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c-h bond activation

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https://www.readbyqxmd.com/read/30317118/toxicity-of-some-prevalent-organic-chemicals-to-tadpoles-and-comparison-with-toxicity-to-fish-based-on-mode-of-toxic-action
#1
Shuo Wang, Li C Yan, Shan S Zheng, Tian T Li, Ling Y Fan, Tao Huang, Chao Li, Yuan H Zhao
Although mode of action (MOA) plays a key role in the understanding of the toxic mechanism of chemicals, the MOAs of class-based compounds to tadpoles have not been investigated. To explore the MOAs, acute toxicity (expressed as log 1/LC50 ) to Rana chensinensis tadpoles were determined and molecular descriptors were calculated. Quantitative structure-activity relationship (QSAR) showed that toxicity to tadpoles is closely related to the chemical octanol/water partition coefficient (log KOW ), energy of the lowest unoccupied molecular orbital (ELUMO ), and number of hydrogen bond donors and acceptors (NHDA ), representing the bio-uptake potential in tadpoles, the electrophilicity and hydrogen bonding capacity with target site(s), respectively...
October 11, 2018: Ecotoxicology and Environmental Safety
https://www.readbyqxmd.com/read/30314382/new-sulfur-containing-polyarsenicals-from-the-new-caledonian-sponge-echinochalina-bargibanti
#2
Petri Tähtinen, Graziano Guella, Giacomo Saielli, Cécile Debitus, Edouard Hnawia, Ines Mancini
Arsenicin A (C₃H₆As₄O₃) was isolated from the New Caledonian poecilosclerid sponge Echinochalina bargibanti , and described as the first natural organic polyarsenic compound. Further bioguided fractionation of the extracts of this sponge led us to isolate the first sulfur-containing organic polyarsenicals ever found in Nature. These metabolites, called arsenicin B and arsenicin C, are built on a noradamantane-type framework that is characterized by an unusual As⁻As bonding. Extensive NMR measurements, in combination with mass spectra, enabled the assignment of the structure for arsenicin B (C₃H₆As₄S₂) as 2 ...
October 11, 2018: Marine Drugs
https://www.readbyqxmd.com/read/30311719/rh-catalyzed-removable-directing-group-assisted-sp2-or-sp3-c-h-bond-functionalization
#3
Naoto Chatani, Supriya Rej
In recent years, transition-metal-catalyzed C-H activation has become a key strategy in the field of organic synthesis. Among the various transition metal complexes, rhodium complexes are widely used as catalysts in a variety of C-H functionalization reactions due to their high reactivity and selectivity. In addition, because a number of rhodium complexes in various oxidation states are available, this results in diverse reaction patterns. Regioselectivity, an important issue in C-H activation chemistry, can be accomplished by using a directing group to assist the reaction...
October 12, 2018: Angewandte Chemie
https://www.readbyqxmd.com/read/30310585/mononuclear-complexes-of-a-tridentate-redox-active-ligand-with-sulfonamido-groups-structure-properties-and-reactivity
#4
Sarah A Cook, Justin A Bogart, Noam Levi, Andrew C Weitz, Curtis Moore, Arnold L Rheingold, Joseph W Ziller, Michael P Hendrich, A S Borovik
The design of molecular complexes of earth-abundant first-row transition metals that can catalyze multi-electron C-H bond activation processes is of interest for achieving efficient, low-cost syntheses of target molecules. To overcome the propensity of these metals to perform single-electron processes, redox-active ligands have been utilized to provide additional electron equivalents. Herein, we report the synthesis of a novel redox active ligand, [ibaps]3- , which binds to transition metals such as FeII and CoII in a meridional fashion through the three anionic nitrogen atoms and provides additional coordination sites for other ligands...
August 21, 2018: Chemical Science
https://www.readbyqxmd.com/read/30310574/a-highly-site-selective-radical-sp-3-c-h-amination-of-azaheterocycles
#5
Keith W Bentley, Krysta A Dummit, Jeffrey F Van Humbeck
This report describes the development of a novel C-H amination strategy using both a Cu(ii) Lewis acid and an organic hydrogen atom transfer catalyst to activate benzylic C-H bonds adjacent to aromatic N-heterocycles. This simple methodology demonstrates very high selectivity towards azaheterocycles without using exogenous directing groups and affords excellent site selectivity in substrates with more than one reactive position. A wide range of heterocyclic structures not compatible with previously reported catalytic systems have proven to be amenable to this approach...
August 14, 2018: Chemical Science
https://www.readbyqxmd.com/read/30310567/rhodium-catalyzed-cascade-cyclization-featuring-b-h-and-c-h-activation-one-step-construction-of-carborane-fused-n-polyheterocycles
#6
Hairong Lyu, Yangjian Quan, Zuowei Xie
A one-pot strategy for efficient and facile synthesis of C,B-substituted carborane-fused N-polyheterocycles is reported. A rhodium catalyzed cascade cyclization of carboranyl N-arylimines with vinyl ketones enables the effective construction of three new B-C and C-C bonds in one reaction. Both carboranyl B-H and aryl C-H bonds are sequentially activated, leading to a series of previously unavailable C,B-substituted carborane-fused cyclopenta[ b ]quinoline derivatives, for potential applications in pharmaceuticals and materials, in a step-economical manner...
August 14, 2018: Chemical Science
https://www.readbyqxmd.com/read/30306990/asymmetric-abstraction-of-two-chemically-equivalent-methylene-hydrogens-significant-enantioselectivity-of-endoperoxide-presented-by-fumitremorgin-b-endoperoxidase
#7
Jian-Nan Ji, Shi-Lu Chen
The combination of the inert C-H bond activation and asymmetric synthesis, especially the transformation of prochiral sp3 precursors to chiral sp3 centers, is a profound challenge. In the present DFT calculations, the unique enantioselectivity in verruculogen biosynthesis catalyzed by fumitremorgin B endoperoxidase (FtmOx1) has been mechanistically investigated, where a prochiral methylene in fumitremorgin B is dominantly converted to an R-chiral eight-membered endoperoxy ring. FtmOx1 is the first-reported mononuclear α-ketoglutarate-dependent non-heme iron enzyme responsible for chiral endoperoxide formation, which handles the substrate using a Tyr224 radical resulting from the hydrogen abstraction by an FeIV[double bond, length as m-dash]O species...
October 11, 2018: Physical Chemistry Chemical Physics: PCCP
https://www.readbyqxmd.com/read/30306980/rationally-designing-mixed-cu-%C3%AE-o-m-m-cu-ag-zn-au-centers-over-zeolite-materials-with-high-catalytic-activity-towards-methane-activation
#8
Guiru Wang, Ling Huang, Wei Chen, Jian Zhou, Anmin Zheng
The direct conversion of methane to methanol on [Cu(μ-O)M]2+ (M = Cu, Ag, Zn, Au) bimetal centers in ZSM-5 zeolite is investigated using periodic density functional theory for the first time. Some conclusions are drawn: (1) methane activation on [Cu(μ-O)M]2+ (M = Cu, Ag, Zn, Au) in the ZSM-5 zeolite proceeds through radical-like transition states, and the ability for CH4 activation decreases in the sequence [Cu(μ-O)Ag]2+ > [Cu(μ-O)Au]2+ > [Cu(μ-O)Cu]2+ > [Cu(μ-O)Zn]2+. (2) There are two factors that can dramatically enhance C-H bond activation: a greater spin density and a less negative charge of the μ-O atom...
October 11, 2018: Physical Chemistry Chemical Physics: PCCP
https://www.readbyqxmd.com/read/30306977/formation-and-characterization-of-nano-and-microstructures-of-twinned-cubic-boron-nitride
#9
Anagh Bhaumik, Jagdish Narayan
Nano- and microstructures of phase-pure cubic boron nitride (c-BN) are synthesized by employing nanosecond pulsed-laser annealing techniques at room temperature and atmospheric pressure. In a highly non-equilibrium synthesis process, nanocrystalline h-BN is directly converted into phase-pure twinned c-BN from a highly undercooled melt state of BN. By changing nucleation and growth rates, we have synthesized a wide range of sizes (90 nm to 25 μm) of c-BN. The electron diffraction patterns show the formation of twinned c-BN with [11[combining macron]1] as the twin axis...
October 11, 2018: Physical Chemistry Chemical Physics: PCCP
https://www.readbyqxmd.com/read/30303005/c-f-bond-activation-of-p-c-6-f-5-3-by-ruthenium-dihydride-complexes-isolation-and-reactivity-of-the-missing-ru-pph-3-3-h-halide-complex-ru-pph-3-3-hf
#10
Mateusz K Cybulski, Caroline J E Davies, John P Lowe, Mary F Mahon, Michael K Whittlesey
The major product of the reaction between Ru(IMe4 )2 (PPh3 )2 H2 (1; IMe4 = 1,3,4,5-tetramethylimidazol-2-ylidene) and P(C6 F5 )3 (PCF) is the five-coordinate complex Ru(IMe4 )2 (PF2 {C6 F5 })(C6 F5 )H (2), which is formed via a complex series of C-F/P-C bond cleavage and P-F bond formation steps. In contrast, hydrodefluorination of all six ortho C-F bonds in PCF occurs with Ru(PPh3 )4 H2 to afford Ru(PPh3 )3 HF (3). NaBArF 4 abstracted the fluoride ligand in 3 to give [Ru({η6 -C6 H5 }PPh2 )(PPh3 )2 H][BArF 4 ], while B2 pin2 reacted with 3 in C6 D6 to yield a mixture of [Ru({η6 -C6 D6 )(PPh3 )2 H]+ and Ru(PPh3 )4 H2 ...
October 10, 2018: Inorganic Chemistry
https://www.readbyqxmd.com/read/30302519/characterization-and-use-of-a-bacterial-lignin-peroxidase-with-an-improved-manganese-oxidative-activity
#11
Elisa Vignali, Fabio Tonin, Loredano Pollegioni, Elena Rosini
Peroxidases are well-known biocatalysts produced by all organisms, especially microorganisms, and used in a number of biotechnological applications. The enzyme DypB from the lignin-degrading bacterium Rhodococcus jostii was recently shown to degrade solvent-obtained fractions of a Kraft lignin. In order to promote the practical use, the N246A variant of DypB, named Rh_DypB, was overexpressed in E. coli using a designed synthetic gene: by employing optimized conditions, the enzyme was fully produced as folded holoenzyme, thus avoiding the need for a further time-consuming and expensive reconstitution step...
October 9, 2018: Applied Microbiology and Biotechnology
https://www.readbyqxmd.com/read/30298739/selective-synthesis-of-aminoisoquinolines-via-rh-iii-catalyzed-c-h-n-h-bond-functionalization-of-n-aryl-amidines-with-cyclic-2-diazo-1-3-diketones
#12
Youpeng Zuo, Xinwei He, Yi Ning, Yuhao Wu, Yongjia Shang
A simple C-H/N-H bond functionalization of N-aryl amidines with cyclic 2-diazo-1,3-diketones for the synthesis of 1-aminoisoquinolines has been accomplished by employing [Cp*RhCl2]2/CsOPiv as the catalyst system. This methodology proceeds by a cascade C-H activation/intramolecular cyclization under mild reaction conditions, features a broad substrate scope, and involves the formation of two new σ bonds (C-C and C-N) in a single operation for the construction of novel 1-aminoisoquinoline skeletons in good to excellent yields...
October 9, 2018: Journal of Organic Chemistry
https://www.readbyqxmd.com/read/30297657/effects-of-ag-additive-in-low-temperature-co-detection-with-in%C3%A2-o%C3%A2-based-gas-sensors
#13
Daniil Naberezhnyi, Marina Rumyantseva, Darya Filatova, Maria Batuk, Joke Hadermann, Alexander Baranchikov, Nikolay Khmelevsky, Anatoly Aksenenko, Elizaveta Konstantinova, Alexander Gaskov
Nanocomposites In₂O₃/Ag obtained by ultraviolet (UV) photoreduction and impregnation methods were studied as materials for CO sensors operating in the temperature range 25⁻250 °C. Nanocrystalline In₂O₃ and In₂O₃/Ag nanocomposites were characterized by X-ray diffraction (XRD), single-point Brunauer-Emmet-Teller (BET) method, scanning electron microscopy (SEM), transmission electron microscopy (TEM), and high angle annular dark field scanning transmission electron microscopy (HAADF-STEM) with energy dispersive X-ray (EDX) mapping...
October 8, 2018: Nanomaterials
https://www.readbyqxmd.com/read/30289247/methane-activation-by-gas-phase-atomic-clusters
#14
Yan-Xia Zhao, Zi-Yu Li, Yuan Yang, Sheng-Gui He
The increasing supply of natural gas has created a strong demand for developing efficient catalytic processes to upgrade methane, the most stable alkane molecule, into value-added chemicals. Currently, methane conversion in laboratory and industry is mostly performed under high-temperature conditions. A lot of effort has been devoted to exploring chemical entities that are able to activate the C-H bond of methane at lower temperatures, preferably room temperature. Gas phase atomic clusters with limited numbers of atoms are ideal models of active sites on heterogeneous catalysts...
October 5, 2018: Accounts of Chemical Research
https://www.readbyqxmd.com/read/30288973/high-throughput-open-air-plasma-activation-of-metal-oxide-thin-films-with-low-thermal-budget
#15
Young Jun Tak, Florian Hilt, Scott Tom Keene, Won-Gi Kim, Reinhold H Dauskardt, Alberto Salleo, Hyun Jae Kim
Sputter processed oxide films are typically annealed at high temperature (activation process) to achieve stable electrical characteristics through the formation of strong metal-oxide chemical bonds. For instance, indium-gallium-zinc oxide (IGZO) films typically need a thermal treatment at 300°C for ≥1 hour as an activation process. We propose an open-air plasma treatment (OPT) to rapidly and effectively activate sputter processed IGZO films. OPT effectively induces metal-oxide chemical bonds in IGZO films at temperatures as low as 240°C with a dwell time on the order of a second...
October 5, 2018: ACS Applied Materials & Interfaces
https://www.readbyqxmd.com/read/30284980/synthesis-crystal-structure-and-cytotoxic-activity-of-novel-5-methyl-4-thiopyrimidine-derivatives
#16
Marcin Stolarczyk, Iwona Bryndal, Agnieszka Matera-Witkiewicz, Tadeusz Lis, Karolina Królewska-Golińska, Marcin Cieślak, Julia Kaźmierczak-Barańska, Jerzy Cieplik
This article presents the synthesis of three new 4-thiopyrimidine derivatives obtained from ethyl 4-methyl-2-phenyl-6-sulfanylpyrimidine-5-carboxylate as the starting material, namely, ethyl 4-[(4-chlorobenzyl)sulfanyl]-6-methyl-2-phenylpyrimidine-5-carboxylate, C21 H19 ClN2 O2 S, (2), {4-[(4-chlorobenzyl)sulfanyl]-6-methyl-2-phenylpyrimidin-5-yl}methanol, C19 H17 ClN2 OS, (3), and 4-[(4-chlorobenzyl)sulfanyl]-5,6-dimethyl-2-phenylpyrimidine, C19 H17 ClN2 S, (4), which vary in the substituent at the 5-position of the pyrimidine ring...
October 1, 2018: Acta Crystallographica. Section C, Structural Chemistry
https://www.readbyqxmd.com/read/30284296/mechanistic-insight-on-water-and-substrate-catalyzed-the-synthesis-of-3-1h-indol-3-yl-2-4-methoxybenzyl-isoindolin-1-one-driving-by-noncovalent-interactions
#17
Haiyan Yuan, Lihan Zhu, Wenliang Li, Jingping Zhang
The mechanisms of the synthesis of 2-substituted-3-(1H-indol-3-yl)-isoindolin-1-one derivatives have been investigated theoretically under unassisted, self-assisted, and water-assisted conditions. Being different from previously proposed catalyst-free by Hu et al., our results show that the title mechanism can be altered and accelerated by solvent and substrate 2. Two types of mechanisms have been developed by DFT calculations differ in the reaction sequence of substrates 1 with 3 (M1) or 2 (M2) followed by 2 (M1) or 3 (M2), and water-assisted M1 is the most favored one...
October 3, 2018: Journal of Computational Chemistry
https://www.readbyqxmd.com/read/30280898/photocatalytic-activation-of-less-reactive-bonds-and-their-functionalization-via-hydrogen-evolution-cross-couplings
#18
Bin Chen, Li-Zhu Wu, Chen-Ho Tung
Cross-coupling reactions have been established as potential tools for manufacture of complex molecular frameworks of diversified interests by connecting two simple molecules through the formation of a carbon-carbon (C-C) or a carbon-heteroatom (C-X) bond. Conventional cross-couplings are transition metal-catalyzed reactions between electrophiles and nucleophiles. Generally, the electrophilic partner is an aryl or alkenyl halide, the nucleophile is an organometallic reagent, and both are obtained from prefunctionalization of their corresponding hydrocarbons...
October 3, 2018: Accounts of Chemical Research
https://www.readbyqxmd.com/read/30280508/electrochemical-transition-metal-catalyzed-c-h-bonds-functionalization-electricity-as-clean-surrogates-of-chemical-oxidants
#19
Jianbin Chen, Shide Lv, Siyu Tian
Transition-metal-catalyzed C-H activation attracts tremendous attentions in organic synthetic community because it obviates pre-functionalization of substrates.[1] Significant advances have been dedicated in the past several decades. However, it should be notated that super stoichiometric chemical oxidants, such as copper- or silver-based metal oxidants, benzoquinones (BQ), organic peroxides, potassium persulfate (K2S2O8), hypervalent iodine molecular oxygen (O2) and so on that are required for most of the reactions...
October 2, 2018: ChemSusChem
https://www.readbyqxmd.com/read/30279311/conformational-changes-on-substrate-binding-revealed-by-structures-of-methylobacterium-extorquens-malate-dehydrogenase
#20
Javier M González, Ricardo Marti-Arbona, Julian C H Chen, Brian Broom-Peltz, Clifford J Unkefer
Three high-resolution X-ray crystal structures of malate dehydrogenase (MDH; EC 1.1.1.37) from the methylotroph Methylobacterium extorquens AM1 are presented. By comparing the structures of apo MDH, a binary complex of MDH and NAD+ , and a ternary complex of MDH and oxaloacetate with ADP-ribose occupying the pyridine nucleotide-binding site, conformational changes associated with the formation of the catalytic complex were characterized. While the substrate-binding site is accessible in the enzyme resting state or NAD+ -bound forms, the substrate-bound form exhibits a closed conformation...
October 1, 2018: Acta Crystallographica. Section F, Structural Biology Communications
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