Chiral separation of agricultural fungicides

Enantioseparation Membranes: Research Status, Challenges, and Trends

The purity of enantiomers plays a critical role in human health and safety. Enantioseparation is an effective way and necessary process to obtain pure chiral compounds. Enantiomer membrane separation is a new chiral resolution technique, which has the potential for industrialization. This paper mainly summarizes the research status of enantioseparation membranes including membrane materials, preparation methods, factors affecting membrane properties, and separation mechanisms. In addition, the key problems and challenges to be solved in the research of enantioseparation membranes are analyzed. Last but not least, the future development trend of the chiral membrane is expected.

Dissipation, residue, stereoselectivity and dietary risk assessment of penthiopyrad and metabolite PAM on cucumber and tomato in greenhouse and field

Penthiopyrad is a broad-spectrum fungicide with wide application in agriculture with preferential degradation of the S (+)-stereoisomer in soil. An understanding of the stereoselective fate of penthiopyrad is crucial for accurate food safety risk assessment. In this study, the dissipation, distribution, and dietary intake risk of penthiopyrad and its main metabolite (PAM) was conducted in cucumber and tomato samples under greenhouse and open field conditions. The half-lives of penthiopyrad in cucumber and tomato samples were < 8 days and the dissipation rates were higher in the open field than in the greenhouse. Due to the enantiomeric fraction data > 0.5, S (+)-stereoisomer dissipated slightly faster than R-(-)-stereoisomer. The residues of total penthiopyrad (sum of rac-penthiopyrad and PAM) were lower than the maximum residue limits in cucumber and tomato samples (risk quotients ≪ 100%). Therefore, the recommended penthiopyrad spraying method does not threaten vegetable cultivations and has negligible dietary intake risk.

Development of a novel HPLC-ESI-MS/MS method to analyze the stereoselective pharmacokinetics and tissue distribution of isoconazole enantiomers in rats

Isoconazole with an asymmetrical carbon is a broad-spectrum antimicrobial imidazole, but there is still lack of relevant report about the potential enantioselectivity in biological samples. The object of this research was to develop and validate a sensitive and effective high performance liquid chromatography-electrospray ionization coupled with tandem mass spectrometry (HPLC-ESI-MS/MS) method for stereoselective separation and determination of isoconazole enantiomers in Sprague-Dawley (SD) rat plasma and tissues. The greater enantioseparation of isoconazole enantiomers was obtained on a Chiralpak IC column with a mobile phase consisted of acetonitrile-10 mM aqueous ammonium acetate (90:10, v/v) under the reversed-phase mode. Subsequently, the studied compounds and internal standard (IS) were detected on a multiple reaction monitoring (MRM) mode with positive electrospray ionization source. The experimental and theoretical Electronic Circular Dichroism (ECD) spectra were employed to confirm the absolute configuration of isoconazole enantiomers. Eventually, after full method validation, the newly developed method was successfully applied to the study of enantioselectivity in plasma and tissues in SD rats. Results illustrated that the enantioselective differences in plasma were observed for the evidence that the concentrations of S-(-)-isoconazole were always higher than R-(+)-isomer. In terms of tissue distribution, liver, kidney, lung, spleen, and small intestine were the mainly distributed tissues and then followed by heart and muscle. This is the first study to reveal the stereoselective behavior of isoconazole enantiomers in vivo, which also provides reliable and valuable reference for further elucidating the enantioselective metabolisms of isoconazole enantiomers.

Chiral Pesticides with Asymmetric Sulfur: Extraction, Separation, and Determination in Different Environmental Matrices

Chiral pesticides with S atoms as asymmetric centers are gaining great importance in the search for new pesticides with new modes of action. As for the rest of the chiral pesticides, the determination of the stereoisomers separately has become crucial in the environmental risks assessment of these pesticides. Therefore, the development of suitable extraction and clean-up methods as well as efficient stereoselective analytical techniques for stereoisomers determination in environmental samples is essential. Currently, liquid/solid phase extraction, microextraction, and QuEChERS-based methods are most commonly used to obtain chiral pesticides from environmental samples. Gas, liquid, and supercritical fluid chromatography together with capillary electrophoresis techniques are the most important for the determination of the stereoisomers of chiral pesticides containing S atoms in its structure. In this study, all these techniques are briefly reviewed, and the advantages and disadvantages of each are discussed

Chiral Nano-Liquid Chromatography and Dispersive Liquid-Liquid Microextraction Applied to the Analysis of Antifungal Drugs in Milk

A novel chromatographic application in chiral separation by using the nano-LC technique is here reported. The chiral recognition of 12 antifungal drugs was obtained through a 75 µm I.D. fused-silica capillary, which was packed with a CSP-cellulose 3,5-dichlorophenylcarbamate (CDCPC), by means of a lab-made slurry packing procedure. The mobile phase composition and the experimental conditions were optimized in order to find the optimum chiral separation for some selected racemic mixtures of imidazole and triazole derivatives. Some important parameters, such as retention faction, enantioresolution, peak efficiency, and peak shape, were investigated as a function of the mobile phase (pH, water content, type and concentration of both the buffer and the organic modifier, and solvent dilution composition). Within one run lasting 25 min, at a flow rate of approximately 400 nL min^-1, eight couples of enantiomers were baseline-resolved and four of them were separated in less than 25 min. The method was then applied to milk samples, which were pretreated using a classical dispersive liquid-liquid microextraction technique preceded by protein precipitation. Finally, the DLLME-nano-LC-UV method was validated in a matrix following the main FDA guidelines for bioanalytical methods.

Micellar electrokinetic chromatography in the determination of triazoles in fruit peel

Triazole fungicides (TAFs) are frequently used fungicides for various antifungal treatments of crops. Tre treatment is provided foliarly. However, some significant amount of TAFs may remain on/in fruits. We have developed a methodology for the determination of penconazole, tebuconazole and cyproconazole in tomato fruit peel. The extraction of TAFs was provided with chloroform (acidified with 0.1% acetic acid). In the electrokinetic chromatography, the mixed micellar pseudo-stationary phase was composed of anionic detergent sodium dodecyl sulphate (15 mM) and randomly highly sulphated gamma-cyclodextrin (17.5 mg/mL). The background electrolyte consisted of 100 mM phosphoric acid and 100 mM Tris in the mixed hydro-organic solvent water/methanol (80/20 v/v), apparent pH 4.8. Complete separation of penconazole, tebuconazole, and two diastereomers of cyproconazole with resolutions higher than 5.1 were achieved within a relatively short time of less than 17 min in the bare fused silica capillary of 425/500 mm total/effective lengths and 50/375 μm I.D./O.D. at separation voltage -15 kV (cathode at injection capillary end) and at constant capillary cassette temperature of 22°C. The TAFs were detected by a UV-spectrophotometric diode array detector set at 200 nm. The limits of detection and limits of quantification were in the range of 71-92 and 214-278 μg/kg of peel, respectively. Analyses of the peel extracts revealed that even 10 days after the last treatment, TAF concentrations were higher than the recommended maximum residue limits in both application ways, as individual as well as in the TAF binary or ternary mixtures.

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.

Chiral Graphene Hybrid Materials: Structures, Properties, and Chiral Applications

Chirality has become an important research subject. The research areas associated with chirality are under substantial development. Meanwhile, graphene is a rapidly growing star material and has hard-wired into diverse disciplines. Rational combination of graphene and chirality undoubtedly creates unprecedented functional materials and may also lead to great findings. This hypothesis has been clearly justified by the sizable number of studies. Unfortunately, there has not been any previous review paper summarizing the scattered studies and advancements on this topic so far. This overview paper attempts to review the progress made in chiral materials developed from graphene and their derivatives, with the hope of providing a systemic knowledge about the construction of chiral graphenes and chiral applications thereof. Recently emerging directions, existing challenges, and future perspectives are also presented. It is hoped this paper will arouse more interest and promote further faster progress in these significant research areas.

A review on the stereospecific fate and effects of chiral conazole fungicides

The production and use of chiral pesticides are triggered by the need for more complex molecules capable of effectively combating a greater spectrum of pests and crop diseases, while sustaining high production yields. Currently, chiral pesticides comprise about 30% of all pesticides in use; however, some pesticide groups such as conazole fungicides (CFs) consist almost exclusively of chiral compounds. CFs are produced and field-applied as racemic (1:1) mixtures of two enantiomers (one chiral center in the molecule) or four diastereoisomers, i.e., two pairs of enantiomers (two chiral centers in the molecule). Research on the stereoselective environmental behavior and effects of chiral pesticides such as CFs has become increasingly important within the fields of environmental chemistry and ecotoxicology. This is motivated by the fact that currently, the fate and effects of chiral pesticides such as CFs that arise due to their stereoselectivity are not fully understood and integrated into risk assessment and regulatory decisions. In order to fill this gap, a summary of the state-of-the-art literature related to the stereospecific fate and effects of CFs is needed. This will also benefit the agrochemistry industry as they enhance their understanding of the environmental implications of CFs which will aid future research and development of chiral products. This review provides a collection of >80 stereoselective studies for CFs related to chiral analytical methods, fungicidal activity, non-target toxicity, and behavior of this broadly used pesticide class in the soil environment. In addition, the review sheds more light on mechanisms behind stereoselectivity, considers possible agricultural and environmental implications, and suggests future directions for the safe use of chiral CFs and the reduction of their environmental footprint.

Past, present, and future developments in enantioselective analysis using capillary electromigration techniques

Enantioseparation of chiral products has become increasingly important in a large diversity of academic and industrial applications. The separation of chiral compounds is inherently challenging and thus requires a suitable analytical technique that can achieve high resolution and sensitivity. In this context, CE has shown remarkable results so far. Chiral CE offers an orthogonal enantioselectivity and is typically considered less costly than chromatographic techniques, since only minute amounts of chiral selectors are needed. Several CE approaches have been developed for chiral analysis, including chiral EKC and chiral CEC. Enantioseparations by EKC benefit from the wide variety of possible pseudostationary phases that can be employed. Chiral CEC, on the other hand, combines chromatographic separation principles with the bulk fluid movement of CE, benefitting from reduced band broadening as compared to pressure-driven systems. Although UV detection is conventionally used for these approaches, MS can also be considered. CE-MS represents a promising alternative due to the increased sensitivity and selectivity, enabling the chiral analysis of complex samples. The potential contamination of the MS ion source in EKC-MS can be overcome using partial-filling and counter-migration techniques. However, chiral analysis using monolithic and open-tubular CEC-MS awaits additional method validation and a dedicated commercial interface. Further efforts in chiral CE are expected toward the improvement of existing techniques, the development of novel pseudostationary phases, and establishing the use of chiral ionic liquids, molecular imprinted polymers, and metal-organic frameworks. These developments will certainly foster the adoption of CE(-MS) as a well-established technique in routine chiral analysis.

Enantioseparation of ketoconazole and miconazole by capillary electrophoresis and a study on their inclusion interactions with β-cyclodextrin and derivatives

A chiral separation method coupled with capillary electrophoresis (CE) analysis for ketoconazole and miconazole enantiomers using chiral selectors such as β-cyclodextrin (β-CD) and hydroxypropyl-β-CD (HP-β-CD) was developed in this study, which included the optimisation, validation and application of the method on the antifungal cream samples. The formation of inclusion complex between the hosts (β-CD and HP-β-CD) and guests (ketoconazole and miconazole) were compared and analysed using ultraviolet-visible spectrophotometry, nuclear magnetic resonance (NMR) spectroscopy and molecular docking methods. Results from the study showed that in a concentration that ranged between 0.25 and 50 mg L^-1 , the linear calibration curves of each enantiomer had a high coefficient of regression (R² > 0.999), low limit of detection (0.075 mg L^-1 ) and low limit of quantification (0.25 mg L^-1 ). The relative standard deviation (RSD) of the intraday and interday analyses ranged from 0.79% to 8.01% and 3.30% to 11.43%, respectively, while the recoveries ranged from 82.0% to 105.7% (RSD < 7%, n = 3). The most probable structure of the inclusion complexes was proposed based on the findings from the molecular docking studies conducted using the PatchDock server.

Enantioselective mechanism of toxic effects of triticonazole against Chlorella pyrenoidosa

The rational use and the environmental safety of chiral pesticides have attracted significant research interest. Here, enantioselective toxic effects and the selective toxic mechanism of triticonazole (TRZ) against the aquatic microalgae Chlorella pyrenoidosa were studied. The 96h-EC₅₀ values of rac-, (R)-(-)-, and (S)-(+)-TRZ were 1.939, 0.853, and 22.002 mg/L, respectively. At a concentration of 1 mg/L, the contents of photosynthetic pigments of C. pyrenoidosa exposed to (R)-(-)-TRZ were lower than if exposed to S-(+)-form and racemate. Transmission electron microscopic images showed that the R-(-)-form compromised the integrity of cells and disrupted the chloroplast structure. R-(-)-TRZ stimulated vast reactive oxygen species (ROS) and significantly increased superoxide dismutase (SOD) and catalase (CAT) activities, as well as malondialdehyde (MDA) content. For lipid accumulation experiments, nicotinamide adenine dinucleotide (NADH) and triacylglycerol (TAG) accumulations in algal cells treated with R-(-)-TRZ were 171.50% and 280.76%, respectively, compared with the control group. This far exceeded levels of algal cells treated with S-(+)- and rac-TRZ. Based on these data, R-(-)-TRZ was concluded to selectively affect the photosynthetic system, antioxidant system, and lipid synthesis of algal cells, thus causing enantioselective toxic effects of TRZ against C. pyrenoidosa, which indicating that the use of racemate may cause unpredictable environmental harm. Therefore, to reduce the hidden dangers of chiral pesticides for the ecological environment, the environmental risk of TRZ should be evaluated at the stereoselective level.

Stereoselective bioactivity of the chiral triazole fungicide prothioconazole and its metabolite

Chiral triazole fungicides have played a significant role in plant pathogen control. Although their enantiomers often exhibit different bioactivity, the mechanism of the stereoselectivity has not been well studied. The stereoselective bioactivity and mechanisms of prothioconazole and its chiral metabolite against plant pathogenic fungi were investigated. The results indicated that the metabolite exerted more fungicidal activities than the activities of the parent compound. R-Prothioconazole and R-prothioconazole-desthio were 6-262 and 19-954 times more potent against pathogenic fungi than the S-enantiomers, respectively. The R-enantiomers were more effective than in inhibiting the biosynthesis of ergosterol and deoxynivalenol the S-enantiomer. Homology modeling and molecular docking suggested that the R-enantiomers of prothioconazole and prothioconazole-desthio possessed better binding modes than S-enantiomers to CYP51B. Moreover, exposure to prothioconazole and its metabolite enantiomers significantly changed the transcription levels of the CYP51 (CYP 51A, CYP51B, CYP 51C) and Tri (Tri5, Tri6, Tri12) genes. The results showed that application of the R-prothioconazole could require a smaller application amount to eliminate the carcinogenic mycotoxins and any environmental risks.

Stability and toxicity studies for duloxetine and econazole on Spirodela polyrhiza using chiral capillary electrophoresis

Stability and toxicity studies for duloxetine and econazole were achieved using individual solutions and their mixtures. Stability of drugs racemates and enantiomers was investigated under abiotic and biotic conditions. Toxicity was evaluated for the first time on Spirodela polyrhiza. EC50 values were calculated for each individual drug and for their binary mixture. Real (not nominal) concentrations determined by Capillary Electrophoresis were employed in the calculations of toxicity parameters. The use of a 25 mM phosphate buffer (pH 3.0) with 1.5% S-β-CD as chiral selector at a temperature of 30 °C and a separation voltage of -20 kV enabled the simultaneous enantiomeric separation of duloxetine and econazole in 7.5 min with enantiomeric resolutions of 7.9 and 6.5, respectively. For individual solutions, decay percentages under abiotic conditions were higher for duloxetine (80%) than for econazole (60%), while in presence of Spirodela polyrhiza they increased for duloxetine but not for econazole. Econazole showed the highest decay percentages under abiotic or biotic conditions (100%) in binary mixtures. EC50 values for duloxetine and econazole enabled to include both drugs within the group of very toxic compounds although econazole showed a higher toxicity than duloxetine and the binary mixture.

Behavior of the Chiral Herbicide Imazamox in Soils: pH-Dependent, Enantioselective Degradation, Formation and Degradation of Several Chiral Metabolites

Many pesticides show a pronounced biphasic degradation in soil, typically with a faster initial phase, followed by a slower decline. For chiral compounds, a biphasic decline of the total concentration may result from enantioselective degradation. In this study with the chiral herbicide imazamox, biphasic degradation was observed in most of the 18 soils investigated. In neutral soils, degradation was, in fact, enantioselective with faster degradation of (+)-imazamox. In slightly acidic soils, differences between enantiomers were not pronounced, and in strongly acidic soils, degradation was again enantioselective, but with reversed preference. Additional experiments with pure enantiomers indicated no interconversion. Enantioselective degradation thus contributed to the biphasic decline of the total concentration in certain soils. However, this was not the only factor since degradation of the individual enantiomers was biphasic in itself. In addition to the observed correlation between enantioselectivity and pH, degradation was generally faster in neutral than in acidic soils with half-lives ranging from only 2 to >120 days. Half-lives were also determined for two known metabolites and a further chiral metabolite, the structure of which was characterized by high resolution tandem mass spectrometry. As for the parent compound, half-lives of the metabolites varied considerably in the different soils.

Effect of Tebuconazole Enantiomers and Environmental Factors on Fumonisin Accumulation and FUM Gene Expression in Fusarium verticillioides

Fusarium verticillioides is an important corn pathogen that can produce fumonisins (FBs) under certain environmental conditions. In this study, we evaluated the enantioselective impact of tebuconazole enantiomers on the growth and FB production of F. verticillioides on maize-based media at different abiotic factors. The expression of FB biosynthetic genes ( FUM1 and FUM6) was quantified by real-time reverse transcription polymerase chain reaction. The results showed that water activity ( a_w), temperature, and types of tebuconazole significantly affected the growth of F. verticillioides. The order of fungicidal activity was (-)-tebuconazole > rac-tebuconazole > (+)-tebuconazole. (-)-tebuconazole exhibited the maximal selective fungicidal activity (242-fold) against F. verticillioides at 0.95 a_w and 35 °C. Production of fumonisin B₁ (FB₁) and fumonisin B₂ (FB₂) by F. verticillioides was influenced by a_w, temperature, types of tebuconazole, and dose. Under most conditions, (-)-tebuconazole showed stronger inhibition for FB₁ and FB₂ production than (+)-tebuconazole (1.87-2.85-fold reduction in FBs) and rac-tebuconazole. The optimal environmental condition for FB production was at 0.99 a_w and 25 °C. Tebuconazole enantiomers differently affected FB biosynthetic gene ( FUM1 and FUM6) expression, but the effects on FB production and gene expression showed no positive correlation. The present study provides a better understanding on ways to minimize FB production in corn treated with fungicides.

Stereoselective Separation of the Fungicide Bitertanol Stereoisomers by High-Performance Liquid Chromatography and Their Degradation in Cucumber

Bitertanol is a widely used triazole fungicide and consists of four stereoisomers. A new high-performance liquid chromatography (HPLC) method was developed for simultaneous analysis of the four stereoisomers in apple, pear, tomato, cucumber, and soil. The mechanism of separation was explained with molecular docking and effects of thermodynamic parameters on the resolution. The absolute configuration and optical rotation of four stereoisomers were confirmed by X-ray diffraction and HPLC tandem circular dichroism, respectively. A good linearity ( R² ≥ 0.999) was obtained for four stereoisomers in all matrix-matched calibration curves in the range of 0.02-10 mg/L. The mean recoveries of four stereoisomers in five matrices ranged from 74.6% to 101.0% with an intraday and interday relative standard deviation from 0.6% to 9.9%. Stereoselective degradation of bitertanol in cucumber was observed: (1 R,2 S)-bitertanol and (1 R,2 R)-bitertanol were preferentially degraded with enantiomeric fraction values from 0.5 to 0.43 at 7 d and 0.42 at 5 d, respectively. This research provides a useful tool for the analysis of bitertanol stereoisomers.

An environmentally friendly method for the enantioseparation and determination of benalaxyl in tobacco and soil by ultra-performance convergence chromatography with tandem mass spectrometry

For the purpose of chiral separation and determination of benalaxyl enantiomers in tobacco and soil, we developed a rapid, green, and sensitive method using ultra-performance convergence chromatography with tandem mass spectrometry. The samples were extracted and purified by the quick, easy, cheap, effective, rugged, and safe method before injection. The baseline separation was obtained on a chiral column in 5 min with carbon dioxide and ethanol as mobile phase. Separation parameters were optimized for the best separation efficiency. Under optimal conditions, the recoveries of both enantiomers were 77.1-98.4% with relative standard deviations <5.0% at spiked level of 0.1, 2.0, and 5.0 mg/kg in two matrices. Good coefficients of determination were achieved over the concentration range of 10-250 ng/mL. The limit of detection and the limit of quantification for all enantiomers ranged from 0.43 to 0.72 μg/kg and from 1.25 to 2.15 μg/kg, respectively. The results show that ultra-performance convergence chromatography with tandem mass spectrometry provides a reliable, green, and rapid method for the separation and determination of benalaxyl enantiomers in tobacco and soil. This method has important theoretical significance for studying the enantioselectivity and bioactivity of benalaxyl in the environment and in organisms.

Simultaneous enantioselective determination of 22 chiral pesticides in fruits and vegetables using chiral liquid chromatography coupled with tandem mass spectrometry

This paper presents a novel multi-residue method for the enantioselective analysis of 22 chiral pesticides in cucumber, tomato, cabbage, grape, mulberry, apple and pear at enantiomeric levels. Pesticides were efficiently extracted by magnetic solid-phase extraction based on graphene as sorbent. Response surface methodology was used to assist the multivariable optimization. The perfect chiral separation of the enantiomers was achieved on a Chiralpak IG column within 47 min by reversed-phase liquid chromatography coupled with tandem mass spectrometry, which is a significant improvement to resolve a large group of chiral compounds under one set of conditions. The method was validated in terms of selectivity, linearity, sensitivity, trueness and precision, which all satisfy the requirement for pesticides residue analysis. The proposed method was successfully applied for monitoring the occurrence and enantiomeric composition of pesticides in different fruits and vegetables, demonstrating its applicability for the routine analysis of chiral pesticide residues in food samples.

Stereoselective degradation behaviour of carfentrazone-ethyl and its metabolite carfentrazone in soils

The stereoselective environmental behaviour of carfentrazone-ethyl and its metabolite carfentrazone enantiomer in three types of soil were studied under aerobic conditions. Under aerobic conditions, significant stereoselective difference in the degradation behaviour of carfentrazone-ethyl and its metabolite carfentrazone enantiomer was observed in Jiangxi red soil, Jilin black soil and Anhui paddy soil. The EF values of the carfentrazone-ethyl enantiomers in Anhui paddy soil, Jilin black soil, and Jiangxi red soil were 0.67, 0.65 and 0.57, respectively. The EF values of the carfentrazone enantiomer in the three types of soil were 0.75, 0.80 and 0.76. No bidirectional chiral inversion of enantiopure carfentrazone-ethyl and carfentrazone enantiomers was observed in Jilin soil. As a result, R-(+)-carfentrazone-ethyl and S-(+)-carfentrazone in soil would be preferentially degraded, while S-(-)-carfentrazone-ethyl and R-(-)-carfentrazone were enriched. The results found in this paper could provide more scientific guidance for the risk assessments of carfentrazone-ethyl from a chiral perspective.

Enantiomer-specific stable carbon isotope analysis (ESIA) to evaluate degradation of the chiral fungicide Metalaxyl in soils

Chiral pesticides are often degraded enantioselectively in soils, leading to disparity among enantiomers that may display different toxicity levels. Monitoring pesticide degradation extents and processes remains out of reach in the field using conventional bulk and enantiomer concentration analyses. Enantioselective stable carbon isotope analysis (ESIA) combines compound specific isotope analysis (CSIA) and enantioselective analysis, and bears potential to distinguish enantiomer degradation from non-destructive dissipation. We developed ESIA of the fungicide Metalaxyl, providing the ¹³C/¹²C ratios for S-Metalaxyl and R-Metalaxyl separately, and applied it to follow degradation in soil incubation experiments. Significant enantioselective degradation (k_S-MTY = 0.007-0.011 day^-1 < k_R-MTY = 0.03-0.07 day^-1) was associated with isotope fractionation (Δδ¹³C_S-MTY ranging from 2 to 6‰). While R-Metalaxyl degradation was rapid (T_1/2≈10 days), concomitant enrichment in heavy isotopes of the persistent S-Metalaxyl occurred after 200 days of incubation (ε_S-Metalaxyl ranging from -1.3 to -2.7‰). In contrast, initial racemic ratios and isotopic compositions were conserved in abiotic experiments, which indicates the predominance of microbial degradation in soils. Degradation products analysis and apparent kinetic isotope effect (AKIE) suggested hydroxylation as a major enantioselective degradation pathway in our soils. Altogether, our study underscores the potential of ESIA to evaluate the degradation extent and mechanisms of chiral micropollutants in soils.

Simultaneous Enantioselective Determination of the Chiral Fungicide Prothioconazole and Its Major Chiral Metabolite Prothioconazole-Desthio in Food and Environmental Samples by Ultraperformance Liquid Chromatography-Tandem Mass Spectrometry

An efficient and sensitive chiral analytical method was established for the determination of the chiral fungicide prothioconazole and its major chiral metabolite prothioconazole-desthio in agricultural and environmental samples using ultraperformance liquid chromatography-tandem mass spectrometry. The optical rotation and absolute configuration of enantiomers were identified by optical rotation detector and electronic circular dichroism spectra. The elution order of prothioconazole and its chiral metabolite enantiomers was R-(+)-prothioconazole-desthio, S-(-)-prothioconazole-desthio, R-(-)-prothioconazole, and S-(+)-prothioconazole. The mean recoveries from the samples was 71.8-102.0% with intraday relative standard deviations (RSDs) of 0.3-11.9% and interday RSDs of 0.9-10.6%. The formation of prothioconazole-desthio was studied in soil under field conditions and enantioselective degradation was observed for chiral prothioconazole. Remarkable enantioselective degradation was observed: R-prothioconazole degraded preferentially with EF values from 0.48 to 0.37. Although prothioconazole-desthio is the most remarkably bioactive metabolite, no obvious enantioselective behavior was observed in soil. These results may help to systematically evaluate prothioconazole and its metabolites in food and environmental safety.

Risk assessment of the endocrine-disrupting effects of nine chiral pesticides

The increased release of chiral pesticides into the environment has generated interest in the role of enantioselectivity in the environmental fate and ecotoxicological effects of these compounds. However, the information on the endocrine disrupting effects (EDEs) of chiral pesticides is still limited and discrepancies are also usually observed among different assays. In this study, we investigated the enantioselectivity of EDEs via estrogen and thyroid hormone receptors for nine chiral pesticides using in vitro and in silico approaches. The results of the luciferase reporter gene assays showed 7 chiral pesticides possessed enantioselective estrogenic activities and 2 chiral pesticides exerted thyroid hormone antagonistic effects. Proliferation assays in MCF-7 and GH3 cells were also used to verify the results of the dual-luciferase reporter gene assays. At last, the molecular docking results indicated that the enantioselective EDEs of chiral pesticides were partially due to enantiospecific binding affinities with receptors. Our data not only show enantioselective EDEs of nine chiral pesticides, but also would be helpful to better understanding the molecular biological mechanisms of enantioselectivity in EDEs of chiral pesticides.

Analytical method development for the determination of eight biocides in various environmental compartments and application for monitoring purposes

The main objective of this study was the development of simple multi-parameter methods for the analyses of biocides in various environmental matrices (wastewater, surface water, and sewage sludge) for measurement and monitoring activities. Eight target substances (triclosan, methyltriclosan (transformation product of triclosan), cybutryne (Irgarol), and the azole fungicides propiconazole, tebuconazole, imazalil, thiabendazole, and cyproconazole) were chosen for determination in selected sample sets. For surface water and wastewater samples a solid-phase extraction (SPE) method and for sewage sludge samples an accelerated solvent extraction (ASE) were developed. The extracts were analyzed by gas chromatographic-mass spectrometric methods (GC/MS), and the analytical methods were checked to ensure sufficient sensitivity by comparing the limits of quantification (LOQs) to the predicted no effect concentrations (PNECs) of the selected biocides. For quality control, recovery rates were determined. Finally, developed methods were checked and validated by application on sample material from various matrices. Sampling took place in seven urban wastewater treatment plants and their corresponding receiving waters. The results revealed that the developed extraction methods are effective and simple and allow the determination of a broad range of biocides in various environmental compartments.

Stereoselective Metabolism of the Sterol Biosynthesis Inhibitor Fungicides Fenpropidin, Fenpropimorph, and Spiroxamine in Grapes, Sugar Beets, and Wheat

Metabolism of chiral pesticides in crops is typically studied using achiral analytical methods and, consequently, the stereoisomer composition of residues is unknown. In this study, we developed an enantioselective GC-MS/MS method to quantify residues of the fungicides fenpropidin, fenpropimorph, and spiroxamine in plant matrices. In field trials, the fungicides were applied to grapevines, sugar beets, or wheat. Fenpropidin was metabolized with no or only weak enantioselectivity. For fenpropimorph, slightly enantioselective metabolism was observed in wheat but more pronounced in sugar beets. This enantioselectivity was due to different rates of metabolism and not due to interconversion of enantiomers. The four stereoisomers of spiroxamine were also metabolized at different rates, but selectivity was only found between diastereomers and not between enantiomers. trans-Spiroxamine was preferentially degraded in grapes and cis-spiroxamine in wheat. These findings may affect the consumer dietary risk assessment because toxicological end points were determined using racemic test substances.

Simultaneous enantioselective determination of phenylpyrazole insecticide flufiprole and its chiral metabolite in paddy field ecosystem by ultra-high performance liquid chromatography/tandem mass spectrometry

A novel and sensitive ultra-high performance liquid chromatography coupled with tandem mass spectrometry (LC-MS/MS) method was developed and validated for simultaneous enantioselective determination of flufiprole and its hydrolysis metabolite in paddy field ecosystem. The separation and determination were performed using reversed-phase chromatography on a novel cellulose chiral stationary phase, a Lux Cellulose-4 (150 mm × 2.0 mm) column, under isocratic conditions at 0.25 mL/min flow rate. The effects of other four different polysaccharide-based chiral stationary phases (CSPs) on the separation and simultaneous enantioseparation of the two target compounds were also evaluated. The elution orders of the eluting enantiomers were identified by an optical rotation detector. Modified QuEChERS (acronym for Quick, Easy, Cheap, Effective, Rugged and Safe) method and solid-phase extraction (SPE) were used for the enrichment and cleanup of paddy water, rice straw, brown rice and paddy soil samples, respectively. Parameters including the matrix effect, linearity, precision, accuracy and stability were evaluated. Under the optimal conditions, the mean recoveries for all enantiomers from the above four sample matrix were ranged from 83.6% to 107%, with relative standard deviations (RSD) in the range of 1.0-5.8%. Coefficients of determination R(2)≥0.998 were achieved for each enantiomer in paddy water, rice straw, brown rice and paddy soil matrix calibration curves within the range of 5-500 μg/kg. The limits of quantification (LOQ) for all stereoisomers in the above four matrices were all below 2.0 μg/kg. The methodology was successfully applied for simultaneously enantioselective analysis of flufiprole enantiomers and their chiral metabolite in the real samples, indicating its efficacy in investigating the environmental stereochemistry of flufiprole in paddy field ecosystem.

Environmental fate of the fungicide metalaxyl in soil amended with composted olive-mill waste and its biochar: An enantioselective study

A large number of pesticides are chiral and reach the environment as mixtures of optical isomers or enantiomers. Agricultural practices can affect differently the environmental fate of the individual enantiomers. We investigated how amending an agricultural soil with composted olive-mill waste (OMWc) or its biochar (BC) at 2% (w:w) affected the sorption, degradation, and leaching of each of the two enantiomers of the chiral fungicide metalaxyl. Sorption of metalaxyl enantiomers was higher on BC (Kd ≈ 145 L kg(-1)) than on OMWc (Kd ≈ 22 L kg(-1)) and was not enantioselective in either case, and followed the order BC-amended>OMWc-amended>unamended soil. Both enantiomers showed greater resistance to desorption from BC-amended soil compared to unamended and OMWc-amended soil. Dissipation studies revealed that the degradation of metalaxyl was more enantioselective (R>S) in unamended and OMWc-amended soil than in BC-amended soil. The leaching of both S- and R-metalaxyl from soil columns was almost completely suppressed after amending the soil with BC and metalaxyl residues remaining in the soil columns were more racemic than those in soil column leachates. Our findings show that addition of BC affected the final enantioselective behavior of metalaxyl in soil indirectly by reducing its bioavailability through sorption, and to a greater extent than OMWc. BC showed high sorption capacity to remove metalaxyl enantiomers from water, immobilize metalaxyl enantiomers in soil, and mitigate the groundwater contamination problems particularly associated with the high leaching potential of the more persistent enantiomer.

Synthesis and Characterization of Modified Polydimethylsiloxane Nanomembrane for Chiral Separation

Polydimethylsiloxane-2-[2-tert-Butoxycarbonylamino-(1H-pyrazol-4-yl)-propionylamino] -3-phenyl-propanoic acid (PDMS-BCPA) is a newly developed stereo-specific membrane that interacts with S configuration of enantiomers as chiral recognition sites. In this study, realization of PDMS-BCPA nanomembrane was achieved via anodized aluminum oxide (AAO) template synthesis approach followed by the attachment of synthesized chiral selector (BCPA) using simple immersion method. The effect of surface modification and the attachment with chiral selector were investigated and characterized using Fourier Transform Infrared spectroscopy (FT-IR), Field Emission Scanning Electron Microscopic (FE-SEM) and Atomic Force Microscopic (AFM) methods. The characterization via these methods indicates the synthesized BCPA as chiral selector was successfully attached onto the PDMS surface. The enantioselectivity of PDMS-BCPA nanomembrane was verified by the separation of alpha cypermethrin enantiomer.