Beibei Gao

Enantioseparation and determination of triticonazole enantiomers in fruits, vegetables, and soil using efficient extraction and clean-up methods.

An efficient and novel enantioseparation and determination method was developed to quantify the enantiomers of chiral triazole fungicide triticonazole in fruit, vegetable, and soil samples. Under the optimal chromatographic conditions, the enantiomers of triticonazole were completely enantioseparated on a cellulose tris(3-chloro-4-methyl phenyl carbamate) column with relatively good resolution (Rs=14.04). Two cleanup methods were compared to quantify the enantiomers of triticonazole. The modified QuEChERS (quick, easy, cheap, effective, rugged and safe) extraction procedure was achieved with sufficient recoveries and low detection limits. Good recoveries were obtained for the two enantiomers ranging from 84.1% to 103.2% in the six matrices, and the relative standard deviation values ranged from 1.7% to 8.4%. Under the optimal conditions, the obtained limits of detection (LODs) were in the range of 0.0012-0.0031mg/kg for the two enantiomers, and the limits of quantification (LOQs) were in the range of 0.0036-0.0091mg/kg, which were lower than the maximum residue levels established in Japan. In addition, the stereochemical structure of triticonazole enantiomers were determined for the first time using a combination of experimental and predicted electronic circular dichroism (ECD) spectra. The first eluted enantiomer was confirmed to be (+)-(S)-triticonazole. These results indicate that the proposed method is convenient and reliable for the enantioselective detection of triticonazole in authentic samples. The proposed method could be widely applicable for investigating the stereoselective degradation of triticonazole in food and environmental matrices, providing additional information for reliable risk assessment of triazole fungicides.

Enantioseparation and determination of the chiral phenylpyrazole insecticide ethiprole in agricultural and environmental samples and its enantioselective degradation in soil

An effective method for the enantioselective determination of ethiprole enantiomers in agricultural and environmental samples was developed. The effects of solvent extraction, mobile phase and thermodynamic parameters for chiral recognition were fully investigated. Complete enantioseparation of the ethiprole enantiomers was achieved on a Lux Cellulose-2 column. The stereochemical structures of ethiprole enantiomers were also determined, and (R)-(+)-ethiprole was first eluted. The average recoveries were 82.7-104.9% with intra-day RSD of 1.7-8.2% in soil, cucumber, spinach, tomato, apple and peach under optimal conditions. Good linearity (R(2)≥0.9991) was obtained for all the matrix calibration curves within a range of 0.1 to 10 mg L(-1). The limits of detection for both enantiomers were estimated to be 0.008 mg kg(-1) in soil, cucumber, spinach and tomato and 0.012 mg kg(-1) in apple and peach, which were lower than the maximum residue levels established in Japan. The results indicate that the proposed method is convenient and reliable for the enantioselective detection of ethiprole in agricultural and environmental samples. The behavior of ethiprole in soil was studied under field conditions and the enantioselective degradation was observed with enantiomer fraction values varying from 0.494 to 0.884 during the experiment. The (R)-(+)-ethiprole (t1/2=11.6 d) degraded faster than (S)-(-)-ethiprole (t1/2=34.7 d). This report is the first describe a chiral analytical method and enantioselective behavior of ethiprole, and these results should be extremely useful for the risk evaluation of ethiprole in food and environmental safety.

Systemic stereoselectivity study of flufiprole: Stereoselective bioactivity, acute toxicity and environmental fate.

In this study, the stereoselectivity of flufiprole enantiomers in regards to their bioactivity, acute toxicity and environmental fate is reported for the first time. Four types of representative insects (Plutella xylostella, Nilaparvata lugens, Mythimna separata and Acyrthosiphon pisum) were used to investigate enantioselective bioactivity. Acute toxicities of flufiprole enantiomers toward two non-target organisms were also evaluated. Moreover, stereoselective degradation in four vegetables under field conditions was studied in response to food safety concerns. The bioactivity of (R)-flufiprole was 1.9-5.1 times higher than that of (S)-flufiprole. (R)-flufiprole also showed 3.7-5.7 times higher acute toxicity to Scenedesmus obliquus and Trichogramma japonicum Ashmead than (S)-flufiprole. Opposite stereoselective degradation of the two enantiomers was observed in pak choi, spinach cucumber, and tomato. (S)-flufiprole degraded faster in pak choi and spinach, resulting in an enrichment of (R)-isomer. By contrast, (R)-isomer was preferentially degraded in cucumber and tomato. Molecular simulation technology was used to illuminate the mechanism of enantioselective bioactivity. The Glide Score (-5.82kcal/mol) for (R)-isomer was better than that (-5.11kcal/mol) of (S)-isomer and this calculation showed (R)-flufiprole was more effective in pest control. Consequently, significant stereoselectivity of flufiprole enantiomers should be taken into account when assessing the environmental health risk of the pesticide.

Simultaneous Enantioselective Determination of the Chiral Fungicide Prothioconazole and its Major Chiral Metabolite Prothioconazole-desthio in Food and Environmental Samples by Ultra-Performance 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.

Enantioselective degradation and transformation of the chiral fungicide prothioconazole and its chiral metabolite in soils

Prothioconazole is a widely used chiral triazole fungicide. In this work, the enantioselective degradation and transformation of prothioconazole and its chiral metabolite prothioconazole-desthio in five kinds of soils were investigated under native and sterile conditions using reversed phase liquid chromatography tandem mass spectrometry with a Lux-cellulose-1 column. The results showed that an enantioselective degradation was observed with R-prothioconazole preferentially degraded in the five soils and enantiomeric fraction values that ranged from 0.32 to 0.41 under native conditions. Furthermore, the major metabolite prothioconazole-desthio was formed rapidly during prothioconazole dissipation. The prothioconazole-desthio enantiomers were degraded slowly, and there was a slight enantioselectivity with enantiomeric fraction values that ranged from 0.45 to 0.51 in the Nanjing and Jilin soils. Under sterile conditions, prothioconazole and its metabolite enantiomers were more slowly degraded with no enantioselectivity. The result of the incubation experiment with single enantiomers verified that R- and S-prothioconazole were transformed to R- and S-prothioconazole-desthio, respectively. No enantiomerization for prothioconazole and its chiral metabolite was observed. In addition, the excellent correlation between organic matter content and degradation rate indicated that organic matter could promote the degradation of prothioconazole and its metabolite enantiomers. The data in this study provide the experimental evidence of the stereoselective degradation and metabolism of both prothioconazole and its chiral metabolite in the environment.

Simultaneous determination of enantiomers of carfentrazone-ethyl and its metabolite in eight matrices using high-performance liquid chromatography with tandem mass spectrometry

A reversed-phase simultaneous determination method for the enantiomers of carfentrazone-ethyl and its metabolite carfentrazone in agricultural and environmental samples was established using high-performance liquid chromatography-tandem mass spectrometry. A complete enantioseparation of carfentrazone-ethyl and its chiral metabolite carfentrazone enantiomers was obtained using a chiral column. The absolute configuration and specific optical rotation of carfentrazone-ethyl and carfentrazone enantiomers were first confirmed as peaks 1, 2, 3, and 4: S-(+)-carfentrazone, R-(-)-carfentrazone, S-(-)-carfentrazone-ethyl, and R-(+)-carfentrazone-ethyl, respectively. The specificity, matrix effect, linearity, precision, accuracy, and stability were surveyed to evaluate the feasibility of the method. The mean recovery was in the range of 77.5-102.8% with relative standard deviations of 0.4-9.8% for the samples. The limits of detection of the enantiomers were evaluated as 0.7 to 6.0 μg/kg, and the limits of quantification were 2.5 to 20 μg/kg. The stereoselective degradation of carfentrazone-ethyl and carfentrazone in rice plant was investigated, and there was no clear enantioselectivity for carfentrazone-ethyl. As for carfentrazone, the enantiomer fractions value reached 0.85 at 7 days after spraying. The developed method was simple and reliable enough for the corresponding risk assessment of carfentrazone-ethyl and its metabolite enantiomers in crop plants, cereal grains, and soil samples.

Stereoselective environmental behavior and biological effect of the chiral organophosphorus insecticide isofenphos‑methyl

The enantiomeric environmental behaviors, bioactivities and toxicities of isofenphos‑methyl enantiomers were characterized systematically in this study. (R)‑Isofenphos‑methyl was degraded preferentially in Yangtze River water and different types of vegetables with an enantiomeric fraction (EF) of 0.6 to 0.96. However, (R)‑isofenphos‑methyl was amplified in both Nanjing (EF = 0.32) and Nanchang (EF = 0.27) soil. Our investigations found that there no bidirectional chiral inversion occurred in either Yangtze River water or soils. The bioactivity of (S)‑isofenphos‑methyl was higher than that of its (R)‑enantiomer against different insect targets, such as Meloidogyne incognita, Nilaparvata lugens, Plutella xylostella and Macrosiphum pisi (3.7 to 149 times). (S)‑Isofenphos‑methyl showed higher toxicity for the nontarget organism (1.1 to 32 times). However, (R)‑isofenphos‑methyl possesses 4.0 times more potency than the (S)-form for the nontarget soil organism Eisenia foetida. This study generally could provide more scientific guidance for the corresponding risk assessments of pesticides in addition to providing a new theoretical basis for scientifically and rationally using isofenphos‑methyl.

Mechanistic Insights into Stereospecific Bioactivity and Dissipation of Chiral Fungicide Triticonazole in Agricultural Management

Research interest in chiral pesticides has increased probably because enantiomers often exhibit different environmental fate and toxicity. An investigation into the enantiomer-specific bioactivity of chiral triticonazole enantiomers in agricultural systems revealed intriguing experimental and theoretical evidence. For nine of the phytopathogens studied ( Rhizoctonia solani, Fusarium verticillioide, Botrytis cinerea (strawberry and tomato), Rhizoctonia cereali, Alternaria solani, Gibberella zeae, Sclerotinia sclerotiorum, and Pyricularia grisea), the fungicidal activity data showed ( R)-triticonazole was 3.11-82.89 times more potent than the ( S) enantiomer. Furthermore, ( R)-triticonazole inhibited ergosterol biosynthesis and cell membrane synthesis 1.80-7.34 times higher than its antipode. Homology modeling and molecular docking studies suggested the distinct bioactivities of the enantiomers of triticonazole were probably due to their different binding modes and affinities to CYP51b. However, field studies demonstrated that ( S)-triticonazole was more persistent than ( R)-triticonazole in fruits and vegetables. The results showed that application of pure ( R)-triticonazole, with its high bioactivity and relatively low resistance risk, instead of the racemate in agricultural management would reduce the application dosage required to eliminate carcinogenic mycotoxins and any environmental risks associated with this fungicide, yielding benefits in food safety and environmental protection.