Search

The enantioselective mechanism of the esterase QeH against the two enantiomers of quizalofop–ethyl (QE) has been primitively studied using computational and experimental approaches. However, it is still unclear how the esterase QeH adjusts its conformation to adapt to substrate binding and promote enzyme–substrate interactions in the catalytic kinetics. The equilibrium processes of enzyme–substrate interactions and catalytic dynamics were reproduced by performing independent molecular dynamics (MD) runs on the QeH-(R)/(S)-QE complexes with a newly developed residue-specific force field (RSFF2C). Our results indicated that the benzene ring of the (R)-QE structure can simultaneously form anion–π and cation–π interactions with the side-chain group of Glu328 and Arg384 in the binding cavity of the QeH-(R)-QE complex, resulting in (R)-QE being closer to its catalytic triplet system (Ser78-Lys81-Tyr189) with the distances measured for the hydroxyl oxygen atom of the catalytic Ser78 of QeH and the carbonyl carbon atom of (R)-QE of 7.39 Å, compared to the 8.87 Å for (S)-QE, whereas the (S)-QE structure can only form an anion–π interaction with the side chain of Glu328 in the QeH-(S)-QE complex, being less close to its catalytic site. The computational alanine scanning mutation (CAS) calculations further demonstrated that the π–π stacking interaction between the indole ring of Trp351 and the benzene ring of (R)/(S)-QE contributed a lot to the binding stability of the enzyme–substrate (QeH-(R)/(S)-QE). These results facilitate the understanding of their catalytic processes and provide new theoretical guidance for the directional design of other key enzymes for the initial degradation of aryloxyphenoxypropionate (AOPP) herbicides with higher catalytic efficiencies. [ABSTRACT FROM AUTHOR]

The enantioselective mechanism of the esterase QeH against the two enantiomers of quizalofop–ethyl (QE) has been primitively studied using computational and experimental approaches. However, it is still unclear how the esterase QeH adjusts its conformation to adapt to substrate binding and promote enzyme–substrate interactions in the catalytic kinetics. The equilibrium processes of enzyme–substrate interactions and catalytic dynamics were reproduced by performing independent molecular dynamics (MD) runs on the QeH-(R)/(S)-QE complexes with a newly developed residue-specific force field (RSFF2C). Our results indicated that the benzene ring of the (R)-QE structure can simultaneously form anion–π and cation–π interactions with the side-chain group of Glu328 and Arg384 in the binding cavity of the QeH-(R)-QE complex, resulting in (R)-QE being closer to its catalytic triplet system (Ser78-Lys81-Tyr189) with the distances measured for the hydroxyl oxygen atom of the catalytic Ser78 of QeH and the carbonyl carbon atom of (R)-QE of 7.39 Å, compared to the 8.87 Å for (S)-QE, whereas the (S)-QE structure can only form an anion–π interaction with the side chain of Glu328 in the QeH-(S)-QE complex, being less close to its catalytic site. The computational alanine scanning mutation (CAS) calculations further demonstrated that the π–π stacking interaction between the indole ring of Trp351 and the benzene ring of (R)/(S)-QE contributed a lot to the binding stability of the enzyme–substrate (QeH-(R)/(S)-QE). These results facilitate the understanding of their catalytic processes and provide new theoretical guidance for the directional design of other key enzymes for the initial degradation of aryloxyphenoxypropionate (AOPP) herbicides with higher catalytic efficiencies.

An analytical method was developed to simultaneously determine pyridate, quizalofop-ethyl, and cyhalofop-butyl in brown rice, soybean, potato, pepper, and mandarin using LC-MS/MS. Purification was optimized using various sorbents: primary–secondary amine, octadecyl (C18) silica gel, graphitized carbon black, zirconium dioxide-modified silica particles, zirconium dioxide-modified silica particles (Z-SEP), and multi-walled carbon nanotubes (MWCNTs). Three versions of QuECHERS methods were then tested using the optimal purification agent. Finally, samples were extracted using acetonitrile and QuEChERS EN salts and purified using the Z-SEP sorbent. A six-point matrix-matched external calibration curve was constructed for the analytes. Good linearity was achieved with a determination coefficient ≥0.999. The limits of detection and quantification were 0.0075 mg/kg and 0.01 mg/kg, respectively. The method was validated after fortifying the target standards to the blank matrices at three concentration levels with five replicates for each concentration. The average recovery was within an acceptable range (70–120%), with a relative standard deviation <20%. The applicability of the developed method was evaluated with real-world market samples, all of which tested negative for these three herbicide residues. Therefore, this method can be used for the routine analysis of pyridate, quizalofop-ethyl, and cyhalofop-butyl in agricultural products. [ABSTRACT FROM AUTHOR]

The research portrays the fate of a new herbicide mixture of fomesafen and quizalofop-ethyl. The soil samples viz. red lateritic soil (A), coastal saline soil (B) and black soil (C) were fortified separately for fomesafen and quizalofop-ethyl at 0.5 (T1) and 1.0 mg kg−1 (T2) doses and incubated at 20, 30 and 40°C. A satisfactory mean recovery, precision and linearity proved that the methods were accurate. Both the herbicides followed first + first order kinetics. Higher persistence of fomesafen was observed in Soil C than Soil B and Soil A with 22.38–53.75 days half-life, whereas quizalofop-ethyl showed higher stability in Soil A than Soils B and C with half-life of 0.93–12.07 days. Both compounds showed faster rates of dissipation at increased temperature, irrespective of soil type. The current study will help to predict the effect of temperature on the dissipation of herbicides in different soil under real field scenario. [ABSTRACT FROM AUTHOR]

An analytical method was developed to simultaneously determine pyridate, quizalofop-ethyl, and cyhalofop-butyl in brown rice, soybean, potato, pepper, and mandarin using LC-MS/MS. Purification was optimized using various sorbents: primary–secondary amine, octadecyl (C18) silica gel, graphitized carbon black, zirconium dioxide-modified silica particles, zirconium dioxide-modified silica particles (Z-SEP), and multi-walled carbon nanotubes (MWCNTs). Three versions of QuECHERS methods were then tested using the optimal purification agent. Finally, samples were extracted using acetonitrile and QuEChERS EN salts and purified using the Z-SEP sorbent. A six-point matrix-matched external calibration curve was constructed for the analytes. Good linearity was achieved with a determination coefficient ≥0.999. The limits of detection and quantification were 0.0075 mg/kg and 0.01 mg/kg, respectively. The method was validated after fortifying the target standards to the blank matrices at three concentration levels with five replicates for each concentration. The average recovery was within an acceptable range (70–120%), with a relative standard deviation

A hydrolytic transformation study was conducted in water of pH 4.0, 7.0 and 9.2 to evaluate the effect of pH on persistence of a new readymix formulation of fomesafen and quizalofop-ethyl. The water samples were fortified at 0.5 and 1 µg mL−1 levels and analysed at 0 (2 h), 1, 3, 7, 15, 30, 60, 90, 120, 150 days interval. Both the analytical methods were validated following SANTE guideline and found accurate based on average recovery of 80–100%, Relative standard deviation (RSD) < 20% and Coefficient of Determination (R2) 0.99. The dissipation of both the molecules was pH dependent and followed first order kinetics. Higher persistence of fomesafen was observed in alkaline pH as compared to neutral and acidic pH with half-life of 41.56–63.24 days, whereas higher stability of quizalofop-ethyl was observed in the water of acidic pH followed by neutral and alkaline pH with half-life of 1.26–8.09 days. [ABSTRACT FROM AUTHOR]

This study investigated the resilience of bacterial diversity in soils restored after autoclaving, in terms of richness, evenness and community structure, and its feedback on the enantioselective transformation of racemic quizalofop‐ethyl (rac‐QE). Microbial biomass carbon (MBC) and bacterial richness (indexed by operational taxonomic units [OTUs]) in restored soil recovered to approximately 50% and 29%, respectively, of the native soil within 43 days. Bacterial evenness was much lower in restored soil than in native soil. The relative proportions of dominant bacterial genera differed significantly (P < .05) between restored and native soils. Importantly, two major bacterial genera that recolonized restored soil were not detected in native soil. Highly enantioselective transformation of rac‐QE was observed in restored soils, whereas QE enantiomers exhibited comparable transformation rates in native soils. The second‐round enantioselective transformation of rac‐QE was altered by the first‐round transformation of enantiopure quizalofop‐P‐ethyl (R‐P‐QE) in restored and native soils through selective effects of R‐P‐QE on the bacterial community. The transformation rate of rac‐QE was predominantly determined by bacterial abundance and richness, while the enantioselectivity was correlated more with bacterial structure. [ABSTRACT FROM AUTHOR]

A field experiment was conducted at the Rajasthan College of Agriculture, Maharana Pratap University of Agriculture and Technology -Udaipur during Kharif season 2015 and 2016 to test the efficacy of different herbicide and herbicide mixtures against weeds in soybean. Monocot weeds were predominant (57.68 %) in the experimental field compared to Broad leaved weeds (42.31 %). However, Echinochloa colona (40.55 %) and Corchorus olitorius (23.68%) were dominant in soybean at 30 DAS. Among different weed control treatments, post-emergence and tank mix combination of propaquizafop + imazethapyr (75+75 g ha-1) and imazethapyr + quizalofop-ethyl (75+60 g ha-1) at 21 DAS were most effective in respect of reducing weed density, weed biomass, nutrient removal by weed and improving yield attributes, yield and quality of soybean compared to other treatments. Highest seed yield (2271 kg ha-1), Haulm yield (3127 kg ha-1) of soybean and maximum net return (... 51550/ha) were also recorded with propaquizafop 75 g ha-1 + imazethapyr 75 g ha-1 followed by imazethapyr + quizalofop-ethyl (75+60 g ha-1). Further, they were also found responsible for highest uptake of N, P and K in soybean and lowest uptake of these plant nutrients by weeds. [ABSTRACT FROM AUTHOR]

• Enantioseparation of quizalofop-ethyl and its acid metabolite on a cellulose-based chiral column. • Liquid-solid extraction from soil and vegetable samples contaminated by quizalofop-ethyl. • Thermodynamic study on the enantioseparation to set the best separation conditions. • Quantitative analysis of quizalofop-ethyl enantiomers in vegetables via HPLC-MS\MS. • Diffusive dynamics of quizalofop-ethyl and its metabolite in the selected samples. In this study, the attention was focused on quizalofop-ethyl, a chiral herbicide whose formulation has recently been marketed as quizalofop-P-ethyl, i.e. the (+)-enantiomer exhibiting herbicidal activity. To verify the real enantiomeric purity of this product as well as to study its environmental fate, the enantioselective separation of the P- and M- enantiomers of quizalofop-ethyl was achieved on Lux Cellulose-2 column (3‑chloro,4-methylphenilcarbamate cellulose) under isocratic conditions in polar organic mode. Once established that the commercial formulation contains ˜ 0.6% (enantiomeric fraction) of M as an impurity, an HPLC-MS/MS method was developed, validated and applied to the analysis of soil, carrots and turnips treated with the herbicide. A simple solid-liquid extraction allowed recoveries greater than 70%; limits of detections of P and M enantiomers were below 5 ng g−1. The analyses of the real samples showed a modification of the enantiomeric fraction of quizalofop-M-ethyl between the commercial formulation (EF M = 0.63 ± 0.03%) and the analysed matrices (EF M = 7.6 ± 0.1% for carrots; EF M = 0% for the other matrices). This outcome highlighted the occurrence of an enantioselective biotic dissipation, responsible for a greater persistency of the distomer in carrots. On the other hand, since screening analyses revealed the occurrence of residues of the metabolite quizalofop-acid with the same EFs as the ester precursor, it was concluded that the hydrolytic conversion was an abiotic process. [ABSTRACT FROM AUTHOR]

Managing emerged weeds that have evolved resistance to acetyl CoA carboxylase (ACCase)-inhibiting herbicides is a challenging task. A dose-response experiment was conducted on barnyardgrass biotypes resistant (R) and susceptible (S) to three aryloxyphenoxypropionate herbicides cyhalofop-butyl (CyB), fenoxaprop-ethyl (FeE), and quizalofop-ethyl (QuE) along with investigations into the potential resistance mechanism of these biotypes. The tested R barnyardgrass biotypes had strong resistance to CyB and FeE (resistant/susceptible ratio: 7.9–14.4) but weak resistance to QuE (resistant/susceptible ratio: 2.4–3.1). Absorption, translocation, and total metabolism of CyB and QuE were not associated with differences among S and R barnyardgrass biotypes. However, differences between S and R barnyardgrass were observed in production of active acid forms of each herbicide (cyhalofop-acid and quizalofop-acid). Production of cyhalofop-acid was >1.6-fold less in R barnyardgrass (3–8%) for 24 h after herbicide application than in the S barnyardgrass (8–16%). Meanwhile, production of quizalofop-acid was less in R barnyardgrass (< 14%) throughout the study period than in the S barnyardgrass (< 22%). Sequencing results of ACCase gene showed no difference between S and R barnyardgrass. Overall results show that a non-target-site resistance mechanism altering metabolism of CyB and QuE likely contributes to resistance of the barnyardgrass biotypes to these herbicides. [Display omitted] • Barnyardgrass was resistant (R) to three aryloxyphenoxypropinonic (FOP) herbicides. • No mutation to ACCase genes was observed in susceptible (S) and R biotypes. • Absorption/translocation of FOP herbicides were similar between S and R biotypes. • No difference was observed in total herbicide metabolism between S and R biotypes. • Reduction of active herbicide forms in R biotypes may relate to the resistance. [ABSTRACT FROM AUTHOR]

A field experiment was conducted during 2008-09 and 2009-10 to evaluate different post emergence herbicides applied against weeds in field pea and their residual effect on succeeding sorghum and mungbean crop. Pendimethalin herbicide applied 1.5 kg ha-1 as pre-emergence gave effective control against all the weeds whereas, among post emergence herbicides imazethapyr was found effective against broadleaf weeds and quizalofop-ethyl was effective only against grassy weeds. During both the years, application of imazethapyr 50 g ha-1 at 30 days after sowing gave effective control of weeds and resulted minimum density and dry biomass of weeds compared to all the post emergence herbicide treatments. During second year, residual effect of imazethapyr was observed only on sorghum crop. [ABSTRACT FROM AUTHOR]

The enantioselective degradation of quizalofop-ethyl and its metabolite quizalofop-acid in two soils, a Wuhan acidic soil and a Baoding alkaline soil, was investigated. The dissipation of quizalofop-ethyl consisted of two phases, a rapidly deceasing first phase that lasted 1 day and a slowly decreasing second phase that extended till the end of the incubation. It is shown that S-quizalofop-ethyl degraded slightly faster than R-quizalofop-ethyl in the two soils. Further incubation of enantiopure enaniomers showed that quizalofop-ethyl was configurationally stable in soil. Quizalofop-acid was produced quickly, and its amount reached a maximum at 1-6 days time and then decreased slowly with half-lives ranging from 11 to 21 days. The results also showed that quizalofop-acid degraded faster in the acidic Wuhan soil than in the alkaline Baoding soil. At last, significant enantiomerization from S-quizalofop-acid to R-quizalofop-acid was observed, and the enantiomerization was fast, resulting in residues enriched with R-quizalofop-acid whatever racemic quizalofop-ethyl or pure enantiomers were initially applied in the soils. Chirality 24:552-557, 2012. © 2012 Wiley Periodicals, Inc. [ABSTRACT FROM AUTHOR]

In this study, the physiological basis for antagonism induced by mixtures of quizalofop-ethyl and bromoxynil was investigated in maize seedlings. In sequential applications, antagonism was observed when bromoxynil was applied before quizalofop-ethyl or in a mixture with quizalofop-ethyl, but was minimal when bromoxynil was applied afterwards. The degree of antagonism differed with application rates of bromoxynil and with the timing of the treatment. When test herbicides were applied locally to the second leaf, the inhibition of photosystem II (PS-II) in the herbicide-treated leaf was higher with the mixture than with bromoxynil or quizalofop-ethyl alone. Subsequent growth of the untreated third leaf inhibited by quizalofop-ethyl alone then recovered, depending on the dose of bromoxynil. There was no evidence that bromoxynil affected absorption of quizalofop-ethyl. In local applications at different positions on the second leaf, antagonism was only observed when quizalofop-ethyl was applied to the distal part of the leaf and bromoxynil applied to the proximal part. The antagonism of bromoxynil + quizalofop-ethyl did not occur at the level of acetyl CoA carboxylase and Hill reaction, as revealed by in vitro assays. These results suggest that bromoxynil inhibits the phloem transport of quizalofop-ethyl and thus antagonises its whole-plant activity in maize. [ABSTRACT FROM AUTHOR]

The enantioselective catabolism of the two enantiomers of the aryloxyphenoxypropionate (AOPP) herbicide, quizalofop-ethyl (QE), in environment by microorganisms is of great interest. In this study, Sphingobium sp. strain QE-1, capable of transforming both enantiomers of QE, was successfully isolated. A novel gene qeH , encoding an esterase capable of initially transforming (R)/(S)-QE to (R)/(S)-quizalofop acid [(R)/(S)-QA], was cloned. QeH showed the highest identity (36.9%) to the β -lactamase MT1414, and the purified QeH displayed optimal activity for (R)-QE at 40 °C and pH 7.0. QeH preferentially hydrolyzed (R) - QE than (S)-QE. Based on molecular docking analyses, the distance between the ligand molecule and the coordination atom was shorter when (R)-QE occupied the active sites as compared to that of (S)-QE, which resulted in a stronger ligand binding affinity for (R)-QE. Besides the two enantiomers of QE, QeH could also convert many other AOPP herbicides with different catalytic efficiency (clodinafop-propargyl > fenoxaprop-P-ethyl > fluazifop-P-butyl > cyhalofop-butyl). This study will enhance our understandings of the enantioselective catabolism of AOPP herbicides by microorganisms. • A new quizalofop-ethyl-transforming strain was isolated. • A novel quizalofop-ethyl-transforming esterase gene qeH was cloned. • QeH preferentially hydrolyzed (R)-quizalofop-ethyl than (S)-quizalofop-ethyl. [ABSTRACT FROM AUTHOR]