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Query: EC:3.4.15.1 (ACE)
 18,300 document(s) hit in 31,850,051 MEDLINE articles (0.00 seconds)

Reductive dehalogenation of 2,4,6-trichlorophenol (2,4,6-TCP) by two types of high carbon iron filings (HCIF), HCIF-1 and HCIF-2 was studied in batch reactors. While the iron, copper, manganese and carbon content of the two types of HCIF was similar, the specific surface area of HCIF-1 and HCIF-2 were 1.944 and 3.418m(2)g(-1), respectively. During interaction with HCIF-1, 2,4,6-TCP adsorbed on HCIF-1 surface resulting in rapid reduction of aqueous phase 2,4,6-TCP concentration. However, reductive dehalogenation of 2,4,6-TCP was negligible. During interaction between 2,4,6-TCP and HCIF-2, both 2,4,6-TCP adsorption on HCIF-2, and 2,4,6,-TCP dechlorination was observed. 2,4,6-TCP partitioning between solid and aqueous phase could be described by a Freundlich isotherm, while 2,4,6-TCP dechlorination could be described by an appropriate rate expression. A mathematical model was developed for describing the overall interaction of 2,4,6-TCP with HCIF-2, incorporating simultaneous adsorption/desorption and dechlorination reactions of 2,4,6-TCP with the HCIF surface. 2,4-Dichlorophenol (2,4-DCP), 2-chlorophenol (2-CP) and minor amounts of 4-chlorophenol (4-CP) evolved as 2,4,6-TCP dechlorination by-products. The evolved 2,4-DCP partitioned strongly to the HCIF surface. 4-CP and 2-CP accumulated in the aqueous phase. No transformation of 2-CP or 4-CP to phenol was observed.
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PMID:Interaction of 2,4,6-trichlorophenol with high carbon iron filings: Reaction and sorption mechanisms. 1883 19

The sorption behaviour of 2,4-dichlorophenol (2,4-DCP), 2,4,6-trichlorophenol (2,4,6-TCP), 2,3,4,5-tetrachlorophenol (2,3,4,5-TeCP) and pentachlorophenol (PCP) with an aquatic humic sorbent (HS) was examined in their single and mixed solutions at different acidities (pH 3, 5.5 and 7). The binding capacities and equilibrium coefficients (K(OC)) obtained were fairly close to the literature values but still underline HS's structural and steric influence on the sorption. The most acidic carboxylic (COOH) groups of the HS structure have unquestionably an essential role in the sorption. The amounts of different chlorophenols bound onto the constant quantity of the aquatic HS were in reality very low demonstrating that the amount of the dissolved organic carbon (DOC) in the environment plays a greater role than the value of K(OC). The ability of the aqueous phase to force chlorophenols to associate with the HS becomes at more neutral acidities weaker and weaker and other binding mechanisms become favoured in comparison to hydrogen or hydrophobic bonds. Sorption isotherms were constructed from sorption data, and conformity to a linear model, non-linear Freundlich equation and Langmuir equation was checked.
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PMID:Sorption behaviour of some chlorophenols in lake aquatic humic matter. 1896 25

In this work, a new kinetic method was proposed for quantification phenoxyl radicals generated in enzyme reaction. Instead of direct detecting the spectral signals of phenoxyl radicals, a molecular probe, the reduced form of nicotinamide adenine dinucleotide (NADH), was employed to indicate the formation of phenoxyl free radicals. It was found that the reactions of NADH and phenoxyl radicals are very fast, but can be followed by using stopped-flow fast scanning spectrophotometric technique. The initial rate of accelerated-oxidation of NADH represents the reactivity of phenoxyl free radical, which is proportional in a certain range to the initial concentration of the parent chlorophenols of the radicals. With this method, the phenoxyl radicals generated in oxidation reaction of chlorophenols (2-CP; 4-CP; 2,4-DCP; 2,4,6-TCP and 2,3,4,6-Tetra-CP) with hydrogen peroxide, catalyzed by horseradish peroxidase, were investigated. The method is highly sensitive. Phenoxyl radicals generated from as low as 1x10(-8)M 2,4-DCP, for example, can be readily detected with the proposed method. The results show that the reactivity of various phenoxyl radicals are in the following order: 2,4-DCP>4-CP>2-CP>2,4,6-TCP>2,3,4,6-Tetra-CP. A mechanism is proposed to explain the possible pathway of the probe reaction. The feasibility of this method was assessed by the determination of enzymatic generation of phenoxyl radicals in lake water samples.
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PMID:A new kinetic method for quantification phenoxyl free radicals. 1897 Jul 70

In this work, changes in superoxide dismutase (SOD), catalase (CAT) and guaiacol peroxidase (POD) activity were determined in the leaves of wheat (Triticum aestivum L.) exposed to 2,4-dichlorophenol (2,4-DCP) and pentachlorophenol (PCP). We analyzed the content of free phenols, the level of lipid peroxidation, and also the oxidation of dihydrorhodamine 123 by 2,4-DCP and PCP. Chlorophenols were spiked to soil in concentrations of 0.5 and 5.0 mg kg(-1). Plant seeds were raised in plastic pots containing soil at a temperature of 25 degrees C with a 16-h photoperiod and irradiance of 250 micromol m(-2) s(-1). The leaves were harvested on the third, sixth and twelfth days of the experiment. The inhibition of SOD activity in the leaves of wheat was observed for 2,4-DCP and PCP. 2,4-DCP and PCP induced changes in CAT activity with a stronger effect for PCP. The compounds markedly increased guaiacol POD activity during 12d of the exposition of wheat to their action. The increase in free phenol content was observed both for 2,4-DCP and PCP. Chlorophenols also induced a powerful lipid peroxidation process between the third and sixth days of the experiment. A higher concentration of chlorophenols used in our study induced greater changes in all of the investigated parameters. 2,4-DCP and PCP oxidized the fluorescent probe - dihydrorhodamine 123 - in the concentrations of 5 and 1 ppm, respectively, and the addition of magnesium ions enhanced the oxidative capacity of the examined xenobiotics.
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PMID:Chlorophenols induce lipid peroxidation and change antioxidant parameters in the leaves of wheat (Triticum aestivum L.). 1902 88

The molecularly imprinted bulk polymer with 2,4,6-trichlorophenol (2,4,6-TCP) as the template molecule and methylacrylic acid (MAA), ethylene glycol dimethacrylate (EGDMA) as functional monomer and the crosslinker, respectively, has been prepared and applied to the molecularly imprinted solid-phase extraction (MISPE) procedure for selective preconcentration of phenolic compounds from environmental water samples. Various parameters affecting the extraction efficiency of the polymer have been evaluated to optimize the selective preconcentration of the phenolic compounds from aqueous samples. The characteristics of the MISPE method were validated by HPLC. The recoveries ranged between 90% and 98% (RSD: 0.9-2.3%, n=3) for tap water, between 85% and 105% (RSD: 2.6-4.9%, n=3) for river water, between 78% and 98% (RSD: 2.6-5.4%, n=3) for sewage water fortified with 0.4 mg L(-1) of phenol, 4-chlorophenol (4-CP), 2,4-dichlorophenol (2,4-DCP), pentachlorophenol (PCP). It was demonstrated that this MISPE-HPLC method could be applied to direct preconcentration and determination of phenolic compounds in environmental water samples.
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PMID:Molecularly imprinted solid-phase extraction combined with high performance liquid chromatography for analysis of phenolic compounds from environmental water samples. 1923 52

The composition and evolution of a brushite-type calcium phosphate cement was investigated by Solid-State NMR and X-ray during the setting process. The cement is obtained by mixing beta-tricalcium phosphate [Ca(3)(PO(4))(2), beta-TCP] and monocalcium phosphate monohydrate [Ca(H(2)PO(4))(2).H(2)O, MCPM] in presence of water, with formation of dicalcium phosphate dihydrate or brushite [CaHPO(2).2H(2)O, DCPD]. Analysis of the initial beta-TCP paste has shown the presence of beta-calcium pyrophosphate [Ca(2)P(2)O(7), beta-CPy] and that of the initial MCPM a mixture of MCPM and dicalcium phosphate [CaHPO(4), DCP]. Follow-up of the chemical composition by (31)P Solid-State NMR enables to show that the chemical setting process appeared to reach an end after 20 min. The constant composition observed at the end of the process was similarly determined.
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PMID:(31)P Solid-State NMR study of the chemical setting process of a dual-paste injectable brushite cements. 1936 21

A sample pretreatment method for the determination of 18 chlorophenols (CPs) in aqueous samples by derivatization liquid-phase microextraction (LPME) was investigated using gas chromatography-mass spectrometry. Derivatization reagent was spiked into the extraction solvent to combine derivatization and extraction into one step. High sensitivity of 18 CPs derivatives could be achieved after optimization of several parameters such as extraction solvent, percentage of derivatization reagent, extraction time, pH, and ionic strength. The results from the optimal method showed that calibration ranging from 0.5 to 500microgL(-1) could be achieved with the RSDs between 1.75% and 9.39%, and the limits of detection (LOD) are ranging from 0.01 to 0.12microgL(-1) for the CPs. Moreover, the proposed LPME method was compared with solid-phase microextraction (SPME) coupled with on-fiber derivatization technique. The results suggested that using both methods are quite agreeable. Furthermore, the recoveries of LPME evaluated by spiked environmental samples ranged from 87.9% (3,5-DCP) to 114.7% (2,3,5,6-TeCP), and environmental water samples collected from the Pearl River were analyzed with the optimized LPME method, the concentrations of 18 CPs ranged from 0.0237microgL(-1) (3,5-DCP) to 0.3623microgL(-1) (2,3,6-TCP).
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PMID:One-step extraction and derivatization liquid-phase microextraction for the determination of chlorophenols by gas chromatography-mass spectrometry. 1964 May 44

The molecularly imprinted polymer with 2,4,6-trichlorophenol (2,4,6-TCP) as the template molecule and methylacrylic acid (MAA), divinylbenzene (DVB) as functional monomer and the crosslinker, respectively, has been prepared and used as molecularly imprinted micro-solid phase extraction (MIMSPE) procedure for the selectively preconcentration of phenolic compounds from environmental water samples. Various parameters for the extraction efficiency of the MIMSPE have been evaluated. The optimized MIMSPE method allowed the extraction of the analytes from the sample matrix followed by a selective washing step using acetonitrile containing 0.3% (v/v) acetic acid. The characteristics of the MIMSPE method were valid by high performance liquid chromatography. The recoveries ranged between 88.9% and 102.5% for tap water, between 80.0% and 94.0% for river water, between 80.0% and 90.5% for sewage water fortified with 0.4 mg L(-1) of phenol, 4-chlorophenol (4-CP), 2,4-dichlorophenol (2,4-DCP), 2,4,6-TCP, pentachlorophenol (PCP) were obtained. This method has been successfully applied to preconcentrate and determine of phenolic compounds in environmental water samples directly.
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PMID:Molecularly imprinted polymer as micro-solid phase extraction combined with high performance liquid chromatography to determine phenolic compounds in environmental water samples. 1972 Jan 76

The degradation of 2-chlorophenol (2-CP), 2,4-dichlorophenol (2,4-DCP), 2,4,6-trichlorophenol (2,4,6-TCP) and pentachlorophenol (PCP) via biological, advanced oxidative process (AOP) and sequential biological-AOP was investigated in this work. The white-rot fungus Trametes pubescens was used for the biodegradation of chlorophenols, while in AOP TiO(2)/UV was used. In the biological degradation, the effect of glucose as a cofactor was also evaluated. The highest degradations were obtained when the reaction medium was supplemented with glucose, ranging from 94.6% to 37.8%, with degradation activity for 2-CP>2,4-DCP>PCP>2,4,6-TCP. During the AOP the removal initial rate increased in the following order 2-CP>2,4,6-TCP>2,4-DCP>PCP, and the obtained degradation range from 82.0% to 24.0%. When biological removal process, supplemented with glucose, was followed for an AOP process, 100% degradation was obtained for all the chlorophenols tested. These results suggest that the white-rot fungi T. pubescens could be used for the degradation of xenobiotic compounds, and its use with an advanced oxidative process, in a sequential mode, may be considered to obtain a complete removal of them.
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PMID:Degradation of chlorophenols by sequential biological-advanced oxidative process using Trametes pubescens and TiO(2)/UV. 2009 65

This study focuses on the homogeneous gas-phase formation of polychlorinated dibenzo-p-dioxins (PCDDs) and dibenzofurans (PCDFs) from the 2,4,6-trichlorophenol (2,4,6-TCP) and 2,4-dichlorophenol (2,4-DCP) precursors, which were found both in the gas phase and in the fly ash samples as the dominating chlorophenol congeners in municipal waste incinerators (MWIs). Molecular orbital theory calculations have been performed for the formation mechanism. The geometrical parameters and vibrational frequencies of all the stationary points were calculated at the MPWB1K level with the 6-31+G(d,p) basis set. Single-point energy calculations were carried out at the MPWB1K/6-311+G(3df,2p) level of theory. Canonical variational transition-state (CVT) theory with small curvature tunneling (SCT) contribution was used to predict the rate constants of crucial elementary steps over the temperature range of interest (600-1200 K). The rate-temperature formulas were fitted for the first time. The pre-exponential factor, the activation energy, and the rate constants are reported. This study shows that at least one chlorine substituent in the ortho position is needed for the formation of PCDDs from the condensation of chlorophenols. The results presented here should help to clarify and detail the formation mechanism of PCDD/PCDFs (PCDD/Fs for short) from chlorophenol precursors in real waste combustion.
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PMID:Quantum chemical and kinetic study on dioxin formation from the 2,4,6-TCP and 2,4-DCP precursors. 2038 Apr 13


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