Enantiomers Of Dichlorprop Research Articles

A new enantioselective dioxygenase for the (S)-enantiomer of the chiral herbicide dichlorprop in Sphingopyxis sp. DBS4

Dichlorprop [(R,S)-2-(2,4-dichlorophenoxy)propanoic acid], a chiral herbicide belonging to phenoxyalkanoic acid herbicides, is extensively used around the world, and is frequently detected in various habitats. Although (S)-dichlorprop has no herbicidal activity, its toxicity and ecological risk are higher than (R)-dichlorprop. In our previous studies, the isolated strain Sphingopyxis sp. DBS4 was confirmed to mineralize both (R)-dichlorprop and (S)-dichlorprop, but the key genes responsible for the initial degradation of (R)-/(S)-dichlorprop were still unclear. Here, based on genome sequencing and enzyme purification, a new dioxygenase gene, spoA, responsible for the initial transformation of (S)-dichlorprop to 2,4-dichlorophenol and pyruvate was cloned from the rac-dichlorprop-utilizing strain of Sphingopyxis sp. DBS4. SpoA, an α-ketoglutarate-dependent dioxygenase, exhibited low amino acid sequence identity to the reported (S)-dichlorprop-transforming dioxygenase SdpA (34.8%), and showed enantioselective activity toward (S)-enantiomers of dichlorprop and mecoprop, but no activity toward the corresponding (R)-enantiomers. The Km value of SpoA for (S)-dichlorprop was 134.3 μM, and the kcat/Km was determined to be 7.5 × 10−2 μM−1 s−1. Molecular docking and site-directed mutagenesis showed that two residues of SdpA, Lys101 and Asp119, are the key sites for the enantioselective transformation of (S)-dichlorprop. Our study identifies a new dioxygenase for the enantioselective transformation of (S)-dichlorprop and deepens our understanding of the microbial catabolism of chiral phenoxyalkanoic acid herbicides.

Selective removal of the non-herbicidal (S)-enantiomer of dichlorprop from agricultural soil by an in-situ enriched consortium

Rac-dichlorprop [(R,S)-2-(2,4-dichlorophenoxy)propanoic acid], a commonly used chiral phenoxyalkanoic acid herbicide, is frequently detected in various environments, posing threats to human health and environmental safety. The (S)-enantiomer of dichlorprop shows a lower herbicidal activity but a higher toxicity as compared to the (R)-enantiomer of dichlorprop. It is of great importance to enantioselectively remove the non-herbicidal (S)-dichlorprop from the rac-dichlorprop in the application sites. In this study, the dissipation of (R)- and (S)-dichlorprop in an agricultural soil was investigated. We found that the dissipation rate of (S)-dichlorprop was higher than that of (R)-dichlorprop in an agricultural soil. Although the influences of different enantiomers of dichlorprop on soil bacterial community were not different, Sphingobium was significantly enriched in the (S)-dichlorprop-treated soil as compared to (R)-dichlorprop, indicating that Sphingobium species played important roles in the dissipation of (S)-dichlorprop. Furthermore, a bacterial consortium containing Sphingobium sp. strain SP-2 (enantioselectively transforming (S)-dichlorprop to 2,4-dichlorophenol) and Sphingopyxis sp. strain DP-21 (mineralizing 2,4-dichlorophenol), which synergistically mineralized the (S)-enantiomer of dichlorprop, was isolated from the agricultural soil. Bioaugmentation with the in-situ isolated consortium (strains SP-2 and DP-21) resulted in the enhanced removal of the non-herbicidal (S)-dichlorprop from the soil and in the adaptation of the inoculated degrading strains. This study offers new insights into the enhanced bioremediation of the non-herbicidal (S)-dichlorprop contaminated soils while simultaneously ensuring environmental safety and crop yield.

A Synergistic Consortium Involved in rac-Dichlorprop Degradation as Revealed by DNA Stable Isotope Probing and Metagenomic Analysis.

rac-Dichlorprop, a commonly used phenoxyalkanoic acid herbicide, is frequently detected in environments and poses threats to environmental safety and human health. Microbial consortia are thought to play key roles in rac-dichlorprop degradation. However, the compositions of the microbial consortia involved in rac-dichlorprop degradation remain largely unknown. In this study, DNA stable isotope probing (SIP) and metagenomic analysis were integrated to reveal the key microbial consortium responsible for rac-dichlorprop degradation in a rac-dichlorprop-degrading enrichment. OTU340 (Sphingobium sp.) and OTU348 (Sphingopyxis sp.) were significantly enriched in the rac-[13C]dichlorprop-labeled heavy DNA fractions. A rac-dichlorprop degrader, Sphingobium sp. strain L3, was isolated from the enrichment by a traditional enrichment method but with additional supplementation of the antibiotic ciprofloxacin, which was instructed by metagenomic analysis of the associations between rac-dichlorprop degraders and antibiotic resistance genes. As revealed by functional profiling of the metagenomes of the heavy DNA, the genes rdpA and sdpA, involved in the initial degradation of the (R)- and (S)-enantiomers of dichlorprop, respectively, were mostly taxonomically assigned to Sphingobium species, indicating that Sphingopyxis species might harbor novel dichlorprop-degrading genes. In addition, taxonomically diverse bacterial genera such as Dyella, Sphingomonas, Pseudomonas, and Achromobacter were presumed to synergistically cooperate with the key degraders Sphingobium/Sphingopyxis for enhanced degradation of rac-dichlorprop. IMPORTANCE Understanding of the key microbial consortium involved in the degradation of the phenoxyalkanoic acid herbicide rac-dichlorprop is pivotal for design of synergistic consortia used for enhanced bioremediation of herbicide-contaminated sites. However, the composition of the microbial consortium and the interactions between community members during the biodegradation of rac-dichlorprop are unclear. In this study, DNA-SIP and metagenomic analysis were integrated to reveal that the metabolite 2,4-dichlorophenol degraders Dyella, Sphingomonas, Pseudomonas, and Achromobacter synergistically cooperated with the key degraders Sphingobium/Sphingopyxis for enhanced degradation of rac-dichlorprop. Our study provides new insights into the synergistic degradation of rac-dichlorprop at the community level and implies the existence of novel degrading genes for rac-dichlorprop in nature.

Enantioselective Phytotoxic Disturbances of Fatty Acids in Arabidopsis thaliana by Dichlorprop.

Plant fatty acids have indispensable physiological functions and nutritional value. However, the overuse of herbicides may cause phytotoxic disturbances of fatty acids in nontarget plants while spraying for weeds. Evidence has shown that the herbicide dichlorprop can inhibit the activity of acetyl-CoA carboxylase (ACCase), a key enzyme involved in fatty acid synthesis. However, the enantioselective phytotoxic effects of dichlorprop enantiomers ((R)-dichlorprop and (S)-dichlorprop) on fatty acids and their related mechanisms remain unclear. To solve this issue, the enantioselective phytotoxicity of dichlorprop in the model plant species Arabidopsis thaliana (A. thaliana) with a focus on fatty acids was evaluated for the first time. The results indicated a significant difference in enantioselectivity and that exposure to (R)-dichlorprop can cause marked fatty acid disturbances in nontarget plant species. Specifically, (R)-dichlorprop decreased the content of three fatty acids by more than 50% by inhibiting the activity of ACCase. In addition, increased malondialdehyde (MDA) and lipid hydroperoxides (LOOHs) contents and membrane permeability reflected herbicide-induced lipid peroxidation, which decreased the unsaturation of fatty acids in membranes and further influenced membrane composition and function. Moreover, an increased level of glutathione peroxidase (GPX) and cytochrome P450 (CYP450) reflected a plant stress-induced response. To summarize, fatty acids represent a new perspective for evaluating the toxicity of chiral pesticides, contributing to a better understanding of the enantioselective phytotoxicity and mechanisms of dichlorprop, and providing evidence for herbicide security and risk assessments.

Enantioselective Phytotoxicity of Dichlorprop to Arabidopsis thaliana: The Effect of Cytochrome P450 Enzymes and the Role of Fe.

The ecotoxicology effects of chiral herbicides have long been recognized and have drawn increasing attention. The toxic mechanisms of herbicides in plants are involved in production of reactive oxygen species (ROS) and cause damage to target enzymes, but the relationship between these two factors in the enantioselectivity of chiral herbicides has rarely been investigated. Furthermore, even though cytochromes P450 enzymes (CYP450s) have been related to the phytotoxicity of herbicides, their roles in the enantioselectivity of chiral herbicides have yet to be explored. To solve this puzzle, the CYP450s suicide inhibitor 1-aminobenzotriazole (ABT) was added to an exposure system made from dichlorprop (DCPP) enantiomers in the model plant Arabidopsis thaliana. The results indicated that different phytotoxicities of DCPP enantiomers by causing oxidative stress and acetyl-CoA carboxylase (ACCase) damage were observed in the presence and the absence of ABT. The addition of ABT decreased the toxicity of (R)-DCPP but was not significantly affected that of (S)-DCPP, resulting in smaller differences between enantiomers. Furthermore, profound differences were also observed in Fe uptake and distribution, exhibiting different distribution patterns in A. thaliana leaves exposed to DCPP and ABT, which helped bridge the relationship between ROS production and target enzyme ACCase damage through the function of CYP450s. These results offer an opportunity for a more-comprehensive understanding of chiral herbicide action mechanism and provide basic evidence for risk assessments of chiral herbicides in the environment.

Enantioselective disturbance of chiral herbicide dichlorprop to nitrogen metabolism of Arabidopsis thaliana: Regular analysis and stable isotope attempt

As the most essential element, nitrogen play a pivotal role in plant physiological process, which is susceptible to contaminants. However, the enantioselective effects of chiral herbicides on nitrogen metabolism have not been comprehensively understood. In this study, effects of chiral herbicide dichlorprop (DCPP) on the nitrogen behaviors in Arabidopsis thaliana were investigated. The results revealed that the uptakes of inorganic nitrogen (NO3− and NH4+) were preferentially impacted by herbicidal active (R)-DCPP, where the transportation of beneficial NO3− was inhibited but the toxic NH4+ was accumulated. As for nitrogen assimilation, enantioselectivity was disappeared and reoccurred when NO3− was assimilated into NH4+. Furthermore, the pathways of NH4+ assimilation differed in Arabidopsis exposed to DCPP enantiomers, where (S)-DCPP remained almost the same to the control relying on GS-GOGAT cycle, but the dominant pathway in (R)-DCPP group was shifted to glutamate dehydrogenase route. Consequently, a profound enantioselectivity was also observed in the effects on amino acids synthesis. As for nitrogen stable isotope fractionation, (R)-DCPP led to more negative δ15N values than (S)-DCPP at 0.3μM, indicating the selective uptake of toxic NH4+ and different discrimination of δ15N was also observed between DCPP enantiomers. Moreover, stable isotopic evidence also revealed the disturbance caused by DCPP to the balance of nitrogen demand and consumption in A. thaliana. All these results may contribute to the final enantioselective toxicity, providing a new sight into the better understanding the action mechanism of chiral herbicides.

Use of chiral derivatization for the determination of dichlorprop in tea samples by ultra performance LC with fluorescence detection

Dichlorprop is available for agricultural use as a chiral pesticide. In this study, the stereoselective determination of dichlorprop enantiomers in tea samples such as green, black, jasmine, and oolong was developed by ultra performance LC with fluorescence spectrometry after covalent chiral derivatization. The separation was achieved on an Acquity BEH C18 column with the mobile phase consisting of 0.1% formic acid in acetonitrile/water at a flow rate of 0.4 mL/min. In the covalent chiral derivatization using (S)-(+)-4-(N,N-dimethylaminosulfonyl)-7-(3-aminopyrrolidin-1-yl)-2,1,3-benzoxadiazole, the peak resolution between the S and R-dichlorprop enantiomers was 2.6. LODs and LOQs values were 10 and 50 ng/mL standard solution. The linearity of the calibration curves yielded the coefficients (r(2) > 0.99, ranging from 0.05 to 5 μg/mL) of determination of each of the dichlorprop enantiomers. SPE extraction was used for the sample preparation of dichlorprop in various tea samples. Recoveries were in the range of 82.4-97.6% with associated precision values (within-day: 82.4-95.8%, n = 6, and between-day: 83.7-97.6% for 3 days) for repeatability and reproducibility. Based on this result, our method has been proven to be highly efficient and suitable for the routine assay of dichlorprop enantiomers in various tea samples. We propose that the ultra performance LC assay after covalent chiral derivatization would be the renewed tools in the era of chiral stationary platform for chiral pesticide residues in foods.

Enantioselective Oxidative Damage of Chiral Pesticide Dichlorprop to Maize

To investigate the enantioselective oxidative damage of the pesticide dichlorprop (DCPP) to maize, young seedlings were exposed to solutions of DCPP enantiomers and racemate at different concentrations. Early root development was more influenced by (R)-DCPP than racemic (rac)- and (S)-DCPP. Inhibition rates of seed germination, seedling biomass, and root and shoot elongation were all in the order of (R)-DCPP > (rac)-DCPP > (S)-DCPP treatments. The antioxidant enzyme activities of superoxide dismutase (SOD) and peroxidase (POD) were significantly upregulated by exposure to lower concentrations of (R)-DCPP than (rac)- and (S)-DCPP. Direct determination of the formation of hydroxyl radical (•OH) with electron paramagnetic resonance (EPR) spectroscopy indicated that the •OH level in maize roots followed the order of (R)-DCPP > (rac)-DCPP > (S)-DCPP treatments. All of these results provide solicited evidence of the significant enantioselective phytotoxicity of DCPP to maize with a higher toxicity of (R)-DCPP than (S)- and (rac)-DCPP.

Effect of Chitosan on the Enantioselective Bioavailability of the Herbicide Dichlorprop to Chlorella pyrenoidosa

Chitosan, a natural polysaccharide, is widely regarded as a biocompatible and potential carrier for controlled-release drug formulations. However, the potential effect of chitosan on the environmental behavior of contaminants is poorly understood, especially on chiral chemicals. In this study, the changes in bioavailability of the chiral herbicide dichlorprop to Chlorella pyrenoidosa by chitosan were investigated. The dissipation of (S)-enantiomer in Chlorella pyrenoidosa culture media without chitosan was faster than that of the herbicidally active (R)-enantiomer, whereas it was inversed to (R)-enantiomer being faster than (S)-enantiomer when chitosan was added into the media. In the absence of chitosan, the toxicity of (R)-enantiomer to Chlorella pyrenoidosa was more potent than that of the (S)-enantiomer. On the contrary, in the presence of chitosan, (R)-enantiomer was less toxic than (S)-enantiomer. These observations clearly suggest that chitosan changed the enantioselective bioavailability of dichlorprop. Fluorescence spectroscopic analysis showed that the interaction between chitosan and dichlorprop enantiomers depended greatly on the steric structure of dichlorprop, which offers a possible explanation as to why the addition of chitosan changed the enantioselective dissipation of dichlorprop by Chlorella pyrenoidosa. This work suggests that the enantioselective behaviors of chiral compounds in the environment might be shifted when interactions with other chiral receptors coexist.

CEC enantioseparations on chiral monolithic columns: A study of the stereoselective degradation of (R/S)‐dichlorprop [2‐(2,4‐dichlorophenoxy)propionic acid] in soil

For the study of the stereoselective degradation of the herbicide 2-aryloxipropionic acid dichlorprop (DCPP) in soil, a porous monolithic chiral column (100 microm id) was prepared by in situ copolymerization of glycidyl methacrylate, methyl methacrylate and ethylene glycol dimethacrylate in the presence of formamide and 1-propanol as the porogen solvents. Subsequently, the epoxide groups at the surface of the monolith were reacted with (+)-1-(4-aminobutyl)-(5R,8S,10R)-terguride as the chiral selector. Optimum conditions for the herbicide resolution by CEC were found using mobile phases consisting of acetic acid/triethylamine mixtures in ACN-methanol (9:1 v/v). Under these conditions fully separation of DCPP enantiomers in the presence of clofibric acid (internal standard) was achieved in about 5 min. Experiments on the incubation of rac-DCPP in soil at room temperature showed the herbicide undergone during 23 incubation days to a degradation to levels </=20% of the initial concentration, with rates for (R)-DCPP slower than (S)-DCPP. More interesting results were observed when herbicide enantiomers were individually incubated. In both the experiments, the formation of the opposite isomer in the presence of the initial one, and reversed enantiomeric interconversion in the case of (S)-DCPP was observed. (R)-DCPP was found to be the most persistent isomer after incubation.

Influence of kaolinite on chiral hydrolysis of methyl dichlorprop enantiomers

The effect of kaolinite on the enzymatic chiral hydrolysis of methyl dichlorprop enantiomers ((R,S)-methyl-2-(2,4- dichlorophenoxy) propanoic acid, 2,4-DPM) was investigated using chiral gas chromatography. Compared with the control without kaolinite, the enantiomeric ratio (ER) increased from 1.35 to 8.33 and the residual ratio of 2,4-DPM decreased from 60.89% to 41.55% in the presence of kaolinite. Kaolinite likely had emotion influence on lipase activity and its enantioselectivity. Moreover, the amount of kaolinite added was also found to be a sensitive factor affecting the enantioselective hydrolysis of 2,4-DPM. Fourier transform infrared (FTIR) spectroscopy studies of the interaction of lipase with kaolinite provided insight into the molecular structure of the complex and offered explanation of the effects of kaolinite on enzymatic hydrolysis of 2,4-DPM. Spectra showed that the effect of kaolinite on the hydrolysis of 2,4-DPM was affected by adsorption of lipase on kaolinite and changes of adsorbed lipase conformation, which led to the modified enantioselectivity.

Physiological and genetic characteristics of two bacterial strains utilizing phenoxypropionate and phenoxyacetate herbicides

Two strains, Rhodoferax sp. P230 and Delftia (Comamonas) acidovorans MCI, have previously been shown to carry activities for the degradation of the two enantiomers of (RS)-2-(2,4-dichlorophenoxy-)propionate (dichlorprop) and (RS)-2-(4-chloro-2-methylphenoxy-)propionate (mecoprop) and, in addition, are capable of degrading phenoxyacetate derivatives 2.4-dichlorophenoxyacetate (2,4-D) and 4-chloro-2-methylphenoxyacetate (MCPA). Metabolism of the herbicides is initiated by alpha-ketoglutarate-dependent dioxygenases for both enantiomers of the phenoxypropionate herbicides and for 2,4-D. These activities were constitutively expressed for both enantiomers of dichlorprop in strain MC1 and for the Renantiomer in strain P230. Enzyme activities for the complete degradation of phenoxyacetate and phenoxypropionate herbicides were induced during incubation on either of these herbicides. Strain MC1 has about threefold higher activities for the degradation of dichlorprop and for growth on this substrate (mumax = 0.15 h(-1)) than strain P230; the maximum growth rate on 2,4-D amounts to 0.045 h(-1) with strain MC1. Dichlorprop is utilized faster than mecoprop and the R-enantiomers are cleaved with higher rates than the S-enantiomers. The degradation of the chlorophenolic intermediates seems to proceed via the modified ortho cleavage pathway as indicated by activities of the respective enzymes. The enzymatic results were supported by genetic investigations by which the presence of the genes tfdB (encoding a dichlorophenol hydroxylase), tfdC (encoding a chlorocatechol 1,2-dioxygenase) and tfdD (encoding a chloromuconate cycloisomerase) could be demonstrated in both strains by PCR after application of respective primers. The presence of the tfdA gene (encoding a 2,4-D/alpha-ketoglutarate dioxygenase) was only shown for strain P230 but was lacking in strain MC1. Sequence analysis of the tfd gene fragments revealed high homology to the degradative genes of other proteobacterial strains degrading chloroaromatic compounds. Strain MC1 carries a plasmid of about 120 kb which apparently harbors herbicide degradative genes as concluded from deletion mutants which have lost 2,4-D[phenoxalkanoate]/alpha-ketoglutarate dioxygenase activities for cleavage of the R- and S-enantiomer, and of 2,4-D. For strain P230, no plasmid could be demonstrated; the activity was stably conserved in this strain during growth under nonselective conditions.

Enantioselective supercritical fluid chromatography using ristocetin A chiral stationary phases.

Racemic mixtures of five acidic drugs have been successfully separated by supercritical fluid chromatography (SFC) using macrocyclic antibiotic chiral stationary phases (CSPs). A ristocetin A CSP has been prepared 'in-house' and effectively applied in packed capillary SFC to separate the enantiomers of dichlorprop (R(s) = 1.4), ketoprofen (R(s) = 0.9) and warfarin (R(s) = 0.9). The commercial ristocetin A CSP (Chirobiotic R) was subsequently studied in packed column SFC with similar results where the enantiomers of warfarin (R(s) = 2.2), coumachlor (R(s) = 2.5) and thalidomide (R(s) = 0.6) were separated. Interestingly, differences were observed between the two differently immobilised CSPs where the enantiomers of dichlorprop and ketoprofen, which were separated on the 'in-house' CSP, could not be separated on the commercial phase.

Comamonas acidovorans strain MC1: a new isolate capable of degrading the chiral herbicides dichlorprop and mecoprop and the herbicides 2,4-D and MCPA

A gram-negative prototrophic bacterial species, strain MC1, was isolated from the vicinity of herbicide-contaminated building rubble and identified by 16S rDNA sequence analysis, its physiological properties, GC content, and fatty acid composition as Comamonas acidovorans. This strain displays activity for the productive degradation of the two enantiomers of dichlorprop [(RS)-2-(2,4-dichlorophenoxy-)propionate; (RS)-2,4-DP] and mecoprop [(RS)-2-(4-chloro-2-methyl-) phenoxypropionate ; (RS)-MCPP] in addition phenoxyacetate herbicides, i.e. 2,4-dichlorophenoxyacetate (2,4-D) and 4-chloro-2-methylphenoxyacetate (MCPA), and various chlorophenols were utilized. Rates amounted to 1.2 mmoles/h g dry mass (2,4-D) and 2.7 mmoles/h g dry mass [(RS)-2,4-DP]. Degradation of (RS)-2,4-DP was not inhibited up to concentrations of 500 mg/l, nor of 2,4-D up to 200 mg/l. The optimum pH value of (RS)-2,4-DP degradation was around 8. The application of respective primers for PCR amplification revealed the presence of tfdB and tfdC genes.

A molecular dynamics investigation on the inclusion of chiral agrochemical molecules in β-cyclodextrin. Complexes with dichlorprop, 2-phenoxypropionic acid and dioxabenzofos

Cyclodextrins are a group of cyclic oligosaccharides with a ring, basket-like structure. These compounds are able to include several kinds of molecules into their internal cavity, leading to important modifications of the properties of the guest compound. The interaction between β-cyclodextrin and the R and S enantiomers of dichlorprop, 2-phenoxypropionic acid and dioxabenzofos was investigated by means of molecular dynamics (MD). Several in vacuo trajectories were calculated for each system imposing a 1:1 stoichiometry. The results account for the formation of adducts which are stable at room temperature. The analysis of statistical data from the MD runs shows that dioxabenzofos exhibits the weakest interaction in the series studied and that the R and S enantiomers of dichlorprop and phenoxypropionic acid interact in a different fashion with the host molecule. © 1998 Society of Chemical Industry

New derivatives of cyclodextrins as chiral selectors for the capillary electrophoretic separation of dichlorprop enantiomers

α-, β- and γ-cyclodextrins (CDs), as well as some of their chemical derivatives, have been tested as chiral resolving agents for the capillary zone electrophoretic resolution of the racemic herbicide dichlorprop, (±)-2-(2,4-dichlorophenoxy)propionic acid, of which only the (+)-isomer is herbicidally active. The complexation constants of the herbicide enantiomers with the cyclodextrin host molecules have been calculated from the electrophoretic migration time data at variable cyclodextrin concentration. The experimental results showed that several of the investigated CDs allowed dichlorprop enantiomer resolution. In particular, a newly synthesised ethylcarbonate derivative of β-CD showed the best enantiomer resolution properties among the tested compounds, while the remaining ones showed inferior or no performances at all. The calculated inclusion constants allowed identification of the best conditions for enantioresolution, and an explanation of the different complexation properties of the investigated compounds has been proposed on the basis of molecular modeling.

Separation of phenoxy acid herbicides and their enantiomers by high-performance capillary electrophoresis

Capillary electrophoresis conditions in the free solution mode (capillary zone electrophoresis) were established for the separation and detection of 2,4-dichlorophenoxyacetic acid and three optically active phenoxy acid herbicides (dichlorprop, mecoprop and fenoprop). A 50 m M acetate buffer at pH 4.5 gave the best separation, using a 50 cm (to detector) × 75 μm I.D. fused-silica column; the column temperature was 30°C. separation voltage 20 kV and optimum detector wavelength 230 nm. Separation of the four herbicides required less than 15 min under these conditions. Baseline separation of the two enantiomers of each of the three optically active herbicides, separately and in mixtures of the three, was accomplished by the addition of 25 m M tri-O-methyl-β-cyclodextrin to the acetate separation buffer. Di-O-methyl- β-cyclodextrin or α-cyclodextrin (CD) separated enantiomers of dichlorprop and mecoprop, but not those of fenoprop; β-CD provided very little separation and γ-CD gave no separation. Addition of methanol to the separation buffer increased separation, but doubled migration times. Over a variety of sample concentrations and injection times, reproducibilities of migration times of racemates and enantìomers ranged from 1.3 to 4.6% R.S.D.; peak area and peak height reproducibilities ranged from 1.6 to 17.9% R.S.D.

Enantiomer Resolution and Assay of Propionic Acid-Derived Herbicides in Formulations by Using Chiral Liquid Chromatography and Achiral Gas Chromatography

Enantiomers of 6 propionic acid-derived herbicides in the form of their esters were resolved using liquid chromatography with a chiral column. Free acids are converted to methyl esters by means of a BF3-catalyzed reaction. Chromatographic resolutions for 6 of 8 herbicides investigated were in the range of 2 to 4. The method was applied for the simultaneous determination of mecoprop and 2,4-D content and individual mecoprop enantiomers in 2 formulations containing racemic and R-mecoprop in mixture with 2,4-D. Precision and accuracy of content determination was comparable to standard methods, and enantiomer contents were in good agreement with declared values. The enantiomers of dichlorprop and mecoprop were also resolved as diastereomeric menthyl esters by achiral high resolution gas chromatography (HRGC). HRGC data on enantiomer composition were in good agreement with those from the LC method and other data.