Photodegradation of hexythiazox in different solvent systems under the influence of ultraviolet light and sunlight in the presence of TiO2, H2O2, and KNO3 and identification of the photometabolites

The photodegradation of the carboxamide acaricide hexythiazox in three different solvent systems (aqueous methanolic, aqueous isopropanolic, and aqueous acetonitrilic solutions) in the presence of H(2)O(2), KNO(3), and TiO(2) under ultraviolet (UV) light (λ(max) ≥ 250 nm) and sunlight (λ(max) ≥290 nm) has been assessed in this work. The kinetics of photodecomposition of hexythiazox and the identification of photoproducts were carried out using liquid chromatography-mass spectrometry. The rate of photodecomposition of hexythiazox in different solvents followed first-order kinetics in both UV radiation and natural sunlight, and the degradation rates were faster under UV light than under sunlight. Hexythiazox was found to be more efficiently photodegraded in the presence of TiO(2) than in the presence of H(2)O(2) and KNO(3). Two major photoproducts were separated in pure form using column chromatography and identified according to IR, (1)H NMR, and mass spectral information as cyclohexylamine and 5-(4-chlorophenyl)-4-methylthiazolidin-2-one. Another nine photoproducts were identified according to LC-MS/MS spectral information. The plausible photodegradation pathways of hexythiazox were proposed according to the structures of the photoproducts.     

Water Remediation by Columns Filled with Micelle–Vermiculite Systems

Photodegradation of four pharmaceuticals (i.e. carbamazepine, ibuprofen, ketoprofen and 17α-ethinylestradiol) in aqueous media was studied using a solar light simulator (Xe lamp irradiation) and sunlight experiments. These experiments were carried out in river and seawater and compared to distilled water. The latter was used to evaluate the direct photodegradation pathways. Irradiation time was up to 400 min and 24 days for the solar light simulator and sunlight assays, respectively. Pharmaceutical photodegradation followed a first-order kinetics and their half-lives calculated in every aqueous matrix. Moreover, the sensitizing effect of DOC was evaluated by comparison with the kinetics obtained in distilled waters. Ketoprofen was rapidly transformed via direct photolysis in all the waters under both sunlight (t _1/2?=?2.4 min) and simulated solar light simulator test (t _1/2?=?0.54 min). Under xenon lamp radiation, ibuprofen and 17α-ethinylestradiol were photodegraded at moderate rate with half-lives from 1 to 5 h. Finally, carbamazepine had the lowest photodegradation rate (t _1/2?=?8–39 h) attributable to indirect photodegradation. Indeed, its elimination was strongly dependent on the DOC concentration present in solution. Finally, several ketoprofen photoproducts were identified and plotted against solar light simulator irradiation time. Accordingly, the photodegradation pathway of ketoprofen was postulated.     

Natural Sunlight Induced Photooxidation of Naphthalene in Aqueous Solution

There is surprisingly little data on the photooxidation of polycyclic aromatic hydrocarbons (PAHs) under environmentally relevant lighting conditions. The aqueous photooxidation reactions of naphthalene (the simplest and most water soluble PAH) were investigated using natural sunlight as a light source.Six of the major reaction products were identified, including 1-naphthol, coumarin, and two hydroxyquinones. The reactionproducts were consistent with initial [2,2] or [2,4] photocycloaddition reactions, with subsequent oxidations and/or rearrangements. The oxidation reactions in aqueous phase favoredproducts different from those observed in atmospheric oxidation reactions. However, similar photoproducts were observed withtitanium catalysts or in the presence of hydrogen peroxide. Theproducts from aqueous photooxidation were also similar to the products resulting from naphthalene metabolism. The observedphotooxidation products were generated by mechanisms that areexpected to occur with other PAHs as well, and thus naphthaleneoxidation provides a model for possible photoreactions of largerPAHs.     

Transformation of a monoterpene ketone, (R)-(+)-pulegone, a potent hepatotoxin, in Mucor piriformis.

Biotransformation of a monoterpene ketone, (R)-(+)-pulegone (I), a potent hepatotoxin, was studied using a fungal strain, Mucor piriformis. Eight metabolites, namely, 5-hydroxypulegone (II), piperitenone (III), 6-hydroxypulegone (IV), 3-hydroxypulegone (V), 5-methyl-2-(1-hydroxy-1-methylethyl)-2-cyclohexene-1-one (VI), 3-hydroxyisopulegone (VII), 7-hydroxypiperitenone (VIII), and 7-hydroxypulegone (IX), have been isolated from the fermentation medium and identified. GC analysis of the metabolites indicated that II was the major metabolite formed. The organism initiates transformation either by hydroxylation at the C-5 position or by hydroxylation of the ring methylenes, the former being the major activity. On the basis of the identification of the metabolites, pathways for the biotransformation of (R)-(+)-pulegone have been proposed. The mode of transformation of (S)-(-)-pulegone by this organism was shown to be similar to that of its (R)-(+)-enantiomer. When isopulegone (X) was used as the substrate, the organism isomerized it to pulegone (I), which was then transformed to metabolites II-IX.     

Epimerization of tea catechins and O-methylated derivatives of (-)-epigallocatechin-3-O-gallate: relationship between epimerization and chemical structure

Epimerization at C-2 of O-methylated catechin derivatives and four major tea catechins were investigated. The epimeric isomers of (-)-epicatechin (I), (-)-epicatechin-3-O-gallate (II), (-)-epigallocatechin (III), (-)-epigallocatechin-3-O-gallate (IV), and (-)-epigallocatechin-3-O-(3-O-methyl)gallate (V) in green tea extracts increased time-dependently at 90 degrees C. The epimerization rates of authentic tea catechins in distilled water are much lower than those in tea infusion or in pH 6.0 buffer solution. The addition of tea infusion to the authentic catechin solution accelerated the epimerization, and the addition of ethylenediaminetetraacetic acid, disodium salt (Na(2)EDTA) decreased the epimerization in the pH 6.0 buffer solution. Therefore, the metal ions in tea infusion may affect the rate of epimerization. The proportions of the epimers to authentic tea catechins [III, IV, V, and (-)-epigallocatechin-3-O-(4-O-methyl)gallate (VI)] in pH 6.0 buffer solution after heating at 90 degrees C for 30 min were 42.4%, 37.0%, 41.7%, and 30.4%, respectively. These values were higher than those of I and II (23.5% and 23.6%, respectively). The O-methylated derivatives at the 4'-position on the B ring of IV and VI were hardly epimerized. These results suggest that the hydroxyl moiety on the B ring of catechins plays an important role in the epimerization in the order 3',4',5'-triol type > 3',4'-diol type > 3',5'-diol type.     

Transformation of the fungicide chlorothalonil by Fenton reagent

A modified Fenton reagent (Fe(3+)/H(2)O(2)) transformed the fungicide chlorothalonil within 60 min in aqueous solution at unadjusted pH. Transformation varied with ferric salt. Transformation was greatest with ferric nitrate and least when ferric sulfate was used. UV irradiation enhanced the transformation of chlorothalonil. The transformation of chlorothalonil was enhanced, which increased with ferric ion or hydrogen peroxide concentration. Maximum transformation was achieved at 2 mM ferric ion and 100 mM hydrogen peroxide. Additionally, chlorothalonil was more dechlorinated in the UV irradiation condition. The proposed reaction pathway includes reduction of chlorothalonil to trichloroisophthalonitrile, dichloroisophthalonitrile, and monochloroisophthalonitrile; oxidation of trichloroisophthalonitrile to trichloro-3-cyanobenzoic acid and 3-carbamyltrichlorobenzoic acid; and oxidation of hydroxychlorothalonil to trichloro-3-cyanohydroxybenzoic acid and trichlorocyanophenol.     

Elucidation of fipronil photodegradation pathways

The phenylpyrazole insecticide fipronil (I) photolyzes to its desthio product (II) in aqueous solution. However, the necessity of an intervening oxidation to a sulfone intermediate (III) has not been resolved, and the photodegradation products of II have not been identified. Using GC-MS, HPLC-UV/vis, electrospray MS, (19)F NMR, and GC-TSD, our objective was to characterize the photodegradation pathways of I, which would clarify the role of III, identify products of II, and explain unbalanced mass accounts in previous studies. Findings showed that II is formed directly and photochemically from I, confirmed by the greater stability of III (t(1/2) 112 h), and that successive oxidations of I to III and then a sulfonate (IV) comprise a second pathway. Compound II underwent photodechlorination, substitution of chlorine by trifluoromethyl, and pyrazole ring cleavage. This work is significant to understanding the photochemistry of novel phenylpyrazole pesticides in the environment.     

Aqueous photolysis of niclosamide

The photodegradation of [(14)C]niclosamide was studied in sterile, pH 5, 7, and 9 buffered aqueous solutions under artificial sunlight at 25.0 +/- 1.0 degrees C. Photolysis in pH 5 buffer is 4.3 times faster than in pH 9 buffer and 1.5 times faster than in pH 7 buffer. In the dark controls, niclosamide degraded only in the pH 5 buffer. After 360 h of continuous irradiation in pH 9 buffer, the chromatographic pattern of the degradates was the same regardless of which ring contained the radiolabel. An HPLC method was developed that confirmed these degradates to be carbon dioxide and two- and four-carbon aliphatic acids formed by cleavage of both aromatic rings. Carbon dioxide was the major degradate, comprising approximately 40% of the initial radioactivity in the 360 h samples from both labels. The other degradates formed were oxalic acid, maleic acid, glyoxylic acid, and glyoxal. In addition, in the chloronitroaniline-labeled irradiated test solution, 2-chloro-4-nitroaniline was observed and identified after 48 h of irradiation but was not detected thereafter. No other aromatic compounds were isolated or observed in either labeled test system.     

Metabolism of fungicide diethofencarb in grape (Vitis vinifera L.): definitive identification of thiolactic acid conjugated metabolites

The metabolic fate of diethofencarb (isopropyl 3,4-diethoxycarbanilate) separately labeled with (14)C at the phenyl ring and 2-position of the isopropyl moiety was studied in grape (Vitis vinifera L.). The acetonitrile solution of (14)C-diethofencarb at a rate of 500 g a.i. ha(-)(1) was once applied topically to fruits or leaves at the maturity stage of fruits (PHI 35 days), and the plants were grown in the greenhouse until harvest. In the grape plants, diethofencarb was scarcely translocated to the untreated portion and was degraded more in the fruit as compared to the leaf. For the fruit, diethofencarb primary underwent O-deethylation at the 4-position of the phenyl ring to form the phenolic derivative, isopropyl 3-ethoxy-4-hydroxycarbanilate (0.9% of the total radioactive residue, TRR). This metabolite was successively transformed via conjugation with glucose at the phenolic hydroxy group (8.1-18.1% TRR) or with thiolactic acid at the 5-position of the phenyl ring (1.5-1.7% TRR). The thiolactic acid conjugate was further metabolized mainly to two different types of glucose conjugates at the 4-position of the phenyl ring (8.7-13.5% TRR) and the hydroxy group in the thiolactic acid moiety (6.4-7.3% TRR), as evidenced by (1)H NMR and atmospheric pressure chemical ionization-liquid chromatography-mass spectrometry together with cochromatographies with synthetic standards.     

TiO2-Assisted Photodegradation of Direct Blue 78 in Aqueous Solution in Sunlight

The photodegradation of azo dyes aqueous solution has been investigated using TiO₂ as catalyst in sunlight. The effect of amount of catalyst, concentration of dye, and pH value on the degradation of Direct Blue 78 was observed. A complete degradation of 100 mg/L Direct Blue 78 solution under solar irradiation was achieved in 6 h at pH?3.0, dosage of TiO₂ 1.0 g/L. A possible pathway for the photodegradation of Direct Blue 78 in sunlight was proposed.     

Thiol-quinone adduct formation in myofibrillar proteins detected by LC-MS

Protein oxidation in meat is considered to decrease meat tenderness due to protein disulfide cross-link formation of thiol-containing amino acid residues. An LC-MS method for detection of thiol-quinone adducts (RS-QH(2)) in myofibrillar proteins was developed to investigate the interaction between phenols, as protective antioxidants, and proteins from meat under oxidative conditions using aqueous solutions of (i) cysteine (Cys), (ii) glutathione (GSH), (iii) bovine serum albumin (BSA), or (iv) a myofibrillar protein isolate (MPI). The aqueous solutions were incubated at room temperature (30 min) with 4-methyl-1,2-benzoquinone (4MBQ) prepared from oxidation of 4-methylcatechol (4MC) by periodate resin or incubated at room temperature (5 h) with 4MC and Fe(II)/H(2)O(2). GSH, BSA, and MPI were hydrolyzed (6 N HCl, 110 °C, 22 h) after incubation, and the cysteine-quinone adduct, Cys-QH(2) (m/z 244.2) was identified according to UV and mass spectra after separation on an RP-C18 column. The thiol-quinone adduct was present in all thiol systems after incubation with 4MBQ or 4MC oxidized by Fe(II)/H(2)O(2). Direct reaction with 4MBQ resulted in each case in increased Cys-QH(2) formation compared to simultaneous oxidation of thiol source and 4MC with Fe(II)/H(2)O(2). The covalent bonds between quinones and thiol groups may act as a potential antioxidant by inhibiting disulfide protein cross-link formation.     

EPR spectra of humic acids and their metal complexes

On the basis of ESR spectra, humic substances are believed to be hydroquinone type polymer radicals with considerable cation exchange and redox capacity. All 3d-transition metal humates appear to be ionic high spin complexes. Manganese (II) ions doped in raw peats and peat humic acids are coordinated octahedrally with six oxygen-containing functional groups, e.g., carboxylate, phenolic, hydroxyl, carbonyl ligands, whereas copper (II) ions are in square planar arrangement with two carboxylate and two aliphatic nitrogen ligands. Doping with vanadyl(II) ions results in a square pyramidal arrangement with four oxygen-containing ligands. Diamagnetic manganese(VII), chromium(VI), molybdenum (VI) and vanadium(V) oxoanions in acidic solution are reduced by humic acids into paramagnetic manganese(II), chromium(III), molybdenum(V) and vanadium(IV) ions. Diamagnetic copper(I) ions, on the other hand, are oxidized by humic acids into paramagnetic copper(II) ions.In contrast to polyronic acid gels with outer-sphere structure, 3d-transition metal ions are generally bound to humic acids as inner-sphere chelate complexes.     

TiO<Subscript>2</Subscript> photocatalytic degradation of 4-chlorobiphenyl as affected by solvents and surfactants

Purpose  

TiO₂ photocatalytic degradation of 4-chlorobiphenyl (PCB3) in aqueous solution under UV irradiation was investigated as affected by different environmental factors, including initial PCB3 concentration, TiO₂ content, UV intensity, H₂O₂ concentration, cosolvents, and surfactants.     

Behaviour of Reduction–Sorption of Chromium (Vi) from an Aqueous Solution on a Modified Sorbent from Rice Husk

A carbonaceous sorbent produced from rice husk via sulphuric acid treatment was used to remove Cr(VI) from aqueous solutions varying contact time, pH, Cr(VI) concentration and sorbent status (wet and dry). Cr(VI) was removed from the aqueous solution via reduction to Cr(III) and sorption. Reduction and sorption processes were investigated in terms of kinetics and equilibrium. The rate of reduction removal of Cr(VI) at pH 2 followed a pseudo first-order model while the rate of sorption of total chromium followed pseudo second-order model. Chromium sorption was highly dependent on the initial pH value with reduction taking place in solution with pH up to 7 showing sorption maxima in the pH range 1.8–2.8 for concentration range 100–500 mg/l with an increase in the equilibrium pH. Carbon dioxide evolved from the sorption media was determined. Reduction–sorption mechanism was investigated via physicochemical tests including cation exchange capacity, base neutralization and sorbent acidity in addition to FTIR studies for sorbent samples before and after sorption reaction.     

Influence of environmental conditions on the stability of oil in water emulsions containing droplets stabilized by lecithin-chitosan membranes

Oil-in-water emulsions containing cationic droplets stabilized by lecithin-chitosan membranes were produced using a two-stage process. A primary emulsion containing anionic lecithin-coated droplets was prepared by homogenizing oil and emulsifier solution using a high-pressure valve homogenizer (5 wt % corn oil, 1 wt % lecithin, 100 mM acetic acid, pH 3.0). A secondary emulsion containing cationic lecithin-chitosan-coated droplets was formed by diluting the primary emulsion with an aqueous chitosan solution (1 wt % corn oil, 0.2 wt % lecithin, 100 mM acetic acid, and 0.036 wt % chitosan). The stabilities of the primary and secondary emulsions with the same oil concentration to thermal processing, freeze-thaw cycling, high calcium chloride concentrations, and lipid oxidation were determined. The results showed that the secondary emulsions had better stability to droplet aggregation during thermal processing (30-90 degrees C for 30 min), freeze-thaw cycling (-10 degrees C for 22 h/30 degrees C for 2 h), and high calcium chloride contents (相似文献   

Direct methylation procedure for converting fatty amides to fatty acid methyl esters in feed and digesta samples

Two direct methylation procedures often used for the analysis of total fatty acids in biological samples were evaluated for their application to samples containing fatty amides. Methylation of 5 mg of oleamide (cis-9-octadecenamide) in a one-step (methanolic HCl for 2 h at 70 degrees C) or a two-step (sodium methoxide for 10 min at 50 degrees C followed by methanolic HCl for 10 min at 80 degrees C) procedure gave 59 and 16% conversions of oleamide to oleic acid, respectively. Oleic acid recovery from oleamide was increased to 100% when the incubation in methanolic HCl was lengthened to 16 h and increased to 103% when the incubation in methoxide was modified to 24 h at 100 degrees C. However, conversion of oleamide to oleic acid in an animal feed sample was incomplete for the modified (24 h) two-step procedure but complete for the modified (16 h) one-step procedure. Unsaturated fatty amides in feed and digesta samples can be converted to fatty acid methyl esters by incubation in methanolic HCl if the time of exposure to the acid catalyst is extended from 2 to 16 h.     

Preparation of High Surface Area Oxidized Activated Carbon from Peanut Shell and Application for the Removal of Organic Pollutants and Heavy Metal Ions

A peanut shell-derived oxidized activated carbon (OAC) with high surface area was prepared by zinc chloride (ZnCl₂) chemical activation and subsequent nitric acid oxidation. OAC was characterized by scanning electron microscope (SEM), Fourier transform infrared spectroscopy (FT-IR), and N₂ adsorption-desorption. The results showed that OAC had the surface area of 1807 m² g^?1, with the total pore volume of 0.725 cm³ g^?1 and average pore diameter of 3.8 nm. More importantly, when OAC acted as an adsorbent, it exhibited high efficiency to remove basic blue 41 (BB-41), congo red (CR), phenol, Cr(VI), and Pb(II) from aqueous solution due to its universality in adsorption. Batch adsorption experiments were carried out to study the effect of various parameters such as pH, initial concentration, temperature, and contact time. Also, the isotherms, kinetic models, and thermodynamics of adsorption process were investigated. The equilibrium data for CR and Pb(II) were fitted to Langmuir isotherm model, while Freundlich model was suitable for the equilibrium isotherm of BB-41, phenol, and Cr(VI), respectively. As the result indicated, peanut shell was a suitable raw material to synthesize OAC which could be employed as an efficient and universal adsorbent for removing organic pollutants and heavy metal ions from wastewater.     

Photodegradation of the herbicide imazethapyr in aqueous solution: effects of wavelength, pH, and natural organic matter (NOM) and analysis of photoproducts

The photodegradation of imazethapyr, 5-ethyl-2-(4-isopropyl-4-methyl-5-oxo-4,5-dihydroimidazol-1H-3-yl)nicotinic acid, has been investigated in phosphate buffers and in buffered solutions containing natural organic matter (NOM). Imazethapyr degrades most quickly under 253.7 nm light and at pH values >4. The presence of NOM in solution caused the reaction rate constants for the photodegradation to decrease, with higher concentrations of NOM having a larger effect. Calculations suggest light screening is the major effect of the NOM. Seven photoproducts have been identified, and a photodegradation mechanism is proposed.     

Structural elucidation of phototransformation products of azimsulfuron in water

The photodegradation of the sulfonylurea herbicide azimsulfuron, N-[[(4,6-dimethoxypyrimidin-2-yl)amino]carbonyl]-1-methyl-4-(2-methyl-2H-tetrazole-5-yl)-1H-pyrazole-5-sulfonamide (AZS), was studied in water at different wavelengths and in the presence of photocatalysts. AZS was rapidly degraded by UV light, affording three photoproducts. The main product, accounting for about 70% of photodegraded herbicide, was identified as 6-amino-5-[(4,6-dimethoxypyrimidin-2-yl)methylamino]-1,5,6,8-tetrahydro-7-oxa-8lambda(6)-tia-1,2,5,6-tetraza-azulen-4-one (ADTA) by single-crystal X-ray diffraction. With simulated sunlight irradiation, the reaction was slower and 2-amino-4,6-dimethoxypyrimidine (DPA) and 1-methyl-4-(2-methyl-2H-tetrazole-5-yl)-1H-pyrazole-5-sulfonamide (MPS), arising from a photohydrolytic cleavage of the sulfonylurea bridge, were the only byproducts observed. The reactions followed first-order kinetics. The addition of dissolved organic matter (DOM) did not modify significantly the AZS photodegradation rate. The presence of Fe2O3 accelerated more than twice the reaction rate affording two major products, DPA and MPS, together with minor amounts of N-[[(5-hydroxy-4,6-dimethoxypyrimidin-2-yl)amino]carbonyl]-1-methyl-4-(2-methyl-2H-tetrazole-5-yl)-1H-pyrazole-5-sulfonamide (AZS-OH). The greatest degradation rate was detected in the presence of TiO2. Only the photohydroxylation product AZS-OH was observed, which was transformed rapidly into oxalic acid.     

影响土壤中铬, 锰的氧化还原反应的环境因素

Disposal of chromium(Cr) hexavalent form,Cr(VI),in soils as additions in organic fertilizers,liming materials or plant nutrient sources can be dangerous since Cr(VI) can be highly toxic to plants,animals,and humans.In order to explore soil conditions that lead to Cr(VI) generation,this study were performed using a Paleudult(Dystic Nitosol) from a region that has a high concentration of tannery operations in the Rio Grande do Sul State,southern Brazil.Three laboratory incubation experiments were carried out to examine the influences of soil moisture content and concentration of cobalt and organic matter additions on soil Cr(VI) formation and release and manganese(Mn) oxide reduction with a salt of chromium chloride(CrCl 3) and tannery sludge as inorganic and organic sources of Cr(III),respectively.The amount of Cr(III) oxidation depended on the concentration of easily reducible Mn oxides and the oxidation was more intense at the soil water contents in which Mn(III/IV) oxides were more stable.Soluble organic compounds in soil decreased Cr(VI) formation due to Cr(III) complexation.This mechanism also resulted in the decrease in the oxidation of Cr(III) due to the tannery sludge additions.Chromium(III) oxidation to Cr(VI) at the solid/solution interface involved the following mechanisms:the formation of a precursor complex on manganese(Mn) oxide surfaces,followed by electron transfer from Cr(III) to Mn(III or IV),the formation of a successor complex with Mn(II) and Cr(VI),and the breakdown of the successor complex and release of Mn(II) and Cr(VI) into the soil solution.