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Dehalogenation

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https://www.readbyqxmd.com/read/28530808/%C3%AE-halo-amides-as-competent-latent-enolates-direct-cata-lytic-asymmetric-mannich-type-reaction
#1
Bo Sun, Pandur Venkatesan Balaji, Naoya Kumagai, Masakatsu Shibasaki
α-Halogenated carbonyl compounds are susceptible to dehalogenation and thus largely neglected as enolate precursors in catalytic enantioselective C-C bond forming reactions. By merging the increased stability of the α-C-halogen bond of amides and the direct enolization methodology of the designed amide, we explored a direct catalytic asymmetric Mannich-type reaction of α-halo 7-azaindoline amides with N-carbamoyl imines. All α-halo sub-stituents, α-F, -Cl, -Br, -I amides, were tolerated to provide the Mannich-adducts in a highly stereoselective manner without undesirable dehalogenation...
May 22, 2017: Journal of the American Chemical Society
https://www.readbyqxmd.com/read/28521164/biotransformation-of-hexabromocyclododecanes-with-hexachlorocyclohexane-transforming-sphingobium-chinhatense-strain-ip26
#2
Norbert V Heeb, Andreas Grubelnik, Birgit Geueke, Hans-Peter E Kohler, Peter Lienemann
Bacterial evolution has resulted in the appearance of several Sphingomonadacea strains that gained the ability to metabolize hexachlorocyclohexanes (HCHs). HCHs have been widely used as pesticides but were banned under the Stockholm Convention on persistent organic pollutants (POPs) in 2009. Here we present evidence for bacterial transformation reactions of hexabromocyclododecanes (HBCDs), which are structurally related to HCHs. HBCDs were used as flame retardants. They are now also considered as POPs and their production and use is restricted since 2013...
May 11, 2017: Chemosphere
https://www.readbyqxmd.com/read/28499743/resolution-of-the-uncertainty-in-the-kinetic-mechanism-for-the-trans-3-chloroacrylic-acid-dehalogenase-catalyzed-reaction
#3
Jamison P Huddleston, Susan C Wang, Kenneth A Johnson, Christian P Whitman
trans- and cis-3-Chloroacrylic acid dehalogenase (CaaD and cis-CaaD, respectively) catalyze the hydrolytic dehalogenation of their respective isomers and represent key steps in the bacterial conversion of 1,3-dichloropropene to acetaldehyde. In prior work, a kinetic mechanism for the CaaD-catalyzed reaction could not be unequivocally determined because (1) the order of product release could not be determined and (2) the fluorescence factor for the enzyme species, E*PQ (where P = bromide and Q = malonate semialdehyde, the two products of the reaction) could not be assigned...
May 9, 2017: Archives of Biochemistry and Biophysics
https://www.readbyqxmd.com/read/28463483/a-field-trial-of-tce-phytoremediation-by-genetically-modified-poplars-expressing-cytochrome-p450-2e1
#4
Emily K Legault, C Andrew James, Keith Stewart, Indulis Muiznieks, Sharon L Doty, Stuart E Strand
A controlled field study was performed to evaluate the effectiveness of transgenic poplars for phytoremediation in a field setting. Three hydraulically contained test beds were planted with twelve transgenic poplars, twelve wild type (WT) poplars, or left unplanted, and dosed with equivalent amounts of trichloroethylene (TCE). Degradation of TCE was enhanced in the transgenic tree bed, but not to the extent of the enhanced removal observed in laboratory studies. Total chlorinated ethene removal was 87% in the CYP2E1 bed, 85% in the WT bed, and 34% in the unplanted bed in 2012...
May 2, 2017: Environmental Science & Technology
https://www.readbyqxmd.com/read/28431360/contrasting-dual-c-cl-isotope-fractionation-offers-potential-to-distinguish-reductive-chloroethene-transformation-from-breakdown-by-permanganate
#5
Eylem Doğan-Subaşı, Martin Elsner, Shiran Qiu, Stefan Cretnik, Siavash Atashgahi, Orfan Shouakar-Stash, Nico Boon, Winnie Dejonghe, Leen Bastiaens
cis-1,2-Dichloroethene (cis-DCE) and trichloroethene (TCE) are persistent, toxic and mobile pollutants in groundwater systems. They are both conducive to reductive dehalogenation and to oxidation by permanganate. In this study, the potential of dual element (C, Cl) compound specific isotope analyses (CSIA) for distinguishing between chemical oxidation and anaerobic reductive dechlorination of cis-DCE and TCE was investigated. Well-controlled cis-DCE degradation batch tests gave similar carbon isotope enrichment factors εC (‰), but starkly contrasting dual element isotope slopes Δδ(13)C/Δδ(37)Cl for permanganate oxidation (εC=-26‰±6‰, Δδ(13)C/Δδ(37)Cl≈-125±47) compared to reductive dechlorination (εC=-18‰±4‰, Δδ(13)C/Δδ(37)Cl≈4...
April 18, 2017: Science of the Total Environment
https://www.readbyqxmd.com/read/28425677/microbial-dehalogenation-an-annotated-selection-of-world-wide-web-sites-relevant-to-the-topics-in-environmental-microbiology
#6
Lawrence P Wackett
No abstract text is available yet for this article.
April 20, 2017: Environmental Microbiology
https://www.readbyqxmd.com/read/28424844/microbial-reductive-dehalogenation-of-trihalomethanes-by-a-dehalobacter-containing-co-culture
#7
Siyan Zhao, Matthew J Rogers, Jianzhong He
Trihalomethanes such as chloroform and bromoform, although well-known as a prominent class of disinfection by-products, are ubiquitously distributed in the environment due to widespread industrial usage in the past decades. Chloroform and bromoform are particularly concerning, of high concentrations detected and with long half-lives up to several hundred days in soils and groundwater. In this study, we report a Dehalobacter- and Desulfovibrio-containing co-culture that exhibits dehalogenation of chloroform (~0...
April 19, 2017: Applied Microbiology and Biotechnology
https://www.readbyqxmd.com/read/28421054/isolation-and-characterization-of-dehalobacter-sp-strain-tecb1-including-identification-of-tcba-a-novel-tetra-and-trichlorobenzene-reductive-dehalogenase
#8
Ricardo Alfán-Guzmán, Haluk Ertan, Mike Manefield, Matthew Lee
Dehalobacter sp. strain TeCB1 was isolated from groundwater near Sydney, Australia, that is polluted with a range of organochlorines. The isolated strain is able to grow by reductive dechlorination of 1,2,4,5-tetrachlorobenzene to 1,3- and 1,4-dichlorobenzene with 1,2,4-trichlorobenzene being the intermediate daughter product. Transient production of 1,2-dichlorobenzene was detected with subsequent conversion to monochlorobenzene. The dehalogenation capability of strain TeCB1 to respire 23 alternative organochlorines was examined and shown to be limited to the use of 1,2,4,5-tetrachlorobenzene and 1,2,4-trichlorobenzene...
2017: Frontiers in Microbiology
https://www.readbyqxmd.com/read/28391934/enhanced-debromination-of-4-bromophenol-by-the-uv-sulfite-process-efficiency-and-mechanism
#9
Bihuang Xie, Xuchun Li, Xianfeng Huang, Zhe Xu, Weiming Zhang, Bingcai Pan
Halogenated aromatic compounds have attracted increasing concerns due to their toxicity and persistency in the environment, and dehalogenation is one of the promising treatment and detoxification methods. Herein, we systematically studied the debromination efficiency and mechanism of para-bromophenol (4-BP) by a recently developed UV/sulfite process. 4-BP underwent rapid degradation with the kinetics accelerated with the increasing sulfite concentration, pH (6.1-10) and temperature, whereas inhibited by dissolved oxygen and organic solvents...
April 2017: Journal of Environmental Sciences (China)
https://www.readbyqxmd.com/read/28378313/microbial-degradation-of-chloroethenes-a-review
#10
Iva Dolinová, Martina Štrojsová, Miroslav Černík, Jan Němeček, Jiřina Macháčková, Alena Ševců
Contamination by chloroethenes has a severe negative effect on both the environment and human health. This has prompted intensive remediation activity in recent years, along with research into the efficacy of natural microbial communities for degrading toxic chloroethenes into less harmful compounds. Microbial degradation of chloroethenes can take place either through anaerobic organohalide respiration, where chloroethenes serve as electron acceptors; anaerobic and aerobic metabolic degradation, where chloroethenes are used as electron donors; or anaerobic and aerobic co-metabolic degradation, with chloroethene degradation occurring as a by-product during microbial metabolism of other growth substrates, without energy or carbon benefit...
April 5, 2017: Environmental Science and Pollution Research International
https://www.readbyqxmd.com/read/28347952/anaerobic-biodegradation-of-emerging-organic-contaminants-in-the-aquatic-environment
#11
REVIEW
Ann-Kathrin Ghattas, Ferdinand Fischer, Arne Wick, Thomas A Ternes
Although strictly anaerobic conditions prevail in several environmental compartments, up to now, biodegradation studies with emerging organic contaminants (EOCs), such as pharmaceuticals and personal care products, have mainly focused on aerobic conditions. One of the reasons probably is the assumption that the aerobic degradation is more energetically favorable than degradation under strictly anaerobic conditions. Certain aerobically recalcitrant contaminants, however, are biodegraded under strictly anaerobic conditions and little is known about the organisms and enzymatic processes involved in their degradation...
June 1, 2017: Water Research
https://www.readbyqxmd.com/read/28314194/electrocatalytic-reduction-of-low-concentration-thiamphenicol-and-florfenicol-in-wastewater-with-multi-walled-carbon-nanotubes-modified-electrode
#12
Dongli Deng, Fei Deng, Bobin Tang, Jinzhong Zhang, Jiang Liu
The electrocatalytic reduction of thiamphenicol (TAP) and florfenicol (FF) was investigated with multi-walled carbon nanotubes (MWCNTs) modified electrode. MWCNTs was dispersed in pure water with the assistance of dihexadecyl phosphate (DHP), and then modified on glassy carbon electrode (GCE). The electrocatalytic reduction conditions, such as bias voltage, supporting electrolyte and its initial pH, and the initial concentrations of TAP and FF, were also optimized. The experimental results indicated that the removal efficiencies of 2mgL(-1) TAP and FF in 0...
March 7, 2017: Journal of Hazardous Materials
https://www.readbyqxmd.com/read/28294243/initiating-radical-reactions-with-non-thermal-plasmas
#13
Yury Gorbanev, Dirk Leifert, Armido Studer, Deborah O'Connell, Victor Chechik
Non-thermal plasmas were used as radical initiators in three radical chain reactions: dehalogenation, 5-exo-trig cyclisation and trifluoromethylation with the Togni II reagent. The use of non-volatile solvents (or solvent-free conditions) gave high yields in all reactions under optimised conditions. Short reaction times and mild conditions make this method an attractive alternative to conventional radical initiators.
March 15, 2017: Chemical Communications: Chem Comm
https://www.readbyqxmd.com/read/28282120/general-and-efficient-c-c-bond-forming-photoredox-catalysis-with-semiconductor-quantum-dots
#14
Jill A Caputo, Leah C Frenette, Norman Zhao, Kelly L Sowers, Todd D Krauss, Daniel J Weix
Photoredox catalysis has become an essential tool in organic synthesis because it enables new routes to important molecules. However, the best available molecular catalysts suffer from high catalyst loadings and rely on precious metals. Here we show that colloidal nanocrystal quantum dots (QDs) can serve as efficient and robust, precious-metal free, photoassisted redox catalysts. A single-sized CdSe quantum dot (3.0 ± 0.2 nm) can replace several different dye catalysts needed for five different photoredox reactions (β-alkylation, β-aminoalkylation, dehalogenation, amine arylation, and decarboxylative radical formation)...
March 16, 2017: Journal of the American Chemical Society
https://www.readbyqxmd.com/read/28281345/singlet-versus-triplet-excited-state-mediated-photoinduced-dehalogenation-reactions-of-itraconazole-in-acetonitrile-and-aqueous-solutions
#15
Ruixue Zhu, Ming-de Li, Lili Du, David Lee Phillips
Photoinduced dehalogenation of the antifungal drug itraconazole (ITR) in acetonitrile (ACN) and ACN/water mixed solutions was investigated using femtosecond and nanosecond time-resolved transient absorption (fs-TA and ns-TA, respectively) and nanosecond time-resolved resonance Raman spectroscopy (ns-TR(3)) experiments. An excited resonance energy transfer is found to take place from the 4-phenyl-4,5-dihydro-3H-1,2,4-triazol-3-one part of the molecule to the 1,3-dichlorobenzene part of the molecule when ITR is excited by ultraviolet light...
March 29, 2017: Journal of Physical Chemistry. B
https://www.readbyqxmd.com/read/28244752/amino-acid-assisted-dehalogenation-of-carbon-tetrachloride-by-green-rust-inhibition-of-chloroform-production
#16
Weizhao Yin, Bjarne W Strobel, Hans Christian B Hansen
Layered Fe(II)-Fe(III) hydroxides (green rusts, GRs) are promising reactants for reductive dechlorination of chlorinated solvents due to high reaction rates and the opportunity to inject reactive slurries of the compounds into contaminant plumes. However, it is necessary to develop strategies that reduce the formation of toxic byproducts such as chloroform (CF). In this study, carbon tetrachloride (CT) dehalogenation by the chloride form of GR (GRCl) was tested in the presence of glycine (GLY) and other selected amino acids...
March 13, 2017: Environmental Science & Technology
https://www.readbyqxmd.com/read/28217790/nanotribological-properties-of-nanostructured-poly-cysteine-methacrylate-brushes
#17
Omed Al-Jaf, Abdullah Alswieleh, Steven P Armes, Graham J Leggett
The nanomechanical properties of zwitterionic poly(cysteine methacrylate) (PCysMA) brushes grown from planar surfaces by atom transfer radical polymerisation have been characterised by friction force microscopy (FFM). FFM provides quantitative insights into polymer structure-property relationships and in particular illuminates the dependence of brush swelling on chain packing in nanostructured materials. In ethanol, which is a poor solvent for PCysMA, a linear friction-load relationship is observed, indicating that energy dissipation occurs primarily through ploughing...
February 20, 2017: Soft Matter
https://www.readbyqxmd.com/read/28213734/dehalococcoides-and-general-bacterial-ecology-of-differentially-trichloroethene-dechlorinating-flow-through-columns
#18
Babur S Mirza, Darwin L Sorensen, Daniel J McGlinn, R Ryan Dupont, Joan E McLean
The diversity of Dehalococcoides mccartyi (Dhc) and/or other organohalide respiring or associated microorganisms in parallel, partial, or complete trichloroethene (TCE) dehalogenating systems has not been well described. The composition of Dhc populations and the associated bacterial community that developed over 7.5 years in the top layer (0-10 cm) of eight TCE-fed columns were examined using pyrosequencing. Columns biostimulated with one of three carbon sources, along with non-stimulated controls, developed into complete (ethene production, whey amended), partial (cis-dichloroethene (DCE) and VC, an emulsified oil with nonionic surfactant), limited (<5 % cis-DCE and 95 % TCE, an emulsified oil), and non- (controls) TCE dehalogenating systems...
February 17, 2017: Applied Microbiology and Biotechnology
https://www.readbyqxmd.com/read/28191945/engineered-surface-immobilized-enzyme-that-retains-high-levels-of-catalytic-activity-in-air
#19
Somayesadat Badieyan, Qiuming Wang, Xingquan Zou, Yaoxin Li, Maggie Herron, Nicholas L Abbott, Zhan Chen, E Neil G Marsh
In the absence of aqueous buffer, most enzymes retain little or no activity; however, "water-free" enzymes would have many diverse applications. Here, we describe the chemically precise immobilization of an enzyme on an engineered surface designed to support catalytic activity in air at ambient humidity. Covalent immobilization of haloalkane dehalogenase on a surface support displaying poly(sorbitol methacrylate) chains resulted in ∼40-fold increase in activity over lyophilized enzyme powders for the gas-phase dehalogenation of 1-bromopropane...
February 16, 2017: Journal of the American Chemical Society
https://www.readbyqxmd.com/read/28191552/a-common-mechanism-for-coenzyme-cobalamin-dependent-reductive-dehalogenases
#20
Linus O Johannissen, David Leys, Sam Hay
Distinct mechanisms have been proposed for the biological dehalogenation catalyzed by cobalamin-dependent enzymes, with two recent crystallographic studies suggesting different mechanisms based on the observed interaction between the organohalide substrate and cobalamin. In one case, involving an aromatic dibromide substrate in NpRdhA, a novel Co(II)-Br interaction was observed using EPR, suggesting a mechanism involving a [CoXR] adduct. However, in the case of trichloroethylene in PceA, a significantly longer Co-Cl distance was observed in X-ray crystal structures, suggesting a dissociative electron transfer mechanism...
February 22, 2017: Physical Chemistry Chemical Physics: PCCP
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