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Dehalogenation

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https://www.readbyqxmd.com/read/28314194/electrocatalytic-reduction-of-low-concentration-thiamphenicol-and-florfenicol-in-wastewater-with-multi-walled-carbon-nanotubes-modified-electrode
#1
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
#2
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
#3
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 10, 2017: Journal of the American Chemical Society
https://www.readbyqxmd.com/read/28281345/singlet-versus-triplet-excited-state-mediated-photoin-duced-dehalogenation-reactions-of-itraconazole-in-acetonitrile-and-aqueous-solutions
#4
Ruixue Zhu, Ming-De Li, Lili Du, David Lee Phillips
The photoinduced dehalogenation of the antifungal drug Itraconazole in acetonitrile and acetonitrile/water mixed solutions was investigated using femtosecond and nanosecond time-resolved transient absorption (fs-TA and ns-TA) and nanosecond time-resolved resonance Raman spectroscopy (ns-TR3) experiments. An excited resonance energy transfer was 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 Itraconazole is excited by ultraviolet light...
March 10, 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
#5
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
#6
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
#7
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
#8
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
#9
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 13, 2017: Physical Chemistry Chemical Physics: PCCP
https://www.readbyqxmd.com/read/28186738/substrate-mediated-c-c-and-c-h-coupling-after-dehalogenation
#10
Huihui Kong, Sha Yang, Hongying Gao, Alexander Timmer, Jonathan P Hill, Oscar Díaz Arado, Harry Mönig, Xinyan Huang, Qin Tang, Qingmin Ji, Wei Liu, Harald Fuchs
Intermolecular C-C coupling after cleavage of C-X (mostly, X = Br or I) bonds has been extensively studied for facilitating the synthesis of polymeric nanostructures. However, the accidental appearance of C-H coupling at the terminal carbon atoms would limit the successive extension of covalent polymers. To our knowledge, the selective C-H coupling after dehalogenation has not so far been reported, which may illuminate another interesting field of chemical synthesis on surfaces besides in situ fabrication of polymers, i...
March 1, 2017: Journal of the American Chemical Society
https://www.readbyqxmd.com/read/28167430/vitamin-b12-in-the-spotlight-again
#11
REVIEW
Jennifer Bridwell-Rabb, Catherine L Drennan
The ability of cobalamin to coordinate different upper axial ligands gives rise to a diversity of reactivity. Traditionally, adenosylcobalamin is associated with radical-based rearrangements, and methylcobalamin with methyl cation transfers. Recently, however, a new role for adenosylcobalamin has been discovered as a light sensor, and a methylcobalamin-dependent enzyme has been identified that is suggested to transfer a methyl anion. Additionally, recent studies have provided a wealth of new information about a third class of cobalamin-dependent enzymes that do not appear to use an upper ligand...
February 3, 2017: Current Opinion in Chemical Biology
https://www.readbyqxmd.com/read/28157283/active-site-binding-is-not-sufficient-for-reductive-deiodination-by-iodotyrosine-deiodinase
#12
Nattha Ingavat, Jennifer M Kavran, Zuodong Sun, Steven E Rokita
The minimal requirements for substrate recognition and turnover by iodotyrosine deiodinase were examined to learn the basis for its catalytic specificity. This enzyme is crucial for iodide homeostasis and the generation of thyroid hormone in chordates. 2-Iodophenol binds only very weakly to the human enzyme and is dehalogenated with a kcat/Km that is more than 4 orders of magnitude lower than that for iodotyrosine. This discrimination likely protects against a futile cycle of iodinating and deiodinating precursors of thyroid hormone biosynthesis...
February 28, 2017: Biochemistry
https://www.readbyqxmd.com/read/28151464/preparation-of-visible-light-activated-metal-complexes-and-their-use-in-photoredox-nickel-dual-catalysis
#13
Christopher B Kelly, Niki R Patel, David N Primer, Matthieu Jouffroy, John C Tellis, Gary A Molander
Visible-light-activated photoredox catalysts provide synthetic chemists with the unprecedented capability to harness reactive radicals through discrete, single-electron transfer (SET) events. This protocol describes the synthesis of two transition metal complexes, [Ir{dF(CF3)2ppy}2(bpy)]PF6 (1a) and [Ru(bpy)3](PF6)2 (2a), that are activated by visible light. These photoredox catalysts are SET agents that can be used to facilitate transformations ranging from proton-coupled electron-transfer-mediated cyclizations to C-C bond constructions, dehalogenations, and H-atom abstractions...
March 2017: Nature Protocols
https://www.readbyqxmd.com/read/28145119/an-efficient-synthesis-of-%C3%A2-dehaloperophoramidine
#14
Anita Hoang, Kirill Popov, Peter Somfai
Perophoramidine and communesin F are structurally related indole alkaloids with an intriguing polycyclic core containing vicinal all-carbon quaternary stereocenters. Dehaloperophoramidine is a dehalogenated synthetic analogue of perophoramidine. Synthetic studies toward the total synthesis of dehaloperophoramidine have led to the discovery of two novel domino processes, the first encompassing four steps and resulting in the formation of an ortho-amide. A thorough study of the reactivity of the ortho-amide functionality revealed the second domino reaction and ultimately yielded the target molecule...
February 8, 2017: Journal of Organic Chemistry
https://www.readbyqxmd.com/read/28126048/dehalogenimonas-formicexedens-sp-nov-a-chlorinated-alkane-respiring-bacterium-isolated-from-contaminated-groundwater
#15
Trent A Key, Kimberly S Bowman, Imchang Lee, Jongsik Chun, Milton da Costa, Luciana Albuquerque, Fred A Rainey, William M Moe
A strictly anaerobic, Gram-stain-negative, non-spore-forming bacterium designated NSZ-14T, isolated from contaminated groundwater in Louisiana (USA), was characterized using a polyphasic approach. Strain NSZ-14T reductively dehalogenated a variety of polychlorinated aliphatic alkanes, producing ethene from 1,2-dichloroethane, propene from 1,2-dichloropropane, a mixture of cis- and trans-1,2-dichloroethene from 1,1,2,2-tetrachloroethane, vinyl chloride from 1,1,2-trichloroethane, and allyl chloride (3-chloro-1-propene) from 1,2,3-trichloropropane...
January 23, 2017: International Journal of Systematic and Evolutionary Microbiology
https://www.readbyqxmd.com/read/28106994/enzymatic-halogenation-and-dehalogenation-reactions-pervasive-and-mechanistically-diverse
#16
Vinayak Agarwal, Zachary D Miles, Jaclyn M Winter, Alessandra S Eustáquio, Abrahim A El Gamal, Bradley S Moore
Naturally produced halogenated compounds are ubiquitous across all domains of life where they perform a multitude of biological functions and adopt a diversity of chemical structures. Accordingly, a diverse collection of enzyme catalysts to install and remove halogens from organic scaffolds has evolved in nature. Accounting for the different chemical properties of the four halogen atoms (fluorine, chlorine, bromine, and iodine) and the diversity and chemical reactivity of their organic substrates, enzymes performing biosynthetic and degradative halogenation chemistry utilize numerous mechanistic strategies involving oxidation, reduction, and substitution...
January 20, 2017: Chemical Reviews
https://www.readbyqxmd.com/read/28105805/toward-three-dimensional-chemical-imaging-of-ternary-cu-sn-pb-alloys-using-femtosecond-laser-ablation-ionization-mass-spectrometry
#17
Valentine Grimaudo, Pavel Moreno-García, Andreas Riedo, Stefan Meyer, Marek Tulej, Maike B Neuland, Miklós Mohos, Christoph Gütz, Siegfried R Waldvogel, Peter Wurz, Peter Broekmann
Femtosecond laser ablation/ionization mass spectrometry (LIMS) has been applied to probe the spatial element composition of three ternary Cu-Sn-Pb model bronze alloys (lead bronzes: CuSn10Pb10, CuSn7Pb15, and CuSn5Pb20), which were recently identified as high-performance cathode materials in the context of electro-organic synthesis (dehalogenation, deoxygenation) of pharmaceutically relevant building blocks. The quantitative and spatially resolved element analysis of such cathode materials will help in understanding the observed profound differences in their electrochemical reactivity and stability...
February 7, 2017: Analytical Chemistry
https://www.readbyqxmd.com/read/28105660/selective-reductions-of-n-n-bis-chloro-aryl-phosphino-amines-yielding-three-five-six-and-eight-membered-cyclic-azaphosphanes
#18
Uwe Rosenthal, Martha Hoehne, Markus Joksch, Katharina Konieczny, Bernd Harald Mueller, Anke Spannenberg, Normen Peulecke
To date a plethora of λ3-P nitrogen containing-compounds is known. A large part of them is used as ligands in coordination chemistry and homogeneous catalysis. PN-containing compounds tend to build up cyclic moieties which have received less attention in regard to their application as ligands in transition metal chemistry. Hence different dehalogenation reactions of N,N-Bis{chloro(aryl)-phosphino}-amines have being developed to synthesize different P-N-P containing cyclic compounds. Their coordination behaviour to group (VI) transition metal carbonyls was explored...
January 20, 2017: Chemistry: a European Journal
https://www.readbyqxmd.com/read/28101613/estimation-of-anaerobic-debromination-rate-constants-of-pbde-pathways-using-an-anaerobic-dehalogenation-model
#19
Filiz Karakas, Ipek Imamoglu
This study aims to estimate anaerobic debromination rate constants (km) of PBDE pathways using previously reported laboratory soil data. km values of pathways are estimated by modifying a previously developed model as Anaerobic Dehalogenation Model. Debromination activities published in the literature in terms of bromine substitutions as well as specific microorganisms and their combinations are used for identification of pathways. The range of estimated km values is between 0.0003 and 0.0241 d(-1). The median and maximum of km values are found to be comparable to the few available biologically confirmed rate constants published in the literature...
April 2017: Bulletin of Environmental Contamination and Toxicology
https://www.readbyqxmd.com/read/28087526/rapid-enrichment-of-dehalococcoides-like-bacteria-by-partial-hydrophobic-separation
#20
Hanna R Temme, Kipp Sande, Tao Yan, Paige J Novak
Organohalide-respiring bacteria can be difficult to enrich and isolate, which can limit research on these important organisms. The goal of this research was to develop a method to rapidly (minutes to days) enrich these organisms from a mixed community. The method presented is based on the hypothesis that organohalide-respiring bacteria would be more hydrophobic than other bacteria as they dehalogenate hydrophobic compounds. The method developed tests this hypothesis by separating a portion of putative organohalide-respiring bacteria, those phylogenetically related to Dehalococcoides mccartyi, at the interface between a hydrophobic organic solvent and an aqueous medium...
March 15, 2017: Applied and Environmental Microbiology
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