Separation, isolation and stereochemical assignment of imazalil enantiomers and their quantitation in an in vitro toxicity test

Gold nanoparticle-based immunochromatographic assay for rapid detection of imazalil

Imazalil (IMZ) is a commonly used fungicide for controlling fungus in agriculture, leaving residual IMZ in crops that could be hazardous to human health. In this work, we designed IMZ haptens for mice immunization and prepared sensitive monoclonal antibody (mAb) against IMZ. The subtype of anti-IMZ mAb is IgG2a. It possessed a half inhibition concentration (IC50) of 0.95 ng mL-1 and showed no cross-reactivity against other chemicals in ic-ELISA. Taking advantage of the mAb, we developed a gold nanoparticle-based immunochromatographic assay (GICA) for the rapid detection of IMZ in grapes and tomatoes. The assay gave a visual limit of detection (vLOD) of 25 ng g-1 and cut-off value of 500 ng g-1 in both samples. According to the calibration curves, the calculated LOD were 4.12 ng g-1 and 4.70 ng g-1 in grapes and tomatoes, respectively. The recovery rates of IMZ ranged from 84.7% to 104.4% with variation coefficients (CVs) of 5.7-11.8% in spiked samples, indicating a potent practicability of the GICA. The whole GICA process took 30 min. Therefore, the developed assay can be used for on-site detection and quantitation of IMZ in grape and tomato samples.

Comparison of different density functional theory methods for the calculation of vibrational circular dichroism spectra

The determination of the absolute configuration (AC) of an organic molecule is still a challenging task for which the combination of spectroscopic with quantum-mechanical methods has become a promising approach. In this study, we investigated the accuracy of DFT methods (480 overall combinations of 15 functionals, 16 basis sets, and 2 solvation models) to calculate the VCD spectra of six chiral organic molecules in order to benchmark their capability to facilitate the determination of the AC.

Highly efficient and enantioselective synthesis of β-heteroaryl amino alcohols via Ru-catalyzed asymmetric hydrogenation

We herein report a highly enantioselective hydrogenation of α-N-heteroaryl ketones catalyzed by chiral ruthenium catalysts, furnishing β-heteroaryl amino alcohols in superb yields and enantioselectivities (up to 99% yield and up to 99% ee).

Vibrational Circular Dichroism Absolute Configuration of Natural Products From 2015 to 2019

Although demonstrated in 1975, vibrational circular dichroism (VCD) finally started to popularize during this century as a reliable tool to determine the absolute configuration (AC) of organic molecules. This research field continues to be a very dynamic one, in particular for the study of natural products which are a unlimited source of chiral molecules. It therefore turns of interest to summarize the accomplishments published in recent years and to comment on some eventual difficulties that emerged in rare cases to complete the AC determination task. Therefore the aim of this review is to update VCD results for the AC assignment of natural products published from 2015 to 2019, a period in which VCD was reported in some 126 publications involving almost 300 molecules. They are organized according the type of studied metabolite allowing an easily search. The molecules correspond to 28 monoterpenes concerning 17 papers, to 42 sesquiterpenes in 14 papers, to 51 diterpenes in 19 publications, to 5 other terpenoids in three papers, to 48 aromatic molecules in 15 reports, to 20 polyketides in 10 publications, to 27 miscellaneous formulas also in 10 papers, and to 76 nitrogen containing compounds, which include alkaloids and their synthetic analogs, in 38 articles. The landscape of reviewed molecules is quite wide as it goes from simple monoterpenes, like borneol or camphor, to very relevant biological molecules like the alkaloid cocaine or tadalafil samples to distinguish genuine and counterfeit Cialis®. In addition, 5 natural products and a simple derivative published outside the reviewed period, were used to illustrate some aspects of density functional theory calculations.

Enantioselective mixture toxicity of the azole fungicide imazalil with the insecticide α-cypermethrin in Chironomus riparius: Investigating the importance of toxicokinetics and enzyme interactions

The fungicide imazalil is a chiral compound with one R- and one S-enantiomer. Enantiomers, while having the same chemical properties, can differ in their biological activity expressed as efficacy/toxicity as well as in their degradation kinetics and pathways. Azoles such as imazalil have been shown to synergize the effect of pyrethroid insecticides like α-cypermethrin through inhibition of cytochrome P450 monooxygenase responsible for pyrethroid detoxification. The aim of this study was to investigate, if the enantiomers of imazalil are selective in their synergistic potential in a mixture with a pyrethroid insecticide tested in Chironomus riparius. Potential enantioselectivity was studied on the level of uptake and elimination, inhibition of cytochrome P450 activity measured in vitro and in vivo and on synergistic potential of α-cypermethrin induced immobilization. Synergy was measured as an increase in α-cypermethrin toxicity after 144h applying a constant non-lethal imazalil concentration of 0.65 μmol/L. The R- and S-imazalil enantiomers increased α-cypermethrin toxicity from an EC50 of 1580 ± 980 pmol/L to an EC50 of 83 ± 10 pmol/L and 53 ± 8 pmol/L, respectively. The relatively small potency difference between imazalil enantiomers could not be explained by the in vitro cytochrome P450 inhibition, as the IC50 values were similar (0.11 ± 0.01 and 0.09 ± 0.01 μmol/L for R- and S-imazalil). Measuring in vivo P450 inhibition and the toxicokinetic of imazalil did not show a clear trend of selectivity towards one or the other enantiomer. The study therefore suggests that cytochrome P450 enzymes involved in detoxification in C. riparius are not enantioselective for imazalil.

Enantioselective uptake, translocation and degradation of the chiral pesticides tebuconazole and imazalil by Phragmites australis

Phytoremediation of realistic environmental concentrations (10 μg L^-1) of the chiral pesticides tebuconazole and imazalil by Phragmites australis was investigated. This study focussed on removal dynamics, enantioselective mechanisms and transformation products (TPs) in both hydroponic growth solutions and plant tissues. For the first time, we documented uptake, translocation and metabolisation of these pesticides inside wetland plants, using enantioselective analysis. Tebuconazole and imazalil removal efficiencies from water reached 96.1% and 99.8%, respectively, by the end of the experiment (day 24). Removal from the solutions could be described by first-order removal kinetics with removal rate constants of 0.14 d^-1 for tebuconazole and 0.31 d^-1 for imazalil. Removal of the pesticides from the hydroponic solution, plant uptake, within plant translocation and degradation occurred simultaneously. Tebuconazole and imazalil concentrations inside Phragmites peaked at day 10 and 5d, respectively, and decreased thereafter. TPs of tebuconazole i.e., (5-(4-Chlorophenyl)-2,2-dimethyl-3-(1H-1,2,4-triazol-1-ylmethyl)-1,3-pentanediol and 5-(3-((1H-1,2,4-Triazol-1-yl)methyl)-3-hydroxy-4,4-dimethylpentyl)-2-chlorophenol) were quantified in solution, while the imazalil TPs (α-(2,4-Dichlorophenyl)-1H-imidazole-1-ethanol and 3-[1-(2,4-Dichlorophenyl)-2-(1H-imidazol-1-yl)ethoxy]-1,2-propanediol) were quantified in both solution and plant tissue. Pesticide uptake by Phragmites was positively correlated with evapotranspiration. Pesticide removal from the hydroponic solution was not enantioselective. However, tebuconazole was degraded enantioselectively both in the roots and shoots. Imazalil translocation and degradation inside Phragmites were also enantioselective: R-imazalil translocated faster than S-imazalil.

Enantioseparation of Imazalil and Monitoring of Its Enantioselective Degradation in Apples and Soils Using Ultrahigh-Performance Liquid Chromatography-Tandem Mass Spectrometry

Imazalil is a widely used systemic chiral fungicide that is still being employed as a racemic mixture without distinguishing the difference between enantiomers, which often leads to its inaccurate risk assessment. In this study, a robust and highly sensitive chiral separation method was developed for imazalil enantiomers by ultrahigh-performance liquid chromatography-tandem mass spectrometry and was further applied to study the degradation dynamics of imazalil enantiomers in apples and field soils at three sites in China. The baseline enantioseparation for imazalil was achieved within 3.5 min on a Lux Cellulose-2 (CCMPC) column with acetonitrile (ACN)/water (65:35, v/v) with a mobile phase at 0.5 mL/min flow rate and a column temperature of 20 °C. The limit of quantitation (LOQ) for each enantiomer was <0.60 μg/kg, with a baseline resolution of approximately 1.75. The research showed that (S)-(+)-imazalil degraded more rapidly than (R)-(-)-imazalil in Gala apples, whereas (R)-(-)-imazalil preferentially degraded in Golden Delicious apples. No significant enantioselectivity was observed in OBIR-2T-47 apples and field soils from the three sites. Results of this study provide useful references for risk assessment and the rational use of imazalil in further agricultural produce practice.