Phenoxyalkanoic Acid Research Articles

Comparative Study on the Removal of Various Phenoxyalkanoic Acid Herbicides from Aqueous Solutions on Polycaprolactone and Activated Carbon

The removal of various phenoxyalkanoic acid herbicides as single solutes (2,4-D; 2,4-DP; 2,4-DB; 2,4,5-T; MCPA) from aqueous solutions were studied by using biodegradable poly(e-caprolactone) (PCL). A comparative study was achieved by using powdered and granular activated carbon as an adsorbent in a batch system. The equilibrium was studied at 25, 35, and 45°C. The results were correlated by using Freundlich Langmuir, Temkin, Redlich-Peterson, and Sips equations. To determine the best fit isotherm, three error analysis methods were used to evaluate the data: correlation coefficient (R2), residual root-mean-square error, and normalized deviation (ΔQ). The results show that all the isotherm models provide an appropriate fitting to the experimental data for the adsorption onto PCL. Adsorption of the studied herbicides onto granular activated carbon, powdered activated carbon, and poly(e-caprolactone) decreased in the order of 2,4-DB>2,4,5-T>2,4-DP>2,4-D>MCPA. The thermodynamic parameters (ΔG°, ΔH°, ΔS°) for ...

Crystal Packing and Supramolecular Motifs in Four Phenoxyalkanoic Acid Herbicides—Low-Temperature Redeterminations

A low-temperature redetermination by X-ray crystallography of four phenoxyalkanoic acid herbicides, 4-chloro-2-methylphenoxyacetic acid (MCPA), rac-2-(4-chloro-2-methylphenoxy)propionic acid (MCPP), 2,4-dichlorophenoxyacetic acid (2,4-D), and 2,4-dichlorophenoxybutyric acid (2,4-DB), allowed the supramolecular structures of these compounds to be precisely described in terms of C⋯O/C–H⋯π interactions. The geometric parameters of the redetermined structures agree with those previously reported, but with improved precision.

Alphaproteobacteria dominate active 2‐methyl‐4‐chlorophenoxyacetic acid herbicide degraders in agricultural soil and drilosphere

2-Methyl-4-chlorophenoxyacetic acid (MCPA) is a widely used phenoxyalkanoic acid herbicide and subject to aerobic microbial degradation. Earthworms stimulate both growth and activity of MCPA-degrading bacteria in soil. Thus, active MCPA degraders in soil and drilosphere (i.e. burrow walls, gut content and cast) were assessed by 16S rRNA stable isotope probing in soil columns under experimental conditions designed to minimize laboratory incubation biases. Agriculturally relevant concentrations of [(13) C]MCPA (20 µg g(dw) (-1)) were degraded in soil within 23 and 27 days in the presence and absence of earthworms respectively. Total 16S rRNA analysis revealed 73 operational taxonomic units indicative of active Acidobacteria, Actinobacteria, Bacteroidetes, Chloroflexi, Cyanobacteria, Firmicutes, Gemmatimonadetes, Planctomycetes, Proteobacteria and Verrucomicrobia in soil and drilosphere derived material. Seven operational taxonomic units indicative of Alpha-, Beta-, Gammaproteobacteria and Firmicutes consumed MCPA-[(13) C]. Dominant consumers of MCPA-[(13) C] were Alphaproteobacteria (Sphingomonadaceae and Bradyrhizobiaceae) in soil and drilosphere. Beta- (Comamonadaceae) and Gammaproteobacteria (Xanthomonadaceae) were also important MCPA-[(13) C] consumers in burrow walls only, indicating that earthworms favour betaproteobacterial MCPA degraders. In oxic microcosms with bulk soil, burrow walls and cast, 20 and 300-400 µg g(dw) (-1) [(13) C]MCPA were consumed within 24 h and 20 days respectively. Gut contents did not facilitate the degradation of [(13) C]MCPA. Sphingomonadaceae dominated MCPA-[(13) C] consumers in bulk soil and burrow wall microcosms, while Beta- and Gammaproteobacteria (Burkholderiacea, Comamonadaceae, Oxalobacteraceae and Xanthomonadaceae) dominated MCPA-[(13) C] consumers in microcosms of cast, indicating that the latter taxa are prone to respond to MCPA in cast. The collective data indicated that Alphaproteobacteria are major MCPA degraders in soil and drilosphere.

The earthworm Aporrectodea caliginosa stimulates abundance and activity of phenoxyalkanoic acid herbicide degraders

2-Methyl-4-chlorophenoxyacetic acid (MCPA) is a widely used phenoxyalkanoic acid (PAA) herbicide. Earthworms represent the dominant macrofauna and enhance microbial activities in many soils. Thus, the effect of the model earthworm Aporrectodea caliginosa (Oligochaeta, Lumbricidae) on microbial MCPA degradation was assessed in soil columns with agricultural soil. MCPA degradation was quicker in soil with earthworms than without earthworms. Quantitative PCR was inhibition-corrected per nucleic acid extract and indicated that copy numbers of tfdA-like and cadA genes (both encoding oxygenases initiating aerobic PAA degradation) in soil with earthworms were up to three and four times higher than without earthworms, respectively. tfdA-like and 16S rRNA gene transcript copy numbers in soil with earthworms were two and six times higher than without earthworms, respectively. Most probable numbers (MPNs) of MCPA degraders approximated 4 × 10(5) g(dw)(-1) in soil before incubation and in soil treated without earthworms, whereas MPNs of earthworm-treated soils were approximately 150 × higher. The aerobic capacity of soil to degrade MCPA was higher in earthworm-treated soils than in earthworm-untreated soils. Burrow walls and 0-5 cm depth bulk soil displayed higher capacities to degrade MCPA than did soil from 5-10 cm depth bulk soil, expression of tfdA-like genes in burrow walls was five times higher than in bulk soil and MCPA degraders were abundant in burrow walls (MPNs of 5 × 10(7) g(dw)(-1)). The collective data indicate that earthworms stimulate abundance and activity of MCPA degraders endogenous to soil by their burrowing activities and might thus be advantageous for enhancing PAA degradation in soil.

Abundance of novel and diverse tfdA-like genes, encoding putative phenoxyalkanoic acid herbicide-degrading dioxygenases, in soil.

Phenoxyalkanoic acid (PAA) herbicides are widely used in agriculture. Biotic degradation of such herbicides occurs in soils and is initiated by alpha-ketoglutarate- and Fe2+-dependent dioxygenases encoded by tfdA-like genes (i.e., tfdA and tfdAalpha). Novel primers and quantitative kinetic PCR (qPCR) assays were developed to analyze the diversity and abundance of tfdA-like genes in soil. Five primer sets targeting tfdA-like genes were designed and evaluated. Primer sets 3 to 5 specifically amplified tfdA-like genes from soil, and a total of 437 sequences were retrieved. Coverages of gene libraries were 62 to 100%, up to 122 genotypes were detected, and up to 389 genotypes were predicted to occur in the gene libraries as indicated by the richness estimator Chao1. Phylogenetic analysis of in silico-translated tfdA-like genes indicated that soil tfdA-like genes were related to those of group 2 and 3 Bradyrhizobium spp., Sphingomonas spp., and uncultured soil bacteria. Soil-derived tfdA-like genes were assigned to 11 clusters, 4 of which were composed of novel sequences from this study, indicating that soil harbors novel and diverse tfdA-like genes. Correlation analysis of 16S rRNA and tfdA-like gene similarity indicated that any two bacteria with D>20% of group 2 tfdA-like gene-derived protein sequences belong to different species. Thus, data indicate that the soil analyzed harbors at least 48 novel bacterial species containing group 2 tfdA-like genes. Novel qPCR assays were established to quantify such new tfdA-like genes. Copy numbers of tfdA-like genes were 1.0x10(6) to 65x10(6) per gram (dry weight) soil in four different soils, indicating that hitherto-unknown, diverse tfdA-like genes are abundant in soils.

Biodegradation of the herbicide mecoprop-p with soil depth and its relationship with class III tfdA genes

Mecoprop-p [(R)-2-(4-chloro-2-methylphenoxy) propanoic acid) is widely used in agriculture and poses an environmental concern because of its susceptibility to leach from soil to water. We investigated the effect of soil depth on mecoprop-p biodegradation and its relationship with the number and diversity of tfdA related genes, which are the most widely known genes involved in degradation of the phenoxyalkanoic acid group of herbicides by bacteria. Mecoprop-p half-life (DT 50) was approximately 12 days in soil sampled from <30 cm depth, and increased progressively with soil depth, reaching over 84 days at 70–80 cm. In sub-soil there was a lag period of between 23 and 34 days prior to a phase of rapid degradation. No lag phase occurred in top-soil samples prior to the onset of degradation. The maximum degradation rate was the same in top-soil and sub-soil samples. Although diverse tfdAα and tfdA genes were present prior to mecoprop-p degradation, real time PCR revealed that degradation was associated with proliferation of tfdA genes. The number of tfdA genes and the most probable number of mecoprop-p degrading organisms in soil prior to mecoprop-p addition were below the limit of quantification and detection respectively. Melting curves from the real time PCR analysis showed that prior to mecoprop-p degradation both class I and class III tfdA genes were present in top- and sub-soil samples. However at all soil depths only tfdA class III genes proliferated during degradation. Denaturing gradient gel electrophoresis confirmed that class III tfdA genes were associated with mecoprop-p degradation. Degradation was not associated with the induction of novel tfdA genes in top- or sub-soil samples, and there were no apparent differences in tfdA gene diversity with soil depth prior to or following degradation.

Effects of Atrazine and Fenoxaprop-Ethyl on Capacitation and the Acrosomal Reaction in Boar Sperm

Atrazine is a herbicide of the chloro-s-triazine family. It inhibits photosynthesis in plants and is an endocrine disruptor, but its effects on human health are controversial. Fenoxaprop-ethyl, an aryloxy phenoxyalkanoic acid herbicide, inhibits the biosynthesis of fatty acids and provokes depolarization of membranes. The aim of this study is to evaluate the in vitro effects of both herbicides on capacitation, spontaneous acrosome reaction (SAR) and progesterone-induced acrosome reaction (PIAR) in boar sperm. Sperm capacitation is done in TALP-HEPES media for 4 hours. Capacitation and SAR are evaluated immediately; PIAR, 30 minutes later. LC50 for fenoxaprop-ethyl is 60 micromolar [corrected] and 40 micromolar [corrected] for atrazine. Fenoxaprop-ethyl induces capacitation at 60 micromolar [corrected] and SAR at all concentrations, also increases significantly PIAR. Atrazine decreased capacitation whereas increase significantly SAR and PIAR at all concentrations. It seems that fenoxaprop-ethyl and atrazine accelerate the capacitation and the acrosomal reaction, possibly via plasma membrane destabilization.

Phenoxyalkanoic acid complexes: Part II. Complexes of selected bivalent metals with 2,4-dichlorophenoxyacetic acid (2,4D) and 2-(2,4-dichlorophenoxy)propionic acid (2,4DP)

Seven new solid complexes have been obtained: Hg(II), Fe(II), Ca(II) and Mg(II) complexes with 2,4D and Hg(II), Fe(II) and Ca(II) complexes with 2,4DP as well as previously described Cu(II), Zn(II), Cd(II), Pb(II), Mn(II), Co(II) and Ni(II) complexes with both ligands. The composition of ML 2· nH 2O complexes, where n = 0–6, was established by chemical analysis methods. Their water solubility has been determined and X-ray, IR and thermal analyses have been carried out. It has been found out that the most sparingly soluble mercury, lead, copper and cadmium compounds precipitate also from a solution of a herbicide which contains 2,4-dichlorophenoxyacetic acid (2,4D) as an active substance. The analysis of powder diffraction patterns of the complexes under study shows that they are crystalline, but have different structures. Their IR spectra have been interpreted in relation to the structural data available. It has been found out that metals are coordinated by the carboxylate groups of the ligands. The IR analysis does not allow to establish precisely the mode of coordination of the metals with the carboxylate groups. The thermal decomposition of all the compounds proceeds in a similar way. In the case of the hydrated complexes first the 1–3 step dehydration process takes place. The decomposition of the anhydrous compounds is a two step process with a complicated course. Total mass losses for the mercury, lead and cadmium complexes are close to 100%, thus in the process of thermal decomposition the metals form volatile compounds.

Catalytic oxidative degradation of s-triazine and phenoxyalkanoic acid based herbicides with metalloporphyrins and hydrogen peroxide: Identification of two distinct reaction schemes

Oxidative degradation of the herbicides atrazine ( 1), atraton ( 2), ametryn ( 3) and mecoprop ( 4), was carried out with hydrogen peroxide and metalloporphyrins as catalysts. Two different reaction conditions were studied, the first involving Mn(TDCPP)Cl in an aprotic solvent with buffer ( S-I), and the second using Fe(TPFPP)Cl in a protic solvent ( S-II). Reaction products were characterized, and based on these it is shown that there are two distinct reaction schemes. In the case of the S-I conditions, it is suggested that the s-triazines were oxidized through hydroxylation of the alkyl side chains followed by dealkylation, while S-II was ineffective for these reactions. In contrast, mecoprop, was oxidized with high efficiency by S-II, leading to decarboxylation and further oxidation, while in the presence of S-I, low substrate conversion was observed, and reaction resulted mainly from oxidation at the benzyl position. Sulfoxidation of ametryn was observed with both systems. The different reactivity shown by the two systems supports the involvement of different reactive species, which we assign to the oxo and hydroperoxy complexes. These routes show similarities with metabolic pathways, with the reactivity pattern of S-I analogous to the reported metabolism of these pollutants with cytochrome P450 enzymes, while S-II catalyses mecoprop decarboxylation via a similar pathway to that seen with peroxidase catalysed reactions.

Synthesis and crystal structures of lanthanide complexes with foliage growth regulator: phenoxyalkanoic acid

Reactions of Ln(ClO4)3 · 6H2O (Ln=La(III), Eu(III), Nd(III)), 1,10-phenanthroline (phen) and phenoxyacetic acid (PA) or 2,4-dichlorophenoxyacetic acid (2,4-D) yield [La(PA)2 (phen)2]2(ClO4)2 (1), [Eu(2,4-D)2(phen)2]2(ClO4)2 (2) and [Nd(2,4-D)3(C2H5OH)] n (3). Compounds 1–3 are characterized by elemental analyses, IR, UV–Vis, ESI-MS spectra and TGA. 1 is also characterized by 1H and 13C NMR. Single crystal X-ray diffraction analyses reveal that 1 and 2 are binuclear, and 3 has a one-dimensional polymeric structure. The La(III), Eu(III) and Nd(III) are nine-coordinate with a distorted tricapped trigonal-prism geometry.

Synthesis, structure and interactions with DNA of novel tetranuclear, [Mn4(II/II/II/IV)] mixed valence complexes

Reaction of Mn(II) with phenoxyalkanoic acids and di-2-pyridyl ketone oxime (Hpko) leads to neutral tetranuclear complexes of the general formula Mn4(O)(pko)4(phenoxyalkanoato)4 (phenoxyalkanoic acids: H-mcpa=2-methyl-4-chloro-phenoxy-acetic acid, H-2,4,5-T=2,4,5-trichloro-phenoxy-acetic acid or H3,4-D=3,4-dichloro-phenoxy-acetic acid). The compounds were synthesized by adding di-2-pyridyl ketone oxime to MnCl2 in the presence of the sodium salts of the alkanoic acids in methanol. The crystal structure of Mn4(II/II/II/IV)(O)(pko)4(2,4,5-T)4·2.5CH3OH·0.25H2O 1 shows that the complex consists of a [Mn4(μ4-O)]8+ core with a Mn(IV) and 3 Mn(II) ions in octahedral environment and a μ4-O atom bridging the four manganese ions. Spectroscopic studies of the interaction of these tetranuclear clusters with DNA showed that these compounds bind to dsDNA. The binding strength of the Mn4(II/II/II/IV)(O)(pko)4(2,4,5-T)4 complex for calf thymus DNA is equal to 1.1×104M−1. Among the deoxyribonucleotides they bind preferentially to deoxyguanylic acid (dGMP). Competitive studies with ethidium bromide (EthBr) showed that the Mn4(II/II/II/IV)(O)(pko)4(2,4,5-T)4 complex exhibited the ability to displace the DNA-bound EthBr indicating that the complex binds to DNA via intercalation in strong competition with EthBr for the intercalative binding site. Additionally, DNA electrophoretic mobility experiments showed that all three complexes, at low cluster concentration, are obviously capable of binding to pDNA causing its cleavage (relaxation) at physiological pH and temperature. At higher cluster concentration, catenated dimer forms of pDNA was formed.

Bacterial diversity in soil enrichment cultures amended with 2 (2‐methyl‐4‐chlorophenoxy) propionic acid (mecoprop)

Summary The tfdA gene encodes for an alpha-ketoglutarate-dependent dioxygenase enzyme which catalyses the first step of the degradation of phenoxyalkanoic acid herbicides such as 2 (2-methyl-4-chlorophenoxy) propionic acid (mecoprop). The bacterial diversity of soil enrichment cultures containing mecoprop was examined by Denaturing Gradient Gel Electrophoresis (DGGE) and clone libraries of both 16S rRNA genes and tfdA genes. The 16S rRNA gene sequences were diverse and clustered with either the Beta- or Gammaproteobacteria. The 16S rRNA gene sequence from a bacterial strain isolated from an enrichment culture, grown on R-mecoprop, which represented a dominant band in the DGGE profiles, had a high 16S rRNA sequence identity (100%) to Burkholderia glathei. This is the first report that B. glathei is implicated in mecoprop degradation. PCR amplification of the tfdA genes detected class III tfdA genes only, and no class I or class II tfdA sequences were detected. To understand the genes involved the degradation of specific mecoprop (R-) and (S-) enantiomers, oligonucleotide probes targeting the tfdA, rdpA, sdpA and cadA genes were hybridized to DNA extracted from enrichment cultures grown on either R-mecoprop or (R/S) racemic mecoprop. Strong hybridization signals were obtained with sdpA and tfdA probes using DNA extracted from cultures grown on racemic mecoprop. A strong hybridization signal was also obtained with the rdpA probe with DNA extracted from the cultures grown on R-mecoprop. This suggests the rdpA gene is involved in R-mecoprop degradation while tfdA, sdpA and cadA genes are involved in the degradation of both R- and S-mecoprop.

Sorption behavior of acidic herbicides on carbon nanotubes

Carbon nanotubes and graphitized carbon are investigated as adsorbents for solid phase extraction of dicamba and 2,4,5-T, two phenoxyalkanoic acid herbicides. These adsorbents have much greater adsorption capability than that of C18 bonded silica, which was also tested for comparison studies. The adsorption capacity increases remarkably at lower pH of the sample solution. Freundlich isotherms were applied to analyze the data. Our studies suggest that carbon nanotubes have great potential applications in environmental analysis.

Interaction of Fe(III) with herbicide-carboxylato ligands – Di-, tri- and tetra-nuclear compounds: Structure and magnetic behavior

The iron complexes with the phenoxyalkanoic acids 3,4-D, 2,3-D and 2,4,5-T in the presence or not of a nitrogen donor heterocyclic ligand, phen, were prepared and characterized. Interaction of Fe(III) with phenoxyalkanoic acids and phen leads to dinuclear neutral complexes while the absence of phen favours trinuclear cationic or tetranuclear neutral forms. The crystal structure of hexakis(2,3-dichlorophenoxyacetato)tris(methanol)oxotri-iron(III) chloride–methanol(1/3), [Fe 3O(2,3-D) 6(MeOH) 3]Cl · 3MeOH ( 2), and tetrakis(dimethyl-sulfoxide)octakis(2,4,5-trichlorophenoxyacetato)dioxotetra-iron(III) methanol(1/2)–water(1/1)–dimethylsulfoxide(1/0.8), {[Fe 4O 2(2,4,5-T) 8(dmso) 4] · 2MeOH · H 2O · 0.8dmso} ( 3), have been determined and refined by least-squares methods using three-dimensional Mo Kα data. Magnetic data of the trimer show antiferromagnetic interaction. The ground state of the system is S = 1/2 with a small percentage of S = 5/2 paramagnetic impurity ρ = 0.7%. For the tetramer, the magnetic data suggest antiferromagnetically coupled system with S = 0 ground state, while for the dimer, {[Fe 2OCl 2(3,4-D) 2(phen) 2] · H 2O · 3.5MeOH} a very strong antiferromagnetic exchange interaction between the two ions has been observed. The fitting results give an exchange interaction of J = 254.1 cm −1, with S = 0 ground state with a small amount of paramagnetic S = 5/2 impurity ( ρ = 0.3%).

Interaction of Fe(III) with herbicide-carboxylato ligands. Di-, tri- and tetra-nuclear compounds: Structure, antimicrobial study and DNA interaction

The iron complexes with the phenoxyalkanoic acids 2,3-D = 2,3-dichlorophenoxyacetic acid, 3,4-D = 3,4-dichlorophenoxyacetic acid, 2,4,5-T = 2,4,5-trichlorophenoxyacetic acid, and mcpa = 2-chloro-4-methyl-phenoxyacetic acid, in the presence or not of a nitrogen donor heterocyclic ligand, py = pyridine, bipy = 2,2′ bipyridine, phen = 1,10-phenanthroline, were prepared and characterized.The interaction of Fe(III) with phenoxyalkanoic acids and bipy or phen leads to dinuclear neutral complexes, while the presence of py favors tetranuclear neutral forms. The crystal structures of [Fe 2OCl 2(mcpa) 2(bipy) 2] · 0.25(bipy) · 0.8MeCN ( 1a), and {[Fe 4O 2(mcpa) 6Cl 2(py) 4] · 2MeCN} ( 3a), have been determined. DNA–Fe(III) complex interaction studies suggest that iron complexes promote the hydrolytic cleavage of double stranded DNA that seems to be oxygen independent, while pDNA shows cross-linking with many molecules of the iron clusters. Antibacterial screening data showed that the presence of chelating agents, bipy or phen, increased the efficiency of iron complexes.

Purification and characterization of two enantioselective alpha-ketoglutarate-dependent dioxygenases, RdpA and SdpA, from Sphingomonas herbicidovorans MH.

Alpha-ketoglutarate-dependent (R)-dichlorprop dioxygenase (RdpA) and alpha-ketoglutarate-dependent (S)-dichlorprop dioxygenase (SdpA), which are involved in the degradation of phenoxyalkanoic acid herbicides in Sphingomonas herbicidovorans MH, were expressed and purified as His6-tagged fusion proteins from Escherichia coli BL21(DE3)(pLysS). RdpA and SdpA belong to subgroup II of the alpha-ketoglutarate-dependent dioxygenases and share the specific motif HXDX(24)TX(131)HX(10)R. Amino acids His-111, Asp-113, and His-270 and amino acids His-102, Asp-104, and His 257 comprise the 2-His-1-carboxylate facial triads and were predicted to be involved in iron binding in RdpA and SdpA, respectively. RdpA exclusively transformed the (R) enantiomers of mecoprop [2-(4-chloro-2-methylphenoxy)propanoic acid] and dichlorprop [2-(2,4-dichlorophenoxy)propanoic acid], whereas SdpA was specific for the (S) enantiomers. The apparent Km values were 99 microM for (R)-mecoprop, 164 microM for (R)-dichlorprop, and 3 microM for alpha-ketoglutarate for RdpA and 132 microM for (S)-mecoprop, 495 microM for (S)-dichlorprop, and 20 microM for alpha-ketoglutarate for SdpA. Both enzymes had high apparent Km values for oxygen; these values were 159 microM for SdpA and >230 microM for RdpA, whose activity was linearly dependent on oxygen at the concentration range measured. Both enzymes had narrow cosubstrate specificity; only 2-oxoadipate was able to replace alpha-ketoglutarate, and the rates were substantially diminished. Ferrous iron was necessary for activity of the enzymes, and other divalent cations could not replace it. Although the results of growth experiments suggest that strain MH harbors a specific 2,4-dichlorophenoxyacetic acid-converting enzyme, tfdA-, tfdAalpha-, or cadAB-like genes were not discovered in a screening analysis in which heterologous hybridization and PCR were used.

The synthesis and characterization of some ortho-substituted phenoxyalkanoic acids and their derivatives

The synthesis of 2-phenoxyalkanoic acids (ethanoic, propanoic, butanoic) was realized by the reaction of ortho-hydroxybenzamide respectively N-phenyl-o-hydroxybenzamide with ?-halogenated acids in aqueous sodium hydroxide solution. 2-[o-(carbamoyl)phenoxy]-2-methyl- and 2-[o-(phenylcarbamoyl)phenoxy]-2-methyl- propanoic acids were obtained by reaction of the appropriate amide with acetone, chloroform and sodium hydroxide. Ethyl esters of 2-phenoxyalkanoic acids were obtained by the reaction of the amide with ethyl esters of ?-halogenated acids in different reaction media. Starting from the ethyl esters of 2-[2-(N-phenylcarbamoyl) phenoxy]alkanoic acids with hydrazine 2-[2-(N-phenylcarbamoyl)phenoxy]alkanoic acids hydrazides were obtained, which are considered key intermediates for the synthesis of several series of new compounds. Schiff bases and N-imido-derivatives were obtained by condensation of hydrazide with substituted aromatic aldehydes respectively maleic anhydride. The synthesized compounds were characterized by physico-chemical methods (FTIR, NMR and mass spectrometry). .

The characterization of prepared organomontmorillonite (DEDMAM) and sorption of phenoxyalkanoic acid herbicides from aqueous solution

The montmorillonite has been subjected to modification through ion-exchange reaction by N, N′-didodecyl- N, N′-tetramethylethanediammoniumdiiodide (DEDMAI). The modified sample was studied by X-ray diffraction (XRD), Fourier transform infrared (FTIR) spectroscopy, and thermogravimetric analysis (TGA). The basal spacing of modified montmorillonite was determined as 28.72 Å. The IR spectra of organomontmorillonite showed changes in C–H vibrations. The characterization of N, N′-didodecyl- N, N′-tetramethylethanediammonium montmorillonite (DEDMAM) and the adsorption of 2,4-dichlorophenoxyacetic acid (2,4-D), 2,4-dichlorophenoxybutyric acid (2,4-DB), 4-chloro-2-methylphenoxyacetic acid (MCPA), and 2,4,5-trichlorophenoxyacetic acid (2,4,5-T) on organomontmorillonite was studied as a function of the solution concentration. The adsorption energy ( E) and adsorption capacity ( q m ) for phenoxyalkanoic acid herbicides adsorbing on organomontmorillonite (DEDMAM) were estimated using the Dubinin–Radushkevic (D–R) equation. These isotherms were modeled according to Freundlich and Dubinin–Radushkevic adsorption isotherms. The sorption of the herbicides on DEDMAM increased in order of MCPA < 2,4-D < 2,4-DB < 2,4,5-T.

Study on the toxicity of phenolic and phenoxy herbicides using the submitochondrial particle assay

A simple and rapid in vitro toxicological assay, utilizing submitochondrial particles (SMP), has been used to evaluate the toxic effects of fifteen herbicides belonging to the phenol and phenoxyalkanoic acid chemical classes. The SMP assay allows the quantitative evaluation of the toxicity of compounds with different mechanisms of action: uncouplers, inhibitors of the enzyme complexes involved in reverse electron transfer and in oxidative phosphorylation and chemicals that alter the membrane structure. The two groups of herbicides showed different levels of toxicity. For phenol derivatives, EC 50 values ranged from 0.16 μM (ioxynil) to 6.7 μM (2,4-dinitrophenol), whereas for phenoxy herbicides EC 50 values ranged from 21 μM (2,4,5-trichlorophenoxyacetic acid, 2,4,5-T) to 110 μM (4-chloro-2-methylphenoxyacetic acid, MCPA). On the average, the toxicity of phenolic compounds is greater than that of phenoxyalkanoic acids by two orders of magnitude. Quantitative structure–activity relationships (QSAR) were developed between EC 50 values and various molecular descriptors. The results suggest the existence of different mechanisms of action for the two classes of compounds. The findings obtained for phenolic herbicides are consistent with a protonophoric uncoupling mechanism, whereas for phenoxy herbicides a non-specific mode of action at membrane level can be hypothesized.

Comparison of Different Sorbents for Solid-Phase Extraction of Phenoxyalkanoic Acid Herbicides

An HPLC procedure for determination of phenoxyalkanoic acid herbicides in water samples is proposed. The analytical column Phenomenex C18(2) Luna 5 µm and UV detection at 225 nm were applied. Baseline resolution was achieved in isocratic mode with a mobile phase consisting of acetonitrile/acetic acid (40/60, v/v), adjusted to pH 2.5. SPE sorbents – C18 BondElut, phenyl-silica, LiChrolut SAX and polymeric sorbents – were compared for isolation and preconcentration of 6 phenoxyalkanoic acid herbicides. Higher (above 95%) and more reproducible recoveries were obtained with polymeric and phenyl-silica sorbents using pure methanol for elution. The method was tested for river water samples with the limit of detection in the range of 2–3 µg L−1 (for 50 mL sample) and a reproducibility of 5% RSD.