Separation and toxicity of salithion enantiomers

Simultaneous Enantioseparation of Three Chiral Antifungal Pesticides by Hydroxypropyl-γ-CD-Modified Micellar Electrokinetic Chromatography

Simultaneous enantioseparation of three commonly used chiral antifungal pesticides (diniconazole, hexaconazole, and imazalil) was first studied based on micellar electrokinetic chromatography (MEKC) with hydroxypropyl-γ-CD (HP-γ-CD) as chiral selector. In this study, the importance of experimental parameters such as chiral selector type and concentration, sodium dodecyl sulfate (SDS) concentration, the ratio of methanol, and separation voltage in optimizing were investigated. The simultaneous enantioseparation of diniconazole, hexaconazole, and imazalil was successfully achieved in 30 mM borate buffer (pH 9.0) containing 10 mM HP-γ-CD and 20 mM SDS with methanol (8%) added as organic modifiers. The resolution of diniconazole, hexaconazole, and imazalil was 15.2, 2.12, and 2.78, respectively, and the peak efficiency (N) was over 566,825 plates/m. This study provides an alternative way to systematically separate chiral antifungal pesticides with high efficiency.

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.

Study on stereoselective bioactivity, acute toxicity, and degradation in cucurbits and soil of chiral fungicide famoxadone

The chiral pesticide famoxadone is mainly applied to control fungal diseases on fruiting vegetables. The fungicidal activity, ecotoxicological effects, and degradation behavior of famoxadone enantiomers are less well known. In this study, a systemic assessment of the stereoselectivity of famoxadone was performed in cucurbits and soil. Famoxadone enantiomers presented distinct inhibitory activities among different fungal species. The bioactivities of R-(-)-famoxadone were 2.7-178 times higher than S-(+)-famoxadone toward five phytopathogens. Based on the obtained LC₅₀ values, famoxadone was super toxic to Eisenia foetida (E. foetida). Moreover, the acute toxicity of R-(-)-famoxadone presented 167 times greater to E. foetida than that of S-(+)-famoxadone, indicating that R-(-)-famoxadone showed higher bioactivity toward target organisms and non-target organisms than S-(+)-famoxadone. In addition, a simple high-performance liquid chromatography (HPLC) method was established to determine the stereoselective degradation of famoxadone in two species of cucurbits (cucumber and chieh-qua) and in field soil. The half-life values of famoxadone degradation were from 5.4 to 14.1 days, indicating that famoxadone was easily degraded. Additionally, no stereoselective degradation was found in cucurbits and soil. The results may provide promising implications for comprehensive environmental and ecological risk assessments of famoxadone.

Enantioselectivity effects of imazethapyr enantiomers to metabolic responses in mice

Imazethapyr (IMZT) is a typical chiral pesticide with two enantiomers with the R-IMZT having the main herbicidal activity. However, the enantioselectivity of the effects of IMZT enantiomers on human and animals is still unclear. In this study, a nuclear magnetic resonance (NMR)-based metabolomics method and determination of oxidative stress were used to evaluate the enantioselectivity of IMZT enantiomers in mice. The results showed that the R-IMZT caused larger disturbances of endogenous metabolites and the S-IMZT had stronger interferences to oxidation defense system. The significantly perturbed metabolic pathways in mice exposed to the R-enantiomer were the valine, leucine and isoleucine biosynthesis pathway as well as the phenylalanine, tyrosine and tryptophan biosynthesis pathway. However, exposure of mice to the S-enantiomer did not significantly affect the metabolic pathways, but exposure led to an increase of catalase (CAT) activity and an increase in malondialdehyde (MDA) content in the liver. These results indicate that we need to conduct a more comprehensive assessment of the health risks of pesticide monomers in the future. In a word, these results provide more evidence for assessing the differences in health risks of IMZT enantiomers to mammals as well as provide more references for the promotion and use of pesticide monomers in the future.

Resolution of alkaloid racemate: a novel microbial approach for the production of enantiopure lupanine via industrial wastewater valorization

BACKGROUND

Lupanine is a plant toxin contained in the wastewater of lupine bean processing industries, which could be used for semi-synthesis of various novel high added-value compounds. This paper introduces an environmental friendly process for microbial production of enantiopure lupanine.

RESULTS

Previously isolated P. putida LPK411, R. rhodochrous LPK211 and Rhodococcus sp. LPK311, holding the capacity to utilize lupanine as single carbon source, were employed as biocatalysts for resolution of racemic lupanine. All strains achieved high enantiomeric excess (ee) of L-(-)-lupanine (> 95%), while with the use of LPK411 53% of the initial racemate content was not removed. LPK411 fed with lupanine enantiomers as single substrates achieved 92% of D-(+)-lupanine biodegradation, whereas L-(-)-lupanine was not metabolized. Monitoring the transcriptional kinetics of the luh gene in cultures supplemented with the racemate as well as each of the enantiomers supported the enantioselectivity of LPK411 for D-(+)-lupanine biotransformation, while (trans)-6-oxooctahydro-1H-quinolizine-3-carboxylic acid was detected as final biodegradation product from D-(+)-lupanine use. Ecotoxicological assessment demonstrated that lupanine enantiomers were less toxic to A. fischeri compared to the racemate exhibiting synergistic interaction.

CONCLUSIONS

The biological chiral separation process of lupanine presented here constitutes an eco-friendly and low-cost alternative to widely used chemical methods for chiral separation.

Applications and stereoselective syntheses of P-chirogenic phosphorus compounds

This review reports the best stereoselective or asymmetric syntheses, the most efficient P*-building blocks and functionalisation of P-chirogenic compounds, in the light of chiral phosphorus compound applications.

Enantioselective changes in oxidative stress and toxin release in Microcystis aeruginosa exposed to chiral herbicide diclofop acid

Enantioselective oxidative stress and toxin release from Microcystis aeruginosa after exposure to the chiral herbicide diclofop acid were investigated. Racemic diclofop acid, R-diclofop acid and S-diclofop acid induced reactive oxygen species (ROS) generation, increased the concentration of malondialdehyde (MDA), enhanced the activity of superoxide dismutase (SOD) and triggered toxin release in M. aeruginosa to varying degrees. The increase in MDA concentration and SOD activity in M. aeruginosa occurred sooner after exposure to diclofop acid than when the cyanobacteria was exposed to either the R- and the S-enantiomer. In addition, enantioselective toxicity of the enantiomers was observed. The R-enantiomer trigged more ROS generation, more SOD activity and more toxin synthesis and release in M. aeruginosa cells than the S-enantiomer. Diclofop acid and its R-enantiomer may collapse the transmembrane proton gradient and destroy the cell membrane through lipid peroxidation and free radical oxidation, whereas the S-enantiomer did not demonstrate such action. R-diclofop acid inhibits the growth of M. aeruginosa in the early stage, but ultimately induced greater toxin release, which has a deleterious effect on the water column. These results indicate that more comprehensive study is needed to determine the environmental safety of the enantiomers, and application of chiral pesticides requires more direct supervision and training. Additionally, lifecycle analysis of chiral pollutants in aquatic system needs more attention to aide in the environmental assessment of chiral pesticides.

Enantiomerization and enantioselective bioaccumulation of benalaxyl in Tenebrio molitor larvae from wheat bran

The enantiomerization and enatioselecive bioaccumulation of benalaxyl by dietary exposure to Tenebrio molitor larvae under laboratory conditions were studied by HPLC-MS/MS. Exposure of enantiopure R-benalaxyl and S-benalaxyl in T. molitor larvae revealed significant enantiomerization with formation of the R enantiomers from the S enantiomers, and vice versa. Enantiomerization was not observed in wheat bran during the period of 21 days. For the bioaccumulation experiment, the enantiomer fraction in T. molitor larvae was maintained approximately at 0.6, whereas the enantiomer fraction in wheat bran was maintained at 0.5; in other words, the bioaccumulation of benalaxyl was enantioselective in T. molitor larvae. Mathematical models for a process of uptake, degradation, and enantiomerization were developed, and the rates of uptake, degradation, and enantiomerization of R-benealaxyl and S-benealaxyl were estimated, respectively. The results were that the rate of uptake of R-benalaxyl (kRa = 0.052 h(-1)) was slightly lower than that of S-benalaxyl (kSa = 0.061 h(-1)) from wheat bran; the rate of degradation of R-benalaxyl (kRd = 0.285 h(-1)) was higher than that of S-benalaxyl (kSd = 0.114 h(-1)); and the rate of enantiomerization of R-benalaxyl (kRS = 0.126 h(-1)) was higher than that of S-benalaxyl (kSR = 0.116 h(-1)). It was suggested that enantioselectivtiy was caused not only by actual degradation and metabolism but also by enantiomerization, which was an important process in the environmental fate and behavior of chiral pesticides.

Enantiomeric separation and toxicity of an organophosporus insecticide, pyraclofos

Despite the fact that the biological processes of chiral pesticides are enantioselective, knowledge of the toxicities of pyraclofos due to enantiospecificity is scarce. In this study, the optical isomers of pyraclofos were separated and their toxicities to butyrylcholinesterase (BChE) and Daphnia magna were assessed. Baseline resolution of the enantiomers was obtained on both Chiralcel OD and Chiralpak AD columns. The effect of the mobile phase composition and column temperature were then discussed. The resolved enantiomers were characterized by their optical rotation and circular dichroism signs. The anti-BChE tests demonstrated that (-)-pyraclofos was about 15 times more potent than its (+)-form. However, acute aquatic assays suggested that (+)-pyraclofos was about 6 times more toxic than its antipode. Moreover, the joint toxicity of pyraclofos enantiomers to D. magna was found to be an additive effect. These results demonstrated that the overall toxicity of pyraclofos should be assessed using the individual enantiomers.

Enantioselective degradation and chiral stability of malathion in environmental samples

The dissipation behaviors of the two enantiomers of the organophosphorus pesticide malathion (MA) in environment samples were elucidated using a normal-phase high-performance liquid chromatography with a cellulose-tris(3,5-dimethylphenylcarbamate) (CDMPC) chiral column. A validated chiral residue analysis method in soil and water was established; the average recoveries for the two enantiomers were 88-102% in soil and 81-99% in water. Racemic and enantiopure R-(+)- and S-(-)-MA were incubated in five soil and water systems. The results of the degradation of racemate in all of the environment samples showed the inactive S-(-)-enantiomer degraded more rapidly than the active R-(+)-enantiomer, resulting in a relative enrichment of the R-form. Moreover, when the enantiopure S-(-)- and R-(+)-MA were incubated in three well-chosen soil and water samples, respectively, inversion from one enantiomer to another was found, indicating that using the optically pure enantiomer will not help to increase the bioactivity and reduce the environmental pollution.

Surface-confined conformers and coassembly-induced conformer resolution

Stereoisomerism is a fundamental chemistry issue and has been intensively investigated because of its importance in organic chemistry, biology, and pharmacology. Molecules with freely rotatable single bonds have many interconvertable conformers. Herein, we report the surface-adsorption-induced conformer resolution by employing azobenzene-3,3-dicarboxylic acid (ADA-33) as a model compound. Two linear assembly phases composed of trans conformers on a highly oriented pyrolytic graphite (HOPG) surface are observed by scanning tunneling microscopy. With the codeposition with 1-octanoic acid (OA), only one trans conformer of ADA-33 can be recognized by OA to form a two-component assembly with alternately arranged ADA-33 and OA stripes, which can be attributed to the epitaxial assembly of ADA-33 and OA on the HOPG surface, and weak hydrogen bonding exists between conformer I and OA molecules. The results are of significance with respect to the discrimination and resolution of conformers on a solid surface and provide molecular insights into the coadsorption assembly on the surface.

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.