was investigated, and the mechanism was explored by molecular docking and detecting succinate dehydrogenase (SDH) activity and content of succinate acid. 1S,4R-(-)-benzovindiflupyr was identified as the most active against the six targeted phytopathogens, which showed higher 1.7-54.5 times than 1R,4S-(+)-benzovindiflupyr. Additionally, 1S,4R-(-)-benzovindiflupyr (LD₅₀: 21.54 μg L^-1) was 103.7 times more toxic than 1R,4S-(+)-benzovindiflupyr against Daphnia magna. 1S,4R-(-)-benzovindiflupyr had a stronger affinity for SDH and significantly inhibited SDH activity, resulting in an increase in succinate acid in the tricarboxylic acid cycle, while its downstream products, fumaric and L-malic acid were significantly reduced. Moreover, the dissipation behavior of benzovindiflupyr on three vegetables was evaluated. 1S,4R-(-)-benzovindiflupyr was preferentially degraded in tomato, but opposite in leaves. The enantioselectivity in pepper and cucumber leaves was the same as in tomato, while there was no enantioselectivity in pepper and cucumber. The study provides a basis for accurate risk assessment and the development of high-effective and low-risk fungicides.

Enantioselectivity in the toxicological effects of chiral pesticides: A review

As a special category of pesticides, chiral pesticides have increased the difficulty in investigating pesticide toxicity. Based on their usage, chiral pesticides can be divided into insecticides, herbicides, and fungicides. Over the past decades, great efforts have been made on elucidating their toxicological effects. However, no literature has reviewed the enantioselective toxicity of chiral pesticides since 2014. In recent years, more chiral pesticides have been registered for application. As such, huge research progresses have been achieved in enantioselective toxicity of chiral pesticides. Generally, more researches have remedied the knowledge gap in toxicological effects of old and new chiral pesticides. And the toxicological endpoints being evaluated have become more specific rather than centering on basic toxicity and target organisms. Besides, the underlying mechanisms accounting for the enantioselectivity in toxicological effects of chiral pesticides have been discussed as well. All in all, this review provides the critical knowledge for risk assessments, and help to drive the green-technology of single- or enriched-enantiomer pesticides and formulation of relevant laws and regulations.

Systematic evaluation of chiral pesticides at the enantiomeric level: A new strategy for the development of highly effective and less harmful pesticides

Over the past few decades, pesticides have been used in large quantities, and they pose potential risks to organisms across various environments. Reducing the use of pesticides and their environmental risks has been an active research focus and difficult issue worldwide. As a class of pesticides with special structures, chiral pesticides generally exhibit enantioselectivity differences in biological activity, ecotoxicity, and environmental behavior. At present, replacing the racemates of chiral pesticides by identifying and developing their individual enantiomers with high efficiency and environmentally friendly characteristics is an effective strategy to reduce the use of pesticides and their environmental risks. In this study, we review the stereoselective behaviors of chiral pesticide, including their environmental behavior, stereoselective biological activity, and ecotoxicity. In addition, we emphasize that the systematic evaluation of chiral pesticides at the enantiomeric level is a promising novel strategy for developing highly effective and less harmful pesticides, which will provide important data support and an empirical basis for reducing pesticide application.

Simultaneous enantioselective determination of two succinate- dehydrogenase-inhibitor fungicides in plant-origin foods by ultra-high performance liquid chromatography-tandem mass spectrometry

Fluindapyr and penthiopyrad are two new succinate-dehydrogenase-inhibitor fungicides both employed as racemic mixtures of enantiomers to control various fungal pathogens. In the present work, a robust and highly-sensitive method for simultaneous determination of fluindapyr and penthiopyrad enantiomers in plant-origin foods (cereals, fruits and vegetables) was developed using UPLC-MS/MS combined with a chiral stationary phase. Rapid baseline chiral separation of four stereoisomers of fluindapyr and penthiopyrad was obtained within 4.2 min on chiral MX(2)-RH column under reversed-phase conditions (with the eluent of acetonitrile/0.1% formic acid in water =70/30 (V:V) and column temperature maintained at 30 °C). The plant-origin samples were extracted quickly with acetonitrile and purified with multi-walled carbon nanotubes. Excellent linearity for the target analytes was observed in the concentration ranging from 1 to 250 µg/L with regression coefficient no less than 0.9967. The mean recoveries of fluindapyr and penthiopyrad enantiomers from six matrices were 77.1-107.2%, with all relative standard deviations values lower than 9.1%. The limit of quantification of four stereoisomers of two target chiral fungicides was 5 µg/kg. The analysis of real samples reveal that the developed method is suitable for the simultaneous chiral determination of fluindapyr and penthiopyrad residues in cereals, fruits and vegetables samples at enantiomeric level and can support their further investigation on enantioselective environmental behaviors and residue surveillance.

Chiral Recognition with Broad Selective Sensor Arrays

The detection and discrimination of chiral analytes has always been a topical theme in food and pharmaceutical industries and environmental monitoring, especially when dealing with chiral drugs and pesticides, whose enantiomeric nature assessment is of crucial importance. The typical approach matches novel chiral receptors designed ad hoc for the discrimination of a target enantiomer with emerging nanotechnologies. The massive synthetic efforts requested and the difficulty of analyzing complex matrices warrant the ever-growing exploitation of sensor array as an alternative route, using a limited number of chiral or both chiral and achiral sensors for the stereoselective identification and dosing of chiral compounds. This review aims to illustrate a little-explored winning strategy in chiral sensing based on sensor arrays. This strategy mimics the functioning of natural olfactory systems that perceive some couples of enantiomeric compounds as distinctive odors (i.e., using an array of a considerable number of broad selective receptors). Thus, fundamental concepts related to the working principle of sensor arrays and the role of data analysis techniques and models have been briefly presented. After the discussion of existing examples in the literature using arrays for discriminating enantiomers and, in some cases, determining the enantiomeric excess, the remaining challenges and future directions are outlined for researchers interested in chiral sensing applications.

Toxicity, bioactivity of triazole fungicide metconazole and its effect on mycotoxin production by Fusarium verticillioides: New perspective from an enantiomeric level

The chiral triazole fungicide metconazole has four stereoisomers, is a broad-spectrum fungicide and is widely used for controlling Fusarium head blight caused by Fusarium species. In this study, systemic assessments of metconazole stereoisomers were performed, including stereoselective toxicity toward the aquatic organism Daphnia magna, fungicidal activity and effects on fumonisin production by the pathogen Fusarium verticillioides (F. verticillioides) in relation to different conditions. The toxicity of metconazole was enantioselective, and there was a 2.1-2.9-fold difference. The activities of superoxide dismutase (SOD) and catalase (CAT) increased and decreased, respectively, after treatment with metconazole stereoisomers, and the differences were observed among the stereoisomers. Among the four stereoisomers, (1S,5R)-metconazole showed the highest fungicidal activity under all assayed conditions, and the differences ranged from 4.4 to 45.2 times. Moreover, metconazole stereoisomers can stereoselectively affect on fumonisin B₁ production by F. verticillioides and abiotic factors, such as water activity and temperature, play an important role. Our study provides new insight into metconazole at the stereoisomeric level, including its toxicity, bioactivity, and effect on Fusarium species producing mycotoxins.

A Novel Enantioseparation Method and Enantioselective Dissipation of Novaluron in Tomatoes Using Ultrahigh-Performance Liquid Chromatography Tandem Mass Spectrometry via a Box-Behnken Design

Enantioseparation parameters of novaluron were optimized on a Chiralpak IG-3 column by ultrahigh-performance liquid chromatography tandem mass spectrometry via response surface methodology. The absolute configuration and elution order were identified as R-(+)-novaluron and S-(-)-novaluron by polarimetry and X-ray diffraction. A modified QuEChERS method was developed for enantioselective determination of novaluron in eight food and environmental samples. Under optimal conditions, the mean recoveries of the novaluron enantiomers in the eight matrices were 74.4-108.1% with intraday relative standard deviations (RSDs) of 0.3-9.7% and interday RSDs of 0.1-4.1%. Enantioselective dissipation was observed in tomatoes. The dissipation of S-(-)-novaluron was faster than that of R-(+)-novaluron with a half-life of 7.1 and 7.9 days, and the enantiomer fraction value changed from 0.49 to 0.53 in 21 days. An effective method for monitoring novaluron enantiomer residues in food and the environment was established for the first time and had been successfully applied to real samples. This study is of great significance for strengthening the risk assessment and supervision level of chiral pesticides.

New Axially Chiral Molecular Scaffolds with Antibacterial Activities against Xanthomonas oryzae pv. oryzae for Protection of Rice

A new class of axially chiral thiazine molecules were constructed and showed promising antibacterial activities against the plant pathogen Xanthomonas oryzae pv. oryzae (Xoo). The axial chiralities of these compounds (R- or S-atropisomer) showed clear impacts on the in vitro inhibitory activities against Xoo. An optimal molecule of this class with the (S)-axially chiral configuration was identified to exhibit inhibitory activity against Xoo with an EC₅₀ value of 4.18 μg/mL. This inhibition efficiency is superior to that of two commercial antibacterial agrochemicals, thiodiazole-copper and bismerthiazol, as the positive controls. This hit compound also performed better than the controls in our in vivo studies. Preliminary mechanistic studies via scanning electron microscopy images showed that our hit compound at a concentration of 10 μg/mL destroyed the bacterial integrity of Xoo. Label-free quantitative proteomics analysis indicated that a total of 366 differentially expressed proteins of the rice plants were significantly influenced in the presence of our hit molecule.

Effects of chiral herbicide dichlorprop on Arabidopsis thaliana metabolic profile and its implications for microbial communities in the phyllosphere

Dichlorprop (2-(2,4-dichlorophenoxy) propionic acid, DCPP), a commonly used herbicide for weed control, can be residually detected in soil. It is still unclear whether chiral DCPP exerts an enantioselective adverse effect on plant metabolism and the microbial community of the phyllosphere. In this study, we selected Arabidopsis thaliana as a model plant to explore the effects of R- and S-DCPP enantiomers on plant physiological activities, metabolism, and associated changes in the phyllosphere microbial community. Results indicated that the fresh weight of plants decreased by 37.6% after R-DCPP treatment, whereas it increased by 7.6% after S-DCPP treatment. The R-DCPP enantiomer also caused stronger disturbance to leaf morphology, mesophyll cell structure, and leaf metabolites compared with S-DCPP. GC-MS analysis of DCPP-treated Arabidopsis leaves pointed out a differential profile mostly in carbohydrates, organic acids, and fatty acids, between S-DCPP and R-DCPP treatments. The diversity of phyllospheric microorganisms decreased and the stability of microbial community in the phyllosphere increased after R-DCPP treatment, whereas the opposite result was detected after S-DCPP exposure. The correlation analysis revealed that chiral herbicides may affect microbial communities in the phyllosphere by influencing leaf metabolism, while sugars and terpenoids were considered the main factors in reshaping the microbial community structure in the phyllosphere. Our study provides a new perspective for evaluating the effect of residual DCPP enantiomers on plant physiology and corresponding phyllosphere microorganism changes via the regulation of leaf metabolism, and clarifies the ecological risk of DCPP enantiomer application in agriculture.

Metabolomic and transcriptomic investigation of the mechanism involved in enantioselective toxicity of imazamox in Lemna minor

Imazamox (IM) is a chiral pesticide that has been widely used in agriculture. Currently, few studies have investigated the toxicity mechanisms of imazamox to aquatic macrophyte from the enantiomer level. In this study, the enantioselective effects of IM on the toxicity and physiological and biochemical system of aquatic macrophyte Lemna minor were systematically investigated. Metabolomic and transcriptomic for Lemna minor were used to identify potential mechanisms of toxicity. 7 d EC₅₀s for racemic-, R-, and S-IM were 0.036, 0.035, and 0.203 mg/L, respectively, showing enantioselective toxicity. In addition, IM caused Lemna minor lipid peroxidation and antioxidant damage, and inhibited the activities of the target enzymes. Metabolomic and transcriptomic data indicated that R-IM interferenced differentially expressed genes and metabolites of Lemna minor which were enriched in carbon fixation during photosynthesis, glutathione metabolic pathway, pentose phosphate pathway, zeatin biosynthesis, and porphyrin and chlorophyll metabolism. S-IM affected phenylalanine metabolism, phenylpropanoid biosynthesis, zeatin biosynthesis and secondary metabolite biosynthesis. Racemic-IM influenced carbon fixation during operation, glutathione metabolic pathway, zeatin biosynthesis and pentose phosphate pathway. The results provide new insights into the enantioselective toxicity mechanisms of IM to Lemna minor, and lay the foundation for conducting environmental risk assessments.

Enantioselective evaluation of the chiral fungicide mandipropamid: Dissipation, distribution and potential dietary intake risk in tomato, cucumber, Chinese cabbage and cowpea

A chiral analytical method was developed and validated for the determination of mandipropamid enantiomers in tomato, cucumber, Chinese cabbage and cowpea. The linearity (R² > 0.99), accuracy (recovery: 73.8-106%) and precision (relative standard deviation: < 11%) were adequate for the detection of mandipropamid enantiomers in four vegetables. Field trials were further conducted to investigate the dissipation and residue distribution of mandipropamid and the possible enantioselectivity in different vegetables. Due to the shorter half-lives, mandipropamid dissipated more rapidly in Chinese cabbage (1.8-2.0 d) and cowpea (1.6-2.4 d) than in tomato (5.0-8.4 d) and cucumber (2.4-5.5 d). The residues of mandipropamid were 45-179 µg/kg in tomato 14 d at low dose, 48-98 µg/kg in cucumber 7 d after spraying twice at low dose, and < 2.5-1942 µg/kg in Chinese cabbage and cowpea in all treatments, which were below the maximum residue limits of mandipropamid set by the European Union and Codex Alimentarius Commission. Enantioselectivity was observed during the mandipropamid dissipation process in four vegetables. The S-(+)-enantiomer dissipated more rapidly than the R-(-)-enantiomer in tomato and Chinese cabbage (enantiomeric fractions > 0.5). For cucumber and cowpea, the dissipation of the R-enantiomer was preferential (enantiomeric fractions < 0.5). According to the risk quotient data (<< 100%), the residues of mandipropamid in four vegetables were safe for Chinese consumers. This study could provide useful information for the dissipation fate and residue distribution of mandipropamid in vegetables at the enantiomer level and offer some guidance for the dietary intake risk evaluation of mandipropamid in vegetables.

Mechanistic Insights into Stereospecific Antifungal Activity of Chiral Fungicide Prothioconazole against Fusarium oxysporum F. sp. cubense

As a typical triazole fungicide, prothioconazole (Pro) has been used extensively due to its broad spectrum and high efficiency. However, as a racemic mixture of two enantiomers (R-Pro and S-Pro), the enantiomer-specific outcomes on the bioactivity have not been fully elucidated. Here, we investigate how chirality affects the activity and mechanism of action of Pro enantiomers on Fusarium oxysporum f. sp. cubense tropical race 4 (Foc TR4), the notorious virulent strain causing Fusarium wilt of banana (FWB). The Pro enantiomers were evaluated in vivo and in vitro with the aid of three bioassay methods for their fungicidal activities against TR4 and the results suggested that the fungicidal activities of Pro enantiomers are stereoselective in a dose-dependent manner with R-Pro making a major contribution to the treatment outcomes. We found that R-Pro led to more severe morphological changes and impairment in membrane integrity than S-Pro. R-Pro also led to the increase of more MDA contents and the reduction of more SOD and CAT activities compared with the control and S-Pro groups. Furthermore, the expression of Cytochrome P450 14α-sterol demethylases (CYP51), the target for triazole fungicides, was significantly increased upon treatment with R-Pro rather than S-Pro, at both transcriptional and translational levels; so were the activities of the Cytochrome P450 enzymes. In addition, surface plasmon resonance (SPR) and molecular docking illuminated the stereoselective interactions between the Pro enantiomers and CYP51 of TR4 at the target site, and R-Pro showed a better binding affinity with CYP51 than S-Pro. These results suggested an enantioselective mechanism of Pro against TR4, which may rely on the enantioselective damages to the fungal cell membrane and the enantiospecific CYP51 binding affinity. Taken together, our study shed some light on the mechanisms underlying the differential activities of the Pro enantiomers against TR4 and demonstrated that Pro can be used as a potential candidate in the treatment of FWB.

Four Propiconazole Stereoisomers: Stereoselective Bioactivity, Separation via Liquid Chromatography-Tandem Mass Spectrometry, and Dissipation in Banana Leaves

In this study, we evaluated the stereoselective bioactivity of four propiconazole stereoisomers against the causal agents of the banana leaf spot disease (Curvularia lunata and Colletotrichum musae). We also evaluated the stereoselective degradation of the stereoisomers in banana leaves under field test conditions. The Superchiral S-OX column successfully separated the four propiconazole stereoisomers. X-ray single-crystal diffraction confirmed that the absolute configuration of the cis-stereoisomer-(+)-A of propiconazole was (2R,4S)-propiconazole and that of the cis-stereoisomer-(-)-A of propiconazole was (2S,4R)-propiconazole. In vitro antibacterial results revealed that (2R,4S)-(+)-propiconazole had the highest activity against the two target plant fungi. In this study, a new and efficient high-performance liquid chromatography tandem mass spectrometry method was developed for the determination of the four stereoisomeric residues of propiconazole in banana leaves. The mean recoveries of the method for the stereoisomers were 76.3-103% with relative standard deviations of 1.25-11.4%. The four propiconazole stereoisomers had a detection limit of 0.002-0.006 mg/kg and a limit of quantification of 0.02-0.03 mg/kg in banana leaves. Propiconazole-(-)-B and propiconazole-(-)-A degraded slightly faster than their corresponding enantiomers propiconazole-(+)-B and propiconazole-(+)-A in banana leaves collected from three typical banana production areas.

Developments in the Catalytic Asymmetric Synthesis of Agrochemicals and Their Synthetic Importance

Catalytic asymmetric synthesis has become an essential tool for the enantioselective synthesis of pharmaceuticals, natural products, and agrochemicals (mainly fungicides, herbicides, insecticides, and pheromones). With continuous growing interest in both modern agricultural chemistry and catalytic asymmetric synthesis chemistry, this review provides a comprehensive overview of some earlier reports as well as the recent successful applications of various catalytic asymmetric syntheses methodologies, such as enantioselective hydroformylation, enantioselective hydrogenation, asymmetric Sharpless epoxidation and dihydroxylation, asymmetric cyclopropanation or isomerization, organocatalyzed asymmetric synthesis, and so forth, which have been used as key steps in the preparation of chiral agrochemicals (on R&D, piloting, and commercial scales). Chiral agrochemicals can also lead the new generation of such chemicals having specific and novel modes of action for achieving sustainable crop protection and production. Some perspectives and challenges for these catalytic asymmetric methodologies in the synthesis of chiral agrochemicals are also briefly discussed in the final section of the manuscript. This review will provide the insight regarding understanding, development, and evaluation of catalytic asymmetric systems for the synthesis of chiral agrochemicals among the agrochemists.

The enantioselective toxicity and oxidative stress of dinotefuran on zebrafish (Danio rerio)

Dinotefuran is a widely used neonicotinoid pesticides in agriculture and it has certain ecological toxicity to aquatic organisms. Studies on the potential toxicological effects of dinotefuran on fish are limited. In the present study, 96 h acute toxicity test indicated that enantiomers of R-(-)-dinotefuran had a greater toxic effect than Rac-dinotefuran on zebrafish, and S-(+)-dinotefuran was the least. In chronic assay, R-(-)-dinotefuran exerted more effects on the development of zebrafish than S-(+)-dinotefuran, and dinotefuran also had enantioselective effect on oxidative stress. Significant changes were observed in the superoxide dismutase (SOD), glutathione S-transferase (GST) and acetylcholinesterase (AChE) activities and malondialdehyde (MDA) contents, which demonstrated dinotefuran induced oxidative stress in zebrafish. Besides, through an ultra-performance liquid chromatography quadrupole-TOF mass spectrometry (UPLC-Q-TOF-MS)-based metabolomics method was used to evaluate the enantioselectivity of dinotefuran enantiomers in zebrafish. The results indicated that R-(-)-dinotefuran caused greater disturbances of endogenous metabolites. Phenylalanine metabolic pathways, glycine, serine and threonine metabolic pathways are only involved in zebrafish exposed to R-(-)-dinotefuran; whereas phenylalanine, tyrosine and tryptophan biosynthesis was only involved in zebrafish exposed to S-(+)-dinotefuran. This study provides a certain reference value for assessing the environmental risks of dinotefuran enantiomers to aquatic organisms, and has practical significance for guiding the ecologically and environmentally safety use of dinotefuran.

Scientific Opinion of the Scientific Panel on Plant Protection Products and their Residues (PPR Panel) on testing and interpretation of comparative in vitro metabolism studies

EFSA asked the Panel on Plant Protection Products and their residues to deliver a Scientific Opinion on testing and interpretation of comparative in vitro metabolism studies for both new active substances and existing ones. The main aim of comparative in vitro metabolism studies of pesticide active substances is to evaluate whether all significant metabolites formed in the human in vitro test system, as a surrogate of the in vivo situation, are also present at comparable level in animal species tested in toxicological studies and, therefore, if their potential toxicity has been appropriately covered by animal studies. The studies may also help to decide which animal model, with regard to a particular compound, is the most relevant for humans. In the experimental strategy, primary hepatocytes in suspension or culture are recommended since hepatocytes are considered the most representative in vitro system for prediction of in vivo metabolites. The experimental design of 3 × 3 × 3 (concentrations, time points, technical replicates, on pooled hepatocytes) will maximise the chance to identify unique (UHM) and disproportionate (DHM) human metabolites. When DHM and UHM are being assessed, test item-related radioactivity recovery and metabolite profile are the most important parameters. Subsequently, structural characterisation of the assigned metabolites is performed with appropriate analytical techniques. In toxicological assessment of metabolites, the uncertainty factor approach is the first alternative to testing option, followed by new approach methodologies (QSAR, read-across, in vitro methods), and only if these fail, in vivo animal toxicity studies may be performed. Knowledge of in vitro metabolites in human and animal hepatocytes would enable toxicological evaluation of all metabolites of concern, and, furthermore, add useful pieces of information for detection and evaluation of metabolites in different matrices (crops, livestock, environment), improve biomonitoring efforts via better toxicokinetic understanding, and ultimately, develop regulatory schemes employing physiologically based or physiology-mimicking in silico and/or in vitro test systems to anticipate the exposure of humans to potentially hazardous substances in plant protection products.

Enantioselective metabolomic modulations in Arabidopsis thaliana leaf induced by the herbicide dichlorprop

Over 40% of herbicides used today are chiral. Dichlorprop (2, 4-DCPP) is a widely used typical broad-spectrum chiral aryloxyphenoxy propionic acid (AOPP) herbicide. However, the molecular mechanism of the enantioselectivity of DCPP enantiomers (S-DCPP and R-DCPP) and their effects on non-target organisms are remain unclear. In the present study, the model plant Arabidopsis thaliana was treated by DCPP enantiomers to directly reveal the effects of DCPP enantiomers on plant growth, as well as metabolic profile. Results showed that the enantioselectivity embodied in that R-DCPP treatment led to the decrease of shoot weight, the significantly variation on morphology of shoot and root, oxidative damage, et al., while the plant morphology also changes to a certain extent associated oxidative damage after treated by S-DCPP. By using metabolomic analysis, it was found that R-DCPP had significant effects on A. thaliana leaf metabolism, including lactose metabolism, starch and sucrose metabolism, TCA cycle, fatty acid biosynthesis pathway and pentose phosphate pathway, and accumulated a lot of antioxidants in plant leaves, while the amino acids and some terpenoids increased in S-DCPP group. Our study provides a new direction to explore the relationship between chiral herbicides on leaf metabolism, and the effect of this relationship on the plant growth.

Enantioselective bioaccumulation and detoxification mechanisms of earthworms (Eisenia fetida) exposed to mandipropamid

As a novel chiral amide fungicide, the enantioselective behaviors of mandipropamid in the soil environment are unclear. Furthermore, there is a need to understand the stress response mechanisms of soil organisms exposed to mandipropamid isomers. Therefore, the selective bioaccumulation of mandipropamid isomers and detoxification mechanisms of earthworms (Eisenia fetida) were investigated in this study. Our results suggested that the enantioselective bioaccumulation of mandipropamid in earthworms occurred with the preferential enrichment of S-(+)-isomer. The activities of detoxification enzymes, such as cytochrome P450 (CYP450), glutathione-S-transferases (GST), and carboxylesterase (CarE), changed significantly upon exposure to S-(+)- and R-(-)-mandipropamid (particularly for CYP450 and GST). A transcriptome analysis revealed that more differentially expressed genes (DEGs) were observed under S-(+)-isomer exposure (15,798) than those under R-(-)-isomer exposure (12,222), as compared to the control group. These DEGs were mainly enriched in bile secretion and thyroid hormone signaling pathways, which were related to the detoxification process in earthworms. Moreover, the 20 DEGs, which exhibited the most profound changes (such as CYP2 and CYP3A4) in these pathways, were screened, clustered, and observed to be mainly involved in regulating the detoxification function of earthworm cells. These results indicated that detoxification systems played an essential role in the stress response to mandipropamid exposure. Additionally, earthworms were more sensitive to the stress induced by S-(+)-mandipropamid than that induced by R-(-)-mandipropamid. This is the first study to elucidate the mandipropamid detoxification mechanism of earthworms at the enantiomer level, which can be beneficial for remediating chiral pollutants.

Effects of Cd2+ and Pb2+ on enantioselective degradation behavior of α-cypermethrin in soils and their combined effect on activities of soil enzymes

Heavy metals may coexist with pesticides in farmland through wastewater irrigation, application of pesticides and chemical fertilizers, or unappropriated waste disposal. Heavy metals are toxic to soil microorganism, which may influence the environmental behavior of pesticides subsequently. In this study, the influence of Cd²⁺ and Pb²⁺ on the degradation of α-cypermethrin and its metabolites, 3-phenoxphenoxybenzoic acid (3-PBA) and 3-(2',2'-dichlorovinyl)-2,2-dimethylcyclopropane carboxylic acid (DCCA), were investigated through soil incubation experiment. It was found heavy metals like Cd²⁺ and Pb²⁺ will inhibit the degradation of α-cypermethrin, especially at high concentrations. Pb²⁺ has a stronger inhibitory effect on the degradation of α-cypermethrin than Cd²⁺ in the same concentration. With the presence of 10 mg/kg Pb²⁺, the half-life of α-cypermethrin increased from 41.1 to 99.9 days, even the half-life was 129.3 days with 50 mg/kg of Pb²⁺. Besides, heavy metals influenced the chiral selective degradation of α-cypermethrin. The enantiomer fraction was near 0.5 when 10 mg/kg of heavy metals existed. Furthermore, the adverse effects of heavy metals on soil urease, catalase, and sucrase activity were assayed. In tested concentrations (10 and 50 mg kg^-1), the heavy metals result in strong inhibition of the activity of the enzymes present on soil, jeopardizing the biodegradation by the microbiome and which may inhibit the degradation of α-cypermethrin.

Chiral Fungicide Famoxadone: Stereoselective Bioactivity, Aquatic Toxicity, and Environmental Behavior in Soils

In this study, the stereoselective bioactivity, acute toxicity, and environmental fate for famoxadone enantiomers were reported for the first time. Five representative pathogens (e.g., Alternaria solani) were used to investigate enantioselective activity, and three non-target organisms (e.g., Selenastrum bibraianum) were used to evaluate acute toxicity. S-Famoxadone was 3.00-6.59 times more effective than R-famoxadone. R-Famoxadone also showed 1.80-6.40 times more toxicity than S-famoxadone toward S. bibraianum and Daphnia magna. The toxicity of R-famoxadone was 100 times more toxic than S-famoxadone toward Danio rerio. Under aerobic conditions, the half-life (t_1/2) for famoxadone enantiomer degradation was 46.2-126 days in different soils and the enantiomeric fraction (EF) ranged from 0.435 to 0.470 after 120 days. R-Famoxadone preferentially degraded in three soils, resulting in an enrichment of S-famoxadone. Under anaerobic conditions, t_1/2 of famoxadone enantiomers was 62.4-147 days in different soils and the EF ranged from 0.489 to 0.495, indicating that famoxadone enantiomers were not enantioselective. This study will be useful for the environmental and health risk assessments for famoxadone enantiomers.

New Target in an Old Enemy: Herbicide (R)-Dichlorprop Induces Ferroptosis-like Death in Plants

Iron is an essential microelement in plants that is involved in several growth processes. The use of herbicides may cause the abnormal aggregation of iron in leaves, but the regulatory mechanisms underlying this phenomenon remain unclear. Here, we show that chiral herbicide (R)-dichlorprop ((R)-DCPP) triggers ferroptosis-like death in Arabidopsis thaliana. (R)-DCPP led to reactive oxygen species (ROS) accumulation and iron aggregation, and these processes were iron dependent. Under (R)-DCPP treatment, ROS, lipid hydrogen peroxides, and malondialdehyde were significantly accumulated. In addition, (R)-DCPP induced the depletion of glutathione, ascorbic acid, and glutathione peroxidase as well as the accumulation of toxic lipid peroxides. Thus, oxidation imbalance led to cell death, and this mode of action could be inhibited by the ferroptosis inhibitor ferrostatin-1 or ciclopirox olamine. NADPH oxidases were found to be involved in herbicide-induced ROS accumulation, and lipoxygenase and NADPH cytochrome P450 oxidase were shown to positively regulate (R)-DCPP-induced lipid peroxidation. Overall, these results indicate that the iron- and ROS-dependent signaling cascades were involved in the (R)-DCPP-induced phytotoxicity pathway, which disrupted the structure of plant cell membranes and triggered ferroptosis. Generally, this study provides new insight into the mechanisms of pesticide phytotoxicity and suggests new therapeutic directions to protect nontarget plants.

Enantiomeric separation of prothioconazole and prothioconazole-desthio by Capillary Electrophoresis. Degradation studies in environmental samples

In this work, two analytical methodologies by Capillary Electrophoresis were developed. The first one enabled the rapid and cost-effective enantioseparation of prothioconazole and was applied to the analysis of prothioconazole-based commercial agrochemical formulations. The second methodology enabled the simultaneous enantioseparation of prothioconazole and its metabolite prothioconazole-desthio and was applied to degradation studies of both compounds in soil and sand samples. The influence of several experimental variables was investigated to develop both methodologies. The separation of prothioconazole enantiomers was achieved in 4.5 min with a resolution of 2.8 employing a neutral cyclodextrin (heptakis(2,3,6-tri-O-methyl)-β-cyclodextrin). Given the nature of prothioconazole-desthio, a neutral cyclodextrin cannot be used for its chiral separation. For this reason, the simultaneous enantioseparation of prothioconazole and prothioconazole-desthio was achieved in 5.5 min with resolution values of 1.9 and 8.2, respectively, using a negatively charged cyclodextrin (sulfated-γ-cyclodextrin). The analytical characteristics of the developed methodologies were evaluated and both methods showed good performance to be applied to the quantitation of the enantiomers of prothioconazole in commercial agrochemical formulations (LOD 0.7 mg L^-1) and to carry out degradation studies for both compounds in environmental matrices (LODs lower than 0.9 and 1.3 mg L^-1 for prothioconazole and prothioconazole-desthio enantiomers, respectively). The recovery values obtained were in the range between 94-104 % for the agrochemical formulations, between 96-99 % for the sand samples and between 97-100 % for the soil samples.

The Role of Ponds in Pesticide Dissipation at the Agricultural Catchment Scale: A Critical Review

Ponds in agricultural areas are ubiquitous water retention systems acting as reactive biogeochemical hotspots controlling pesticide dissipation and transfer at the catchment scale. Several issues need to be addressed in order to understand, follow-up and predict the role of ponds in limiting pesticide transfer at the catchment scale. In this review, we present a critical overview of functional processes underpinning pesticide dissipation in ponds. We highlight the need to distinguish degradative and non-degradative processes and to understand the role of the sediment-water interface in pesticide dissipation. Yet it is not well-established how pesticide dissipation in ponds governs the pesticide transfer at the catchment scale under varying hydro-climatic conditions and agricultural operation practices. To illustrate the multi-scale and dynamic aspects of this issue, we sketch a modelling framework integrating the role of ponds at the catchment scale. Such an integrated framework can improve the spatial prediction of pesticide transfer and risk assessment across the catchment-ponds-river continuum to facilitate management rules and operations.

A rapid method for the simultaneous stereoselective determination of the triazole fungicides in tobacco by supercritical fluid chromatography-tandem mass spectrometry combined with pass-through cleanup

This work presents a simple, rapid and green chiral analysis method for five triazole fungicides (penconazole, tebuconazole, triadimefon, myclobutanil, and triadimenol) in tobacco, by which the samples were cleaned up by the novel pass-through solid phase extraction and subsequently the stereoisomers were separated and determined by the supercritical fluid chromatography-tandem mass spectrometry (SFC-MS/MS). Optimized separation of the stereoisomers was achieved on an ACQUITY UPC2 Trefoil AMY 1 column within 6 min. Under fortified concentration levels of 0.1, 0.5 and 2.0 mg/kg, the mean recoveries were 82.8-106.6%, the intra-day relative standard deviations (RSDs) were 1.1-6.6%, and the inter-day RSDs were 2.5-5.6%. The correlation coefficient was greater than 0.9926 for all studied analytes within the range of 10-500 ng/mL. The limits of detection (LODs) for all stereoisomers ranged from 0.26 μg/kg to 3.24 μg/kg. The established method was subsequently successfully applied to analyze authentic samples, confirming that this method is a novel, rapid and environmentally friendly method for the stereoselective separation of triazole fungicides in tobacco.

Enantioselective Bioaccumulation of the Chiral Insecticide Indoxacarb in Zebrafish (Danio rerio)

Indoxacarb is a typical chiral insecticide widely used in agricultural pest control. In the present study, zebrafish was used as a model animal to explore the enantioselective bioaccumulation behavior of indoxacarb to nontarget species in aquatic environments. Zebrafish were exposed to 0.025 and 0.1 mg/L rac-indoxacarb solution for 12 d under the semistatic method, and the bioconcentration factor (BCF) and enantiomeric fraction of zebrafish were investigated. The results showed that the (-)-R-indoxacarb preferentially accumulated in zebrafish. The BCF values at 0.025 mg/L exposure levels were 1079.8 and 83.4 L/kg for (-)-R-indoxacarb and (+)-S-indoxacarb after 12 d, respectively. The BCF values at 0.1 mg/L exposure levels were 1752.1 and 137.0 L/kg for (-)-R-indoxacarb and (+)-S-indoxacarb after 10 d, respectively. The half-life values of (-)-R-indoxacarb and (+)-S-indoxacarb were 3.47 and 2.05 d for 0.025 mg/L concentration exposure and 4.95 and 2.66 d for 0.1 mg/L concentration exposure, respectively. The enantiomeric fraction values were in the range of 0.48 to 0.55 and 0.89 to 1.00 for water and zebrafish samples, respectively. Studies on the enantioselective bioaccumulation behavior of indoxacarb will provide data for assessing the environmental fate and potential toxic effects of indoxacarb on aquatic organisms. Environ Toxicol Chem 2021;40:1007-1016. © 2020 SETAC.

Determination of etoxazole in different parts of citrus fruit and its potential dietary exposure risk assessment

In this study, the profile of etoxazole in whole citrus, peel and pulp samples collected from Chongqing, Guangdong and Anhui provinces was monitored and their dietary risk to human had also been assessed. The final residual levels and distributions of etoxazole in citrus samples were detected by using an ultra-performance liquid chromatography coupled with tandem mass spectrometry (UPLC-MS/MS). The results showed that final concentrations of etoxazole in whole citrus, peel, and pulp were ranged at 0.012-0.174, 0.010-0.637, and 0.010-0.011 mg kg^-1, respectively. The assessment of dietary risk suggested that chronic dietary risk of etoxazole in whole fruit and peel were 0.010-0.197% and 0.035-0.951%, respectively. Our findings indicated that the chronic risk of daily consumption of citrus fruit is acceptable at recommended dosage.

Enantioselective effects of the fungicide metconazole on photosynthetic activity in Microcystis flos-aquae

Enantiomers of chiral fungicides usually display different toxic effects on nontarget organisms in the surrounding environment, although there are rare reports on the enantioselective toxicity of metconazole (MEZ) to aquatic organisms, such as Microcystis flos-aquae (M. flos-aquae). To explore the enantioselective toxicity of MEZ in algae, the impact of various concentrations (0.001, 0.003, 0.01, 0.03 and 0.1 mg/L) of MEZ on M. flos-aquae over 8 days was investigated. Significant differences were observed between the four enantiomers in chlorophyll a (Chl a) contents, carotenoids, photochemical efficiency (F_v/F_m), rapid light-response curves (RLCs), utilization efficiency of light energy (α) and protein contents during treatment time. MEZ can enantioselectively stimulate the chlorophyll fluorescence parameters (RLCs, F_v/F_m and α) and carotenoid and Chl a contents of M. flos-aquae, especially at low concentrations (0.001 or 0.003 mg/L). At high concentrations of 0.03 or 0.1 mg/L, the chlorophyll fluorescence parameters (RLCs, F_v/F_m and α), protein and Chl a contents of M. flos-aquae exposed to cis-enantiomers were lower than those of M. flos-aquae exposed to trans-enantiomers. These observations indicated that the enantiomers of MEZ pose different toxicities to M. flos-aquae, with the cis-enantiomers more toxic than the trans-enantiomers. These results are beneficial for understanding the enantioselective effects of MEZ enantiomers on nontarget organisms and helpful for evaluating their eco-environment risk.

Application of nanoparticles in chiral analysis and chiral separation

Chiral molecules in relation to particular biological roles are stereoselective. Enantiomers differ significantly in their biochemical responses in biological environment. Despite the current advancement in drug discovery and pharmaceutical biotechnology, the chiral separation of some racemic mixtures continues to be one of the greatest challenges, because the available techniques are too costly and time consuming for the assessment of therapeutic drugs in the early stages of development worldwide. Various nanoparticles became one of the most investigated and explored nanotechnology-derived nanostructures especially in chirality where several studies are reported to improve enantiomeric separation of different racemic mixtures. The production of surface-modified nanoparticles has contributed to these limitations in terms of sensitivity, accuracy, and enantioselectivity that can be optimized and therefore makes these surface-modified nanoparticles convenient for enantiomeric identification and separation.

Oxidative Stress and Enantioselective Degradation of Dufulin on Tubifex

Dufulin is a new type of chiral antiplant virus agent independently developed in China. The present study was conducted to determine the effects of different concentrations of rac-dufulin and dufulin enantiomers (1, 5, and 10 mg/L) on oxidative stress in Tubifex after exposure for 3, 7, and 14 d. Results showed that rac-dufulin and individual enantiomers had no significant effects on total protein content and glutathione reductase activities. Increased superoxide dismutase demonstrated the generation of superoxide anion radical. The increase in glutathione S-transferase may be due to detoxification mechanisms. The different changes in catalase activities could be due to oxidative stress. The increase in malondialdehyde may be due to the accumulation and toxicity of contaminations. The degradation behavior of dufulin enantiomers was studied through spiked-water and spiked-soil tests. The degradation rate of S-(+)-dufulin was faster than that of R-(-)-dufulin. The present study demonstrated the occurrence of enantioselectivity in the degradation and oxidative stress of dufulin to Tubifex. In spiked soil, the concentrations of dufulin enantiomers in underlying soil were significantly higher than those in overlying water; but after 5 d of degradation, the bioturbation of Tubifex could facilitate part of dufulin diffusing from the underlying soil into the overlying water and altered the partitioning of dufulin. The present study provided a basis for conducting environmental safety risk assessments and rationally using dufulin as a chiral pesticide. Environ Toxicol Chem 2020;39:2136-2146. © 2020 SETAC.

Stereoselective Physiological Effects of Metconazole on Seed Germination and Seedling Growth of Wheat

In addition to their fungicidal activity, many triazole fungicides function as plant regulators, which might impose adverse effects on the growth and development of crops. For chiral triazole fungicides, these effects can be alleviated by applying stereoisomers with high fungicidal and low regulator activities. This study investigated the stereoselectivity of four stereoisomers and the racemate of metconazole (2.5 g/100 kg seeds) on emergence and growth of seedlings (BBCH 01-14) in wheat. Wheat seedlings, coated with cis-1S,5R-metconazole, had a significantly lower seedling emergence ratio and shoot length than other metconazole treatments; however, the opposite effects were observed in the trans-1S,5S-metconazole treatment. With regard to the hormonal level, enzyme activity, and gene transcription of gibberellin (GA) and jasmonic acid (JA), cis-1S,5R-metconazole treatment inhibited GA biosynthesis while trans-1S,5S-metconazole treatment promoted GA biosynthesis. Moreover, cis-1S,5R-metconazole, trans-1S,5S-metconazole, trans-1R,5R-metconazole, and racemate treatments increased JA biosynthesis. The oxidative stress responses in trans-1R,5R-metconazole and racemate treatments were more intensive. Therefore, compared with the control, treatment with cis-1R,5S-metcoanzole exhibited minimal influence on wheat seedling growth. The results showed that the application of pure cis-1R,5S-metcoanzole (instead of the racemate) in agricultural management could decrease the risks associated with crop growth and developmental damage.

Effects of multi-walled carbon nanotubes on the enantioselective toxicity of the chiral insecticide indoxacarb toward zebrafish (Danio rerio)

The mass production and usage of carbon nanotubes (CNTs) have led to the inevitable release into the environment, and the effects of CNTs on the toxicity of co-existing pollutants have been well documented. However, knowledge of the effects of CNTs on the enantioselective toxicity of chiral compounds is limited. Using zebrafish as an experimental model, the enantioselective expression of the apoptosis, CYP3C and EAAT-related genes were analyzed following exposure to multi-walled carbon nanotubes (MWCNTs) (0.05 and 0.5 mg/L), rac-/R-/S-indoxacarb (0.01 mg/L), or the combination of rac-/R-/S-indoxacarb mixed with MWCNTs for 28d. Sex-specific differences were observed in both the liver and brain of zebrafish. The expression of apoptosis and CYP3C-related genes was 16.55-44.29 times higher in the livers of males treated with R-indoxacarb than in S-indoxacarb treated groups. The EAAT-related genes were expressed at 1.38-2.56 times higher levels in the brain of females treated with R-indoxacarb than in S-indoxacarb-treated groups. In the presence of MWCNTs, the expression of caspase-3, cyp3c3, cyp3c4, eaat1a, eaat1b and eaat2 in the livers of males and brains of females treated with S-indoxacarb were 1.65-15.33 times higher than in fish treated with R-indoxacarb. Based on these results, MWCNTs affected the enantioselective toxicity of indoxacarb toward zebrafish.

Enantioselective disposition and metabolic products of isofenphos-methyl in rats and the hepatotoxic effects

Isofenphos-methyl (IFP), a chiral organophosphorus pesticide, is one of the main chemicals used to control underground insects and nematodes. Recently, the use of IFP on vegetables and fruits has been prohibited due to its high toxicity. In this study, we investigated the enantioselective distribution and metabolism of IFP and its metabolites, namely, isofenphos-methyl oxon (IFPO) and isocarbophos oxon (ICPO), in male Sprague Dawley (SD) rats. Forty eight hours (48 h) after exposure, ICPO was the main detectable compound in blood (up to 75%) and urine (up to 77%), and we found that (S)-ICPO was significantly more stable than (R)-ICPO (p < 0.05). Therefore, (S)-ICPO was proposed as a suitable candidate biomarker for the biomonitoring of IFP in human urine and blood. After 48 h exposure, 21.2-41.0%, 4.1-15.1%, and 8.6-18.7% of dosed IFP was detected in the liver of racemic, R and S enantiomer-exposed rats, respectively, and R-IFP and R-IFPO showed a faster degradation (p < 0.05). Our results showed that after one week of consecutive exposure to IFP, ICPO was accumulated in the liver of rats in both racemic and enantiopure groups (no difference between the groups, p > 0.05). We found that cytochrome P450 (CYP) (i.e. CYP2C11, CYP2D2 and CYP3A2 enzymes and carboxylesterases) is responsible for the enantioselective metabolism of IFP in liver. In addition, rats exposed to (S)-IFP exhibited hepatic lipid peroxidation, liver inflammation and hepatic fibrosis. This study provides useful information and a reference for the biomonitoring and risk assessment of IFP and organophosphorus pesticide exposure.

Elucidating the potential neurotoxicity of chiral phenthoate: Molecular insight from experimental and computational studies

Chiral organophosphorus pollutants are existed ubiquitously in the ecological environment, but the enantioselective toxicities of these nerve agents to humans and their molecular bases have not been fully elucidated. Using experimental and computational approaches, this story was to explore the neurotoxic response process of the target acetylcholinesterase (AChE) to chiral phenthoate and further decipher the microscopic mechanism of such toxicological effect at the enantiomeric level. The results showed that the toxic reaction of AChE with chiral phenthoate exhibited significant enantioselectivity, and (R)-phenthoate (K＝1.486 × 10⁵ M^-1) has a bioaffinity for the nerve enzyme nearly three times that of (S)-phenthoate (K＝4.503 × 10⁴ M^-1). Dynamic research outcomes interpreted the wet experiments, and the inherent conformational flexibility of the target enzyme has a great influence on the enantioselective neurotoxicological action processes, especially reflected in the conformational changes of the three key loop regions (i.e. residues His-447, Gly-448, and Tyr-449; residues Gly-122, Phe-123, and Tyr-124; and residues Thr-75, Leu-76, and Tyr-77) around the reaction patch. This was supported by the quantitative results of conformational studies derived from circular dichroism spectroscopy (α-helix: 34.7%→30.2%/31.6%; β-sheet: 23.6%→19.5%/20.7%; turn: 19.2%→22.4%/21.9%; and random coil: 22.5%→27.9%/25.8%). Meanwhile, via analyzing the modes of toxic action and free energies, we can find that (R)-phenthoate has a strong inhibitory effect on the enzymatic activity of AChE, as compared with (S)-phenthoate, and electrostatic energy (-23.79/－17.77 kJ mol^-1) played a critical role in toxicological reactions. These points were the underlying causes of chiral phenthoate displaying different degrees of enantioselective neurotoxicity.

Quick and Sensitive Enantioselective Determination of Permethrin in Fruits and Vegetables by Combining Supramolecular Solvents and Chiral Liquid Chromatography-Tandem Mass Spectrometry

Permethrin (PM) is one of the chiral insecticides most widely used around the world. The significant differential toxicity of its four enantiomers and its important adverse effects on human health highlights the need for determination of PM enantiomers. The aim of this work was to develop the first enantioselective method for quantification of PM in fruits and vegetables. The method is based on the extraction of PM enantiomers in supramolecular solvents with restricted access properties (SUPRAS-RAM) and their separation/detection by chiral liquid chromatography-tandem mass spectrometry (LC-MS/MS) which is first reported in this article. SUPRAS-RAM-based extraction is proposed as an innovative treatment approach that drastically reduces solvent consumption and avoids the need for sample cleanup. Extraction of PM enantiomers is quick (vortexing for 5 min) and efficient (recoveries 93-107%). The method is sensitive (quantification limits from 1.0 to 1.2 μg kg^-1) and suitable for control of PM enantiomers in agri-food products.

Enantioselectivity in transplacental transfer of perfluoro-1-methylheptanesulfonate (1m-PFOS): Human biomonitoring and in silico study

Perfluorooctane sulfonates (PFOS) are one of the most prominent perfluoroalkyl contaminants in humans and wildlife. Currently, information regarding enantiomer-specific exposure to PFOS in humans through transplacental transfer is lacking. This study examined 32 matched maternal serum, cord serum and placenta samples collected from mother-infant pairs in Wuhan, China. The enantiomer fraction (EF) value of perfluoro-1-methylhptanesulfonate (1m-PFOS) was lower in cord sera (0.362 ± 0.062, n = 23) compared to maternal sera (0.422 ± 0.048, n = 21) and placenta (0.410 ± 0.060, n = 16). Evaluations of the difference between EF_1m-PFOS suggested enantioselective transplacental transfer of 1m-PFOS. In silico evaluation of the binding affinity of 1m-PFOS to human serum albumin (HSA) showed that the two 1m-PFOS enantiomers enantioselectively interacted with the HSA. This result hints the enantioselective carrier protein affinity may be a key factor for stereoselective 1m-PFOS transplacental transfer. The percentage of branched PFOS (%br-PFOS) and EF_1m-PFOS was correlated in maternal sera, but not in cord sera and placentas. These data indicated that %br-PFOS and EF_1m-PFOS may be less reliable in identifying PreFOS exposure when it comes to complex biological processes, such as transplacental transport. This study could expand our understanding of stereoselective placental contaminant transfer in humans.