Enantiomer separation of triazole fungicides by high-performance liquid chromatography

Green and sensitive supercritical fluid chromatographic-tandem mass spectrometric method for the separation and determination of flutriafol enantiomers in vegetables, fruits, and soil

A green and sensitive chiral analytical method was developed to determine flutriafol enantiomers in vegetables (tomato, cucumber), fruits (apple, grape), and soil by supercritical fluid chromatography-tandem mass spectrometry. The enantioseparation was performed within 3.50 min using Chiralpak IA-3 column with CO2/methanol (88:12, v/v) as the mobile phase at a 2.2 mL/min flow rate. The postcolumn compensation technology provided with 1% formic acid/methanol greatly improved the ionization efficiency of mass spectrometry. Column temperature, auto back pressure regulator pressure, and flow rate of compensation solvent were optimized to 30 °C, 2200 psi, and 0.1 mL/min, respectively. The simple and fast QuEChERS pretreatment method was adopted. Mean recoveries for flutriafol enantiomers were 77.2-98.9% with RSDs ≤ 9.6% in all matrices. The limits of quantification ranged from 0.41 to 1.18 μg/kg. Well-applied to analyze authentic samples, the developed method could act as a versatile strategy for the analysis of flutriafol enantiomers in food and environmental matrices.

Comparative study of the selective degradations of two enantiomers in the racemate and an enriched concentration of indoxacarb in soils

In this study, selective degradations of the two enantiomers of indoxacarb in the concentrate (2.33S/1R) and racemate (1S/1R) are examined. The absolute configurations of indoxacarb enantiomers were determined using X-ray diffraction. The results showed that in two alkaline soils, the S-(+)-indoxacarb was preferentially degraded in both the concentrate and racemate. In one acid soil, the two enantiomers degraded no-selectivity. In another acid soil and one neutral soil, the R-(-)-indoxacarb was preferentially degraded in both the concentrate and racemate. Indoxacarb enantiomers were configurationally stable in the five soils, and no interconversion was observed during the incubation. Because no significant difference in degradation was observed after samples were sterilized, the observed enantioselectivity may be attributed primarily to microbial activity in soils. The results indicate that the selective degradation behavior was the same for both formulations that were tested.

Enantioselective toxic effects and degradation of myclobutanil enantiomers in Scenedesmus obliquus

Research on the enantioselective environmental behavior of chiral pesticides has been a hot spot of environmental chemistry recently. In this study, the acute toxicity of myclobutanil enantiomers was investigated with the aquatic algae Scendesmus obliquus. After exposure for 96 h, the EC50 values for (-)-myclobutanil, rac-myclobutanil and (+)-myclobutanil were 3.951, 2.760, and 2.128 mg/L, respectively. The photosynthetic pigment (chlorophyll a, chlorophyll b, and carotenoids) and antioxidant enzyme activities catalase (CAT) were determined to evaluate the different toxic effects when S. obliquus were exposed to 1.5, 5 and 15 mg/L of rac-myclobutanil, (-)-myclobutanil, and (+)-myclobutanil for 96 h, respectively. In addition, the degradation of myclobutanil enantiomers in S. obliquus was also studied. Myclobutanil in the medium inoculated with algae degraded faster than in the uninoculated medium. The degradation of (-)-myclobutanil was faster than that of (+)-myclobutanil at a concentration of 3 mg/L. On the basis of these data, the acute toxicity and toxic effects of myclobutanil against S. obliquus were concluded to be enantioselective, and such enantiomeric differences should be taken into consideration in pesticide risk assessment.

Development of a multi-residue enantiomeric analysis method for 9 pesticides in soil and water by chiral liquid chromatography/tandem mass spectrometry

A novel and sensitive chiral liquid chromatography coupled with tandem mass spectrometry (LC-MS/MS) method was developed and validated for simultaneous measuring individual enantiomers of 9 pesticides including herbicides, insecticides, and fungicides in soil and water. The separation and determination were performed using reversed-phase chromatography on an amylose chiral stationary phase, a Chiralpak AD-RH column, under gradient elution using a mixture of ACN-2mM ammonium acetate in water as the mobile phase at 0.45 mL/min flow rate. The effects of three cellulose-based columns and three amylose-based columns on the separation were also investigated. The QuEChERS (acronym for Quick, Easy, Cheap, Effective, Rugged and Safe) method and solid-phase extraction (SPE) were used for the extraction and clean-up of the soil and water samples, respectively. Parameters including the matrix effect, linearity, precision, accuracy and stability were undertaken. Under optimal conditions, the mean recoveries for all enantiomers from the soil and water samples were ranged from 77.8% to 106.2% with the relative standard deviations (RSD) less than 14.2%. Good linearity (at least R(2) ≥ 0.9986) was obtained for all studied analytes in the soil and water matrix calibration curves over the range from 2.0 to 125 μg/L. The limits of detection (LOD) for all enantiomers in the soil and water were less than 1.8 μg/kg or μg/L, whereas the limit of quantification (LOQ) did not exceed 5.0 μg/kg or μg/L. The results of the method validation confirm that this proposed method is convenient and reliable for the enantioselective determination of the enantiomers of 9 chiral pesticides in soil and water.

Enantioselective analysis of triazole fungicide myclobutanil in cucumber and soil under different application modes by chiral liquid chromatography/tandem mass spectrometry

A sensitive and enantioselective method was developed and validated for the determination of myclobutanil enantiomers by chiral liquid chromatography coupled with tandem mass spectrometry. The separation and determination were performed using reversed-phase chromatography on a Chiralcel OD-RH column, with ACN-water (70/30, v/v) as the mobile phase under isocratic conditions at 0.5 mL/min flow rate. The matrix effect, linearity, precision, accuracy, and stability were evaluated. The proposed method then was successfully applied to the study of enantioselective degradation of rac-myclobutanil in cucumber and soil under different application modes. The results showed that the preferential degradation of (+)-myclobutanil resulted in an enrichment of the (-)-myclobutanil residue in plant and soil. Moreover, in cucumber, the stereoselective intensity of myclobutanil under root douche treatment was stronger than that under foliar spraying treatment, whereas in soil, the intensity was exactly opposite. The probable reasons underlying these enantioselective effects were also discussed. This study highlighted the importance of examining the fate of both enantiomers in the greenhouse system for the correct use of chiral pesticides.

Residue analysis and degradation studies of fenbuconazole and myclobutanil in strawberry by chiral high-performance liquid chromatography-tandem mass spectrometry

A simple and sensitive enantioselective method for the determination of fenbuconazole and myclobutanil in strawberry was developed by high-performance liquid chromatography-tandem mass spectrometry (HPLC-MS/MS). Fenbuconazole and myclobutanil residues in strawberry were extracted with acetonitrile containing 1% acetic acid, and an aliquot was cleaned up with PSA (primary and secondary amine) and C(18) sorbent. The direct resolution of fenbuconazole and myclobutanil enantiomers was performed on a cellulose tris (3,5-dimethylphenylcarbamate) column using acetonitrile-0.1% formic acid solution (60:40, v/v) as the mobile phase. Quantification was achieved using matrix-matched standard calibration curves, and the limits of quantification for fenbuconazole and myclobutanil enantiomers in strawberry were both 2 μg/kg. The method was successfully utilized to investigate the probable enantioselective degradation of fenbuconazole and myclobutanil in strawberry. The results showed that the degradation of the fenbuconazole and myclobutanil enantiomers in strawberry followed pseudofirst-order kinetics (R(2) > 0.97). The results from this study revealed that the degradation of fenbuconazole in strawberry was not enantioselective, while the degradation of myclobutanil was enantioselective, and the (+)-myclobutanil showed a faster degradation than (-)-myclobutanil in strawberry, resulting in the relative enrichment of (-)-myclobutanil in residue. The results could provide a reference to fully evaluate the risks of these two fungicides.

Enantioselectivity in estrogenicity of the organochlorine insecticide acetofenate in human trophoblast and MCF-7 cells

Previous studies have showed that some chiral pesticides with estrogenic activity possess enantioselectivity in endocrine disruption. Despite the assessment of enantioselectivity in the estrogenic potential of chiral pesticides, which deserve particular attention, there has been limited research into their molecular mechanisms of human health risk. In this study, the role of enantioselectivity in the endocrine disruption and potential human maternal-fetal health risk of acetofenate (AF), an organochlorine insecticide, were investigated in both MCF-7 and JEG-3 cells. The two in vitro assays showing a clear enantioselectivity in the estrogenic activity with S-(+)-AF showed stronger effects than R-(-)-AF and rac-AF. Moreover, the racemate's estrogenicity was in between that of enantiomers. Our results also demonstrated that S-(+)-AF possesses the strongest potential effects in disruption of hormone secretion, maternal immune tolerance, and steroidogenesis in the trophoblast. The results suggest that assessment of the health risk of chiral contaminants should consider the role of enantioselectivity.

Enantioselective determination of triazole fungicide simeconazole in vegetables, fruits, and cereals using modified QuEChERS (quick, easy, cheap, effective, rugged and safe) coupled to gas chromatography/tandem mass spectrometry

A rapid and effective method for enantioselective determination of simeconazole enantiomers in food products (cucumber, tomato, apple, pear, wheat and rice) has been developed. The enantiomers were resolved by capillary gas chromatography (GC) using a commercial chiral column (BGB-172) and a temperature program from 150°C (held for 1 min) and then raised at 10°C min(-1) to 240°C (held for 10 min). This enantioselective gas chromatographic separation was combined with a clean-up/enrichment procedure based on the modification of QuEChERS (quick, easy, cheap, effective, rugged and safe) method. Co-extractives were removed with graphitized carbon black/primary secondary amine (GCB/PSA) solid-phase extraction (SPE) cartridges using acetonitrile:toluene (3:1, v/v) as eluent. Gas chromatography/ion trap mass spectrometry (GC-ITMS) with electron ionization (EI) was then used for qualitative and quantitative determination of the simeconazole enantiomers. Two precursor-to-product ion transitions (m/z 121-101 and 195-153) with the best signal intensity were chosen to build the multiple-reaction monitoring (MRM) acquisition method. The limits of detection for each enantiomer of simeconazole in six food products ranged between 0.4 and 0.9 μg kg(-1), which were much lower than maximum residue levels (MRLs) established by Japan. The methodology was successfully applied for the enantioselective analysis of simeconazole enantiomers in real samples, indicating its efficacy in investigating the environmental stereochemistry of simeconazole in food matrix.

The role of oxidative stress in enantiomer-specific, bifenthrin-induced cytotoxicity in PC12 cells

With the widespread use of synthetic pyrethroids (SPs), the various toxic effects of these compounds have attracted much interest with respect to the investigation of involved mechanisms. However, research on molecular mechanisms of enantioselective toxicity of SPs has been limited. Our previous investigations suggested that enantiomers of cis-bifenthrin (cis-BF) behaved enantioselectively in endocrine disruption and mammalian cytotoxicity. While little is known about the molecular mechanism of the enantioselective toxicity of cis-BF, recent experiments implicated oxidative stress in the cytotoxicity of many SPs. Therefore, the aim of this study was to determine whether cis-BF enantioselectively induced oxidative stress lead to enantioselective cytotoxicity. In this article, we used the rat pheochromocytoma PC12 cell line as an in vitro model to evaluate the involvement of the oxidative stress pathway in enantioselective cytotoxicity of cis-BF. Following exposure of cells to cis-BF and its enantiomers, a significant reduction in cell survival and superoxide dimutase, as well as increased production of lactate dehydrogenase, intracellular reactive oxygen species and malondialdehyde, was observed in 1S-cis-BF, while 1R-cis-BF exhibited these effects to a lesser degree. These results clearly demonstrated that enantiomer-specific cis-BF-induced oxidative damage is possibly an initiating event and contributes, at least in part, to the mechanism of cis-BF-induced enantioselective cytotoxicity. Furthermore, our study also indicated that enantioselectivity should be considered when evaluating the ecotoxicological effects and the health risks of chiral contaminants.

Enantioselective phytotoxicity of the herbicide imazethapyr on the response of the antioxidant system and starch metabolism in Arabidopsis thaliana

BACKGROUND

The enantiomers of a chiral compound possess different biological activities, and one of the enantiomers usually shows a higher level of toxicity. Therefore, the exploration of the causative mechanism of enantioselective toxicity is regarded as one of primary goals of biological chemistry. Imazethapyr (IM) is an acetolactate synthase (ALS)-inhibiting chiral herbicide that has been widely used in recent years with racemate. We investigated the enantioselectivity between R- and S-IM to form reactive oxygen species (ROS) and to regulate antioxidant gene transcription and enzyme activity.

RESULTS

Dramatic differences between the enantiomers were observed: the enantiomer of R-IM powerfully induced ROS formation, yet drastically reduced antioxidant gene transcription and enzyme activity, which led to an oxidative stress. The mechanism by which IM affects carbohydrate metabolism in chloroplasts has long remained a mystery. Here we report evidence that enantioselectivity also exists in starch metabolism. The enantiomer of R-IM resulted in the accumulation of glucose, maltose and sucrose in the cytoplasm or the chloroplast and disturbed carbohydrates utilization.

CONCLUSION

The study suggests that R-IM more strongly retarded plant growth than S-IM not only by acting on ALS, but also by causing an imbalance in the antioxidant system and the disturbance of carbohydrate metabolism with enantioselective manner.

Enantioselectivity in environmental risk assessment of modern chiral pesticides

Chiral pesticides comprise a new and important class of environmental pollutants nowadays. With the development of industry, more and more chiral pesticides will be introduced into the market. But their enantioselective ecotoxicology is not clear. Currently used synthetic pyrethroids, organophosphates, acylanilides, phenoxypropanoic acids and imidazolinones often behave enantioselectively in agriculture use and they always pose unpredictable enantioselective ecological risks on non-target organisms or human. It is necessary to explore the enantioselective toxicology and ecological fate of these chiral pesticides in environmental risk assessment. The enantioselective toxicology and the fate of these currently widely used pesticides have been discussed in this review article.

Dual enantioselective effect of the insecticide bifenthrin on locomotor behavior and development in embryonic-larval zebrafish

Bifenthrin (BF) is a synthetic pyrethroid that targets the nervous system of insects and may have adverse effects on the behavior and development of nontarget organisms. However, no reports have been issued on the effects of different enantiomers on locomotor behavior for synthetic pyrethroids (SPs) in zebrafish, and whether locomotor activity is associated with the developmental toxicities remains unclear. In this study, enantioselectivity of BF (1S and 1R) on the acute locomotor activity and developmental toxicities of embryonic-larval zebrafish were first evaluated. The results indicated that 1R-BF was more toxic, causing morphological impairments, with a 96-h median effective concentration (EC50) of 226 microg/L for pericardial edema and 145 microg/L for curved body axis. Administration of 20 microg/L of one enantiomer of BF had differential effects on the locomotor activity of zebrafish larvae at 4 d postfertilization (dpf) under alternating light and dark conditions. Larvae treated with 1R-BF were not sensitive to the alteration of light to dark, and the locomotor activities were reduced to a level similar to that observed in light, which otherwise increased rapidly and markedly. However, 1S-BF did not alter the general pattern of zebrafish response to the light or dark compared with the control. The results demonstrated that the differential effects on development might have contributed to the enantioselectivity in the locomotor activity. The consistency of enantioselectivity with insecticidal activity may also indicate a common mode of action. Furthermore, 1R-BF accelerated the spontaneous movement and hatching process, whereas 1S-BF seemed to be inhibitory. The results suggest the need to link behavioral changes to developmental toxicities in order to achieve more comprehensive health risk assessments of chiral pesticides.

Enantioselective induction of oxidative stress by permethrin in rat adrenal pheochromocytoma (PC12) cells

Synthetic pyrethroid (SP) insecticides are chiral compounds with multiple asymmetric positions. Several recent studies have focused on the effect of enantioselectivity of SPs in acute aquatic toxicity, endocrine-disrupting activities, and immunotoxicity. However, the relevant molecular mechanisms are still unknown. The potential relationship between ecotoxicological effects and oxidative stress could contribute to SP-induced enantioselective cytotoxicity, but this requires further investigation. Therefore, this study was undertaken to evaluate the role of oxidative stress in enantiomer-specific permethrin (PM)-induced cytotoxicity in rat adrenal pheochromocytoma (PC12) cells. The study demonstrated that PM induced enantioselective oxidative stress and cytotoxicity. The reactive oxygen species (ROS) generation and lipid peroxidation production of malondialdehyde (MDA) were obviously increased, whereas the activity of antioxidant enzymes (superoxide dismutase [SOD] and catalase [CAT]) and glutathione (GSH) content had declined after exposure in 1R-trans-PM at a concentration of 30 mg/L. Meanwhile, the result of the cytotoxicity assay showed a clear, dose-dependent growth-inhibition effect of PM in an enantioselective manner. The most toxic effect on PC12 cells was shown by 1R-trans-PM and was approximately 1.6 times higher than that with 1S-cis-PM, which exhibited only a slightly toxic effect at a concentration of 20 mg/L. These results suggested that PM exhibited significant enantioselectivity in oxidative stress, which may be one of the initial events in PM-induced enantioselective cytotoxicity. The present study also improved understanding of enantiomer-specific, SP-induced cytotoxicity. The enantioselectivity should be taken into consideration when assessing ecological effects and development of new chiral pesticides.

Enantioselective phytotoxicity of the herbicide imazethapyr in rice

Research increasingly suggests that enantiomer selectivity may be a part of the toxicological effects of chiral contaminants. In this study, we selected Japonica rice variety Xiushui 63 seedlings to evaluate the enantioselectivity of imazethapyr (IM). Significant differences in rice seedling morphology, antioxidant enzyme, oxidant marker and gene transcription were observed between the two IM enantiomers. In the seedling morphological assay, IM enantiomers inhibited elongation of primary roots and shoots, and reduced the number of adventitious roots and the density of root hairs. The inhibitory effects were enhanced with increasing concentrations of IM. The maximal root relative inhibition rate reached 80.4%, 67.0%, and 73.5% for R-(-)-IM, S-(+)-IM and racemate at the concentration of 0.5 mg L(-1), respectively, and the maximal shoot relative inhibition rate reached 77.7%, 26.9%, and 61.7%, respectively. The activities of SOD, POD and CAT and the content of MDA increased at 0.5 mg L(-1) of R-(-)-IM treatment, and were 1.8, 3.3, 1.4, and 2.2 times, respectively, over the activities S-(+)-IM. Real-time PCR showed that R-(-)-IM minimized the transcript abundance of ALS in shoot tissue to 12.2% of the S-(+)-IM, and minimized the transcript abundance of PC in seed to 9.2% of the S-(+)-IM. R-(-)-IM maximized the transcript abundance of beta-amylase in shoots to 8.6-time of the S-(+)-IM. Results from this study imply that R-(-)-IM has stronger toxicity on the growth of rice than S-(+)-IM.