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Sample records for mediated c-h activation

  1. Gold(I)-mediated C-H activation of arenes.

    PubMed

    Lu, Pengfei; Boorman, Tanya C; Slawin, Alexandra M Z; Larrosa, Igor

    2010-04-28

    We demonstrate the first Au(I)-mediated C-H activation of arenes. Au(I) salts undergo C-H activation with electron-poor arenes, in stark contrast to Au(III) salts, which activate electron-rich arenes. This operationally simple and highly regioselective process occurs under very mild conditions and gives access to a variety of Au(I)-arene complexes in excellent yields.

  2. Palladium mediated intramolecular multiple C-X/C-H cross coupling and C-H activation: synthesis of carbazole alkaloids calothrixin B and murrayaquinone A.

    PubMed

    Kaliyaperumal, Srinivasan A; Banerjee, Shyamapada; U K, Syam Kumar

    2014-08-28

    Straightforward palladium mediated syntheses of calothrixin B and murrayaquinone A are described. Regioselective palladium mediated intramolecular multiple C-X/C-H cross coupling reaction on N-(4-((2-bromophenyl)amino)-2,5-dimethoxybenzyl)-N-(2-iodophenyl)acetamide followed by CAN oxidation afforded calothrixin B in excellent yield in two steps. A linear synthesis has also been developed for calothrixin B. Utilizing C-H functionalization as well as palladium mediated intramolecular C-X/C-H cross coupling reaction, murrayaquinone A synthesis was achieved. Overall, these synthetic methodologies provide an expedient entry to these biologically active alkaloids in a short reaction sequence.

  3. Synthesis of new class of alkyl azarene pyridinium zwitterions via iodine mediated sp3 C-H bond activation.

    PubMed

    Kumar, Atul; Gupta, Garima; Srivastava, Suman

    2011-12-16

    An efficient and conceptually different approach toward C-H bond activation by using iodine mediated sp(3) C-H functionalization for the synthesis of alkyl azaarene pyridinium zwitterions is described. This work has the interesting distinction of being the first synthesis of a new class of alkyl azaarene pyridinium zwitterion via transition-metal-free sp(3) C-H bond activation of an alkyl azaarene.

  4. Elaboration of copper-oxygen mediated C-H activation chemistry in consideration of future fuel and feedstock generation.

    PubMed

    Lee, Jung Yoon; Karlin, Kenneth D

    2015-04-01

    To contribute solutions to current energy concerns, improvements in the efficiency of dioxygen mediated C-H bond cleavage chemistry, for example, selective oxidation of methane to methanol, could minimize losses in natural gas usage or produce feedstocks for fuels. Oxidative C-H activation is also a component of polysaccharide degradation, potentially affording alternative biofuels from abundant biomass. Thus, an understanding of active-site chemistry in copper monooxygenases, those activating strong C-H bonds is briefly reviewed. Then, recent advances in the synthesis-generation and study of various copper-oxygen intermediates are highlighted. Of special interest are cupric-superoxide, Cu-hydroperoxo and Cu-oxy complexes. Such investigations can contribute to an enhanced future application of C-H oxidation or oxygenation processes using air, as concerning societal energy goals.

  5. A theoretical view on CrO2+-mediated C-H bond activation in ethane

    NASA Astrophysics Data System (ADS)

    Tong, YongChun; Zhang, XiaoYong; Wang, QingYun; Xu, XinJian; Wang, YongCheng

    2015-06-01

    The gas-phase reaction of C-H bond activation in ethane by CrO2+ has been investigated using density functional theory (DFT) at the UB3LYP/6-311G(2d,p) level. Our results reveal that the activation process is actually a spin-forbidden reaction. The involved crossing point between the doublet and quartet potential energy surfaces (PES) has been discussed by two well-known methods, i.e., intrinsic reaction coordinate (IRC) approach for crossing point (CP) and Harvey's algorithm for minimum energy crossing point (MECP). The obtained single ( P1ISC = 2.48 × 10-3) and double ( P1ISC = 4.95 × 10-3) passes estimated at MECP show that the intersystem crossing (ISC) occurs with a little probability. The C-H bond activation processes should proceed to be endothermic by 73.16 kJ/mol on the doublet surface without any spin change.

  6. Transition-state metal aryl bond stability determines regioselectivity in palladium acetate mediated C-H bond activation of heteroarenes.

    PubMed

    Petit, Alban; Flygare, Josh; Miller, Alex T; Winkel, Gerrit; Ess, Daniel H

    2012-07-20

    Density functional calculations reveal that the stability of developing metal aryl bonds in Pd(II)-acetate C-H activation transition states determines regioselectivity in arene and heteroarene compounds. This kinetic-thermodynamic connection explains the general preference for activation of the strongest C-H bond and provides the possibility for regioselectivity prediction.

  7. Two-State Reactivity in Low-Valent Iron-Mediated C-H Activation and the Implications for Other First-Row Transition Metals.

    PubMed

    Sun, Yihua; Tang, Hao; Chen, Kejuan; Hu, Lianrui; Yao, Jiannian; Shaik, Sason; Chen, Hui

    2016-03-23

    C-H bond activation/functionalization promoted by low-valent iron complexes has recently emerged as a promising approach for the utilization of earth-abundant first-row transition metals to carry out this difficult transformation. Herein we use extensive density functional theory and high-level ab initio coupled cluster calculations to shed light on the mechanism of these intriguing reactions. Our key mechanistic discovery for C-H arylation reactions reveals a two-state reactivity (TSR) scenario in which the low-spin Fe(II) singlet state, which is initially an excited state, crosses over the high-spin ground state and promotes C-H bond cleavage. Subsequently, aryl transmetalation occurs, followed by oxidation of Fe(II) to Fe(III) in a single-electron transfer (SET) step in which dichloroalkane serves as an oxidant, thus promoting the final C-C coupling and finalizing the C-H functionalization. Regeneration of the Fe(II) catalyst for the next round of C-H activation involves SET oxidation of the Fe(I) species generated after the C-C bond coupling. The ligand sphere of iron is found to play a crucial role in the TSR mechanism by stabilization of the reactive low-spin state that mediates the C-H activation. This is the first time that the successful TSR concept conceived for high-valent iron chemistry is shown to successfully rationalize the reactivity for a reaction promoted by low-valent iron complexes. A comparative study involving other divalent middle and late first-row transition metals implicates iron as the optimum metal in this TSR mechanism for C-H activation. It is predicted that stabilization of low-spin Mn(II) using an appropriate ligand sphere should produce another promising candidate for efficient C-H bond activation. This new TSR scenario therefore emerges as a new strategy for using low-valent first-row transition metals for C-H activation reactions.

  8. An iridium-mediated C-H activation/CO2-carboxylation reaction of 1,1-bisdiphenylphosphinomethane.

    PubMed

    Langer, Jens; Fabra, María José; García-Orduña, Pilar; Lahoz, Fernando J; Görls, Helmar; Oro, Luis A; Westerhausen, Matthias

    2010-09-07

    The reaction of 1,1-bisdiphenylphosphinomethane (dppm, 4 eq.) with [IrCl(coe)(2)](2) results in a solvent dependent equilibrium from which the complexes [IrCl(dppm)(dppm-H)(H)] (1) and [Ir(dppm)(2)]Cl (2) were isolated. When 2 is dissolved in methanol, [IrCl(dppm)(2)(H)][OCH(3)] (4) is formed as dominant species in solution. The C-H activation reaction which leads to 1 and 4 can be suppressed by adding an additional dppm ligand per iridium center resulting in the formation of [Ir(dppm)(3)]Cl (5). If the reaction of dppm with [IrX(coe)(2)](2) (X = Cl, I) is performed under an atmosphere of CO(2) the complexes [IrX(dppm)(H){(Ph(2)P)(2)C-COOH}] (6: X = Cl; 7: X = I) are formed by a CH activation/CO(2) carboxylation sequence. The reaction of 6 with NH(4)PF yields [IrCl(dppm)(2)(H)]PF(6).(10). Additionally the lithium compounds [Li(dme)(2)(dppm-H)] (3) and [Li(dme){(Ph(2)P)(2)CHCOO}](2) (8) were prepared for comparison. The molecular structures of the compounds 1, 3, 5, 7, 8 and of the related iridium complex [IrCl(dppm)(2)(H)]I (11) are reported.

  9. Beyond ferryl-mediated hydroxylation: 40 years of the rebound mechanism and C-H activation.

    PubMed

    Huang, Xiongyi; Groves, John T

    2017-04-01

    Since our initial report in 1976, the oxygen rebound mechanism has become the consensus mechanistic feature for an expanding variety of enzymatic C-H functionalization reactions and small molecule biomimetic catalysts. For both the biotransformations and models, an initial hydrogen atom abstraction from the substrate (R-H) by high-valent iron-oxo species (Fe(n)=O) generates a substrate radical and a reduced iron hydroxide, [Fe(n-1)-OH ·R]. This caged radical pair then evolves on a complicated energy landscape through a number of reaction pathways, such as oxygen rebound to form R-OH, rebound to a non-oxygen atom affording R-X, electron transfer of the incipient radical to yield a carbocation, R(+), desaturation to form olefins, and radical cage escape. These various flavors of the rebound process, often in competition with each other, give rise to the wide range of C-H functionalization reactions performed by iron-containing oxygenases. In this review, we first recount the history of radical rebound mechanisms, their general features, and key intermediates involved. We will discuss in detail the factors that affect the behavior of the initial caged radical pair and the lifetimes of the incipient substrate radicals. Several representative examples of enzymatic C-H transformations are selected to illustrate how the behaviors of the radical pair [Fe(n-1)-OH ·R] determine the eventual reaction outcome. Finally, we discuss the powerful potential of "radical rebound" processes as a general paradigm for developing novel C-H functionalization reactions with synthetic, biomimetic catalysts. We envision that new chemistry will continue to arise by bridging enzymatic "radical rebound" with synthetic organic chemistry.

  10. Pd(II)-catalyzed regioselective 2-alkylation of indoles via a norbornene-mediated C-H activation: mechanism and applications.

    PubMed

    Jiao, Lei; Herdtweck, Eberhardt; Bach, Thorsten

    2012-09-05

    A palladium-catalyzed direct 2-alkylation reaction of free N-H indoles was developed based on a norbornene-mediated regioselective cascade C-H activation. The detailed reaction mechanism was investigated by NMR spectroscopic analyses, characterization of the key intermediate, deuterium labeling experiments, and kinetic studies. The results indicate that a catalytic cycle operates, in which an N-norbornene type palladacycle is formed as the key intermediate. Oxidative addition of alkyl bromide to the Pd(II) center in this intermediate is the rate-determining step of the reaction. The synthetic utility of this indole 2-alkylation method was demonstrated by its application in natural product total synthesis. A new and general strategy to synthesize Aspidosperma alkaloids was established employing the indole 2-alkylation reaction as the key step, and two structurally different Aspidosperma alkaloids, aspidospermidine and goniomitine, were synthesized in concise routes.

  11. Lanthanum-mediated C-H bond activation of propyne and identification of La(C₃H₂) isomers.

    PubMed

    Hewage, Dilrukshi; Roudjane, Mourad; Silva, W Ruchira; Kumari, Sudesh; Yang, Dong-Sheng

    2015-03-26

    η(2)-Propadienylidenelanthanum [La(η(2)-CCCH2)] and deprotiolanthanacyclobutadiene [La(HCCCH)] of La(C3H2) are identified from the reaction mixture of neutral La atom activation of propyne in the gas phase. The two isomers are characterized with mass-analyzed threshold ionization spectroscopy combined with electronic structure calculations and spectral simulations. La(η(2)-CCCH2) and La(HCCCH) are formed by concerted 1,3- and 3,3-dehydrogenation, respectively. Both isomers prefer a doublet ground state with a La 6s-based unpaired electron, and La(η(2)-CCCH2) is slightly more stable than La(HCCCH). Ionization of the neutral doublet state of either isomer produces a singlet ion state by removing the La-based electron. The geometry change upon ionization results in the excitation of a symmetric metal-hydrocarbon stretching mode in the ionic state, whereas thermal excitation leads to the observation of the same stretching mode in the neutral state. Although the La atom is in a formal oxidation state of +2, the ionization energies of these metal-hydrocarbon radicals are lower than that of the neutral La atom. Deuteration has a very small effect on the ionization energies of the two isomers and the metal-hydrocarbon stretching mode of La(η(2)-CCCH2), but it reduces considerably the metal-ligand stretching frequencies of La(HCCCH).

  12. Oxidative esterification via photocatalytic C-H activation

    EPA Science Inventory

    Direct oxidative esterification of alcohol via photocatalytic C-H activation has been developed using VO@g-C3N4 catalyst; an expeditious esterification of alcohols occurs under neutral conditions using visible light as the source of energy.

  13. Oxidative esterification via photocatalytic C-H activation

    EPA Pesticide Factsheets

    Direct oxidative esterification of alcohol via photocatalytic C??H activation has been developed using VO@g-C3N4 catalyst; an expeditious esterification of alcohols occurs under neutral conditions using visible light as the source of energy.This dataset is associated with the following publication:Varma , R., S. Verma, R.B.N. Baig, C. Han, and M. Nadagouda. Oxidative esterification via photocatalytic C-H activation. GREEN CHEMISTRY. Royal Society of Chemistry, Cambridge, UK, 18: 251-254, (2015).

  14. C-H bond activation by f-block complexes.

    PubMed

    Arnold, Polly L; McMullon, Max W; Rieb, Julia; Kühn, Fritz E

    2015-01-02

    Most homogeneous catalysis relies on the design of metal complexes to trap and convert substrates or small molecules to value-added products. Organometallic lanthanide compounds first gave a tantalizing glimpse of their potential for catalytic C-H bond transformations with the selective cleavage of one C-H bond in methane by bis(permethylcyclopentadienyl)lanthanide methyl [(η(5) -C5 Me5 )2 Ln(CH3 )] complexes some 25 years ago. Since then, numerous metal complexes from across the periodic table have been shown to selectively activate hydrocarbon C-H bonds, but the challenges of closing catalytic cycles still remain; many f-block complexes show great potential in this important area of chemistry.

  15. Divergence between organometallic and single-electron-transfer mechanisms in copper(II)-mediated aerobic C-H oxidation.

    PubMed

    Suess, Alison M; Ertem, Mehmed Z; Cramer, Christopher J; Stahl, Shannon S

    2013-07-03

    Copper(II)-mediated C-H oxidation is the subject of extensive interest in synthetic chemistry, but the mechanisms of many of these reactions are poorly understood. Here, we observe different products from Cu(II)-mediated oxidation of N-(8-quinolinyl)benzamide, depending on the reaction conditions. Under basic conditions, the benzamide group undergoes directed C-H methoxylation or chlorination. Under acidic conditions, the quinoline group undergoes nondirected chlorination. Experimental and computational mechanistic studies implicate an organometallic C-H activation/functionalization mechanism under the former conditions and a single-electron-transfer mechanism under the latter conditions. This rare observation of divergent, condition-dependent mechanisms for oxidation of a single substrate provides a valuable foundation for understanding Cu(II)-mediated C-H oxidation reactions.

  16. Copper-mediated stereospecific C-H oxidative sulfenylation of terminal alkenes with disulfides.

    PubMed

    Tu, Hai-Yong; Hu, Bo-Lun; Deng, Chen-Liang; Zhang, Xing-Guo

    2015-11-04

    A copper and iodine-mediated C-H oxidative sulfenylation of olefins with diaryl disulfides has been developed for the stereospecific synthesis of vinyl thioether. With the combination of Cu(OTf)2 and I2, a variety of terminal alkenes underwent oxidative coupling reaction with various diaryl disulfides successfully to afford the corresponding E-vinyl sulfides in moderate to good yields.

  17. C-H activation: Complex peptides made simple

    NASA Astrophysics Data System (ADS)

    Bartlett, Sean; Spring, David R.

    2017-01-01

    Nature oxidizes biosynthetic intermediates into structurally and functionally diverse peptides. An iron-catalysed C-H oxidation mimics this approach in the lab, enabling chemists to synthesize structural analogues with ease.

  18. Enzyme catalysis: C-H activation is a Reiske business

    NASA Astrophysics Data System (ADS)

    Bruner, Steven D.

    2011-05-01

    Enzymes that selectively oxidize unactivated C-H bonds are capable of constructing complex molecules with high efficiency. A new member of this enzyme family is RedG, a Reiske-type oxygenase that catalyses chemically challenging cyclizations in the biosynthesis of prodiginine natural products.

  19. Metal-free synthesis of N-fused heterocyclic iodides via C-H functionalization mediated by tert-butylhydroperoxide.

    PubMed

    Sharma, Krishna K; Patel, Dhananjay I; Jain, Rahul

    2015-10-21

    Direct, regioselective and metal-free synthesis of fused N-heterocyclic iodides is reported. This regioselective C-H functionalization is mediated by tert-butylhydroperoxide (TBHP), via dual activation of molecular iodine and a heterocyclic substrate, resulting in the in situ generation of electrophilic iodine species (I(+)), and free radical(s) (t)BuO˙ or (t)BuOO˙, driving the iodination reaction.

  20. Copper-catalyzed oxaziridine-mediated oxidation of C-H bonds.

    PubMed

    Motiwala, Hashim F; Gülgeze, Belgin; Aubé, Jeffrey

    2012-08-17

    The highly regio- and chemoselective oxidation of activated C-H bonds has been observed via copper-catalyzed reactions of oxaziridines. The oxidation proceeded with a variety of substrates, primarily comprising allylic and benzylic examples, as well as one example of an otherwise unactivated tertiary C-H bond. The mechanism of the reaction is proposed to involve single-electron transfer to the oxaziridines to generate a copper-bound radical anion, followed by hydrogen atom abstraction and collapse to products, with regeneration of the catalyst by a final single-electron transfer event. The involvement of allylic radical intermediates was supported by a radical-trapping experiment with TEMPO.

  1. Metal-free oxidative olefination of primary amines with benzylic C-H bonds through direct deamination and C-H bond activation.

    PubMed

    Gong, Liang; Xing, Li-Juan; Xu, Tong; Zhu, Xue-Ping; Zhou, Wen; Kang, Ning; Wang, Bin

    2014-09-14

    An oxidative olefination reaction between aliphatic primary amines and benzylic sp(3) C-H bonds has been achieved using N-bromosuccinimide as catalyst and tert-butyl hydroperoxide as oxidant. The olefination proceeds under mild metal-free conditions through direct deamination and benzylic C-H bond activation, and provides easy access to biologically active 2-styrylquinolines with (E)-configuration.

  2. Rh(III)-Catalyzed C-H Bond Addition/Amine-Mediated Cyclization of Bis-Michael Acceptors.

    PubMed

    Potter, Tyler J; Ellman, Jonathan A

    2016-08-05

    A Rh(III)-catalyzed C-H bond addition/primary amine-promoted cyclization of bis-Michael acceptors is reported. The C-H bond addition step occurs with high chemoselectivity, and the subsequent intramolecular Michael addition, mediated by a primary amine catalyst, sets three contiguous stereocenters with high diastereoselectivity. A broad range of directing groups and both aromatic and alkenyl C-H bonds were shown to be effective in this transformation, affording functionalized piperidines, tetrahydropyrans, and cyclohexanes.

  3. Silver-mediated palladium-catalyzed direct C-H arylation of 3-bromoisothiazole-4-carbonitrile.

    PubMed

    Ioannidou, Heraklidia A; Koutentis, Panayiotis A

    2011-03-18

    Silver(I) fluoride-mediated Pd-catalyzed C-H direct arylation/heteroarylation of 3-bromoisothiazole-4-carbonitrile (1a) gives twenty-four 5-aryl/heteroaryl-3-bromoisothiazole-4-carbonitriles. The reaction was partially optimized with respect to catalyst, ligand, and base. During this study 3,3'-dibromo-5,5'-biisothiazole-4,4'-dicarbonitrile (3a) was isolated as a byproduct and subsequently prepared via the silver-mediated Pd-catalyzed oxidative dimerization of 3-bromoisothiazole-4-carbonitrile in 67% yield. The analogous phenylation and oxidative dimerization of 3-chloroisothiazole-4-carbonitrile (1b) gave 3-chloro-5-phenylisothiazole-4-carbonitrile (4) and 3,3'-dichloro-5,5'-biisothiazole-4,4'-dicarbonitrile (3b) in 96% and 69% yields, respectively.

  4. Surface-Controlled Mono/Diselective ortho C-H Bond Activation.

    PubMed

    Li, Qing; Yang, Biao; Lin, Haiping; Aghdassi, Nabi; Miao, Kangjian; Zhang, Junjie; Zhang, Haiming; Li, Youyong; Duhm, Steffen; Fan, Jian; Chi, Lifeng

    2016-03-02

    One of the most charming and challenging topics in organic chemistry is the selective C-H bond activation. The difficulty arises not only from the relatively large bond-dissociation enthalpy, but also from the poor reaction selectivity. In this work, Au(111) and Ag(111) surfaces were used to address ortho C-H functionalization and ortho-ortho couplings of phenol derivatives. More importantly, the competition between dehydrogenation and deoxygenation drove the diversity of reaction pathways of phenols on surfaces, that is, diselective ortho C-H bond activation on Au(111) surfaces and monoselective ortho C-H bond activation on Ag(111) surfaces. The mechanism of this unprecedented phenomenon was extensively explored by scanning tunneling microscopy, density function theory, and X-ray photoelectron spectroscopy. Our findings provide new pathways for surface-assisted organic synthesis via the mono/diselective C-H bond activation.

  5. Electrostatic and Charge-Induced Methane Activation by a Concerted Double C-H Bond Insertion.

    PubMed

    Geng, Caiyun; Li, Jilai; Weiske, Thomas; Schlangen, Maria; Shaik, Sason; Schwarz, Helmut

    2017-02-01

    A mechanistically unique, simultaneous activation of two C-H bonds of methane has been identified during the course of its reaction with the cationic copper carbide, [Cu-C](+). Detailed high-level quantum chemical calculations support the experimental findings obtained in the highly diluted gas phase using FT-ICR mass spectrometry. The behavior of [Cu-C](+)/CH4 contrasts that of [Au-C](+)/CH4, for which a stepwise bond-activation scenario prevails. An explanation for the distinct mechanistic differences of the two coinage metal complexes is given. It is demonstrated that the coupling of [Cu-C](+) with methane to form ethylene and Cu(+) is modeled very well by the reaction of a carbon atom with methane mediated by an oriented external electric field of a positive point charge.

  6. RhCl(PPh3)3-mediated C-H oxyfunctionalization of pyrrolido-functionalized bisazoaromatic pincers: a combined experimental and theoretical scrutiny of redox-active and spectroscopic properties.

    PubMed

    Ghorui, Tapas; Roy, Sima; Pramanik, Shuvam; Pramanik, Kausikisankar

    2016-04-07

    A potentially symmetrical NNN pyrrolido-functionalized pincer ligand, HL = 2,5-bis(phenylazo)-1H-pyrrole, reacts with [Rh(I)Cl(PPh3)3] in toluene in the presence of air, affording an emerald crystalline solid of the composition [Rh(III)(L(O))Cl(PPh3)2]. A spontaneous C-H oxyfunctionalization of the aromatic ring with atmospheric oxygen leads to phenoxido functionalized organic transformation at room temperature. X-ray diffraction and MASS spectral analyses authenticate the unsymmetrical NNO coordination of the title ligand with a dangling phenylazo moiety. Cyclic voltammetry of redox innocent Rh(iii) complexes exhibits a reversible oxidative response at E1/2≈ 0.9 V vs. Ag/AgCl along with a quasi-reversible reductive response near -1.0 V. The electronic structures of the electro-active species are scrutinized by DFT calculations at the B3LYP-level of theory and both the responses are found to be ligand-centered (LC) in nature. Furthermore, an EPR study of the one-electron oxidized radical cation [Rh(III)(L(O))Cl(PPh3)2]˙(+) validates that the oxidation process is confined exclusively on the ligand framework (spin density: ρPhenoxido≈-0.50 and ρPyrrolido≈-0.40). Moreover, an appreciable involvement of the pyrrolido function apart from the phenoxido group of the redox-active ligand (L(O)) is apparent in the oxidation process from the nature of HOMO and thus, this type of ligand system provides two oxidizable domains within the single ligand backbone. A comparison of the relative oxidizability power between the two potential oxidizable centers viz. pyrrolido and phenoxido rings reveals that the former is somewhat less efficient for oxidation. In contrast, reductive response is mainly associated with both the coordinated and free azo chromophores. Time-dependent DFT and natural transition orbital (NTO) analyses on the complexes elucidate the origin of UV-vis absorptions.

  7. Zinc(II)-Mediated Carbene Insertion into C-H Bonds in Alkanes.

    PubMed

    Kulkarni, Naveen V; Dash, Chandrakanta; Jayaratna, Naleen B; Ridlen, Shawn G; Karbalaei Khani, Sarah; Das, Animesh; Kou, Xiaodi; Yousufuddin, Muhammed; Cundari, Thomas R; Dias, H V Rasika

    2015-12-07

    The cationic zinc adduct {[HB(3,5-(CF3)2Pz)3]Zn(NCMe)2}ClO4 catalyzes the functionalization of tertiary, secondary, and primary C-H bonds of alkanes via carbene insertion. Ethyl diazoacetate serves as the :CHCO2Et carbene precursor. The counteranion, supporting ligand, and coordinating solvents affect the catalytic activity. An in situ generated {[HB(3,5-(CF3)2Pz)3]Zn}(+) species containing a bulkier {B[3,5-(CF3)2C6H3]4}(-) anion gives the best results among the zinc catalysts used.

  8. Manganese(I)-Catalyzed Dispersion-Enabled C-H/C-C Activation.

    PubMed

    Meyer, Tjark H; Liu, Weiping; Feldt, Milica; Wuttke, Axel; Mata, Ricardo A; Ackermann, Lutz

    2017-03-20

    C-H/C-C Functionalizations were achieved with the aid of a versatile manganese(I) catalyst. Thus, an organometallic manganese-catalyzed C-H activation set the stage for silver-free C-H/C-C transformations with ample substrate scope and excellent levels of chemo-, site-, and diastereo-selectivities. The robust nature of the manganese(I) catalysis regime was reflected by the first C-H/C-C functionalization on amino acids under racemization-free reaction conditions. Detailed experimental and computational mechanistic studies provided strong evidence for a facile C-H activation and a rate-determining C-C cleavage, with considerable contribution from London dispersion interactions.

  9. Transition-metal-catalyzed additions of C-H bonds to C-X (X = N, O) multiple bonds via C-H bond activation.

    PubMed

    Yan, Guobing; Wu, Xiangmei; Yang, Minghua

    2013-09-14

    Chemical transformations via catalytic C-H bond activation have been established as one of the most powerful tools in organic synthetic chemistry. Transition-metal-catalyzed addition reactions of C-H bonds to polar C-X (X = N, O) multiple bonds, such as aldehydes, ketones, imines, isocyanates, nitriles, isocyanides, carbon monoxide and carbon dioxide, have undergone a rapid development in recent years. In this review, recent advances in this active area have been highlighted and their mechanisms have been discussed.

  10. Intramolecular iron-mediated C-H bond heterolysis with an assist of pendant base in a [FeFe]-hydrogenase model.

    PubMed

    Zheng, Dehua; Wang, Ning; Wang, Mei; Ding, Shengda; Ma, Chengbing; Darensbourg, Marcetta Y; Hall, Michael B; Sun, Licheng

    2014-12-03

    Although many metalloenzymes containing iron play a prominent role in biological C-H activation processes, to date iron-mediated C(sp(3))-H heterolysis has not been reported for synthetic models of Fe/S-metalloenzymes. In contrast, ample precedent has established that nature's design for reversible hydrogen activation by the diiron hydrogenase ([FeFe]-H2ase) active site involves multiple irons, sulfur bridges, a redox switch, and a pendant amine base, in an intricate arrangement to perform H-H heterolytic cleavage. In response to whether this strategy might be extended to C-H activation, we report that a [FeFe]-H2ase model demonstrates iron-mediated intramolecular C-H heterolytic cleavage via an agostic C-H interaction, with proton removal by a nearby pendant amine, affording Fe(II)-[Fe'(II)-CH-S] three-membered-ring products, which can be reduced back to 1 by Cp2Co in the presence of HBF4. The function of the pendant base as a proton shuttle was confirmed by the crystal structures of the N-protonated intermediate and the final deprotonated product in comparison with that of a similar but pendant-amine-free complex that does not show evidence of C-H activation. The mechanism of the process was backed up by DFT calculations.

  11. Synthesis of 1H-indazoles and 1H-pyrazoles via FeBr3/O2 mediated intramolecular C-H amination.

    PubMed

    Zhang, Tianshui; Bao, Weiliang

    2013-02-01

    A new synthesis of substituted 1H-indazoles and 1H-pyrazoles from arylhydrazones via FeBr(3)/O(2) mediated C-H activation/C-N bond formation reactions is reported. The corresponding 1,3-diaryl-substituted indazoles and trisubstituted pyrazoles were obtained in moderate to excellent yields under mild conditions.

  12. Synthesis of Dihydropyridines and Pyridines from Imines and Alkynes via C-H Activation

    SciTech Connect

    Ellman, Jonathan A.; Colby, Denise; Bergman, Robert

    2007-11-20

    A convenient one-pot C-H alkenylation/electrocyclization/aromatization sequence has been developed for the synthesis of highly substituted pyridine derivatives from alkynes and {alpha},{beta}-unsaturated N-benzyl aldimines and ketimines that proceeds through dihydropyridine intermediates. A new class of ligands for C-H activation was developed, providing broader scope for the alkenylation step than could be achieved with previously reported ligands. Substantial information was obtained about the mechanism of the reaction. This included the isolation of a C-H activated complex and its structure determination by X-ray analysis; in addition, kinetic simulations using the Copasi software were employed to determine rate constants for this transformation, implicating facile C-H oxidative addition and slow reductive elimination steps.

  13. Synthesis of dihydropyridines and pyridines from imines and alkynes via C-H activation.

    PubMed

    Colby, Denise A; Bergman, Robert G; Ellman, Jonathan A

    2008-03-19

    A convenient one-pot C-H alkenylation/electrocyclization/aromatization sequence has been developed for the synthesis of highly substituted pyridine derivatives from alkynes and alpha,beta-unsaturated N-benzyl aldimines and ketimines that proceeds through dihydropyridine intermediates. A new class of ligands for C-H activation was developed, providing broader scope for the alkenylation step than could be achieved with previously reported ligands. Substantial information was obtained about the mechanism of the reaction. This included the isolation of a C-H activated complex and its structure determination by X-ray analysis; in addition, kinetic simulations using the Copasi software were employed to determine rate constants for this transformation, implicating facile C-H oxidative addition and slow reductive elimination steps.

  14. Activation of remote meta-C-H bonds assisted by an end-on template.

    PubMed

    Leow, Dasheng; Li, Gang; Mei, Tian-Sheng; Yu, Jin-Quan

    2012-06-27

    Functionalization of unactivated carbon-hydrogen (C-H) single bonds is an efficient strategy for rapid generation of complex molecules from simpler ones. However, it is difficult to achieve selectivity when multiple inequivalent C-H bonds are present in the target molecule. The usual approach is to use σ-chelating directing groups, which lead to ortho-selectivity through the formation of a conformationally rigid six- or seven-membered cyclic pre-transition state. Despite the broad utility of this approach, proximity-driven reactivity prevents the activation of remote C-H bonds. Here we report a class of easily removable nitrile-containing templates that direct the activation of distal meta-C-H bonds (more than ten bonds away) of a tethered arene. We attribute this new mode of C-H activation to a weak 'end-on' interaction between the linear nitrile group and the metal centre. The 'end-on' coordination geometry relieves the strain of the cyclophane-like pre-transition state of the meta-C-H activation event. In addition, this template overrides the intrinsic electronic and steric biases as well as ortho-directing effects with two broadly useful classes of arene substrates (toluene derivatives and hydrocinnamic acids).

  15. Ligand Lone-Pair Influence on Hydrocarbon C-H Activation. A Computational Perspective

    SciTech Connect

    Ess, Daniel H.; Gunnoe, T. Brent; Cundari, Thomas R.; Goddard, William A.; Periana, Roy A.

    2010-12-03

    Mid to late transition metal complexes that break hydrocarbon C-H bonds by transferring the hydrogen to a heteroatom ligand while forming a metal-alkyl bond offer a promising strategy for C-H activation. Here we report a density functional (B3LYP, M06, and X3LYP) analysis of cis-(acac)2MX and TpM(L)X (M = Ir, Ru, Os, and Rh; acac = acetylacetonate, Tp = tris(pyrazolyl)borate; X = CH3, OH, OMe, NH2, and NMe2) systems for methane C-H bond activation reaction kinetics and thermodynamics. We address the importance of whether a ligand lone pair provides an intrinsic kinetic advantage through possible electronic dπ-pπ repulsions for M-OR and M-NR2 systems versus M-CH3 systems. This involves understanding the energetic impact of the X ligand group on ligand loss, C-H bond coordination, and C-H bond cleavage steps as well as understanding how the nucleophilicity of the ligand X group, the electrophilicity of the transition metal center, and cis-ligand stabilization effect influence each of these steps. We also explore how spectator ligands and second- versus third-row transition metal centers impact the energetics of each of these C-H activation steps.

  16. C-H and C-N Activation at Redox-Active Pyridine Complexes of Iron.

    PubMed

    MacLeod, K Cory; Lewis, Richard A; DeRosha, Daniel E; Mercado, Brandon Q; Holland, Patrick L

    2017-01-19

    Pyridine activation by inexpensive iron catalysts has great utility, but the steps through which iron species can break the strong (105-111 kcal mol(-1) ) C-H bonds of pyridine substrates are unknown. In this work, we report the rapid room-temperature cleavage of C-H bonds in pyridine, 4-tert-butylpyridine, and 2-phenylpyridine by an iron(I) species, to give well-characterized iron(II) products. In addition, 4-dimethylaminopyridine (DMAP) undergoes room-temperature C-N bond cleavage, which forms a dimethylamidoiron(II) complex and a pyridyl-bridged tetrairon(II) square. These facile bond-cleaving reactions are proposed to occur through intermediates having a two-electron reduced pyridine that bridges two iron centers. Thus, the redox non-innocence of the pyridine can play a key role in enabling high regioselectivity for difficult reactions.

  17. Computational study on the mechanism and selectivity of C-H bond activation and dehydrogenative functionalization in the synthesis of rhazinilam.

    PubMed

    Ellis, Corey S; Ess, Daniel H

    2011-09-02

    The key platinum mediated C-H bond activation and functionalization steps in the synthesis of (-)-rhazinilam (Johnson, J. A.; Li, N.; Sames, D. J. Am. Chem. Soc. 2002, 124, 6900) were investigated using the M06 and B3LYP density functional approximation methods. This computational study reveals that ethyl group dehydrogenation begins with activation of a primary C-H bond in preference to a secondary C-H bond in an insertion/methane elimination pathway. The C-H activation step is found to be reversible while the methane elimination (reductive elimination) transition state controls rate and diastereoselectivity. The chiral oxazolinyl ligand induces ethyl group selectivity through stabilizing weak interactions between its phenyl group (or cyclohexyl group) and the carboxylate group. After C-H activation and methane elimination steps, Pt-C bond functionalization occurs through β-hydride elimination to give the alkene platinum hydride complex.

  18. C-H activation reactions as useful tools for medicinal chemists.

    PubMed

    Caro-Diaz, Eduardo J E; Urbano, Mariangela; Buzard, Daniel J; Jones, Robert M

    2016-11-15

    In recent years, there has been an exponential rise in the number of reports describing synthetic methods that utilize catalytic sp(3) and sp(2) C-H bond activation. Many have emerged as powerful synthetic tools for accessing biologically active motifs. Indeed, application to C-C and C-heteroatom bond formation, provides new directives for the construction of new pharmaceutical entities. Herein, we highlight some recent novel C-H activation processes that exemplify the utility of these transformations in medicinal chemistry.

  19. Oxidation-promoted activation of a ferrocene C-H bond by a rhodium complex.

    PubMed

    Labande, Agnès; Debono, Nathalie; Sournia-Saquet, Alix; Daran, Jean-Claude; Poli, Rinaldo

    2013-05-14

    The oxidation of a rhodium(I) complex containing a ferrocene-based heterodifunctional phosphine N-heterocyclic carbene (NHC) ligand produces a stable, planar chiral rhodium(III) complex with an unexpected C-H activation on ferrocene. The oxidation of rhodium(I) to rhodium(III) may be accomplished by initial oxidation of ferrocene to ferrocenium and subsequent electron transfer from rhodium to ferrocenium. Preliminary catalytic tests showed that the rhodium(III) complex is active for the Grignard-type arylation of 4-nitrobenzaldehyde via C-H activation of 2-phenylpyridine.

  20. Efficient photocatalytic selective nitro-reduction and C-H bond oxidation over ultrathin sheet mediated CdS flowers.

    PubMed

    Pahari, Sandip Kumar; Pal, Provas; Srivastava, Divesh N; Ghosh, Subhash Ch; Panda, Asit Baran

    2015-06-28

    We report here a visible light driven selective nitro-reduction and oxidation of saturated sp(3) C-H bonds using ultrathin (0.8 nm) sheet mediated uniform CdS flowers as catalyst under a household 40 W CFL lamp and molecular oxygen as oxidant. The CdS flowers were synthesized using a simple surfactant assisted hydrothermal method.

  1. A steric tethering approach enables palladium-catalysed C-H activation of primary amino alcohols.

    PubMed

    Calleja, Jonas; Pla, Daniel; Gorman, Timothy W; Domingo, Victoriano; Haffemayer, Benjamin; Gaunt, Matthew J

    2015-12-01

    Aliphatic primary amines are a class of chemical feedstock essential to the synthesis of higher-order nitrogen-containing molecules, commonly found in biologically active compounds and pharmaceutical agents. New methods for the construction of complex amines remain a continuous challenge to synthetic chemists. Here, we outline a general palladium-catalysed strategy for the functionalization of aliphatic C-H bonds within amino alcohols, an important class of small molecule. Central to this strategy is the temporary conversion of catalytically incompatible primary amino alcohols into hindered secondary amines that are capable of undergoing a sterically promoted palladium-catalysed C-H activation. Furthermore, a hydrogen bond between amine and catalyst intensifies interactions around the palladium and orients the aliphatic amine substituents in an ideal geometry for C-H activation. This catalytic method directly transforms simple, easily accessible amines into highly substituted, functionally concentrated and structurally diverse products, and can streamline the synthesis of biologically important amine-containing molecules.

  2. A steric tethering approach enables palladium-catalysed C-H activation of primary amino alcohols

    NASA Astrophysics Data System (ADS)

    Calleja, Jonas; Pla, Daniel; Gorman, Timothy W.; Domingo, Victoriano; Haffemayer, Benjamin; Gaunt, Matthew J.

    2015-12-01

    Aliphatic primary amines are a class of chemical feedstock essential to the synthesis of higher-order nitrogen-containing molecules, commonly found in biologically active compounds and pharmaceutical agents. New methods for the construction of complex amines remain a continuous challenge to synthetic chemists. Here, we outline a general palladium-catalysed strategy for the functionalization of aliphatic C-H bonds within amino alcohols, an important class of small molecule. Central to this strategy is the temporary conversion of catalytically incompatible primary amino alcohols into hindered secondary amines that are capable of undergoing a sterically promoted palladium-catalysed C-H activation. Furthermore, a hydrogen bond between amine and catalyst intensifies interactions around the palladium and orients the aliphatic amine substituents in an ideal geometry for C-H activation. This catalytic method directly transforms simple, easily accessible amines into highly substituted, functionally concentrated and structurally diverse products, and can streamline the synthesis of biologically important amine-containing molecules.

  3. Iodine-mediated [Formula: see text] C-H functionalization of methyl ketones: a one-pot synthesis of functionalized indolizines via the 1,3-dipolar cycloaddition reaction between pyridinium ylides and ynones.

    PubMed

    Yavari, Issa; Sheykhahmadi, Jamil; Naeimabadi, Maryam; Halvagar, Mohammad Reza

    2017-02-01

    An efficient transition-metal-free approach toward C-H bond activation by using molecular [Formula: see text]-mediated [Formula: see text] C-H bond functionalization for the synthesis of indolizine derivatives via 1,3-dipolar cycloaddition reaction of nitrogen ylides with ynones is described.

  4. Mechanism of a C-H bond activation reaction in room-temperature alkane solution

    SciTech Connect

    Bromberg, S.E.; Yang, H.; Asplund, M.C.

    1997-10-10

    Chemical reactions that break alkane carbon-hydrogen (C-H) bonds are normally carried out under conditions of high temperature and pressure because these bonds are extremely strong ({approx} 100 kilocalories per mole), but certain metal complexes can activate C-H bonds in alkane solution under the mild conditions of room temperature and pressure. Time-resolved infrared experiments probing the initial femtosecond dynamics through the nano- and microsecond kinetics to the final stable products have been used to generate a detailed picture of the C-H activation reaction. Structures of all of the intermediates involved in the reaction of Tp*Rh(CO){sub 2} (Tp* = HB-Pz{sub 3}*, Pz* = 3,5-di-methylpyrazolyl) in alkane solution have been identified and assigned, and energy barriers for each reaction step from solvation to formation of the final alkyl hydride product have been estimated from transient lifetimes. 27 refs., 6 figs.

  5. The mechanism of a C-H Bond Activation reaction in roomtemperature alkane solution

    SciTech Connect

    Bromberg, Steven E.; Yang, Haw; Asplund, Matthew C.; Lian, T.; McNamara, B.K.; Kotz, K.T.; Yeston, J.S.; Wilkens, M.; Frei, H.; Bergman,Robert G.; Harris, C.B.

    1997-07-31

    Chemical reactions that break alkane carbon-hydrogen (C-H) bonds are normally carried out under conditions of high temperature and pressure because these bonds are extremely strong ({approx}100 kilocalories per mole), but certain metal complexes can activate C-H bonds in alkane solution under the mild conditions of room temperature and pressure. Time-resolved infrared experiments probing the initial femtosecond dynamics through the nano- and microsecond kinetics to the final stable products have been used to generate a detailed picture of the C-H activation reaction. Structures of all of the intermediates involved in the reaction of Tp*Rh(CO)2 (Tp* = HB-Pz3*, Pz* = 3,5-dimethylpyrazolyl) in alkane solution have been identified and assigned, and energy barriers for each reaction step from solvation to formation of the final alkylhydride product have been estimated from transient lifetimes.

  6. Activation of C-H bonds in nitrones leads to iridium hydrides with antitumor activity.

    PubMed

    Song, Xiaoda; Qian, Yong; Ben, Rong; Lu, Xiang; Zhu, Hai-Liang; Chao, Hui; Zhao, Jing

    2013-08-22

    We report the design and synthesis of a series of new cyclometalated iridium hydrides derived from the C-H bond activation of aromatic nitrones and the biological evaluation of these iridium hydrides as antitumor agents. The nitrone ligands are based on the structure of a popular antioxidant, α-phenyl-N-tert-butylnitrone (PBN). Compared to cisplatin, the iridium hydrides exhibit excellent antitumor activity on HepG2 cells. The metal-coordinated compound with the most potent anticancer activity, 2f, was selected for further analysis because of its ability to induce apoptosis and interact with DNA. During in vitro studies and in vivo efficacy analysis with tumor xenograft models in Institute of Cancer Research (ICR) mice, complex 2f exhibited antitumor activity that was markedly superior to that of cisplatin. Our results suggest, for the first time, that metal hydrides could be a new type of metal-based antitumor agent.

  7. Copper/silver-mediated direct ortho-ethynylation of unactivated (hetero)aryl C-H bonds with terminal alkyne.

    PubMed

    Liu, Yue-Jin; Liu, Yan-Hua; Yin, Xue-Song; Gu, Wen-Jia; Shi, Bing-Feng

    2015-01-02

    A copper/silver-mediated oxidative ortho-ethynylation of unactivated aryl C-H bonds with terminal alkyne has been developed. The reaction uses the removable PIP directing group and features broad substrate scope, high functional-group tolerance, and compatibility with a wide range of heterocycles, providing an efficient synthesis of aryl alkynes. This procedure highlights the potential of copper catalysts to promote unique, synthetically enabling C-H functionalization reactions that lie outside of the current scope of precious metal catalysis.

  8. Consequences of metal-oxide interconversion for C-H bond activation during CH4 reactions on Pd catalysts.

    PubMed

    Chin, Ya-Huei Cathy; Buda, Corneliu; Neurock, Matthew; Iglesia, Enrique

    2013-10-16

    Mechanistic assessments based on kinetic and isotopic methods combined with density functional theory are used to probe the diverse pathways by which C-H bonds in CH4 react on bare Pd clusters, Pd cluster surfaces saturated with chemisorbed oxygen (O*), and PdO clusters. C-H activation routes change from oxidative addition to H-abstraction and then to σ-bond metathesis with increasing O-content, as active sites evolve from metal atom pairs (*-*) to oxygen atom (O*-O*) pairs and ultimately to Pd cation-lattice oxygen pairs (Pd(2+)-O(2-)) in PdO. The charges in the CH3 and H moieties along the reaction coordinate depend on the accessibility and chemical state of the Pd and O centers involved. Homolytic C-H dissociation prevails on bare (*-*) and O*-covered surfaces (O*-O*), while C-H bonds cleave heterolytically on Pd(2+)-O(2-) pairs at PdO surfaces. On bare surfaces, C-H bonds cleave via oxidative addition, involving Pd atom insertion into the C-H bond with electron backdonation from Pd to C-H antibonding states and the formation of tight three-center (H3C···Pd···H)(‡) transition states. On O*-saturated Pd surfaces, C-H bonds cleave homolytically on O*-O* pairs to form radical-like CH3 species and nearly formed O-H bonds at a transition state (O*···CH3(•)···*OH)(‡) that is looser and higher in enthalpy than on bare Pd surfaces. On PdO surfaces, site pairs consisting of exposed Pd(2+) and vicinal O(2-), Pd(ox)-O(ox), cleave C-H bonds heterolytically via σ-bond metathesis, with Pd(2+) adding to the C-H bond, while O(2-) abstracts the H-atom to form a four-center (H3C(δ-)···Pd(ox)···H(δ+)···O(ox))(‡) transition state without detectable Pd(ox) reduction. The latter is much more stable than transition states on *-* and O*-O* pairs and give rise to a large increase in CH4 oxidation turnover rates at oxygen chemical potentials leading to Pd to PdO transitions. These distinct mechanistic pathways for C-H bond activation, inferred from theory

  9. Synthesis of a Benzodiazepine-derived Rhodium NHC Complex by C-H Bond Activation

    SciTech Connect

    Bergman, Roberg G.; Gribble, Jr., Michael W.; Ellman, Jonathan A.

    2008-01-30

    The synthesis and characterization of a Rh(I)-NHC complex generated by C-H activation of 1,4-benzodiazepine heterocycle are reported. This complex constitutes a rare example of a carbene tautomer of a 1,4-benzodiazepine aldimine stabilized by transition metal coordination and demonstrates the ability of the catalytically relevant RhCl(PCy{sub 3}){sub 2} fragment to induce NHC-forming tautomerization of heterocycles possessing a single carbene-stabilizing heteroatom. Implications for the synthesis of benzodiazepines and related pharmacophores via C-H functionalization are discussed.

  10. Late-stage diversification of biologically active pyridazinones via a direct C-H functionalization strategy.

    PubMed

    Li, Wei; Fan, Zhoulong; Geng, Kaijun; Xu, Youjun; Zhang, Ao

    2015-01-14

    Divergent C-H functionalization reactions (arylation, carboxylation, olefination, thiolation, acetoxylation, halogenation, naphthylation) using a pyridazinone moiety as an internal directing group were successfully established. This approach offers a late-stage, ortho-selective diversification of a biologically active pyridazinone scaffold. Seven series of novel pyridazinone analogues were synthesized conveniently as the synthetic precursors of potential sortase A (SrtA) inhibitors.

  11. Magnetic graphitic carbon nitride: its application in the C-H activation of amines.

    PubMed

    Verma, Sanny; Nasir Baig, R B; Han, Changseok; Nadagouda, Mallikarjuna N; Varma, Rajender S

    2015-11-04

    Magnetic graphitic carbon nitride, Fe@g-C3N4, has been synthesized by adorning a graphitic carbon nitride (g-C3N4) support with iron oxide via non-covalent interaction. The magnetically recyclable catalyst showed excellent reactivity for the expeditious C-H activation and cyanation of amines.

  12. Revealing the nature of the active site on the carbon catalyst for C-H bond activation.

    PubMed

    Sun, XiaoYing; Li, Bo; Su, Dangsheng

    2014-09-28

    A reactivity descriptor for the C-H bond activation on the nanostructured carbon catalyst is proposed. Furthermore the calculations reveal that the single ketone group can be an active site in ODH reaction.

  13. Time resolved infrared studies of C-H bond activation by organometallics

    SciTech Connect

    Asplund, M.C. |

    1998-06-01

    This work describes how step-scan Fourier Transform Infrared spectroscopy and visible and near infrared ultrafast lasers have been applied to the study of the photochemical activation of C-H bonds in organometallic systems, which allow for the selective breaking of C-H bonds in alkanes. The author has established the photochemical mechanism of C-H activation by Tp{sup *}Rh(CO){sub 2}(Tp{sup *} = HB-Pz{sup *}{sub 3}, Pz = 3,5-dimethylpyrazolyl) in alkane solution. The initially formed monocarbonyl forms a weak solvent complex, which undergoes a change in Tp{sup *} ligand connectivity. The final C-H bond breaking step occurs at different time scales depending on the structure of the alkane. In linear solvents, the time scale is <50 ns and cyclic alkanes is {approximately}200 ps. The reactivity of the Tp{sup *}Rh(CO){sub 2} system has also been studied in aromatic solvents. Here the reaction proceeds through two different pathways, with very different time scales. The first proceeds in a manner analogous to alkanes and takes <50 ns. The second proceeds through a Rh-C-C complex, and takes place on a time scale of 1.8 {micro}s.

  14. I2-Mediated 2H-indazole synthesis via halogen-bond-assisted benzyl C-H functionalization.

    PubMed

    Yi, Xiangli; Jiao, Lei; Xi, Chanjuan

    2016-10-18

    I2-Mediated benzyl C-H functionalization has been developed for the synthesis of 2H-indazoles, which features high efficiency, simple conditions and no need for metals. Mechanistic experiments and DFT calculations have revealed halogen bond assistance and a radical chain process for this reaction. The azo group and the bound iodine cooperate in the hydrogen abstraction step, which circumvents the thermodynamic disfavor of direct hydrogen abstraction by a simple iodine radical.

  15. Highly Active Gold(I)-Silver(I) Oxo Cluster Activating sp³ C-H Bonds of Methyl Ketones under Mild Conditions.

    PubMed

    Pei, Xiao-Li; Yang, Yang; Lei, Zhen; Chang, Shan-Shan; Guan, Zong-Jie; Wan, Xian-Kai; Wen, Ting-Bin; Wang, Quan-Ming

    2015-04-29

    The activation of C(sp(3))-H bonds is challenging, due to their high bond dissociation energy, low proton acidity, and highly nonpolar character. Herein we report a unique gold(I)-silver(I) oxo cluster protected by hemilabile phosphine ligands [OAu3Ag3(PPhpy2)3](BF4)4 (1), which can activate C(sp(3))-H bonds under mild conditions for a broad scope of methyl ketones (RCOCH3, R = methyl, phenyl, 2-methylphenyl, 2-aminophenyl, 2-hydroxylphenyl, 2-pyridyl, 2-thiazolyl, tert-butyl, ethyl, isopropyl). Activation happens via triple deprotonation of the methyl group, leading to formation of heterometallic Au(I)-Ag(I) clusters with formula RCOCAu4Ag4(PPhpy2)4(BF4)5 (PPhpy2 = bis(2-pyridyl)phenylphosphine). Cluster 1 can be generated in situ via the reaction of [OAu3Ag(PPhpy2)3](BF4)2 with 2 equiv of AgBF4. The oxo ion and the metal centers are found to be essential in the cleavage of sp(3) C-H bonds of methyl ketones. Interestingly, cluster 1 selectively activates the C-H bonds in -CH3 rather than the N-H bonds in -NH2 or the O-H bond in -OH which is traditionally thought to be more reactive than C-H bonds. Control experiments with butanone, 3-methylbutanone, and cyclopentanone as substrates show that the auration of the C-H bond of the terminal methyl group is preferred over secondary or tertiary sp(3) C-H bonds; in other words, the C-H bond activation is influenced by steric effect. This work highlights the powerful reactivity of metal clusters toward C-H activation and sheds new light on gold(I)-mediated catalysis.

  16. Mild and Efficient Palladium-Catalyzed Direct Trifluoroethylation of Aromatic Systems by C-H Activation.

    PubMed

    Tóth, Balázs L; Kovács, Szabolcs; Sályi, Gergő; Novák, Zoltán

    2016-02-05

    The introduction of trifluoroalkyl groups into aromatic molecules is an important transformation in the field of organic and medicinal chemistry. However, the direct installation of fluoroalkyl groups onto aromatic molecules still represents a challenging and highly demanding synthetic task. Herein, a simple trifluoroethylation process that relies on the palladium-catalyzed C-H activation of aromatic compounds is described. With the utilization of a highly active trifluoroethyl(mesityl)iodonium salt, the developed catalytic method enables the first highly efficient and selective trifluoroethylation of aromatic compounds. The robust catalytic procedure provides the desired products in up to 95 % yield at 25 °C in 1.5 to 3 hours and tolerates a broad range of functional groups. The utilization of hypervalent reagents opens new synthetic possibilities for direct alkylations and fluoroalkylations in the field of transition-metal-catalyzed C-H activation.

  17. Electrophilic, Ambiphilic, and Nucleophilic C-H bond Activation. Understanding the electronic continuum of C-H bond activation through transition-state and reaction pathway interaction energy decompositions

    SciTech Connect

    Ess, Daniel H.; Goddard, William A.; Periana, Roy A.

    2010-10-29

    The potential energy and interaction energy profiles for metal- and metal-ligand-mediated alkane C-H bond activation were explored using B3LYP density functional theory (DFT) and the absolutely localized molecular orbital energy decomposition analysis (ALMO-EDA). The set of complexes explored range from late transition metal group 10 (Pt and Pd) and group 11 (Au) metal centers to group 7-9 (Ir, Rh, Ru, and W) metal centers as well as a group 3 Sc complex. The coordination geometries, electron metal count (d8, d6, d4, and d0), and ligands (N-heterocycles, O-donor, phosphine, and Cp*) are also diverse. Quantitative analysis using ALMO-EDA of both directions of charge-transfer stabilization (occupied to unoccupied orbital stabilization) energies between the metal-ligand fragment and the coordinated C-H bond in the transition state for cleavage of the C-H bond allows classification of C-H activation reactions as electrophilic, ambiphilic, or nucleophilic on the basis of the net direction of charge-transfer energy stabilization. This bonding pattern transcends any specific mechanistic or bonding paradigm, such as oxidative addition, σ-bond metathesis, or substitution. Late transition metals such as Au(III), Pt(II), Pd(II), and Rh(III) metal centers with N-heterocycle, halide, or O-donor ligands show electrophilically dominated reaction profiles with forward charge-transfer from the C-H bond to the metal, leading to more stabilization than reverse charge transfer from the metal to the C-H bond. Transition states and reaction profiles for d6 Ru(II) and Ir(III) metals with Tp and acac ligands were found to have nearly equal forward and reverse charge-transfer energy stabilization. This ambiphilic region also includes the classically labeled electrophilic cationic species Cp*(PMe3)Ir(Me). Nucleophilic character, where the metal to C-H bond charge-transfer interaction is most stabilizing, was found in

  18. Late-Stage Diversification of Biologically Active Molecules via Chemoenzymatic C-H Functionalization.

    PubMed

    Durak, Landon J; Payne, James T; Lewis, Jared C

    2016-03-04

    Engineered variants of rebeccamycin halogenase were used to selectively halogenate a number of biologically active aromatic compounds. Subsequent Pd-catalyzed cross-coupling reactions on the crude extracts of these reactions were used to install aryl, amine, and ether substituents at the halogenation site. This simple, chemoenzymatic method enables non-directed functionalization of C-H bonds on a range of substrates to provide access to derivatives that would be challenging or inefficient to prepare by other means.

  19. Ruthenium(II)-catalyzed C-H activation with isocyanates: a versatile route to phthalimides.

    PubMed

    De Sarkar, Suman; Ackermann, Lutz

    2014-10-20

    A cationic ruthenium(II)-complex was utilized in the efficient synthesis of phthalimide derivatives by C-H activation with synthetically useful amides. The reaction proceeded through a mechanistically unique insertion of a cycloruthenated species into a C-Het multiple bond of isocyanate. The novel method also proved applicable for the synthesis of heteroaromatic unsymmetric diamides as well as a potent COX-2 enzyme inhibitor.

  20. Asymmetric Intramolecular Alkylation of Chiral Aromatic Imines via Catalytic C-H Bond Activation

    SciTech Connect

    Watzke, Anja; Wilson, Rebecca; O'Malley, Steven; Bergman, Robert; Ellman, Jonathan

    2007-04-16

    The asymmetric intramolecular alkylation of chiral aromatic aldimines, in which differentially substituted alkenes are tethered meta to the imine, was investigated. High enantioselectivities were obtained for imines prepared from aminoindane derivatives, which function as directing groups for the rhodium-catalyzed C-H bond activation. Initial demonstration of catalytic asymmetric intramolecular alkylation also was achieved by employing a sterically hindered achiral imine substrate and catalytic amounts of a chiral amine.

  1. Photocatalytic C??H Activation of Hydrocarbons over VO@g??C3N4

    EPA Pesticide Factsheets

    A highly selective and sustainable method has been developed for the oxidation of methyl arenes and their analogues. The VO@g-C3N4 catalyst is very efficient in the C??H activation and oxygen insertion reaction resulting in formation of the corresponding carbonyl compounds and phenols.This dataset is associated with the following publication:Verma, S., R.B. Nasir Baig, M. Nadagouda , and R. Varma. Photocatalytic C−H Activation of Hydrocarbons over VO@g‑C3N4. ACS Sustainable Chemistry & Engineering. American Chemical Society, Washington, DC, USA, 4(4): 2333-2336, (2016).

  2. Radical-Mediated C-H Functionalization: A Strategy for Access to Modified Cyclodextrins.

    PubMed

    Alvarez-Dorta, Dimitri; León, Elisa I; Kennedy, Alan R; Martín, Angeles; Pérez-Martín, Inés; Suárez, Ernesto

    2016-12-02

    A simple and efficient radical C-H functionalization to access modified cyclodextrins (CDs) has been developed. The well-defined conformation of glycosidic and aglyconic bonds in α-, β-, and γ-CDs favors the intramolecular 1,8-hydrogen atom transfer (HAT) promoted by the 6(I)-O-yl radical, which abstracts regioselectively the hydrogen at C5(II) of the contiguous pyranose. The C5(II)-radical evolves by a polar crossover mechanism to a stable 1,3,5-trioxocane ring between two adjacent glucoses or alternatively triggers the inversion of one α-d-glucose into a 5-C-acetoxy-β-l-idose unit possessing a (1)C4 conformation. The 6(I,IV)- and 6(I,III)-diols of α- and β-CDs behave similarly to the monoalcohols, forming mostly compounds originating from two 1,8-HAT consecutive processes. In the case of 6(I,II)-diols the proximity of the two 6-O-yl radicals in adjacent sugar units allows the formation of unique lactone rings within the CD framework via a 1,8-HAT-β-scission tandem mechanism. X-ray diffraction carried out on the crystalline 1,4-bis(trioxocane)-α-CD derivative shows a severe distortion toward a narrower elliptical shape for the primary face.

  3. C-H Bond Activation/Arylation Catalyzed by Arene-Ruthenium-Aniline Complexes in Water.

    PubMed

    Binnani, Chinky; Tyagi, Deepika; Rai, Rohit K; Mobin, Shaikh M; Singh, Sanjay K

    2016-11-07

    Water-soluble arene-ruthenium complexes coordinated with readily available aniline-based ligands were successfully employed as highly active catalysts in the C-H bond activation and arylation of 2-phenylpyridine with aryl halides in water. A variety of (hetero)aryl halides were also used for the ortho-C-H bond arylation of 2-phenylpyridine to afford the corresponding ortho- monoarylated products as major products in moderate to good yields. Our investigations, including time-scaled NMR spectroscopy and mass spectrometry studies, evidenced that the coordinating aniline-based ligands, having varying electronic and steric properties, had a significant influence on the catalytic activity of the resulting arene-ruthenium-aniline-based complexes. Moreover, mass spectrometry identification of the cycloruthenated species, {(η(6) -arene)Ru(κ(2) -C,N-phenylpyridine)}(+) , and several ligand-coordinated cycloruthenated species, such as [(η(6) -arene)Ru(4-methylaniline)(κ(2) -C,N-phenylpyridine)](+) , found during the reaction of 2-phenylpyridine with the arene-ruthenium-aniline complexes further authenticated the crucial roles of these species in the observed highly active and tuned catalyst. At last, the structures of a few of the active catalysts were also confirmed by single-crystal X-ray diffraction studies.

  4. Pd-Catalyzed C-H activation/oxidative cyclization of acetanilide with norbornene: concise access to functionalized indolines.

    PubMed

    Gao, Yang; Huang, Yubing; Wu, Wanqing; Huang, Kefan; Jiang, Huanfeng

    2014-08-07

    An efficient Pd-catalyzed oxidative cyclization reaction for the synthesis of functionalized indolines by direct C-H activation of acetanilide has been developed. The norbornylpalladium species formed via direct ortho C-H activation of acetanilides is supposed to be a key intermediate in this transformation.

  5. Understanding trends in C-H bond activation in heterogeneous catalysis.

    PubMed

    Latimer, Allegra A; Kulkarni, Ambarish R; Aljama, Hassan; Montoya, Joseph H; Yoo, Jong Suk; Tsai, Charlie; Abild-Pedersen, Frank; Studt, Felix; Nørskov, Jens K

    2017-02-01

    While the search for catalysts capable of directly converting methane to higher value commodity chemicals and liquid fuels has been active for over a century, a viable industrial process for selective methane activation has yet to be developed. Electronic structure calculations are playing an increasingly relevant role in this search, but large-scale materials screening efforts are hindered by computationally expensive transition state barrier calculations. The purpose of the present letter is twofold. First, we show that, for the wide range of catalysts that proceed via a radical intermediate, a unifying framework for predicting C-H activation barriers using a single universal descriptor can be established. Second, we combine this scaling approach with a thermodynamic analysis of active site formation to provide a map of methane activation rates. Our model successfully rationalizes the available empirical data and lays the foundation for future catalyst design strategies that transcend different catalyst classes.

  6. Understanding trends in C-H bond activation in heterogeneous catalysis

    NASA Astrophysics Data System (ADS)

    Latimer, Allegra A.; Kulkarni, Ambarish R.; Aljama, Hassan; Montoya, Joseph H.; Yoo, Jong Suk; Tsai, Charlie; Abild-Pedersen, Frank; Studt, Felix; Nørskov, Jens K.

    2016-10-01

    While the search for catalysts capable of directly converting methane to higher value commodity chemicals and liquid fuels has been active for over a century, a viable industrial process for selective methane activation has yet to be developed. Electronic structure calculations are playing an increasingly relevant role in this search, but large-scale materials screening efforts are hindered by computationally expensive transition state barrier calculations. The purpose of the present letter is twofold. First, we show that, for the wide range of catalysts that proceed via a radical intermediate, a unifying framework for predicting C-H activation barriers using a single universal descriptor can be established. Second, we combine this scaling approach with a thermodynamic analysis of active site formation to provide a map of methane activation rates. Our model successfully rationalizes the available empirical data and lays the foundation for future catalyst design strategies that transcend different catalyst classes.

  7. Annulation of Aromatic Imines via Directed C-H BondActivation

    SciTech Connect

    Thalji, Reema K.; Ahrendt, Kateri A.; Bergman, Robert G.; Ellman,Jonathan A.

    2005-04-14

    A directed C-H bond activation approach to the synthesis of indans, tetralins, dihydrofurans, dihydroindoles, and other polycyclic aromatic compounds is presented. Cyclization of aromatic ketimines and aldimines containing alkenyl groups tethered at the meta position relative to the imine directing group has been achieved using (PPh{sub 3}){sub 3}RhCl (Wilkinson's catalyst). The cyclization of a range of aromatic ketimines and aldimines provides bi- and tricyclic ring systems with good regioselectivity. Different ring sizes and substitution patterns can be accessed through the coupling of monosubstituted, 1,1- or 1,2-disubstituted, and trisubstituted alkenes bearing both electron-rich and electron-deficient functionality.

  8. Selective molecular recognition, C-H bond activation, and catalysis in nanoscale reaction vessels

    SciTech Connect

    Fiedler, Dorothea; Leung, Dennis H.; Raymond, Kenneth N.; Bergman, Robert G.

    2004-11-27

    Supramolecular chemistry represents a way to mimic enzyme reactivity by using specially designed container molecules. We have shown that a chiral self-assembled M{sub 4}L{sub 6} supramolecular tetrahedron can encapsulate a variety of cationic guests, with varying degrees of stereoselectivity. Reactive iridium guests can be encapsulated and the C-H bond activation of aldehydes occurs, with the host cavity controlling the ability of substrates to interact with the metal center based upon size and shape. In addition, the host container can act as a catalyst by itself. By restricting reaction space and preorganizing the substrates into reactive conformations, it accelerates the sigmatropic rearrangement of enammonium cations.

  9. The Effect of Nano Confinement on the C-H Activation and its Corresponding Structure-Activity Relationship

    NASA Astrophysics Data System (ADS)

    Shao, Jing; Yuan, Linghua; Hu, Xingbang; Wu, Youting; Zhang, Zhibing

    2014-11-01

    The C-H activation of methane, ethane, and t-butane on inner and outer surfaces of nitrogen-doped carbon nanotube (NCNTs) are investigated using density functional theory. It includes NCNTs with different diameters, different N and O concentrations, and different types (armchair and zigzag). A universal structure-reactivity relationship is proposed to characterize the C-H activation occurring both on the inner and outer surfaces of the nano channel. The C-O bond distance, spin density and charge carried by active oxygen are found to be highly related to the C-H activation barriers. Based on these theoretical results, some useful strategies are suggested to guide the rational design of more effective catalysts by nano channel confinement.

  10. The effect of nano confinement on the C-h activation and its corresponding structure-activity relationship.

    PubMed

    Shao, Jing; Yuan, Linghua; Hu, Xingbang; Wu, Youting; Zhang, Zhibing

    2014-11-27

    The C-H activation of methane, ethane, and t-butane on inner and outer surfaces of nitrogen-doped carbon nanotube (NCNTs) are investigated using density functional theory. It includes NCNTs with different diameters, different N and O concentrations, and different types (armchair and zigzag). A universal structure-reactivity relationship is proposed to characterize the C-H activation occurring both on the inner and outer surfaces of the nano channel. The C-O bond distance, spin density and charge carried by active oxygen are found to be highly related to the C-H activation barriers. Based on these theoretical results, some useful strategies are suggested to guide the rational design of more effective catalysts by nano channel confinement.

  11. C-H Activation on Co,O Sites: Isolated Surface Sites versus Molecular Analogs.

    PubMed

    Estes, Deven P; Siddiqi, Georges; Allouche, Florian; Kovtunov, Kirill V; Safonova, Olga V; Trigub, Alexander L; Koptyug, Igor V; Copéret, Christophe

    2016-11-16

    The activation and conversion of hydrocarbons is one of the most important challenges in chemistry. Transition-metal ions (V, Cr, Fe, Co, etc.) isolated on silica surfaces are known to catalyze such processes. The mechanisms of these processes are currently unknown but are thought to involve C-H activation as the rate-determining step. Here, we synthesize well-defined Co(II) ions on a silica surface using a metal siloxide precursor followed by thermal treatment under vacuum at 500 °C. We show that these isolated Co(II) sites are catalysts for a number of hydrocarbon conversion reactions, such as the dehydrogenation of propane, the hydrogenation of propene, and the trimerization of terminal alkynes. We then investigate the mechanisms of these processes using kinetics, kinetic isotope effects, isotopic labeling experiments, parahydrogen induced polarization (PHIP) NMR, and comparison with a molecular analog. The data are consistent with all of these reactions occurring by a common mechanism, involving heterolytic C-H or H-H activation via a 1,2 addition across a Co-O bond.

  12. 2008 C. H. McCloy lecture. Social psychology and physical activity: back to the future.

    PubMed

    Gill, Diane L

    2009-12-01

    In the early 1970s, both my academic career and the psychology subdiscipline within kinesiology began as "social psychology and physical activity. "Since then, sport and exercise psychology research has shifted away from the social to a narrower biopsycho-(no social) approach, and professional practice has focused on the elite rather than the larger public. Psychology can contribute to an integrative and relevant professional discipline by going back to the future as social psychology and physical activity and by incorporating three of C. H. McCloy's themes (a) evidence-based practice, (b) beyond dualisms, and (c) commitment to public service. Our scholarship must move beyond dualisms to recognize complexities and connections and be truly scholarship for practice. Social psychology and physical activity can serve the public by advocating for inclusive, empowering physical activity programs that promote health and well being for all.

  13. Palladium-catalyzed oxidative arylalkylation of activated alkenes: dual C-H bond cleavage of an arene and acetonitrile.

    PubMed

    Wu, Tao; Mu, Xin; Liu, Guosheng

    2011-12-23

    Not one but two: The title reaction proceeds through the dual C-H bond cleavage of both aniline and acetonitrile. The reaction affords a variety of cyano-bearing indolinones in excellent yield. Mechanistic studies demonstrate that this reaction involves a fast arylation of the olefin and a rate-determining C-H activation of the acetonitrile.

  14. Carbon-Hydrogen (C-H) Bond Activation at PdIV: A Frontier in C–H Functionalization Catalysis

    PubMed Central

    Topczewski, Joseph J.; Sanford, Melanie S.

    2014-01-01

    The direct functionalization of carbon-hydrogen (C-H) bonds has emerged as a versatile strategy for the synthesis and derivatization of organic molecules. Among the methods for C-H bond activation, catalytic processes that utilize a PdII/PdIV redox cycle are increasingly common. The C-H activation step in most of these catalytic cycles is thought to occur at a PdII centre. However, a number of recent reports have suggested the feasibility of C-H cleavage occurring at PdIV complexes. Importantly, these latter processes often result in complementary reactivity and selectivity relative to analogous transformations at PdII. This Mini Review highlights proposed examples of C-H activation at PdIV centres. Applications of this transformation in catalysis as well as mechanistic details obtained from stoichiometric model studies are discussed. Furthermore, challenges and future perspectives for the field are reviewed. PMID:25544882

  15. Enhanced Reactivity in Hydrogen Atom Transfer from Tertiary Sites of Cyclohexanes and Decalins via Strain Release: Equatorial C-H Activation vs Axial C-H Deactivation.

    PubMed

    Salamone, Michela; Ortega, Vanesa B; Bietti, Massimo

    2015-05-01

    Absolute rate constants for hydrogen atom transfer (HAT) from cycloalkanes and decalins to the cumyloxyl radical (CumO(•)) were measured by laser flash photolysis. Very similar reactivities were observed for the C-H bonds of cyclopentane and cyclohexane, while the tertiary C-H bond of methylcyclopentane was found to be 6 times more reactive than the tertiary axial C-H bond of methylcyclohexane, pointing toward a certain extent of tertiary axial C-H bond deactivation. Comparison between the cis and trans isomers of 1,2-dimethylcyclohexane, 1,4-dimethylcyclohexane and decalin provides a quantitative evaluation of the role played by strain release in these reactions. kH values for HAT from tertiary equatorial C-H bonds were found to be at least 1 order of magnitude higher than those for HAT from the corresponding tertiary axial C-H bonds (kH(eq)/kH(ax) = 10-14). The higher reactivity of tertiary equatorial C-H bonds was explained in terms of 1,3-diaxial strain release in the HAT transition state. Increase in torsional strain in the HAT transition state accounts instead for tertiary axial C-H bond deactivation. The results are compared with those obtained for the corresponding C-H functionalization reactions by dioxiranes and nonheme metal-oxo species indicating that CumO(•) can represent a convenient model for the reactivity patterns of these oxidants.

  16. A study on Zr-Ir multiple bonding active for C-H bond cleavage.

    PubMed

    Oishi, Masataka; Oshima, Masato; Suzuki, Hiroharu

    2014-07-07

    Zr-Ir hydrido complexes with ansa-(cyclopentadienyl)(amide) as the supporting ligand in the zirconium fragment, e.g., (L(1)ZrR)(Cp*Ir)(μ-H)3 [L(1) = Me2Si(η(5)-C5Me4)(N(t)Bu), R = Cl (5), Ph (7), Me (10), alkyl, and aryl] were designed, synthesized, and isolated as tractable early-late heterodinuclear complexes. Despite the presence of the three supporting hydride ligands, Zr-Ir distances in the crystal structures of 5, alkyl, and aryl complexes [2.74-2.76 Å] were slightly longer than the sum of the element radii of Zr and Ir [2.719 Å]. These hydrocarbyl complexes displayed the thermolytic C-H activation of a variety of aromatic compounds and several organometallic compounds. Also, the substrate scope and limitation in the Zr-Ir system were studied. The regiochemical outcomes during the C-H activation of pyridine derivatives and methoxyarenes suggested the in situ generation of a Lewis acidic active intermediate, i.e., (L(1)Zr)(Cp*IrH2) (III). The existence of III and relevant σ-complex intermediates {L(1)Zr(η(2)-R-H)}(Cp*IrH2) (IIR) (R = Me, Ph) in the ligand exchange was demonstrated by the direct isolation of a Et3PO-adduct of III (39b) from 7 and kinetic studies. The structure of the direct Zr-Ir bonds in IIPh, IIMe, III, and 39b were probed using computational studies. The unprecedented strong M-M' interactions in the early-late heterobimetallic (ELHB) complexes have been proposed herein.

  17. Rh(III)-catalyzed synthesis of sultones through C-H activation directed by a sulfonic acid group.

    PubMed

    Qi, Zisong; Wang, Mei; Li, Xingwei

    2014-09-04

    A new rhodium-catalyzed synthesis of sultones via the oxidative coupling of sulfonic acids with internal alkynes is described. The reaction proceeds via aryl C-H activation assisted by a sulfonic acid group.

  18. Iron Mineral Catalyzed C-H Activation As a Potential Pathway for Halogenation Processes

    NASA Astrophysics Data System (ADS)

    Tubbesing, C.; Schoeler, H. F.; Benzing, K.; Krause, T.; Lippe, S.; Rudloff, M.

    2014-12-01

    Due to increasing drinking water demand of mankind and an expected climate change the impact of salt lakes and salt deserts will increase within the next decades. Furthermore, a rising sea level influences coastal areas like salt marshes and abets processes which will lead to elevated organohalogen formation. An additional increase of the global warming potential, of particle formation and stratospheric ozone depletion is expected. Understanding these multifaceted processes is essential for mankind to be prepared for these alterations of the atmosphere. For example, Keppler et al. (2000) described the production of volatile halogenated organic compounds via oxidation of organic matter driven by ferric iron. However, the formation of long-chained alkyl halides in salt lakes is yet undisclosed. Despite the relative "inertness" of alkanes a direct halogenation of these compounds might be envisaged. In 2005 Vaillancourt et al. discovered a nonheme iron enzyme which is able to halogenate organic compounds via generating the high valent ferryl cation as reaction center. Based on various publications about C-H activation (Bergman, 2007) we postulate a halogenation process in which an iron containing minerals catalyse the C-H bond cleavage of organic compounds in soils. The generated organic radicals are highly reactive towards halides connected to the iron complex. We suggest that next to diagenetically altered iron containing enzymes, minerals such as oxides, hydroxides and sulfides are involved in abiotic halogenation processes. We applied the amino acid methionine as organic model compound and soluble iron species as reactants. All samples were incubated in aqueous phases containing various NaCl concentrations. As a result various halogenated ethanes and ethenes were identified as reaction products. References Bergman, R. G. (2007) Nature, 446(7134) 391-393 Keppler, F., et al. (2000) Nature, 403(6767) 298-301 Vaillancourt, F. H., et al. (2005) Nature, 436(7054) 1191-1194

  19. Direct Functionalization of Nitrogen Heterocycles via Rh-Catalyzed C-H Bond Activation

    SciTech Connect

    Lewis, Jared; Bergman, Robert; Ellman, Jonathan

    2008-02-04

    Nitrogen heterocycles are present in many compounds of enormous practical importance, ranging from pharmaceutical agents and biological probes to electroactive materials. Direct funtionalization of nitrogen heterocycles through C-H bond activation constitutes a powerful means of regioselectively introducing a variety of substituents with diverse functional groups onto the heterocycle scaffold. Working together, our two groups have developed a family of Rh-catalyzed heterocycle alkylation and arylation reactions that are notable for their high level of functional-group compatibility. This Account describes their work in this area, emphasizing the relevant mechanistic insights that enabled synthetic advances and distinguished the resulting transformations from other methods. They initially discovered an intramolecular Rh-catalyzed C-2-alkylation of azoles by alkenyl groups. That reaction provided access to a number of di-, tri-, and tetracyclic azole derivatives. They then developed conditions that exploited microwave heating to expedite these reactions. While investigating the mechanism of this transformation, they discovered that a novel substrate-derived Rh-N-heterocyclic carbene (NHC) complex was involved as an intermediate. They then synthesized analogous Rh-NHC complexes directly by treating precursors to the intermediate [RhCl(PCy{sub 3}){sub 2}] with N-methylbenzimidazole, 3-methyl-3,4-dihydroquinazolein, and 1-methyl-1,4-benzodiazepine-2-one. Extensive kinetic analysis and DFT calculations supported a mechanism for carbene formation in which the catalytically active RhCl(PCy{sub 3}){sub 2} fragment coordinates to the heterocycle before intramolecular activation of the C-H bond occurs. The resulting Rh-H intermediate ultimately tautomerizes to the observed carbene complex. With this mechanistic information and the discovery that acid co-catalysts accelerate the alkylation, they developed conditions that efficiently and intermolecularly alkylate a variety of

  20. Graphene Oxide Catalyzed C-H Bond Activation: The Importance Oxygen Functional Groups for Biaryl Construction

    SciTech Connect

    Gao, Yongjun; Tang, Pei; Zhou, Hu; Zhang, Wei; Yang, Hanjun; Yan, Ning; Hu, Gang; Mei, Donghai; Wang, Jianguo; Ma, Ding

    2016-02-24

    A heterogeneous, inexpensive and environment-friendly carbon catalytic system was developed for the C-H bond arylation of benzene resulting in the subsequent formation of biaryl compounds. The oxygen-containing groups on these graphene oxide sheets play an essential role in the observed catalytic activity. The catalytic results of model compounds and DFT calculations show that these functional groups promote this reaction by stabilization and activation of K ions at the same time of facilitating the leaving of I. And further mechanisms studies show that it is the charge induced capabilities of oxygen groups connected to specific carbon skeleton together with the giant π-reaction platform provided by the π-domain of graphene that played the vital roles in the observed excellent catalytic activity. D. Mei acknowledges the support from the US Department of Energy (DOE), Office of Science, Office of Basic Energy Sciences, Division of Chemical Sciences, Geosciences & Biosciences. Pacific Northwest National Laboratory (PNNL) is a multiprogram national laboratory operated for DOE by Battelle. Computing time was granted by the grand challenge of computational catalysis of the William R. Wiley Environmental Molecular Sciences Laboratory.

  1. Mechanistic Insight into the Rh(III)-Catalyzed C-H Activation of 2-Acetyl-1-Arythydrazines in Water.

    PubMed

    Wu, Weirong; Liu, Tao; Huang, Caiyun; Zhang, Jing; Man, Xiaoping

    2017-03-02

    A mechanistic study of the Cp*Rh(III)-catalyzed C-H functionalization of 2-acetyl-1-arythydrazines with diazo compounds in water was carried out by using density functional theory calculations. The results reveal that the acetyl-bonded N-H deprotonation is prior to the phenyl C-H activation. The mechanisms from protonation by acetic acid disagree with the proposal by the Wang group. Different from the Rh(III)-catalyzed C-H activation reported by experimental literature, the rate-determining step of the whole catalytic cycle with an overall barrier of 31.7 kcal mol(-1) (IV → TS12-P') is the protonation process of hydroxy O rather than the C-H bond cleavage step. The present theoretical study rationalizes the experimental observation at the molecular level.

  2. Functionalization of non-activated C-H bonds in the synthesis of vitamin D metabolites and analogs.

    PubMed

    Moman, Edelmiro

    2014-01-01

    The development of non-microbial methods for the selective functionalization of non-activated C-H bonds has constituted a challenge, with important economical and environmental implications, for chemists for over a century. The present review provides a comprehensive and current compendium that illustrates the power of C-H functionalization and, namely, of remote functionalization strategies, to expeditiously access vitamin D analogs with intricate structures.

  3. Unexpected C-H activation of Ru(II)-dithiomaltol complexes upon oxidation.

    PubMed

    Backlund, Malin; Ziller, Joseph; Farmer, Patrick J

    2008-04-07

    Thione-substituted derivatives of maltol are of interest in several applications of metal-based drugs. In order to investigate the effect of the oxygenation on such thione chelates, Ru complexes of 3-hydroxy-2-methyl-4-thiopyrone (thiomaltol or Htma) and 3-hydroxy-2-methyl-4H-thiopyran-4-thione (dithiomaltol or Httma), [Ru(bpy)2(tma)](+), 1, and [Ru(bpy) 2(ttma)] (+), 2, were synthesized as diamagnetic PF6(-) salts. Peroxidation of 2 unexpectedly generated products of C-H activation at its pendant methyl group; an air-stable aldehyde [Ru(bpy)2(ttma-aldehyde)](+), 4, was the major product. In addition, an intermediate oxidation product [Ru(bpy) 2(ttma-alcohol)](PF6), 3, was characterized. Both 3 and 4 are also formed by reaction of 2 with outersphere oxidants (e.g., Na2IrCl6) and by bulk electrolysis under anaerobic conditions. Similar oxidations of the analogous [Ru(bpy)2(ettma)](+), 2' , complex (3-hydroxy-2-ethyl-4H-thiopyran-4-thione; ethyl dithiomaltol or Hettma) formed the corresponding ketone, [Ru(bpy)2(ettma-ketone)](PF6), 4', by oxidation at the same position adjacent to the conjugated ring. The structures of the aldehyde 4 and starting materials 1 and 2 have been confirmed by X-ray crystallography, and all complexes have been characterized by UV-vis, (1)H NMR, and IR spectroscopies. Initial mechanistic investigations are discussed.

  4. Chemically Non-Innocent Cyclic (Alkyl)(Amino)Carbenes: Ligand Rearrangement, C-H and C-F Bond Activation.

    PubMed

    Turner, Zoë R

    2016-08-01

    A cyclic (alkyl)(amino)carbene (CAAC) was found to undergo unprecedented rearrangements and transformations of its core structure in the presence of Group 1 and 2 metals. Although the carbene was also found to be prone to intramolecular C-H activation, it was competent for intermolecular activation of a variety of sp-, sp(2) -, and sp(3) -hybridized C-H bonds. Double C-F activation of hexafluorobenzene was also observed in this work. These processes all hold relevance to the role of these carbenes in catalysis, as well as to their use in the synthesis of new and unusual main group or transition metal complexes.

  5. Advancements in the Synthesis and Applications of Cationic N-Heterocycles through Transition Metal-Catalyzed C-H Activation.

    PubMed

    Gandeepan, Parthasarathy; Cheng, Chien-Hong

    2016-02-18

    Cationic N-heterocycles are an important class of organic compounds largely present in natural and bioactive molecules. They are widely used as fluorescent dyes for biological studies, as well as in spectroscopic and microscopic methods. These compounds are key intermediates in many natural and pharmaceutical syntheses. They are also a potential candidate for organic light-emitting diodes (OLEDs). Because of these useful applications, the development of new methods for the synthesis of cationic N-heterocycles has received a lot of attention. In particular, many C-H activation methodologies that realize high step- and atom-economies toward these compounds have been developed. In this review, recent advancements in the synthesis and applications of cationic N-heterocycles through C-H activation reactions are summarized. The new C-H activation reactions described in this review are preferred over their classical analogs.

  6. Amidines for versatile ruthenium(II)-catalyzed oxidative C-H activations with internal alkynes and acrylates.

    PubMed

    Li, Jie; John, Michael; Ackermann, Lutz

    2014-04-25

    Cationic ruthenium complexes derived from KPF6 or AgOAc enabled efficient oxidative CH functionalizations on aryl and heteroaryl amidines. Thus, oxidative annulations of diversely decorated internal alkynes provided expedient access to 1-aminoisoquinolines, while catalyzed C-H activations with substituted acrylates gave rise to structurally novel 1-iminoisoindolines. The powerful ruthenium(II) catalysts displayed a remarkably high site-, regio- and, chemoselectivity. Therefore, the catalytic system proved tolerant of a variety of important electrophilic functional groups. Detailed mechanistic studies provided strong support for the cationic ruthenium(II) catalysts to operate by a facile, reversible C-H activation.

  7. Highly Active Nickel Catalysts for C-H Functionalization Identified through Analysis of Off-Cycle Intermediates.

    PubMed

    Nett, Alex J; Zhao, Wanxiang; Zimmerman, Paul M; Montgomery, John

    2015-06-24

    An inhibitory role of 1,5-cyclooctadiene (COD) in nickel-catalyzed C-H functionalization processes was identified and studied. The bound COD participates in C-H activation by capturing the hydride, leading to a stable off-cycle π-allyl complex that greatly diminished overall catalytic efficiency. Computational studies elucidated the origin of the effect and enabled identification of a 1,5-hexadiene-derived pre-catalyst that avoids the off-cycle intermediate and provides catalytic efficiencies that are superior to those of catalysts derived from Ni(COD)2.

  8. Single-Component Phosphinous Acid Ruthenium(II) Catalysts for Versatile C-H Activation by Metal-Ligand Cooperation.

    PubMed

    Zell, Daniel; Warratz, Svenja; Gelman, Dmitri; Garden, Simon J; Ackermann, Lutz

    2016-01-22

    Well-defined ruthenium(II) phosphinous acid (PA) complexes enabled chemo-, site-, and diastereoselective C-H functionalization of arenes and alkenes with ample scope. The outstanding catalytic activity was reflected by catalyst loadings as low as 0.75 mol %, and the most step-economical access reported to date to angiotensin II receptor antagonist blockbuster drugs. Mechanistic studies indicated a kinetically relevant C-X cleavage by a single-electron transfer (SET)-type elementary process, and provided evidence for a PA-assisted C-H ruthenation step.

  9. Cationic Pd(II)-catalyzed C-H activation/cross-coupling reactions at room temperature: synthetic and mechanistic studies.

    PubMed

    Nishikata, Takashi; Abela, Alexander R; Huang, Shenlin; Lipshutz, Bruce H

    2016-01-01

    Cationic palladium(II) complexes have been found to be highly reactive towards aromatic C-H activation of arylureas at room temperature. A commercially available catalyst [Pd(MeCN)4](BF4)2 or a nitrile-free cationic palladium(II) complex generated in situ from the reaction of Pd(OAc)2 and HBF4, effectively catalyzes C-H activation/cross-coupling reactions between aryl iodides, arylboronic acids and acrylates under milder conditions than those previously reported. The nature of the directing group was found to be critical for achieving room temperature conditions, with the urea moiety the most effective in promoting facile coupling reactions at an ortho C-H position. This methodology has been utilized in a streamlined and efficient synthesis of boscalid, an agent produced on the kiloton scale annually and used to control a range of plant pathogens in broadacre and horticultural crops. Mechanistic investigations led to a proposed catalytic cycle involving three steps: (1) C-H activation to generate a cationic palladacycle; (2) reaction of the cationic palladacycle with an aryl iodide, arylboronic acid or acrylate, and (3) regeneration of the active cationic palladium catalyst. The reaction between a cationic palladium(II) complex and arylurea allowed the formation and isolation of the corresponding palladacycle intermediate, characterized by X-ray analysis. Roles of various additives in the stepwise process have also been studied.

  10. Metal-free oxidative hydroxyalkylarylation of activated alkenes by direct sp3 C-H functionalization of alcohols.

    PubMed

    Meng, Yuan; Guo, Li-Na; Wang, Hua; Duan, Xin-Hua

    2013-09-04

    A metal-free tandem radical addition/cyclization reaction of activated alkenes and alcohols has been developed. The process provides an efficient and atom economical access to various valuable hydroxyl-containing oxindoles through the direct sp(3) C-H functionalization of alcohols.

  11. Rhodium(III)-catalyzed C-H activation/annulation with vinyl esters as an acetylene equivalent.

    PubMed

    Webb, Nicola J; Marsden, Stephen P; Raw, Steven A

    2014-09-19

    The behavior of electron-rich alkenes in rhodium-catalyzed C-H activation/annulation reactions is investigated. Vinyl acetate emerges as a convenient acetylene equivalent, facilitating the synthesis of sixteen 3,4-unsubstituted isoquinolones, as well as select heteroaryl-fused pyridones. The complementary regiochemical preferences of enol ethers versus enol esters/enamides is discussed.

  12. C-H bond activation enables the rapid construction and late-stage diversification of functional molecules

    NASA Astrophysics Data System (ADS)

    Wencel-Delord, Joanna; Glorius, Frank

    2013-05-01

    The beginning of the twenty-first century has witnessed significant advances in the field of C-H bond activation, and this transformation is now an established piece in the synthetic chemists' toolbox. This methodology has the potential to be used in many different areas of chemistry, for example it provides a perfect opportunity for the late-stage diversification of various kinds of organic scaffolds, ranging from relatively small molecules like drug candidates, to complex polydisperse organic compounds such as polymers. In this way, C-H activation approaches enable relatively straightforward access to a plethora of analogues or can help to streamline the lead-optimization phase. Furthermore, synthetic pathways for the construction of complex organic materials can now be designed that are more atom- and step-economical than previous methods and, in some cases, can be based on synthetic disconnections that are just not possible without C-H activation. This Perspective highlights the potential of metal-catalysed C-H bond activation reactions, which now extend beyond the field of traditional synthetic organic chemistry.

  13. Conversion of 1-alkenes into 1,4-diols through an auxiliary-mediated formal homoallylic C-H oxidation.

    PubMed

    Ghavtadze, Nugzar; Melkonyan, Ferdinand S; Gulevich, Anton V; Huang, Chunhui; Gevorgyan, Vladimir

    2014-02-01

    The ubiquitous nature of C-H bonds in organic molecules makes them attractive as a target for rapid complexity generation, but brings with it the problem of achieving selective reactions. In developing new methodologies for C-H functionalization, alkenes are an attractive starting material because of their abundance and low cost. Here we describe the conversion of 1-alkenes into 1,4-diols. The method involves the installation of a new Si,N-type chelating auxiliary group on the alkene followed by iridium-catalysed C-H silylation of an unactivated δ-C(sp(3))-H bond to produce a silolane intermediate. Oxidation of the C-Si bonds affords a 1,4-diol. The method is demonstrated to have broad scope and good functional group compatibility by application to the selective 1,4-oxygenation of several natural products and derivatives.

  14. Rhodium-Catalyzed C-C Bond Formation via Heteroatom-Directed C-H Bond Activation

    SciTech Connect

    Colby, Denise; Bergman, Robert; Ellman, Jonathan

    2010-05-13

    Once considered the 'holy grail' of organometallic chemistry, synthetically useful reactions employing C-H bond activation have increasingly been developed and applied to natural product and drug synthesis over the past decade. The ubiquity and relative low cost of hydrocarbons makes C-H bond functionalization an attractive alternative to classical C-C bond forming reactions such as cross-coupling, which require organohalides and organometallic reagents. In addition to providing an atom economical alternative to standard cross - coupling strategies, C-H bond functionalization also reduces the production of toxic by-products, thereby contributing to the growing field of reactions with decreased environmental impact. In the area of C-C bond forming reactions that proceed via a C-H activation mechanism, rhodium catalysts stand out for their functional group tolerance and wide range of synthetic utility. Over the course of the last decade, many Rh-catalyzed methods for heteroatom-directed C-H bond functionalization have been reported and will be the focus of this review. Material appearing in the literature prior to 2001 has been reviewed previously and will only be introduced as background when necessary. The synthesis of complex molecules from relatively simple precursors has long been a goal for many organic chemists. The ability to selectively functionalize a molecule with minimal pre-activation can streamline syntheses and expand the opportunities to explore the utility of complex molecules in areas ranging from the pharmaceutical industry to materials science. Indeed, the issue of selectivity is paramount in the development of all C-H bond functionalization methods. Several groups have developed elegant approaches towards achieving selectivity in molecules that possess many sterically and electronically similar C-H bonds. Many of these approaches are discussed in detail in the accompanying articles in this special issue of Chemical Reviews. One approach that has

  15. Activation of Propane C-H and C-C Bonds by Gas-Phase Pt Atom: A Theoretical Study

    PubMed Central

    Li, Fang-Ming; Yang, Hua-Qing; Ju, Ting-Yong; Li, Xiang-Yuan; Hu, Chang-Wei

    2012-01-01

    The reaction mechanism of the gas-phase Pt atom with C3H8 has been systematically investigated on the singlet and triplet potential energy surfaces at CCSD(T)//BPW91/6-311++G(d, p), Lanl2dz level. Pt atom prefers the attack of primary over secondary C-H bonds in propane. For the Pt + C3H8 reaction, the major and minor reaction channels lead to PtC3H6 + H2 and PtCH2 + C2H6, respectively, whereas the possibility to form products PtC2H4 + CH4 is so small that it can be neglected. The minimal energy reaction pathway for the formation of PtC3H6 + H2, involving one spin inversion, prefers to start at the triplet state and afterward proceed along the singlet state. The optimal C-C bond cleavages are assigned to C-H bond activation as the first step, followed by cleavage of a C-C bond. The C-H insertion intermediates are kinetically favored over the C-C insertion intermediates. From C-C to C-H oxidative insertion, the lowering of activation barrier is mainly caused by the more stabilizing transition state interaction ΔE≠int, which is the actual interaction energy between the deformed reactants in the transition state. PMID:22942766

  16. Oxygen activation and intramolecular C-H bond activation by an amidate-bridged diiron(II) complex.

    PubMed

    Jones, Matthew B; Hardcastle, Kenneth I; Hagen, Karl S; MacBeth, Cora E

    2011-07-18

    A diiron(II) complex containing two μ-1,3-(κN:κO)-amidate linkages has been synthesized using the 2,2',2''-tris(isobutyrylamido)triphenylamine (H(3)L(iPr)) ligand. The resulting diiron complex, 1, reacts with dioxygen (or iodosylbenzene) to effect intramolecular C-H bond activation at the methine position of the ligand isopropyl group. The ligand-activated product, 2, has been isolated and characterized by a variety of methods including X-ray crystallography. Electrospray ionization mass spectroscopy of 2 prepared from(18)O(2) was used to confirm that the oxygen atom incorporated into the ligand framework is derived from molecular oxygen.

  17. Tandem C-H activation/arylation catalyzed by low-valent iron complexes with bisiminopyridine ligands.

    PubMed

    Salanouve, Elise; Bouzemame, Ghania; Blanchard, Sébastien; Derat, Etienne; Desage-El Murr, Marine; Fensterbank, Louis

    2014-04-14

    Tandem C-H activation/arylation between unactivated arenes and aryl halides catalyzed by iron complexes that bear redox-active non-innocent bisiminopyridine ligands is reported. Similar reactions catalyzed by first-row transition metals have been shown to involve substrate-based aryl radicals, whereas our catalytic system likely involves ligand-centered radicals. Preliminary mechanistic investigations based on spectroscopic and reactivity studies, in conjunction with DFT calculations, led us to propose that the reaction could proceed through an inner-sphere C-H activation pathway, which is rarely observed in the case of iron complexes. This bielectronic noble-metal-like behavior could be sustained by the redox-active non-innocent bisiminopyridine ligands.

  18. C-H bond activation of benzene by unsaturated η2-cyclopropene and η2-benzyne complexes of niobium.

    PubMed

    Boulho, Cédric; Oulié, Pascal; Vendier, Laure; Etienne, Michel; Pimienta, Véronique; Locati, Abel; Bessac, Fabienne; Maseras, Feliu; Pantazis, Dimitrios A; McGrady, John E

    2010-10-13

    We report the synthesis of a niobium cyclopropyl complex, Tp(Me2)NbMe(c-C(3)H(5))(MeCCMe), and show that thermal loss of methane from this compound generates an intermediate that is capable of activating both aliphatic and aromatic C-H bonds. Isotopic labeling, trapping studies, a detailed kinetic analysis, and density functional theory all suggest that the active intermediate is an η(2)-cyclopropene complex formed via β-hydrogen abstraction rather than an isomeric cyclopropylidene species. C-H activation chemistry of this type represents a rather unusual reactivity pattern for η(2)-alkene complexes but is favored in this case by the strain in the C(3) ring which prevents the decomposition of the key intermediate via loss of cyclopropene.

  19. C-H bond activation of methane in aqueous solution: a hybrid quantum mechanical/effective fragment potential study.

    PubMed

    Da Silva, Júlio C S; Rocha, Willian R

    2011-12-01

    In this study, we investigated the C-H bond activation of methane catalyzed by the complex [PtCl(4)](2-), using the hybrid quantum mechanical/effective fragment potential (EFP) approach. We analyzed the structures, energetic properties, and reaction mechanism involved in the elementary steps that compose the catalytic cycle of the Shilov reaction. Our B3LYP/SBKJC/cc-pVDZ/EFP results show that the methane activation may proceed through two pathways: (i) electrophilic addition or (ii) direct oxidative addition of the C-H bond of the alkane. The electrophilic addition pathway proceeds in two steps with formation of a σ-methane complex, with a Gibbs free energy barrier of 24.6 kcal mol(-1), followed by the cleavage of the C-H bond, with an energy barrier of 4.3 kcal mol(-1) . The activation Gibbs free energy, calculated for the methane uptake step was 24.6 kcal mol(-1), which is in good agreement with experimental value of 23.1 kcal mol(-1) obtained for a related system. The results shows that the activation of the C-H bond promoted by the [PtCl(4)](2-) catalyst in aqueous solution occurs through a direct oxidative addition of the C-H bond, in a single step, with an activation free energy of 25.2 kcal mol(-1), as the electrophilic addition pathway leads to the formation of a σ-methane intermediate that rapidly undergoes decomposition. The inclusion of long-range solvent effects with polarizable continuum model does not change the activation energies computed at the B3LYP/SBKJC/cc-pVDZ/EFP level of theory significantly, indicating that the large EFP water cluster used, obtained from Monte Carlo simulations and analysis of the center-of-mass radial pair distribution function, captures the most important solvent effects.

  20. Copper-dioxygen complex mediated C-H bond oxygenation: relevance for particulate methane monooxygenase (pMMO).

    PubMed

    Himes, Richard A; Karlin, Kenneth D

    2009-02-01

    Particulate methane monooxygenase (pMMO), an integral membrane protein found in methanotrophic bacteria, catalyzes the oxidation of methane to methanol. Expression and greater activity of the enzyme in the presence of copper ion suggest that pMMO is a cuprous metalloenzyme. Recent advances - especially the first crystal structures of pMMO - have energized the field, but the nature of the active site(s) and the mechanism of methane oxidation remain poorly understood-yet hotly contested. Herein the authors briefly review the current understanding of the pMMO metal sites and discuss advances in small molecule Cu-O(2) chemistry that may contribute to an understanding of copper-ion mediated hydrocarbon oxidation chemistry.

  1. Reactivity of oxygen radical anions bound to scandia nanoparticles in the gas phase: C-H bond activation.

    PubMed

    Tian, Li-Hua; Meng, Jing-Heng; Wu, Xiao-Nan; Zhao, Yan-Xia; Ding, Xun-Lei; He, Sheng-Gui; Ma, Tong-Mei

    2014-01-20

    The activation of C-H bonds in alkanes is currently a hot research topic in chemistry. The atomic oxygen radical anion (O(-·)) is an important species in C-H activation. The mechanistic details of C-H activation by O(-·) radicals can be well understood by studying the reactions between O(-·) containing transition metal oxide clusters and alkanes. Here the reactivity of scandium oxide cluster anions toward n-butane was studied by using a high-resolution time-of-flight mass spectrometer coupled with a fast flow reactor. Hydrogen atom abstraction (HAA) from n-butane by (Sc2O3)(N)O(-) (N=1-18) clusters was observed. The reactivity of (Sc2O3)(N)O(-) (N=1-18) clusters is significantly sizedependent and the highest reactivity was observed for N=4 (Sc8O13(-)) and 12 (Sc24O37(-)). Larger (Sc2O3)(N)O(-) clusters generally have higher reactivity than the smaller ones. Density functional theory calculations were performed to interpret the reactivity of (Sc2O3)(N)O(-) (N=1-5) clusters, which were found to contain the O(-·) radicals as the active sites. The local charge environment around the O(-·) radicals was demonstrated to control the experimentally observed size-dependent reactivity. This work is among the first to report HAA reactivity of cluster anions with dimensions up to nanosize toward alkane molecules. The anionic O(-·) containing scandium oxide clusters are found to be more reactive than the corresponding cationic ones in the C-H bond activation.

  2. Ru(ii)-Catalyzed C-H activation and annulation of salicylaldehydes with monosubstituted and disubstituted alkynes.

    PubMed

    Baruah, Swagata; Kaishap, Partha Pratim; Gogoi, Sanjib

    2016-10-27

    The Ru(ii)-catalyzed C-H activation and annulation reaction of salicylaldehydes and disubstituted alkynes affords chromones in high yields. This reaction also works with terminal alkynes and tolerates a wide range of sensitive functional groups. The selectivity pattern of this Ru(ii)-catalyzed annulation reaction is different from the known Au(i), Rh(iii)-catalyzed annulation reactions of salicylaldehydes and terminal alkynes.

  3. Easy activation of two C-H bonds of an N-heterocyclic carbene N-methyl group.

    PubMed

    Cabeza, Javier A; del Río, Ignacio; Miguel, Daniel; Sánchez-Vega, M Gabriela

    2005-08-21

    The first trinuclear clusters containing NHC ligands are described; the compound [Ru3(Me2Im)(CO)11](Me2Im=1,3-dimethylimidazol-2-ylidene) is easily converted into [Ru3(mu-H)2(mu3-MeImCH)(CO)9] by a process involving the activation of two C-H bonds of a methyl group that is an example of degradation of a metal-coordinated NHC ligand under mild conditions.

  4. Palladium-catalyzed C-H activation/intramolecular amination reaction: a new route to 3-aryl/alkylindazoles.

    PubMed

    Inamoto, Kiyofumi; Saito, Tadataka; Katsuno, Mika; Sakamoto, Takao; Hiroya, Kou

    2007-07-19

    A method for the catalytic C-H activation of hydrazone compounds followed by intramolecular amination is described. It requires the use of a catalytic amount of Pd(OAc)2 in the presence of Cu(OAc)2 and AgOCOCF3, which efficiently effects the cyclization to afford variously substituted indazoles. The reactions proceed under relatively mild conditions and thus tolerate a variety of functional groups, including alkoxycarbonyl and cyano groups and halogen atoms.

  5. Vapour-induced solid-state C-H bond activation for the clean synthesis of an organopalladium biothiol sensor.

    PubMed

    Monas, Andrea; Užarević, Krunoslav; Halasz, Ivan; Kulcsár, Marina Juribašić; Ćurić, Manda

    2016-10-27

    Room-temperature accelerated aging in the solid state has been applied for atom- and energy-efficient activation of either one or two C-H bonds of azobenzene and methyl orange by palladium(ii) acetate. Organopalladium complexes are prepared in quantitative reactions without potentially harmful side products. Dicyclopalladated methyl orange is water-soluble and is a selective chromogenic biothiol sensor at physiologically-relevant micromolar concentrations in buffered aqueous media.

  6. Synthesis and catalytic applications of 1,2,3-triazolylidene gold(i) complexes in silver-free oxazoline syntheses and C-H bond activation.

    PubMed

    Pretorius, René; Fructos, Manuel R; Müller-Bunz, Helge; Gossage, Robert A; Pérez, Pedro J; Albrecht, Martin

    2016-10-07

    A series of novel 1,2,3-triazolylidene gold(i) chloride complexes have been synthesised and fully characterised. Silver-free methodologies for chloride ion abstraction of these complexes were evaluated for their potential as Au-based catalyst precursors. Using simple potassium salts or MeOTf as chloride scavengers produced metal complexes that catalyse both the regioselective synthesis of oxazolines and the C-H activation of benzene or styrene for carbene transfer from ethyl diazoacetate. These results indicate that Ag-free activation of 1,2,3-triazolylidene gold(i) chloride complexes is feasible for the generation of catalytically active Au triazolylidene species. However, silver-mediated activation imparts substantially higher catalytic activity in oxazoline synthesis.

  7. Oxidative C-H/C-H Coupling Reactions between Two (Hetero)arenes.

    PubMed

    Yang, Yudong; Lan, Jingbo; You, Jingsong

    2017-01-13

    Transition metal-mediated C-H bond activation and functionalization represent one of the most straightforward and powerful tools in modern organic synthetic chemistry. Bi(hetero)aryls are privileged π-conjugated structural cores in biologically active molecules, organic functional materials, ligands, and organic synthetic intermediates. The oxidative C-H/C-H coupling reactions between two (hetero)arenes through 2-fold C-H activation offer a valuable opportunity for rapid assembly of diverse bi(hetero)aryls and further exploitation of their applications in pharmaceutical and material sciences. This review provides a comprehensive overview of the fundamentals and applications of transition metal-mediated/catalyzed oxidative C-H/C-H coupling reactions between two (hetero)arenes. The substrate scope, limitation, reaction mechanism, regioselectivity, and chemoselectivity, as well as related control strategies of these reactions are discussed. Additionally, the applications of these established methods in the synthesis of natural products and exploitation of new organic functional materials are exemplified. In the last section, a short introduction on oxidant- or Lewis acid-mediated oxidative Ar-H/Ar-H coupling reactions is presented, considering that it is a very powerful method for the construction of biaryl units and polycylic arenes.

  8. Cu-catalyzed cross-dehydrogenative coupling: A versatile strategy for C-C bond formations via the oxidative activation of sp3 C-H bonds

    NASA Astrophysics Data System (ADS)

    Li, Zhiping; Bohle, D. Scott; Li, Chao-Jun

    2006-06-01

    Cu-catalyzed cross-dehydrogenative coupling (CDC) methodologies were developed based on the oxidative activation of sp3 C-H bonds adjacent to a nitrogen atom. Various sp, sp2, and sp3 C-H bonds of pronucleophiles were used in the Cu-catalyzed CDC reactions. Based on these results, the mechanisms of the CDC reactions also are discussed. C-H activation | catalysis | Baylis-Hillman reaction | Mannich reaction | Friedel-Crafts reaction

  9. Mechanism of cooperative catalysis in a Lewis acid promoted nickel-catalyzed dual C-H activation reaction.

    PubMed

    Anand, Megha; Sunoj, Raghavan B

    2012-09-07

    The mechanism of cooperativity offered by AlMe(3) in a Ni-catalyzed dehydrogenative cycloaddition between substituted formamides and an alkyne is investigated by using DFT(SMD(toluene)/M06/6-31G**) methods. The preferred pathway is identified to involve dual C-H activation, with first a higher barrier formyl C(sp(2))-H oxidative insertion followed by benzylic methyl C(sp(3))-H activation. The cooperativity is traced to be of kinetic origin as evidenced by stabilized transition states when AlMe(3) is bound to the formyl group, particularly in the oxidative insertion step.

  10. Direct Synthesis of Protoberberine Alkaloids by Rh-Catalyzed C-H Bond Activation as the Key Step.

    PubMed

    Jayakumar, Jayachandran; Cheng, Chien-Hong

    2016-01-26

    A one-pot reaction of substituted benzaldehydes with alkyne-amines by a Rh-catalyzed C-H activation and annulation to afford various natural and unnatural protoberberine alkaloids is reported. This reaction provides a convenient route for the generation of a compound library of protoberberine salts, which recently have attracted great attention because of their diverse biological activities. In addition, pyridinium salt derivatives can also be formed in good yields from α,β-unsaturated aldehydes and amino-alkynes. This reaction proceeds with excellent regioselectivity and good functional group compatibility under mild reaction conditions by using O2 as the oxidant.

  11. Physical Activity, Physical Fitness, and Health. C.H. McCloy Research Lecture: 1993.

    ERIC Educational Resources Information Center

    Blair, Steven N.

    1993-01-01

    Examines recent evidence on the relations between physical activity, physical fitness, and health, noting the possible causal nature of the associations. The article evaluates the public health burden of sedentary lifestyles in the United States and provides suggestions for increasing participation in physical activity. (SM)

  12. 2009 C. H. McCloy Lecture. Seeing Is Believing: Observing Physical Activity and Its Contexts

    ERIC Educational Resources Information Center

    McKenzie, Thomas L.

    2010-01-01

    Direct (systematic) observation has been a mainstay of my research for over three decades. I believe it is an important tool for assessing physical activity, because it can simultaneously provide contextually rich data on the setting in which the activity occurs. It is particularly useful for those interested in using ecological and…

  13. Double N,B-Type Bidentate Boryl Ligands Enabling a Highly Active Iridium Catalyst for C-H Borylation.

    PubMed

    Wang, Guanghui; Xu, Liang; Li, Pengfei

    2015-07-01

    Boryl ligands hold promise in catalysis due to their very high electron-donating property. In this communication double N,B-type boryl anions were designed as bidentate ligands to promote an sp(2) C-H borylation reaction. A symmetric pyridine-containing tetraaminodiborane(4) compound (1) was readily prepared as the ligand precursor that could be used, in combination with [Ir(OMe)(COD)]2, to in situ generate a highly active catalyst for a broad range of (hetero)arene substrates including highly electron-rich and/or sterically hindered ones. This work provides the first example of a bidentate boryl ligand in supporting homogeneous organometallic catalysis.

  14. Synthesis of Active Hexafluoroisopropyl Benzoates through a Hydrogen-Bond-Enabled Palladium(II)-Catalyzed C-H Alkoxycarbonylation Reaction.

    PubMed

    Wang, Yang; Gevorgyan, Vladimir

    2017-03-13

    A Pd(II) -catalyzed ortho C-H alkoxycarbonylation reaction of aryl silanes toward active hexafluoroisopropyl (HFIP) benzoate esters has been developed. This efficient reaction features high selectivity and good functional-group tolerance. Notably, given the general nature of the silyl-tethered directing group, this method delivers products bearing two independently modifiable sites. NMR studies reveal the presence of hydrogen bonding between HFIP and a pyrimidine nitrogen atom of the directing group, and it is thought to be crucial for the success of this alkoxycarbonylation reaction.

  15. Rhodium(III)-Catalyzed Enantiotopic C-H Activation Enables Access to P-Chiral Cyclic Phosphinamides.

    PubMed

    Sun, Yang; Cramer, Nicolai

    2017-01-02

    Compounds with stereogenic phosphorus atoms are frequently used as ligands for transition-metal as well as organocatalysts. A direct catalytic enantioselective method for the synthesis of P-chiral compounds from easily accessible diaryl phosphinamides is presented. The use of rhodium(III) complexes equipped with a suitable atropochiral cyclopentadienyl ligand is shown to enable an enantiodetermining C-H activation step. Upon trapping with alkynes, a broad variety of cyclic phosphinamides with a stereogenic phosphorus(V) atom are formed in high yields and enantioselectivities. Moreover, these can be reduced enantiospecifically to P-chiral phosphorus(III) compounds.

  16. Reactivity of mononuclear alkylperoxo copper(II) complex. O-O bond cleavage and C-H bond activation.

    PubMed

    Kunishita, Atsushi; Ishimaru, Hirohito; Nakashima, Satoru; Ogura, Takashi; Itoh, Shinobu

    2008-04-02

    A detailed reactivity study has been carried out for the first time on a new mononuclear alkylperoxo copper(II) complex, which is generated by the reaction of copper(II) complex supported by the bis(pyridylmethyl)amine tridentate ligand containing a phenyl group at the 6-position of the pyridine donor groups and cumene hydroperoxide (CmOOH) in CH3CN. The cumylperoxo copper(II) complex thus obtained has been found to undergo homolytic cleavage of the O-O bond and induce C-H bond activation of exogenous substrates, providing important insights into the catalytic mechanism of copper monooxygenases.

  17. C. H. McCloy Lecture: Fifty Years of Advancements in Fitness and Activity Research

    ERIC Educational Resources Information Center

    Corbin, Charles B.

    2012-01-01

    Over the past 50 years progress in fitness and activity research has been influenced by social events, technical innovations, and changes in the field of physical education and kinesiology. The conventional wisdom of the 1950s yielded to a new wisdom based on research evidence. The author's research, as well as the research of others, from 1960 to…

  18. Palladium-catalyzed meta-selective C-H bond activation with a nitrile-containing template: computational study on mechanism and origins of selectivity.

    PubMed

    Yang, Yun-Fang; Cheng, Gui-Juan; Liu, Peng; Leow, Dasheng; Sun, Tian-Yu; Chen, Ping; Zhang, Xinhao; Yu, Jin-Quan; Wu, Yun-Dong; Houk, K N

    2014-01-08

    Density functional theory investigations have elucidated the mechanism and origins of meta-regioselectivity of Pd(II)-catalyzed C-H olefinations of toluene derivatives that employ a nitrile-containing template. The reaction proceeds through four major steps: C-H activation, alkene insertion, β-hydride elimination, and reductive elimination. The C-H activation step, which proceeds via a concerted metalation-deprotonation (CMD) pathway, is found to be the rate- and regioselectivity-determining step. For the crucial C-H activation, four possible active catalytic species-monomeric Pd(OAc)2, dimeric Pd2(OAc)4, heterodimeric PdAg(OAc)3, and trimeric Pd3(OAc)6-have been investigated. The computations indicated that the C-H activation with the nitrile-containing template occurs via a Pd-Ag heterodimeric transition state. The nitrile directing group coordinates with Ag while the Pd is placed adjacent to the meta-C-H bond in the transition state, leading to the observed high meta-selectivity. The Pd2(OAc)4 dimeric mechanism also leads to the meta-C-H activation product but with higher activation energies than the Pd-Ag heterodimeric mechanism. The Pd monomeric and trimeric mechanisms require much higher activation free energies and are predicted to give ortho products. Structural and distortion energy analysis of the transition states revealed significant effects of distortions of the template on mechanism and regioselectivity, which provided hints for further developments of new templates.

  19. Uranium azide photolysis results in C-H bond activation and provides evidence for a terminal uranium nitride

    NASA Astrophysics Data System (ADS)

    Thomson, Robert K.; Cantat, Thibault; Scott, Brian L.; Morris, David E.; Batista, Enrique R.; Kiplinger, Jaqueline L.

    2010-09-01

    Uranium nitride [U≡N]x is an alternative nuclear fuel that has great potential in the expanding future of nuclear power; however, very little is known about the U≡N functionality. We show, for the first time, that a terminal uranium nitride complex can be generated by photolysis of an azide (U-N=N=N) precursor. The transient U≡N fragment is reactive and undergoes insertion into a ligand C-H bond to generate new N-H and N-C bonds. The mechanism of this unprecedented reaction has been evaluated through computational and spectroscopic studies, which reveal that the photochemical azide activation pathway can be shut down through coordination of the terminal azide ligand to the Lewis acid B(C6F5)3. These studies demonstrate that photochemistry can be a powerful tool for inducing redox transformations for organometallic actinide complexes, and that the terminal uranium nitride fragment is reactive, cleaving strong C-H bonds.

  20. The role of group 14 element hydrides in the activation of C-H bonds in cyclic olefins.

    PubMed

    Summerscales, Owen T; Caputo, Christine A; Knapp, Caroline E; Fettinger, James C; Power, Philip P

    2012-09-05

    Formally, triple-bonded dimetallynes ArEEAr [E = Ge (1), Sn (2); Ar = C(6)H(3)-2,6-(C(6)H(3)-2,6-(i)Pr(2))(2)] have been previously shown to activate aliphatic, allylic C-H bonds in cyclic olefins, cyclopentadiene (CpH), cyclopentene (c-C(5)H(8)) and 1,4-cyclohexadiene, with intriguing selectivity. In the case of the five-membered carbocycles, cyclopentadienyl species ArECp [E = Ge (3), Sn (4)] are formed. In this study, we examine the mechanisms for activation of CpH and c-C(5)H(8) using experimental methods and describe a new product found from the reaction between 1 and c-C(5)H(8), an asymmetrically substituted digermene ArGe(H)Ge(c-C(5)H(9))Ar (5), crystallized in 46% yield. This compound contains a hydrogenated cyclopentyl moiety and is found to be produced in a 3:2 ratio with 3, explaining the fate of the liberated H atoms following triple C-H activation. We show that when these C-H activation reactions are carried out in the presence of tert-butyl ethylene (excess), compounds {ArE(CH(2)CH(2)tBu)}(2) [E = Ge(8), Sn(9)] are obtained in addition to ArECp; in the case of CpH, the neohexyl complexes replace the production of H(2) gas, and for c-C(5)H(8) they displace cyclopentyl product 5 and account for all the hydrogen removed in the dehydroaromatization reactions. To confirm the source of 8 and 9, it was demonstrated that these molecules are formed cleanly between the reaction of (ArEH)(2) [E = Ge(6), Sn(7)] and tert-butyl ethylene, new examples of noncatalyzed hydro-germylation and -stannylation. Therefore, the presence of transient hydrides of the type 6 and 7 can be surmised to be reactive intermediates in the production of 3 and 4, along with H(2), from 1 and 2 and CpH (respectively), or the formation of 3 and 5 from 1. The reaction of 6 or 7 with CpH gave 3 or 4, respectively, with concomitant H(2) evolution, demonstrating the basic nature of these low-valent group 14 element hydrides and their key role in the 'cascade' of C-H activation steps

  1. Activation of C-H bond in methane by Pd atom from the bonding evolution theory perspective.

    PubMed

    Nizovtsev, Anton S

    2013-08-15

    We report detailed study focused on the electron density redistribution during the simple oxidative addition reaction being the crucial stage of various catalytic processes. The bonding evolution theory based on the electron localization function and Thom's catastrophe theory shows that activation of methane's C-H bond by Pd atom consist of six elementary steps. The important feature revealed is the pronounced reorganization of Pd's outer core maxima corresponding to N-shell electrons of metal. Electronic rearrangements identified in this model reaction are likely to be the case in the more complex reactions of the same type involving transition metal compounds and, in principle, can be observed by modern ultrafast spectroscopy and diffraction techniques.

  2. Activation of C-H and B-H bonds through agostic bonding: an ELF/QTAIM insight.

    PubMed

    Zins, Emilie-Laure; Silvi, Bernard; Alikhani, M Esmaïl

    2015-04-14

    Agostic bonding is of paramount importance in C-H bond activation processes. The reactivity of the σ C-H bond thus activated will depend on the nature of the metallic center, the nature of the ligand involved in the interaction and co-ligands, as well as on geometric parameters. Because of their importance in organometallic chemistry, a qualitative classification of agostic bonding could be very much helpful. Herein we propose descriptors of the agostic character of bonding based on the electron localization function (ELF) and Quantum Theory of Atoms in Molecules (QTAIM) topological analysis. A set of 31 metallic complexes taken, or derived, from the literature was chosen to illustrate our methodology. First, some criteria should prove that an interaction between a metallic center and a σ X-H bond can indeed be described as "agostic" bonding. Then, the contribution of the metallic center in the protonated agostic basin, in the ELF topological description, may be used to evaluate the agostic character of bonding. A σ X-H bond is in agostic interaction with a metal center when the protonated X-H basin is a trisynaptic basin with a metal contribution strictly larger than the numerical uncertainty, i.e. 0.01 e. In addition, it was shown that the weakening of the electron density at the X-Hagostic bond critical point with respect to that of X-Hfree well correlates with the lengthening of the agostic X-H bond distance as well as with the shift of the vibrational frequency associated with the νX-H stretching mode. Furthermore, the use of a normalized parameter that takes into account the total population of the protonated basin, allows the comparison of the agostic character of bonding involved in different complexes.

  3. A Highly Reactive Mononuclear Non-Heme Manganese(IV)-Oxo Complex That Can Activate the Strong C-H Bonds of Alkanes

    SciTech Connect

    Wu, Xiujuan; Seo, Mi Sook; Davis, Katherine M; Lee, Yong-Min; Chen, Junying; Cho, Kyung-Bin; Pushkar, Yulia N; Nam, Wonwoo

    2012-03-15

    A mononuclear non-heme manganese(IV)-oxo complex has been synthesized and characterized using various spectroscopic methods. The Mn(IV)-oxo complex shows high reactivity in oxidation reactions, such as C-H bond activation, oxidations of olefins, alcohols, sulfides, and aromatic compounds, and N-dealkylation. In C-H bond activation, the Mn(IV)-oxo complex can activate C-H bonds as strong as those in cyclohexane. It is proposed that C-H bond activation by the non-heme Mn(IV)-oxo complex does not occur via an oxygen-rebound mechanism. The electrophilic character of the non-heme Mn(IV)-oxo complex is demonstrated by a large negative ρ value of ~4.4 in the oxidation of para-substituted thioanisoles.

  4. Rationalizing current strategies to protect N-heterocyclic carbene-based ruthenium catalysts active in olefin metathesis from C-H (de)activation.

    PubMed

    Poater, Albert; Bahri-Laleh, Naeimeh; Cavallo, Luigi

    2011-06-21

    Defending second generation Ru-catalysts in olefin metathesis from C-H (de)activation reactions requires precise catalyst design strategies. Computer simulations are used here to rationalize precisely the role of the currently used catalyst structural modifications, and the way these modifications cooperate.

  5. Overcoming the Limitations of C-H Activation with Strongly Coordinating N-Heterocycles by Cobalt Catalysis.

    PubMed

    Wang, Hui; Lorion, Mélanie M; Ackermann, Lutz

    2016-08-22

    Strongly coordinating nitrogen heterocycles, including pyrimidines, oxazolines, pyrazoles, and pyridines, were fully tolerated in cobalt-catalyzed C-H amidations by imidate assistance. Structurally complex quinazolines are thus accessible in a step-economic manner. Our findings also establish the relative powers of directing groups in cobalt(III)-catalyzed C-H functionalization for the first time.

  6. Non-innocent additives in a palladium(II)-catalyzed C-H bond activation reaction: insights into multimetallic active catalysts.

    PubMed

    Anand, Megha; Sunoj, Raghavan B; Schaefer, Henry F

    2014-04-16

    The role of a widely employed additive (AgOAc) in a palladium acetate-catalyzed ortho-C-H bond activation reaction has been examined using the M06 density functional theory. A new hetero-bimetallic Pd-(μ-OAc)3-Ag is identified as the most likely active species. This finding could have far-reaching implications with respect to the notion of the active species in palladium catalysis in the presence of other metal salt additives.

  7. Computational rationalization of the selective C-H and C-F activations of fluoroaromatic imines and ketones by cobalt complexes.

    PubMed

    Li, Jingjing; Zhang, Dongju; Sun, Hongjian; Li, Xiaoyan

    2014-03-28

    While selective C-H and C-F activations of fluoroaromatic imines and ketones with transition metal complexes supported by PMe3 have been successfully achieved in recent publications, insight into the molecular mechanism and energetics of those reactions is still lacking. Focusing on three typical substrates, 2,6-difluorobenzophenone imine (A) and 2,6-difluorobenzophenone (B), and 2,4'-difluorobenzophenone (C), the present work theoretically studied their C-H and C-F cyclometalation reactions promoted by the activator Co(PMe3)4 or CoMe(PMe3)4. It is found that reaction A + Co(PMe3)4 favors the C-F activation, reaction A + CoMe(PMe3)4 prefers the C-H activation, whereas both the C-H and C-F activation pathways may be viable for reactions B + CoMe(PMe3)4 and C + CoMe(PMe3)4. The experimentally observed C-H and C-F cyclometalation products have been rationalized by analyzing the thermodynamic and kinetic properties of two activation pathways. From calculated results combined with the experimental observations, we believe that three factors, i.e. the oxidation state of the metal center in the activators, the anchoring group of substrates, and substituted fluoroatom counts of the aromatic ring in substrates, affect the selectivity of C-H and C-F activations of fluoroaromatic ketones and imines. Calculated results are enlightening about the rational design of activators and substrates of fluoroaromatic imines and ketones to obtain the exclusive C-H or C-F bond activation product.

  8. Preferential activation of primary C-H bonds in the reactions of small alkanes with the diatomic MgO(+*) cation.

    PubMed

    Schröder, Detlef; Roithová, Jana; Alikhani, Esmail; Kwapien, Karolina; Sauer, Joachim

    2010-04-06

    The C-H bond activation of small alkanes by the gaseous MgO(+*) cation is probed by mass spectrometric means. In addition to H-atom abstraction from methane, the MgO(+*) cation reacts with ethane, propane, n- and iso-butane through several pathways, which can all be assigned to the occurrence of initial C-H bond activations. Specifically, the formal C-C bond cleavages observed are assigned to C-H bond activation as the first step, followed by cleavage of a beta-C-C bond concomitant with release of the corresponding alkyl radical. Kinetic modeling of the observed product distributions reveals a high preference of MgO(+*) for the attack of primary C-H bonds. This feature represents a notable distinction of the main-group metal oxide MgO(+*) from various transition-metal oxide cations, which show a clear preference for the attack of secondary C-H bonds. The results of complementary theoretical calculations indicate that the C-H bond activation of larger alkanes by the MgO(+*) cation is subject to pronounced kinetic control.

  9. (13)C ENDOR Spectroscopy of Lipoxygenase-Substrate Complexes Reveals the Structural Basis for C-H Activation by Tunneling.

    PubMed

    Horitani, Masaki; Offenbacher, Adam R; Carr, Cody A Marcus; Yu, Tao; Hoeke, Veronika; Cutsail, George E; Hammes-Schiffer, Sharon; Klinman, Judith P; Hoffman, Brian M

    2017-02-08

    In enzymatic C-H activation by hydrogen tunneling, reduced barrier width is important for efficient hydrogen wave function overlap during catalysis. For native enzymes displaying nonadiabatic tunneling, the dominant reactive hydrogen donor-acceptor distance (DAD) is typically ca. 2.7 Å, considerably shorter than normal van der Waals distances. Without a ground state substrate-bound structure for the prototypical nonadiabatic tunneling system, soybean lipoxygenase (SLO), it has remained unclear whether the requisite close tunneling distance occurs through an unusual ground state active site arrangement or by thermally sampling conformational substates. Herein, we introduce Mn(2+) as a spin-probe surrogate for the SLO Fe ion; X-ray diffraction shows Mn-SLO is structurally faithful to the native enzyme. (13)C ENDOR then reveals the locations of (13)C10 and reactive (13)C11 of linoleic acid relative to the metal; (1)H ENDOR and molecular dynamics simulations of the fully solvated SLO model using ENDOR-derived restraints give additional metrical information. The resulting three-dimensional representation of the SLO active site ground state contains a reactive (a) conformer with hydrogen DAD of ∼3.1 Å, approximately van der Waals contact, plus an inactive (b) conformer with even longer DAD, establishing that stochastic conformational sampling is required to achieve reactive tunneling geometries. Tunneling-impaired SLO variants show increased DADs and variations in substrate positioning and rigidity, confirming previous kinetic and theoretical predictions of such behavior. Overall, this investigation highlights the (i) predictive power of nonadiabatic quantum treatments of proton-coupled electron transfer in SLO and (ii) sensitivity of ENDOR probes to test, detect, and corroborate kinetically predicted trends in active site reactivity and to reveal unexpected features of active site architecture.

  10. The Stereoselective Formation of Bicyclic Enamines with Bridgehead Unsaturation via Tandem C-H Bond Activation/Alkenylation/Electrocyclization

    SciTech Connect

    Ellman, Jonathan A.; Yotphan, Sirilata; Bergman, Robert

    2007-12-10

    Rhodium-catalyzed intermolecular C-H activation of {alpha}, {beta}-unsaturated imines in the presence of alkynes leads to a tandem process in which coupling to the alkyne occurs at the {beta}-C-H bond of the imine, followed by electrocyclization of the resulting azatriene intermediates to give dihydropyridines (eq 1). Consideration of the intramolecular version of this overall transformation (Scheme 1) raises interesting regiochemical issues. For example in a compound such as 1, where the nitrogen and alkyne are connected by a 4-carbon tether, the presumed first-formed hydrido(vinyl)rhodium function can add to the triple bond in a 1,2-fashion, producing complex 2 with a new endocyclic double bond. Alternatively, addition might occur in a 2,1-fashion, leading to product 4 with an exocyclic double bond. We now wish to report that this intramolecular cyclization occurs smoothly at 100 C, and the exocyclic double bond route is exclusively followed. Remarkably, products such as 4 do not resist further cyclization. Even though both the transition state for this process and the resulting product are presumably strained, the overall transformation leads to good yields of unusual bridgehead doubly-bonded enamines such as 5. The unique chemistry of conjugated enamine 5 is consistent with the increased strain of this molecule as well as with inhibited conjugation between the nitrogen lone pair and the adjacent double bond (vida infra). We began our investigation into the C-H activation/cyclization of alkyne-tethered imine 1 by extensive screening of transition metal catalysts for this process. Rhodium-based catalysts were found to be the most efficient (Table 1), leading exclusively to the bridgehead dienamine; none of the catalysts that were employed in the screening led to quinolizidine 3 or to the product of intramolecular Diels-Alder reaction. The optimized reaction conditions employ the electron-rich monophosphine ligand (p-NMe{sub 2})PhPEt{sub 2} in 1:1 ratio relative

  11. Heterolytic Activation of C-H Bonds on Cr(III)-O Surface Sites Is a Key Step in Catalytic Polymerization of Ethylene and Dehydrogenation of Propane.

    PubMed

    Conley, Matthew P; Delley, Murielle F; Núñez-Zarur, Francisco; Comas-Vives, Aleix; Copéret, Christophe

    2015-06-01

    We describe the reactivity of well-defined chromium silicates toward ethylene and propane. The initial motivation for this study was to obtain a molecular understanding of the Phillips polymerization catalyst. The Phillips catalyst contains reduced chromium sites on silica and catalyzes the polymerization of ethylene without activators or a preformed Cr-C bond. Cr(II) sites are commonly proposed active sites in this catalyst. We synthesized and characterized well-defined chromium(II) silicates and found that these materials, slightly contaminated with a minor amount of Cr(III) sites, have poor polymerization activity and few active sites. In contrast, chromium(III) silicates have 1 order of magnitude higher activity. The chromium(III) silicates initiate polymerization by the activation of a C-H bond of ethylene. Density functional theory analysis of this process showed that the C-H bond activation step is heterolytic and corresponds to a σ-bond metathesis type process. The same well-defined chromium(III) silicate catalyzes the dehydrogenation of propane at elevated temperatures with activities similar to those of a related industrial chromium-based catalyst. This reaction also involves a key heterolytic C-H bond activation step similar to that described for ethylene but with a significantly higher energy barrier. The higher energy barrier is consistent with the higher pKa of the C-H bond in propane compared to the C-H bond in ethylene. In both cases, the rate-determining step is the heterolytic C-H bond activation.

  12. The Unexpected Reactivity of the Carbon Sites on the Nanostructured Carbon Catalysts towards the C-H Bond Activation from the Analysis of the Aromaticity.

    PubMed

    Sun, XiaoYing; Li, Bo; Su, DangSheng

    2016-06-06

    It is believed that the oxygen groups on the carbon catalysts are responsible for the observed reactivity for C-H bond activations. On the other hand, the oxygen groups also reduce the aromaticity of the host. The loss of the aromaticity increases reactivities of the carbon atoms and they become the active sites for the C-H bond activation. The newly identified C-C site exhibits the comparable catalytic performance in the oxidative dehydrogenation (ODH) of propane compared with the conventional oxygen groups like quinone and ketone. A series of calculations indicate that the aromaticity might be a useful descriptor for the carbon catalysts.

  13. Structural, kinetic, and thermodynamic study of the reversible thermal C-H activation/reductive elimination of alkanes at iridium

    SciTech Connect

    Buchanan, J.M.; Stryker, J.M.; Bergman, R.G.

    1986-04-02

    The hydrido alkyl iridium complex Cp*(PMe/sub 3/)Ir(Cy)(H) (1, Cp* = eta/sup 5/-C/sub 5/; Cy = cyclohexyl) has been isolated by air-free chromatography at -80/sup 0/C, and its molecular structure has been determined by X-ray diffraction. Thermolysis of 1 in benzene cleanly produces cyclohexane and Cp*(PMe/sub 3/)Ir(Ph)(H) (2). The rate of reaction is first-order in 1, zero-order in benzene, and inhibited by cyclohexane; its activation parameters are ..delta..H/sup + +/ = 35.6 +/- 0.5 kcal/mol and ..delta..S/sup + +/ = +10 +/- 2 eu. An inverse isotope effect, kappa/sub h/kappa/sub d/ = 0.7 +/- 0.1, is calculated from rates of cyclohexane and cyclohexane-d/sub 12/ reductive elimination at 130/sup 0/C, and deuterium scrambling between the hydride and ..cap alpha..-cyclohexyl positions is observed to occur competitively with reductive elimination. A mechanism is proposed in which cyclohexane loss from 1 is reversible and produces (Cp*(PMe/sub 3/)Ir), which oxidatively adds to a C-H bond in a benzene solvent molecule to form 2. Evidence is also presented for the possible intermediacy of a cyclohexane/(Cp*(PMe/sub 3/)Ir) sigma-complex, which is formed before free (Cp*(PMe/sub 3/)Ir) is released. Equilibrium constants for the equilibration of several pairs of alkanes and their corresponding iridium(III) hydrido alkyl complexes have been determined and imply the following trend in solution phase iridium-carbon bond dissociation enthalpies: phenyl >> n-pentyl > 2,3-dimethylbutyl > cyclopentyl approx. cyclohexyl > neopentyl.

  14. Hydroxy functionalization of non-activated C-H and C=C bonds: new perspectives for the synthesis of alcohols through biocatalytic processes.

    PubMed

    Gröger, Harald

    2014-03-17

    New perspectives through enzymes: Recent breakthroughs have been achieved in the selective hydroxy functionalization of non-activated C-H and C=C bonds. Enzymes turned out to be suitable catalysts for the ω-hydroxylation of (substituted) alkanes and regioselective hydroxylation of aromatic hydrocarbons with atmospheric oxygen as the oxidant, and the asymmetric addition of water to non-activated alkenes.

  15. C-H functionalization: thoroughly tuning ligands at a metal ion, a chemist can greatly enhance catalyst's activity and selectivity.

    PubMed

    Shul'pin, Georgiy B

    2013-09-28

    This brief essay consists of a few "exciting stories" devoted to relations within a metal-complex catalyst between a metal ion and a coordinated ligand. When, as in the case of a human couple, the rapport of the partners is cordial and a love cements these relations, a chemist finds an ideal married couple, in other words he obtains a catalyst of choice which allows him to functionalize C-H bonds very efficiently and selectively. Examples of such lucky marriages in the catalytic world of ions and ligands are discussed here. Activity of the catalyst is characterized by turnover number (TON) or turnover frequency (TOF) as well as by yield of a target product. Introducing a chelating N,N- or N,O-ligand to the catalyst molecule (this can be an iron or manganese derivative) sharply enhances its activity. However, the activity of vanadium derivatives (with additionally added to the solution pyrazinecarboxylic acid, PCA) as well as of various osmium complexes does not dramatically depend on the nature of ligands surrounding metal ions. Complexes of these metals are very efficient catalysts in oxidations with H2O2. Osmium derivatives are record-holders exhibiting extremely high TONs whereas vanadium complexes are on the second position. Finally, elegant examples of alkane functionalization on the ions of non-transition metals (aluminium, gallium etc.) are described when one ligand within the metal complex (namely, hydroperoxyl ligand HOO(-)) helps other ligand of this complex (H2O2 molecule coordinated to the metal) to disintegrate into two species, generating very reactive hydroxyl radical. Hydrogen peroxide molecule, even ligated to the metal ion, is perfectly stable without the assistance of the neighboring HOO(-) ligand. This ligand can be easily oxidized donating an electron to its partner ligand (H2O2). In an analogous case, when the central ion in the catalyst is a transition metal, this ion changing its oxidation state can donate an electron to the coordinated H2O2

  16. Synthesis of Isocoumarins from Cyclic 2-Diazo-1,3-diketones and Benzoic Acids via Rh(III)-Catalyzed C-H Activation and Esterification.

    PubMed

    Yang, Cheng; He, Xinwei; Zhang, Lanlan; Han, Guang; Zuo, Youpeng; Shang, Yongjia

    2017-02-17

    A mild and efficient Rh(III)-catalyzed C-H activation/esterification reaction for the synthesis of isocoumarins has been developed. This procedure uses readily available benzoic acids and cyclic diazo-1,3-diketones as starting materials and involves domino intermolecular C-H activation in combination with intramolecular esterification to give the corresponding isocoumarins in moderate to excellent yields. This process provides a facile approach for the construction of isocoumarins containing various functional groups that does not require any additives.

  17. Mechanistic insights on iodine(III) promoted metal-free dual C-H activation involved in the formation of a spirocyclic bis-oxindole.

    PubMed

    Sreenithya, A; Sunoj, Raghavan B

    2014-12-05

    The mechanism of a metal-free, phenyliodine(III) bis(trifluoroacetate) promoted, dual aryl C-H activation of an anilide to a spirocyclic bis-oxindole is examined using density functional theory (M06-2X). The most preferred pathway proceeds through the involvement of a novel iodonium ion intermediate and a pivotal trifluoroacetate counterion. The two sequential aryl C-H activations, assisted by trifluoroacetate as well as the superior leaving group ability of PhI, facilitate the formation of spirocyclic bis-oxindole.

  18. Asymmetric Synthesis of (-)-Incarvillateine Employing an Intramolecular Alkylation via Rh-Catalyzed Olefinic C-H Bond Activation

    SciTech Connect

    Tsai, Andy; Bergman, Robert; Ellman, Jonathan

    2008-02-18

    An asymmetric total synthesis of (-)-incarvillateine, a natural product having potent analgesic properties, has been achieved in 11 steps and 15.4% overall yield. The key step is a rhodium-catalyzed intramolecular alkylation of an olefinic C-H bond to set two stereocenters. Additionally, this transformation produces an exocyclic, tetrasubstituted alkene through which the bicyclic piperidine moiety can readily be accessed.

  19. Rhodium-Catalyzed β-Selective Oxidative Heck-Type Coupling of Vinyl Acetate via C-H Activation.

    PubMed

    Zhang, Hui-Jun; Lin, Weidong; Su, Feng; Wen, Ting-Bin

    2016-12-16

    An efficient Rh(III)-catalyzed direct ortho-C-H olefination of acetanilides with vinyl acetate was developed. This protocol provides a straightforward pathway to a series of (E)-2-acetamidostyryl acetates, giving access to indole derivatives following a simple hydrolysis/cyclization process.

  20. Palladium-Catalyzed Enantioselective C-H Activation of Aliphatic Amines Using Chiral Anionic BINOL-Phosphoric Acid Ligands.

    PubMed

    Smalley, Adam P; Cuthbertson, James D; Gaunt, Matthew J

    2017-02-01

    The design of an enantioselective Pd(II)-catalyzed C-H amination reaction is described. The use of a chiral BINOL phosphoric acid ligand enables the conversion of readily available amines into synthetically valuable aziridines in high enantiomeric ratios. The aziridines can be derivatized to afford a range of chiral amine building blocks incorporating motifs readily encountered in pharmaceutically relevant molecules.

  1. Synthesis of ferrocene derivatives with planar chirality via palladium-catalyzed enantioselective C-H bond activation.

    PubMed

    Pi, Chao; Cui, Xiuling; Liu, Xiuyan; Guo, Mengxing; Zhang, Hanyu; Wu, Yangjie

    2014-10-03

    The first catalytic and enantioselective C-H direct acylation of ferrocene derivatives has been developed. A series of 2-acyl-1-dimethylaminomethylferrocenes with planar chirality were provided under highly efficient and concise one-pot conditions with up to 85% yield and 98% ee. The products obtained could be easily converted to various chiral ligands via diverse transformations.

  2. Distinctive activation and functionalization of hydrocarbon C-H bonds initiated by Cp*W(NO)(η(3)-allyl)(CH2CMe3) complexes.

    PubMed

    Baillie, Rhett A; Legzdins, Peter

    2014-02-18

    Converting hydrocarbon feedstocks into value-added chemicals continues to offer challenges to contemporary preparative chemists. A particularly important remaining challenge is the selective activation and functionalization of the C(sp(3))-H linkages of alkanes, which are relatively abundant but chemically inert. This Account outlines the discovery and development of C-H bond functionalization mediated by a family of tungsten organometallic nitrosyl complexes. Specifically, it describes how gentle thermolyses of any of four 18-electron Cp*W(NO)(η(3)-allyl)(CH2CMe3) complexes (Cp* = η(5)-C5Me5; η(3)-allyl = η(3)-H2CCHCHMe, η(3)-H2CCHCHSiMe3, η(3)-H2CCHCHPh, or η(3)-H2CCHCMe2) results in the loss of neopentane and the transient formation of a 16-electron intermediate species, Cp*W(NO)(η(2)-allene) and/or Cp*W(NO)(η(2)-diene). We have never detected any of these species spectroscopically, but we infer their existence based on trapping experiments with trimethylphosphine (PMe3) and labeling experiments using deuterated hydrocarbon substrates. This Account first summarizes the syntheses and properties of the four chiral Cp*W(NO)(η(3)-allyl)(CH2CMe3) complexes. It then outlines the various types of C-H activations we have effected with each of the 16-electron (η(2)-allene) or (η(2)-diene) intermediate nitrosyl complexes, and presents the results of mechanistic investigations of some of these processes. It next describes the characteristic chemical properties of the Cp*W(NO)(η(3)-allyl)(η(1)-hydrocarbyl) compounds formed by the single activations of C(sp(3))-H bonds, with particular emphasis on those reactions that result in the selective functionalization of the original hydrocarbon substrate. We are continuing development of methods to release the acyl ligands from the metal centers while keeping the Cp*W(NO)(η(3)-allyl) fragments intact, with the ultimate aim of achieving these distinctive conversions of alkanes into functionalized organics in a

  3. The Effect of the Electronic Nature of Spectator Ligands in the C-H Bond Activation of Ethylene by Cr(III) Silicates: An ab initio Study.

    PubMed

    Núñez-Zarur, Francisco; Comas-Vives, Aleix

    2015-01-01

    The Phillips catalyst, chromium oxides supported on silica, is one of the most widely used catalysts for the industrial production of polyethylene (PE). We recently synthesized a well-defined mononuclear Cr(III) silicate as active site model of the Phillips catalyst. The catalytic activity of this well-defined catalyst was similar to the industrial Phillips catalyst. We proposed that C-H bond activation of ethylene over a Cr-O bond initiates polymerization in this Cr(III) catalyst. Our results also showed that the presence of a second ethylene olefin in the coordination sphere of Cr decreases the intrinsic energy barrier of the C-H activation of ethylene. In order to understand the effect of this additional ligand in the C-H activation of ethylene by the Cr(III) catalyst, we evaluated the energetics of this step with different spectator ligands (C2H4, C2F4, N2 and CO) coordinated to the Cr center. The Charge Decomposition Analysis (CDA) of the bonding interactions between the Cr(III) catalyst and the ligands showed that the intrinsic energy barrier for the C-H activation of ethylene decreases with the increasing electron-donor properties of the spectator ligand.

  4. Interplay of Tunneling, Two-State Reactivity, and Bell-Evans-Polanyi Effects in C-H Activation by Nonheme Fe(IV)O Oxidants.

    PubMed

    Mandal, Debasish; Shaik, Sason

    2016-02-24

    The study of C-H bond activation reactions by nonheme Fe(IV)O species with nine hydrocarbons shows that the kinetic isotope effect (KIE) involves strong tunneling and is a signature of the reactive spin states. Theory reproduces the observed spike-like appearance of plots of KIE(exp) against the C-H bond dissociation energy, and its origins are discussed. The experimentally observed Bell-Evans-Polanyi correlations, in the presence of strong tunneling, are reproduced, and the pattern is rationalized.

  5. Mn-salen catalysed benzylic C-H activation for the synthesis of aryl [(18)F]CF3-containing PET probes.

    PubMed

    Carroll, L; Evans, H L; Spivey, A C; Aboagye, E O

    2015-05-18

    The development of a Mn-salen complex catalysed oxidative benzylic fluorination of non-activated C-H bonds using [(18)F]fluoride is described for installation of [(18)F]CHRF, [(18)F]CR2F and particularly [(18)F]CF3 containing groups in the presence of other functional groups.

  6. Air/Water-Stable Tridentate NHC-PdII Complex; Catalytic C-H Activation of Hydrocarbons via H/D Exchange Process in D2O

    PubMed Central

    Lee, Joo Ho; Yoo, Kyung Soo; Park, Chan Pil; Olsen, Janet M.; Sakaguchi, Satoshi; Surya Prakash, G. K.; Mathew, Thomas; Jung, Kyung Woon

    2009-01-01

    While developing novel catalysts for carbon-carbon or carbon-heteroatom coupling (N, O, or F), we were able to introduce tridentate NHC-amidate-alkoxide palladium(II) complexes. In aqueous solution, these NHC-Pd(II) complexes showed high ability for C-H activation of various hydrocarbons (cyclohexane, cyclopentane, dimethyl ether, THF, acetone, and toluene) under mild conditions. PMID:20221298

  7. Elementary steps of iron catalysis: exploring the links between iron alkyl and iron olefin complexes for their relevance in C-H activation and C-C bond formation.

    PubMed

    Casitas, Alicia; Krause, Helga; Goddard, Richard; Fürstner, Alois

    2015-01-26

    The alkylation of complexes 2 and 7 with Grignard reagents containing β-hydrogen atoms is a process of considerable relevance for the understanding of C-H activation as well as C-C bond formation mediated by low-valent iron species. Specifically, reaction of 2 with EtMgBr under an ethylene atmosphere affords the bis-ethylene complex 1 which is an active precatalyst for prototype [2+2+2] cycloaddition reactions and a valuable probe for mechanistic studies. This aspect is illustrated by its conversion into the bis-alkyne complex 6 as an unprecedented representation of a cycloaddition catalyst loaded with two substrates molecules. On the other hand, alkylation of 2 with 1 equivalent of cyclohexylmagnesium bromide furnished the unique iron alkyl species 11 with a 14-electron count, which has no less than four β-H atoms but is nevertheless stable at low temperature against β-hydride elimination. In contrast, the exhaustive alkylation of 1 with cyclohexylmagnesium bromide triggers two consecutive C-H activation reactions mediated by a single iron center. The resulting complex has a diene dihydride character in solution (15), whereas its structure in the solid state is more consistent with an η(3) -allyl iron hydride rendition featuring an additional agostic interaction (14). Finally, the preparation of the cyclopentadienyl iron complex 25 illustrates how an iron-mediated C-H activation cascade can be coaxed to induce a stereoselective CC bond formation. The structures of all relevant new iron complexes in the solid state are presented.

  8. Palladium(II)-Catalyzed C-H Bond Activation/C-C and C-O Bond Formation Reaction Cascade: Direct Synthesis of Coumestans.

    PubMed

    Neog, Kashmiri; Borah, Ashwini; Gogoi, Pranjal

    2016-12-02

    A palladium catalyzed cascade reaction of 4-hydroxycoumarins and in situ generated arynes has been developed for the direct synthesis of coumestans. This cascade strategy proceeds via C-H bond activation/C-O and C-C bond formations in a single reaction vessel. This methodology affords moderate to good yields of coumestans and is tolerant of a variety of functional groups including halide. The methodology was applied to the synthesis of natural product flemichapparin C.

  9. Iodine-catalyzed [Formula: see text] C-H bond activation by selenium dioxide: synthesis of diindolylmethanes and di(3-indolyl)selanides.

    PubMed

    Naidu, P Seetham; Majumder, Swarup; Bhuyan, Pulak J

    2015-11-01

    An efficient reaction protocol was developed for the synthesis of several diindolylmethane derivatives via the [Formula: see text] C-H bond activation of aryl methyl ketones by [Formula: see text] and indoles in the presence of catalytic amounts of [Formula: see text] at 80 [Formula: see text] using dioxane as solvent. Unexpectedly, an interesting class of di(3-indolyl)selenide compounds was isolated when the reaction was carried out at room temperature.

  10. Density functional theory study of Rh(III)-catalyzed C-H activations and intermolecular annulations between benzamide derivatives and allenes.

    PubMed

    Xing, Zhong; Huang, Fang; Sun, Chuanzhi; Zhao, Xue; Liu, Jianbiao; Chen, Dezhan

    2015-04-20

    Density functional theory has been applied to gain insight into the Cp*Rh(OAc)2-catalyzed C-H activation and intermolecular annulation of benzamide derivatives with allenes. The study shows that the reactions proceed in three steps: (1) C-H activation induced by Rh catalyst reacting with benzamide derivatives, (2) carborhodation of allene, and (3) regeneration of Rh catalyst. The results indicate that the N-H deprotonation makes the following C-H activation much easier. The regio- and stereoselectivities of 1a (N-pivaloyloxy benzamide)/2a (cyclohexylallene) and 1b (N-pivaloyloxy-4-methyl-benzamide)/2b (1,1-dimethyl allene) depend on the allene carborhodation step. The steric hindrance effect is the dominant factor. We also discuss the reaction mechanism of 1c (N-methoxy benzamide)/2a. The chemoselectivity between 1c/2a is determined by the N-O cleavage step. Replacement of OPiv by OMe leads to loss of the stabilization effect provided by C=O in OPiv. Additionally, Cp*Rh(OAc)(OPiv) is produced in the Cp*Rh(OAc)2 regeneration step, which can work as catalyst as well.

  11. Promotional effects of chemisorbed oxygen and hydroxide in the activation of C-H and O-H bonds over transition metal surfaces

    NASA Astrophysics Data System (ADS)

    Hibbitts, David; Neurock, Matthew

    2016-08-01

    Electronegative coadsorbates such as atomic oxygen (O*) and hydroxide (OH*) can act as Brønsted bases when bound to Group 11 as well as particular Group 8-10 metal surfaces and aid in the activation of X-H bonds. First-principle density functional theory calculations were carried out to systematically explore the reactivity of the C-H bonds of methane and surface methyl intermediates as well as the O-H bond of methanol directly and with the assistance of coadsorbed O* and OH* intermediates over Group 11 (Cu, Ag, and Au) and Group 8-10 transition metal (Ru, Rh, Pd, Os, Ir, and Pt) surfaces. C-H as well as O-H bond activation over the metal proceeds via a classic oxidative addition type mechanism involving the insertion of the metal center into the C-H or O-H bond. O* and OH* assist C-H and O-H activation over particular Group 11 and Group 8-10 metal surfaces via a σ-bond metathesis type mechanism involving the oxidative addition of the C-H or O-H bond to the metal along with a reductive deprotonation of the acidic C-H and O-H bond over the M-O* or M-OH* site pair. The O*- and OH*-assisted C-H activation paths are energetically preferred over the direct metal catalyzed C-H scission for all Group 11 metals (Cu, Ag, and Au) with barriers that are 0.4-1.5 eV lower than those for the unassisted routes. The barriers for O*- and OH*-assisted C-H activation of CH4 on the Group 8-10 transition metals, however, are higher than those over the bare transition metal surfaces by as much as 1.4 eV. The C-H activation of adsorbed methyl species show very similar trends to those for CH4 despite the differences in structure between the weakly bound methane and the covalently adsorbed methyl intermediates. The activation of the O-H bond of methanol is significantly promoted by O* as well as OH* intermediates over both the Group 11 metals (Cu, Ag, and Au) as well as on all Group 8-10 metals studied (Ru, Rh, Pd, Os, Ir, and Pt). The O*- and OH*-assisted CH3O-H barriers are 0.6 to 2

  12. Regioselective introduction of heteroatoms at the C-8 position of quinoline N-oxides: remote C-H activation using N-oxide as a stepping stone.

    PubMed

    Hwang, Heejun; Kim, Jinwoo; Jeong, Jisu; Chang, Sukbok

    2014-07-30

    Reported herein is the metal-catalyzed regioselective C-H functionalization of quinoline N-oxides at the 8-position: direct iodination and amidation were developed using rhodium and iridium catalytic systems, respectively. Mechanistic study of the amidation revealed that the unique regioselectivity is achieved through the smooth formation of N-oxide-chelated iridacycle and that an acid additive plays a key role in the rate-determining protodemetalation step. While this approach of remote C-H activation using N-oxide as a directing group could readily be applied to a wide range of heterocyclic substrates under mild conditions with high functional group tolerance, an efficient synthesis of zinquin ester (a fluorescent zinc indicator) was demonstrated.

  13. Simultaneous structure-activity studies and arming of natural products by C-H amination reveal cellular targets of eupalmerin acetate

    NASA Astrophysics Data System (ADS)

    Li, Jing; Cisar, Justin S.; Zhou, Cong-Ying; Vera, Brunilda; Williams, Howard; Rodríguez, Abimael D.; Cravatt, Benjamin F.; Romo, Daniel

    2013-06-01

    Natural products have a venerable history of, and enduring potential for the discovery of useful biological activity. To fully exploit this, the development of chemical methodology that can functionalize unique sites within these complex structures is highly desirable. Here, we describe the use of rhodium(II)-catalysed C-H amination reactions developed by Du Bois to carry out simultaneous structure-activity relationship studies and arming (alkynylation) of natural products at ‘unfunctionalized’ positions. Allylic and benzylic C-H bonds in the natural products undergo amination while olefins undergo aziridination, and tertiary amine-containing natural products are converted to amidines by a C-H amination-oxidation sequence or to hydrazine sulfamate zwitterions by an unusual N-amination. The alkynylated derivatives are ready for conversion into cellular probes that can be used for mechanism-of-action studies. Chemo- and site-selectivity was studied with a diverse library of natural products. For one of these—the marine-derived anticancer diterpene, eupalmerin acetate—quantitative proteome profiling led to the identification of several protein targets in HL-60 cells, suggesting a polypharmacological mode of action.

  14. Activation of two C-H bonds of NHC N-methyl groups on triosmium and triruthenium carbonyl clusters.

    PubMed

    Cabeza, Javier A; Del Río, Ignacio; Miguel, Daniel; Pérez-Carreño, Enrique; Sánchez-Vega, M Gabriela

    2008-04-14

    The thermolysis of the NHC triosmium cluster [Os3(Me2Im)(CO)11] (1a; Me2Im = 1,3-dimethylimidazol-2-ylidene) in toluene at reflux temperature sequentially affords the edge-bridged cluster [Os3(micro-H)(micro-kappa2-MeImCH2)(CO)10] () and the face-capped derivative [Os3(micro-H)2(micro3-kappa2-MeImCH)(CO)9] (3a). These products result from the sequential oxidative addition of one (2a) and two (3a) N-methyl C-H bonds of the original NHC ligand. The related face-capped triruthenium cluster [Ru3(micro-H)2(micro3-kappa2-MeImCH)(CO)9] (3b) has been prepared by heating the NHC triruthenium cluster [Ru3(Me2Im)(CO)11] (1b) in THF at reflux temperature. In this case, the pentanuclear derivatives [Ru5(Me2Im)(micro4-kappa2-CO)(CO)14] (4b) and [Ru5(Me2Im)2(micro4-kappa2-CO)(CO)13] (5b) are minor reaction products, but a ruthenium cluster analogous to has not been obtained. The face-capped oxazole-derived NHC triruthenium cluster [Ru3(micro-H)2(micro3-kappa2-OxCH)(CO)9] (3c; MeOx = N-methyloxazol-2-ylidene) is the only isolated product of the thermolysis of [Ru3(MeOx)(CO)11] (1c) in THF at reflux temperature.

  15. Ruthenium(II)-Catalyzed C-H Activation of Imidamides and Divergent Couplings with Diazo Compounds: Substrate-Controlled Synthesis of Indoles and 3H-Indoles.

    PubMed

    Li, Yunyun; Qi, Zisong; Wang, He; Yang, Xifa; Li, Xingwei

    2016-09-19

    Indoles are an important structural motif that is commonly found in biologically active molecules. In this work, conditions for divergent couplings between imidamides and acceptor-acceptor diazo compounds were developed that afforded NH indoles and 3H-indoles under ruthenium catalysis. The coupling of α-diazoketoesters afforded NH indoles by cleavage of the C(N2 )-C(acyl) bond whereas α-diazomalonates gave 3H-indoles by C-N bond cleavage. This reaction constitutes the first intermolecular coupling of diazo substrates with arenes by ruthenium-catalyzed C-H activation.

  16. Efficient synthesis of frutinone A and its derivatives through palladium-catalyzed C - H activation/carbonylation.

    PubMed

    Shin, Yongje; Yoo, Changho; Moon, Youngtaek; Lee, Yunho; Hong, Sungwoo

    2015-04-01

    Frutinone A, a biologically active ingredient of an antimicrobial herbal extract, demonstrates potent inhibitory activity towards the CYP1A2 enzyme. A three-step total synthesis of frutinone A with an overall yield of 44 % is presented. The construction of the chromone-annelated coumarin core was achieved through palladium-catalyzed CH carbonylation of 2-phenolchromones. The straightforward synthetic route allowed facile substitutions around the frutinone A core and thus rapid exploration of the structure-activity relationship (SAR) profile of the derivatives. The inhibitory activity of the synthesized frutinone A derivatives were determined for CYP1A2, and ten compounds exhibited one-to-two digit nanomolar inhibitory activity towards the CYP1A2 enzyme.

  17. 9,10-Dihydrophenanthrene derivatives and one 1,4-anthraquinone firstly isolated from Dioscorea zingiberensis C. H. Wright and their biological activities.

    PubMed

    Du, Dan; Zhang, Rui; Xing, Zhihua; Liang, Yuyan; Li, Shengfu; Jin, Tao; Xia, Qing; Long, Dan; Xin, Guang; Wang, Guangzhi; Huang, Wen

    2016-03-01

    Two new phenanthrene derivatives, 2,5,7-trimethoxy-9,10-dihydrophenanthrene-1,4-dione (1) and 2,5,6-trihydroxy-3,4-dimethoxy-9,10-dihydrophenanthrene (3), one new anthracenedione, 2,5,7-trimethoxyanthracene-1,4-dione (2), together with two known 9,10-dihydrophenanthrenes (4-5) were isolated from the rhizomes of Dioscorea zingiberensis C. H. Wright. The structures of these new compounds were established based on extensive NMR spectroscopy. Several isolated compounds were evaluated for the inhibition against nitric oxide (NO) production in the lipopolysaccharide (LPS)-activated RAW 264.7 macrophage cell line, DPPH radical scavenging, and inhibitory activity on Free Fatty Acids (FFAs) induced triglyceride accumulation in HepG2 cells. Compound 2 exhibited moderate anti-inflammatory activity, compound 3 possessed comparable DPPH radical scavenging activity as Vitamin C, compounds 2 and 4 showed potent inhibitory activities on triglyceride accumulation.

  18. Rh(III)-Catalyzed Carbocyclization of 3-(Indolin-1-yl)-3-oxopropanenitriles with Alkynes and Alkenes through C-H Activation.

    PubMed

    Zhou, Tao; Wang, Yanwei; Li, Bin; Wang, Baiquan

    2016-10-07

    Rh(III)-catalyzed carbocyclization reactions of 3-(indolin-1-yl)-3-oxopropanenitriles with alkynes and alkenes have been developed to form 1,7-fused indolines through C-H activation. These reactions have a broad range of substrates and high yields. Unsymmetrical aryl-alkyl substituted alkynes proceeded smoothly with high regioselectivity. Electron-rich alkynes could undergo further oxidative coupling reaction to form polycyclic compounds. For alkenes, 1,2-dihydro-4H-pyrrolo[3,2,1-ij]quinolin-4-ones were formed via C(sp(2))-H bond alkenylation and C(sp(2))-H, C(sp(3))-H oxidative coupling reactions.

  19. Tuning reactivity and site selectivity of simple arenes in C-H activation: ortho-arylation of anisoles via arene-metal π-complexation.

    PubMed

    Ricci, Paolo; Krämer, Katrina; Larrosa, Igor

    2014-12-31

    Current approaches to achieve site selectivity in the C-H activation of arenes involve the use of directing groups or highly electron-poor arenes. In contrast, simple arenes, such as anisole, are characterized by poor reactivity and selectivity. We report that π-complexation to a Cr(CO)3 unit enhances the reactivity of anisoles providing an unprecedented ortho-selective arylation. This mild methodology can be used for the late stage functionalization of bioactive compounds containing the anisole motif, allowing the construction of novel organic scaffolds with few synthetic steps.

  20. Iridium(I)-catalyzed regioselective C-H activation and hydrogen-isotope exchange of non-aromatic unsaturated functionality.

    PubMed

    Kerr, William J; Mudd, Richard J; Paterson, Laura C; Brown, Jack A

    2014-11-03

    Isotopic labelling is a key technology of increasing importance for the investigation of new CH activation and functionalization techniques, as well as in the construction of labelled molecules for use within both organic synthesis and drug discovery. Herein, we report for the first time selective iridium-catalyzed CH activation and hydrogen-isotope exchange at the β-position of unsaturated organic compounds. The use of our highly active [Ir(cod)(IMes)(PPh3 )][PF6 ] (cod=1,5-cyclooctadiene) catalyst, under mild reaction conditions, allows the regioselective β-activation and labelling of a range of α,β-unsaturated compounds with differing steric and electronic properties. This new process delivers high levels of isotope incorporation over short reaction times by using low levels of catalyst loading.

  1. The Children's Health and Activity Modification Program (C.H.A.M.P.): participants' perspectives of a four-week lifestyle intervention for children with obesity.

    PubMed

    Pearson, Erin S; Irwin, Jennifer D; Burke, Shauna M

    2012-12-01

    To date, there is a paucity of qualitative research examining the influence of community-based interventions for childhood obesity on the participants themselves. This study explored the experiences of children who participated in the Children's Health and Activity Modification Program (C.H.A.M.P.), a four-week day camp for children with obesity aged 8-14, in order to uncover key program elements for positive behavior change. Following the intervention, children (n = 36) participated in focus groups where they were asked about their experiences pertaining to physical activity and nutrition, what it was like to be part of a team, and how they felt about themselves. Findings revealed that participants perceived C.H.A.M.P. as helpful (e.g. in making healthier food choices, being more active, and feeling more confident and self-aware). This pilot study offers unique insights into the perspectives of children with obesity. Results are discussed with respect to future program development and research for childhood obesity treatment.

  2. 2008 C. H. McCloy Lecture: Social Psychology and Physical Activity--Back to the Future

    ERIC Educational Resources Information Center

    Gill, Diane L.

    2009-01-01

    In the early 1970s, both my academic career and the psychology subdiscipline within kinesiology began as "social psychology and physical activity." Since then, sport and exercise psychology research has shifted away from the social to a narrower bio-psycho-(no social) approach, and professional practice has focused on the elite rather…

  3. 1994 C. H. McCloy Research Lecture: Does Physical Activity Play a Role in Preventing Osteoporosis?

    ERIC Educational Resources Information Center

    Drinkwater, Barbara L.

    1994-01-01

    Review considers problems encountered in relating women's physical activity to increases in bone mass, noting the implications of recommending exercise to help prevent osteoporosis based on that information. Research indicates that for the full benefit of exercise on skeletal health, there must be adequate gonadal hormone levels. (SM)

  4. Access to Silylated Pyrazole Derivatives by Palladium-Catalyzed C-H Activation of a TMS group.

    PubMed

    Mistico, Laetitia; Querolle, Olivier; Meerpoel, Lieven; Angibaud, Patrick; Durandetti, Muriel; Maddaluno, Jacques

    2016-07-04

    A simple and efficient approach to new silylated heterocycles of potential interest in medicinal chemistry is presented. A set of bromophenyl trimethylsilyl pyrazole intermediates can be transformed by direct organometallic routes into two families of regioisomeric iodoaryl substrates; using either arylzinc or aryllithium chemistry, the TMS group remains on the pyrazole ring or translocates to the aryl moiety. These two families can then be efficiently transformed into benzo silino pyrazoles thanks to a single-step cyclization relying on the Pd-catalyzed activation of a non-activated C(sp(3) )-H bond alpha to a silicon atom. The experimental conditions used, which are fully compatible with the pyrazole ring, suggest that this reaction evolves through a concerted metalation-deprotonation (CMD) mechanism.

  5. Synthesis, Characterization, and C-H Activation Reactions of Novel Organometallic O-donor Ligated Rh(III) Complexes

    SciTech Connect

    Tenn, William J.; Conley, Brian L.; Bischof, Steven M.; Periana, Roy A.

    2010-09-17

    The synthesis and characterization of the O-donor ligated, air and water stable organometallic complexes trans- (2), and cis-(hfac-O,O) 2Rh(CH3)(py) (3), trans-(hfac-O,O)2Rh(C6H5)(py) (4), cis-(hfac-O,O)2Rh(C6H5)(py) (5), and cis-(hfac-O,O)2Rh(Mes)(py) (6) (where hfac-O,O = κ 2-O,O-1,1,1,5,5,5-hexafluoroacetylacetonato) are reported. These compounds are analogues to the O-donor iridium complexes that are active catalysts for the hydroarylation and C–H activation reactions as well as the bis-acetylacetonato rhodium complexes, which we recently reported. The trans-complex 2 undergoes a quantitative trans to cis isomerization in cyclohexane to form 3, which activates C–H bonds in both benzene and mesitylene to form compounds 5 and 6, respectively. All of these compounds are air and water stable and do not lead to decomposition products. Complex 5 promotes hydroarylation of styrene by benzene to generate dihydrostilbene.

  6. C/H{sub 2}O reaction under supercritical conditions and their repercussions in the preparation of activated carbon

    SciTech Connect

    Salvador, F.; Senchez-Montero, M.J.; Izquierdo, C.

    2007-09-15

    Two chars prepared by carbonization of oak wood and anthracite were used to perform a comparative study of the gasification with supercritical water (SCW) and with steam. This work reports the effects of the type of char, the activating agent, temperature, flow rate, and particle size employed on the kinetics, mechanism of reaction, and the characteristics of the activated carbons obtained. The results show that the reactivity of the two chars is much higher with SCW than with steam. Although this increase can be explained in terms of the greater penetration of SCW and diffusional effects in the pore structure of the chars, some aspects suggest a possible change in the mechanism of reaction favored by the formation of clusters in SCW. The evolution of porosity was also found to differ when the char was gasified with SCW and with steam, being governed strongly by the starting material. When the oak char was activated with SCW, the smallest microporosity was broadened from the very first moments due to its very open pore structure, providing carbons with larger micropores and some mesoporosity. In contrast, in the case of the anthracite char, with a narrower pore structure, the evolution of the porosity was slower and less uniform, favoring external gasification of the particle. Accordingly, the carbons had a broader distribution of micropores, and mesoporosity was scarce.

  7. Trimethylsilylmethyl complexes of the rare-earth metals with sterically hindered N-heterocyclic carbene ligands: adduct formation and C-H bond activation.

    PubMed

    Fegler, Waldemar; Spaniol, Thomas P; Okuda, Jun

    2010-08-07

    Tris(trimethylsilylmethyl) complexes of yttrium and lutetium [LnR(3)(THF)(2)] (R = CH(2)SiMe(3)) were treated with sterically bulky N-heterocyclic carbenes (NHC) 1,3-bis(2,6-diisopropylphenyl)imidazol-2-ylidene (IPr) and 1,3-bis(2,4,6-trimethylphenyl)imidazol-2-ylidene (IMes). IPr gave labile mono-adducts [LnR(3)(NHC)], isolated as thermally robust crystals and fully characterized by NMR spectroscopy and X-ray diffraction. IMes gave a similar lutetium mono-adduct [LuR(3)(IMes)] with the lutetium alkyl [LuR(3)(THF)(2)], whereas the yttrium alkyl [YR(3)(THF)(2)] resulted in the formation of an ortho-metalated product. This compound, isolated as a crystalline bis(THF) adduct, contains a strained six-membered chelate ring that has been formed by the C-H bond activation of one of the ortho-methyl groups of the mesityl group. In contrast [LuR(3)(IMes)] only slowly underwent a similar C-H bond activation.

  8. Low-energy reaction rate constants for the Ni+-assisted decomposition of acetaldehyde: observation of C-H and C-C activation.

    PubMed

    Dee, S Jason; Castleberry, Vanessa A; Villarroel, Otsmar J; Laboren, Ivanna E; Bellert, Darrin J

    2010-02-04

    Rate constants for the low-energy Ni(+)-assisted dissociative reaction of acetaldehyde have been measured under jet-cooled conditions in the gas phase. The rate constants are acquired through monitoring the time dependence of fragment Ni(+)CO formation. The decomposition of the precursor Ni(+)-acetaldehyde cluster ion proceeds via consecutive, parallel reaction coordinates that originate with the Ni(+)-assisted cleavage of either a C-C or an aldehyde C-H bond. The energies used to initiate these reactions are well below that required to cleave sigma-bonds in the isolated acetaldehyde molecule. Direct measurement of the reaction kinetics over a range of energies indicates that the rate-limiting step in the dissociative mechanism changes at cluster ion internal energies = 17,200 +/- 400 cm(-1). Arguments are presented that this energy marks the closure of the dissociative coordinate that initiates with C-H sigma-bond activation and thus provides a measure of the activation energy of this dissociative pathway.

  9. Direct arylation of benzene with aryl bromides using high-temperature/high-pressure process windows: expanding the scope of C-H activation chemistry.

    PubMed

    Pieber, Bartholomäus; Cantillo, David; Kappe, C Oliver

    2012-04-16

    A detailed investigation on the direct arylation of benzene with aryl bromides by using first-row transition metals under high-temperature/high-pressure (high-T/p) conditions is described. By employing a parallel reactor platform for rapid reaction screening and discovery at elevated temperatures, various metal/ligand/base combinations were evaluated for their ability to enable biaryl formation through C-H activation. The combination of cobalt(III) acetylacetonate and lithium bis(trimethylsilyl)amide was subjected to further process intensification at 200 °C (15 bar), allowing a significant reduction of the catalyst/base loading and a dramatic increase in catalytic efficiency (turnover frequency) by a factor of 1000 compared to traditional protocols. The high-throughput screening additionally identified novel nickel- and copper-based metal/ligand combinations that favored an amination pathway competing with C-H activation, with the addition of ligands, such as 1,10-phenanthroline, having a profound influence on the selectivity. In addition to metal-based catalysts, high-T/p process windows were also successfully applied to transition-metal-free systems, utilizing 1,10-phenanthroline as organocatalyst.

  10. Bipyridine- and phenanthroline-based metal-organic frameworks for highly efficient and tandem catalytic organic transformations via directed C-H activation.

    PubMed

    Manna, Kuntal; Zhang, Teng; Greene, Francis X; Lin, Wenbin

    2015-02-25

    We report here the synthesis of a series of robust and porous bipyridyl- and phenanthryl-based metal-organic frameworks (MOFs) of UiO topology (BPV-MOF, mBPV-MOF, and mPT-MOF) and their postsynthetic metalation to afford highly active single-site solid catalysts. While BPV-MOF was constructed from only bipyridyl-functionalized dicarboxylate linker, both mBPV- and mPT-MOF were built with a mixture of bipyridyl- or phenanthryl-functionalized and unfunctionalized dicarboxylate linkers. The postsynthetic metalation of these MOFs with [Ir(COD)(OMe)]2 provided Ir-functionalized MOFs (BPV-MOF-Ir, mBPV-MOF-Ir, and mPT-MOF-Ir), which are highly active catalysts for tandem hydrosilylation of aryl ketones and aldehydes followed by dehydrogenative ortho-silylation of benzylicsilyl ethers as well as C-H borylation of arenes using B2pin2. Both mBPV-MOF-Ir and mPT-MOF-Ir catalysts displayed superior activities compared to BPV-MOF-Ir due to the presence of larger open channels in the mixed-linker MOFs. Impressively, mBPV-MOF-Ir exhibited high TONs of up to 17,000 for C-H borylation reactions and was recycled more than 15 times. The mPT-MOF-Ir system is also active in catalyzing tandem dehydrosilylation/dehydrogenative cyclization of N-methylbenzyl amines to azasilolanes in the absence of a hydrogen acceptor. Importantly, MOF-Ir catalysts are significantly more active (up to 95 times) and stable than their homogeneous counterparts for all three reactions, strongly supporting the beneficial effects of active site isolation within MOFs. This work illustrates the ability to increase MOF open channel sizes by using the mixed linker approach and shows the enormous potential of developing highly active and robust single-site solid catalysts based on MOFs containing nitrogen-donor ligands for important organic transformations.

  11. Self-optimisation and model-based design of experiments for developing a C-H activation flow process.

    PubMed

    Echtermeyer, Alexander; Amar, Yehia; Zakrzewski, Jacek; Lapkin, Alexei

    2017-01-01

    A recently described C(sp(3))-H activation reaction to synthesise aziridines was used as a model reaction to demonstrate the methodology of developing a process model using model-based design of experiments (MBDoE) and self-optimisation approaches in flow. The two approaches are compared in terms of experimental efficiency. The self-optimisation approach required the least number of experiments to reach the specified objectives of cost and product yield, whereas the MBDoE approach enabled a rapid generation of a process model.

  12. Rh(I)-Catalyzed Arylation of Heterocycles via C-H Bond Activation: Expanded Scope Through Mechanistic Insight

    SciTech Connect

    Lewis, Jared; Berman, Ashley; Bergman, Robert; Ellman, Jonathan

    2007-07-18

    A practical, functional group tolerant method for the Rh-catalyzed direct arylation of a variety of pharmaceutically important azoles with aryl bromides is described. Many of the successful azole and aryl bromide coupling partners are not compatible with methods for the direct arylation of heterocycles using Pd(0) or Cu(I) catalysts. The readily prepared, low molecular weight ligand, Z-1-tert-butyl-2,3,6,7-tetrahydrophosphepine, which coordinates to Rh in a bidentate P-olefin fashion to provide a highly active yet thermally stable arylation catalyst, is essential to the success of this method. By using the tetrafluoroborate salt of the corresponding phosphonium, the reactions can be assembled outside of a glove box without purification of reagents or solvent. The reactions are also conducted in THF or dioxane, which greatly simplifies product isolation relative to most other methods for direct arylation of azoles employing high-boiling amide solvents. The reactions are performed with heating in a microwave reactor to obtain excellent product yields in two hours.

  13. Computational Mechanistic Study of Redox-Neutral Rh(III)-Catalyzed C-H Activation Reactions of Arylnitrones with Alkynes: Role of Noncovalent Interactions in Controlling Selectivity.

    PubMed

    Xing, Yang-Yang; Liu, Jian-Biao; Tian, Ying-Ying; Sun, Chuan-Zhi; Huang, Fang; Chen, De-Zhan

    2016-11-23

    The mechanism of redox-neutral Rh(III)-catalyzed coupling reactions of arylnitrones with alkynes was investigated by density functional theory (DFT) calculations. The free energy profiles associated with the catalytic cycle, involving C(sp(2))-H activation, insertion of alkyne, transfer of O atom, cyclization and protodemetalation, are presented and analyzed. An overwhelming preference for alkyne insertion into Rh-C over Rh-O is observed among all pathways, and the most favorable route is determined. The pivalate-assisted C-H activation step is turnover-limiting, and the cyclization step determines the diastereoselectivity of the reaction, with the stereoselectivity arising mainly from the difference of noncovalent interactions in key transition states. The detailed mechanism of O atom transfer, Rh(III)-Rh(I)-Rh(III) versus Rh(III)-Rh(V)-Rh(III) cycle, is discussed.

  14. Aliphatic Halogenase Enables Late-Stage C-H Functionalization: Selective Synthesis of a Brominated Fischerindole Alkaloid with Enhanced Antibacterial Activity.

    PubMed

    Zhu, Qin; Hillwig, Matthew L; Doi, Yohei; Liu, Xinyu

    2016-03-15

    The anion promiscuity of a newly discovered standalone aliphatic halogenase WelO5 was probed and enabled the selective synthesis of 13R-bromo-12-epi-fischerindole U via late-stage enzymatic functionalization of an unactivated sp(3) C-H bond. Pre-saturating the WelO5 active site with a non-native bromide anion was found to be critical to the highly selective in vitro transfer of bromine, instead of chlorine, to the target carbon center and also allowed the relative binding affinity of bromide and chloride towards the WelO5 enzyme to be assessed. This study further revealed the critical importance of halogen substitution on modulating the antibiotic activity of fischerindole alkaloids and highlights the promise of WelO5-type aliphatic halogenases as enzymatic tools to fine-tune the bioactivity of complex natural products.

  15. An active-site phenylalanine directs substrate binding and C-H cleavage in the alpha-ketoglutarate-dependent dioxygenase TauD.

    PubMed

    McCusker, Kevin P; Klinman, Judith P

    2010-04-14

    Enzymes that cleave C-H bonds are often found to depend on well-packed hydrophobic cores that influence the distance between the hydrogen donor and acceptor. Residue F159 in taurine alpha-ketoglutarate dioxygenase (TauD) is demonstrated to play an important role in the binding and orientation of its substrate, which undergoes a hydrogen atom transfer to the active site Fe(IV)=O. Mutation of F159 to smaller hydrophobic side chains (L, V, A) leads to substantially reduced rates for substrate binding and for C-H bond cleavage, as well as increased contribution of the chemical step to k(cat) under steady-state turnover conditions. The greater sensitivity of these substrate-dependent processes to mutation at position 159 than observed for the oxygen activation process supports a previous conclusion of modularity of function within the active site of TauD (McCusker, K. P.; Klinman, J. P. Proc. Natl. Acad. Sci. U.S.A. 2009, 106, 19791-19795). Extraction of intrinsic deuterium kinetic isotope effects (KIEs) using single turnover transients shows 2- to 4-fold increase in the size of the KIE for F159V in relation to wild-type and F159L. It appears that there is a break in behavior following removal of a single methylene from the side chain of F159L to generate F159V, whereby the protein active site loses its ability to restore the internuclear distance between substrate and Fe(IV)=O that supports optimal hydrogenic wave function overlap.

  16. The ansa effect in permethylmolybdenocene chemistry: A [Me{sub 2}Si] ansa bridge promotes intermolecular C-H and C-C bond activation

    SciTech Connect

    Churchill, D.; Shin, J.H.; Hascall, T.; Hahn, J.M.; Bridgewater, B.M.; Parkin, G.

    1999-06-21

    Access to the [Me{sub 2}Si] ansa-bridged permethylmolybdenocene system is provided by the synthesis of [Me{sub 2}Si(C{sub 5}Me{sub 4}){sub 2}]MoCl{sub 2} from the reaction of MoCl{sub 5} with a mixture of [Me{sub 2}Si(C{sub 5}Me{sub 4}){sub 2}]Li{sub 2} and NaBH{sub 4}, followed by treatment with CHCl{sub 3}. Comparison with the chemistry of the non-ansa Cp{sup *}{sub 2}MoX{sub 2} system indicates that incorporation of the [Me{sub 2}Si] ansa bridge promotes intermolecular C-H and C-C bond activation reactions.

  17. Merging allylic C-H bond activation and C-C bond cleavage en route to the formation of a quaternary carbon stereocenter in acyclic systems.

    PubMed

    Vasseur, Alexandre; Marek, Ilan

    2017-01-01

    This protocol describes a diastereoselective approach for the synthesis of complex molecular architectures containing two stereogenic centers in a 1,4 relationship, one of which being an all-carbon quaternary stereogenic center. Such molecules could be intermediates in the synthesis of steroids, for example. Conceived as a single-flask synthetic sequence from ω-ene cyclopropanes, the protocol involves a concerted allylic C-H and C-C bond activation promoted by the Negishi reagent (Cp2Zr(η(2)-butene)). This zirconium-promenade-based procedure affords bifunctionalized products in high diastereomeric ratios after reaction of ω-ene cyclopropanes with the Negishi complex, followed by a thermal treatment and sequential addition of two different electrophiles. The method proves to be particularly efficient when carbonyl compounds are used as first electrophiles and hydrogen or elemental halides are used as second electrophiles. In addition, it offers the opportunity to create new C-C bonds via remote functionalization of a (sp(3))-C-H bond, a result of a copper or copper/palladium transmetalation step that extends the scope of the process to alkyl, acyl and aromatic halide compounds as second electrophiles. The typical described protocol allows the synthesis of the highly diastereo-enriched 2-((1R*,2S*)-2-butyl-2 propylcyclopropyl)ethanol and may provide a new entry to access complex molecular segments of natural products such as steroids or C30 botryococcene. It requires a simple reaction setup and takes ∼18.5 h to run the reaction and 2 h for isolation and purification.

  18. Rare-earth-metal alkylaluminates supported by N-donor-functionalized cyclopentadienyl ligands: C-H bond activation and performance in isoprene polymerization.

    PubMed

    Jende, Lars N; Maichle-Mössmer, Cäcilia; Anwander, Reiner

    2013-11-25

    Homoleptic tetramethylaluminate complexes [Ln(AlMe4)3] (Ln=La, Nd, Y) reacted with HCp(NMe2) (Cp(NMe2) =1-[2-(N,N-dimethylamino)-ethyl]-2,3,4,5-tetramethyl-cyclopentadienyl) in pentane at -35 °C to yield half-sandwich rare-earth-metal complexes, [{C5 Me4CH2CH2NMe2 (AlMe3)}Ln(AlMe4)2]. Removal of the N-donor-coordinated trimethylaluminum group through donor displacement by using an equimolar amount of Et2O at ambient temperature only generated the methylene-bridged complexes [{C5Me4CH2CH2NMe(μ-CH2)AlMe3}Ln(AlMe4)] with the larger rare-earth-metal ions lanthanum and neodymium. X-ray diffraction analysis revealed the formation of isostructural complexes and the C-H bond activation of one aminomethyl group. The formation of Ln(μ-CH2)Al moieties was further corroborated by (13)C and (1)H-(13)C HSQC NMR spectroscopy. In the case of the largest metal center, lanthanum, this C-H bond activation could be suppressed at -35 °C, thereby leading to the isolation of [(Cp(NMe2))La(AlMe4)2], which contains an intramolecularly coordinated amino group. The protonolysis reaction of [Ln(AlMe4)3] (Ln=La, Nd) with the anilinyl-substituted cyclopentadiene HCp(AMe2) (Cp(AMe2) =1-[1-(N,N-dimethylanilinyl)]-2,3,4,5-tetramethylcyclopentadienyl) at -35 °C generated the half-sandwich complexes [(Cp(AMe2))Ln(AlMe4)2]. Heating these complexes at 75 °C resulted in the C-H bond activation of one of the anilinium methyl groups and the formation of [{C5Me4C6H4NMe(μ-CH2)AlMe3}Ln(AlMe4)] through the elimination of methane. In contrast, the smaller yttrium metal center already gave the aminomethyl-activated complex at -35 °C, which is isostructural to those of lanthanum and neodymium. The performance of complexes [{C5Me4CH2CH2NMe(μ-CH2 )AlMe3}-Ln(AlMe4)], [(Cp(AMe2))Ln(AlMe4)2], and [{C5Me4C6H4NMe(μ-CH2)AlMe3}Ln(AlMe4)] in the polymerization of isoprene was investigated upon activation with [Ph3C][B(C6F5)4], [PhNMe2 H][B(C6F5)4], and B(C6F5)3. The highest stereoselectivities were observed

  19. Iridium-imine and -amine complexes relevant to the (S)-metolachlor process: structures, exchange kinetics, and C-H activation by Iri causing racemization.

    PubMed

    Dorta, Romano; Broggini, Diego; Kissner, Reinhard; Togni, Antonio

    2004-09-20

    Iridium complexes of DMA-imine [2,6-dimethylphenyl-1'-methyl-2'-methoxyethylimine, 1 a) and (R)-DMA-amine [(1'R)-2,6-dimethylphenyl-1'-methyl-2'-methoxyethylamine, 2 a] that are relevant to the catalytic imine hydrogenation step of the Syngenta (S)-Metolachlor process were synthesized: metathetical exchange of [Ir2Cl2(cod)2] (cod=1,5-cyclooctadiene) with [Ag(1 a)2]BF4 and [Ag((R)-2 a)2]BF4 afforded [Ir(cod)(kappa2- -1 a)]BF4 (11) and [Ir(cod)(kappa2-(R)-2 a)]BF4 ((R)-19)), respectively. These complexes were then used in stopped-flow experiments to study the displacement of amine 2 a from complex 19 by imine 1 a to form the imine complex 11, thus modeling the product/substrate exchange step in the catalytic cycle. The data suggest a two-step associative mechanism characterized by k1=(2.6+/-0.3) x 10(2) M(-1) s(-1) and k2=(4.3+/-0.6) x 10(-2) s(-1) with the respective activation energies EA1=(7.5+/-0.6) kJ mol(-1) and EA2=(37+/-3) kJ mol(-1). Furthermore, complex 11 reacted with H2O to afford the hydrolysis product [Ir(cod)(eta(6-)-2,6-dimethylaniline)]BF4 (12), and with I2 to liberate quantitatively the DMA-iminium salt 14. On the other hand, the chiral amine complex (R)-19 formed the optically inactive eta6-bound compound [Ir(cod)(eta6-rac-2 a)]BF4 (rac-18) upon dissolution in THF at room temperature, presumably via intramolecular C-H activation. This racemization was found to be a two-step event with k'1=9.0 x 10(-4) s(-1) and k2=2.89 x 10(-5) s(-1), featuring an optically active intermediate prior to sp3 C-H activation. Compounds 11, 12, rac-18, and (R)-19 were structurally characterized by single-crystal X-ray analyses.

  20. The Molybdenum Active Site of Formate Dehydrogenase Is Capable of Catalyzing C-H Bond Cleavage and Oxygen Atom Transfer Reactions.

    PubMed

    Hartmann, Tobias; Schrapers, Peer; Utesch, Tillmann; Nimtz, Manfred; Rippers, Yvonne; Dau, Holger; Mroginski, Maria Andrea; Haumann, Michael; Leimkühler, Silke

    2016-04-26

    Formate dehydrogenases (FDHs) are capable of performing the reversible oxidation of formate and are enzymes of great interest for fuel cell applications and for the production of reduced carbon compounds as energy sources from CO2. Metal-containing FDHs in general contain a highly conserved active site, comprising a molybdenum (or tungsten) center coordinated by two molybdopterin guanine dinucleotide molecules, a sulfido and a (seleno-)cysteine ligand, in addition to a histidine and arginine residue in the second coordination sphere. So far, the role of these amino acids in catalysis has not been studied in detail, because of the lack of suitable expression systems and the lability or oxygen sensitivity of the enzymes. Here, the roles of these active site residues is revealed using the Mo-containing FDH from Rhodobacter capsulatus. Our results show that the cysteine ligand at the Mo ion is displaced by the formate substrate during the reaction, the arginine has a direct role in substrate binding and stabilization, and the histidine elevates the pKa of the active site cysteine. We further found that in addition to reversible formate oxidation, the enzyme is further capable of reducing nitrate to nitrite. We propose a mechanistic scheme that combines both functionalities and provides important insights into the distinct mechanisms of C-H bond cleavage and oxygen atom transfer catalyzed by formate dehydrogenase.

  1. Development of a supramolecular ensemble of an AIEE active hexaphenylbenzene derivative and Ag@Cu2O core-shell NPs: an efficient photocatalytic system for C-H activation.

    PubMed

    Chopra, Radhika; Kumar, Manoj; Bhalla, Vandana

    2016-08-09

    A supramolecular ensemble having Ag@Cu2O core-shell nanoparticles stabilized by aggregates of a hexaphenylbenzene derivative has been developed which exhibits excellent photocatalytic efficiency in reactions involving preparation of imidazole and benzimidazole derivatives via C-H activation.

  2. Ligand versus Complex: C-F and C-H Bond Activation of Polyfluoroaromatics at a Cyclic (Alkyl)(Amino)Carbene.

    PubMed

    Paul, Ursula S D; Radius, Udo

    2017-03-17

    C-F and C-H bond activation reactions of polyfluoroaromatics at the cyclic (alkyl)(amino)carbene (cAAC) cAAC(methyl) (1) are reported. Studies on the C-F bond activation using the cAAC-stabilized nickel(0) complex [Ni(cAAC(methyl) )2 ] (2) have shown that 2 does not react with fluorinated arenes. However, these investigations led to the observation of C-F bond cleavage of perfluorinated arenes by the carbene ligand cAAC(methyl) (1) itself. The reaction of 1 with C6 F6 , C6 F5 -C6 F5 , C6 F5 -CF3 , and C5 F5 N afforded the insertion products of cAAC into one of the C-F bonds of the substrate, that is, the C-F bond activation products (cAAC(methyl) )F(Ar(f) ) (Ar(f) =C6 F5 4 a, C6 F4 -C6 F5 4 b, C6 F4 -CF3 4 c, C5 F4 N 4 d). These products decompose readily upon heating to 80 °C within a few hours in solution with formation of ionic iminium salts [(cAAC(methyl) )(Ar(f) )][X] 6 a-d or neutral alkenyl perfluoroaryl imine compounds 7 a-d. The compounds (cAAC(methyl) )F(Ar(f) ) 4 a-d readily transfer fluoride, which has been exemplified by the fluoride transfer of all compounds using BF3 etherate as fluoride acceptor. Fluoride transfer has also been achieved starting from (cAAC(methyl) )F(C6 F4 -CF3 ) (4 c) or (cAAC(methyl) )F(C5 F4 N) (4 d) to other selected substrates such as trimethylchlorosilane, benzoyl chloride and tosyl chloride. Instead of C-F bond activation, insertion of the cAAC into the C-H bond was observed if 1 was treated with the partially fluorinated arenes C6 F5 H, 1,2,4,5-C6 F4 H2 , 1,3,5-C6 F3 H3 , and 1,3-C6 F2 H4 . The compounds (cAAC(methyl) )H(Ar(f) ) (Ar(f) =C6 F5 12 e, 2,3,5,6-C6 F4 H 12 f, 2,4,6-C6 F3 H2 12 g and 2,6-C6 F2 H3 12 h) have been isolated in good yields and have been characterized including X-ray analysis. Fluorobenzene C6 FH5 (pKa ≈37), the least C-H acidic fluoroarene used in this study, does not react. In order to investigate the scope and limitations of this type of cAAC C-H bond activation

  3. A kinetico-mechanistic study on the C-H bond activation of primary benzylamines; cooperative and solid-state cyclopalladation on dimeric complexes.

    PubMed

    Font, Helena; Font-Bardia, Mercè; Gómez, Kerman; González, Gabriel; Granell, Jaume; Macho, Israel; Martínez, Manuel

    2014-09-28

    The cyclometallation reactions of dinuclear μ-acetato complexes of the type [Pd(AcO)(μ-AcO)L]2 (L = 4-RC6H4CH2NH2, R = H, Cl, F, CF3), a process found to occur readily even in the solid state, have been studied from a kinetico-mechanistic perspective. Data indicate that the dinuclear acetato bridged derivatives are excellent starting materials to activate carbon-hydrogen bonds in a facile way. In all cases the established concerted ambiphilic proton abstraction by a coordinated acetato ligand has been proved. The metallation has also been found to occur in a cooperative manner, with the metallation of the first palladium unit of the dimeric complex being rate determining; no intermediate mono-metallated compounds are observed in any of the processes. The kinetically favoured bis-cyclopalladated compound obtained after complete C-H bond activation does not correspond to the final isolated XRD-characterized complexes. This species, bearing the classical open-book dimeric form, has a much more complex structure than the final isolated compound, with different types of acetato ligands.

  4. Nitro and amino substitution in the D-ring of 5-(2-dimethylaminoethyl)- 2,3-methylenedioxy-5H-dibenzo[c,h][1,6]naphthyridin-6-ones: effect on topoisomerase-I targeting activity and cytotoxicity.

    PubMed

    Singh, Sudhir K; Ruchelman, Alexander L; Li, Tsai-Kun; Liu, Angela; Liu, Leroy F; LaVoie, Edmond J

    2003-05-22

    5H-8,9-dimethoxy-5-(2-N,N-dimethylaminoethyl)-2,3-methylenedioxydibenzo[c,h][1,6]naphthyridin-6-one exhibits potent TOP1-targeting activity and pronounced antitumor activity. It was hypothesized that replacement of the two methoxyl groups with a nitro substituent would allow for retention of similar activity. In this study 8-, 9-, and 10-nitro-5H-2,3-methylenedioxy-5-(2-N,N-dimethylaminoethyl)dibenzo[c,h][1,6]naphthyridin-6-one and their amino derivatives were synthesized and assessed for their relative TOP1-targeting activity and cytotoxicity. In the case of both the 8- and 9-nitro analogues, their TOP1-targeting activity and cytotoxicity are greater than that of camptothecin and comparable to that of 5H-8,9-dimethoxy-5-(2-N,N-dimethylaminoethyl)-2,3-methylenedioxydibenzo[c,h][1,6]naphthyridin-6-one.

  5. C-H activation in pyridoxal-5'-phosphate Schiff bases: the role of the imine nitrogen. A combined experimental and computational study.

    PubMed

    Casasnovas, Rodrigo; Adrover, Miquel; Ortega-Castro, Joaquin; Frau, Juan; Donoso, Josefa; Muñoz, Francisco

    2012-09-06

    The origins of C-H activation in pyridoxal-5'-phosphate (PLP) Schiff bases and modulation of reaction specificity in PLP-enzymes are still not completely understood. There are no available studies that compare the reactivity of C4' carbons in ketimine Schiff bases with that of Cα carbons in their aldimine counterparts, which is essential to unravel the mechanisms that govern the evolution of their common carbanionic intermediates. Second-order rate constants for phosphate-catalyzed proton/deuterium exchange reactions in D(2)O of C4' carbons suffer a 10(5)-fold increase due to Schiff base formation (k(B) = 5.3 × 10(1) M(-1) s(-1)) according to NMR measurements. The C4' carbon acidity is also increased to pK(a) = 9.8, which is significantly higher than that of Cα in PLP-aldimines. DFT calculations reveal the role of each heteroatom in modulating the electrophilicity of C4' and Cα carbons. Specifically, the protonation state of pyridine nitrogen is the main factor in determining the absolute carbon acidity in aldimines (pK(a) of Cα varies from ∼14 to ∼23) and ketimines (pK(a) of C4' varies from ∼12 to ∼18), whereas the protonation state of both imine nitrogen and O3' phenol oxygen modulates the relative acidities of Cα and C4' from 1.5 to 7.5 pK(a) units. Our results provide an explanation to the modulation of reaction specificity observed in different PLP-enzymes based on the differences in the protonation state of the cofactor and H-bonding patterns in the active site.

  6. Rh(III)-Catalyzed Diastereoselective Annulation of Amides with Quinone Monoacetals: Access to Bridged Nine-Membered Heterocycles via C-H Activation.

    PubMed

    Yang, Wei; Dong, Jinhuan; Wang, Jingyi; Xu, Xianxiu

    2017-02-03

    An unprecedented Rh(III)-catalyzed annulation of various benzamides and acrylamides with quinone monoacetals was developed for the facile and efficient one-pot synthesis of bridged nine-membered benzo[c]azonine-1,5(2H)-diones and 2-azabicyclo[4.3.1]dec-4-ene-3,8-diones. It is the first example of synthesis of nine-membered heterocycles through Rh(III)-catalyzed C-H bond functionalization, and both aryl and vinyl C-H bonds are tolerant in this reaction. A plausible mechanism is proposed on the basis of control experiments.

  7. Variable coordination of amine functionalised N-heterocyclic carbene ligands to Ru, Rh and Ir: C-H and N-H activation and catalytic transfer hydrogenation.

    PubMed

    Cross, Warren B; Daly, Christopher G; Boutadla, Youcef; Singh, Kuldip

    2011-10-14

    Chelating amine and amido complexes of late transition metals are highly valuable bifunctional catalysts in organic synthesis, but complexes of bidentate amine-NHC and amido-NHC ligands are scarce. Hence, we report the reactions of a secondary-amine functionalised imidazolium salt 2a and a primary-amine functionalised imidazolium salt 2b with [(p-cymene)RuCl(2)](2) and [Cp*MCl(2)](2) (M = Rh, Ir). Treating 2a with [Cp*MCl(2)](2) and NaOAc gave the cyclometallated compounds Cp*M(C,C)I (M = Rh, 3; M = Ir, 4), resulting from aromatic C-H activation. In contrast, treating 2b with [(p-cymene)RuCl(2)](2), Ag(2)O and KI gave the amine-NHC complex [(p-cymene)Ru(C,NH(2))I]I (5). The reaction of 2b with [Cp*MCl(2)](2) (M = Rh, Ir), NaO(t)Bu and KI gave the amine-NHC complex [Cp*Rh(NH(2))I]I (6) or the amido-NHC complex Cp*Ir(C,NH)I (7); both protonation states of the Ir complex could be accessed: treating 7 with trifluoroacetic acid gave the amine-NHC complex [Cp*Ir(C,NH(2))I][CF(3)CO(2)] (8). These are the first primary amine- or amido-NHC complexes of Rh and Ir. Solid-state structures of the complexes 3-8 have been determined by single crystal X-ray diffraction. Complexes 5, 6 and 7 are pre-catalysts for the catalytic transfer hydrogenation of acetophenone to 1-phenylethanol, with ruthenium complex 5 demonstrating especially high reactivity.

  8. RNA-mediated gene activation

    PubMed Central

    Jiao, Alan L; Slack, Frank J

    2014-01-01

    The regulation of gene expression by non-coding RNAs (ncRNAs) has become a new paradigm in biology. RNA-mediated gene silencing pathways have been studied extensively, revealing diverse epigenetic and posttranscriptional mechanisms. In contrast, the roles of ncRNAs in activating gene expression remains poorly understood. In this review, we summarize the current knowledge of gene activation by small RNAs, long non-coding RNAs, and enhancer-derived RNAs, with an emphasis on epigenetic mechanisms. PMID:24185374

  9. Three closely related 1-(naphthalen-2-yl)prop-2-en-1-ones: pseudosymmetry, disorder and supramoleular assembly mediated by C-H...π and C-Br...π interactions.

    PubMed

    Girisha, Marisiddaiah; Sagar, Belakavadi K; Yathirajan, Hemmige S; Rathore, Ravindranath S; Glidewell, Christopher

    2017-02-01

    It has been observed that when electron-rich naphthyl rings are present in chalcones they can participate in π-π stacking interactions, and this can play an important role in orientating inhibitors within the active sites of enzymes, while chalcones containing heterocyclic substituents additionally exhibit fungistatic and fungicidal properties. With these considerations in mind, three new chalcones containing 2-naphthyl substituents were prepared. 3-(4-Fluorophenyl)-1-(naphthalen-2-yl)prop-2-en-1-one, C19H13FO, (I), crystallizes with Z' = 2 in the space group P-1 and the four molecules in the unit cell adopt an arrangement which resembles that in the space group P21/a. Although 3-(4-bromophenyl)-1-(naphthalen-2-yl)prop-2-en-1-one, C19H13BrO, (II), with Z' = 1, is not isostructural with (I), the molecules of (I) and (II) adopt very similar conformations. In 1-(naphthalen-2-yl)-3-(thiophen-2-yl)prop-2-en-1-one, C17H12OS, (III), the thiophene unit is disordered over two sets of atomic sites, with occupancies of 0.780 (3) and 0.220 (3), which are related by a near 180° rotation of the thiophene unit about its exocyclic C-C bond. The molecules of compound (I) are linked by three independent C-H...π(arene) hydrogen bonds to form centrosymmetric octamolecular aggregates, whereas the molecules of compound (II) are linked into molecular ladders by a combination of C-H...π(arene) and C-Br...π(arene) interactions, and those of compound (III) are linked into centrosymmetric dimers by C-H...π(thiophene) interactions.

  10. Aerobic synthesis of substituted quinoline from aldehyde and aniline: copper-catalyzed intermolecular C-H active and C-C formative cyclization.

    PubMed

    Yan, Rulong; Liu, Xingxing; Pan, Congming; Zhou, Xiaoqiang; Li, Xiaoni; Kang, Xing; Huang, Guosheng

    2013-09-20

    An efficient method for the direct synthesis of substituted quinolines from anilines and aldehydes through C-H functionalization, C-C/C-N bond formation, and C-C bond cleavage has been developed. The method is simple and practical and employs air as an oxidant.

  11. DFT Mechanistic Study of Rh(III)-Catalyzed [3 + 2]/[5 + 2] Annulation of 4-Aryl-1,2,3-triazoles and Alkynes Unveils the Dual C-H Activation Strategy.

    PubMed

    Zhang, Zhongchao; Yang, Shengwen; Li, Juan; Liao, Xiaojian

    2016-10-21

    Li and co-workers recently developed a dual C-H bond activation strategy, using a Rh(III) catalyst, for [3 + 2]/[5 + 2] annulation of primary 4-aryl-1,2,3-triazoles and alkynes. The Rh(III)-catalyzed dual annulation of 4-aryl-1,2,3-triazoles and alkynes is challenging because only single annulation is achieved using Rh(II) and Ni(0) catalysts. Intrigued by the novel strategy, we performed a density functional theory study to unravel this challenging dual C-H bond activation. A Friedel-Crafts type mechanism proved be more favorable than a concerted metalation-deprotonation (CMD) mechanism for the first C-H bond activation. The second C-H bond activation proceeded via a CMD mechanism. More importantly, the calculation explained why only AgSbF6, among several candidates, performed perfectly, whereas others failed, and why the dual annulation of 4-aryl-1,2,3-triazoles with alkynes was achieved with a Rh(III) catalyst but not with Rh(II) and Ni(0) catalysts. Due to the active catalyst being [Cp*Rh(OAc)](+), AgSbF6, in which SbF6(-) is a stable anion, among several candidates performed perfectly. The success of the Rh(III)-catalyzed dual C-H bond activation has two origins: (i) the active catalyst [Cp*Rh(OAc)](+) is more stable than Cp*Rh(OAc)2 when the Ag salt is AgSbF6, and this facilitates the first alkyne insertion; and (ii) a rhodium-carbene is easily formed.

  12. C-H bond activation of the methyl group of the supporting ligand in an osmium(III) complex upon reaction with H2O2: formation of an organometallic osmium(IV) complex.

    PubMed

    Sugimoto, Hideki; Ashikari, Kenji; Itoh, Shinobu

    2013-01-18

    Oxidation of the hydroxoosmium(III) complex resulted in C-H bond activation of the methyl group of the supporting ligand (N,N'-dimethyl-2,11-diaza[3.3](2,6)pyridinophane). The product was an osmium(IV) complex exhibiting a seven-coordinate structure with an additional Os-CH(2) bond.

  13. Radical-Induced Metal and Solvent-Free Cross-Coupling Using TBAI-TBHP: Oxidative Amidation of Aldehydes and Alcohols with N-Chloramines via C-H Activation.

    PubMed

    Achar, Tapas Kumar; Mal, Prasenjit

    2015-01-02

    A solvent-free cross-coupling method for oxidative amidation of aldehydes and alcohols via a metal-free radial pathway has been demonstrated. The proposed methodology uses the TBAI-TBHP combination which efficiently induces metal-free C-H activation of aldehydes under neat conditions at 50 °C or ball-milling conditions at room temperature.

  14. Cobalt-catalyzed C-H borylation.

    PubMed

    Obligacion, Jennifer V; Semproni, Scott P; Chirik, Paul J

    2014-03-19

    A family of pincer-ligated cobalt complexes has been synthesized and are active for the catalytic C-H borylation of heterocycles and arenes. The cobalt catalysts operate with high activity and under mild conditions and do not require excess borane reagents. Up to 5000 turnovers for methyl furan-2-carboxylate have been observed at ambient temperature with 0.02 mol % catalyst loadings. A catalytic cycle that relies on a cobalt(I)-(III) redox couple is proposed.

  15. A Prussian blue/carbon dot nanocomposite as an efficient visible light active photocatalyst for C-H activation of amines.

    PubMed

    Maaoui, Houcem; Kumar, Pawan; Kumar, Anurag; Pan, Guo-Hui; Chtourou, Radouane; Szunerits, Sabine; Boukherroub, Rabah; Jain, Suman L

    2016-10-05

    A Prussian blue/carbon dot (PB/CD) nanocomposite was synthesised and used as a visible-light active photocatalyst for the oxidative cyanation of tertiary amines to α-aminonitriles by using NaCN/acetic acid as a cyanide source and H2O2 as an oxidant. The developed photocatalyst afforded high yields of products after 8 h of visible light irradiation at room temperature. The catalyst was recycled and reused several times without any significant loss in its activity.

  16. P450-catalyzed intramolecular sp(3) C-H amination with arylsulfonyl azide substrates.

    PubMed

    Singh, Ritesh; Bordeaux, Melanie; Fasan, Rudi

    2014-01-06

    The direct amination of aliphatic C-H bonds represents a most valuable transformation in organic chemistry. While a number of transition metal-based catalysts have been developed and investigated for this purpose, the possibility to execute this transformation with biological catalysts has remained largely unexplored. Here, we report that cytochrome P450 enzymes can serve as efficient catalysts for mediating intramolecular benzylic C-H amination reactions in a variety of arylsulfonyl azide compouds. Under optimized conditions, the P450 catalysts were found to support up to 390 total turnovers leading to the formation of the desired sultam products with excellent regioselectivity. In addition, the chiral environment provided by the enzyme active site allowed for the reaction to proceed in a stereo- and enantioselective manner. The C-H amination activity, substrate profile, and enantio/stereoselectivity of these catalysts could be modulated by utilizing enzyme variants with engineered active sites.

  17. Unexpected intermediates and products in the C-F bond activation of tetrafluorobenzenes with a bis(triethylphosphine)nickel synthon: direct evidence of a rapid and reversible C-H bond activation by Ni(0).

    PubMed

    Johnson, Samuel A; Huff, Carla W; Mustafa, Ferheen; Saliba, Mark

    2008-12-24

    The reaction of (PEt(3))(2)Ni(eta(2)-C(14)H(10)), a source of the reactive Ni(PEt(3))(2) moiety, with 1,2,4,5-F(4)C(6)H(2) yields a mixture of three C-F bond activation products that include the unexpected products (PEt(3))(2)NiF-2,3,5,6-F(4)C(6)H and (PEt(3))(2)NiF-2,3,5-F(3)C(6)H(2). Monitoring the reaction mixture via (19)F and (1)H NMR also reveals the presence of the C-H bond activation product, (PEt(3))(2)NiH-2,3,5,6-F(4)C(6)H which is produced in a rapid equilibrium reaction. This observation provides insight into the steps necessary to modify nickel complexes for selective C-F bond activation in a variety of polyfluorinated aromatic substrates, but also expands the potential of simple nickel compounds for C-H bond activation and functionalization reactions.

  18. N-Doped Cationic PAHs by Rh(III)-Catalyzed Double C-H Activation and Annulation of 2-Arylbenzimidazoles with Alkynes.

    PubMed

    Villar, José M; Suárez, Jaime; Varela, Jesús A; Saá, Carlos

    2017-04-07

    A novel class of N-doped cationic PAHs (polycyclic aromatic hydrocarbons) bearing the benzo[c,d]fluoranthene scaffold has been synthesized by the Rh(III)-catalyzed double-oxidative annulation of 2-arylbenzimidazoles with alkynes. The overall process involves a double C-N bond formation through a double C-H/N-H functionalization.The solid-state structures and electronic properties of the new N-doped PAHs were analyzed. These cationic azapolycycles were readily reduced in the presence of LiAlH4 or by the addition of PhLi to give interesting phenyl and diphenylmethanediamine derivatives.

  19. C-H activation on a diphosphine and hydrido-bridged diiridium complex: generation and detection of an active IrII-IrII species [(Cp*Ir)2(micro-dmpm)(micro-H)]+.

    PubMed

    Takahashi, Yoshinori; Nonogawa, Mitsuru; Fujita, Ken-ichi; Yamaguchi, Ryohei

    2008-07-21

    Reaction of [Cp*Ir(micro-H)](2) (5) (Cp* = eta(5)-C(5)Me(5)) with bis(dimethylphosphino)methane (dmpm) gives a new neutral diiridium complex [(Cp*Ir)(2)(micro-dmpm)(micro-H)(2)] (3). Treatment of 3 with methyl triflate at -30 degrees C results in the formation of [(Cp*Ir)(H)(micro-dmpm)(micro-H)(Me)(IrCp*)][OTf] (6). Warming a solution of above 0 degrees C brings about predominant generation of 32e(-) Ir(II)-Ir(II) species [(Cp*Ir)(micro-dmpm)(micro-H)(IrCp*)][OTf] (7). Further heating of the solution of 7 up to 30 degrees C for 14 h leads to quantitative formation of a new complex [(Cp*Ir)(H)(micro-Me(2)PCH(2)PMeCH(2))(micro-H)(IrCp*)][OTf] (8), which is formed by intramolecular oxidative addition of the methyl C-H bond of the dmpm ligand. Intermolecular C-H bond activation reactions with 7 are also examined. Reactions of 7 with aromatic molecules (benzene, toluene, furan, and pyridine) at room temperature result in the smooth sp(2) C-H activation to give [(Cp*Ir)(H)(micro-dmpm)(micro-H)(Ar)(IrCp*)][OTf] (Ar = Ph (9); Ar = m-Tol (10a) or p-Tol (10b); Ar = 2-Fur (11)) and [(Cp*Ir)(H)(micro-dmpm)(micro-C(5)H(4)N)(H)(IrCp*)][OTf] (12), respectively. Complex also reacts with cyclopentene at 0 degrees C to give [(Cp*Ir)(H)(micro-dmpm)(micro-H)(1-cyclopentenyl)(IrCp*)][OTf] (13). Structures of 3, 8 and 12 have been confirmed by X-ray analysis.

  20. A Tale of Copper Coordination Frameworks: Controlled Single-Crystal-to-Single-Crystal Transformations and Their Catalytic C-H Bond Activation Properties.

    PubMed

    Chen, Yifa; Feng, Xiao; Huang, Xianqiang; Lin, Zhengguo; Pei, Xiaokun; Li, Siqing; Li, Jikun; Wang, Shan; Li, Rui; Wang, Bo

    2015-09-28

    Metal-organic frameworks (MOFs), as a class of microporous materials with well-defined channels and rich functionalities, hold great promise for various applications. Yet the formation and crystallization processes of various MOFs with distinct topology, connectivity, and properties remain largely unclear, and the control of such processes is rather challenging. Starting from a 0D Cu coordination polyhedron, MOP-1, we successfully unfolded it to give a new 1D-MOF by a single-crystal-to-single-crystal (SCSC) transformation process at room temperature as confirmed by SXRD. We also monitored the continuous transformation states by FTIR and PXRD. Cu MOFs with 2D and 3D networks were also obtained from this 1D-MOF by SCSC transformations. Furthermore, Cu MOFs with 0D, 1D, and 3D networks, MOP-1, 1D-MOF, and HKUST-1, show unique performances in the kinetics of the C-H bond catalytic oxidation reaction.

  1. Correlating Reactivity and Selectivity to Cyclopentadienyl Ligand Properties in Rh(III)-Catalyzed C-H Activation Reactions: An Experimental and Computational Study.

    PubMed

    Piou, Tiffany; Romanov-Michailidis, Fedor; Romanova-Michaelides, Maria; Jackson, Kelvin E; Semakul, Natthawat; Taggart, Trevor D; Newell, Brian S; Rithner, Christopher D; Paton, Robert S; Rovis, Tomislav

    2017-01-25

    Cp(X)Rh(III)-catalyzed C-H functionalization reactions are a proven method for the efficient assembly of small molecules. However, rationalization of the effects of cyclopentadienyl (Cp(X)) ligand structure on reaction rate and selectivity has been viewed as a black box, and a truly systematic study is lacking. Consequently, predicting the outcomes of these reactions is challenging because subtle variations in ligand structure can cause notable changes in reaction behavior. A predictive tool is, nonetheless, of considerable value to the community as it would greatly accelerate reaction development. Designing a data set in which the steric and electronic properties of the Cp(X)Rh(III) catalysts were systematically varied allowed us to apply multivariate linear regression algorithms to establish correlations between these catalyst-based descriptors and the regio-, diastereoselectivity, and rate of model reactions. This, in turn, led to the development of quantitative predictive models that describe catalyst performance. Our newly described cone angles and Sterimol parameters for Cp(X) ligands served as highly correlative steric descriptors in the regression models. Through rational design of training and validation sets, key diastereoselectivity outliers were identified. Computations reveal the origins of the outstanding stereoinduction displayed by these outliers. The results are consistent with partial η(5)-η(3) ligand slippage that occurs in the transition state of the selectivity-determining step. In addition to the instructive value of our study, we believe that the insights gained are transposable to other group 9 transition metals and pave the way toward rational design of C-H functionalization catalysts.

  2. The amide C-N bond of isatins as the directing group and the internal oxidant in Ru-catalyzed C-H activation and annulation reactions: access to 8-amido isocoumarins.

    PubMed

    Kaishap, Partha Pratim; Sarma, Bipul; Gogoi, Sanjib

    2016-07-28

    The N-O, N-N and O-O bonds are the frequently used internally oxidative directing groups used in various redox-neutral coupling reactions. The sole use of the C-N bond as the oxidizing directing group was reported recently by Li X. and co-workers for the Rh(iii)-catalyzed C-H activation of phenacyl ammonium salts. Herein, we report the use of the amide C-N bond of isatins as the oxidizing directing group for the Ru(ii)-catalyzed redox-neutral C-H activation and annulation reactions with alkynes which afford 8-amido isocoumarins. The reaction also features excellent regioselectivity with alkyl aryl substituted alkynes.

  3. Rh(III)-Catalyzed Cascade Annulation/C-H Activation of o-Ethynylanilines with Diazo Compounds: One-Pot Synthesis of Benzo[a]carbazoles via 1,4-Rhodium Migration.

    PubMed

    Guo, Songjin; Yuan, Kai; Gu, Meng; Lin, Aijun; Yao, Hequan

    2016-10-05

    A Rh(III)-catalyzed cascade annulation/C-H activation of o-ethynylanilines with diazo compounds has been developed. This concise method allows for the rapid formation of a number of benzo[a]carbazoles in high yields, exhibiting good functional group tolerance and scalability. The key to the success of this approach involves one C-N bond and two C-C bond formation, and an aryl-to-aryl 1,4-rhodium migration.

  4. Rare-earth metal complexes having an unusual indolyl-1,2-dianion through C-H activation with a novel η1:(μ2-η1:η1) bonding with metals.

    PubMed

    Zhu, Xiancui; Zhou, Shuangliu; Wang, Shaowu; Wei, Yun; Zhang, Lijun; Wang, Fenhua; Wang, Shaoyin; Feng, Zhijun

    2012-12-21

    Studies on the reactions of 3-(tert-butyliminomethine)indole or 3-(tert-butylaminomethylene)indole with rare-earth metal amides [(Me(3)Si)(2)N](3)RE(III)(μ-Cl)Li(THF)(3) (RE = Y, Yb) led to the discovery of different reactivity patterns with isolation of novel rare-earth metal complexes having a unique indolyl-1,2-dianion in a novel η(1):(μ(2)-η(1):η(1)) bonding mode through C-H activation.

  5. 1,2-Diphosphonium dication: a strong P-based Lewis acid in frustrated lewis pair (FLP)-activations of B-H, Si-H, C-H, and H-H bonds.

    PubMed

    Holthausen, Michael H; Bayne, Julia M; Mallov, Ian; Dobrovetsky, Roman; Stephan, Douglas W

    2015-06-17

    A highly Lewis acidic diphosphonium dication [(C10H6)(Ph2P)2](2+) (1), in combination with a Lewis basic phosphine, acts as a purely phosphorus-based frustrated Lewis pair (FLP) and abstracts hydride from [HB(C6F5)3](-) and Et3SiH demonstrating the remarkable hydridophilicity of 1. The P-based FLP is also shown to activate H2 and C-H bonds.

  6. C-H fluorination: U can fluorinate unactivated bonds

    NASA Astrophysics Data System (ADS)

    Neumann, Constanze N.; Ritter, Tobias

    2016-09-01

    Introducing C-F bonds into organic molecules is a challenging task, particularly through C-H activation methods. Now, a uranium-based photocatalyst turns traditional selectivity rules on their heads and fluorinates unfunctionalized alkane Csp3-H bonds, even in the presence of C-H bonds that are typically more reactive.

  7. Symbolic Mediation in Cognitive Activity

    ERIC Educational Resources Information Center

    Veraksa, Alexander N.

    2011-01-01

    This article used two studies to investigate sign and symbol mediation in children aged 8-11 years. In role play, children exist at one at the same time in objective reality and their representation of reality. We cannot observe their mental representation directly, but the issue of whether signs or symbols mediate early role play is an important…

  8. Metal-Catalyzed Decarboxylative C-H Functionalization.

    PubMed

    Wei, Ye; Hu, Peng; Zhang, Min; Su, Weiping

    2017-03-07

    C-H bond activation and decarboxylation are two significant processes in organic synthesis. The combination of these processes provides a novel synthetic strategy, that is, decarboxylative C-H bond functionalization. Considerable attention has been focused on such an active research field. This review offers an overview of the utility of decarboxylative C-H bond functionalization in the synthesis of various organic compounds, such as styrenes, chalcones, biaryls, and heterocycles, covering most of the recent advances of the decarboxylative functionalization of Csp-H, Csp(2)-H, and Csp(3)-H bonds, as well as their scopes, limitations, practical applications, and synthetic potentials.

  9. Iron-Catalyzed C-H Alkylation of Heterocyclic C-H Bonds.

    PubMed

    Babu, Kaki Raveendra; Zhu, Nengbo; Bao, Hongli

    2017-01-06

    An efficient, iron-catalyzed C-H alkylation of benzothiazoles by using alkyl diacyl peroxides and alkyl tert-butyl peresters which are readily accessible from carboxylic acids to synthesize 2-alkylbenzothiazoles is developed. This reaction is environmentally benign and compatible with a broad range of functional groups. Various primary, secondary, and tertiary alkyl groups can be efficiently incorporated into diverse benzothiazoles. The effectiveness of this method is illustrated by late-stage functionalization of biologically active heterocycles.

  10. Moving to Sustainable Metals. Multifunctional Ligands in Catalytic, Outer Sphere C-H, N-H and O-H Activation

    SciTech Connect

    Crabtree, Robert

    2015-03-03

    Much of our work during this grant period has emphasized green chemistry and sustainability. For example, we were able to convert glycerine, a waste byproduct of biodiesel production, into lactic acid, a compound with numerous applications, notably in the food and cosmetics industry, as well as being a source material for a biodegradable plastic. This work required a catalyst, that ceases to work after a certain lapse of time. We were able to identify the way in which this deactivation occurs by identifying some of the metal catalyst deactivation products. These proved to be multimetallic clusters containing up to six metals and up to 14 hydrogen atoms. Both the catalytic reaction itself and the deactivation structures are novel and unexpected. We have previously proposed that nitrogen heterocycles could be good energy carriers in a low CO2 future world. In another part of our study, we found catalysts for introduction of hydrogen, an energy carrier that is hard to store, into nitrogen heterocycles. The mechanism of this process proved to be unusual in that the catalyst transfers the H2 to the heterocycle in the form of H+ and H-, first transferring the H+ and only then the H-. In a third area of study, some of our compounds, originally prepared for DOE catalysis purposes, also proved useful in hydrocarbon oxidation and in water oxidation. The latter is important in solar-to-fuel work, because, by analogy with natural photosynthesis, the goal of the Yale Solar Group of four PIs is to convert sunlight to hydrogen and oxygen, which requires water splitting catalysts. The catalysts that proved useful mediate the latter reaction: water oxidation to oxygen. In a more technical study, we developed methods for distinguishing the case where catalysis is mediated by a soluble catalyst from cases where catalysis arises from a deposit of finely divided solid. One particular application involved electrocatalysis

  11. Bipyridine- and phenanthroline-based metal-organic frameworks for highly efficient and tandem catalytic organic transformations via directed C-H activation

    SciTech Connect

    Manna, Kuntal; Zhang, Teng; Greene, Francis X.; Lin, Wenbin

    2015-02-16

    We report here the synthesis of a series of robust and porous bipyridyl- and phenanthryl-based metal–organic frameworks (MOFs) of UiO topology (BPV-MOF, mBPV-MOF, and mPT-MOF) and their postsynthetic metalation to afford highly active single-site solid catalysts. While BPV-MOF was constructed from only bipyridyl-functionalized dicarboxylate linker, both mBPV- and mPT-MOF were built with a mixture of bipyridyl- or phenanthryl-functionalized and unfunctionalized dicarboxylate linkers. The postsynthetic metalation of these MOFs with [Ir(COD)(OMe)]2 provided Ir-functionalized MOFs (BPV-MOF-Ir, mBPV-MOF-Ir, and mPT-MOF-Ir), which are highly active catalysts for tandem hydrosilylation of aryl ketones and aldehydes followed by dehydrogenative ortho-silylation of benzylicsilyl ethers as well as C–H borylation of arenes using B₂pin₂. Both mBPV-MOF-Ir and mPT-MOF-Ir catalysts displayed superior activities compared to BPV-MOF-Ir due to the presence of larger open channels in the mixed-linker MOFs. Impressively, mBPV-MOF-Ir exhibited high TONs of up to 17000 for C–H borylation reactions and was recycled more than 15 times. The mPT-MOF-Ir system is also active in catalyzing tandem dehydrosilylation/dehydrogenative cyclization of N-methylbenzyl amines to azasilolanes in the absence of a hydrogen acceptor. Importantly, MOF-Ir catalysts are significantly more active (up to 95 times) and stable than their homogeneous counterparts for all three reactions, strongly supporting the beneficial effects of active site isolation within MOFs. This work illustrates the ability to increase MOF open channel sizes by using the mixed linker approach and shows the enormous potential of developing highly active and robust single-site solid catalysts based on MOFs containing nitrogen-donor ligands for important organic transformations.

  12. Review of biological and pharmacological activities of the endemic Taiwanese bitter medicinal mushroom, Antrodia camphorata (M. Zang et C. H. Su) Sh. H. Wu et al. (higher Basidiomycetes).

    PubMed

    Yue, Patrick Ying-Kit; Wong, Yi-Yi; Chan, Tony Yuk-Kit; Law, Carman Ka-Man; Tsoi, Yeuk-Ki; Leung, Kelvin Sze-Yin

    2012-01-01

    Antrodia camphorata is an extremely rare fungus native to the forested regions of Taiwan. It is also a traditional Chinese medicine, and Taiwanese aborigines applied it for treating liver diseases and protecting from food and drug intoxication. Scientific studies have demonstrated that A. camphorata crude extracts and pure compounds possess a variety of beneficial functions, such as anti-hypertensive, anti-hyperlipidemic, anti-inflammatory, anti-oxidant, anti-tumor, and immuno-modulatory activities. Recent studies have shown that many of these biological and pharmacological activities can be attributed to various active constituents, including polysaccharides, terpenoids, steroids, lignans, benzoquinone derivatives, benzenoids, and maleic and succinic acid derivatives. A. camphorata has been considered as a novel phytotherapeutic agent. However, detailed mechanistic studies or even clinical trials on A. camphorata are still rare. With the help of modern analytical techniques, it is not surprising that many novel constituents are being identified or fractionated from A. camphorata mycelium and fruiting bodies. This review summarizes the latest published results from A. camphorata research, focusing on the biological and pharmacological activities of the crude extract and known constituents of A. camphorata.

  13. Dry Reforming of Methane on a Highly-Active Ni-CeO2 Catalyst: Effects of Metal-Support Interactions on C-H Bond Breaking.

    PubMed

    Liu, Zongyuan; Grinter, David C; Lustemberg, Pablo G; Nguyen-Phan, Thuy-Duong; Zhou, Yinghui; Luo, Si; Waluyo, Iradwikanari; Crumlin, Ethan J; Stacchiola, Dario J; Zhou, Jing; Carrasco, Javier; Busnengo, H Fabio; Ganduglia-Pirovano, M Verónica; Senanayake, Sanjaya D; Rodriguez, José A

    2016-06-20

    Ni-CeO2 is a highly efficient, stable and non-expensive catalyst for methane dry reforming at relative low temperatures (700 K). The active phase of the catalyst consists of small nanoparticles of nickel dispersed on partially reduced ceria. Experiments of ambient pressure XPS indicate that methane dissociates on Ni/CeO2 at temperatures as low as 300 K, generating CHx and COx species on the surface of the catalyst. Strong metal-support interactions activate Ni for the dissociation of methane. The results of density-functional calculations show a drop in the effective barrier for methane activation from 0.9 eV on Ni(111) to only 0.15 eV on Ni/CeO2-x (111). At 700 K, under methane dry reforming conditions, no signals for adsorbed CHx or C species are detected in the C 1s XPS region. The reforming of methane proceeds in a clean and efficient way.

  14. C-H activation by a mononuclear manganese(III) hydroxide complex: synthesis and characterization of a manganese-lipoxygenase mimic?

    PubMed

    Goldsmith, Christian R; Cole, Adam P; Stack, T Daniel P

    2005-07-13

    Lipoxygenases are mononuclear non-heme metalloenzymes that regio- and stereospecifically convert 1,4-pentadiene subunit-containing fatty acids into alkyl peroxides. The rate-determining step is generally accepted to be hydrogen atom abstraction from the pentadiene subunit of the substrate by an active metal(III)-hydroxide species to give a metal(II)-water species and an organic radical. All known plant and animal lipoxygenases contain iron as the active metal; recently, however, manganese was found to be the active metal in a fungal lipoxygenase. Reported here are the synthesis and characterization of a mononuclear Mn(III) complex, [Mn(III)(PY5)(OH)](CF(3)SO(3))(2) (PY5 = 2,6-bis(bis(2-pyridyl)methoxymethane)pyridine), that reacts with hydrocarbon substrates in a manner most consistent with hydrogen atom abstraction and provides chemical precedence for the proposed reaction mechanism. The neutral penta-pyridyl ligation of PY5 endows a strong Lewis acidic character to the metal center allowing the Mn(III) compound to perform this oxidation chemistry. Thermodynamic analysis of [Mn(III)(PY5)(OH)](2+) and the reduced product, [Mn(II)(PY5)(H(2)O)](2+), estimates the strength of the O-H bond in the metal-bound water in the Mn(II) complex to be 82 (+/-2) kcal mol(-)(1), slightly less than that of the O-H bond in the related reduced iron complex, [Fe(II)(PY5)(MeOH)](2+). [Mn(III)(PY5)(OH)](2+) reacts with hydrocarbon substrates at rates comparable to those of the analogous [Fe(III)(PY5)(OMe)](2+) at 323 K. The crystal structure of [Mn(III)(PY5)(OH)](2+) displays Jahn-Teller distortions that are absent in [Mn(II)(PY5)(H(2)O)](2+), notably a compression along the Mn(III)-OH axis. Consequently, a large internal structural reorganization is anticipated for hydrogen atom transfer, which may be correlated to the lessened dependence of the rate of substrate oxidation on the substrate bond dissociation energy as compared to other metal complexes. The results presented here suggest

  15. Gold Nanoparticles Deposited on Surface Modified Carbon Xerogels as Reusable Catalysts for Cyclohexane C-H Activation in the Presence of CO and Water.

    PubMed

    Ribeiro, Ana Paula da Costa; Martins, Luísa Margarida Dias Ribeiro de Sousa; Carabineiro, Sónia Alexandra Correia; Figueiredo, José Luís; Pombeiro, Armando José Latourrette

    2017-04-09

    The use of gold as a promotor of alkane hydrocarboxylation is reported for the first time. Cyclohexane hydrocarboxylation to cyclohexanecarboxylic acid (up to 55% yield) with CO, water, and peroxodisulfate in a water/acetonitrile medium at circa 50 °C has been achieved in the presence of gold nanoparticles deposited by a colloidal method on a carbon xerogel in its original form (CX), after oxidation with HNO₃ (-ox), or after oxidation with HNO₃ and subsequent treatment with NaOH (-ox-Na). Au/CX-ox-Na behaves as re-usable catalyst maintaining its initial activity and selectivity for at least seven consecutive cycles. Green metric values of atom economy or carbon efficiency also attest to the improvement brought by this novel catalytic system to the hydrocarboxylation of cyclohexane.

  16. Generation and reactivity of putative support systems, Ce-Al neutral binary oxide nanoclusters: CO oxidation and C-H bond activation

    NASA Astrophysics Data System (ADS)

    Wang, Zhe-Chen; Yin, Shi; Bernstein, Elliot R.

    2013-11-01

    Both ceria (CeO2) and alumina (Al2O3) are very important catalyst support materials. Neutral binary oxide nanoclusters (NBONCs), CexAlyOz, are generated and detected in the gas phase and their reactivity with carbon monoxide (CO) and butane (C4H10) is studied. The very active species CeAlO4• can react with CO and butane via O atom transfer (OAT) and H atom transfer (HAT), respectively. Other CexAlyOz NBONCs do not show reactivities toward CO and C4H10. The structures, as well as the reactivities, of CexAlyOz NBONCs are studied theoretically employing density functional theory (DFT) calculations. The ground state CeAlO4• NBONC possesses a kite-shaped structure with an OtCeObObAlOt configuration (Ot, terminal oxygen; Ob, bridging oxygen). An unpaired electron is localized on the Ot atom of the AlOt moiety rather than the CeOt moiety: this Ot centered radical moiety plays a very important role for the reactivity of the CeAlO4• NBONC. The reactivities of Ce2O4, CeAlO4•, and Al2O4 toward CO are compared, emphasizing the importance of a spin-localized terminal oxygen for these reactions. Intramolecular charge distributions do not appear to play a role in the reactivities of these neutral clusters, but could be important for charged isoelectronic BONCs. DFT studies show that the reaction of CeAlO4• with C4H10 to form the CeAlO4H•C4H9• encounter complex is barrierless. While HAT processes have been previously characterized for cationic and anionic oxide clusters, the reported study is the first observation of a HAT process supported by a ground state neutral oxide cluster. Mechanisms for catalytic oxidation of CO over surfaces of AlxOy/MmOn or MmOn/AlxOy materials are proposed consistent with the presented experimental and theoretical results.

  17. Ethane C-H bond activation on the Fe(iv)-oxo species in a Zn-based cluster of metal-organic frameworks: a density functional theory study.

    PubMed

    Impeng, Sarawoot; Siwaipram, Siwarut; Bureekaew, Sareeya; Probst, Michael

    2017-02-01

    We first investigate the feasibility of designing a Fe-oxo complex for the activation of alkane C-H bonds by (a) incorporating an Fe ion into a Zn-based cluster derived from a metal-organic framework (MOF) and (b) creating the Fe-oxo complex via decomposition of N2O over a Fe(2+)-substituted Zn-based cluster (Fe-Zn3O(pyrazole)6). From the energy profile, it turns out that both steps should be feasible and that the resulting Fe-oxo complex is stable. In the main step, we then investigate the reactivity of this Fe-oxo cluster for the C-H bond cleavage of ethane by calculating the reaction energy profile and analyzing the electronic structure along the relevant steps. Two mechanisms, namely the σ and π pathways on the triplet and quintet potential energy surfaces, were unraveled for this study of catalytic activity. It is shown that the σ pathway on the quintet surface is kinetically and thermodynamically favorable with an energy barrier of 22.5 kcal mol(-1). The π pathway on the quintet and triplet surfaces has activation energies of 26.9 kcal mol(-1) and 24.9 kcal mol(-1), respectively. An alternative unusual pathway called the δ mechanism on the triplet surface is also observed with an energy barrier of 12.6 kcal mol(-1). It is, however, thermodynamically at a disadvantage compared to the σ pathway on the quintet surface. Favorable d-d interaction on the Fe center and less steric hindrance from the equatorial ligands at the transition state are the key factors that cause the σ pathway on the quintet surface to have the lowest activation energy. All our calculations are of the cluster type and have been performed at the B3LYP-D3/def2-TZVP level of theory.

  18. Reactivity of Tp(Me2) -supported yttrium alkyl complexes toward aromatic N-heterocycles: ring-opening or C-C bond formation directed by C-H activation.

    PubMed

    Yi, Weiyin; Zhang, Jie; Huang, Shujian; Weng, Linhong; Zhou, Xigeng

    2014-01-13

    Unusual chemical transformations such as three-component combination and ring-opening of N-heterocycles or formation of a carbon-carbon double bond through multiple C-H activation were observed in the reactions of Tp(Me2) -supported yttrium alkyl complexes with aromatic N-heterocycles. The scorpionate-anchored yttrium dialkyl complex [Tp(Me2) Y(CH2 Ph)2 (THF)] reacted with 1-methylimidazole in 1:2 molar ratio to give a rare hexanuclear 24-membered rare-earth metallomacrocyclic compound [Tp(Me2) Y(μ-N,C-Im)(η(2) -N,C-Im)]6 (1; Im=1-methylimidazolyl) through two kinds of C-H activations at the C2- and C5-positions of the imidazole ring. However, [Tp(Me2) Y(CH2 Ph)2 (THF)] reacted with two equivalents of 1-methylbenzimidazole to afford a C-C coupling/ring-opening/C-C coupling product [Tp(Me2) Y{η(3) -(N,N,N)-N(CH3 )C6 H4 NHCHC(Ph)CN(CH3 )C6 H4 NH}] (2). Further investigations indicated that [Tp(Me2) Y(CH2 Ph)2 (THF)] reacted with benzothiazole in 1:1 or 1:2 molar ratio to produce a C-C coupling/ring-opening product {(Tp(Me2) )Y[μ-η(2) :η(1) -SC6 H4 N(CHCHPh)](THF)}2 (3). Moreover, the mixed Tp(Me2) /Cp yttrium monoalkyl complex [(Tp(Me2) )CpYCH2 Ph(THF)] reacted with two equivalents of 1-methylimidazole in THF at room temperature to afford a trinuclear yttrium complex [Tp(Me2) CpY(μ-N,C-Im)]3 (5), whereas when the above reaction was carried out at 55 °C for two days, two structurally characterized metal complexes [Tp(Me2) Y(Im-Tp(Me2) )] (7; Im-Tp(Me2) =1-methyl-imidazolyl-Tp(Me2) ) and [Cp3 Y(HIm)] (8; HIm=1-methylimidazole) were obtained in 26 and 17 % isolated yields, respectively, accompanied by some unidentified materials. The formation of 7 reveals an uncommon example of construction of a CC bond through multiple C-H activations.

  19. Dehydrofluorination of Hydrofluorocarbons by Titanium Alkylidynes via Sequential C-H/C-F Bond Activation Reactions. A Synthetic, Structural, and Mechanistic Study of 1,2-CH Bond Addition and [beta]-Fluoride Elimination

    SciTech Connect

    Fout, A.R.; Scott, J.; Miller, D.L.; Bailey, B.C.; Pink, M.; Mindiola, D.J.

    2009-01-07

    The neopentylidene-neopentyl complex (PNP)Ti=CH{sup t}Bu(CH{sub 2}{sup t}Bu) (1); (PNP{sup -} = N[2-P(CHMe{sub 2}){sub 2}-4-methylphenyl]{sub 2}) extrudes neopentane in neat fluorobenzene under mild conditions (25 C) to generate the transient titanium alkylidyne (PNP)Ti-C{sup t}Bu (A), which subsequently undergoes regioselective 1,2-CH bond addition of a fluorobenzene across the Ti-C linkage to generate (PNP)Ti=CH{sup t}Bu(o-FC{sub 6}H{sub 4}) (2). Kinetic and mechanistic studies suggest that the C-H activation process is pseudo-first-order in titanium, with the {alpha}-hydrogen abstraction being the rate-determining step and the post-rate-determining step being the C-H bond activation of fluorobenzene. At 100 C complex 2 does not equilibrate back to A and the preference for C-H activation in benzene versus fluorobenzene is 2:3, respectively. Compound 1 also reacts readily, and in most cases cleanly, with a series of hydrofluoroarenes (HAr{sub F}), to form a family of alkylidene-arylfluoride derivatives of the type (PNP)Ti=CH{sup t}Bu(Ar{sub F}). Thermolysis of the latter compounds generates the titanium alkylidene-fluoride (PNP)Ti=CH{sup t}Bu(F) (14) by a {beta}-fluoride elimination, concurrent with formation of o-benzyne. {beta}-Fluoride elimination to yield 14 occurs from 2 under elevated temperatures with k{sub average} = 4.96(16) x 10{sup -5} s{sup -1} and with activation parameters {Delta}H{sub {-+}} = 29(1) kcal/mol and {Delta}S{sub {-+}} = -3(4) cal/mol {center_dot}K. It was found that {beta}-fluoride elimination is accelerated when electron-rich groups are adjacent to the fluoride group, thus implying that a positive charge buildup at the arylfluoride ring occurs in the activated complex of 2. The alkylidene derivative (PNP)Ti=CHSiMe{sub 3}(CH{sub 2}SiMe{sub 3}) (15) also undergoes {alpha}-hydrogen abstraction to form the putative (PNP)Ti'-CSiMe{sub 3} (B) at higher temperatures (>70 C) and dehydrofluorinates the same series of HArF when the reaction

  20. General allylic C-H alkylation with tertiary nucleophiles.

    PubMed

    Howell, Jennifer M; Liu, Wei; Young, Andrew J; White, M Christina

    2014-04-16

    A general method for intermolecular allylic C-H alkylation of terminal olefins with tertiary nucleophiles has been accomplished employing palladium(II)/bis(sulfoxide) catalysis. Allylic C-H alkylation furnishes products in good yields (avg. 64%) with excellent regio- and stereoselectivity (>20:1 linear:branched, >20:1 E:Z). For the first time, the olefin scope encompasses unactivated aliphatic olefins as well as activated aromatic/heteroaromatic olefins and 1,4-dienes. The ease of appending allyl moieties onto complex scaffolds is leveraged to enable this mild and selective allylic C-H alkylation to rapidly diversify phenolic natural products. The tertiary nucleophile scope is broad and includes latent functionality for further elaboration (e.g., aliphatic alcohols, α,β-unsaturated esters). The opportunities to effect synthetic streamlining with such general C-H reactivity are illustrated in an allylic C-H alkylation/Diels-Alder reaction cascade: a reactive diene is generated via intermolecular allylic C-H alkylation and approximated to a dienophile contained within the tertiary nucleophile to furnish a common tricyclic core found in the class I galbulimima alkaloids.

  1. Direct bis-arylation of cyclobutanecarboxamide via double C-H activation: an auxiliary-aided diastereoselective Pd-catalyzed access to trisubstituted cyclobutane scaffolds having three contiguous stereocenters and an all-cis stereochemistry.

    PubMed

    Parella, Ramarao; Gopalakrishnan, Bojan; Babu, Srinivasarao Arulananda

    2013-12-06

    An auxiliary-aided Pd-catalyzed highly diastereoselective double C-H activation and direct bis-arylation of methylene C(sp(3))-H bonds of cyclobutanecarboxamides and the syntheses of several novel trisubstituted cyclobutanecarboxamide scaffolds having an all-cis stereochemistry are reported. Extensive screening of various auxiliaries and reaction conditions was performed to firmly establish the optimized reaction conditions required for effecting the mono- or double C-H arylation of cyclobutanecarboxamides. The auxiliary-attached cyclobutanecarboxamides 15a, 15g, and 15h, prepared from the auxiliaries such as, 8-aminoquinoline, 2-(methylthio)aniline, and N',N'-dimethylethane-1,2-diamine were found to undergo an efficient direct bis-arylation. The Pd-catalyzed arylation reaction of N-(quinolin-8-yl)cyclobutanecarboxamide 15a with one equivalent or more of aryl iodides, afforded the corresponding bis-arylated cyclobutanecarboxamides 16a-y. Nevertheless, the Pd-catalyzed arylation of 15a with just 0.5 equiv of the aryl iodides 13a, 13b, 13e, and 13m, selectively gave the corresponding monoarylated cyclobutanecarboxamides 17a-17d. The Pd-catalyzed arylation of 15g or 15h with one equivalent or more of aryl iodides afforded the bis-arylated cyclobutanecarboxamides 19a-19c and 21a-21m, respectively. However, the Pd-catalyzed arylations of compounds 15g or 15h with just 0.5 equiv of aryl iodides were ineffective. The stereochemistry of compounds obtained in this work was unambiguously assigned from the X-ray structures of representative products.

  2. The selective activation of a C-F bond with an auxiliary strong Lewis acid: a method to change the activation preference of C-F and C-H bonds.

    PubMed

    Wang, Lin; Sun, Hongjian; Li, Xiaoyan; Fuhr, Olaf; Fenske, Dieter

    2016-11-15

    The selective activation of the C-F bonds in substituted (2,6-difluorophenyl)phenylimines (2,6-F2H3C6-(C[double bond, length as m-dash]NH)-n'-R-C6H4 (n' = 2, R = H (1); n' = 2, R = Me (2); n' = 4, R = tBu (3))) by Fe(PMe3)4 with an auxiliary strong Lewis acid (LiBr, LiI, or ZnCl2) was explored. As a result, iron(ii) halides ((H5C6-(C[double bond, length as m-dash]NH)-2-FH3C6)FeX(PMe3)3 (X = Br (8); Cl (9)) and (n-RH4C6-(C[double bond, length as m-dash]NH)-2'-FH3C6)FeX(PMe3)3 (n = 2, R = Me, X = Br (11); n = 4, R = tBu, X = I (12))) were obtained. Under similar reaction conditions, using LiBF4 instead of LiBr or ZnCl2, the reaction of (2,6-difluorophenyl)phenylimine with Fe(PMe3)4 afforded an ionic complex [(2,6-F2H3C6-(C[double bond, length as m-dash]NH)-H4C6)Fe(PMe3)4](BF4) (10) via the activation of a C-H bond. The method of C-F bond activation with an auxiliary strong Lewis acid is appropriate for monofluoroarylmethanimines. Without the Lewis acid, iron(ii) hydrides ((2-RH4C6-(C[double bond, length as m-dash]NH)-2'-FH3C6)FeH(PMe3)3 (R = H (13); Me (14))) were generated from the reactions of Fe(PMe3)4 with the monofluoroarylmethanimines (2-FH4C6-(C[double bond, length as m-dash]NH)-2'-RC6H4 (R = H (4); Me (5))); however, in the presence of ZnCl2 or LiBr, iron(ii) halides ((2-RH4C6-(C[double bond, length as m-dash]NH)-H4C6)FeX(PMe3)3 (R = H, X = Cl (15); R = Me, X = Br (16))) could be obtained through the activation of a C-F bond. Furthermore, a C-F bond activation with good regioselectivity in (pentafluorophenyl)arylmethanimines (F5C6-(C[double bond, length as m-dash]NH)-2,6-Y2C6H3 (Y = F (6); H (7))) could be realized in the presence of ZnCl2 to produce iron(ii) chlorides ((2,6-Y2H3C6-(C[double bond, length as m-dash]NH)-F4C6)FeCl(PMe3)3 (Y = F (17); H (18))). This series of iron(ii) halides could be used to catalyze the hydrosilylation reaction of aldehydes. Due to the stability of iron(ii) halides to high temperature, the reaction mixture was allowed to be

  3. Assessment of DFT methods for computing activation energies of Mo/W-mediated reactions.

    PubMed

    Hu, Lianrui; Chen, Hui

    2015-10-13

    Using high level ab initio coupled cluster calculations as reference, the performances of 15 commonly used density functionals (DFs) on activation energy calculations for typical Mo/W-mediated reactions have been systematically assessed for the first time in this work. The selected representative Mo/W-mediated reactions cover a wide range from enzymatic reactions to organometallic reactions, which include Mo-catalyzed aldehyde oxidation (aldehyde oxidoreductase), Mo-catalyzed dimethyl sulfoxide (DMSO) reduction (DMSO reductase), W-catalyzed acetylene hydration (acetylene hydratase), Mo/W-mediated olefin metathesis, Mo/W-mediated olefin epoxidation, W-mediated alkyne metathesis, and W-mediated C-H bond activation. Covering both Mo- and W-mediated reactions, four DFs of B2GP-PLYP, M06, B2-PLYP, and B3LYP are uniformly recommended with and without DFT empirical dispersion correction. Among these four DFs, B3LYP is notably improved in performance by DFT empirical dispersion correction. In addition to the absolute value of calculation error, if the trend of DFT results is also a consideration, B2GP-PLYP, B2-PLYP, and M06 keep better performance than other functionals tested and constitute our final recommendation of DFs for both Mo- and W-mediated reactions.

  4. Selective activation of C-F and C-H bonds with iron complexes, the relevant mechanism study by DFT calculations and study on the chemical properties of hydrido iron complex.

    PubMed

    Xu, Xiaofeng; Jia, Jiong; Sun, Hongjian; Liu, Yuxia; Xu, Wengang; Shi, Yujie; Zhang, Dongju; Li, Xiaoyan

    2013-03-14

    The reactions of (2,6-difluorophenyl)phenylmethanone (2,6-F(2)C(6)H(3)-C(=O)-C(6)H(5)) (1) and (2,6-difluorophenyl)phenylmethanimine (2,6-F(2)C(6)H(3)-C(=NH)-C(6)H(5)) (3) with Fe(PMe(3))(4) afforded different selective C-F/C-H bond activation products. The reaction of 1 with Fe(PMe(3))(4) gave rise to bis-chelate iron(II) complex [C(6)H(5)-C(=O)-3-FC(6)H(3))Fe(PMe(3))](2) (2) via C-F bond activation. The reaction of 3 with Fe(PMe(3))(4) delivered chelate hydrido iron(II) complex 2,6-F(2)C(6)H(3)-C(=NH)-C(6)H(4))Fe(H)(PMe(3))(3) (4) through C-H bond activation. The DFT calculations show the detailed elementary steps of the mechanism of formation of hydrido complex 4 and indicate 4 is the kinetically preferred product. Complex 4 reacted with HCl, CH(3)Br and CH(3)I delivered the chelate iron halides (2,6-F(2)C(6)H(3)-C(=NH)-C(6)H(4))Fe(PMe(3))(3)X (X = Cl (5); Br (6); I (7)). A ligand (PMe(3)) replacement by CO of 4 was observed giving (2,6-F(2)C(6)H(3)-C(=NH)-C(6)H(4))Fe(H)(CO)(PMe(3))(2) (8). The chelate ligand exchange occurred through the reaction of 4 with salicylaldehydes. The reaction of 4 with Me(3)SiC[triple bond, length as m-dash]CH afforded (2,6-F(2)C(6)H(3)-C([double bond, length as m-dash]N)-C(6)H(5))Fe(C≡C-SiMe(3))(PMe(3))(3) (11). A reaction mechanism from 4 to 11 was discussed with the support of IR monitoring. The molecular structures of complexes 2, 4, 6, 7, 10 and 11 were determined by X-ray diffraction.

  5. Formation and High Reactivity of the anti-Dioxo Form of High-Spin μ-Oxodioxodiiron(IV) as the Active Species That Cleaves Strong C-H Bonds.

    PubMed

    Kodera, Masahito; Ishiga, Shin; Tsuji, Tomokazu; Sakurai, Katsutoshi; Hitomi, Yutaka; Shiota, Yoshihito; Sajith, P K; Yoshizawa, Kazunari; Mieda, Kaoru; Ogura, Takashi

    2016-04-18

    Recently, it was shown that μ-oxo-μ-peroxodiiron(III) is converted to high-spin μ-oxodioxodiiron(IV) through O-O bond scission. Herein, the formation and high reactivity of the anti-dioxo form of high-spin μ-oxodioxodiiron(IV) as the active oxidant are demonstrated on the basis of resonance Raman and electronic-absorption spectral changes, detailed kinetic studies, DFT calculations, activation parameters, kinetic isotope effects (KIE), and catalytic oxidation of alkanes. Decay of μ-oxodioxodiiron(IV) was greatly accelerated on addition of substrate. The reactivity order of substrates is tolueneC-H bond cleavage of ethylbenzene than the most reactive diiron system reported so far. The KIE for the reaction with toluene/[D8 ]toluene is 95 at -30 °C, which the largest in diiron systems reported so far. The present diiron complex efficiently catalyzes the oxidation of various alkanes with H2 O2 .

  6. Mechanistic insights into C-H amination via dicopper nitrenes.

    PubMed

    Aguila, Mae Joanne B; Badiei, Yosra M; Warren, Timothy H

    2013-06-26

    We examine important reactivity pathways relevant to stoichiometric and catalytic C-H amination via isolable β-diketiminato dicopper alkylnitrene intermediates {[Cl2NN]Cu}2(μ-NR). Kinetic studies involving the stoichiometric amination of ethylbenzene by {[Cl2NN]Cu}2(μ-N(t)Bu) (3) demonstrate that the terminal nitrene [Cl2NN]Cu═N(t)Bu is the active intermediate in C-H amination. Initial rates exhibit saturation behavior at high ethylbenzene loadings and an inverse dependence on the copper species [Cl2NN]Cu, both consistent with dissociation of a [Cl2NN]Cu fragment from 3 prior to C-H amination. C-H amination experiments employing 1,4-dimethylcyclohexane and benzylic radical clock substrate support a stepwise H-atom abstraction/radical rebound pathway. Dicopper nitrenes [Cu]2(μ-NCHRR') derived from 1° and 2° alkylazides are unstable toward tautomerization to copper(I) imine complexes [Cu](HN═CRR'), rendering 1° and 2° alkylnitrene complexes unsuitable for C-H amination.

  7. FT-IR spectroscopy, intra-molecular C-H⋯O interactions, HOMO, LUMO, MESP analysis and biological activity of two natural products, triclisine and rufescine: DFT and QTAIM approaches

    NASA Astrophysics Data System (ADS)

    Srivastava, Ambrish Kumar; Pandey, Anoop Kumar; Jain, Sudha; Misra, Neeraj

    2015-02-01

    The present study deals with two natural products, triclisine and rufescine which are extracted from the Amazonian wines but ubiquitous in nature. The quantum chemical density functional method at B3PW91/6-311+G(d,p) level is used to obtain the equilibrium geometries of these molecules. The quantum theory of atoms-in-molecule approach is employed to study various intra-molecular C-H⋯O interactions within these molecules. We have also performed vibrational analyses of triclisine and rufescine at their equilibrium geometries and presented the complete assignments of the significant vibrational modes. The calculated vibrational frequencies are shown to be in perfect agreement with the experimentally observed FTIR spectra of molecules under study. In addition, the electronic properties of these molecules are also discussed with the help of HOMO-LUMO and MESP surfaces and a number of electronic as well as thermodynamic parameters are calculated which are closely related to their chemical reactivity and reaction paths. The biological activities of both molecules have also been predicted which highlight their pharmacological importance.

  8. Enzyme-controlled nitrogen-atom transfer enables regiodivergent C-H amination.

    PubMed

    Hyster, Todd K; Farwell, Christopher C; Buller, Andrew R; McIntosh, John A; Arnold, Frances H

    2014-11-05

    We recently demonstrated that variants of cytochrome P450BM3 (CYP102A1) catalyze the insertion of nitrogen species into benzylic C-H bonds to form new C-N bonds. An outstanding challenge in the field of C-H amination is catalyst-controlled regioselectivity. Here, we report two engineered variants of P450BM3 that provide divergent regioselectivity for C-H amination-one favoring amination of benzylic C-H bonds and the other favoring homo-benzylic C-H bonds. The two variants provide nearly identical kinetic isotope effect values (2.8-3.0), suggesting that C-H abstraction is rate-limiting. The 2.66-Å crystal structure of the most active enzyme suggests that the engineered active site can preorganize the substrate for reactivity. We hypothesize that the enzyme controls regioselectivity through localization of a single C-H bond close to the iron nitrenoid.

  9. Quinoline-2-carboimine copper complex immobilized on amine functionalized silica coated magnetite nanoparticles: a novel and magnetically retrievable catalyst for the synthesis of carbamates via C-H activation of formamides.

    PubMed

    Sharma, R K; Dutta, Sriparna; Sharma, Shivani

    2015-01-21

    In the present study, we report the synthesis of a highly efficient and magnetically retrievable catalytic system (Cu-2QC@Am-SiO2@Fe3O4) through the covalent immobilization of quinoline-2-carboxaldehyde (2QC) on an amine functionalized silica coated ferrite nanosupport followed by metallation with copper acetate. The structure of the organic-inorganic hybrid nanomaterial has been confirmed using various physicochemical techniques such as Powder X-Ray Diffraction (XRD), Fourier Transform Infrared Spectroscopy (FT-IR), Scanning Electron Microscopy (SEM), Transmission Electron Microscopy (TEM), Energy Dispersive X-Ray Spectroscopy (EDS), Energy Dispersive X-Ray Fluorescence Spectroscopy (ED-XRF), Atomic Absorption Spectroscopy (AAS), Inductively Coupled Plasma Spectroscopy (ICP) and Vibrating Sample Magnetometry (VSM). The resulting nanocatalyst exhibits a remarkable catalytic efficacy in the synthesis of industrially and pharmaceutically significant carbamates via the C-H activation of formamides under solvent free conditions. The most important attribute of the present methodology is that the catalyst can be recovered simply through an external magnetic force and reused several times without any significant deterioration in its activity. Furthermore, the heterogeneity test has been carried out in order to ensure the intrinsic stability of the nanostructured catalyst. The activity of the Cu-2QC@Am-SiO2@Fe3O4 nanocatalyst has been found to be far more superior in comparison with the literature precedents in terms of the product yield, cost and reusability of the catalyst. Besides, ambient reaction conditions, simple workup procedure, wide substrate scope and cost effectiveness are some of the other outstanding features of this protocol that make it economical and sustainable.

  10. C. H. Patterson: The Counselor's Counselor.

    ERIC Educational Resources Information Center

    Goodyear, Rodney K.; Watkins, C. Edward, Jr.

    1983-01-01

    Interviewed C. H. Patterson, spokesperson for client-centered therapy and for counseling itself. Discusses some of the books and articles he has written and their impact on the profession. The interview reviews Patterson's career and focuses on him as a person and as a professional. (JAC)

  11. Cell Cholesterol Homeostasis: Mediation by Active Cholesterol

    PubMed Central

    Steck, Theodore L.; Lange, Yvonne

    2010-01-01

    Recent evidence suggests that the major pathways mediating cell cholesterol homeostasis respond to a common signal: active membrane cholesterol. Active cholesterol is that fraction which exceeds the complexing capacity of the polar bilayer lipids. Increments in plasma membrane cholesterol exceeding this threshold have an elevated chemical activity (escape tendency) and redistribute via diverse transport proteins to both circulating plasma lipoproteins and intracellular organelles. Active cholesterol prompts several feedback responses thereby. It is the substrate for its own esterification and for the synthesis of regulatory side-chain oxysterols. It also stimulates manifold pathways that down-regulate the biosynthesis, curtail the ingestion and increase the export of cholesterol. Thus, the abundance of cholesterol is tightly coupled to that of its polar lipid partners through active cholesterol. PMID:20843692

  12. Scalable C-H Oxidation with Copper: Synthesis of Polyoxypregnanes.

    PubMed

    See, Yi Yang; Herrmann, Aaron T; Aihara, Yoshinori; Baran, Phil S

    2015-11-04

    Steroids bearing C12 oxidations are widespread in nature, yet only one preparative chemical method addresses this challenge in a low-yielding and not fully understood fashion: Schönecker's Cu-mediated oxidation. This work shines new light onto this powerful C-H oxidation method through mechanistic investigation, optimization, and wider application. Culminating in a scalable, rapid, high-yielding, and operationally simple protocol, this procedure is applied to the first synthesis of several parent polyoxypregnane natural products, representing a gateway to over 100 family members.

  13. First principles (DFT) characterization of Rh(I) /dppp-catalyzed C-H activation by tandem 1,2-addition/1,4-Rh shift reactions of norbornene to phenylboronic acid.

    PubMed

    Kantchev, Eric Assen B; Pangestu, Surya R; Zhou, Feng; Sullivan, Michael B; Su, Hai-Bin

    2014-11-17

    The C-H activation in the tandem, "merry-go-round", [(dppp)Rh]-catalyzed (dppp=1,3-bis(diphenylphosphino)propane), four-fold addition of norborene to PhB(OH)2 has been postulated to occur by a C(alkyl)H oxidative addition to square-pyramidal Rh(III) -H species, which in turn undergoes a C(aryl)-H reductive elimination. Our DFT calculations confirm the Rh(I) /Rh(III) mechanism. At the IEFPCM(toluene, 373.15 K)/PBE0/DGDZVP level of theory, the oxidative addition barrier was calculated to be 12.9 kcal mol(-1) , and that of reductive elimination was 5.0 kcal mol(-1) . The observed selectivity of the reaction correlates well with the relative energy barriers of the cycle steps. The higher barrier (20.9 kcal mol(-1) ) for norbornyl-Rh protonation ensures that the reaction is steered towards the 1,4-shift (total barrier of 16.3 kcal mol(-1) ), acting as an equilibration shuttle. The carborhodation (13.2 kcal mol(-1) ) proceeds through a lower barrier than the protonation (16.7 kcal mol(-1) ) of the rearranged aryl-Rh species in the absence of o- or m-substituents, ensuring multiple carborhodations take place. However, for 2,5-dimethylphenyl, which was used as a model substrate, the barrier for carborhodation is increased to 19.4 kcal mol(-1) , explaining the observed termination of the reaction at 1,2,3,4-tetra(exo-norborn-2-yl)benzene. Finally, calculations with (Z)-2-butene gave a carborhodation barrier of 20.2 kcal mol(-1) , suggesting that carborhodation of non-strained, open-chain substrates would be disfavored relative to protonation.

  14. Generating Cu(II)-Oxyl / Cu(III)-Oxo Species from Cu(I)-α-Ketocarboxylate Complexes and O2: In silico Studies on Ligand Effects and C-H-activation Reactivity

    PubMed Central

    Huber, Stefan M.; Ertem, M. Zahid; Aquilante, Francesco

    2010-01-01

    A mechanism for the oxygenation of Cu(I) complexes with α-ketocarboxylate ligands is elaborated that is based on a combination of density functional theory and multireference second-order perturbation theory (CASSCF/CASPT2) calculations. The reaction proceeds in a manner largely analogous to those of similar Fe(II) α-ketocarboxylate systems, i.e. by initial attack of a coordinated oxygen molecule on a ketocarboxylate ligand with concomitant decarboxylation. Subsequently, two reactive intermediates may be generated, a Cu-peracid structure and a [CuO]+ species, both of which are capable of oxidizing a phenyl ring that is a component of the supporting ligand. Hydroxylation by the [CuO]+ species is predicted to proceed with a smaller activation free energy. The effects of electronic and steric variatons on the oxygenation mechanisms were studied by introducing substituents at several positions of the ligand backbone and by investigating various N-donor ligands. In general, more electron-donation by the N-donor ligand leads to increased stabilization of the more Cu(II)/Cu(III)-like intermediates (oxygen adducts and [CuO]+ species) relative to the more Cu(I)-like peracid intermediate. For all ligands investi-gated, the [CuO]+ intermediates are best described as Cu(II)-O•- species having triplet ground states. The reactivity of these compounds in C-H abstraction reactions decreases with more electron-donating N-donor ligands, which also increase the Cu-O bond strength, although the Cu-O bond is generally predicted to be rather weak (with a bond order of about 0.5). A comparison of several methods to obtain singlet energies for the reaction intermediates indicates that multireference second-order perturbation theory is likely more accurate for the initial oxygen adducts, but not necessarily for subsequent reaction intermediates. PMID:19322769

  15. Rh(III)-Catalyzed meta-C-H Olefination Directed by a Nitrile Template.

    PubMed

    Xu, Hua-Jin; Lu, Yi; Farmer, Marcus E; Wang, Huai-Wei; Zhao, Dan; Kang, Yan-Shang; Sun, Wei-Yin; Yu, Jin-Quan

    2017-02-15

    A range of Rh(III)-catalyzed ortho-C-H functionalizations have been developed; however, extension of this reactivity to remote C-H functionalizations through large-ring rhodacyclic intermediates has yet to be demonstrated. Herein we report the first example of the use of a U-shaped nitrile template to direct Rh(III)-catalyzed remote meta-C-H activation via a postulated 12-membered macrocyclic intermediate. Because the ligands used for Rh(III) catalysts are significantly different from those of Pd(II) catalysts, this offers new opportunities for future development of ligand-promoted meta-C-H activation reactions.

  16. Ruthenium-catalyzed direct C-H amidation of arenes including weakly coordinating aromatic ketones.

    PubMed

    Kim, Jiyu; Kim, Jinwoo; Chang, Sukbok

    2013-06-03

    C-H activation: The ruthenium-catalyzed direct sp(2) C-H amidation of arenes by using sulfonyl azides as the amino source is presented (see scheme). A wide range of substrates were readily amidated including arenes bearing weakly coordinating groups. Synthetic utility of the thus obtained products was demonstrated in the preparation of biologically active heterocycles.

  17. A General Strategy for the Nickel-Catalyzed C-H Alkylation of Anilines.

    PubMed

    Ruan, Zhixiong; Lackner, Sebastian; Ackermann, Lutz

    2016-02-24

    The C-H alkylation of aniline derivatives with both primary and secondary alkyl halides was achieved with a versatile nickel catalyst of a vicinal diamine ligand. Step-economic access to functionalized 2-pyrimidyl anilines, key structural motifs in anticancer drugs, is thus provided. The C-H functionalization proceeded through facile C-H activation and SET-type C-X bond cleavage with the assistance of a monodentate directing group, which could be removed in a traceless fashion.

  18. An Iminium Salt Organocatalyst for Selective Aliphatic C-H Hydroxylation.

    PubMed

    Wang, Daoyong; Shuler, William G; Pierce, Conor J; Hilinski, Michael K

    2016-08-05

    The first examples of catalysis of aliphatic C-H hydroxylation by an iminium salt are presented. The method allows the selective organocatalytic hydroxylation of unactivated 3° C-H bonds at room temperature using hydrogen peroxide as the terminal oxidant. Hydroxylation of an unactivated 2° C-H bond is also demonstrated. Furthermore, improved functional group compatibility over other catalytic methods is reported in the form of selectivity for aliphatic C-H hydroxylation over alcohol oxidation. On the basis of initial mechanistic studies, an oxaziridinium species is proposed as the active oxidant.

  19. Mechanochemical Rhodium(III)-Catalyzed C-H Bond Functionalization of Acetanilides under Solventless Conditions in a Ball Mill.

    PubMed

    Hermann, Gary N; Becker, Peter; Bolm, Carsten

    2015-06-15

    In a proof-of-principle study, a planetary ball mill was applied to rhodium(III)-catalyzed C-H bond functionalization. Under solventless conditions and in the presence of a minute amount of Cu(OAc)2, the mechanochemical activation led to the formation of an active rhodium species, thus enabling an oxidative Heck-type cross-coupling reaction with dioxygen as the terminal oxidant. The absence of an organic solvent, the avoidance of a high reaction temperature, the possibility of minimizing the amount of the metallic mediator, and the simplicity of the protocol result in a powerful and environmentally benign alternative to the common solution-based standard protocol.

  20. Approximate thermochemical tables for some C-H and C-H-O species

    NASA Technical Reports Server (NTRS)

    Bahn, G. S.

    1973-01-01

    Approximate thermochemical tables are presented for some C-H and C-H-O species and for some ionized species, supplementing the JANAF Thermochemical Tables for application to finite-chemical-kinetics calculations. The approximate tables were prepared by interpolation and extrapolation of limited available data, especially by interpolations over chemical families of species. Original estimations have been smoothed by use of a modification for the CDC-6600 computer of the Lewis Research Center PACl Program which was originally prepared for the IBM-7094 computer Summary graphs for various families show reasonably consistent curvefit values, anchored by properties of existing species in the JANAF tables.

  1. Mechanistic Variants in Gas-Phase Metal-Oxide Mediated Activation of Methane at Ambient Conditions.

    PubMed

    Li, Jilai; Zhou, Shaodong; Zhang, Jun; Schlangen, Maria; Usharani, Dandamudi; Shaik, Sason; Schwarz, Helmut

    2016-09-07

    The C-H bond activation of methane mediated by a prototypical heteronuclear metal-oxide cluster, [Al2Mg2O5](•+), was investigated by using Fourier transform ion cyclotron resonance mass spectrometry (FT-ICR-MS) in conjunction with high-level quantum mechanical calculations. Experimentally, hydrogen-atom abstraction from methane by the cluster ion [Al2Mg2O5](•+) takes place at ambient conditions. As to the mechanism, according to our computational findings, both the proton-coupled electron transfer (PCET) and the conventional hydrogen-atom transfer (HAT) are feasible and compete with each other. This is in distinct contrast to the [XYO2](+) (X, Y = Mg, Al, Si) cluster oxide ions which activate methane exclusively via the PCET route (Li, J.; Zhou, S.; Zhang, J.; Schlangen, M.; Weiske, T.; Usharani, D.; Shaik, S.; Schwarz, H. J. Am. Chem. Soc. 2016, 138, 7973-7981). The electronic origins of the mechanistically rather complex reactivity scenarios of the [Al2Mg2O5](•+)/CH4 couple were elucidated. For the PCET mechanism, in which the Lewis acid-base pair [Al(+)-O(-)] of the cluster acts as the active site, a clear correlation has been established between the nature of the transition state, the corresponding barrier height, the Lewis acidity-basicity of the [M(+)-O(-)] unit, as well as the bond order of the M(+)-O(-) bond. Also addressed is the role of the spin and charge distributions of a terminal oxygen radical site in the direct HAT route. The knowledge of the factors that control the reactivity of PCET and HAT pathways not only deepens our mechanistic understanding of metal-oxide mediated C-H bond activation but may also provide guidance for the rational design of catalysts.

  2. Directing group-controlled regioselectivity in an enzymatic C-H bond oxygenation.

    PubMed

    Negretti, Solymar; Narayan, Alison R H; Chiou, Karoline C; Kells, Petrea M; Stachowski, Jessica L; Hansen, Douglas A; Podust, Larissa M; Montgomery, John; Sherman, David H

    2014-04-02

    Highly regioselective remote hydroxylation of a natural product scaffold is demonstrated by exploiting the anchoring mechanism of the biosynthetic P450 monooxygenase PikCD50N-RhFRED. Previous studies have revealed structural and biochemical evidence for the role of a salt bridge between the desosamine N,N-dimethylamino functionality of the natural substrate YC-17 and carboxylate residues within the active site of the enzyme, and selectivity in subsequent C-H bond functionalization. In the present study, a substrate-engineering approach was conducted that involves replacing desosamine with varied synthetic N,N-dimethylamino anchoring groups. We then determined their ability to mediate enzymatic total turnover numbers approaching or exceeding that of the natural sugar, while enabling ready introduction and removal of these amino anchoring groups from the substrate. The data establish that the size, stereochemistry, and rigidity of the anchoring group influence the regioselectivity of enzymatic hydroxylation. The natural anchoring group desosamine affords a 1:1 mixture of regioisomers, while synthetic anchors shift YC-17 analogue C-10/C-12 hydroxylation from 20:1 to 1:4. The work demonstrates the utility of substrate engineering as an orthogonal approach to protein engineering for modulation of regioselective C-H functionalization in biocatalysis.

  3. Arene-metal π-complexation as a traceless reactivity enhancer for C-H arylation.

    PubMed

    Ricci, Paolo; Krämer, Katrina; Cambeiro, Xacobe C; Larrosa, Igor

    2013-09-11

    Current approaches to facilitate C-H arylation of arenes involve the use of either strongly electron-withdrawing substituents or directing groups. Both approaches require structural modification of the arene, limiting their generality. We present a new approach where C-H arylation is made possible without altering the connectivity of the arene via π-complexation of a Cr(CO)3 unit, greatly enhancing the reactivity of the aromatic C-H bonds. We apply this approach to monofluorobenzenes, highly unreactive arenes, which upon complexation become nearly as reactive as pentafluorobenzene itself in their couplings with iodoarenes. DFT calculations indicate that C-H activation via a concerted metalation-deprotonation transition state is facilitated by the predisposition of C-H bonds in (Ar-H)Cr(CO)3 to bend out of the aromatic plane.

  4. VTST/MT studies of the catalytic mechanism of C-H activation by transition metal complexes with [Cu2(μ-O2)], [Fe2(μ-O2)] and Fe(IV)-O cores based on DFT potential energy surfaces.

    PubMed

    Kim, Yongho; Mai, Binh Khanh; Park, Sumin

    2017-04-01

    High-valent Cu and Fe species, which are generated from dioxygen activation in metalloenzymes, carry out the functionalization of strong C-H bonds. Understanding the atomic details of the catalytic mechanism has long been one of the main objectives of bioinorganic chemistry. Large H/D kinetic isotope effects (KIEs) were observed in the C-H activation by high-valent non-heme Cu or Fe complexes in enzymes and their synthetic models. The H/D KIE depends significantly on the transition state properties, such as structure, energies, frequencies, and shape of the potential energy surface, when the tunneling effect is large. Therefore, theoretical predictions of kinetic parameters such as rate constants and KIEs can provide a reliable link between atomic-level quantum mechanical mechanisms and experiments. The accurate prediction of the tunneling effect is essential to reproduce the kinetic parameters. The rate constants and HD/KIE have been calculated using the variational transition-state theory including multidimensional tunneling based on DFT potential energy surfaces along the reaction coordinate. Excellent agreement was observed between the predicted and experimental results, which assures the validity of the DFT potential energy surfaces and, therefore, the proposed atomic-level mechanisms. The [Cu2(μ-O)2], [Fe2(μ-O)2], and Fe(IV)-oxo species were employed for C-H activation, and their role as catalysts was discussed at an atomic level.

  5. Mediators of change following a senior school physical activity intervention.

    PubMed

    Lubans, David R; Sylva, Kathy

    2009-01-01

    It has been suggested that the low level of effectiveness of youth interventions is due to a lack of knowledge regarding the mechanisms responsible for behaviour change. The identification of behaviour mediators is necessary for the progression of physical activity research, as it allows researchers to determine which components of an intervention are responsible for mediating behaviour change. The purpose of this study was to identify mediators of behaviour change in a physical activity intervention for senior school students. Participants (n=78) were randomly allocated to control or intervention conditions for a period of 10 weeks. Moderate-to-vigorous physical activity (MVPA) and potential mediators were assessed at baseline and post-intervention (10 weeks). Hypothesized mediators were derived from Bandura's Social Cognitive Theory and included: peer support, exercise self-efficacy and outcome expectancy. Mediation was assessed using the product-of-coefficients test described by MacKinnon and colleagues, based on the criteria for mediation identified by Baron and Kenny. While none of the variables satisfied all four criteria for mediation among males or females, self-efficacy was able to satisfy the first three criteria among females in the study. Exercise self-efficacy may be a mediator of physical activity behaviour in adolescent girls.

  6. Asymmetric Allylic C-H Oxidation for the Synthesis of Chromans.

    PubMed

    Wang, Pu-Sheng; Liu, Peng; Zhai, Yu-Jia; Lin, Hua-Chen; Han, Zhi-Yong; Gong, Liu-Zhu

    2015-10-14

    An enantioselective intramolecular allylic C-H oxidation to generate optically active chromans has been accomplished under the cooperative catalysis of a palladium complex of chiral phosphoramidite ligand and 2-fluorobenzoic acid. Mechanistic studies suggest that this reaction commences with a Pd-catalyzed allylic C-H activation event and then undergoes asymmetric allylic alkoxylation. The synthetic significance of the method has been embodied by concisely building up a key chiral intermediate to access (+)-diversonol.

  7. meta-C-H Bromination on Purine Bases by Heterogeneous Ruthenium Catalysis.

    PubMed

    Warratz, Svenja; Burns, David J; Zhu, Cuiju; Korvorapun, Korkit; Rogge, Torben; Scholz, Julius; Jooss, Christian; Gelman, Dmitri; Ackermann, Lutz

    2017-02-01

    Methods for positionally selective remote C-H functionalizations are in high demand. Herein, we disclose the first heterogeneous ruthenium catalyst for meta-selective C-H functionalizations, which enabled remote halogenations with excellent site selectivity and ample scope. The versatile heterogeneous Ru@SiO2 catalyst was broadly applicable and could be easily recovered and reused, which set the stage for the direct fluorescent labeling of purines. In contrast to palladium, rhodium, iridium, or cobalt complexes, solely the ruthenium catalysis manifold provided access to meta-halogenated purine derivatives, illustrating the unique power of ruthenium C-H activation catalysis.

  8. Structure of an isolated unglycosylated antibody C(H)2 domain.

    PubMed

    Prabakaran, Ponraj; Vu, Bang K; Gan, Jianhua; Feng, Yang; Dimitrov, Dimiter S; Ji, Xinhua

    2008-10-01

    The C(H)2 (C(H)3 for IgM and IgE) domain of an antibody plays an important role in mediating effector functions and preserving antibody stability. It is the only domain in human immunoglobulins (Igs) which is involved in weak interchain protein-protein interactions with another C(H)2 domain solely through sugar moieties. The N-linked glycosylation at Asn297 is conserved in mammalian IgGs as well as in homologous regions of other antibody isotypes. To examine the structural details of the C(H)2 domain in the absence of glycosylation and other antibody domains, the crystal structure of an isolated unglycosylated antibody gamma1 C(H)2 domain was determined at 1.7 A resolution and compared with corresponding C(H)2 structures from intact Fc, IgG and Fc receptor complexes. Furthermore, the oligomeric state of the protein in solution was studied using size-exclusion chromatography. The results suggested that the unglycosylated human antibody C(H)2 domain is a monomer and that its structure is similar to that found in the intact Fc, IgG and Fc receptor complex structures. However, certain structural variations were observed in the Fc receptor-binding sites. Owing to its small size, stability and non-immunogenic Ig template, the C(H)2-domain structure could be useful for the development by protein design of antibody domains exerting effector functions and/or antigen specificity and as a robust scaffold in protein-engineering applications.

  9. PIC Activation through Functional Interplay between Mediator and TFIIH.

    PubMed

    Malik, Sohail; Molina, Henrik; Xue, Zhu

    2017-01-06

    The multiprotein Mediator coactivator complex functions in large part by controlling the formation and function of the promoter-bound preinitiation complex (PIC), which consists of RNA polymerase II and general transcription factors. However, precisely how Mediator impacts the PIC, especially post-recruitment, has remained unclear. Here, we have studied Mediator effects on basal transcription in an in vitro transcription system reconstituted from purified components. Our results reveal a close functional interplay between Mediator and TFIIH in the early stages of PIC development. We find that under conditions when TFIIH is not normally required for transcription, Mediator actually represses transcription. TFIIH, whose recruitment to the PIC is known to be facilitated by the Mediator, then acts to relieve Mediator-induced repression to generate an active form of the PIC. Gel mobility shift analyses of PICs and characterization of TFIIH preparations carrying mutant XPB translocase subunit further indicate that this relief of repression is achieved through expending energy via ATP hydrolysis, suggesting that it is coupled to TFIIH's established promoter melting activity. Our interpretation of these results is that Mediator functions as an assembly factor that facilitates PIC maturation through its various stages. Whereas the overall effect of the Mediator is to stimulate basal transcription, its initial engagement with the PIC generates a transcriptionally inert PIC intermediate, which necessitates energy expenditure to complete the process.

  10. Ni nanoparticle catalyzed growth of MWCNTs on Cu NPs @ a-C:H substrate

    NASA Astrophysics Data System (ADS)

    Ghodselahi, T.; Solaymani, S.; Akbarzadeh Pasha, M.; Vesaghi, M. A.

    2012-11-01

    NiCu NPs @ a-C:H thin films with different Cu content were prepared by co-deposition by RF-sputtering and RF-plasma enhanced chemical vapor deposition (RF-PECVD) from acetylene gas and Cu and Ni targets. The prepared samples were used as catalysts for growing multi-wall carbon nanotubes (MWCNTs) from liquid petroleum gas (LPG) at 825 °C by thermal chemical vapor deposition (TCVD). By addition of Cu NPs @ a-C:H thin layer as substrate for Ni NPs catalyst, the density of the grown CNTs is greatly enhanced in comparison to bare Si substrate. Furthermore the average diameter of the grown CNTs decreases by decreasing of Cu content of Cu NPs @ a-C:H thin layer. However Cu NPs @ a-C:H by itself has no catalytic property in MWCNTs growth. Morphology and electrical and optical properties of Cu NPs @ a-C:H thin layer is affected by Cu content and each of them is effective parameter on growth of MWCNTs based on Ni NPs catalyst. Moreover, adding of a low amount of Ni NPs doesn't vary optical, electrical and morphology properties of Cu NPs @ a-C:H thin layer but it has a profound effect on its catalytic activity. Finally the density and diameter of MWCNTs can be optimized by selection of the Cu NPs @ a-C:H thin layer as substrate of Ni NPs.

  11. Trends in applying C-H oxidation to the total synthesis of natural products.

    PubMed

    Qiu, Yuanyou; Gao, Shuanhu

    2016-04-01

    Covering: 2006 to 2015C-H functionalization remains one of the frontier challenges in organic chemistry and drives quite an active area of research. It has recently been applied in various novel strategies for the synthesis of natural products. It can dramatically increase synthetic efficiency when incorporated into retrosynthetic analyses of complex natural products, making it an essential part of current trends in organic synthesis. In this Review, we focus on selected case studies of recent applications of C-H oxidation methodologies in which the C-H bond has been exploited effectively to construct C-O and C-N bonds in natural product syntheses. Examples of syntheses representing different types of C-H oxidation are discussed to illustrate the potential of this approach and inspire future applications.

  12. Pushing the limits of catalytic C-H amination in polyoxygenated cyclobutanes.

    PubMed

    Nocquet, Pierre-Antoine; Hensienne, Raphaël; Wencel-Delord, Joanna; Laigre, Eugénie; Sidelarbi, Khadidja; Becq, Frédéric; Norez, Caroline; Hazelard, Damien; Compain, Philippe

    2016-03-07

    A synthetic route to a new class of conformationally constrained iminosugars based on a 5-azaspiro[3.4]octane skeleton has been developed by way of Rh(ii)-catalyzed C(sp(3))-H amination. The pivotal stereocontrolled formation of the quaternary C-N bond by insertion into the C-H bonds of the cyclobutane ring was explored with a series of polyoxygenated substrates. In addition to anticipated regioselective issues induced by the high density of activated α-ethereal C-H bonds, this systematic study showed that cyclobutane C-H bonds were, in general, poorly reactive towards catalytic C-H amination. This was demonstrated inter alia by the unexpected formation of a oxathiazonane derivative, which constitutes a very rare example of the formation of a 9-membered ring by way of catalyzed C(sp(3))-H amination. A complete stereocontrol could be however achieved by activating the key insertion position as an allylic C-H bond in combination with reducing the electron density at the undesired C-H insertion sites by using electron-withdrawing protecting groups. Preliminary biological evaluations of the synthesized spiro-iminosugars were performed, which led to the identification of a new class of correctors of the defective F508del-CFTR gating involved in cystic fibrosis.

  13. Manganese Porphyrins Catalyze Selective C-H Bond Halogenations

    SciTech Connect

    Liu, Wei; Groves, John T.

    2010-08-31

    We report a manganese porphyrin mediated aliphatic C-H bond chlorination using sodium hypochlorite as the chlorine source. In the presence of catalytic amounts of phase transfer catalyst and manganese porphyrin Mn(TPP)Cl 1, reaction of sodium hypochlorite with different unactivated alkanes afforded alkyl chlorides as the major products with only trace amounts of oxygenation products. Substrates with strong C-H bonds, such as neopentane (BDE =~100 kcal/mol) can be also chlorinated with moderate yield. Chlorination of a diagnostic substrate, norcarane, afforded rearranged products indicating a long-lived carbon radical intermediate. Moreover, regioselective chlorination was achieved by using a hindered catalyst, Mn(TMP)Cl, 2. Chlorination of trans-decalin with 2 provided 95% selectivity for methylene-chlorinated products as well as a preference for the C2 position. This novel chlorination system was also applied to complex substrates. With 5α-cholestane as the substrate, we observed chlorination only at the C2 and C3 positions in a net 55% yield, corresponding to the least sterically hindered methylene positions in the A-ring. Similarly, chlorination of sclareolide afforded the equatorial C2 chloride in a 42% isolated yield. Regarding the mechanism, reaction of sodium hypochlorite with the MnIII porphyrin is expected to afford a reactive MnV=O complex that abstracts a hydrogen atom from the substrate, resulting in a free alkyl radical and a MnIV—OH complex. We suggest that this carbon radical then reacts with a MnIV—OCl species, providing the alkyl chloride and regenerating the reactive MnV=O complex. The regioselectivity and the preference for CH2 groups can be attributed to nonbonded interactions between the alkyl groups on the substrates and the aryl groups of the manganese porphyrin. The results are indicative of a bent [Mnv=O---H---C] geometry due to the C—H approach to the Mn

  14. Catalytic C-H bond silylation of aromatic heterocycles.

    PubMed

    Toutov, Anton A; Liu, Wen-Bo; Betz, Kerry N; Stoltz, Brian M; Grubbs, Robert H

    2015-12-01

    This protocol describes a method for the direct silylation of the carbon-hydrogen (C-H) bond of aromatic heterocycles using inexpensive and abundant potassium tert-butoxide (KOt-Bu) as the catalyst. This catalytic cross-dehydrogenative coupling of simple hydrosilanes and various electron-rich aromatic heterocycles enables the synthesis of valuable silylated heteroarenes. The products thus obtained can be used as versatile intermediates, which facilitate the divergent synthesis of pharmaceutically relevant compound libraries from a single Si-containing building block. Moreover, a variety of complex Si-containing motifs, such as those produced by this protocol, are being actively investigated as next-generation therapeutic agents, because they can have improved pharmacokinetic properties compared with the original all-carbon drug molecules. Current competing methods for C-H bond silylation tend to be incompatible with functionalities, such as Lewis-basic heterocycles, that are often found in pharmaceutical substances; this leaves de novo synthesis as the principal strategy for preparation of the target sila-drug analog. Moreover, competing methods tend to be limited in the scope of hydrosilane that can be used, which restricts the breadth of silicon-containing small molecules that can be accessed. The approach outlined in this protocol enables the chemoselective and regioselective late-stage silylation of small heterocycles, including drugs and drug derivatives, with a broad array of hydrosilanes in the absence of precious metal catalysts, stoichiometric reagents, sacrificial hydrogen acceptors or high temperatures. Moreover, H2 is the only by-product generated. The procedure normally requires 48-75 h to be completed.

  15. Effect of Bridgehead Steric Bulk on the Intramolecular C-H Heterolysis of [FeFe]-Hydrogenase Active Site Models Containing a P2N2 Pendant Amine Ligand.

    PubMed

    Zheng, Dehua; Wang, Mei; Wang, Ning; Cheng, Minglun; Sun, Licheng

    2016-01-19

    A series of pendant amine-containing [FeFe]-hydrogenase models, [X(CH2S-μ)2{Fe(CO)3}{Fe(CO)(P2(Ph)N2(Bn))}] (1H, X = CH2; 2Me, C(CH3)2; 3Et, C(CH2CH3)2; and P2(Ph)N2(Bn) = 1,5-dibenzyl-3,7-diphenyl-1,5-diaza-3,7-diphosphacyclooctane) with different groups at the bridgehead carbon of the S-to-S linker were synthesized. The oxidations of these complexes as well as the reverse reduction reaction were studied by cyclic voltammetry and in situ IR spectroscopy. Regardless of the bridgehead steric bulk, all three complexes demonstrate intramolecular iron-mediated C(sp(3))-H bond heterolytic cleavage with the assistance of the pendant amine base within the chelating diphosphine ligand in the two-electron oxidation process. X-ray crystallographic analysis shows that the doubly oxidized products, [1'H](+), [2'Me](+), and [3'Et](+), all have a rigid FeSC three-membered ring at the open apical site of the rotated iron center. The most noticeable difference in structures of the oxidized complexes is that the single CO ligand of the rotated Fe(P2(Ph)N2(Bn))(CO) unit in [1'H](+) and [2'Me](+) is found below the Fe···Fe vector, while in [3'Et](+) an unusually rotated Fe(P2(Ph)N2(Bn))(CO) moiety positions one of the P donors within the bidentate ligand under the Fe···Fe vector. The starting Fe(I)Fe(I) complexes can be recovered from their corresponding doubly oxidized complexes by reduction in the presence of Brönsted acid.

  16. C-H Bond Activation of Methane by PtII-N-Heterocyclic Carbene Complexes. The Importance of Having the Ligands in the Right Place at the Right Time

    SciTech Connect

    Prince, Bruce M.; Cundari, Thomas R

    2012-02-13

    A DFT study of methane C–H activation barriers for neutral NHC–PtII–methoxy complexes yielded 22.8 and 26.1 kcal/mol for oxidative addition (OA) and oxidative hydrogen migration (OHM), respectively. Interestingly, this is unlike the case for cationic NHC–PtII–methoxy complexes, whereby OHM entails a calculated barrier of 26.9 kcal/mol but the OA barrier is only 14.4 kcal/mol. Comparing transition state (TS) and ground state (GS) geometries implies an ~10 kcal/mol “penalty” to the barriers arising from positioning the NHC and OMe ligands into a relative orientation that is preferred in the GS to the orientation that is favored in the TS. The results thus imply an intrinsic barrier arising from C–H scission of ~15 ± 2 kcal/mol for NHC–PtII–methoxy complexes. Calculations show the importance of designing C–H activation catalysts where the GS active species is already structurally “prepared” and which either does not need to undergo any geometric perturbations to access the methane C–H activation TS or is not energetically prohibited from such perturbations.

  17. Is It Fe(III)-Oxyl Radical That Abstracts Hydrogen in the C-H Activation of TauD? A Theoretical Study Based on the DFT Potential Energy Surfaces.

    PubMed

    Mai, Binh Khanh; Kim, Yongho

    2016-04-18

    Taurine:α-ketoglutarate dioxygenase (TauD) is one of the most important enzymes in the α-ketoglutarate dioxygenase family, which are involved in many important biochemical processes. TauD converts taurine into amino acetaldehyde and sulfite at its nonheme iron center, and a large H/D kinetic isotope effect (KIE) has been found in the hydrogen atom transfer (HAT) of taurine suggesting a large tunneling effect. Recently, highly electrophilic Fe(III)-oxyl radicals have been proposed as a key species for HAT in the catalytic mechanism of C–H activation, which might be prepared prior to the actual HAT. In order to investigate this hypothesis and large tunneling effect, DFT potential energy surfaces along the intrinsic reaction path were generated. The predicted rate constants and H/D KIEs using variational transition-state theory including multidimensional tunneling, based on these potential surfaces, have excellent agreement with experimental data. This study revealed that the reactive processes of C–H activation consisted of two distinguishable parts: (1) the substrate approaching the Fe(IV)-oxo center without C–H bond cleavage, which triggers the catalytic process by inducing metal-to-ligand charge transfer to form the Fe(III)-oxyl species, and (2) the actual HAT from the substrate to the Fe(III)-oxyl species. Most of the activation energy was used in the first part, and the actual HAT required only a small amount of energy to overcome the TS with a very large tunneling effect. The donor–acceptor interaction between σC–H and σ*Fe–O orbitals reduced the activation energy significantly to make C–H activation feasible.

  18. Evolution of C-H Bond Functionalization from Methane to Methodology.

    PubMed

    Hartwig, John F

    2016-01-13

    This Perspective presents the fundamental principles, the elementary reactions, the initial catalytic systems, and the contemporary catalysts that have converted C-H bond functionalization from a curiosity to a reality for synthetic chemists. Many classes of elementary reactions involving transition-metal complexes cleave C-H bonds at typically unreactive positions. These reactions, coupled with a separate or simultaneous functionalization process lead to products containing new C-C, C-N, and C-O bonds. Such reactions were initially studied for the conversion of light alkanes to liquid products, but they have been used (and commercialized in some cases) most often for the synthesis of the more complex structures of natural products, medicinally active compounds, and aromatic materials. Such a change in direction of research in C-H bond functionalization is remarkable because the reactions must occur at an unactivated C-H bond over functional groups that are more reactive than the C-H bond toward classical reagents. The scope of reactions that form C-C bonds or install functionality at an unactivated C-H bond will be presented, and the potential future utility of these reactions will be discussed.

  19. Transition-metal-catalyzed π-bond-assisted C - H bond functionalization: an emerging trend in organic synthesis.

    PubMed

    Gandeepan, Parthasarathy; Cheng, Chien-Hong

    2015-04-01

    Transition-metal-catalyzed C - H activation is considered to be an important tool in organic synthesis and has been accepted and widely used by chemists because it is straightforward, cost-effective, and environmentally friendly. A variety of functional groups have been used to direct metal complexes and achieve regioselective C - H activation. Most directing is achieved through the σ-bond coordination of functional groups to the metal catalyst, followed by ortho-selective C - H bond cleavage. However, recent work has demonstrated that π-coordinating functional groups can also assist in guiding metal complexes for site-selective C - H bond activation. This emerging approach significantly expands the scope of C - H activation reactions in organic synthesis. Herein, recent developments in this field are summarized.

  20. Direct catalytic oxyamination of benzene to aniline over Cu(II) nanoclusters supported on CuCr2O4 spinel nanoparticles via simultaneous activation of C-H and N-H bonds.

    PubMed

    Acharyya, Shankha S; Ghosh, Shilpi; Bal, Rajaram

    2014-11-11

    We report the facile synthesis of a highly efficient, reusable catalyst comprising Cu(II) nanoclusters supported on CuCr2O4 spinel nanoparticles for the oxyamination of benzene to aniline (H2O2 + NH3) under mild aqueous reaction conditions. The synergy between the Cu(II) nanoclusters and CuCr2O4 spinel nanoparticles plays the most vital role towards its high catalytic activity.

  1. Uranium-mediated activation of small molecules.

    PubMed

    Arnold, Polly L

    2011-08-28

    Molecular complexes of uranium are capable of activating a range of industrially and economically important small molecules such as CO, CO(2), and N(2); new and often unexpected reactions provide insight into an element that needs to be well-understood if future clean-energy solutions are to involve nuclear power.

  2. Mediation of mouse natural cytotoxic activity by tumour necrosis factor

    NASA Astrophysics Data System (ADS)

    Ortaldo, John R.; Mason, Llewellyn H.; Mathieson, Bonnie J.; Liang, Shu-Mei; Flick, David A.; Herberman, Ronald B.

    1986-06-01

    Natural cell-mediated cytotoxic activity in the mouse has been associated with two types of effector cells, the natural killer (NK) cell and the natural cytotoxic (NC) cell, which seem to differ with regard to their patterns of target selectivity, cell surface characteristics and susceptibility to regulatory factors1. During studies on the mechanism of action of cytotoxic molecules, it became evident that WEHI-164, the prototype NC target cell, was highly susceptible to direct lysis by both human and mouse recombinant tumour necrosis factor (TNF). Here we show that NC, but not NK activity mediated by normal splenocytes, is abrogated by rabbit antibodies to recombinant and natural TNF, respectively. Thus, the cell-mediated activity defined as NC is due to release of TNF by normal spleen cells and does not represent a unique natural effector mechanism.

  3. Pleiotrophin mediates hematopoietic regeneration via activation of RAS.

    PubMed

    Himburg, Heather A; Yan, Xiao; Doan, Phuong L; Quarmyne, Mamle; Micewicz, Eva; McBride, William; Chao, Nelson J; Slamon, Dennis J; Chute, John P

    2014-11-01

    Hematopoietic stem cells (HSCs) are highly susceptible to ionizing radiation-mediated death via induction of ROS, DNA double-strand breaks, and apoptotic pathways. The development of therapeutics capable of mitigating ionizing radiation-induced hematopoietic toxicity could benefit both victims of acute radiation sickness and patients undergoing hematopoietic cell transplantation. Unfortunately, therapies capable of accelerating hematopoietic reconstitution following lethal radiation exposure have remained elusive. Here, we found that systemic administration of pleiotrophin (PTN), a protein that is secreted by BM-derived endothelial cells, substantially increased the survival of mice following radiation exposure and after myeloablative BM transplantation. In both models, PTN increased survival by accelerating the recovery of BM hematopoietic stem and progenitor cells in vivo. PTN treatment promoted HSC regeneration via activation of the RAS pathway in mice that expressed protein tyrosine phosphatase receptor-zeta (PTPRZ), whereas PTN treatment did not induce RAS signaling in PTPRZ-deficient mice, suggesting that PTN-mediated activation of RAS was dependent upon signaling through PTPRZ. PTN strongly inhibited HSC cycling following irradiation, whereas RAS inhibition abrogated PTN-mediated induction of HSC quiescence, blocked PTN-mediated recovery of hematopoietic stem and progenitor cells, and abolished PTN-mediated survival of irradiated mice. These studies demonstrate the therapeutic potential of PTN to improve survival after myeloablation and suggest that PTN-mediated hematopoietic regeneration occurs in a RAS-dependent manner.

  4. Pleiotrophin mediates hematopoietic regeneration via activation of RAS

    PubMed Central

    Himburg, Heather A.; Yan, Xiao; Doan, Phuong L.; Quarmyne, Mamle; Micewicz, Eva; McBride, William; Chao, Nelson J.; Slamon, Dennis J.; Chute, John P.

    2014-01-01

    Hematopoietic stem cells (HSCs) are highly susceptible to ionizing radiation–mediated death via induction of ROS, DNA double-strand breaks, and apoptotic pathways. The development of therapeutics capable of mitigating ionizing radiation–induced hematopoietic toxicity could benefit both victims of acute radiation sickness and patients undergoing hematopoietic cell transplantation. Unfortunately, therapies capable of accelerating hematopoietic reconstitution following lethal radiation exposure have remained elusive. Here, we found that systemic administration of pleiotrophin (PTN), a protein that is secreted by BM-derived endothelial cells, substantially increased the survival of mice following radiation exposure and after myeloablative BM transplantation. In both models, PTN increased survival by accelerating the recovery of BM hematopoietic stem and progenitor cells in vivo. PTN treatment promoted HSC regeneration via activation of the RAS pathway in mice that expressed protein tyrosine phosphatase receptor-zeta (PTPRZ), whereas PTN treatment did not induce RAS signaling in PTPRZ-deficient mice, suggesting that PTN-mediated activation of RAS was dependent upon signaling through PTPRZ. PTN strongly inhibited HSC cycling following irradiation, whereas RAS inhibition abrogated PTN-mediated induction of HSC quiescence, blocked PTN-mediated recovery of hematopoietic stem and progenitor cells, and abolished PTN-mediated survival of irradiated mice. These studies demonstrate the therapeutic potential of PTN to improve survival after myeloablation and suggest that PTN-mediated hematopoietic regeneration occurs in a RAS-dependent manner. PMID:25250571

  5. Age mediation of frontoparietal activation during visual feature search.

    PubMed

    Madden, David J; Parks, Emily L; Davis, Simon W; Diaz, Michele T; Potter, Guy G; Chou, Ying-hui; Chen, Nan-kuei; Cabeza, Roberto

    2014-11-15

    Activation of frontal and parietal brain regions is associated with attentional control during visual search. We used fMRI to characterize age-related differences in frontoparietal activation in a highly efficient feature search task, detection of a shape singleton. On half of the trials, a salient distractor (a color singleton) was present in the display. The hypothesis was that frontoparietal activation mediated the relation between age and attentional capture by the salient distractor. Participants were healthy, community-dwelling individuals, 21 younger adults (19-29 years of age) and 21 older adults (60-87 years of age). Top-down attention, in the form of target predictability, was associated with an improvement in search performance that was comparable for younger and older adults. The increase in search reaction time (RT) associated with the salient distractor (attentional capture), standardized to correct for generalized age-related slowing, was greater for older adults than for younger adults. On trials with a color singleton distractor, search RT increased as a function of increasing activation in frontal regions, for both age groups combined, suggesting increased task difficulty. Mediational analyses disconfirmed the hypothesized model, in which frontal activation mediated the age-related increase in attentional capture, but supported an alternative model in which age was a mediator of the relation between frontal activation and capture.

  6. Chemoselective hydroxylation of aliphatic sp3 C-H bonds using a ketone catalyst and aqueous H2O2.

    PubMed

    Pierce, Conor J; Hilinski, Michael K

    2014-12-19

    The first ketone-catalyzed method for the oxidation of aliphatic C-H bonds is reported. The reaction conditions employ aryl trifluoromethyl ketones in catalytic amounts and hydrogen peroxide as the terminal oxidant. Hydroxylation is stereospecific and chemoselective for tertiary over secondary C-H bonds. A catalytic cycle invoking a dioxirane as the active oxidant is proposed.

  7. SUMOylation of p53 mediates interferon activities

    PubMed Central

    Marcos-Villar, Laura; Pérez-Girón, José V; Vilas, Jéssica M; Soto, Atenea; de la Cruz-Hererra, Carlos F; Lang, Valerie; Collado, Manuel; Vidal, Anxo; Rodríguez, Manuel S; Muñoz-Fontela, César; Rivas, Carmen

    2013-01-01

    There is growing evidence that many host proteins involved in innate and intrinsic immunity are regulated by SUMOylation, and that SUMO contributes to the regulatory process that governs the initiation of the type I interferon (IFN) response. The tumor suppressor p53 is a modulator of the IFN response that plays a role in virus-induced apoptosis and in IFN-induced senescence. Here we demonstrate that IFN treatment increases the levels of SUMOylated p53 and induces cellular senescence through a process that is partially dependent upon SUMOylation of p53. Similarly, we show that vesicular stomatitis virus (VSV) infection induces p53 SUMOylation, and that this modification favors the control of VSV replication. Thus, our study provides evidence that IFN signaling induces p53 SUMOylation, which results in the activation of a cellular senescence program and contributes to the antiviral functions of interferon. PMID:23966171

  8. Adenine suppresses IgE-mediated mast cell activation.

    PubMed

    Silwal, Prashanta; Shin, Keuna; Choi, Seulgi; Kang, Seong Wook; Park, Jin Bong; Lee, Hyang-Joo; Koo, Suk-Jin; Chung, Kun-Hoe; Namgung, Uk; Lim, Kyu; Heo, Jun-Young; Park, Jong Il; Park, Seung-Kiel

    2015-06-01

    Nucleobase adenine is produced by dividing human lymphoblasts mainly from polyamine synthesis and inhibits immunological functions of lymphocytes. We investigated the anti-allergic effect of adenine on IgE-mediated mast cell activation in vitro and passive cutaneous anaphylaxis (PCA) in mice. Intraperitoneal injection of adenine to IgE-sensitized mice attenuated IgE-mediated PCA reaction in a dose dependent manner, resulting in a median effective concentration of 4.21 mg/kg. In mast cell cultures, only adenine among cytosine, adenine, adenosine, ADP and ATP dose-dependently suppressed FcɛRI (a high affinity receptor for IgE)-mediated degranulation with a median inhibitory concentration of 1.6mM. It also blocked the production of LTB4, an inflammatory lipid mediator, and inflammatory cytokines TNF-α and IL-4. In addition, adenine blocked thapsigargin-induced degranulation which is FcɛRI-independent but shares FcɛRI-dependent signaling events. Adenine inhibited the phosphorylation of signaling molecules important to FcɛRI-mediated allergic reactions such as Syk, PLCγ2, Gab2, Akt, and mitogen activated protein kinases ERK and JNK. From this result, we report for the first time that adenine inhibits PCA in mice and allergic reaction by inhibiting FcɛRI-mediated signaling events in mast cells. Therefore, adenine may be useful for the treatment of mast cell-mediated allergic diseases. Also, the upregulation of adenine production may provide another mechanism for suppressing mast cell activity especially at inflammatory sites.

  9. LIME mediates immunological synapse formation through activation of VAV.

    PubMed

    Son, Myoungsun; Park, Inyoung; Lee, Ok-Hee; Rhee, Inmoo; Park, Changwon; Yun, Yungdae

    2012-04-01

    Lck Interacting Membrane protein (LIME) was previously characterized as a transmembrane adaptor protein mediating TCR-dependent T cell activation. Here, we show that LIME associates with Vav in response to TCR stimulation and is required for Vav guanine nucleotide exchange factor (GEF) activity for Rac1. Consistent with this finding, actin polymerization at the immunological synapse (IS) was markedly enhanced by overexpression of LIME, but was reduced by expression of a LIME shRNA. Moreover, TCR-mediated cell adhesion to ICAM-1, laminin, or fibronectin was downregulated by expression of LIME shRNA. In addition, in the IS, LIME but not LAT was found to localize at the peripheral-supramolecular activation cluster (p-SMAC) where the integrins were previously shown to be localized. Together, these results establish LIME as a transmembrane adaptor protein linking TCR stimulation to IS formation and integrin activation through activation of Vav.

  10. Benzylic C-H trifluoromethylation of phenol derivatives.

    PubMed

    Egami, Hiromichi; Ide, Takafumi; Kawato, Yuji; Hamashima, Yoshitaka

    2015-12-04

    Phenol derivatives were trifluoromethylated using copper/Togni reagent. In dimethylformamide, the benzylic C-H bond at the para position of the hydroxyl group was selectively substituted with a CF3 group. In contrast, aromatic C-H trifluoromethylation occurred in alcoholic solvents. Practical utility of the reactions was demonstrated by application to the synthesis of a potent enoyl-acyl carrier protein reductase (FabI) inhibitor.

  11. Mechanism of catalytic functionalization of primary C-H bonds using a silylation strategy.

    PubMed

    Parija, Abhishek; Sunoj, Raghavan B

    2013-08-16

    The mechanism of Ir-catalyzed γ-functionalization of a primary sp(3)(C-H) bond in 2-methyl cyclohexanol is examined using the density functional theory (M06). The nature of the active catalyst for the initial silylation of alcohol is identified as the monomer derived from [Ir(cod)OMe]2 while that for γ-sp(3)(C-H) activation leading to oxasilolane is [IrH(nbe)(phen)]. The rate-determining step is found to involve Si-C coupling through reductive elimination.

  12. Terminal olefins to chromans, isochromans, and pyrans via allylic C-H oxidation.

    PubMed

    Ammann, Stephen E; Rice, Grant T; White, M Christina

    2014-08-06

    The synthesis of chroman, isochroman, and pyran motifs has been accomplished via a combination of Pd(II)/bis-sulfoxide C-H activation and Lewis acid co-catalysis. A wide range of alcohols are found to be competent nucleophiles for the transformation under uniform conditions (catalyst, solvent, temperature). Mechanistic studies suggest that the reaction proceeds via initial C-H activation followed by a novel inner-sphere functionalization pathway. Consistent with this, the reaction shows reactivity trends orthogonal to those of traditional Pd(0)-catalyzed allylic substitutions.

  13. Carboxylate-assisted ruthenium-catalyzed alkyne annulations by C-H/Het-H bond functionalizations.

    PubMed

    Ackermann, Lutz

    2014-02-18

    To improve the atom- and step-economy of organic syntheses, researchers would like to capitalize upon the chemistry of otherwise inert carbon-hydrogen (C-H) bonds. During the past decade, remarkable progress in organometallic chemistry has set the stage for the development of increasingly viable metal catalysts for C-H bond activation reactions. Among these methods, oxidative C-H bond functionalizations are particularly attractive because they avoid the use of prefunctionalized starting materials. For example, oxidative annulations that involve sequential C-H and heteroatom-H bond cleavages allow for the modular assembly of regioselectively decorated heterocycles. These structures serve as key scaffolds for natural products, functional materials, crop protecting agents, and drugs. While other researchers have devised rhodium or palladium complexes for oxidative alkyne annulations, my laboratory has focused on the application of significantly less expensive, yet highly selective ruthenium complexes. This Account summarizes the evolution of versatile ruthenium(II) complexes for annulations of alkynes via C-H/N-H, C-H/O-H, or C-H/N-O bond cleavages. To achieve selective C-H bond functionalizations, we needed to understand the detailed mechanism of the crucial C-H bond metalation with ruthenium(II) complexes and particularly the importance of carboxylate assistance in this process. As a consequence, our recent efforts have resulted in widely applicable methods for the versatile preparation of differently decorated arenes and heteroarenes, providing access to among others isoquinolones, 2-pyridones, isoquinolines, indoles, pyrroles, or α-pyrones. Most of these reactions used Cu(OAc)2·H2O, which not only acted as the oxidant but also served as the essential source of acetate for the carboxylate-assisted ruthenation manifold. Notably, the ruthenium(II)-catalyzed oxidative annulations also occurred under an ambient atmosphere of air with cocatalytic amounts of Cu(OAc)2

  14. Iron Complex Catalyzed Selective C-H Bond Oxidation with Broad Substrate Scope.

    PubMed

    Jana, Sandipan; Ghosh, Munmun; Ambule, Mayur; Sen Gupta, Sayam

    2017-02-17

    The use of a peroxidase-mimicking Fe complex has been reported on the basis of the biuret-modified TAML macrocyclic ligand framework (Fe-bTAML) as a catalyst to perform selective oxidation of unactivated 3° C-H bonds and activatedC-H bonds with low catalyst loading (1 mol %) and high product yield (excellent mass balance) under near-neutral conditions and broad substrate scope (18 substrates which includes arenes, heteroaromatics, and polar functional groups). Aliphatic C-H oxidation of 3° and 2° sites of complex substrates was achieved with predictable selectivity using steric, electronic, and stereoelectronic rules that govern site selectivity, which included oxidation of (+)-artemisinin to (+)-10β-hydroxyartemisinin. Mechanistic studies indicate Fe(V)(O) to be the active oxidant during these reactions.

  15. Intrinsic-mediated caspase activation is essential for cardiomyocyte hypertrophy.

    PubMed

    Putinski, Charis; Abdul-Ghani, Mohammad; Stiles, Rebecca; Brunette, Steve; Dick, Sarah A; Fernando, Pasan; Megeney, Lynn A

    2013-10-22

    Cardiomyocyte hypertrophy is the cellular response that mediates pathologic enlargement of the heart. This maladaptation is also characterized by cell behaviors that are typically associated with apoptosis, including cytoskeletal reorganization and disassembly, altered nuclear morphology, and enhanced protein synthesis/translation. Here, we investigated the requirement of apoptotic caspase pathways in mediating cardiomyocyte hypertrophy. Cardiomyocytes treated with hypertrophy agonists displayed rapid and transient activation of the intrinsic-mediated cell death pathway, characterized by elevated levels of caspase 9, followed by caspase 3 protease activity. Disruption of the intrinsic cell death pathway at multiple junctures led to a significant inhibition of cardiomyocyte hypertrophy during agonist stimulation, with a corresponding reduction in the expression of known hypertrophic markers (atrial natriuretic peptide) and transcription factor activity [myocyte enhancer factor-2, nuclear factor kappa B (NF-κB)]. Similarly, in vivo attenuation of caspase activity via adenoviral expression of the biologic effector caspase inhibitor p35 blunted cardiomyocyte hypertrophy in response to agonist stimulation. Treatment of cardiomyocytes with procaspase 3 activating compound 1, a small-molecule activator of caspase 3, resulted in a robust induction of the hypertrophy response in the absence of any agonist stimulation. These results suggest that caspase-dependent signaling is necessary and sufficient to promote cardiomyocyte hypertrophy. These results also confirm that cell death signal pathways behave as active remodeling agents in cardiomyocytes, independent of inducing an apoptosis response.

  16. Mediating role of activity level in the depressive realism effect.

    PubMed

    Blanco, Fernando; Matute, Helena; A Vadillo, Miguel

    2012-01-01

    Several classic studies have concluded that the accuracy of identifying uncontrollable situations depends heavily on depressive mood. Nondepressed participants tend to exhibit an optimistic illusion of control, whereas depressed participants tend to better detect a lack of control. Recently, we suggested that the different activity levels (measured as the probability of responding during a contingency learning task) exhibited by depressed and nondepressed individuals is partly responsible for this effect. The two studies presented in this paper provide further support for this mediational hypothesis, in which mood is the distal cause of the illusion of control operating through activity level, the proximal cause. In Study 1, the probability of responding, P(R), was found to be a mediator variable between the depressive symptoms and the judgments of control. In Study 2, we intervened directly on the mediator variable: The P(R) for both depressed and nondepressed participants was manipulated through instructions. Our results confirm that P(R) manipulation produced differences in the participants' perceptions of uncontrollability. Importantly, the intervention on the mediator variable cancelled the effect of the distal cause; the participants' judgments of control were no longer mood dependent when the P(R) was manipulated. This result supports the hypothesis that the so-called depressive realism effect is actually mediated by the probability of responding.

  17. Transition metal-free intramolecular regioselective couplings of aliphatic and aromatic C-H bonds.

    PubMed

    Tian, Hua; Yang, Haijun; Zhu, Changjin; Fu, Hua

    2016-01-29

    Cross-dehydrogenative couplings of two different C-H bonds have emerged as an attractive goal in organic synthesis. However, achieving regioselective C-H activation is a great challenge because C-H bonds are ubiquitous in organic compounds. Actually, the regioselective couplings promoted by enzymes are a common occurrence in nature. Herein, we have developed simple, efficient and general transition metal-free intramolecular couplings of alphatic and aromatic C-H bonds. The protocol uses readily available aryl triazene as the radical initiator, cheap K2S2O8 as the oxidant, and the couplings were performed well with excellent tolerance of functional groups. Interestingly, α-carbon configuration of some amino acid residues in the substrates was kept after the reactions, and the couplings for substrates with substituted phenylalanine residues exhibited complete β-carbon diastereoselectivity for induction of the chiral α-carbon. Therefore, the present study should provide a novel strategy for regioselective cross-dehydrogenative couplings of two different C-H bonds.

  18. Scalable and sustainable electrochemical allylic C-H oxidation

    NASA Astrophysics Data System (ADS)

    Horn, Evan J.; Rosen, Brandon R.; Chen, Yong; Tang, Jiaze; Chen, Ke; Eastgate, Martin D.; Baran, Phil S.

    2016-05-01

    New methods and strategies for the direct functionalization of C-H bonds are beginning to reshape the field of retrosynthetic analysis, affecting the synthesis of natural products, medicines and materials. The oxidation of allylic systems has played a prominent role in this context as possibly the most widely applied C-H functionalization, owing to the utility of enones and allylic alcohols as versatile intermediates, and their prevalence in natural and unnatural materials. Allylic oxidations have featured in hundreds of syntheses, including some natural product syntheses regarded as “classics”. Despite many attempts to improve the efficiency and practicality of this transformation, the majority of conditions still use highly toxic reagents (based around toxic elements such as chromium or selenium) or expensive catalysts (such as palladium or rhodium). These requirements are problematic in industrial settings; currently, no scalable and sustainable solution to allylic oxidation exists. This oxidation strategy is therefore rarely used for large-scale synthetic applications, limiting the adoption of this retrosynthetic strategy by industrial scientists. Here we describe an electrochemical C-H oxidation strategy that exhibits broad substrate scope, operational simplicity and high chemoselectivity. It uses inexpensive and readily available materials, and represents a scalable allylic C-H oxidation (demonstrated on 100 grams), enabling the adoption of this C-H oxidation strategy in large-scale industrial settings without substantial environmental impact.

  19. Iron-Catalyzed Oxyfunctionalization of Aliphatic Amines at Remote Benzylic C-H Sites.

    PubMed

    Mbofana, Curren T; Chong, Eugene; Lawniczak, James; Sanford, Melanie S

    2016-09-02

    We report the development of an iron-catalyzed method for the selective oxyfunctionalization of benzylic C(sp(3))-H bonds in aliphatic amine substrates. This transformation is selective for benzylic C-H bonds that are remote (i.e., at least three carbons) from the amine functional group. High site selectivity is achieved by in situ protonation of the amine with trifluoroacetic acid, which deactivates more traditionally reactive C-H sites that are α to nitrogen. The scope and synthetic utility of this method are demonstrated via the synthesis and derivatization of a variety of amine-containing, biologically active molecules.

  20. A Chiral Nitrogen Ligand for Enantioselective, Iridium-Catalyzed Silylation of Aromatic C-H Bonds.

    PubMed

    Su, Bo; Zhou, Tai-Gang; Li, Xian-Wei; Shao, Xiao-Ru; Xu, Pei-Lin; Wu, Wen-Lian; Hartwig, John F; Shi, Zhang-Jie

    2017-01-19

    Iridium catalysts containing dative nitrogen ligands are highly active for the borylation and silylation of C-H bonds, but chiral analogs of these catalysts for enantioselective silylation reactions have not been developed. We report a new chiral pyridinyloxazoline ligand for enantioselective, intramolecular silylation of symmetrical diarylmethoxy diethylsilanes. Regioselective and enantioselective silylation of unsymmetrical substrates was also achieved in the presence of this newly developed system. Preliminary mechanistic studies imply that C-H bond cleavage is irreversible, but not the rate-determining step.

  1. Catalytic intermolecular amination of C-H bonds: method development and mechanistic insights.

    PubMed

    Fiori, Kristin Williams; Du Bois, J

    2007-01-24

    Reaction methodology for intermolecular C-H amination of benzylic and 3 degrees C-H bonds is described. This process uses the starting alkane as the limiting reagent, gives optically pure tetrasubstituted amines through stereospecific insertion into enantiomeric 3 degrees centers, displays high chemoselectivity for benzylic oxidation, and enables the facile preparation of isotopically enriched 15N-labeled compounds. Access to substituted amines, amino alcohols, and diamines is thereby made possible in a single transformation. Important information relevant to understanding the initial steps in the catalytic cycle, reaction chemoselectivity, the nature of the active oxidant, and pathways for catalyst inactivation has been gained through mechanistic analysis; these studies are also presented.

  2. Selective intermolecular amination of C-H bonds at tertiary carbon centers.

    PubMed

    Roizen, Jennifer L; Zalatan, David N; Du Bois, J

    2013-10-18

    C-H insertion: A method for intermolecular amination of tertiary CH bonds is described that uses limiting amounts of substrate and a convenient phenol-derived nitrogen source. Structure-selectivity and mechanistic studies suggest that steric interaction between the substrate and active oxidant is the principal determinant of product selectivity.

  3. Teaching enantioselectivity to C-H bond functionalizations: initial steps of a rather long shot.

    PubMed

    Cramer, Nicolai

    2012-01-01

    The direct functionalization of non-activated C-H bonds, especially in an enantioselective manner, requires metal catalysts equipped with ligands with specifically designed properties. Examples for asymmetric C(sp(2))-H and C(sp(3))-H functionalizations using palladium- and rhodium catalysts are shown. This work was rewarded by the 2012 Werner Prize of the Swiss Chemical Society.

  4. Repression of p53 activity by Smyd2-mediated methylation.

    PubMed

    Huang, Jing; Perez-Burgos, Laura; Placek, Brandon J; Sengupta, Roopsha; Richter, Mario; Dorsey, Jean A; Kubicek, Stefan; Opravil, Susanne; Jenuwein, Thomas; Berger, Shelley L

    2006-11-30

    Specific sites of lysine methylation on histones correlate with either activation or repression of transcription. The tumour suppressor p53 (refs 4-7) is one of only a few non-histone proteins known to be regulated by lysine methylation. Here we report a lysine methyltransferase, Smyd2, that methylates a previously unidentified site, Lys 370, in p53. This methylation site, in contrast to the known site Lys 372, is repressing to p53-mediated transcriptional regulation. Smyd2 helps to maintain low concentrations of promoter-associated p53. We show that reducing Smyd2 concentrations by short interfering RNA enhances p53-mediated apoptosis. We find that Set9-mediated methylation of Lys 372 inhibits Smyd2-mediated methylation of Lys 370, providing regulatory cross-talk between post-translational modifications. In addition, we show that the inhibitory effect of Lys 372 methylation on Lys 370 methylation is caused, in part, by blocking the interaction between p53 and Smyd2. Thus, similar to histones, p53 is subject to both activating and repressing lysine methylation. Our results also predict that Smyd2 may function as a putative oncogene by methylating p53 and repressing its tumour suppressive function.

  5. Caspase-9 mediates Puma activation in UCN-01-induced apoptosis.

    PubMed

    Nie, C; Luo, Y; Zhao, X; Luo, N; Tong, A; Liu, X; Yuan, Z; Wang, C; Wei, Y

    2014-10-30

    The protein kinase inhibitor 7-hydroxystaurosporine (UCN-01) is one of the most potent and frequently used proapoptotic stimuli. The BH3-only molecule of Bcl-2 family proteins has been reported to contribute to UCN-01-induced apoptosis. Here we have found that UCN-01 triggers Puma-induced mitochondrial apoptosis pathway. Our data confirmed that Akt-FoxO3a pathway mediated Puma activation. Importantly, we elucidate the detailed mechanisms of Puma-induced apoptosis. Our data have also demonstrated that caspase-9 is a decisive molecule of Puma induction after UCN-01 treatment. Caspase-9 mediates apoptosis through two kinds of feedback loops. On the one hand, caspase-9 enhances Puma activation by cleaving Bcl-2 and Bcl-xL independent of caspase-3. On the other hand, caspase-9 directly activated caspase-3 in the presence of caspase-3. Caspase-3 could cleave XIAP in an another positive feedback loop to further sensitize cancer cells to UCN-01-induced apoptosis. Therefore, caspase-9 mediates Puma activation to determine the threshold for overcoming chemoresistance in cancer cells.

  6. Palladium-Catalyzed Allylic C-H Bond Functionalization of Olefins

    NASA Astrophysics Data System (ADS)

    Liu, Guosheng; Wu, Yichen

    Transition metal-mediated carbon-hydrogen bond cleavage and functionalization is a mechanistically interesting and synthetically attractive process. One of the important cases is the removal of a allylic hydrogen from an olefin by a PdII salt to yield a π-allylpalladium complex, followed by nucleophilic attack to efficient produce allylic derivatives. In contrast to the well-known allylic acetoxylation of cyclohexene, the reaction of open-chain olefins is fairly poor until recent several years. Some palladium catalytic systems have been reported to achieve allylic C-H functionalization, including acetoxylation, amination and alkylation of terminal alkenes. In the most of cases, ligand is crucial to the success of the transformation. This review surveys the recent development of palladium-catalyzed allylic C-H functionalziation of alkenes. These results promise a significant increase in the scope of olefin transformation.

  7. Catalytic C-H bond functionalisation chemistry: the case for quasi-heterogeneous catalysis.

    PubMed

    Reay, Alan J; Fairlamb, Ian J S

    2015-11-25

    This feature article examines the potential of heterogeneous Pd species to mediate catalytic C-H bond functionalisation processes employing suitable substrates (e.g. aromatic/heteroaromatic compounds). A focus is placed on the reactivity of supported and non-supported Pd nanoparticle (PdNPs) catalysts, in addition to the re-appropriation of well-established heterogeneous Pd catalysts such as Pd/C. Where possible, reasonable comparisons are made between PdNPs and traditional 'homogeneous' Pd precatalyst sources (which form PdNPs). The involvement of higher order Pd species in traditional cross-coupling processes, such as Mizoroki-Heck, Sonogashira and Suzuki-Miyaura reactions, allows the exemplification of potential future topics for study in the area of catalytic C-H bond functionalisation processes.

  8. Spillover-mediated feedforward-inhibition functionally segregates interneuron activity

    PubMed Central

    Coddington, Luke T.; Rudolph, Stephanie; Lune, Patrick Vande; Overstreet-Wadiche, Linda; Wadiche, Jacques I.

    2013-01-01

    Summary Neurotransmitter spillover represents a form of neural transmission not restricted to morphologically defined synaptic connections. Communication between climbing fibers (CFs) and molecular layer interneurons (MLIs) in the cerebellum is mediated exclusively by glutamate spillover. Here, we show how CF stimulation functionally segregates MLIs based on their location relative to glutamate release. Excitation of MLIs that reside within the domain of spillover diffusion coordinates inhibition of MLIs outside the diffusion limit. CF excitation of MLIs is dependent on extrasynaptic NMDA receptors that enhance the spatial and temporal spread of CF signaling. Activity mediated by functionally segregated MLIs converges onto neighboring Purkinje cells (PCs) to generate a long-lasting biphasic change in inhibition. These data demonstrate how glutamate release from single CFs modulates excitability of neighboring PCs, thus expanding the influence of CFs on cerebellar cortical activity in a manner not predicted by anatomical connectivity. PMID:23707614

  9. Nitric oxide mediates local activity-dependent excitatory synapse development.

    PubMed

    Nikonenko, Irina; Nikonenko, Alexander; Mendez, Pablo; Michurina, Tatyana V; Enikolopov, Grigori; Muller, Dominique

    2013-10-29

    Learning related paradigms play an important role in shaping the development and specificity of synaptic networks, notably by regulating mechanisms of spine growth and pruning. The molecular events underlying these synaptic rearrangements remain poorly understood. Here we identify NO signaling as a key mediator of activity-dependent excitatory synapse development. We find that chronic blockade of NO production in vitro and in vivo interferes with the development of hippocampal and cortical excitatory spine synapses. The effect results from a selective loss of activity-mediated spine growth mechanisms and is associated with morphological and functional alterations of remaining synapses. These effects of NO are mediated by a cGMP cascade and can be reproduced or prevented by postsynaptic expression of vasodilator-stimulated phosphoprotein phospho-mimetic or phospho-resistant mutants. In vivo analyses show that absence of NO prevents the increase in excitatory synapse density induced by environmental enrichment and interferes with the formation of local clusters of excitatory synapses. We conclude that NO plays an important role in regulating the development of excitatory synapses by promoting local activity-dependent spine-growth mechanisms.

  10. PKG-1α mediates GATA4 transcriptional activity.

    PubMed

    Ma, Yanlin; Wang, Jun; Yu, Yanhong; Schwartz, Robert J

    2016-06-01

    GATA4, a zinc-finger transcription factor, is central for cardiac development and diseases. Here we show that GATA4 transcriptional activity is mediated by cell signaling via cGMP dependent PKG-1α activity. Protein kinase G (PKG), a serine/tyrosine specific kinase is the major effector of cGMP signaling. We observed enhanced transcriptional activity elicited by co-expressed GATA4 and PKG-1α. Phosphorylation of GATA4 by PKG-1α was detected on serine 261 (S261), while the C-terminal activation domain of GATA4 associated with PKG-1α. GATA4's DNA binding activity was enhanced by PKG-1α via by both phosphorylation and physical association. More importantly, a number of human disease-linked GATA4 mutants exhibited impaired S261 phosphorylation, pointing to defective S261 phosphorylation in the elaboration of human heart diseases. We showed S261 phosphorylation was favored by PKG-1α but not by PKA, and several other kinase signaling pathways such as MAPK and PKC. Our observations demonstrate that cGMP-PKG signaling mediates transcriptional activity of GATA4 and links defective GATA4 and PKG-1α mutations to the development of human heart disease.

  11. Interneuron-mediated inhibition synchronizes neuronal activity during slow oscillation

    PubMed Central

    Chen, Jen-Yung; Chauvette, Sylvain; Skorheim, Steven; Timofeev, Igor; Bazhenov, Maxim

    2012-01-01

    The signature of slow-wave sleep in the electroencephalogram (EEG) is large-amplitude fluctuation of the field potential, which reflects synchronous alternation of activity and silence across cortical neurons. While initiation of the active cortical states during sleep slow oscillation has been intensively studied, the biological mechanisms which drive the network transition from an active state to silence remain poorly understood. In the current study, using a combination of in vivo electrophysiology and thalamocortical network simulation, we explored the impact of intrinsic and synaptic inhibition on state transition during sleep slow oscillation. We found that in normal physiological conditions, synaptic inhibition controls the duration and the synchrony of active state termination. The decline of interneuron-mediated inhibition led to asynchronous downward transition across the cortical network and broke the regular slow oscillation pattern. Furthermore, in both in vivo experiment and computational modelling, we revealed that when the level of synaptic inhibition was reduced significantly, it led to a recovery of synchronized oscillations in the form of seizure-like bursting activity. In this condition, the fast active state termination was mediated by intrinsic hyperpolarizing conductances. Our study highlights the significance of both intrinsic and synaptic inhibition in manipulating sleep slow rhythms. PMID:22641778

  12. Pd-catalyzed C-H fluorination with nucleophilic fluoride.

    PubMed

    McMurtrey, Kate B; Racowski, Joy M; Sanford, Melanie S

    2012-08-17

    The palladium-catalyzed C-H fluorination of 8-methylquinoline derivatives with nucleophilic fluoride is reported. This transformation involves the use of AgF as the fluoride source in combination with a hypervalent iodine oxidant. Both the scope and mechanism of the reaction are discussed.

  13. Project T.E.A.C.H.: An Evaluative Study.

    ERIC Educational Resources Information Center

    Howarth, Les

    A survey of 17 graduates of Project T.E.A.C.H. (Teacher Effectiveness and Classroom Handling), an inservice education program offered through the Ontario (Canada) Public School Men Teacher's Association in conjunction with Lesley College, used closed- and open-ended questions to obtain evaluations of the project's effectiveness. Five project areas…

  14. Emerging activity in bilayered dispersions with wake-mediated interactions

    NASA Astrophysics Data System (ADS)

    Bartnick, Jörg; Kaiser, Andreas; Löwen, Hartmut; Ivlev, Alexei V.

    2016-06-01

    In a bilayered system of particles with wake-mediated interactions, the action-reaction symmetry for the effective forces between particles of different layers is broken. Under quite general conditions we show that, if the interaction nonreciprocity exceeds a certain threshold, this creates an active dispersion of self-propelled clusters of Brownian particles. The emerging activity promotes unusual melting scenarios and an enormous diffusivity in the dense fluid. Our results are obtained by computer simulation and analytical theory and can be verified in experiments with colloidal dispersions and complex plasmas.

  15. Chelation-assisted Pd-catalysed ortho-selective oxidative C-H/C-H cross-coupling of aromatic carboxylic acids with arenes and intramolecular Friedel-Crafts acylation: one-pot formation of fluorenones.

    PubMed

    Sun, Denan; Li, Bijin; Lan, Jingbo; Huang, Quan; You, Jingsong

    2016-03-04

    Pd-Catalysed ortho-selective oxidative C-H/C-H cross-coupling of aromatic carboxylic acids with arenes and subsequent intramolecular Friedel-Crafts acylation has been accomplished for the first time through a chelation-assisted C-H activation strategy. Starting from the readily available substrates, a variety of fluorenone derivatives are obtained in one pot. The direct use of naturally occurring carboxylic acid functionalities as directing groups avoids unnecessary steps for installation and removal of an extra directing group.

  16. Weak coordination as a powerful means for developing broadly useful C-H functionalization reactions.

    PubMed

    Engle, Keary M; Mei, Tian-Sheng; Wasa, Masayuki; Yu, Jin-Quan

    2012-06-19

    Reactions that convert carbon-hydrogen (C-H) bonds into carbon-carbon (C-C) or carbon-heteroatom (C-Y) bonds are attractive tools for organic chemists, potentially expediting the synthesis of target molecules through new disconnections in retrosynthetic analysis. Despite extensive inorganic and organometallic study of the insertion of homogeneous metal species into unactivated C-H bonds, practical applications of this technology in organic chemistry are still rare. Only in the past decade have metal-catalyzed C-H functionalization reactions become more widely utilized in organic synthesis. Research in the area of homogeneous transition metal-catalyzed C-H functionalization can be broadly grouped into two subfields. They reflect different approaches and goals and thus have different challenges and opportunities. One approach involves reactions of completely unfunctionalized aromatic and aliphatic hydrocarbons, which we refer to as "first functionalization". Here the substrates are nonpolar and hydrophobic and thus interact very weakly with polar metal species. To overcome this weak affinity and drive metal-mediated C-H cleavage, chemists often use hydrocarbon substrates in large excess (for example, as solvent). Because highly reactive metal species are needed in first functionalization, controlling the chemoselectivity to avoid overfunctionalization is often difficult. Additionally, because both substrates and products are comparatively low-value chemicals, developing cost-effective catalysts with exceptionally high turnover numbers that are competitive with alternatives (including heterogeneous catalysts) is challenging. Although an exciting field, first functionalization is beyond the scope of this Account. The second subfield of C-H functionalization involves substrates containing one or more pre-existing functional groups, termed "further functionalization". One advantage of this approach is that the existing functional group (or groups) can be used to chelate

  17. Human Neutrophil-Mediated Nonoxidative Antifungal Activity against Cryptococcus neoformans

    PubMed Central

    Mambula, Salamatu S.; Simons, Elizabeth R.; Hastey, Ryan; Selsted, Michael E.; Levitz, Stuart M.

    2000-01-01

    It has long been appreciated that polymorphonuclear leukocytes (PMN) kill Cryptococcus neoformans, at least in part via generation of fungicidal oxidants. The aim of this study was to examine the contribution of nonoxidative mechanisms to the inhibition and killing of C. neoformans. Treatment of human PMN with inhibitors and scavengers of respiratory burst oxidants only partially reversed anticryptococcal activity, suggesting that both oxidative and nonoxidative mechanisms were operative. To define the mediators of nonoxidative anticryptococcal activity, PMN were fractionated into cytoplasmic, primary (azurophil) granule, and secondary (specific) granule fractions. Incubation of C. neoformans with these fractions for 18 h resulted in percents inhibition of growth of 67.4 ± 3.4, 84.6 ± 4.4, and 29.2 ± 10.5 (mean ± standard error, n = 3), respectively. Anticryptococcal activity of the cytoplasmic fraction was abrogated by zinc and depletion of calprotectin. Antifungal activity of the primary granules was significantly reduced by pronase treatment, boiling, high ionic strength, and magnesium but not calcium. Fractionation of the primary granules by reverse phase high-pressure liquid chromatography on a C4 column over an acetonitrile gradient revealed multiple peaks with anticryptococcal activity. Of these, peaks 1 and 6 had substantial fungistatic and fungicidal activity. Peak 1 was identified by acid-urea polyacrylamide gel electrophoresis (PAGE) and mass spectroscopy as human neutrophil proteins (defensins) 1 to 3. Analysis of peak 6 by sodium dodecyl sulfate-PAGE revealed multiple bands. Thus, human PMN have nonoxidative anticryptococcal activity residing principally in their cytoplasmic and primary granule fractions. Calprotectin mediates the cytoplasmic activity, whereas multiple proteins, including defensins, are responsible for activity of the primary granules. PMID:11035733

  18. Rhodium mediated bond activation: from synthesis to catalysis

    SciTech Connect

    Ho, Hung-An

    2012-01-01

    Recently, our lab has developed monoanionic tridentate ligand, ToR, showing the corresponding coordination chemistry and catalyst reactivity of magnesium, zirconium, zinc and iridium complexes. This thesis details synthetic chemistry, structural study and catalytic reactivity of the ToR-supported rhodium compounds. Tl[ToR] has been proved to be a superior ligand transfer agent for synthesizing rhodium complexes. The salt metathesis route of Tl[ToM] with [Rh(μ-Cl)(CO)]2 and [Rh(μ- Cl)(COE)]2 gives ToMRh(CO)2 (2.2) and ToMRhH(β3-C8H13) (3.1) respectively while Tl[ToM] with [Rh(μ-Cl)(CO)]2 affords ToPRh(CO)2 (2.3). 2.2 reacts with both strong and weak electrophiles, resulting in the oxazoline N-attacked and the metal center-attacked compounds correspondingly. Using one of the metal center-attacked electrophiles, 2.3 was demonstrated to give high diastereoselectivity. Parallel to COE allylic C-H activation complex 3.1, the propene and allylbenzene allylic C-H activation products have also been synthesized. The subsequent functionalization attempts have been examined by treating with Brønsted acids, Lewis acids, electrophiles, nucleophiles, 1,3-dipolar reagents and reagents containing multiple bonds able to be inserted. Various related complexes have been obtained under these conditions, in which one of the azide insertion compounds reductively eliminates to give an allylic functionalization product stoichiometrically. 3.1 reacts with various primary alcohols to give the decarbonylation dihydride complex ToMRh(H)2CO (4.1). 4.1 shows catalytic reactivity for primary alcohol decarbonylation under a photolytic condition. Meanwhile, 2.2 has been found to be more reactive than 4.1 for catalytic alcohol decarbonylation under the same condition. Various complexes and primary

  19. Determining the vibrational pattern via overtone cold spectra: C-H methyl stretches of propyne.

    PubMed

    Portnov, Alex; Bespechansky, Evgeny; Ganot, Yuval; Rosenwaks, Salman; Bar, Ilana

    2005-06-08

    Vibrationally mediated photodissociation and photoacoustic (PA) spectroscopy were employed for studying the intramolecular dynamics of propyne initially excited to the first through fourth overtone of methyl C-H stretching modes. Room-temperature PA and jet-cooled action spectra, monitoring the absorption of the parent and the yield of the ensuing H photofragments, respectively, were obtained. The PA spectra exhibit mainly broad features, while the action spectra, due to inhomogeneous structure reduction, expose multiple peaks of recognizable shapes in the differing overtone manifolds. Symmetric rotor simulations of the band contours of the action spectra allowed retrieving of band origins and linewidths. The linewidths of the bands in each manifold enabled estimates for energy redistribution times out of the corresponding states to the bath states, the times ranging from 18+/-6 ps for two quanta of C-H excitation to subpicosecond for five quanta. The data were also analyzed in terms of a normal-mode model and a joint local-/normal-mode model. These models enabled determination of harmonic frequencies, anharmonicities, and interaction parameters reproducing the observed data in all monitored regions and provided spectral assignments. The measured Doppler profiles were well fitted by Gaussians with widths suggesting low average translational energies for the released H photofragments. These low energies and their similarities to those for dissociation of propyne isotopomers preexcited to acetylenic C-H stretches were ascribed to an indirect dissociation process occurring after internal conversion to the ground electronic state and isomerization to allene.

  20. Metal-catalysed azidation of tertiary C-H bonds suitable for late-stage functionalization.

    PubMed

    Sharma, Ankit; Hartwig, John F

    2015-01-29

    Many enzymes oxidize unactivated aliphatic C-H bonds selectively to form alcohols; however, biological systems do not possess enzymes that catalyse the analogous aminations of C-H bonds. The absence of such enzymes limits the discovery of potential medicinal candidates because nitrogen-containing groups are crucial to the biological activity of therapeutic agents and clinically useful natural products. In one prominent example illustrating the importance of incorporating nitrogen-based functionality, the conversion of the ketone of erythromycin to the -N(Me)CH2- group in azithromycin leads to a compound that can be dosed once daily with a shorter treatment time. For such reasons, synthetic chemists have sought catalysts that directly convert C-H bonds to C-N bonds. Most currently used catalysts for C-H bond amination are ill suited to the intermolecular functionalization of complex molecules because they require excess substrate or directing groups, harsh reaction conditions, weak or acidic C-H bonds, or reagents containing specialized groups on the nitrogen atom. Among C-H bond amination reactions, those forming a C-N bond at a tertiary alkyl group would be particularly valuable, because this linkage is difficult to form from ketones or alcohols that might be created in a biosynthetic pathway by oxidation. Here we report a mild, selective, iron-catalysed azidation of tertiary C-H bonds that occurs without excess of the valuable substrate. The reaction tolerates aqueous environments and is suitable for the functionalization of complex structures in the late stages of a multistep synthesis. Moreover, this azidation makes it possible to install a range of nitrogen-based functional groups, including those from Huisgen 'click' cycloadditions and the Staudinger ligation. We anticipate that these reactions will create opportunities to modify natural products, their precursors and their derivatives to produce analogues that contain different polarity and charge as a

  1. Metal-catalysed azidation of tertiary C-H bonds suitable for late-stage functionalization

    NASA Astrophysics Data System (ADS)

    Sharma, Ankit; Hartwig, John F.

    2015-01-01

    Many enzymes oxidize unactivated aliphatic C-H bonds selectively to form alcohols; however, biological systems do not possess enzymes that catalyse the analogous aminations of C-H bonds. The absence of such enzymes limits the discovery of potential medicinal candidates because nitrogen-containing groups are crucial to the biological activity of therapeutic agents and clinically useful natural products. In one prominent example illustrating the importance of incorporating nitrogen-based functionality, the conversion of the ketone of erythromycin to the -N(Me)CH2- group in azithromycin leads to a compound that can be dosed once daily with a shorter treatment time. For such reasons, synthetic chemists have sought catalysts that directly convert C-H bonds to C-N bonds. Most currently used catalysts for C-H bond amination are ill suited to the intermolecular functionalization of complex molecules because they require excess substrate or directing groups, harsh reaction conditions, weak or acidic C-H bonds, or reagents containing specialized groups on the nitrogen atom. Among C-H bond amination reactions, those forming a C-N bond at a tertiary alkyl group would be particularly valuable, because this linkage is difficult to form from ketones or alcohols that might be created in a biosynthetic pathway by oxidation. Here we report a mild, selective, iron-catalysed azidation of tertiary C-H bonds that occurs without excess of the valuable substrate. The reaction tolerates aqueous environments and is suitable for the functionalization of complex structures in the late stages of a multistep synthesis. Moreover, this azidation makes it possible to install a range of nitrogen-based functional groups, including those from Huisgen `click' cycloadditions and the Staudinger ligation. We anticipate that these reactions will create opportunities to modify natural products, their precursors and their derivatives to produce analogues that contain different polarity and charge as a

  2. Palladium-catalyzed allylic C-H fluorination.

    PubMed

    Braun, Marie-Gabrielle; Doyle, Abigail G

    2013-09-04

    The first catalytic allylic C-H fluorination reaction using a nucleophilic fluoride source is reported. Under the influence of a Pd/Cr cocatalyst system, simple olefin substrates undergo fluorination with Et3N·3HF in good yields with high branched:linear regioselectivity. The mild conditions and broad scope make this reaction a powerful alternative to established methods for the preparation of allylic fluorides from prefunctionalized substrates.

  3. Elaboration of Copper-Oxygen Mediated C–H Activation Chemistry in Consideration of Future Fuel and Feedstock Generation

    PubMed Central

    Lee, Jung Yoon; Karlin, Kenneth D

    2015-01-01

    To contribute solutions for current energy concerns, improvements in the efficiency of C-H bond cleavage chemistry, e.g., selective oxidation of methane to methanol, could minimize losses in natural gas usage or produce feedstocks for fuels. Oxidative C-H activation is also a component of polysaccharide degradation, affording alternative biofuels from abundant biomass. Thus, an understanding of active-site chemistry in copper monooxygenases, those activating strong C-H bonds is briefly reviewed. Then, recent advances in the synthesis-generation and study of various copper-oxygen intermediates are highlighted. Of special interest are cupric-superoxide, Cu-hydroperoxo and Cu-oxy complexes. Such investigations can contribute to an enhanced future application of C-H oxidation or oxygenation processes using air, as concerning societal energy goals. PMID:25756327

  4. AhR-mediated and antiestrogenic activity of humic substances.

    PubMed

    Janosek, J; Bittner, M; Hilscherová, K; Bláha, L; Giesy, J P; Holoubek, I

    2007-04-01

    Humic substances (HS) were for decades regarded as inert in the ecosystems with respect to their possible toxicity. However, HS have been recently shown to elicit various adverse effects generally attributed to xenobiotics. In our study, we used MVLN and H4IIE-luc cell lines stably transfected with luciferase gene under control of estrogen receptor (ER) and Ah receptor (AhR; receptor connected with so-called dioxin-like toxicity) for assessment of anti/estrogenic and AhR-mediated effects of 12 commercially available humic substances. Out of those, five humic acids were shown to induce AhR-mediated activity with relative potencies related to TCDD 2.6 x 10(-8)-7.4 x 10(-8). Organic extracts of HS solutions also elicited high activities what means that lipophilic molecules are responsible for a great part of effect. However, relatively high activity remaining in extracted solution suggests also presence of polar AhR-agonists. Contribution of persistent organic compounds to the observed effects was ruled out by H(2)SO(4) treatment. Eight out of twelve HS elicited significant antiestrogenic effects with IC(50) ranging from 40 to 164 mg l(-1). The possible explanations of the antiestrogenic effect include sorption of 17-beta-estradiol (E2) on HS, changes in membrane permeability for E2 or another specific mechanism.

  5. Pt +-mediated activation of methane: theory and experiment

    NASA Astrophysics Data System (ADS)

    Heinemann, Christoph; Wesendrup, Ralf; Schwarz, Helmut

    1995-06-01

    A combined theoretical and experimental study on the Pt +-mediated activation of methane is presented. Dehydrogenation of CH 4 by thermalized Pt + cations (Pt + + CH 4 ← PtCH 2+ + H 2) proceeds along a doublet ground state potential energy surface and is found to be reversible under the conditions of Fourier transform ion-cyclotron resonance mass spectrometry. The recently reported oxidation of the cationic platinum carbene PtCH 2+ by O 2 produces electronically excited Pt + cations, which are detected in the 4F9/2 state by means of charge-transfer bracketing experiments.

  6. Serum Inflammatory Mediators as Markers of Human Lyme Disease Activity

    PubMed Central

    Soloski, Mark J.; Crowder, Lauren A.; Lahey, Lauren J.; Wagner, Catriona A.

    2014-01-01

    Chemokines and cytokines are key signaling molecules that orchestrate the trafficking of immune cells, direct them to sites of tissue injury and inflammation and modulate their states of activation and effector cell function. We have measured, using a multiplex-based approach, the levels of 58 immune mediators and 7 acute phase markers in sera derived from of a cohort of patients diagnosed with acute Lyme disease and matched controls. This analysis identified a cytokine signature associated with the early stages of infection and allowed us to identify two subsets (mediator-high and mediator-low) of acute Lyme patients with distinct cytokine signatures that also differed significantly (p<0.0005) in symptom presentation. In particular, the T cell chemokines CXCL9 (MIG), CXCL10 (IP-10) and CCL19 (MIP3B) were coordinately increased in the mediator-high group and levels of these chemokines could be associated with seroconversion status and elevated liver function tests (p = 0.027 and p = 0.021 respectively). There was also upregulation of acute phase proteins including CRP and serum amyloid A. Consistent with the role of CXCL9/CXCL10 in attracting immune cells to the site of infection, CXCR3+ CD4 T cells are reduced in the blood of early acute Lyme disease (p = 0.01) and the decrease correlates with chemokine levels (p = 0.0375). The levels of CXCL9/10 did not relate to the size or number of skin lesions but elevated levels of serum CXCL9/CXCL10 were associated with elevated liver enzymes levels. Collectively these results indicate that the levels of serum chemokines and the levels of expression of their respective chemokine receptors on T cell subsets may prove to be informative biomarkers for Lyme disease and related to specific disease manifestations. PMID:24740099

  7. The Impact of EFL Teachers' Mediation in Wiki-Mediated Collaborative Writing Activities on Student-Student Collaboration

    ERIC Educational Resources Information Center

    Alghasab, Maha

    2016-01-01

    This paper focuses on how teachers mediate wiki collaborative writing activities, and the impact of their mediations on students' collaboration. It is based on a study conducted with three English as a Foreign Language (EFL) teachers and their students (aged 17-18 years) at two government-funded girls' high schools in Kuwait. The selected groups…

  8. Synthesis of antiviral tetrahydrocarbazole derivatives by photochemical and acid-catalyzed C-H functionalization via intermediate peroxides (CHIPS).

    PubMed

    Gulzar, Naeem; Klussmann, Martin

    2014-06-20

    The direct functionalization of C-H bonds is an important and long standing goal in organic chemistry. Such transformations can be very powerful in order to streamline synthesis by saving steps, time and material compared to conventional methods that require the introduction and removal of activating or directing groups. Therefore, the functionalization of C-H bonds is also attractive for green chemistry. Under oxidative conditions, two C-H bonds or one C-H and one heteroatom-H bond can be transformed to C-C and C-heteroatom bonds, respectively. Often these oxidative coupling reactions require synthetic oxidants, expensive catalysts or high temperatures. Here, we describe a two-step procedure to functionalize indole derivatives, more specifically tetrahydrocarbazoles, by C-H amination using only elemental oxygen as oxidant. The reaction uses the principle of C-H functionalization via Intermediate PeroxideS (CHIPS). In the first step, a hydroperoxide is generated oxidatively using visible light, a photosensitizer and elemental oxygen. In the second step, the N-nucleophile, an aniline, is introduced by Brønsted-acid catalyzed activation of the hydroperoxide leaving group. The products of the first and second step often precipitate and can be conveniently filtered off. The synthesis of a biologically active compound is shown.

  9. Controlling factors for C-H functionalization versus cyclopropanation of dihydronaphthalenes.

    PubMed

    Nadeau, Etienne; Ventura, Dominic L; Brekan, Jonathan A; Davies, Huw M L

    2010-03-19

    Rhodium(II)-catalyzed reactions of vinyldiazoacetates with dihydronaphthalenes were systematically studied. These substrates underwent cyclopropanantion and/or the combined C-H activation/Cope rearrangement in good overall yield and with good diastereo- and enantiocontrol. The selectivity of these reactions was profoundly influenced by the nature of the chiral catalyst, the vinyldiazoacetate, and the dihydronaphthalene. The best combinations for achieving the highest selectivity in the cyclopropanation and the combined C-H activation/Cope rearrangement of 1,2-dihydronaphthalenes are methyl 2-diazopent-3-enoate (2a)/Rh(2)(S-DOSP)(4) and methyl 3-(tert-butyldimethylsilyloxy)-2-diazopent-3-enoate (2b)/Rh(2)(S-PTAD)(4). These combinations are very effective at enantiodivergent reactions of 1-methyl-1,2-dihydronaphthalenes.

  10. Ferroptosis as a p53-mediated activity during tumour suppression.

    PubMed

    Jiang, Le; Kon, Ning; Li, Tongyuan; Wang, Shang-Jui; Su, Tao; Hibshoosh, Hanina; Baer, Richard; Gu, Wei

    2015-04-02

    Although p53-mediated cell-cycle arrest, senescence and apoptosis serve as critical barriers to cancer development, emerging evidence suggests that the metabolic activities of p53 are also important. Here we show that p53 inhibits cystine uptake and sensitizes cells to ferroptosis, a non-apoptotic form of cell death, by repressing expression of SLC7A11, a key component of the cystine/glutamate antiporter. Notably, p53(3KR), an acetylation-defective mutant that fails to induce cell-cycle arrest, senescence and apoptosis, fully retains the ability to regulate SLC7A11 expression and induce ferroptosis upon reactive oxygen species (ROS)-induced stress. Analysis of mutant mice shows that these non-canonical p53 activities contribute to embryonic development and the lethality associated with loss of Mdm2. Moreover, SLC7A11 is highly expressed in human tumours, and its overexpression inhibits ROS-induced ferroptosis and abrogates p53(3KR)-mediated tumour growth suppression in xenograft models. Our findings uncover a new mode of tumour suppression based on p53 regulation of cystine metabolism, ROS responses and ferroptosis.

  11. Mild Palladium Catalyzed ortho C-H Bond Functionalizations of Aniline Derivatives.

    PubMed

    Tischler, Ms Orsolya; Tóth, Mr Balázs; Novák, Zoltán

    2017-02-01

    This account collects the developments and transformations which avoid the utilization of harsh reaction conditions in the field of palladium catalyzed, ortho-directed C-H activation of aniline derivatives from the first attempts to up-to-date results, including the results of our research laboratory. The discussed functionalizations performed under mild conditions include acylation, olefination, arylation, alkylation, alkoxylation reactions. Beside the optimization studies and the synthetic applications mechanistic investigations are also presented.

  12. The antileishmanial activity of xanthohumol is mediated by mitochondrial inhibition.

    PubMed

    Monzote, Lianet; Lackova, Alexandra; Staniek, Katrin; Steinbauer, Silvia; Pichler, Gerald; Jäger, Walter; Gille, Lars

    2016-12-12

    Xanthohumol (Xan) is a natural constituent of human nutrition. Little is known about its actions on leishmanial parasites and their mitochondria as putative target. Therefore, we determined the antileishmanial activity of Xan and resveratrol (Res, as alternative compound with antileishmanial activity) with respect to mitochondria in Leishmania amazonensis promastigotes/amastigotes (LaP/LaA) in comparison with their activity in peritoneal macrophages from mouse (PMM) and macrophage cell line J774A.1 (J774). Mechanistic studies were conducted in Leishmania tarentolae promastigotes (LtP) and mitochondrial fractions isolated from LtP. Xan and Res demonstrated antileishmanial activity in LaA [half inhibitory concentration (IC50): Xan 7 µ m, Res 14 µ m]; while they had less influence on the viability of PMM (IC50: Xan 70 µ m, Res >438 µ m). In contrast to Res, Xan strongly inhibited oxygen consumption in Leishmania (LtP) but not in J774 cells. This was based on the inhibition of the mitochondrial electron transfer complex II/III by Xan, which was less pronounced with Res. Neither Xan nor Res increased mitochondrial superoxide release in LtP, while both decreased the mitochondrial membrane potential in LtP. Bioenergetic studies showed that LtP mitochondria have no spare respiratory capacity in contrast to mitochondria in J774 cells and can therefore much less adapt to stress by mitochondrial inhibitors, such as Xan. These data show that Xan may have antileishmanial activity, which is mediated by mitochondrial inhibition.

  13. Polyoxometalate active charge-transfer material for mediated redox flow battery

    DOEpatents

    Anderson, Travis Mark; Hudak, Nicholas; Staiger, Chad; Pratt, Harry

    2017-01-17

    Redox flow batteries including a half-cell electrode chamber coupled to a current collecting electrode are disclosed herein. In a general embodiment, a separator is coupled to the half-cell electrode chamber. The half-cell electrode chamber comprises a first redox-active mediator and a second redox-active mediator. The first redox-active mediator and the second redox-active mediator are circulated through the half-cell electrode chamber into an external container. The container includes an active charge-transfer material. The active charge-transfer material has a redox potential between a redox potential of the first redox-active mediator and a redox potential of the second redox-active mediator. The active charge-transfer material is a polyoxometalate or derivative thereof. The redox flow battery may be particularly useful in energy storage solutions for renewable energy sources and for providing sustained power to an electrical grid.

  14. Amphetamine activates calcium channels through dopamine transporter-mediated depolarization.

    PubMed

    Cameron, Krasnodara N; Solis, Ernesto; Ruchala, Iwona; De Felice, Louis J; Eltit, Jose M

    2015-11-01

    Amphetamine (AMPH) and its more potent enantiomer S(+)AMPH are psychostimulants used therapeutically to treat attention deficit hyperactivity disorder and have significant abuse liability. AMPH is a dopamine transporter (DAT) substrate that inhibits dopamine (DA) uptake and is implicated in DA release. Furthermore, AMPH activates ionic currents through DAT that modify cell excitability presumably by modulating voltage-gated channel activity. Indeed, several studies suggest that monoamine transporter-induced depolarization opens voltage-gated Ca(2+) channels (CaV), which would constitute an additional AMPH mechanism of action. In this study we co-express human DAT (hDAT) with Ca(2+) channels that have decreasing sensitivity to membrane depolarization (CaV1.3, CaV1.2 or CaV2.2). Although S(+)AMPH is more potent than DA in transport-competition assays and inward-current generation, at saturating concentrations both substrates indirectly activate voltage-gated L-type Ca(2+) channels (CaV1.3 and CaV1.2) but not the N-type Ca(2+) channel (CaV2.2). Furthermore, the potency to achieve hDAT-CaV electrical coupling is dominated by the substrate affinity on hDAT, with negligible influence of L-type channel voltage sensitivity. In contrast, the maximal coupling-strength (defined as Ca(2+) signal change per unit hDAT current) is influenced by CaV voltage sensitivity, which is greater in CaV1.3- than in CaV1.2-expressing cells. Moreover, relative to DA, S(+)AMPH showed greater coupling-strength at concentrations that induced relatively small hDAT-mediated currents. Therefore S(+)AMPH is not only more potent than DA at inducing hDAT-mediated L-type Ca(2+) channel currents but is a better depolarizing agent since it produces tighter electrical coupling between hDAT-mediated depolarization and L-type Ca(2+) channel activation.

  15. Seeing the B-A-C-H motif

    NASA Astrophysics Data System (ADS)

    Catravas, Palmyra

    2005-09-01

    Musical compositions can be thought of as complex, multidimensional data sets. Compositions based on the B-A-C-H motif (a four-note motif of the pitches of the last name of Johann Sebastian Bach) span several centuries of evolving compositional styles and provide an intriguing set for analysis since they contain a common feature, the motif, buried in dissimilar contexts. We will present analyses which highlight the content of this unusual set of pieces, with emphasis on visual display of information.

  16. Cyanate-mediated inhibition of neutrophil myeloperoxidase activity.

    PubMed Central

    Qian, M; Eaton, J W; Wolff, S P

    1997-01-01

    Cyanate (CNO-) forms spontaneously in solutions containing urea, and is present in urine and the body fluids of uraemic patients. We have explored the possibility that CNO- might be one of the unknown substances responsible for the reported impairment, by urine and uraemic plasma, of neutrophil oxidative metabolism (especially as measured by luminol-enhanced chemiluminescence). Luminol-enhanced chemiluminescence generated by human neutrophils derives predominantly from the activity of myeloperoxidase (MPO) which produces hypochlorous acid from H2O2 and Cl-. We hypothesized that CNO- (which resembles the 'pseudohalide' thiocyanate, an alternative substrate for MPO) might somehow interfere with the activity of MPO. In support of this, we find: (i) CNO- inhibits both peroxidative and halogenating activities of MPO and also inhibits the enzyme within intact human neutrophils; (ii) the inhibition is H2O2-dependent, irreversible, accompanied by covalent addition of [14C]CNO- (or a carbon-containing fragment thereof) to the enzyme; (iii) CNO- also inhibits Cl-/H2O2/MPO-mediated bacterial killing. Impairment of this arm of neutrophil bactericidal activity by CNO- formed from urea may be one factor in the risk of urinary-tract infection associated with urinary stasis and perhaps in the generalized increase in susceptibility to infection in uraemic patients. PMID:9337863

  17. H2S mediated thermal and photochemical methane activation

    PubMed Central

    Baltrusaitis, Jonas; de Graaf, Coen; Broer, Ria; Patterson, Eric

    2013-01-01

    Sustainable, low temperature methods of natural gas activation are critical in addressing current and foreseeable energy and hydrocarbon feedstock needs. Large portions of natural gas resources are still too expensive to process due to their high content of hydrogen sulfide gas (H2S) in mixture with methane, CH4, altogether deemed as sub-quality or “sour” gas. We propose a unique method for activating this “sour” gas to form a mixture of sulfur-containing hydrocarbon intermediates, CH3SH and CH3SCH3, and an energy carrier, such as H2. For this purpose, we computationally investigated H2S mediated methane activation to form a reactive CH3SH species via direct photolysis of sub-quality natural gas. Photoexcitation of hydrogen sulfide in the CH4+H2S complex results in a barrier-less relaxation via a conical intersection to form a ground state CH3SH+H2 complex. The resulting CH3SH can further be heterogeneously coupled over acidic catalysts to form higher hydrocarbons while the H2 can be used as a fuel. This process is very different from a conventional thermal or radical-based processes and can be driven photolytically at low temperatures, with enhanced controllability over the process conditions currently used in industrial oxidative natural gas activation. Finally, the proposed process is CO2 neutral, as opposed to the currently industrially used methane steam reforming (SMR). PMID:24150813

  18. H2S-mediated thermal and photochemical methane activation.

    PubMed

    Baltrusaitis, Jonas; de Graaf, Coen; Broer, Ria; Patterson, Eric V

    2013-12-02

    Sustainable, low-temperature methods for natural gas activation are critical in addressing current and foreseeable energy and hydrocarbon feedstock needs. Large portions of natural gas resources are still too expensive to process due to their high content of hydrogen sulfide gas (H2S) mixed with methane, deemed altogether as sub-quality or "sour" gas. We propose a unique method of activation to form a mixture of sulfur-containing hydrocarbon intermediates, CH3SH and CH3SCH3 , and an energy carrier such as H2. For this purpose, we investigated the H2S-mediated methane activation to form a reactive CH3SH species by means of direct photolysis of sub-quality natural gas. Photoexcitation of hydrogen sulfide in the CH4 + H2S complex resulted in a barrierless relaxation by a conical intersection to form a ground-state CH3SH + H2 complex. The resulting CH3SH could further be coupled over acidic catalysts to form higher hydrocarbons, and the resulting H2 used as a fuel. This process is very different from conventional thermal or radical-based processes and can be driven photolytically at low temperatures, with enhanced control over the conditions currently used in industrial oxidative natural gas activation. Finally, the proposed process is CO2 neutral, as opposed to the current industrial steam methane reforming (SMR).

  19. Aqua mediated synthesis of bio-active compounds.

    PubMed

    Panda, Siva S

    2013-05-01

    Recently the aqueous medium has attracted the interest of organic chemists, and many. Moreover, in the past 20 years, the drug-discovery process has undergone extraordinary changes, and high-throughput biological screening of potential drug candidates has led to an ever-increasing demand for novel drug-like compounds. Noteworthy advantages were observed during the course of study on aqua mediated synthesis of compounds of medicinal importance. The established advantages of water as a solvent for reactions are, water is the most abundant and available resource on the planet and many biochemical processes occur in aqueous medium. This review will focus on describing new developments in the application of water in medicinal chemistry for the synthesis of bio-active compounds possessing various biological properties.

  20. INCREASED ENDOCRINE ACTIVITY OF XENOBIOTIC CHEMICALS AS MEDIATED BY METABOLIC ACTIVATION

    EPA Science Inventory

    This research is part of an effort to develop in vitro assays and QSARs applicable to untested chemicals on EPA inventories through study of estrogen receptor (ER) binding and estrogen mediated gene expression in fish. The current effort investigates metabolic activation of chemi...

  1. Fine Control over Site and Substrate Selectivity in Hydrogen Atom Transfer-Based Functionalization of Aliphatic C-H Bonds.

    PubMed

    Salamone, Michela; Carboni, Giulia; Bietti, Massimo

    2016-10-07

    The selective functionalization of unactivated aliphatic C-H bonds over intrinsically more reactive ones represents an ongoing challenge of synthetic chemistry. Here we show that in hydrogen atom transfer (HAT) from the aliphatic C-H bonds of alkane, ether, alcohol, amide, and amine substrates to the cumyloxyl radical (CumO(•)) fine control over site and substrate selectivity is achieved by means of acid-base interactions. Protonation of the amines and metal ion binding to amines and amides strongly deactivates the C-H bonds of these substrates toward HAT to CumO(•), providing a powerful method for selective functionalization of unactivated or intrinsically less reactive C-H bonds. With 5-amino-1-pentanol, site-selectivity has been drastically changed through protonation of the strongly activating NH2 group, with HAT that shifts to the C-H bonds that are adjacent to the OH group. In the intermolecular selectivity studies, trifluoroacetic acid, Mg(ClO4)2, and LiClO4 have been employed in a orthogonal fashion for selective functionalization of alkane, ether, alcohol, and amide (or amine) substrates in the presence of an amine (or amide) one. Ca(ClO4)2, that promotes deactivation of amines and amides by Ca(2+) binding, offers, moreover, the opportunity to selectively functionalize the C-H bonds of alkane, ether, and alcohol substrates in the presence of both amines and amides.

  2. Catalytic alkylation of remote C-H bonds enabled by proton-coupled electron transfer

    NASA Astrophysics Data System (ADS)

    Choi, Gilbert J.; Zhu, Qilei; Miller, David C.; Gu, Carol J.; Knowles, Robert R.

    2016-11-01

    Despite advances in hydrogen atom transfer (HAT) catalysis, there are currently no molecular HAT catalysts that are capable of homolysing the strong nitrogen-hydrogen (N-H) bonds of N-alkyl amides. The motivation to develop amide homolysis protocols stems from the utility of the resultant amidyl radicals, which are involved in various synthetically useful transformations, including olefin amination and directed carbon-hydrogen (C-H) bond functionalization. In the latter process—a subset of the classical Hofmann-Löffler-Freytag reaction—amidyl radicals remove hydrogen atoms from unactivated aliphatic C-H bonds. Although powerful, these transformations typically require oxidative N-prefunctionalization of the amide starting materials to achieve efficient amidyl generation. Moreover, because these N-activating groups are often incorporated into the final products, these methods are generally not amenable to the direct construction of carbon-carbon (C-C) bonds. Here we report an approach that overcomes these limitations by homolysing the N-H bonds of N-alkyl amides via proton-coupled electron transfer. In this protocol, an excited-state iridium photocatalyst and a weak phosphate base cooperatively serve to remove both a proton and an electron from an amide substrate in a concerted elementary step. The resultant amidyl radical intermediates are shown to promote subsequent C-H abstraction and radical alkylation steps. This C-H alkylation represents a catalytic variant of the Hofmann-Löffler-Freytag reaction, using simple, unfunctionalized amides to direct the formation of new C-C bonds. Given the prevalence of amides in pharmaceuticals and natural products, we anticipate that this method will simplify the synthesis and structural elaboration of amine-containing targets. Moreover, this study demonstrates that concerted proton-coupled electron transfer can enable homolytic activation of common organic functional groups that are energetically inaccessible using

  3. Catalytic alkylation of remote C-H bonds enabled by proton-coupled electron transfer.

    PubMed

    Choi, Gilbert J; Zhu, Qilei; Miller, David C; Gu, Carol J; Knowles, Robert R

    2016-11-10

    Despite advances in hydrogen atom transfer (HAT) catalysis, there are currently no molecular HAT catalysts that are capable of homolysing the strong nitrogen-hydrogen (N-H) bonds of N-alkyl amides. The motivation to develop amide homolysis protocols stems from the utility of the resultant amidyl radicals, which are involved in various synthetically useful transformations, including olefin amination and directed carbon-hydrogen (C-H) bond functionalization. In the latter process-a subset of the classical Hofmann-Löffler-Freytag reaction-amidyl radicals remove hydrogen atoms from unactivated aliphatic C-H bonds. Although powerful, these transformations typically require oxidative N-prefunctionalization of the amide starting materials to achieve efficient amidyl generation. Moreover, because these N-activating groups are often incorporated into the final products, these methods are generally not amenable to the direct construction of carbon-carbon (C-C) bonds. Here we report an approach that overcomes these limitations by homolysing the N-H bonds of N-alkyl amides via proton-coupled electron transfer. In this protocol, an excited-state iridium photocatalyst and a weak phosphate base cooperatively serve to remove both a proton and an electron from an amide substrate in a concerted elementary step. The resultant amidyl radical intermediates are shown to promote subsequent C-H abstraction and radical alkylation steps. This C-H alkylation represents a catalytic variant of the Hofmann-Löffler-Freytag reaction, using simple, unfunctionalized amides to direct the formation of new C-C bonds. Given the prevalence of amides in pharmaceuticals and natural products, we anticipate that this method will simplify the synthesis and structural elaboration of amine-containing targets. Moreover, this study demonstrates that concerted proton-coupled electron transfer can enable homolytic activation of common organic functional groups that are energetically inaccessible using

  4. Activation of AhR-mediated toxicity pathway by emerging ...

    EPA Pesticide Factsheets

    Polychlorinated diphenyl sulfides (PCDPSs) are a group of environmental pollutants for which limited toxicological information is available. This study tested the hypothesis that PCDPSs could activate the mammalian aryl hydrocarbon receptor (AhR) mediated toxicity pathways. Eighteen PCDPSs were tested in the H4IIE-luc transactivation assay, with 13/18 causing concentration-dependent AhR activation. Potencies of several congeners were similar to those of mono-ortho substituted polychlorinated biphenyls. A RNA sequencing (RNA-seq)-based transcriptomic analysis was performed on H4IIE cells treated with two PCDPS congeners, 2,2',3,3',4,5,6-hepta-CDPS, and 2,4,4',5-tetra-CDPS. Results of RNA-seq revealed a remarkable modulation on a relatively short gene list by exposure to the tested concentrations of PCDPSs, among which, Cyp1 responded with the greatest fold up-regulation. Both the identities of the modulated transcripts and the associated pathways were consistent with targets and pathways known to be modulated by other types of AhR agonists and there was little evidence for significant off-target effects within the cellular context of the H4IIE bioassay. The results suggest AhR activation as a toxicologically relevant mode of action for PCDPSs suggests the utility of AhR-related toxicity pathways for predicting potential hazards associated with PCDPS exposure in mammals and potentially other vertebrates. Polychlorinated diphenyl sulfides (PCDPSs) are a group of en

  5. Retinoic Acid-mediated Nuclear Receptor Activation and Hepatocyte Proliferation

    PubMed Central

    Bushue, Nathan; Wan, Yu-Jui Yvonne

    2016-01-01

    Due to their well-known differentiation and apoptosis-inducing abilities, retinoic acid (RA) and its analogs have strong anti-cancer efficacy in human cancers. However, in vivo RA is a liver mitogen. While speculation has persisted that RA-mediated signaling is likely involved in hepatocyte proliferation during liver regeneration, direct evidence is still required. Findings in support of this proposition include observations that a release of retinyl palmitate (the precursor of RA) occurs in liver stellate cells following liver injury. Nevertheless, the biological action of this released vitamin A is virtually unknown. More likely is that the released vitamin A is converted to RA, the biological form, and then bound to a specific receptor (retinoid x receptor; RXRα), which is most abundantly expressed in the liver. Considering the mitogenic effects of RA, the RA-activated RXRα would likely then influence hepatocyte proliferation and liver tissue repair. At present, the mechanism by which RA stimulates hepatocyte proliferation is largely unknown. This review summarizes the activation of nuclear receptors (peroxisome proliferator activated receptor-α, pregnane x receptor, constitutive androstane receptor, and farnesoid x receptor) in an RXRα dependent manner to induce hepatocyte proliferation, providing a link between RA and its proliferative role. PMID:27635169

  6. Enantioselective functionalization of allylic C-H bonds following a strategy of functionalization and diversification.

    PubMed

    Sharma, Ankit; Hartwig, John F

    2013-11-27

    We report the enantioselective functionalization of allylic C-H bonds in terminal alkenes by a strategy involving the installation of a temporary functional group at the terminal carbon atom by C-H bond functionalization, followed by the catalytic diversification of this intermediate with a broad scope of reagents. The method consists of a one-pot sequence of palladium-catalyzed allylic C-H bond oxidation under neutral conditions to form linear allyl benzoates, followed by iridium-catalyzed allylic substitution. This overall transformation forms a variety of chiral products containing a new C-N, C-O, C-S, or C-C bond at the allylic position in good yield with a high branched-to-linear selectivity and excellent enantioselectivity (ee ≤97%). The broad scope of the overall process results from separating the oxidation and functionalization steps; by doing so, the scope of nucleophile encompasses those sensitive to direct oxidative functionalization. The high enantioselectivity of the overall process is achieved by developing an allylic oxidation that occurs without acid to form the linear isomer with high selectivity. These allylic functionalization processes are amenable to an iterative sequence leading to (1,n)-functionalized products with catalyst-controlled diastereo- and enantioselectivity. The utility of the method in the synthesis of biologically active molecules has been demonstrated.

  7. Dirhodium Catalyzed C-H Arene Amination using Hydroxylamines

    PubMed Central

    Paudyal, Mahesh P.; Adebesin, Adeniyi Michael; Burt, Scott R.; Ess, Daniel H.; Ma, Zhiwei; Kürti, László; Falck, John R.

    2016-01-01

    Primary and N-alkyl arylamine motifs are key functional groups in pharmaceuticals, agrochemicals and functional materials as well as in bioactive natural products. However, there is a dearth of generally applicable methods for the direct replacement of aryl hydrogens with –NH2/-NH-alkyl moieties. Here, we present a mild dirhodium-catalyzed C-H amination for conversion of structurally diverse monocyclic and fused aromatics to the corresponding primary and N-alkyl arylamines using either NH2/NHalkyl-O-(sulfonyl)hydroxylamines as aminating agents; the relatively weak RSO2O-N bond functions as an internal oxidant. The methodology is operationally simple, scalable, and fast at or below ambient temperature, furnishing arylamines in moderate-to-good yields and with good regioselectivity. It can be readily extended to the synthesis of fused N-heterocycles. PMID:27609890

  8. Hydrogen-bond-assisted controlled C-H functionalization via adaptive recognition of a purine directing group.

    PubMed

    Kim, Hyun Jin; Ajitha, Manjaly J; Lee, Yongjae; Ryu, Jaeyune; Kim, Jin; Lee, Yunho; Jung, Yousung; Chang, Sukbok

    2014-01-22

    We have developed the Rh-catalyzed selective C-H functionalization of 6-arylpurines, in which the purine moiety directs the C-H bond activation of the aryl pendant. While the first C-H amination proceeds via the N1-chelation assistance, the subsequent second C-H bond activation takes advantage of an intramolecular hydrogen-bonding interaction between the initially formed amino group and one nitrogen atom, either N1 or N7, of the purinyl part. Isolation of a rhodacycle intermediate and the substrate variation studies suggest that N1 is the main active site for the C-H functionalization of both the first and second amination in 6-arylpurines, while N7 plays an essential role in controlling the degree of functionalization serving as an intramolecular hydrogen-bonding site in the second amination process. This pseudo-Curtin-Hammett situation was supported by density functional calculations, which suggest that the intramolecular hydrogen-bonding capability helps second amination by reducing the steric repulsion between the first installed ArNH and the directing group.

  9. Pd(II)-Catalyzed Alkylation of Tertiary Carbon via Directing-Group-Mediated C(sp(3))-H Activation: Synthesis of Chiral 1,1,2-Trialkyl Substituted Cyclopropanes.

    PubMed

    Hoshiya, Naoyuki; Takenaka, Kei; Shuto, Satoshi; Uenishi, Jun'ichi

    2016-01-04

    A Pd(OAc)2-catalyzed alkylation reaction of the tertiary carbon of chiral cyclopropane substrates with alkyl iodides and bromides via C(sp(3))-H activation has been developed. This is an elusive example of a C-H activation-mediated alkylation of tertiary carbon to effectively construct a quaternary carbon center. The alkylation proceeded with various alkyl halides, including those of functional groups, to provide a variety of chiral cis- and trans-1,1,2,-trialkyl substituted cyclopropanes of medicinal chemical importance.

  10. Enantiotopos-selective C-H oxygenation catalyzed by a supramolecular ruthenium complex.

    PubMed

    Frost, James R; Huber, Stefan M; Breitenlechner, Stefan; Bannwarth, Christoph; Bach, Thorsten

    2015-01-07

    Spirocyclic oxindoles undergo an enantioselective oxygenation reaction (nine examples; e.r. up to 97:3) upon catalysis by a chiral ruthenium porphyrin complex (1 mol %). The catalyst exhibits a lactam ring, which is responsible for substrate association through hydrogen bonds, and an active ruthenium center, which is in a defined spatial relationship to the oxygenation substrate. DFT calculations illustrate the perfect alignment of the active site with the reactive C-H bond and suggest--in line with the kinetic isotope effect--an oxygen rebound mechanism for the reaction.

  11. M-cadherin-mediated intercellular interactions activate satellite cell division.

    PubMed

    Marti, Merce; Montserrat, Núria; Pardo, Cristina; Mulero, Lola; Miquel-Serra, Laia; Rodrigues, Alexandre Miguel Cavaco; Andrés Vaquero, José; Kuebler, Bernd; Morera, Cristina; Barrero, María José; Izpisua Belmonte, Juan Carlos

    2013-11-15

    Adult muscle stem cells and their committed myogenic precursors, commonly referred to as the satellite cell population, are involved in both muscle growth after birth and regeneration after damage. It has been previously proposed that, under these circumstances, satellite cells first become activated, divide and differentiate, and only later fuse to the existing myofiber through M-cadherin-mediated intercellular interactions. Our data show that satellite cells fuse with the myofiber concomitantly to cell division, and only when the nuclei of the daughter cells are inside the myofiber, do they complete the process of differentiation. Here we demonstrate that M-cadherin plays an important role in cell-to-cell recognition and fusion, and is crucial for cell division activation. Treatment of satellite cells with M-cadherin in vitro stimulates cell division, whereas addition of anti-M-cadherin antibodies reduces the cell division rate. Our results suggest an alternative model for the contribution of satellite cells to muscle development, which might be useful in understanding muscle regeneration, as well as muscle-related dystrophies.

  12. Enzymatic hydroxylation of an unactivated methylene C-H bond guided by molecular dynamics simulations

    NASA Astrophysics Data System (ADS)

    Narayan, Alison R. H.; Jiménez-Osés, Gonzalo; Liu, Peng; Negretti, Solymar; Zhao, Wanxiang; Gilbert, Michael M.; Ramabhadran, Raghunath O.; Yang, Yun-Fang; Furan, Lawrence R.; Li, Zhe; Podust, Larissa M.; Montgomery, John; Houk, K. N.; Sherman, David H.

    2015-08-01

    The hallmark of enzymes from secondary metabolic pathways is the pairing of powerful reactivity with exquisite site selectivity. The application of these biocatalytic tools in organic synthesis, however, remains under-utilized due to limitations in substrate scope and scalability. Here, we report how the reactivity of a monooxygenase (PikC) from the pikromycin pathway is modified through computationally guided protein and substrate engineering, and applied to the oxidation of unactivated methylene C-H bonds. Molecular dynamics and quantum mechanical calculations were used to develop a predictive model for substrate scope, site selectivity and stereoselectivity of PikC-mediated C-H oxidation. A suite of menthol derivatives was screened computationally and evaluated through in vitro reactions, where each substrate adhered to the predicted models for selectivity and conversion to product. This platform was also expanded beyond menthol-based substrates to the selective hydroxylation of a variety of substrate cores ranging from cyclic to fused bicyclic and bridged bicyclic compounds.

  13. Acid-catalyzed oxidative addition of a C-H bond to a square planar d⁸ iridium complex.

    PubMed

    Hackenberg, Jason D; Kundu, Sabuj; Emge, Thomas J; Krogh-Jespersen, Karsten; Goldman, Alan S

    2014-06-25

    While the addition of C-H bonds to three-coordinate Ir(I) fragments is a central theme in the field of C-H bond activation, addition to square planar four-coordinate complexes is far less precedented. The dearth of such reactions may be attributed, at least in part, to kinetic factors elucidated in seminal work by Hoffmann. C-H additions to square planar carbonyl complexes in particular are unprecedented, in contrast to the extensive chemistry of oxidative addition of other substrates (e.g., H2, HX) to Vaska's Complex and related species. We report that Bronsted acids will catalyze the addition of the alkynyl C-H bond of phenylacetylene to the pincer complex (PCP)Ir(CO). The reaction occurs to give exclusively the trans-C-H addition product. Our proposed mechanism, based on kinetics and DFT calculations, involves initial protonation of (PCP)Ir(CO) to generate a highly active five-coordinate cationic intermediate, which forms a phenylacetylene adduct that is then deprotonated to give product.

  14. The PI3K-mediated activation of CRAC independently regulates adenylyl cyclase activation and chemotaxis.

    PubMed

    Comer, Frank I; Lippincott, Christopher K; Masbad, Joseph J; Parent, Carole A

    2005-01-26

    The ability of a cell to detect an external chemical signal and initiate a program of directed migration along a gradient comprises the fundamental process called chemotaxis. Investigations in Dictyostelium discoideum and neutrophils have established that pleckstrin homology (PH) domain-containing proteins that bind to the PI3K products PI(3,4)P2 and PI(3,4,5)P3, such as CRAC (cytosolic regulator of adenylyl cyclase) and Akt/PKB, translocate specifically to the leading edge of chemotaxing cells. CRAC is essential for the chemoattractant-mediated activation of the adenylyl cyclase ACA, which converts ATP into cAMP, the primary chemoattractant for D. discoideum. The mechanisms by which CRAC activates ACA remain to be determined. We now show that in addition to its essential role in the activation of ACA, CRAC is involved in regulating chemotaxis. Through mutagenesis, we show that these two functions are independently regulated downstream of PI3K. A CRAC mutant that has lost the capacity to bind PI3K products does not support chemotaxis and shows minimal ACA activation. Finally, overexpression of CRAC and various CRAC mutants show strong effects on ACA activation with little effect on chemotaxis. These findings establish that chemoattractant-mediated activation of PI3K is important for the CRAC-dependent regulation of both chemotaxis and adenylyl cyclase activation.

  15. Histone Acetyltransferase Complexes Can Mediate Transcriptional Activation by the Major Glucocorticoid Receptor Activation Domain

    PubMed Central

    Wallberg, Annika E.; Neely, Kristen E.; Gustafsson, Jan-Åke; Workman, Jerry L.; Wright, Anthony P. H.; Grant, Patrick A.

    1999-01-01

    Previous studies have shown that the Ada adapter proteins are important for glucocorticoid receptor (GR)-mediated gene activation in yeast. The N-terminal transactivation domain of GR, τ1, is dependent upon Ada2, Ada3, and Gcn5 for transactivation in vitro and in vivo. Using in vitro techniques, we demonstrate that the GR-τ1 interacts directly with the native Ada containing histone acetyltransferase (HAT) complex SAGA but not the related Ada complex. Mutations in τ1 that reduce τ1 transactivation activity in vivo lead to a reduced binding of τ1 to the SAGA complex and conversely, mutations increasing the transactivation activity of τ1 lead to an increased binding of τ1 to SAGA. In addition, the Ada-independent NuA4 HAT complex also interacts with τ1. GAL4-τ1-driven transcription from chromatin templates is stimulated by SAGA and NuA4 in an acetyl coenzyme A-dependent manner. Low-activity τ1 mutants reduce SAGA- and NuA4-stimulated transcription while high-activity τ1 mutants increase transcriptional activation, specifically from chromatin templates. Our results demonstrate that the targeting of native HAT complexes by the GR-τ1 activation domain mediates transcriptional stimulation from chromatin templates. PMID:10454542

  16. Rv3168 phosphotransferase activity mediates kanamycin resistance in Mycobacterium tuberculosis.

    PubMed

    Ahn, Jae-Woo; Kim, Kyung-Jin

    2013-11-28

    Tuberculosis is a worldwide epidemic disease caused by Mycobacterium tuberculosis, with an estimated one-third of the human population currently affected. Treatment of this disease with aminoglycoside antibiotics has become less effective owing to antibiotic resistance. Recent determination of the crystal structure of the M. tuberculosis Rv3168 protein suggests a structure similar to that of Enterococcus faecalis APH(3')-IIIa, and that this protein may be an aminoglycoside phosphotransferase. To determine whether Rv3168 confers antibiotic resistance against kanamycin, we performed dose-response antibiotic resistance experiments using kanamycin. Expression of the Rv3168 protein in Escherichia coli conferred antibiotic resistance against 100 μM kanamycin, a concentration that effected cell growth arrest in the parental E. coli strain and an E. coli strain expressing the Rv3168(D249A) mutant, in which the catalytic Asp249 residue was mutated to alanine. Furthermore, we detected phosphotransferase activity of Rv3168 against kanamycin as a substrate. Moreover, docking simulation of kanamycin into the Rv3168 structure suggests that kanamycin fits well into the substrate binding pocket of the protein, and that the phosphorylation-hydroxyl-group of kanamycin was located at a position similar to that in E. faecalis APH(3')-IIIa. On the basis of these results, we suggest that the Rv3168 mediates kanamycin resistance in M. tuberculosis, likely through phosphotransferase targeting of kanamycin.

  17. Plasma-activated air mediates plasmid DNA delivery in vivo

    PubMed Central

    Edelblute, Chelsea M; Heller, Loree C; Malik, Muhammad A; Bulysheva, Anna; Heller, Richard

    2016-01-01

    Plasma-activated air (PAA) provides a noncontact DNA transfer platform. In the current study, PAA was used for the delivery of plasmid DNA in a 3D human skin model, as well as in vivo. Delivery of plasmid DNA encoding luciferase to recellularized dermal constructs was enhanced, resulting in a fourfold increase in luciferase expression over 120 hours compared to injection only (P < 0.05). Delivery of plasmid DNA encoding green fluorescent protein (GFP) was confirmed in the epidermal layers of the construct. In vivo experiments were performed in BALB/c mice, with skin as the delivery target. PAA exposure significantly enhanced luciferase expression levels 460-fold in exposed sites compared to levels obtained from the injection of plasmid DNA alone (P < 0.001). Expression levels were enhanced when the plasma reactor was positioned more distant from the injection site. Delivery of plasmid DNA encoding GFP to mouse skin was confirmed by immunostaining, where a 3-minute exposure at a 10 mm distance displayed delivery distribution deep within the dermal layers compared to an exposure at 3 mm where GFP expression was localized within the epidermis. Our findings suggest PAA-mediated delivery warrants further exploration as an alternative approach for DNA transfer for skin targets. PMID:27110584

  18. Observation of Fe(V)=O using variable-temperature mass spectrometry and its enzyme-like C-H and C=C oxidation reactions

    NASA Astrophysics Data System (ADS)

    Prat, Irene; Mathieson, Jennifer S.; Güell, Mireia; Ribas, Xavi; Luis, Josep M.; Cronin, Leroy; Costas, Miquel

    2011-10-01

    Oxo-transfer chemistry mediated by iron underpins many biological processes and today is emerging as synthetically very important for the catalytic oxidation of C-H and C=C moieties that are hard to activate conventionally. Despite the vast amount of research in this area, experimental characterization of the reactive species under catalytic conditions is very limited, although a Fe(V)=O moiety was postulated. Here we show, using variable-temperature mass spectrometry, the generation of a Fe(V)=O species within a synthetic non-haem complex at -40 °C and its reaction with an olefin. Also, with isotopic labelling we were able both to follow oxygen-atom transfer from H2O2/H2O through Fe(V)=O to the products and to probe the reactivity as a function of temperature. This study pioneers the implementation of variable-temperature mass spectrometry to investigate reactive intermediates.

  19. alpha-Diimine Ligand Coordination and C H Bond Activation in the Reaction of Os3(CO)10(MeCN)2 with 6-R-2,2'-Bipyridine (where R = Et, Ph): X-ray Diffraction Structures of the Ortho-Metalated

    SciTech Connect

    Carrano, Carl J.; Wang, Xiaoping; Poola, Bhaskar; Powell, Cynthia B.; Richmond, Michael G.

    2009-01-01

    The reactivity of the labile cluster Os3(CO)10(MeCN)2 (1) with the monofunctionalized heterocyclic ligands 6-R-2,2 -bipyridine (where R = Et, Ph) has been investigated. The alkyl-substituted heterocycle 6-Et-2,2 -bipyridine reacts with 1 in refluxing CH2Cl2 to give an isomeric mixture of HOs3(CO)9(N2C12H11) due to cyclometalation of the side-chain ethyl group (2) and ortho metalation of the unsubstituted bipyridine ring (3). The solid-state structure of the latter cluster, HOs3(CO)9(N2C10H6-6-Et) (3), has unequivocally established the site of the C-H bond activation in the product. Treatment of 1 with the aryl-substituted ligand 6-Ph-2,2 -bipyridine proceeds similarly with ortho metalation at the ancillary phenyl group and the C-6 ortho site of the unsubstituted bipyridine ring, as verified by 1H NMR spectroscopy. The X-ray diffraction structure of the thermodynamically more stable bipyridine-metalated cluster HOs3(CO)9(N2C10H6-6-Ph) (5) has been determined. The course of these reactions is discussed with respect to our recent study involving the reaction of cluster 1 with the ligand 6-Me-2,2 -bipyridine. Graphical Abstract The reaction between the labile cluster Os3(CO)10(MeCN)2 (1) and the monofunctionalized heterocyclic ligand 6-Et-2,2 -bipyridine proceeds readily at room temperature to furnish an isomeric mixture of the cyclometalated and ortho-metalated hydride-bridged clusters HOs3(CO)9(N2C12H11) (2 and 3). Treatment of 1 with 6-Ph-2,2 -bipyridine also yields two distinct hydride-containing clusters that result from independent ortho-metalation paths involving the 6-phenyl substituent and unsubstituted bipyridine group. The bipyridine-derived ortho metalation attendant in the new clusters HOs3(CO)9(N2C10H6-6-Et) (3) and HOs3(CO)9(N2C10H6-6-Ph) (5) has been established by X-ray crystallography.

  20. Signal-Induced Transcriptional Activation by Dif Requires the dTRAP80 Mediator Module

    PubMed Central

    Park, Jin Mo; Kim, Jung Mo; Kim, Lark Kyun; Kim, Se Nyun; Kim-Ha, Jeongsil; Hoe Kim, Jung; Kim, Young-Joon

    2003-01-01

    The Mediator complex is the major multiprotein transcriptional coactivator complex in Drosophila melanogaster. Mediator components interact with diverse sets of transcriptional activator proteins to elicit the sophisticated regulation of gene expression. The distinct phenotypes associated with certain mutations in some of the Mediator genes and the specific in vitro interactions of Mediator gene products with transcriptional activator proteins suggest the presence of activator-specific binding subunits within the Mediator complex. However, the physiological relevance of these selective in vitro interactions has not been addressed. Therefore, we analyzed dTRAP80, one of the putative activator-binding subunits of the Mediator, for specificity of binding to a number of natural transcriptional activators from Drosophila. Among the group of activator proteins that requires the Mediator complex for transcriptional activation, only a subset of these proteins interacted with dTRAP80 in vitro and only these dTRAP80-interacting activators were defective for activation under dTRAP80-deficient in vivo conditions. In particular, activation of Drosophila antimicrobial peptide drosomycin gene expression by the NF-κB-like transcription factor Dif during induction of the Toll signaling pathway was dependent on the dTRAP80 module. These results, and the indirect support from the dTRAP80 artificial recruitment assay, indicate that dTRAP80 serves as a genuine activator-binding target responsible for a distinct group of activators. PMID:12556495

  1. Palladium-Catalyzed Construction of Heteroatom-Containing π-Conjugated Systems by Intramolecular Oxidative C-H/C-H Coupling Reaction.

    PubMed

    Saito, Kenta; Chikkade, Prasanna Kumara; Kanai, Motomu; Kuninobu, Yoichiro

    2015-06-01

    Synthesis of heteroatom-containing ladder-type π-conjugated molecules was successfully achieved via a palladium-catalyzed intramolecular oxidative C-H/C-H cross-coupling reaction. This reaction provides a variety of π-conjugated molecules bearing heteroatoms, such as nitrogen, oxygen, phosphorus, and sulfur atoms, and a carbonyl group. The π-conjugated molecules were synthesized efficiently, even in gram scale, and larger π-conjugated molecules were also obtained by a double C-H/C-H cross-coupling reaction and successive oxidative cycloaromatization.

  2. Spiraeoside inhibits mast cells activation and IgE-mediated allergic responses by suppressing phospholipase C-γ-mediated signaling.

    PubMed

    Kim, Jung Kuk; Seo, Young-Kyo; Park, Sehoon; Park, Soo-Ah; Lim, Seyoung; Lee, Susie; Kwon, Ohman; Seo, Jeong Kon; Choi, Ung-Kyu; Ryu, Sung Ho; Suh, Pann-Ghill

    2015-06-01

    Mast cells are responsible for IgE-mediated allergic responses through the secretion of various inflammatory cytokines and mediators. Therefore, the pharmacological regulation of mast cell activation is an important goal in the development of novel anti-allergic drugs. In this study, we found that spiraeoside (SP) inhibits mast cell activation and allergic responses in vivo. SP dose-dependently inhibited the degranulation induced by IgE-antigen (Ag) stimulation in RBL-2H3 mast cells without cytotoxic effects. At the molecular level, SP reduced the Ag-induced phosphorylation and subsequent activation of phospholipase C-γ2 (PLC-γ2). Moreover, SP inhibited the phosphorylation of spleen tyrosine kinase (Syk), linker for activation of T cells (LAT), and downstream MAPKs, such as ERK1/2, p38, and JNK, eventually attenuating expression of TNF-α and IL-4. Finally, we found that SP significantly inhibited IgE-mediated passive cutaneous anaphylaxis (PCA) in mice. Taken together, our results strongly suggest that SP suppresses IgE-mediated mast cell activation and allergic responses by inhibiting Lyn-induced PLC-γ2/MAPK signaling in mast cells.

  3. Substituting activities mediates the effect of cognitive flexibility on physical activity: a daily diary study.

    PubMed

    Kelly, Scout M; Updegraff, John A

    2017-03-02

    Pursuit of physical activity goals often requires modifying plans, but research on these flexible processes is limited. Cognitive flexibility may heighten one's likelihood of using flexible self-regulatory strategies (e.g., substitution), thereby increasing physical activity. This study used daily diary methodology to test the indirect effect of cognitive flexibility on physical activity via activity substitution. A sample of 128 college students (73% female, mean age 19.9) completed baseline measures and cognitive flexibility assessments, then logged physical activity daily for 2 weeks. Activity substitution was defined as adopting an alternate activity on a day another planned activity was unfulfilled. Controlling for baseline activity, intentions, and time, a multilevel mediation model revealed a significant indirect effect of cognitive flexibility on physical activity via activity substitution (b = 81.36, p = .041). Our results indicate that people with greater cognitive flexibility are more likely to use flexible self-regulation, leading to greater physical activity.

  4. Palladium-catalyzed direct ortho C-H arylation of 2-arylpyridine derivatives with aryltrimethoxysilane.

    PubMed

    Li, Wu; Yin, Zhangwei; Jiang, Xiaoqing; Sun, Peipei

    2011-10-21

    A Pd(OAc)(2)-catalyzed cross-coupling reaction between 2-arylpyridine and aryltrimethoxysilane in the presence of AgF and BQ in 1,4-dioxane was studied. After various reaction parameters (catalyst, oxidant, additive, solvent and reaction temperature) were examined, the optimal conditions for the reaction were identified. The synthesis is compatible to aryltrimethoxysilane with both electron-withdrawing and electron-donating groups on the aryl moiety with moderate yields. The kinetic isotope effect (k(H)/k(D)) for the C-H bond activation was provided.

  5. Diarylindenotetracenes via a selective cross-coupling/C-H functionalization: electron donors for organic photovoltaic cells.

    PubMed

    Gu, Xingxian; Luhman, Wade A; Yagodkin, Elisey; Holmes, Russell J; Douglas, Christopher J

    2012-03-16

    A direct synthesis of new donor materials for organic photovoltaic cells is reported. Diaryindenotetracenes were synthesized utilizing a Kumada-Tamao-Corriu cross-coupling of peri-substituted tetrachlorotetracene with spontaneous indene annulation via C-H activation. Vacuum deposited planar heterojunction organic photovoltaic cells incorporating these molecules as electron donors exhibit power conversion efficiencies exceeding 1.5% with open-circuit voltages ranging from 0.7 to 1.1 V when coupled with C(60) as an electron acceptor.

  6. Site-Selective Aliphatic C-H Chlorination Using N-Chloroamides Enables a Synthesis of Chlorolissoclimide.

    PubMed

    Quinn, Ryan K; Könst, Zef A; Michalak, Sharon E; Schmidt, Yvonne; Szklarski, Anne R; Flores, Alex R; Nam, Sangkil; Horne, David A; Vanderwal, Christopher D; Alexanian, Erik J

    2016-01-20

    Methods for the practical, intermolecular functionalization of aliphatic C-H bonds remain a paramount goal of organic synthesis. Free radical alkane chlorination is an important industrial process for the production of small molecule chloroalkanes from simple hydrocarbons, yet applications to fine chemical synthesis are rare. Herein, we report a site-selective chlorination of aliphatic C-H bonds using readily available N-chloroamides and apply this transformation to a synthesis of chlorolissoclimide, a potently cytotoxic labdane diterpenoid. These reactions deliver alkyl chlorides in useful chemical yields with substrate as the limiting reagent. Notably, this approach tolerates substrate unsaturation that normally poses major challenges in chemoselective, aliphatic C-H functionalization. The sterically and electronically dictated site selectivities of the C-H chlorination are among the most selective alkane functionalizations known, providing a unique tool for chemical synthesis. The short synthesis of chlorolissoclimide features a high yielding, gram-scale radical C-H chlorination of sclareolide and a three-step/two-pot process for the introduction of the β-hydroxysuccinimide that is salient to all the lissoclimides and haterumaimides. Preliminary assays indicate that chlorolissoclimide and analogues are moderately active against aggressive melanoma and prostate cancer cell lines.

  7. Schisandra polysaccharide evokes immunomodulatory activity through TLR 4-mediated activation of macrophages.

    PubMed

    Zhao, Ting; Feng, Yun; Li, Jing; Mao, Riwen; Zou, Ye; Feng, Weiwei; Zheng, Daheng; Wang, Wei; Chen, Yao; Yang, Liuqing; Wu, Xiangyang

    2014-04-01

    Schisandra chinensis (Turcz.) Baill has been used in traditional Chinese medicine for centuries. Previous studies have shown that Schisandra polysaccharide (SCPP11) has robust antitumor activity in vivo. In this study, the immunomodulatory activity and mechanisms of action of SCPP11 were investigated further to reveal its mechanism of action against tumors. Results showed that SCPP11 increased the thymus and spleen indices, pinocytic activity of peritoneal macrophages, and hemolysin formation in CTX-induced immunosuppressed mice. Moreover, SCPP11 significantly increased immunoglobulin levels, cytokines levels in vivo and induced RAW264.7 cells to secrete cytokines in vitro. RAW264.7 cells pretreated with SCPP11 significantly inhibited the proliferation of HepG-2 cells. In addition, SCPP11 promoted both the expression of iNOS protein and of iNOS and TNF-α mRNA. TLR-4 is a possible receptor for SCPP11-mediated macrophage activation. Therefore, the data suggest that SCPP11 exerted its antitumor activity by improving immune system functions through TLR-4-mediated up-regulation of NO and TNF-α.

  8. Nickel-Catalyzed Insertion of Alkynes and Electron-Deficient Olefins into Unactivated sp(3) C-H Bonds.

    PubMed

    Maity, Soham; Agasti, Soumitra; Earsad, Arif Mahammad; Hazra, Avijit; Maiti, Debabrata

    2015-08-03

    Insertion of unsaturated systems such as alkynes and olefins into unactivated sp(3) C-H bonds remains an unexplored problem. We herein address this issue by successfully incorporating a wide variety of functionalized alkynes and electron-deficient olefins into the unactivated sp(3) C-H bond of pivalic acid derivatives with excellent syn- and linear- selectivity. A strongly chelating 8-aminoquinoline directing group proved beneficial for these insertion reactions, while an air-stable and inexpensive Ni(II) salt has been employed as the active catalyst.

  9. Palladium(II)-catalyzed ortho-C-H arylation/alkylation of N-benzoyl α-amino ester derivatives.

    PubMed

    Misal Castro, Luis C; Chatani, Naoto

    2014-04-14

    The palladium-catalyzed arylation/alkylation of ortho-C-H bonds in N-benzoyl α-amino ester derivatives is described. In such a system both the NH-amido and the CO2R groups in the α-amino ester moieties play a role in successful C-H activation/C-C bond formation using iodoaryl coupling partners. A wide variety of functional groups and electron-rich/deficient iodoarenes are tolerated. The yields obtained range from 20 to 95%.

  10. Asymmetric Lewis acid organocatalysis of the Diels-Alder reaction by a silylated C-H acid.

    PubMed

    Gatzenmeier, Tim; van Gemmeren, Manuel; Xie, Youwei; Höfler, Denis; Leutzsch, Markus; List, Benjamin

    2016-02-26

    Silylium ion equivalents have shown promise as Lewis acid catalysts for a range of important C-C bond-forming reactions. Here we describe chiral C-H acids that upon in situ silylation, generate silylium-carbanion pairs, which are extremely active Lewis acid catalysts for enantioselective Diels-Alder reactions of cinnamates with cyclopentadiene. Enantiomeric ratios of up to 97:3 and diastereomeric ratios of more than 20:1 are observed across a diverse set of substitution patterns with 1 mole percent (mol %) of C-H acid catalyst and 10 mol % of a silylating reagent. The results show promise for broad applications of such C-H acid-derived silylium ion equivalents in asymmetric Lewis acid catalysis.

  11. Growth mechanism and composition of ultrasmooth a-C:H:Si films grown from energetic ions for superlubricity

    SciTech Connect

    Chen, Xinchun Kato, Takahisa

    2014-01-28

    Growth mechanism and ion energy dependence of composition of ultrasmooth a-C:H:Si films grown from ionization of tetramethylsilane (TMS) and toluene mixture at a fixed gas ratio have been investigated by varying the applied bias voltage. The dynamic scaling theory is employed to evaluate the roughness evolution of a-C:H:Si films, and to extract roughness and growth exponents of α ∼ 0.51 and β ∼ 0, respectively. The atomically smooth surface of a-C:H:Si films with Ra ∼ 0.1 nm is thermally activated by the energetic ion-impact induced subsurface “polishing” process for ion dominated deposition. The ion energy (bias voltage) plays a paramount role in determining the hydrogen incorporation, bonding structure and final stoichiometry of a-C:H:Si films. The hydrogen content in the films measured by ERDA gradually decreases from 36.7 to 17.3 at. % with increasing the bias voltage from 0.25 to 3.5 kV, while the carbon content in the films increases correspondingly from 52.5 to 70.1 at. %. The Si content is kept almost constant at ∼9–10 at. %. Depending on the ion-surface interactions, the bonding structure of a-C:H:Si films grown in different ion energy regions evolves from chain-developed polymer-like to cross-linked diamond-like to sp{sup 2}-bonded a–C as revealed by XPS, Raman, and FTIR analysis. Such a structural evolution is reflected in their measured nanomechanical properties such as hardness, modulus, and compressive stress. An enhanced viscoplastic behavior (i.e., viscoplastic exponent of ∼0.06) is observed for polymeric a-C:H:Si films. A hydrogen content threshold (H > 20 at. %) exists for the as-grown a-C:H:Si films to exhibit superlow friction in dry N{sub 2} atmosphere. An extremely low friction coefficient of ∼0.001 can be obtained for polymer-like a-C:H:Si film. These near-frictionless a-C:H:Si films are strongly promising for applications in industrial lubricating systems.

  12. Growth mechanism and composition of ultrasmooth a-C:H:Si films grown from energetic ions for superlubricity

    NASA Astrophysics Data System (ADS)

    Chen, Xinchun; Kato, Takahisa

    2014-01-01

    Growth mechanism and ion energy dependence of composition of ultrasmooth a-C:H:Si films grown from ionization of tetramethylsilane (TMS) and toluene mixture at a fixed gas ratio have been investigated by varying the applied bias voltage. The dynamic scaling theory is employed to evaluate the roughness evolution of a-C:H:Si films, and to extract roughness and growth exponents of α ˜ 0.51 and β ˜ 0, respectively. The atomically smooth surface of a-C:H:Si films with Ra ˜ 0.1 nm is thermally activated by the energetic ion-impact induced subsurface "polishing" process for ion dominated deposition. The ion energy (bias voltage) plays a paramount role in determining the hydrogen incorporation, bonding structure and final stoichiometry of a-C:H:Si films. The hydrogen content in the films measured by ERDA gradually decreases from 36.7 to 17.3 at. % with increasing the bias voltage from 0.25 to 3.5 kV, while the carbon content in the films increases correspondingly from 52.5 to 70.1 at. %. The Si content is kept almost constant at ˜9-10 at. %. Depending on the ion-surface interactions, the bonding structure of a-C:H:Si films grown in different ion energy regions evolves from chain-developed polymer-like to cross-linked diamond-like to sp2-bonded a-C as revealed by XPS, Raman, and FTIR analysis. Such a structural evolution is reflected in their measured nanomechanical properties such as hardness, modulus, and compressive stress. An enhanced viscoplastic behavior (i.e., viscoplastic exponent of ˜0.06) is observed for polymeric a-C:H:Si films. A hydrogen content threshold (H > 20 at. %) exists for the as-grown a-C:H:Si films to exhibit superlow friction in dry N2 atmosphere. An extremely low friction coefficient of ˜0.001 can be obtained for polymer-like a-C:H:Si film. These near-frictionless a-C:H:Si films are strongly promising for applications in industrial lubricating systems.

  13. Role of Lewis acid additives in a palladium catalyzed directed C-H functionalization reaction of benzohydroxamic acid to isoxazolone.

    PubMed

    Athira, C; Sunoj, Raghavan B

    2016-12-20

    Metallic salts as well as protic additives are widely employed in transition metal catalyzed C-H bond functionalization reactions to improve the efficiency of catalytic protocols. In one such example, ZnCl2 and pivalic acid are used as additives in a palladium catalyzed synthesis of isoxazolone from a readily available benzohydroxamic acid under one pot conditions. In this article, we present some important mechanistic insights into the role of ZnCl2 and pivalic acid, gained by using density functional theory (M06) computations. Two interesting modes of action of ZnCl2 are identified in various catalytic steps involved in the formation of isoxazolone. The conventional Lewis acid coordination wherein zinc chloride (ZnCl2·(DMA)) binds to the carbonyl group is found to be more favored in the C-H activation step. However, the participation of a hetero-bimetallic Pd-Zn species is preferred in reductive elimination leading to Caryl-N bond formation. Pivalic acid helps in relay proton transfer in C-H bond activation through a cyclometallation deprotonation (CMD) process. The explicit inclusion of ZnCl2 and solvent N,N-dimethyl acetamide (DMA) stabilizes the transition state and also helps reduce the activation barrier for the C-H bond activation step. The electronic communication between the two metal species is playing a crucial role in stabilizing the Caryl-N bond formation transition state through a Pd-Zn hetero-bimetallic interaction.

  14. Fujiwara-Moritani Reaction of Weinreb Amides using a Ruthenium-Catalyzed C-H Functionalization Reaction.

    PubMed

    Das, Riki; Kapur, Manmohan

    2015-07-01

    The ruthenium-catalyzed Fujiwara-Moritani reaction (oxidative-Heck reaction) of Weinreb amides is reported herein. The reaction affords exclusively ortho-C-H olefination products, has excellent substrate scope and tolerates halogen functionalities, which increase the synthetic utility of the method. A variety of activated olefins as well as styrenes can be employed as coupling partners.

  15. Synthesis of spiro-oxoindoles through Pd-catalyzed remote C-H alkylation using α-diazocarbonyl compounds.

    PubMed

    Pérez-Gómez, Marta; Hernández-Ponte, Sergio; Bautista, Delia; García-López, José-Antonio

    2017-03-02

    In this communication we describe a new route to spiro-oxoindole derivatives through a novel Pd-catalyzed cascade process. This reaction is based on the remote C-H activation performed by σ-alkyl Pd(ii) species generated in situ via intramolecular carbopalladation of alkenes, followed by insertion of a carbenoid coupling partner.

  16. Induction of aryl hydrocarbon receptor-mediated and estrogen receptor-mediated activities, and modulation of cell proliferation by dinaphthofurans.

    PubMed

    Vondrácek, Jan; Chramostová, Katerina; Plísková, Martina; Bláha, Ludek; Brack, Werner; Kozubík, Alois; Machala, Miroslav

    2004-09-01

    A group of heterocyclic aromatic compounds, dinaphthofurans (DNFs), recently have been identified as potentially significant contaminants in freshwater sediments. In the present study, a battery of in vitro assays was used for detection of toxic effects of DNFs that are potentially associated with endocrine disruption and tumor promotion. Dinaphthofurans were found to act as relatively potent inducers of aryl hydrocarbon receptor (AhR)-mediated activity in the chemical-activated luciferase reporter gene expression DR-CALUX assay. The relative AhR-inducing potencies of DNFs were similar or even higher than relative potencies of unsubstituted polycyclic aromatic hydrocarbons (PAHs), with dinaphtho[1,2-b;2'3'-d]furan being the most potent AhR agonist. Two compounds, dinaphtho[2,1-b;2'3'-d]furan and dinaphtho[1,2-b;1'2'-d]furan, induced estrogen receptor (ER)-mediated activity in the estrogen receptor-mediated CALUX (the ER-CALUX) assay. Two types of potential tumor-promoting effects of DNFs were investigated, using in vitro bioassays for detection of inhibition of gap-junctional intercellular communication and detection of a release from contact inhibition. Although the acute inhibition of gap-junctional intercellular communication was not observed, all six tested DNFs were able to release rat liver epithelial WB-F344 cells from contact inhibition at concentrations as low as 100 nM. In summary, the present study indicated that DNFs can exert multiple biological effects in vitro, including induction of the AhR-mediated activity, release of cells from contact inhibition, and induction of ER-mediated activity.

  17. Room-temperature C-H arylation: merger of Pd-catalyzed C-H functionalization and visible-light photocatalysis.

    PubMed

    Kalyani, Dipannita; McMurtrey, Kate B; Neufeldt, Sharon R; Sanford, Melanie S

    2011-11-23

    This communication describes the development of a room-temperature ligand-directed C-H arylation reaction using aryldiazonium salts. This was achieved by the successful merger of palladium-catalyzed C-H functionalization and visible-light photoredox catalysis. The new method is general for a variety of directing groups and tolerates many common functional groups.

  18. Oxidative addition of methane and benzene C--H bonds to rhodium center: A DFT study

    NASA Astrophysics Data System (ADS)

    Bi, Siwei; Zhang, Zhenwei; Zhu, Shufen

    2006-11-01

    A density functional theory study on mechanisms of the oxidative addition of methane and benzene C-H bonds to the rhodium center containing Cp and PMe 3 ligands has been performed. Our calculated results confirm that the C-H bond cleavage from a sigma complex to a hydride alkyl complex is the rate-determining step. Compared with the case of methane C-H bond, the oxidative addition of benzene C-H bond is more favorable kinetically and thermodynamically. Stronger backdonation from metal center to the σ ∗ antibonding orbital of benzene C-H bond is responsible for the observations.

  19. A versatile tripodal Cu(I) reagent for C-N bond construction via nitrene-transfer chemistry: catalytic perspectives and mechanistic insights on C-H aminations/amidinations and olefin aziridinations.

    PubMed

    Bagchi, Vivek; Paraskevopoulou, Patrina; Das, Purak; Chi, Lingyu; Wang, Qiuwen; Choudhury, Amitava; Mathieson, Jennifer S; Cronin, Leroy; Pardue, Daniel B; Cundari, Thomas R; Mitrikas, George; Sanakis, Yiannis; Stavropoulos, Pericles

    2014-08-13

    A Cu(I) catalyst (1), supported by a framework of strongly basic guanidinato moieties, mediates nitrene-transfer from PhI═NR sources to a wide variety of aliphatic hydrocarbons (C-H amination or amidination in the presence of nitriles) and olefins (aziridination). Product profiles are consistent with a stepwise rather than concerted C-N bond formation. Mechanistic investigations with the aid of Hammett plots, kinetic isotope effects, labeled stereochemical probes, and radical traps and clocks allow us to conclude that carboradical intermediates play a major role and are generated by hydrogen-atom abstraction from substrate C-H bonds or initial nitrene-addition to one of the olefinic carbons. Subsequent processes include solvent-caged radical recombination to afford the major amination and aziridination products but also one-electron oxidation of diffusively free carboradicals to generate amidination products due to carbocation participation. Analyses of metal- and ligand-centered events by variable temperature electrospray mass spectrometry, cyclic voltammetry, and electron paramagnetic resonance spectroscopy, coupled with computational studies, indicate that an active, but still elusive, copper-nitrene (S = 1) intermediate initially abstracts a hydrogen atom from, or adds nitrene to, C-H and C═C bonds, respectively, followed by a spin flip and radical rebound to afford intra- and intermolecular C-N containing products.

  20. EGFR trans-activation mediates pleiotrophin-induced activation of Akt and Erk in cultured osteoblasts.

    PubMed

    Fan, Jian-Bo; Liu, Wei; Yuan, Kun; Zhu, Xin-Hui; Xu, Da-Wei; Chen, Jia-Jia; Cui, Zhi-Ming

    2014-05-09

    Pleiotrophin (Ptn) plays an important role in bone growth through regulating osteoblasts' functions. The underlying signaling mechanisms are not fully understood. In the current study, we found that Ptn induced heparin-binding epidermal growth factor (HB-EGF) release to trans-activate EGF-receptor (EGFR) in both primary osteoblasts and osteoblast-like MC3T3-E1 cells. Meanwhile, Ptn activated Akt and Erk signalings in cultured osteoblasts. The EGFR inhibitor AG1478 as well as the monoclonal antibody against HB-EGF (anti-HB-EGF) significantly inhibited Ptn-induced EGFR activation and Akt and Erk phosphorylations in MC3T3-E1 cells and primary osteoblasts. Further, EGFR siRNA depletion or dominant negative mutation suppressed also Akt and Erk activation in MC3T3-E1 cells. Finally, we observed that Ptn increased alkaline phosphatase (ALP) activity and inhibited dexamethasone (Dex)-induced cell death in both MC3T3-E1 cells and primary osteoblasts, such effects were alleviated by AG1478 or anti-HB-EGF. Together, these results suggest that Ptn-induced Akt/Erk activation and some of its pleiotropic functions are mediated by EGFR trans-activation in cultured osteoblasts.

  1. Hippocampal activity mediates the relationship between circadian activity rhythms and memory in older adults.

    PubMed

    Sherman, Stephanie M; Mumford, Jeanette A; Schnyer, David M

    2015-08-01

    Older adults experience parallel changes in sleep, circadian rhythms, and episodic memory. These processes appear to be linked such that disruptions in sleep contribute to deficits in memory. Although more variability in circadian patterns is a common feature of aging and predicts pathology, little is known about how alterations in circadian activity rhythms within older adults influence new episodic learning. Following 10 days of recording sleep-wake patterns using actigraphy, healthy older adults underwent fMRI while performing an associative memory task. The results revealed better associative memory was related to more consistent circadian activity rhythms, independent of total sleep time, sleep efficiency, and level of physical activity. Moreover, hippocampal activity during successful memory retrieval events was positively correlated with associative memory accuracy and circadian activity rhythm (CAR) consistency. We demonstrated that the link between consistent rhythms and associative memory performance was mediated by hippocampal activity. These findings provide novel insight into how the circadian rhythm of sleep-wake cycles are associated with memory in older adults and encourage further examination of circadian activity rhythms as a biomarker of cognitive functioning.

  2. Mechanism and Site Selectivity in Visible-Light Photocatalyzed C-H Functionalization: Insights from DFT Calculations.

    PubMed

    Demissie, Taye B; Hansen, Jørn H

    2016-08-19

    Visible-light photocatalyzed (VLPC) late-stage C-H functionalization is a powerful addition to the chemical synthesis toolkit. VLPC has a demonstrated potential for discovery of elusive and valuable transformations, particularly in functionalization of bioactive heterocycles. In order to fully harvest the potential of VLPC in the context of complex molecule synthesis, a thorough understanding of the elementary processes involved is crucial. This would enable more rational design of suitable reagents and catalysts, as well as prediction of activated C-H sites for functionalization. Such knowledge is essential when VLPC is to be employed in retrosynthetic analysis of complex molecules. Herein, we present a density functional theory (DFT) study of mechanistic details in the C-H functionalization of bioactive heterocycles exemplified by the methylation of the antifungal agent voriconazole. Moreover, we show that readily computed atomic charges can predict major site-selectivity in good agreement with experimental studies and thus be informative tools for the identification of active C-H functionalization sites in synthetic planning.

  3. Implementation Planning and Progress on Physical Activity Goals: The Mediating Role of Life-Management Strategies

    ERIC Educational Resources Information Center

    Dugas, Michelle; Gaudreau, Patrick; Carraro, Natasha

    2012-01-01

    This 4-week prospective study examined whether the use of life-management strategies mediates the relationship between implementation planning and short-term progress on physical activity goals. In particular, the strategies of elective selection, compensation, and loss-based selection were disentangled to assess their specific mediating effects.…

  4. Participation in Organized Activities and Conduct Problems in Elementary School: The Mediating Effect of Social Skills

    ERIC Educational Resources Information Center

    Denault, Anne-Sophie; Déry, Michèle

    2015-01-01

    The goal of this study was to test a mediation model in which social skills mediate the relationship between participation in organized activities and conduct problems among elementary school children. Two moderators of these associations were also examined, namely, gender and reception of special education services. A total of 563 children (45%…

  5. A systematic review of intervention effects on potential mediators of children’s physical activity

    PubMed Central

    2013-01-01

    Background Many interventions aiming to increase children’s physical activity have been developed and implemented in a variety of settings, and these interventions have previously been reviewed; however the focus of these reviews tends to be on the intervention effects on physical activity outcomes without consideration of the reasons and pathways leading to intervention success or otherwise. To systematically review the efficacy of physical activity interventions targeting 5-12 year old children on potential mediators and, where possible, to calculate the size of the intervention effect on the potential mediator. Methods A systematic search identified intervention studies that reported outcomes on potential mediators of physical activity among 5-12 year old children. Original research articles published between 1985 and April 2012 were reviewed. Results Eighteen potential mediators were identified from 31 studies. Positive effects on cognitive/psychological potential mediators were reported in 15 out of 31 studies. Positive effects on social environmental potential mediators were reported in three out of seven studies, and no effects on the physical environment were reported. Although no studies were identified that performed a mediating analysis, 33 positive intervention effects were found on targeted potential mediators (with effect sizes ranging from small to large) and 73% of the time a positive effect on the physical activity outcome was reported. Conclusions Many studies have reported null intervention effects on potential mediators of children’s physical activity; however, it is important that intervention studies statistically examine the mediating effects of interventions so the most effective strategies can be implemented in future programs. PMID:23433143

  6. Adolescents' physical activities and peer norms: the mediating role of self-efficacy.

    PubMed

    Lu, Frank J H; Lin, Ju-Han; Hsu, Ya-Wen; Chou, Chien-Chih; Wang, Erica T W; Yeh, Li-Chin

    2014-04-01

    The purpose of the present study was to examine the relations among adolescents' self-efficacy and social norms, and physical activity and whether self-efficacy mediated the relationship between social norms and physical activity. 400 junior high school students (202 boys, 198 girls, 2 not identified; M age = 15.3yr., SD = 0.6) completed a demographic questionnaire, the International Physical Activity Questionnaire (IPAQ), the Perceived Self-Efficacy in Physical Activity Scale, and the Physical Activity Social Norms Scale. Regression analyses indicated that both self-efficacy and social norms predicted physical activity. Self-efficacy fully mediated the relationship between peer norms and physical activity for boys but partially mediated the relationship for girls. An application of the results may be to foster self-efficacy and peer norms as a motivational strategy for supporting increased physical activity.

  7. Activation of AhR-mediated toxicity pathway by emerging pollutants polychlorinated diphenyl sulfides

    EPA Science Inventory

    Polychlorinated diphenyl sulfides (PCDPSs) are a group of environmental pollutants for which limited toxicological information is available. This study tested the hypothesis that PCDPSs could activate the mammalian aryl hydrocarbon receptor (AhR) mediated toxicity pathways. Eight...

  8. Transition Metal-Free Selective Double sp(3) C-H Oxidation of Cyclic Amines to 3-Alkoxyamine Lactams.

    PubMed

    Osorio-Nieto, Urbano; Chamorro-Arenas, Delfino; Quintero, Leticia; Höpfl, Herbert; Sartillo-Piscil, Fernando

    2016-09-16

    The first chemical method for selective dual sp(3) C-H functionalization at the alpha-and beta positions of cyclic amines to their corresponding 3-alkoxyamine lactams is reported. Unlike traditional Cα-H oxidation of amines to amides mediated by transition metals, the present protocol, which involves the use of NaClO2/TEMPO/NaClO in either aqueous or organic solvent, not only allows the Cα-H oxidation but also the subsequent functionalization of the unreactive β-methylene group in an unprecedented tandem fashion and using environmentally friendly reactants.

  9. Iridium-catalyzed C-H borylation of heteroarenes: scope, regioselectivity, application to late-stage functionalization, and mechanism.

    PubMed

    Larsen, Matthew A; Hartwig, John F

    2014-03-19

    A study on the iridium-catalyzed C-H borylation of heteroarenes is reported. Several heteroarenes containing multiple heteroatoms were found to be amenable to C-H borylation catalyzed by the combination of an iridium(I) precursor and tetramethylphenanthroline. The investigations of the scope of the reaction led to the development of powerful rules for predicting the regioselectivity of borylation, foremost of which is that borylation occurs distal to nitrogen atoms. One-pot functionalizations are reported of the heteroaryl boronate esters formed in situ, demonstrating the usefulness of the reported methodology for the synthesis of complex heteroaryl structures. Application of this methodology to the synthesis and late-stage functionalization of biologically active compounds is also demonstrated. Mechanistic studies show that basic heteroarenes can bind to the catalyst and alter the resting state from the olefin-bound complex observed during arene borylation to a species containing a bound heteroarene, leading to catalyst deactivation. Studies on the origins of the observed regioselectivity show that borylation occurs distal to N-H bonds due to rapid N-H borylation, creating an unfavorable steric environment for borylation adjacent to these bonds. Computational studies and mechanistic studies show that the lack of observable borylation of C-H bonds adjacent to basic nitrogen is not the result of coordination to a bulky Lewis acid prior to C-H activation, but the combination of a higher-energy pathway for the borylation of these bonds relative to other C-H bonds and the instability of the products formed from borylation adjacent to basic nitrogen.

  10. GABAA Receptor-Mediated Activity in a Model of Cortical Dysplasia

    DTIC Science & Technology

    2012-06-29

    a model of cortical dysplasia" Name of Candidate: Joseph Abbah Doctor of Philosophy Degree June 29, 2012 DISSERTATION AND ABSTRACT APPROVED...receptor-mediated activity in a model of cortical dysplasia’ is appropriately acknowledged and, beyond brief excerpts, is with the permission of the...certifies that the use of any copyrighted material in this dissertation manuscript entitled: “GABAA receptor-mediated activity in a model of

  11. Alcohols as alkylating agents in heteroarene C-H functionalization

    NASA Astrophysics Data System (ADS)

    Jin, Jian; MacMillan, David W. C.

    2015-09-01

    Redox processes and radical intermediates are found in many biochemical processes, including deoxyribonucleotide synthesis and oxidative DNA damage. One of the core principles underlying DNA biosynthesis is the radical-mediated elimination of H2O to deoxygenate ribonucleotides, an example of `spin-centre shift', during which an alcohol C-O bond is cleaved, resulting in a carbon-centred radical intermediate. Although spin-centre shift is a well-understood biochemical process, it is underused by the synthetic organic chemistry community. We wondered whether it would be possible to take advantage of this naturally occurring process to accomplish mild, non-traditional alkylation reactions using alcohols as radical precursors. Because conventional radical-based alkylation methods require the use of stoichiometric oxidants, increased temperatures or peroxides, a mild protocol using simple and abundant alkylating agents would have considerable use in the synthesis of diversely functionalized pharmacophores. Here we describe the development of a dual catalytic alkylation of heteroarenes, using alcohols as mild alkylating reagents. This method represents the first, to our knowledge, broadly applicable use of unactivated alcohols as latent alkylating reagents, achieved via the successful merger of photoredox and hydrogen atom transfer catalysis. The value of this multi-catalytic protocol has been demonstrated through the late-stage functionalization of the medicinal agents, fasudil and milrinone.

  12. Rh(III)-catalyzed addition of alkenyl C-H bond to isocyanates and intramolecular cyclization: direct synthesis 5-ylidenepyrrol-2(5H)-ones.

    PubMed

    Hou, Wei; Zhou, Bing; Yang, Yaxi; Feng, Huijin; Li, Yuanchao

    2013-04-19

    The rhodium-catalyzed addition of an alkenyl C-H bond to isocyanates via sp(2) C-H bond activation followed by an intramolecular cyclization is described. This atom-economic and catalytic reaction affords a simple and straightforward access to biologically relevant 5-ylidene pyrrol-2(5H)-ones and can be carried out under mild and neutral conditions in the absence of any additives and environmentally hazardous waste production.

  13. Understanding Synchronous Computer-Mediated Classroom Discussion through Cultural-Historical Activity Theory

    ERIC Educational Resources Information Center

    Park, Yangjoo

    2015-01-01

    This study is about graduate students' discourse practices in classroom text-based synchronous computer mediated discussions (SCMD). Cultural historical activity theory (in short, Activity Theory) is the primary theoretical lens through which the data are analyzed. Engeström's (1987) Activity System model among the various theoretical positions or…

  14. Evidence for Multiple Mediator Complexes in Yeast Independently Recruited by Activated Heat Shock Factor

    PubMed Central

    Anandhakumar, Jayamani; Moustafa, Yara W.; Chowdhary, Surabhi; Kainth, Amoldeep S.

    2016-01-01

    Mediator is an evolutionarily conserved coactivator complex essential for RNA polymerase II transcription. Although it has been generally assumed that in Saccharomyces cerevisiae, Mediator is a stable trimodular complex, its structural state in vivo remains unclear. Using the “anchor away” (AA) technique to conditionally deplete select subunits within Mediator and its reversibly associated Cdk8 kinase module (CKM), we provide evidence that Mediator's tail module is highly dynamic and that a subcomplex consisting of Med2, Med3, and Med15 can be independently recruited to the regulatory regions of heat shock factor 1 (Hsf1)-activated genes. Fluorescence microscopy of a scaffold subunit (Med14)-anchored strain confirmed parallel cytoplasmic sequestration of core subunits located outside the tail triad. In addition, and contrary to current models, we provide evidence that Hsf1 can recruit the CKM independently of core Mediator and that core Mediator has a role in regulating postinitiation events. Collectively, our results suggest that yeast Mediator is not monolithic but potentially has a dynamic complexity heretofore unappreciated. Multiple species, including CKM-Mediator, the 21-subunit core complex, the Med2-Med3-Med15 tail triad, and the four-subunit CKM, can be independently recruited by activated Hsf1 to its target genes in AA strains. PMID:27185874

  15. Pd(II)-catalyzed ortho- or meta-C-H olefination of phenol derivatives.

    PubMed

    Dai, Hui-Xiong; Li, Gang; Zhang, Xing-Guo; Stepan, Antonia F; Yu, Jin-Quan

    2013-05-22

    A combination of weakly coordinating auxiliaries and ligand acceleration allows for the development of both ortho- and meta-selective C-H olefination of phenol derivatives. These reactions demonstrate the feasibility of directing C-H functionalizations when functional groups are distal to target C-H bonds. The meta-C-H functionalization of electron-rich phenol derivatives is unprecedented and orthogonal to previous electrophilic substitution of phenols in terms of regioselectivity. These methods are also applied to functionalize α-phenoxyacetic acids, a fibrate class of drug scaffolds.

  16. Pressure-dependent studies on hydration of the C-H group in formic acid

    NASA Astrophysics Data System (ADS)

    Chang, Hai-Chou; Jiang, Jyh-Chiang; Chao, Ming-Chi; Lin, Ming-Shan; Lin, Sheng Hsien; Chen, Hsin-Yen; Hsueh, Hung-Chung

    2001-11-01

    The infrared spectroscopic profiles of HCOOD/D2O mixtures were measured as a function of pressure and concentration. The C-H bond of HCOOD shortens as the pressure is elevated, while the increase in C-H bond length upon diluting HCOOD with D2O was observed. Based on the experimental results, the shift in frequency of C-H stretching band is concluded to relate to the mechanism of the hydration of the C-H group and the water structure in the vicinity of the C-H group. The pressure-dependent results can be attributed to the strengthening of C-H---O electrostatic/dispersion interaction upon increasing pressure. The observations are in accord with ab initio calculation forecasting a blueshift of the C-H stretching mode via C-H---O interaction in HCOOD-water/(HCOOD)2-(D2O) complexes relative to the noninteracting monomer/dimer. Hydrogen-bonding nonadditivity and the size of water clusters are suggested to be responsible to cause the redshift in C-H stretching mode upon dilution HCOOD with D2O.

  17. Cellular Mechanisms of Calcium-Mediated Triggered Activity

    NASA Astrophysics Data System (ADS)

    Song, Zhen

    Life-threatening cardiac arrhythmias continue to pose a major health problem. Ventricular fibrillation, which is a complex form of electrical wave turbulence in the lower chambers of the heart, stops the heart from pumping and is the largest cause of natural death in the United States. Atrial fibrillation, a related form of wave turbulence in the upper heart chambers, is in turn the most common arrhythmia diagnosed in clinical practice. Despite extensive research to date, mechanisms of cardiac arrhythmias remain poorly understood. It is well established that both spatial disorder of the refractory period of heart cells and triggered activity (TA) jointly contribute to the initiation and maintenance of arrhythmias. TA broadly refers to the abnormal generation of a single or a sequence of abnormal excitation waves from a small submillimeter region of the heart in the interval of time between two normal waves generated by the heart's natural pacemaker (the sinoatrial node). TA has been widely investigated experimentally and occurs in several pathological conditions where the intracellular concentration of free Ca2+ ions in heart cells becomes elevated. Under such conditions, Ca2+ can be spontaneously released from intracellular stores, thereby driving an electrogenic current that exchanges 3Na+ ions for one Ca2+ ion across the cell membrane. This current in turn depolarizes the membrane of heart cells after a normal excitation. If this calcium-mediated "delayed after depolarization'' (DAD) is sufficiently large, it can generate an action potential. While the arrhythmogenic importance of spontaneous Ca2+ release and DADs is well appreciated, the conditions under which they occur in heart pathologies remain poorly understood. Calcium overload is only one factor among several other factors that can promote DADs, including sympathetic nerve stimulation, different expression levels of membrane ion channels and calcium handling proteins, and different mutations of those

  18. MST1 activation by curcumin mediates JNK activation, Foxo3a nuclear translocation and apoptosis in melanoma cells

    SciTech Connect

    Yu, Teng; Ji, Jiang; Guo, Yong-li

    2013-11-08

    Highlights: •Curcumin activates MST1 in melanoma cells. •MST1 mediates curcumin-induced apoptosis of melanoma cells. •ROS production is involved in curcumin-induced MST1 activation. •MST1 mediates curcumin-induced JNK activation in melanoma cells. •MST1 mediates curcumin-induced Foxo3a nuclear translocation and Bim expression. -- Abstract: Different groups including ours have shown that curcumin induces melanoma cell apoptosis, here we focused the role of mammalian Sterile 20-like kinase 1 (MST1) in it. We observed that curcumin activated MST1-dependent apoptosis in cultured melanoma cells. MST1 silencing by RNA interference (RNAi) suppressed curcumin-induced cell apoptosis, while MST1 over-expressing increased curcumin sensitivity. Meanwhile, curcumin induced reactive oxygen species (ROS) production in melanoma cells, and the ROS scavenger, N-acetyl-cysteine (NAC), almost blocked MST1 activation to suggest that ROS might be required for MST1 activation by curcumin. c-Jun N-terminal protein kinase (JNK) activation by curcumin was dependent on MST1, since MST1 inhibition by RNAi or NAC largely inhibited curcumin-induced JNK activation. Further, curcumin induced Foxo3 nuclear translocation and Bim-1 (Foxo3 target gene) expression in melanoma cells, such an effect by curcumin was inhibited by MST1 RNAi. In conclusion, we suggested that MST1 activation by curcumin mediates JNK activation, Foxo3a nuclear translocation and apoptosis in melanoma cells.

  19. Lithium potentiates GSK-3β activity by inhibiting phosphoinositide 3-kinase-mediated Akt phosphorylation

    SciTech Connect

    Tian, Nie; Kanno, Takeshi; Jin, Yu; Nishizaki, Tomoyuki

    2014-07-18

    Highlights: • Lithium suppresses Akt activity by reducing PI3K-mediated Akt phosphorylation. • Lithium enhances GSK-3β activity by reducing Akt-mediated GSK-3β phosphorylation. • Lithium suppresses GSK-3β activity through its direct inhibition. - Abstract: Accumulating evidence has pointed to the direct inhibitory action of lithium, an anti-depressant, on GSK-3β. The present study investigated further insight into lithium signaling pathways. In the cell-free assay Li{sub 2}CO{sub 3} significantly inhibited phosphoinositide 3-kinase (PI3K)-mediated phosphorylation of Akt1 at Ser473, but Li{sub 2}CO{sub 3} did not affect PI3K-mediated PI(3,4,5)P{sub 3} production and 3-phosphoinositide-dependent protein kinase 1 (PDK1)-mediated phosphorylation of Akt1 at Thr308. This indicates that lithium could enhance GSK-3β activity by suppressing Akt-mediated Ser9 phosphorylation of GSK-3β in association with inhibition of PI3K-mediated Akt activation. There was no direct effect of Li{sub 2}CO{sub 3} on Akt1-induced phosphorylation of GSK-3β at Ser9, but otherwise Li{sub 2}CO{sub 3} significantly reduced GSK-3β-mediated phosphorylation of β-catenin at Ser33/37 and Thr41. This indicates that lithium directly inhibits GSK-3β in an Akt-independent manner. In rat hippocampal slices Li{sub 2}CO{sub 3} significantly inhibited phosphorylation of Akt1/2 at Ser473/474, GSK-3β at Ser9, and β-catenin at Ser33/37 and Thr41. Taken together, these results indicate that lithium exerts its potentiating and inhibiting bidirectional actions on GSK-3β activity.

  20. Origin of superlubricity in a-C:H:Si films: a relation to film bonding structure and environmental molecular characteristic.

    PubMed

    Chen, Xinchun; Kato, Takahisa; Nosaka, Masataka

    2014-08-27

    Superlubricity of Si-containing hydrogenated amorphous carbon (a-C:H:Si) films has been systematically investigated in relation to the film bonding structure and the environmental atmosphere. Structural diversity induced by hydrogen incorporation (i.e., 17.3-36.7 at. % H), namely sp(2)-bonded a-C, diamond-like or polymer-like, and tribointeractions activated by the participation of environmental gaseous molecules mainly determine the frictional behaviors of a-C:H:Si films. A suitable control of hydrogen content in the film (i.e., the inherent hydrogen coverage) is obligate to obtain durable superlubricity in a distinct gaseous atmosphere such as dry N2, reactive H2 or humid air. Rapid buildup of running-in-induced antifriction tribolayers at the contact interface, which is more feasible in self-mated sliding, is crucial for achieving a superlubric state. Superior tribological performances have been observed for the polymer-like a-C:H:Si (31.9 at. % H) film, as this hydrogen-rich sample can exhibit superlow friction in various atmospheres including dry inert N2 (μ ∼ 0.001), Ar (μ ∼ 0.012), reactive H2 (μ ∼ 0.003) and humid air (μ ∼ 0.004), and can maintain ultralow friction in corrosive O2 (μ ∼ 0.084). Hydrogen is highlighted for its decisive role in obtaining superlow friction. The occurrence of superlubricity in a-C:H:Si films is generally attributed to a synergistic effect of phase transformation, surface passivation and shear localization, for instance, the near-frictionless state occurred in dry N2. The contribution of each mechanism to the friction reduction depends on the specific intrafilm and interfilm interactions along with the atmospheric effects. These antifriction a-C:H:Si films are promising for industrial applications as lubricants.

  1. Studies of the cAMP mediated aggregation in Dictyostelium discoideum: receptor mediated activation of the adenylate cyclase

    SciTech Connect

    Theibert, W.E.A.B.

    1985-01-01

    Dictyostelium discoideum, a eukaryotic amoeba of the cellular slime mold family, provides an interesting paradigm in developmental biology. During development, hundreds of thousands of cells aggregate to form a multicellular aggregate. Aggregation is mediated by chemotaxis and chemical signaling. Waves of adenosine 3'-5' cyclic monophosphate (cAMP) propagate through the monolayer and provide transient gradients for chemotaxis. The author has used a reversible inhibitor of the cAMP signaling response to demonstrate that adaptation to cAMP is independent of the activation of the adenylate cyclase and therefore is not caused by the rise in intracellular cAMP. Next, it is shown that adenosine inhibits the cAMP signaling response. Inhibition is rapid, reversible, and depends on the cAMP stimulus concentration. Then the specificity of the cAMP receptors which mediates signaling is determined and compared with the receptors which mediate chemotaxis, the cGMP response, and cAMP binding antagonism. The cAMP surface receptor has been identified by photoaffinity labeling intact cells with (/sup 32/P)-8-N/sub 3/-cAMP using an ammonium sulfate binding stabilization technique. The photoactivated ligand specifically labels a polypeptide, localized to the membrane fraction, which migrates as a closely spaced doublet on SDS Page.

  2. Intramolecular cyclopropanation and C-H insertion reactions with metal carbenoids generated from cyclopropenes.

    PubMed

    Archambeau, Alexis; Miege, Frédéric; Meyer, Christophe; Cossy, Janine

    2015-04-21

    Activation of unsaturated carbon-carbon bonds by means of transition metal catalysts is an exceptionally active research field in organic synthesis. In this context, due to their high ring strain, cyclopropenes constitute an interesting class of substrates that displays a versatile reactivity in the presence of transition metal catalysts. Metal complexes of vinyl carbenes are involved as key intermediates in a wide variety of transition metal-catalyzed ring-opening reactions of cyclopropenes. Most of the reported transformations rely on intermolecular or intramolecular addition of nucleophiles to these latter reactive species. This Account focuses specifically on the reactivity of carbenoids resulting from the ring-opening of cyclopropenes in cyclopropanation and C-H insertion reactions, which are arguably two of the most representative transformations of metal complexes of carbenes. Compared with the more conventional α-diazo carbonyl compounds, the use of cyclopropenes as precursors of metal carbenoids in intramolecular cyclopropanation or C-H insertion reactions has been largely underexploited. One of the challenges is to devise appropriately substituted and readily available cyclopropenes that would not only undergo regioselective ring-opening under mild conditions but also trigger the subsequent desired transformations with a high level of chemoselectivity and stereoselectivity. These goals were met by considering several substrates derived from the readily available 3,3-dimethylcyclopropenylcarbinols or 3,3-dimethylcyclopropenylcarbinyl amines. In the case of 1,6-cyclopropene-enes, highly efficient and diastereoselective gold(I)-catalyzed ring-opening/intramolecular cyclopropanations were developed as a route to diversely substituted heterocycles and carbocycles possessing a bicyclo[4.1.0]heptane framework. The use of rhodium(II) catalysts enabled us to widen the scope of this transformation for the synthesis of medium-sized heterocyclic scaffolds

  3. Neuroprotective Activity of (−)-Epigallocatechin Gallate against Lipopolysaccharide-Mediated Cytotoxicity

    PubMed Central

    Liu, Jin-Biao; Zhou, Li; Wang, Yi-Zhong; Wang, Xu; Zhou, Yu; Ho, Wen-Zhe; Li, Jie-Liang

    2016-01-01

    Lipopolysaccharide- (LPS-) mediated systemic inflammation plays a critical role in neurodegenerative diseases. The present study was conducted to evaluate the protective effects of epigallocatechin gallate (EGCG), the major component in green tea, on LPS-mediated inflammation and neurotoxicity. LPS treatment of macrophages induced expression of proinflammatory cytokines (TNF-α, IL-1β, and IL-6). However, EGCG pretreatment of macrophages significantly inhibited LPS-mediated induction of these cytokines. In addition, EGCG significantly diminished LPS-induced inflammatory cytokines in the peripheral mononuclear blood cells (PBMCs). Supernatant from EGCG-pretreated and LPS-activated macrophage cultures was found to be less cytotoxic to neurons than that from non-EGCG-pretreated and LPS-activated macrophage cultures. Furthermore, EGCG treatment of neurons could inhibit LPS-induced production of reactive oxygen species (ROS). Thus EGCG represents a potent and useful neuroprotective agent for inflammation-mediated neurological disorders. PMID:27191001

  4. The C-H Dissociation Energy of C2H6

    NASA Technical Reports Server (NTRS)

    Bauschlicher, Charles W., Jr.; Partridge, Harry; Langhoff, Stephen R. (Technical Monitor)

    1994-01-01

    The C-H bond energy in C2H6 is computed to be 99.76 +/- 0.35 kcal/mol, which is in excellent agreement with the most recent experimental values. The calculation of the C-H bond energy by direct dissociation and by an isodesmic reaction is discussed.

  5. Compact and highly active next-generation libraries for CRISPR-mediated gene repression and activation

    PubMed Central

    Horlbeck, Max A; Gilbert, Luke A; Villalta, Jacqueline E; Adamson, Britt; Pak, Ryan A; Chen, Yuwen; Fields, Alexander P; Park, Chong Yon; Corn, Jacob E; Kampmann, Martin; Weissman, Jonathan S

    2016-01-01

    We recently found that nucleosomes directly block access of CRISPR/Cas9 to DNA (Horlbeck et al., 2016). Here, we build on this observation with a comprehensive algorithm that incorporates chromatin, position, and sequence features to accurately predict highly effective single guide RNAs (sgRNAs) for targeting nuclease-dead Cas9-mediated transcriptional repression (CRISPRi) and activation (CRISPRa). We use this algorithm to design next-generation genome-scale CRISPRi and CRISPRa libraries targeting human and mouse genomes. A CRISPRi screen for essential genes in K562 cells demonstrates that the large majority of sgRNAs are highly active. We also find CRISPRi does not exhibit any detectable non-specific toxicity recently observed with CRISPR nuclease approaches. Precision-recall analysis shows that we detect over 90% of essential genes with minimal false positives using a compact 5 sgRNA/gene library. Our results establish CRISPRi and CRISPRa as premier tools for loss- or gain-of-function studies and provide a general strategy for identifying Cas9 target sites. DOI: http://dx.doi.org/10.7554/eLife.19760.001 PMID:27661255

  6. Does perceived neighborhood walkability and safety mediate the association between education and meeting physical activity guidelines?

    PubMed

    Pratt, Michael; Yin, Shaoman; Soler, Robin; Njai, Rashid; Siegel, Paul Z; Liao, Youlian

    2015-04-09

    The role of neighborhood walkability and safety in mediating the association between education and physical activity has not been quantified. We used data from the 2010 and 2012 Communities Putting Prevention to Work Behavioral Risk Factor Surveillance System and structural equation modeling to estimate how much of the effect of education level on physical activity was mediated by perceived neighborhood walkability and safety. Neighborhood walkability accounts for 11.3% and neighborhood safety accounts for 6.8% of the effect. A modest proportion of the important association between education and physical activity is mediated by perceived neighborhood walkability and safety, suggesting that interventions focused on enhancing walkability and safety could reduce the disparity in physical activity associated with education level.

  7. Activity-Regulated Genes as Mediators of Neural Circuit Plasticity

    PubMed Central

    Leslie, Jennifer H.; Nedivi, Elly

    2011-01-01

    Modifications of neuronal circuits allow the brain to adapt and change with experience. This plasticity manifests during development and throughout life, and can be remarkably long lasting. Many electrophysiological and molecular mechanisms are common to the seemingly diverse types of activity-dependent functional adaptation that take place during developmental critical periods, learning and memory, and alterations to sensory map representations in the adult. Experience-dependent plasticity is triggered when neuronal excitation activates cellular signaling pathways from the synapse to the nucleus that initiate new programs of gene expression. The protein products of activity-regulated genes then work via a diverse array of cellular mechanisms to modify neuronal functional properties. They fine-tune brain circuits by strengthening or weakening synaptic connections or by altering synapse numbers. Their effects are further modulated by posttranscriptional regulatory mechanisms, often also dependent on activity, that control activity-regulated gene transcript and protein function. Thus, the cellular response to neuronal activity integrates multiple tightly coordinated mechanisms to precisely orchestrate long-lasting, functional and structural changes in brain circuits. PMID:21601615

  8. Double C-H functionalization in sequential order: direct synthesis of polycyclic compounds by a palladium-catalyzed C-H alkenylation-arylation cascade.

    PubMed

    Ohno, Hiroaki; Iuchi, Mutsumi; Kojima, Naoto; Yoshimitsu, Takehiko; Fujii, Nobutaka; Tanaka, Tetsuaki

    2012-04-23

    Palladium-catalyzed cascade C-H alkenylation and arylation provides convenient access to polycyclic aromatic compounds. Treatment of 3-bromoaniline derivatives bearing a bromocinnamyl group on the nitrogen atom with a catalytic amount of [Pd(OAc)(2)] and PCy(3)·HBF(4) in the presence of Cs(2)CO(3) in dioxane affords naphthalene-fused indole derivatives in good yields. This double cyclization reaction is also applicable to heterocyclic substrates, giving fused indoles containing a heteroaromatic ring such as dibenzofuran, dibenzothiophene, carbazole, indole, or benzofuran through heterocyclic C-H arylation. When using a 2,6-unsubstituted aniline derivative, the first C-H arylation preferentially proceeds at the more hindered position of the aniline ring.

  9. a-C:H/a-C:H(N) thin film deposition using 2.45 GHz expanding surface wave sustained plasmas

    NASA Astrophysics Data System (ADS)

    Hong, Suk-Ho; Douai, David; Berndt, Johannes; Winter, Jörg

    2005-08-01

    Thin film properties such as homogeneity (radial profiles), optical constants, carbon density in the film, and the surface structures are strongly dependent on deposition conditions. We have investigated a-C:H/a-C:H(N) thin film deposition by expanding Ar-CH4 and Ar/N2-CH4 surface wave sustained plasmas at a frequency of 2.45 GHz. The influence of the plasma parameters such as pressure, input power, gas mixture rate, and an external bias voltage on the change of the film properties is systematically studied. An external bias applied to the substrate leads to more dense and harder a-C:H films, i.e. change from soft polymer-like to hard diamond-like. Rutherford backscattering and atomic force microscope surface topology confirm the densification of the films.

  10. Iridium-Catalyzed, Hydrosilyl-Directed Borylation of Unactivated Alkyl C-H Bonds.

    PubMed

    Larsen, Matthew A; Cho, Seung Hwan; Hartwig, John

    2016-01-27

    We report the iridium-catalyzed borylation of primary and secondary alkyl C-H bonds directed by a Si-H group to form alkylboronate esters site selectively. The reactions occur with high selectivity at primary C-H bonds γ to the hydrosilyl group to form primary alkyl bisboronate esters. In the absence of such primary C-H bonds, the borylation occurs selectively at a secondary C-H bond γ to the hydrosilyl group, and these reactions of secondary C-H bonds occur with high diastereoselectivity. The hydrosilyl-containing alkyl boronate esters formed by this method undergo transformations selectively at the carbon-boron or carbon-silicon bonds of these products under distinct conditions to give the products of amination, oxidation, and arylation.

  11. The Mediational Role of Adolescents' Friends in Relations between Activity Breadth and Adjustment

    ERIC Educational Resources Information Center

    Simpkins, Sandra D.; Eccles, Jacquelynne S.; Becnel, Jennifer N.

    2008-01-01

    This investigation addresses the mediational role of friends' characteristics between adolescents' activity breadth (i.e., variety in activity participation) and their later adjustment. Data were drawn from 2 longitudinal studies: the Childhood and Beyond (CAB; N = 925) study and the Maryland Adolescent Development in Context Study (MADICS; N =…

  12. Influence of very low doses of mediators on fungal laccase activity - nonlinearity beyond imagination

    PubMed Central

    Malarczyk, Elzbieta; Kochmanska-Rdest, Janina; Jarosz-Wilkolazka, Anna

    2009-01-01

    Laccase, an enzyme responsible for aerobic transformations of natural phenolics, in industrial applications requires the presence of low-molecular substances known as mediators, which accelerate oxidation processes. However, the use of mediators is limited by their toxicity and the high costs of exploitation. The activation of extracellular laccase in growing fungal culture with highly diluted mediators, ABTS and HBT is described. Two high laccase-producing fungal strains, Trametes versicolor and Cerrena unicolor, were used in this study as a source of enzyme. Selected dilutions of the mediators significantly increased the activity of extracellular laccase during 14 days of cultivation what was distinctly visible in PAGE technique and in colorimetric tests. The same mediator dilutions increased demethylation properties of laccase, which was demonstrated during incubation of enzyme with veratric acid. It was established that the activation effect was assigned to specific dilutions of mediators. Our dose-response dilution process smoothly passes into the range of action of homeopathic dilutions and is of interest for homeopaths. PMID:19732425

  13. Nanoparticle-mediated remote control of enzymatic activity.

    PubMed

    Knecht, Leslie D; Ali, Nur; Wei, Yinan; Hilt, J Zach; Daunert, Sylvia

    2012-10-23

    Nanomaterials have found numerous applications as tunable, remotely controlled platforms for drug delivery, hyperthermia cancer treatment, and various other biomedical applications. The basis for the interest lies in their unique properties achieved at the nanoscale that can be accessed via remote stimuli. These properties could then be exploited to simultaneously activate secondary systems that are not remotely actuatable. In this work, iron oxide nanoparticles are encapsulated in a bisacrylamide cross-linked polyacrylamide hydrogel network along with a model dehalogenase enzyme, L-2-HAD(ST). This thermophilic enzyme is activated at elevated temperatures and has been shown to have optimal activity at 70 °C. By exposing the Fe(3)O(4) nanoparticles to a remote stimulus, an alternating magnetic field (AMF), enhanced system heating can be achieved, thus remotely activating the enzyme. The internal heating of the nanocomposite hydrogel network in the AMF results in a 2-fold increase in enzymatic activity as compared to the same hydrogel heated externally in a water bath, suggesting that the internal heating of the nanoparticles is more efficient than the diffusion-limited heating of the water bath. This system may prove useful for remote actuation of biomedical and environmentally relevant enzymes and find applications in a variety of fields.

  14. Sulfation mediates activity of zosteric acid against biofilm formation.

    PubMed

    Kurth, Caroline; Cavas, Levent; Pohnert, Georg

    2015-01-01

    Zosteric acid (ZA), a metabolite from the marine sea grass Zostera marina, has attracted much attention due to its attributed antifouling (AF) activity. However, recent results on dynamic transformations of aromatic sulfates in marine phototrophic organisms suggest potential enzymatic desulfation of metabolites like ZA. The activity of ZA was thus re-investigated using biofilm assays and simultaneous analytical monitoring by liquid chromatography/mass spectrometry (LC/MS). Comparison of ZA and its non-sulfated form para-coumaric acid (CA) revealed that the active substance was in all cases the non-sulfated CA while ZA was virtually inactive. CA exhibited a strong biofilm inhibiting activity against Escherichia coli and Vibrio natriegens. The LC/MS data revealed that the apparent biofilm inhibiting effects of ZA on V. natriegens can be entirely attributed to CA released from ZA by sulfatase activity. In the light of various potential applications, the (a)biotic transformation of ZA to CA has thus to be considered in future AF formulations.

  15. C-H bonds as ubiquitous functionality: preparation of multiple regioisomers of arylated 1,2,4-triazoles via C-H arylation.

    PubMed

    Joo, Jung Min; Guo, Pengfei; Sames, Dalibor

    2013-01-18

    We describe a general approach for the synthesis of complex aryl 1,2,4-triazoles. The electronic character of the C-H bonds and the triazole ring allows for the regioselective C-H arylation of 1-alkyl- and 4-alkyltriazoles under catalytic conditions. We have also developed the SEM and THP switch as well as trans-N-alkylation, which enable sequential arylation of the triazole ring to prepare 3,5-diaryltriazoles. This new strategy provides rapid access to a variety of arylated 1,2,4-triazoles and well complements existing cyclization methods.

  16. Androgen receptor serine 81 mediates Pin1 interaction and activity

    PubMed Central

    La Montagna, Raffaele; Caligiuri, Isabella; Maranta, Pasquale; Lucchetti, Chiara; Esposito, Luca; Paggi, Marco G.; Toffoli, Giuseppe; Rizzolio, Flavio; Giordano, Antonio

    2012-01-01

    Hormone-dependent tumors are characterized by deregulated activity of specific steroid receptors, allowing aberrant expression of many genes involved in cancer initiation, progression and metastasis. In prostate cancer, the androgen receptor (AR) protein has pivotal functions, and over the years it has been the target of different drugs. AR is a nuclear receptor whose activity is regulated by a phosphorylation mechanism controlled by hormone and growth factors. Following phosphorylation, AR interacts with many cofactors that closely control its function. Among such cofactors, Pin1 is a peptidyl-prolyl isomerase that is involved in the control of protein phosphorylation and has a prognostic value in prostate cancer. In the present study, we demonstrate that ARSer81 is involved in the interaction with Pin1, and that this interaction is important for the transcriptional activity of AR. Since Pin1 expression positively correlates with tumor grade, our results suggest that Pin1 can participate in this process by modulating AR function. PMID:22894932

  17. Disorder-mediated crowd control in an active matter system

    PubMed Central

    Pinçe, Erçağ; Velu, Sabareesh K. P.; Callegari, Agnese; Elahi, Parviz; Gigan, Sylvain; Volpe, Giovanni; Volpe, Giorgio

    2016-01-01

    Living active matter systems such as bacterial colonies, schools of fish and human crowds, display a wealth of emerging collective and dynamic behaviours as a result of far-from-equilibrium interactions. The dynamics of these systems are better understood and controlled considering their interaction with the environment, which for realistic systems is often highly heterogeneous and disordered. Here, we demonstrate that the presence of spatial disorder can alter the long-term dynamics in a colloidal active matter system, making it switch between gathering and dispersal of individuals. At equilibrium, colloidal particles always gather at the bottom of any attractive potential; however, under non-equilibrium driving forces in a bacterial bath, the colloids disperse if disorder is added to the potential. The depth of the local roughness in the environment regulates the transition between gathering and dispersal of individuals in the active matter system, thus inspiring novel routes for controlling emerging behaviours far from equilibrium. PMID:26956085

  18. Disorder-mediated crowd control in an active matter system

    NASA Astrophysics Data System (ADS)

    Pinçe, Erçağ; Velu, Sabareesh K. P.; Callegari, Agnese; Elahi, Parviz; Gigan, Sylvain; Volpe, Giovanni; Volpe, Giorgio

    2016-03-01

    Living active matter systems such as bacterial colonies, schools of fish and human crowds, display a wealth of emerging collective and dynamic behaviours as a result of far-from-equilibrium interactions. The dynamics of these systems are better understood and controlled considering their interaction with the environment, which for realistic systems is often highly heterogeneous and disordered. Here, we demonstrate that the presence of spatial disorder can alter the long-term dynamics in a colloidal active matter system, making it switch between gathering and dispersal of individuals. At equilibrium, colloidal particles always gather at the bottom of any attractive potential; however, under non-equilibrium driving forces in a bacterial bath, the colloids disperse if disorder is added to the potential. The depth of the local roughness in the environment regulates the transition between gathering and dispersal of individuals in the active matter system, thus inspiring novel routes for controlling emerging behaviours far from equilibrium.

  19. Centrally formed acetaldehyde mediates ethanol-induced brain PKA activation.

    PubMed

    Tarragon, E; Baliño, P; Aragon, C M G

    2014-09-19

    Centrally formed acetaldehyde has proven to be responsible for several psychopharmacological effects induced by ethanol. In addition, it has been suggested that the cAMP-PKA signaling transduction pathway plays an important role in the modulation of several ethanol-induced behaviors. Therefore, we hypothesized that acetaldehyde might be ultimately responsible for the activation of this intracellular pathway. We used three pharmacological agents that modify acetaldehyde activity (α-lipoic acid, aminotriazole, and d-penicillamine) to study the role of this metabolite on EtOH-induced PKA activation in mice. Our results show that the injection of α-lipoic acid, aminotriazole and d-penicillamine prior to acute EtOH administration effectively blocks the PKA-enhanced response to EtOH in the brain. These results strongly support the hypothesis of a selective release of acetaldehyde-dependent Ca(2+) as the mechanism involved in the neurobehavioral effects elicited by EtOH.

  20. Chiral Cyclopentadienyls: Enabling Ligands for Asymmetric Rh(III)-Catalyzed C-H Functionalizations.

    PubMed

    Ye, Baihua; Cramer, Nicolai

    2015-05-19

    instance, this catalyst is used for directed C-H activations of aryl hydroxamates and the subsequent enantioselective trapping with olefins, providing dihydroisoquinolones in very high enantioselectivities. In addition, we have established highly selective intramolecular trapping reactions with tethered higher substituted alkenes giving dihydrobenzofurans with quaternary stereogenic centers. Concerning intermolecular reactions, allene coupling partners allow for an enantioselective hydroarylation yielding substituted allylated compounds. A trapping process of the cyclometalated intermediate with diazo reactants enables the enantioselective construction of isoindolinones. Moreover, the catalysts can be used for the construction of atropchiral biaryl motives using a dehydrogenative Heck-type reaction. The development of flexibly adjustable chiral Cp(x) ligands is described in this Account showcasing their applicability for a variety of Rh(III) catalyzed C-H functionalization reactions. These Cp(x) derivatives hold promise as powerful steering ligands for further transition-metals used in asymmetric catalysis.

  1. Mediators Affecting Girls’ Levels of Physical Activity Outside of School: Findings from the Trial of Activity in Adolescent Girls

    PubMed Central

    Lytle, Leslie A.; Murray, David M.; Evenson, Kelly R.; Moody, Jamie; Pratt, Charlotte A.; Metcalfe, Lauve; Parra-Medina, Deborah

    2010-01-01

    Background Providing after school activities is a community level approach for reducing the decline in physical activity of girls as they reach early adolescence. Purpose The purpose of this study was to examine psychosocial, environmental, and behavioral factors as potential mediators of after school physical activity in adolescent girls. Methods We assessed objectively measured levels of physical activity occurring outside of school and potential predictors and mediators of activity in girls participating in the Trial of Activity in Adolescent Girls (TAAG). Results We found that the TAAG intervention had a statistically significant and positive effect on out of school activity in the 2006 cohort. Self-efficacy, friends’ social support, total social support, and difficulty getting to and from community activities mediated the level of moderate to vigorous physical activity in girls. Conclusions Parents, communities, and schools should provide and enhance opportunities outside of the school day for adolescents to be active. Reducing transportation barriers and enlisting social support appear to be key. PMID:20012810

  2. Late-Stage C-H Coupling Enables Rapid Identification of HDAC Inhibitors: Synthesis and Evaluation of NCH-31 Analogues.

    PubMed

    Sekizawa, Hiromi; Amaike, Kazuma; Itoh, Yukihiro; Suzuki, Takayoshi; Itami, Kenichiro; Yamaguchi, Junichiro

    2014-05-08

    We previously reported the discovery of NCH-31, a potent histone deacetylase (HDAC) inhibitor. By utilizing our C-H coupling reaction, we rapidly synthesized 16 analogues (IYS-1 through IYS-15 and IYS-Me) of NCH-31 with different aryl groups at the C4-position of 2-aminothiazole core of NCH-31. Subsequent biological testing of these derivatives revealed that 3-fluorophenyl (IYS-10) and 4-fluorophenyl (IYS-15) derivatives act as potent pan-HDAC inhibitor. Additionally, 4-methylphenyl (IYS-1) and 3-fluoro-4-methylphenyl (IYS-14) derivatives acted as HDAC6-insensitive inhibitors. The present work clearly shows the power of the late-stage C-H coupling approach to rapidly identify novel and highly active/selective biofunctional molecules.

  3. Carboxylic acids as traceless directing groups for the rhodium(III)-catalyzed decarboxylative C-H arylation of thiophenes.

    PubMed

    Zhang, Yuanfei; Zhao, Huaiqing; Zhang, Min; Su, Weiping

    2015-03-16

    A rhodium(III)-catalyzed carboxylic acid directed decarboxylative C-H/C-H cross-coupling of carboxylic acids with thiophenes has been developed. With a slight adjustment of the reaction conditions based on the nature of the substrates, aryl carboxylic acids with a variety of substituents could serve as suitable coupling partners, and a broad variety of functional groups were tolerated. This method provides straightforward access to biaryl scaffolds with diverse substitution patterns, many of which have conventionally been synthesized through lengthy synthetic sequences. An illustrative example is the one-step gram-scale synthesis of a biologically active 3,5-substituted 2-arylthiophene by way of the current method.

  4. Haemocompatibility of hydrogenated amorphous carbon (a-C:H) films synthesized by plasma immersion ion implantation-deposition

    NASA Astrophysics Data System (ADS)

    Yang, P.; Kwok, S. C. H.; Chu, P. K.; Leng, Y. X.; Chen, J. Y.; Wang, J.; Huang, N.

    2003-05-01

    Diamond-like-carbon has attracted much attention recently as a potential biomaterial in blood contacting biomedical devices. However, previous reports in this area have not adequately addressed the biocompatibility and acceptability of the materials in blood contacting applications. In this study, hydrogenated amorphous carbon (a-C:H) films were fabricated on silicon wafers (1 0 0) using plasma immersion ion implantation-deposition. A series of a-C:H films with different structures and chemical bonds were fabricated under different substrate voltages. The results indicate that film graphitization is promoted at higher substrate bias. The film deposited at a lower substrate bias of -75 V possesses better blood compatibility than the films at higher bias and stainless steel. Our results suggest two possible paths to improve the blood compatibility, suppression of the endogenic clotting system and reduction of platelet activation.

  5. Ortho-Functionalized Aryltetrazines by Direct Palladium-Catalyzed C-H Halogenation: Application to Fast Electrophilic Fluorination Reactions.

    PubMed

    Testa, Christelle; Gigot, Élodie; Genc, Semra; Decréau, Richard; Roger, Julien; Hierso, Jean-Cyrille

    2016-04-25

    A general catalyzed direct C-H functionalization of s-tetrazines is reported. Under mild reaction conditions, N-directed ortho-C-H activation of tetrazines allows the introduction of various functional groups, thus forming carbon-heteroatom bonds: C-X (X=I, Br, Cl) and C-O. Based on this methodology, we developed electrophilic mono- and poly-ortho-fluorination of tetrazines. Microwave irradiation was optimized to afford fluorinated s-aryltetrazines, with satisfactory selectivity, within only ten minutes. This work provides an efficient and practical entry for further accessing highly substituted tetrazine derivatives (iodo, bromo, chloro, fluoro, and acetate precursors). It gives access to ortho-functionalized aryltetrazines which are difficult to obtain by classical Pinner-like syntheses.

  6. CRISPR-mediated Activation of Latent HIV-1 Expression.

    PubMed

    Limsirichai, Prajit; Gaj, Thomas; Schaffer, David V

    2016-03-01

    Complete eradication of HIV-1 infection is impeded by the existence of cells that harbor chromosomally integrated but transcriptionally inactive provirus. These cells can persist for years without producing viral progeny, rendering them refractory to immune surveillance and antiretroviral therapy and providing a permanent reservoir for the stochastic reactivation and reseeding of HIV-1. Strategies for purging this latent reservoir are thus needed to eradicate infection. Here, we show that engineered transcriptional activation systems based on CRISPR/Cas9 can be harnessed to activate viral gene expression in cell line models of HIV-1 latency. We further demonstrate that complementing Cas9 activators with latency-reversing compounds can enhance latent HIV-1 transcription and that epigenome modulation using CRISPR-based acetyltransferases can also promote viral gene activation. Collectively, these results demonstrate that CRISPR systems are potentially effective tools for inducing latent HIV-1 expression and that their use, in combination with antiretroviral therapy, could lead to improved therapies for HIV-1 infection.

  7. Activating transcription factor 6 derepression mediates neuroprotection in Huntington disease.

    PubMed

    Naranjo, José R; Zhang, Hongyu; Villar, Diego; González, Paz; Dopazo, Xose M; Morón-Oset, Javier; Higueras, Elena; Oliveros, Juan C; Arrabal, María D; Prieto, Angela; Cercós, Pilar; González, Teresa; De la Cruz, Alicia; Casado-Vela, Juan; Rábano, Alberto; Valenzuela, Carmen; Gutierrez-Rodriguez, Marta; Li, Jia-Yi; Mellström, Britt

    2016-02-01

    Deregulated protein and Ca2+ homeostasis underlie synaptic dysfunction and neurodegeneration in Huntington disease (HD); however, the factors that disrupt homeostasis are not fully understood. Here, we determined that expression of downstream regulatory element antagonist modulator (DREAM), a multifunctional Ca2+-binding protein, is reduced in murine in vivo and in vitro HD models and in HD patients. DREAM downregulation was observed early after birth and was associated with endogenous neuroprotection. In the R6/2 mouse HD model, induced DREAM haplodeficiency or blockade of DREAM activity by chronic administration of the drug repaglinide delayed onset of motor dysfunction, reduced striatal atrophy, and prolonged life span. DREAM-related neuroprotection was linked to an interaction between DREAM and the unfolded protein response (UPR) sensor activating transcription factor 6 (ATF6). Repaglinide blocked this interaction and enhanced ATF6 processing and nuclear accumulation of transcriptionally active ATF6, improving prosurvival UPR function in striatal neurons. Together, our results identify a role for DREAM silencing in the activation of ATF6 signaling, which promotes early neuroprotection in HD.

  8. Activating transcription factor 6 derepression mediates neuroprotection in Huntington disease

    PubMed Central

    Naranjo, José R.; Zhang, Hongyu; Villar, Diego; González, Paz; Dopazo, Xose M.; Morón-Oset, Javier; Higueras, Elena; Oliveros, Juan C.; Arrabal, María D.; Prieto, Angela; Cercós, Pilar; González, Teresa; De la Cruz, Alicia; Casado-Vela, Juan; Rábano, Alberto; Valenzuela, Carmen; Gutierrez-Rodriguez, Marta; Li, Jia-Yi; Mellström, Britt

    2016-01-01

    Deregulated protein and Ca2+ homeostasis underlie synaptic dysfunction and neurodegeneration in Huntington disease (HD); however, the factors that disrupt homeostasis are not fully understood. Here, we determined that expression of downstream regulatory element antagonist modulator (DREAM), a multifunctional Ca2+-binding protein, is reduced in murine in vivo and in vitro HD models and in HD patients. DREAM downregulation was observed early after birth and was associated with endogenous neuroprotection. In the R6/2 mouse HD model, induced DREAM haplodeficiency or blockade of DREAM activity by chronic administration of the drug repaglinide delayed onset of motor dysfunction, reduced striatal atrophy, and prolonged life span. DREAM-related neuroprotection was linked to an interaction between DREAM and the unfolded protein response (UPR) sensor activating transcription factor 6 (ATF6). Repaglinide blocked this interaction and enhanced ATF6 processing and nuclear accumulation of transcriptionally active ATF6, improving prosurvival UPR function in striatal neurons. Together, our results identify a role for DREAM silencing in the activation of ATF6 signaling, which promotes early neuroprotection in HD. PMID:26752648

  9. CRISPR-mediated Activation of Latent HIV-1 Expression

    PubMed Central

    Limsirichai, Prajit; Gaj, Thomas; Schaffer, David V

    2016-01-01

    Complete eradication of HIV-1 infection is impeded by the existence of cells that harbor chromosomally integrated but transcriptionally inactive provirus. These cells can persist for years without producing viral progeny, rendering them refractory to immune surveillance and antiretroviral therapy and providing a permanent reservoir for the stochastic reactivation and reseeding of HIV-1. Strategies for purging this latent reservoir are thus needed to eradicate infection. Here, we show that engineered transcriptional activation systems based on CRISPR/Cas9 can be harnessed to activate viral gene expression in cell line models of HIV-1 latency. We further demonstrate that complementing Cas9 activators with latency-reversing compounds can enhance latent HIV-1 transcription and that epigenome modulation using CRISPR-based acetyltransferases can also promote viral gene activation. Collectively, these results demonstrate that CRISPR systems are potentially effective tools for inducing latent HIV-1 expression and that their use, in combination with antiretroviral therapy, could lead to improved therapies for HIV-1 infection. PMID:26607397

  10. Saturated fatty acids activate TLR-mediated proinflammatory signaling pathways.

    PubMed

    Huang, Shurong; Rutkowsky, Jennifer M; Snodgrass, Ryan G; Ono-Moore, Kikumi D; Schneider, Dina A; Newman, John W; Adams, Sean H; Hwang, Daniel H

    2012-09-01

    Toll-like receptor 4 (TLR4) and TLR2 were shown to be activated by saturated fatty acids (SFAs) but inhibited by docosahexaenoic acid (DHA). However, one report suggested that SFA-induced TLR activation in cell culture systems is due to contaminants in BSA used for solubilizing fatty acids. This report raised doubt about proinflammatory effects of SFAs. Our studies herein demonstrate that sodium palmitate (C16:0) or laurate (C12:0) without BSA solubilization induced phosphorylation of inhibitor of nuclear factor-κB α, c-Jun N-terminal kinase (JNK), p44/42 mitogen-activated-kinase (ERK), and nuclear factor-κB subunit p65, and TLR target gene expression in THP1 monocytes or RAW264.7 macrophages, respectively, when cultured in low FBS (0.25%) medium. C12:0 induced NFκB activation through TLR2 dimerized with TLR1 or TLR6, and through TLR4. Because BSA was not used in these experiments, contaminants in BSA have no relevance. Unlike in suspension cells (THP-1), BSA-solubilized C16:0 instead of sodium C16:0 is required to induce TLR target gene expression in adherent cells (RAW264.7). C16:0-BSA transactivated TLR2 dimerized with TLR1 or TLR6 and through TLR4 as seen with C12:0. These results and additional studies with the LPS sequester polymixin B and in MyD88(-/-) macrophages indicated that SFA-induced activation of TLR2 or TLR4 is a fatty acid-specific effect, but not due to contaminants in BSA or fatty acid preparations.

  11. Fur-mediated activation of gene transcription in the human pathogen Neisseria gonorrhoeae.

    PubMed

    Yu, Chunxiao; Genco, Caroline Attardo

    2012-04-01

    It is well established that the ferric uptake regulatory protein (Fur) functions as a transcriptional repressor in diverse microorganisms. Recent studies demonstrated that Fur also functions as a transcriptional activator. In this study we defined Fur-mediated activation of gene transcription in the sexually transmitted disease pathogen Neisseria gonorrhoeae. Analysis of 37 genes which were previously determined to be iron induced and which contained putative Fur boxes revealed that only 30 of these genes exhibited reduced transcription in a gonococcal fur mutant strain. Fur-mediated activation was established by examining binding of Fur to the putative promoter regions of 16 Fur-activated genes with variable binding affinities observed. Only ∼50% of the newly identified Fur-regulated genes bound Fur in vitro, suggesting that additional regulatory circuits exist which may function through a Fur-mediated indirect mechanism. The gonococcal Fur-activated genes displayed variable transcription patterns in a fur mutant strain, which correlated with the position of the Fur box in each (promoter) region. These results suggest that Fur-mediated direct transcriptional activation is fulfilled by multiple mechanisms involving either competing with a repressor or recruiting RNA polymerase. Collectively, our studies have established that gonococcal Fur functions as an activator of gene transcription through both direct and indirect mechanisms.

  12. Psychosocial mediators of group cohesion on physical activity intention of older adults.

    PubMed

    Caperchione, Cristina; Mummery, Kerry

    2007-01-01

    Considerable evidence has indicated that group-based physical activity may be a promising approach to reducing and preventing age-related illness. However, this research has not examined the mechanisms by which cohesion may impact on behaviour. The purpose of the present research was to utilise the theory of planned behaviour to investigate the mechanism by which group cohesion may affect physical activity intention. Participants were recruited from an existing physical activity intervention studying the effects of group cohesion on physical activity behaviour. The outcomes of this intervention are reported elsewhere. This paper presents data from a sub-sample of the intervention population (N=74) that examined the mediating relationships between the theory of planned behaviour and group cohesion on physical activity intention. Analyses showed that attitude and perceived behavioural control mediated the relationship between specific group cohesion concepts and physical activity intention. The direct measure of subjective norm failed to display a mediating relationship. The mediating relationships displayed between attitude and perceived behavioural control and physical activity intention provide insight into potential mechanisms by which group cohesion may affect behaviour.

  13. Self-Efficacy and Social Support as Mediators Between Culturally Specific Dance and Lifestyle Physical Activity

    PubMed Central

    Murrock, Carolyn J.; Madigan, Elizabeth

    2013-01-01

    Culturally specific dance has the potential to generate health benefits but is seldom used even among studies advocating culturally specific interventions. This study examined the components of self-efficacy and social support as mediators between culturally specific dance and lifestyle physical activity in African American women (N = 126). An experimental design compared intervention and control groups for mediating effects of self-efficacy and social support on lifestyle physical activity. Findings indicated that only outcome expectations and social support from friends mediated effects. Culturally specific dance is a first step in encouraging African American women to become more physically active and improve health outcomes. The implications are that culturally specific dance programs can improve health outcomes by including members of underserved populations. PMID:18763475

  14. Ethanol inhibits epileptiform activity and NMDA receptor-mediated synaptic transmission in rat amygdaloid slices

    SciTech Connect

    Gean, P.W. )

    1992-02-26

    The effect of ethanol on the epileptiform activity induced by Mg{sup ++}-free solution was studied in rat amygdalar slices using intracellular recording techniques. The spontaneous and evoked epileptiform discharges consisting of an initial burst followed by afterdischarges were observed 20-30 min after switching to Mg{sup ++}-free medium. Superfusion with ethanol reversibly reduced the duration of spontaneous and evoked bursting discharges in a concentration-dependent manner. Synaptic response mediated by N-methyl-D-aspartate (NMDA) receptor activation was isolated by application of a solution containing the non-NMDA receptor antagonist 6-cyano-7-nitroquinoxaline-2,3-dione (CNQX) and either in Mg{sup ++}-free solution or in the presence of 50 {mu}M bicuculline. Application of ethanol reversibly suppressed the duration of NMDA receptor-mediated synaptic response. These results suggest that intoxicating concentrations of ethanol possess anticonvulsant activity through blocking the NMDA receptor-mediated synaptic excitation.

  15. ALDH2 Mediates 5-Nitrofuran Activity in Multiple Species

    PubMed Central

    Zhou, Linna; Ishizaki, Hironori; Spitzer, Michaela; Taylor, Kerrie L.; Temperley, Nicholas D.; Johnson, Stephen L.; Brear, Paul; Gautier, Philippe; Zeng, Zhiqiang; Mitchell, Amy; Narayan, Vikram; McNeil, Ewan M.; Melton, David W.; Smith, Terry K.; Tyers, Mike; Westwood, Nicholas J.; Patton, E. Elizabeth

    2012-01-01

    Summary Understanding how drugs work in vivo is critical for drug design and for maximizing the potential of currently available drugs. 5-nitrofurans are a class of prodrugs widely used to treat bacterial and trypanosome infections, but despite relative specificity, 5-nitrofurans often cause serious toxic side effects in people. Here, we use yeast and zebrafish, as well as human in vitro systems, to assess the biological activity of 5-nitrofurans, and we identify a conserved interaction between aldehyde dehydrogenase (ALDH) 2 and 5-nitrofurans across these species. In addition, we show that the activity of nifurtimox, a 5-nitrofuran anti-trypanosome prodrug, is dependent on zebrafish Aldh2 and is a substrate for human ALDH2. This study reveals a conserved and biologically relevant ALDH2-5-nitrofuran interaction that may have important implications for managing the toxicity of 5-nitrofuran treatment. PMID:22840776

  16. Monoamine mediation of the morphine-induced activation of mice

    PubMed Central

    Carroll, Bernard J.; Sharp, Peter T.

    1972-01-01

    1. The dose-response relationship for hyperactivity in grouped mice following the injection of morphine sulphate has been established. 2. The activation response can be modified by drugs which affect either catecholamines or indoleamines. 3. The monoamine precursors L-DOPA and 5-hydroxytryptophan potentiate the response. 4. The monoamine synthesis inhibitors α-methyl-p-tyrosine and p-chlorophenylalanine reduce the response. 5. Inhibition of monoamine oxidase activity by pargyline caused a great increase in the response. The simultaneous administration of reserpine resulted in a further potentiation. 6. Reserpine blocked the response whenever it was given alone, either before, with or after the injection of morphine. 7. Blockade of α-adrenoceptors with phentolamine or phenoxybenzamine reduced the response. 8. Blockade of tryptaminergic receptors with methysergide or cinanserin also antagonized the response. 9. The major tranquillizers haloperidol and chlorpromazine reduced the response. Haloperidol was especially effective in this regard. 10. The tricyclic antidepressant drug imipramine potentiated the response. 11. The morphine antagonist nalorphine completely prevented the response. 12. The anticholinergic agent atropine and the antihistaminic drug mepyramine did not affect the response. 13. We conclude that dopamine, noradrenaline and 5-hydroxytryptamine are all involved in the normal activation response of grouped mice to morphine, with dopaminergic mechanisms being of primary importance. PMID:4263794

  17. Specific pathways mediating inflammasome activation by Candida parapsilosis

    PubMed Central

    Tóth, Adél; Zajta, Erik; Csonka, Katalin; Vágvölgyi, Csaba; Netea, Mihai G.; Gácser, Attila

    2017-01-01

    Candida albicans and C. parapsilosis are human pathogens causing severe infections. The NLRP3 inflammasome plays a crucial role in host defence against C. albicans, but it has been previously unknown whether C. parapsilosis activates this complex. Here we show that C. parapsilosis induces caspase-1 activation and interleukin-1β (IL-1β) secretion in THP-1, as well as primary, human macrophages. IL-1β secretion was dependent on NLRP3, K+-efflux, TLR4, IRAK, Syk, caspase-1, caspase-8 and NADPH-oxidase. Importantly, while C. albicans induced robust IL-1β release after 4 h, C. parapsilosis was not able to stimulate the production of IL-1β after this short incubation period. We also found that C. parapsilosis was phagocytosed to a lesser extent, and induced significantly lower ROS production and lysosomal cathepsin B release compared to C. albicans, suggesting that the low extent of inflammasome activation by C. parapsilosis may result from a delay in the so-called “signal 2”. In conclusion, this is the first study to examine the molecular pathways responsible for the IL-1β production in response to a non-albicans Candida species, and these results enhance our understanding about the immune response against C. parapsilosis. PMID:28225025

  18. Liposome-Mediated Cellular Delivery of Active gp91phox

    PubMed Central

    Marques, Bruno; Liguori, Lavinia; Paclet, Marie-Hélène; Villegas-Mendéz, Ana; Rothe, Romy; Morel, Françoise; Lenormand, Jean-Luc

    2007-01-01

    Background Gp91phox is a transmembrane protein and the catalytic core of the NADPH oxidase complex of neutrophils. Lack of this protein causes chronic granulomatous disease (CGD), a rare genetic disorder characterized by severe and recurrent infections due to the incapacity of phagocytes to kill microorganisms. Methodology Here we optimize a prokaryotic cell-free expression system to produce integral mammalian membrane proteins. Conclusions Using this system, we over-express truncated forms of the gp91phox protein under soluble form in the presence of detergents or lipids resulting in active proteins with a “native-like” conformation. All the proteins exhibit diaphorase activity in the presence of cytosolic factors (p67phox, p47phox, p40phox and Rac) and arachidonic acid. We also produce proteoliposomes containing gp91phox protein and demonstrate that these proteins exhibit activities similar to their cellular counterpart. The proteoliposomes induce rapid cellular delivery and relocation of recombinant gp91phox proteins to the plasma membrane. Our data support the concept of cell-free expression technology for producing recombinant proteoliposomes and their use for functional and structural studies or protein therapy by complementing deficient cells in gp91phox protein. PMID:17848987

  19. Activities, self-referent memory beliefs, and cognitive performance: evidence for direct and mediated relations.

    PubMed

    Jopp, Daniela; Hertzog, Christopher

    2007-12-01

    In this study, the authors investigated the role of activities and self-referent memory beliefs for cognitive performance in a life-span sample. A factor analysis identified 8 activity factors, including Developmental Activities, Experiential Activities, Social Activities, Physical Activities, Technology Use, Watching Television, Games, and Crafts. A second-order general activity factor was significantly related to a general factor of cognitive function as defined by ability tests. Structural regression models suggested that prediction of cognition by activity level was partially mediated by memory beliefs, controlling for age, education, health, and depressive affect. Models adding paths from general and specific activities to aspects of crystallized intelligence suggested additional unique predictive effects for some activities. In alternative models, nonsignificant effects of beliefs on activities were detected when cognition predicted both variables, consistent with the hypothesis that beliefs derive from monitoring cognition and have no influence on activity patterns.

  20. Dimethylphosphinate bridged binuclear Rh(i) catalysts for the alkoxycarbonylation of aromatic C-H bonds.

    PubMed

    Iturmendi, Amaia; Sanz Miguel, Pablo J; Popoola, Saheed A; Al-Saadi, Abdulaziz A; Iglesias, Manuel; Oro, Luis A

    2016-11-14

    A variety of binuclear rhodium(i) complexes featuring two bridging dimethylphosphinate ligands ((CH3)2PO2(-)) have been prepared and tested in the alkoxycarbonylation of aromatic C-H bonds. The complex [Rh(μ-κO,O'-(CH3)2PO2)(cod)]2 has been prepared by a reaction of [Rh(μ-MeO)(cod)]2 with 2 equivalents of dimethylphosphinic acid. Binuclear complexes [Rh(μ-κO,O'-(CH3)2PO2)(CO)L]2 (L = PPh3, P(OMe)Ph2 and P(OPh)3) were obtained by carbonylation of the related mononuclear complexes [Rh(κO-(CH3)2PO2)(cod)(L)], which were prepared in situ by the reaction of [Rh(μ-κO,O'-(CH3)2PO2)(cod)]2 with 2 equivalents of L. Conversely, if L = IPr, the reaction of [Rh(μ-κO,O'-(CH3)2PO2)(CO)L]2 with carbon monoxide affords the mononuclear complex [Rh(κO-(CH3)2PO2)(CO)2IPr]. The subsequent reaction with trimethylamine N-oxide gives the corresponding binuclear complex [Rh(μ-κO,O'-(CH3)2PO2)(CO)(IPr)]2 by abstraction of one of the carbonyl ligands. Complexes [Rh(μ-κO,O'-(CH3)2PO2)(cod)]2 and [Rh(κO-(CH3)2PO2)(cod)(L)] (L = IPr, PPh3, P(OMe)Ph2, P(OPh)3) are active precatalysts in the alkoxycarbonylation of C-H bonds, with the ligand system playing a key role in the catalytic activity. The complexes that feature more labile Rh-L bonds give rise to better catalysts, probably due to the more straightforward substitution of L by a second carbonyl ligand, since a more electrophilic carbonyl carbon atom is more susceptible toward aryl migration. In fact, complexes [Rh(μ-κO,O'-(CH3)2PO2)(CO)2]2 and [Rh(μ-Cl)(CO)2]2, generated in situ from [Rh(μ-κO,O'-(CH3)2PO2)(cod)]2 and [Rh(μ-Cl)(cod)2]2, respectively, are the most active catalysts tested in this work.

  1. Fractalkine mediates inflammatory pain through activation of satellite glial cells.

    PubMed

    Souza, Guilherme R; Talbot, Jhimmy; Lotufo, Celina M; Cunha, Fernando Q; Cunha, Thiago M; Ferreira, Sérgio H

    2013-07-02

    The activation of the satellite glial cells (SGCs) surrounding the dorsal root ganglion (DRG) neurons appears to play a role in pathological pain. We tested the hypothesis that fractalkine, which is constitutively expressed by primary nociceptive neurons, is the link between peripheral inflammation and the activation of SGCs and is thus responsible for the genesis of the inflammatory pain. The injection of carrageenin into the rat hind paw induced a decrease in the mechanical nociceptive threshold (hypernociception), which was associated with an increase in mRNA and GFAP protein expression in the DRG. Both events were inhibited by anti-fractalkine antibody administered directly into the DRG (L5) [intraganglionar (i.gl.)]. The administration of fractalkine into the DRG (L5) produced mechanical hypernociception in a dose-, time-, and CX3C receptor-1 (CX3CR1)-dependent manner. Fractalkine's hypernociceptive effect appears to be indirect, as it was reduced by local treatment with anti-TNF-α antibody, IL-1-receptor antagonist, or indomethacin. Accordingly, the in vitro incubation of isolated and cultured SGC with fractalkine induced the production/release of TNF-α, IL-1β, and prostaglandin E2. Finally, treatment with i.gl. fluorocitrate blocked fractalkine (i.gl.)- and carrageenin (paw)-induced hypernociception. Overall, these results suggest that, during peripheral inflammation, fractalkine is released in the DRG and contributes to the genesis of inflammatory hypernociception. Fractalkine's effect appears to be dependent on the activation of the SGCs, leading to the production of TNFα, IL-1β, and prostanoids, which are likely responsible for the maintenance of inflammatory pain. Thus, these results indicate that the inhibition of fractalkine/CX3CR1 signaling in SGCs may serve as a target to control inflammatory pain.

  2. BAX channel activity mediates lysosomal disruption linked to Parkinson disease.

    PubMed

    Bové, Jordi; Martínez-Vicente, Marta; Dehay, Benjamin; Perier, Celine; Recasens, Ariadna; Bombrun, Agnes; Antonsson, Bruno; Vila, Miquel

    2014-05-01

    Lysosomal disruption is increasingly regarded as a major pathogenic event in Parkinson disease (PD). A reduced number of intraneuronal lysosomes, decreased levels of lysosomal-associated proteins and accumulation of undegraded autophagosomes (AP) are observed in PD-derived samples, including fibroblasts, induced pluripotent stem cell-derived dopaminergic neurons, and post-mortem brain tissue. Mechanistic studies in toxic and genetic rodent PD models attribute PD-related lysosomal breakdown to abnormal lysosomal membrane permeabilization (LMP). However, the molecular mechanisms underlying PD-linked LMP and subsequent lysosomal defects remain virtually unknown, thereby precluding their potential therapeutic targeting. Here we show that the pro-apoptotic protein BAX (BCL2-associated X protein), which permeabilizes mitochondrial membranes in PD models and is activated in PD patients, translocates and internalizes into lysosomal membranes early following treatment with the parkinsonian neurotoxin MPTP, both in vitro and in vivo, within a time-frame correlating with LMP, lysosomal disruption, and autophagosome accumulation and preceding mitochondrial permeabilization and dopaminergic neurodegeneration. Supporting a direct permeabilizing effect of BAX on lysosomal membranes, recombinant BAX is able to induce LMP in purified mouse brain lysosomes and the latter can be prevented by pharmacological blockade of BAX channel activity. Furthermore, pharmacological BAX channel inhibition is able to prevent LMP, restore lysosomal levels, reverse AP accumulation, and attenuate mitochondrial permeabilization and overall nigrostriatal degeneration caused by MPTP, both in vitro and in vivo. Overall, our results reveal that PD-linked lysosomal impairment relies on BAX-induced LMP, and point to small molecules able to block BAX channel activity as potentially beneficial to attenuate both lysosomal defects and neurodegeneration occurring in PD.

  3. Enhanced liposome-mediated activity of piperacillin against staphylococci.

    PubMed Central

    Nacucchio, M C; Bellora, M J; Sordelli, D O; D'Aquino, M

    1985-01-01

    This study showed that encapsulation of the beta-lactam antibiotic piperacillin (PIP) by liposomes prepared with phosphatidylcholine and cholesterol (1:1) protected the drug from hydrolysis by staphylococcal beta-lactamase. This was demonstrated by growth inhibition of Staphylococcus aureus in the presence of the liposomal preparation containing PIP at a 50% MIC. Growth inhibition was also seen when exogenous beta-lactamase was added. Furthermore, adsorption of PIP onto the surface of liposomes containing buffer conferred a significant degree of protection against enzymatic hydrolysis of the drug, thus enhancing its antistaphylococcal activity. PMID:3872624

  4. ELF5-Mediated AR Activation Regulates Prostate Cancer Progression

    PubMed Central

    Li, Kai; Guo, Yongmin; Yang, Xiong; Zhang, Zhihong; Zhang, Changwen; Xu, Yong

    2017-01-01

    The transcription factor E74-like factor 5 (ELF5) is a potent antioncogene that can prevent epithelial-mesenchymal transition (EMT) and metastasis in prostate cancer (PCa). However, little is known how it suppress the tumor growth and if it can interact with androgen receptor (AR). In this study, we find that the ELF5 is frequently expressed in AR activated PCa cells, where it binds to AR acting as a physiological partner and negatively regulates its transcriptional activity. In addition, the interaction between ELF5 and AR is androgen-dependent. Downregulation of ELF5 by shRNA increases the expression of AR-response genes and the progression of PCa. Moreover, ELF5 is a AR-dependent gene that its expression can be induced by androgen and suppressed by antiandrogen treatment. Notably, forced reduction of ELF5 in LNCaP cells facilitates the binding of AR to ARE in ELF5 gene and enabling its transcription, so that low level ELF5 can turn up its own expression by the negative feedback loop. PMID:28287091

  5. Photocatalytic degradation of sunscreen active ingredients mediated by nanostructured materials

    NASA Astrophysics Data System (ADS)

    Soto-Vazquez, Loraine

    Water scarcity and pollution are environmental issues with terrible consequences. In recent years several pharmaceutical and personal care products, such as sunscreen active ingredients, have been detected in different water matrices. Its recalcitrant behavior in the environment has caused controversies and generated countless questions about its safety. During this research, we employed an advanced oxidation process (photocatalysis) to degrade sunscreen active ingredients. For this study, we used a 3x3 system, evaluating three photocatalysts and three different contaminants. From the three catalysts employed, two of them were synthesized. ZnO nanoparticles were obtained using zinc acetate dihydrated as the precursor, and TiO2 nanowires were synthesized from titanium tetrachloride precursor. The third catalyst employed (namely, P25) was obtained commercially. The synthesized photocatalysts were characterized in terms of the morphology, elemental composition, crystalline structure, elemental oxidation states, vibrational modes and surface area, using SEM-EDS, XRD, XPS, Raman spectroscopy and BET measurements, respectively. The photocatalysts were employed during the study of the degradation of p-aminobenzoic acid, phenylbenzimidazole sulfonic acid, and benzophenone-4. In all the cases, at least 50% degradation was achieved. P25 showed degradation efficiencies above 90%, and from the nine systems, 7 of them degraded at least 86%.

  6. Fructokinase activity mediates dehydration-induced renal injury.

    PubMed

    Roncal Jimenez, Carlos A; Ishimoto, Takuji; Lanaspa, Miguel A; Rivard, Christopher J; Nakagawa, Takahiko; Ejaz, A Ahsan; Cicerchi, Christina; Inaba, Shinichiro; Le, MyPhuong; Miyazaki, Makoto; Glaser, Jason; Correa-Rotter, Ricardo; González, Marvin A; Aragón, Aurora; Wesseling, Catharina; Sánchez-Lozada, Laura G; Johnson, Richard J

    2014-08-01

    The epidemic of chronic kidney disease in Nicaragua (Mesoamerican nephropathy) has been linked with recurrent dehydration. Here we tested whether recurrent dehydration may cause renal injury by activation of the polyol pathway, resulting in the generation of endogenous fructose in the kidney that might subsequently induce renal injury via metabolism by fructokinase. Wild-type and fructokinase-deficient mice were subjected to recurrent heat-induced dehydration. One group of each genotype was provided water throughout the day and the other group was hydrated at night, after the dehydration. Both groups received the same total hydration in 24 h. Wild-type mice that received delayed hydration developed renal injury, with elevated serum creatinine, increased urinary NGAL, proximal tubular injury, and renal inflammation and fibrosis. This was associated with activation of the polyol pathway, with increased renal cortical sorbitol and fructose levels. Fructokinase-knockout mice with delayed hydration were protected from renal injury. Thus, recurrent dehydration can induce renal injury via a fructokinase-dependent mechanism, likely from the generation of endogenous fructose via the polyol pathway. Access to sufficient water during the dehydration period can protect mice from developing renal injury. These studies provide a potential mechanism for Mesoamerican nephropathy.

  7. Parthanatos Mediates AIMP2 Activated Age Dependent Dopaminergic Neuronal Loss

    PubMed Central

    Lee, Yunjong; Karuppagounder, Senthilkumar S.; Shin, Joo-Ho; Lee, Yun-Il; Ko, Han Seok; Swing, Debbie; Jiang, Haisong; Kang, Sung-Ung; Lee, Byoung Dae; Kang, Ho Chul; Kim, Donghoon; Tessarollo, Lino; Dawson, Valina L.; Dawson, Ted M.

    2013-01-01

    The defining pathogenic feature of Parkinson’s disease is the age dependent loss of dopaminergic neurons. Mutations and inactivation of parkin, an ubiquitin E3 ligase, cause Parkinson’s disease through accumulation of pathogenic substrates. Here we show that transgenic overexpression of the parkin substrate, aminoacyl-tRNA synthetase complex interacting multifunctional protein-2 (AIMP2) leads to a selective, age-dependent progressive loss of dopaminergic neurons via activation of poly(ADP-ribose) polymerase-1 (PARP1). AIMP2 accumulation in vitro and in vivo results in PARP1 overactivation and dopaminergic cell toxicity via direct association of these proteins in the nucleus providing a new path to PARP1 activation other than DNA damage. Inhibition of PARP1 through gene deletion or drug inhibition reverses behavioral deficits and protects in vivo against dopamine neuron death in AIMP2 transgenic mice. These data indicate that brain permeable PARP inhibitors could be effective in delaying or preventing disease progression in Parkinson’s disease. PMID:23974709

  8. ELF5-Mediated AR Activation Regulates Prostate Cancer Progression.

    PubMed

    Li, Kai; Guo, Yongmin; Yang, Xiong; Zhang, Zhihong; Zhang, Changwen; Xu, Yong

    2017-03-13

    The transcription factor E74-like factor 5 (ELF5) is a potent antioncogene that can prevent epithelial-mesenchymal transition (EMT) and metastasis in prostate cancer (PCa). However, little is known how it suppress the tumor growth and if it can interact with androgen receptor (AR). In this study, we find that the ELF5 is frequently expressed in AR activated PCa cells, where it binds to AR acting as a physiological partner and negatively regulates its transcriptional activity. In addition, the interaction between ELF5 and AR is androgen-dependent. Downregulation of ELF5 by shRNA increases the expression of AR-response genes and the progression of PCa. Moreover, ELF5 is a AR-dependent gene that its expression can be induced by androgen and suppressed by antiandrogen treatment. Notably, forced reduction of ELF5 in LNCaP cells facilitates the binding of AR to ARE in ELF5 gene and enabling its transcription, so that low level ELF5 can turn up its own expression by the negative feedback loop.

  9. PKCα mediates acetylcholine-induced activation of TRPV4-dependent calcium influx in endothelial cells

    PubMed Central

    Adapala, Ravi K.; Talasila, Phani K.; Bratz, Ian N.; Zhang, David X.; Suzuki, Makoto; Meszaros, J. Gary

    2011-01-01

    Transient receptor potential vanilloid channel 4 (TRPV4) is a polymodally activated nonselective cationic channel implicated in the regulation of vasodilation and hypertension. We and others have recently shown that cyclic stretch and shear stress activate TRPV4-mediated calcium influx in endothelial cells (EC). In addition to the mechanical forces, acetylcholine (ACh) was shown to activate TRPV4-mediated calcium influx in endothelial cells, which is important for nitric oxide-dependent vasodilation. However, the molecular mechanism through which ACh activates TRPV4 is not known. Here, we show that ACh-induced calcium influx and endothelial nitric oxide synthase (eNOS) phosphorylation but not calcium release from intracellular stores is inhibited by a specific TRPV4 antagonist, AB-159908. Importantly, activation of store-operated calcium influx was not altered in the TRPV4 null EC, suggesting that TRPV4-dependent calcium influx is mediated through a receptor-operated pathway. Furthermore, we found that ACh treatment activated protein kinase C (PKC) α, and inhibition of PKCα activity by the specific inhibitor Go-6976, or expression of a kinase-dead mutant of PKCα but not PKCε or downregulation of PKCα expression by chronic 12-O-tetradecanoylphorbol-13-acetate treatment, completely abolished ACh-induced calcium influx. Finally, we found that ACh-induced vasodilation was inhibited by the PKCα inhibitor Go-6976 in small mesenteric arteries from wild-type mice, but not in TRPV4 null mice. Taken together, these findings demonstrate, for the first time, that a specific isoform of PKC, PKCα, mediates agonist-induced receptor-mediated TRPV4 activation in endothelial cells. PMID:21705673

  10. Activity and specificity of TRV-mediated gene editing in plants.

    PubMed

    Ali, Zahir; Abul-Faraj, Aala; Piatek, Marek; Mahfouz, Magdy M

    2015-01-01

    Plant trait engineering requires efficient targeted genome-editing technologies. Clustered regularly interspaced palindromic repeats (CRISPRs)/ CRISPR associated (Cas) type II system is used for targeted genome-editing applications across eukaryotic species including plants. Delivery of genome engineering reagents and recovery of mutants remain challenging tasks for in planta applications. Recently, we reported the development of Tobacco rattle virus (TRV)-mediated genome editing in Nicotiana benthamiana. TRV infects the growing points and possesses small genome size; which facilitate cloning, multiplexing, and agroinfections. Here, we report on the persistent activity and specificity of the TRV-mediated CRISPR/Cas9 system for targeted modification of the Nicotiana benthamiana genome. Our data reveal the persistence of the TRV- mediated Cas9 activity for up to 30 d post-agroinefection. Further, our data indicate that TRV-mediated genome editing exhibited no off-target activities at potential off-targets indicating the precision of the system for plant genome engineering. Taken together, our data establish the feasibility and exciting possibilities of using virus-mediated CRISPR/Cas9 for targeted engineering of plant genomes.

  11. Exercise as a mediator of hepcidin activity in athletes.

    PubMed

    Peeling, Peter

    2010-11-01

    Iron is a trace mineral used by the body in many physiological processes that are essential for athletic performance. However, it is common that an athlete's iron stores are compromised via several well-established exercise-related mechanisms such as hemolysis, hematuria, sweating and gastrointestinal bleeding. Recently, however, a new mechanism for athletics-induced iron deficiency has been proposed, involving the influence of physical activity on the post-exercise hepcidin response. Hepcidin is a liver-produced hormone that regulates iron metabolism in the gut and macrophages. This hormone has become the focus of recent investigations into altered iron metabolism in athletes, and may be a mitigating factor implicated in athletics-induced iron deficiency. This review attempts to summarize and disseminate the collective knowledge currently held regarding exercise and hepcidin expression, in addition to suggesting the direction for future research in this area.

  12. Structure-activity relationship in cationic lipid mediated gene transfection.

    PubMed

    Niculescu-Duvaz, Dan; Heyes, James; Springer, Caroline J

    2003-07-01

    Non-viral synthetic vectors for gene delivery represent a safer alternative to viral vectors. Their main drawback is the low transfection efficiency, especially in vivo. Among the non-viral vectors currently in use, the cationic liposomes composed of cationic lipids are the most common. This review discusses the physicochemical properties of cationic lipids, the formation, macrostructure and specific parameters of the corresponding formulated liposomes, and the effect of all these parameters on transfection efficiency. The optimisation of liposomal vectors requires both the understanding of the biological variables involved in the transfection process, and the effect of the structural elements of the cationic lipids on these biological variables. The biological barriers relevant for in vitro and in vivo transfection are identified, and solutions to overcome them based on rational design of the cationic lipids are discussed. The review focuses on the relationship between the structure of the cationic lipid and the transfection activity. The structure is analysed in a modular manner. The hydrophobic domain, the cationic head group, the backbone that acts as a scaffold for the other domains, the linkers between backbone, hydrophobic domain and cationic head group, the polyethyleneglycol chains and the targeting moiety are identified as distinct elements of the cationic lipids used in gene therapy. The main chemical functionalities used to built these domains, as well as overall molecular features such as architecture and geometry, are presented. Studies of structure-activity relationships of each cationic lipid domain, including the authors', and the trends identified by these studies, help furthering the understanding of the mechanism governing the formation and behaviour of cationic liposomes in gene delivery, and therefore the rational design of new improved cationic lipids vectors capable of achieving clinical significance.

  13. Polymer- and silica-supported iron BPMEN-inspired catalysts for C-H bond functionalization reactions.

    PubMed

    Feng, Yan; Moschetta, Eric G; Jones, Christopher W

    2014-11-01

    Direct catalytic C-H bond functionalization is a key challenge in synthetic chemistry, with many popular C-H activation methodologies involving precious-metal catalysts. In recent years, iron catalysts have emerged as a possible alternative to the more common precious-metal catalysts, owing to its high abundance, low cost, and low toxicity. However, iron catalysts are plagued by two key factors: the ligand cost and the low turnover numbers (TONs) typically achieved. In this work, two approaches are presented to functionalize the popular N(1),N(2)-dimethyl-N(1),N(2)-bis(pyridin-2-ylmethyl)ethane-1,2-diamine (BPMEN) ligand, so that it can be supported on porous silica or polymer resin supports. Four new catalysts are prepared and evaluated in an array of catalytic C-H functionalization reactions by using cyclohexane, cyclohexene, cyclooctane, adamantane, benzyl alcohol, and cumene with aqueous hydrogen peroxide. Catalyst recovery and recycling is demonstrated by using supported catalysts, which allows for a modest increase in the TON achieved with these catalysts.

  14. NR2D-containing NMDA receptors mediate tissue plasminogen activator-promoted neuronal excitotoxicity.

    PubMed

    Baron, A; Montagne, A; Cassé, F; Launay, S; Maubert, E; Ali, C; Vivien, D

    2010-05-01

    Although the molecular bases of its actions remain debated, tissue-type plasminogen activator (tPA) is a paradoxical brain protease, as it favours some learning/memory processes, but increases excitotoxic neuronal death. Here, we show that, in cultured cortical neurons, tPA selectively promotes NR2D-containing N-methyl-D-aspartate receptor (NMDAR)-dependent activation. We show that tPA-mediated signalling and neurotoxicity through the NMDAR are blocked by co-application of an NR2D antagonist (phenanthrene derivative (2S(*), 3R(*))-1-(phenanthrene-2-carbonyl)piperazine-2,3-dicarboxylic acid, PPDA) or knockdown of neuronal NR2D expression. In sharp contrast with cortical neurons, hippocampal neurons do not exhibit NR2D both in vitro and in vivo and are consequently resistant to tPA-promoted NMDAR-mediated neurotoxicity. Moreover, we have shown that activation of synaptic NMDAR prevents further tPA-dependent NMDAR-mediated neurotoxicity and sensitivity to PPDA. This study shows that the earlier described pro-neurotoxic effect of tPA is mediated by NR2D-containing NMDAR-dependent extracellular signal-regulated kinase activation, a deleterious effect prevented by synaptic pre-activation.

  15. Key mediators of intracellular amino acids signaling to mTORC1 activation.

    PubMed

    Duan, Yehui; Li, Fengna; Tan, Kunrong; Liu, Hongnan; Li, Yinghui; Liu, Yingying; Kong, Xiangfeng; Tang, Yulong; Wu, Guoyao; Yin, Yulong

    2015-05-01

    Mammalian target of rapamycin complex 1 (mTORC1) is activated by amino acids to promote cell growth via protein synthesis. Specifically, Ras-related guanosine triphosphatases (Rag GTPases) are activated by amino acids, and then translocate mTORC1 to the surface of late endosomes and lysosomes. Ras homolog enriched in brain (Rheb) resides on this surface and directly activates mTORC1. Apart from the presence of intracellular amino acids, Rag GTPases and Rheb, other mediators involved in intracellular amino acid signaling to mTORC1 activation include human vacuolar sorting protein-34 (hVps34) and mitogen-activating protein kinase kinase kinase kinase-3 (MAP4K3). Those molecular links between mTORC1 and its mediators form a complicate signaling network that controls cellular growth, proliferation, and metabolism. Moreover, it is speculated that amino acid signaling to mTORC1 may start from the lysosomal lumen. In this review, we discussed the function of these mediators in mTORC1 pathway and how these mediators are regulated by amino acids in details.

  16. Asparagine deprivation mediated by Salmonella asparaginase causes suppression of activation-induced T cell metabolic reprogramming.

    PubMed

    Torres, AnnMarie; Luke, Joanna D; Kullas, Amy L; Kapilashrami, Kanishk; Botbol, Yair; Koller, Antonius; Tonge, Peter J; Chen, Emily I; Macian, Fernando; van der Velden, Adrianus W M

    2016-02-01

    Salmonellae are pathogenic bacteria that induce immunosuppression by mechanisms that remain largely unknown. Previously, we showed that a putative type II l-asparaginase produced by Salmonella Typhimurium inhibits T cell responses and mediates virulence in a murine model of infection. Here, we report that this putative L-asparaginase exhibits L-asparagine hydrolase activity required for Salmonella Typhimurium to inhibit T cells. We show that L-asparagine is a nutrient important for T cell activation and that L-asparagine deprivation, such as that mediated by the Salmonella Typhimurium L-asparaginase, causes suppression of activation-induced mammalian target of rapamycin signaling, autophagy, Myc expression, and L-lactate secretion. We also show that L-asparagine deprivation mediated by the Salmonella Typhimurium L-asparaginase causes suppression of cellular processes and pathways involved in protein synthesis, metabolism, and immune response. Our results advance knowledge of a mechanism used by Salmonella Typhimurium to inhibit T cell responses and mediate virulence, and provide new insights into the prerequisites of T cell activation. We propose a model in which l-asparagine deprivation inhibits T cell exit from quiescence by causing suppression of activation-induced metabolic reprogramming.

  17. Effects of CYP7B1-mediated catalysis on estrogen receptor activation.

    PubMed

    Pettersson, Hanna; Lundqvist, Johan; Norlin, Maria

    2010-09-01

    Most of the many biological effects of estrogens are mediated via the estrogen receptors ERalpha and beta. The current study examines the role of CYP7B1-mediated catalysis for activation of ER. Several reports suggest that CYP7B1 may be important for hormonal action but previously published studies are contradictory concerning the manner in which CYP7B1 affects ERbeta-mediated response. In the current study, we examined effects of several CYP7B1-related steroids on ER activation, using an estrogen response element (ERE) reporter system. Our studies showed significant stimulation of ER by 5-androstene-3beta,17beta-diol (Aene-diol) and 5alpha-androstane-3beta,17beta-diol (3beta-Adiol). In contrast, the CYP7B1-formed metabolites from these steroids did not activate the receptor, indicating that CYP7B1-mediated metabolism abolishes the ER-stimulating effect of these compounds. The mRNA level of HEM45, a gene known to be stimulated by estrogens, was strongly up-regulated by Aene-diol but not by its CYP7B1-formed metabolite, further supporting this concept. We did not observe stimulation by dehydroepiandrosterone (DHEA) or 7alpha-hydroxy-DHEA, previously suggested to affect ERbeta-mediated response. As part of these studies we examined metabolism of Aene-diol in pig liver which is high in CYP7B1 content. These experiments indicate that CYP7B1-mediated metabolism of Aene-diol is of a similar rate as the metabolism of the well-known CYP7B1 substrates DHEA and 3beta-Adiol. CYP7B1-mediated metabolism of 3beta-Adiol has been proposed to influence ERbeta-mediated growth suppression. Our results indicate that Aene-diol also might be important for ER-related pathways. Our data indicate that low concentrations of Aene-diol can trigger ER-mediated response equally well for both ERalpha and beta and that CYP7B1-mediated conversion of Aene-diol into a 7alpha-hydroxymetabolite will result in loss of action.

  18. HTLV-1 Tax-mediated TAK1 activation involves TAB2 adapter protein

    SciTech Connect

    Yu Qingsheng; Minoda, Yasumasa; Yoshida, Ryoko; Yoshida, Hideyuki; Iha, Hidekatsu; Kobayashi, Takashi; Yoshimura, Akihiko; Takaesu, Giichi

    2008-01-04

    Human T cell leukemia virus type 1 (HTLV-1) Tax is an oncoprotein that plays a crucial role in the proliferation and transformation of HTLV-1-infected T lymphocytes. It has recently been reported that Tax activates a MAPKKK family, TAK1. However, the molecular mechanism of Tax-mediated TAK1 activation is not well understood. In this report, we investigated the role of TAK1-binding protein 2 (TAB2) in Tax-mediated TAK1 activation. We found that TAB2 physically interacts with Tax and augments Tax-induced NF-{kappa}B activity. Tax and TAB2 cooperatively activate TAK1 when they are coexpressed. Furthermore, TAK1 activation by Tax requires TAB2 binding as well as ubiquitination of Tax. We also found that the overexpression of TRAF2, 5, or 6 strongly induces Tax ubiquitination. These results suggest that TAB2 may be critically involved in Tax-mediated activation of TAK1 and that NF-{kappa}B-activating TRAF family proteins are potential cellular E3 ubiquitin ligases toward Tax.

  19. Television viewing: Moderator or mediator of an adolescent physical activity intervention?

    PubMed Central

    Graham, Dan J.; Schneider, Margaret; Cooper, Dan M.

    2012-01-01

    Purpose To determine whether amount of TV watched by participants enrolled in a physical activity intervention mediates or moderates program effectiveness Design Nine-month controlled school-based physical activity intervention Setting Public high school Participants One hundred twenty two sedentary adolescent females (mean age = 15.04 ± 0.79 years) Intervention Supervised in-class exercise, health education, and internet-based self-monitoring Measures Physical Activity - 3 Day Physical Activity Recall; Television Viewing – self-report; Cardiovascular Fitness – Cycle Ergometer Analysis T-tests were conducted to examine between-group differences. Linear regression equations tested the mediating and/or moderating role of television watching relative to the intervention. Results TV viewing moderated the intervention’s effect on vigorous activity; the intervention significantly predicted physical activity among high (β = −.45; p <.001), but not low (p >.05), TV watchers. TV viewing did not mediate the intervention effect. Conclusions Consistent with displacement theory, adolescents who watched more television prior to the intervention showed post-intervention increases in vigorous physical activity and concomitant decreases in television viewing, whereas those who watched less TV showed no change in physical activity or television viewing. PMID:19004156

  20. A water-mediated allosteric network governs activation of Aurora kinase A.

    PubMed

    Cyphers, Soreen; Ruff, Emily F; Behr, Julie M; Chodera, John D; Levinson, Nicholas M

    2017-04-01

    The catalytic activity of many protein kinases is controlled by conformational changes of a conserved Asp-Phe-Gly (DFG) motif. We used an infrared probe to track the DFG motif of the mitotic kinase Aurora A (AurA) and found that allosteric activation by the spindle-associated protein Tpx2 involves an equilibrium shift toward the active DFG-in state. Förster resonance energy transfer experiments show that the activation loop undergoes a nanometer-scale movement that is tightly coupled to the DFG equilibrium. Tpx2 further activates AurA by stabilizing a water-mediated allosteric network that links the C-helix to the active site through an unusual polar residue in the regulatory spine. The polar spine residue and water network of AurA are essential for phosphorylation-driven activation, but an alternative form of the water network found in related kinases can support Tpx2-driven activation, suggesting that variations in the water-mediated hydrogen bond network mediate regulatory diversification in protein kinases.

  1. BARYON LOADING OF ACTIVE GALACTIC NUCLEUS JETS MEDIATED BY NEUTRONS

    SciTech Connect

    Toma, K.; Takahara, F.

    2012-08-01

    Plasmas of geometrically thick, black hole (BH) accretion flows in active galactic nuclei (AGNs) are generally collisionless for protons, and involve magnetic field turbulence. Under such conditions a fraction of protons can be accelerated stochastically and create relativistic neutrons via nuclear collisions. These neutrons can freely escape from the accretion flow and decay into protons in the dilute polar region above the rotating BH to form relativistic jets. We calculate geometric efficiencies of the neutron energy and mass injections into the polar region, and show that this process can deposit luminosity as high as L{sub j}{approx}2 Multiplication-Sign 10{sup -3} M-dot c{sup 2} and mass loading M-dot{sub j}{approx}6 Multiplication-Sign 10{sup -4} M-dot for the case of the BH mass M {approx} 10{sup 8} M{sub Sun }, where M-dot is the mass accretion rate. The terminal Lorentz factors of the jets are {Gamma} {approx} 3, and they may explain the AGN jets having low luminosities. For higher luminosity jets, which can be produced by additional energy inputs such as Poynting flux, the neutron decay still can be a dominant mass loading process, leading to, e.g., {Gamma} {approx} 50 for L{sub j,tot}{approx}3 Multiplication-Sign 10{sup -2} M-dot c{sup 2}.

  2. Photobiologic-mediated fabrication of silver nanoparticles with antibacterial activity.

    PubMed

    Lee, Jeong-Ho; Lim, Jeong-Muk; Velmurugan, Palanivel; Park, Yool-Jin; Park, Youn-Jong; Bang, Keuk-Soo; Oh, Byung-Taek

    2016-09-01

    We present the simple, eco-friendly synthesis of silver nanoparticles (AgNPs) using sunlight or green, red, blue, or white LED light together with Dryopteris crassirhizoma rhizome extract (DCRE) as the reducing and capping agent. The preliminary indication of AgNP production was a color change from yellowish green to brown after light exposure in the presence of DCRE. Optimization of parameters such as pH, inoculum dose, and metal ion concentration played an important role in achieving nanoparticle production in 30min. The spectroscopic and morphological properties of AgNPs were characterized using UV-Vis spectroscopy through the presence of a characteristic surface plasmon resonance (SPR) band for AgNPs, Fourier transform infrared spectroscopy (FT-IR), high-resolution transmission electron microscopy (HR-TEM), and X-ray diffraction (XRD). The FT-IR results indicated that the phytochemical present in DCRE was the probable reducing/capping agent involved in the synthesis of AgNPs, and light radiation enhanced nanoparticle production. HR-TEM revealed that the AgNPs were almost spherical with an average size of 5-60nm under all light sources. XRD studies confirmed the face cubic center (fcc) unit cell structure of AgNPs. The synthesized AgNPs showed good antimicrobial activity against Bacillus cereus and Pseudomonas aeruginosa. This study will bring a new insight in ecofriendly production of metal nanoparticles.

  3. Frontal lobe activation mediates the relation between sensation seeking and cortisol increases.

    PubMed

    Freeman, Hani D; Beer, Jennifer S

    2010-10-01

    Low sensation seekers are theorized to avoid risk more often because risk is emotionally more costly for them (in comparison to high sensation seekers). Therefore, individual differences in sensation seeking should predict differences in risk task-induced cortisol changes. Furthermore, the neural mediation that accounts for the relation between sensation seeking and cortisol changes has not been studied. The current study tested whether individual differences in sensation seeking predicted cortisol changes in relation to a risk task and whether this relation was mediated by frontal lobe activation. Participants (N=17) who varied in sensation seeking completed an fMRI study in which they rated the likelihood they would take various risks. Cortisol was measured from saliva samples collected prior to and after the fMRI procedure. The findings show that low sensation seekers showed the greatest rise in cortisol after the risk procedure, and this relation was partially mediated by increased orbitofrontal cortex activity.

  4. Rh/Cu-Catalyzed Cascade [4+2] Vinylic C-H O-Annulation and Ring Contraction of α-Aryl Enones with Alkynes in Air.

    PubMed

    Zhao, Yinsong; Li, Shiqing; Zheng, Xuesong; Tang, Junbin; She, Zhijie; Gao, Ge; You, Jingsong

    2017-04-03

    An unprecedented Rh-catalyzed ketone-directed vinylic C-H activation/[4+2] O-annulation of α-aryl enones with internal alkynes followed by a Cu-catalyzed ring contraction in air to provide multiaryl-substituted furan derivatives has been developed. The preliminary mechanism study identifies the active pyrylium salt as the key intermediate.

  5. Charge-transfer-directed radical substitution enables para-selective C-H functionalization

    NASA Astrophysics Data System (ADS)

    Boursalian, Gregory B.; Ham, Won Seok; Mazzotti, Anthony R.; Ritter, Tobias

    2016-08-01

    Efficient C-H functionalization requires selectivity for specific C-H bonds. Progress has been made for directed aromatic substitution reactions to achieve ortho and meta selectivity, but a general strategy for para-selective C-H functionalization has remained elusive. Herein we introduce a previously unappreciated concept that enables nearly complete para selectivity. We propose that radicals with high electron affinity elicit arene-to-radical charge transfer in the transition state of radical addition, which is the factor primarily responsible for high positional selectivity. We demonstrate with a simple theoretical tool that the selectivity is predictable and show the utility of the concept through a direct synthesis of aryl piperazines. Our results contradict the notion, widely held by organic chemists, that radical aromatic substitution reactions are inherently unselective. The concept of radical substitution directed by charge transfer could serve as the basis for the development of new, highly selective C-H functionalization reactions.

  6. Oxidative addition of C--H bonds in organic molecules to transition metal centers

    SciTech Connect

    Bergman, R.G.

    1989-04-01

    Alkanes are among the most chemically inert organic molecules. They are reactive toward a limited range of reagents, such as highly energetic free radicals and strongly electrophilic and oxidizing species. This low reactivity is a consequence of the C--H bond energies in most saturated hydrocarbons. These values range from 90 to 98 kcal/mole for primary and secondary C--H bonds; in methane, the main constituent of natural gas, the C--H bond energy is 104 kcal/mole. This makes methane one of the most common but least reactive organic molecules in nature. This report briefly discusses the search for metal complexes capable of undergoing the C--H oxidative addition process allowing alkane chemistry to be more selective than that available using free radical reagents. 14 refs.

  7. Manganese-catalyzed late-stage aliphatic C-H azidation.

    PubMed

    Huang, Xiongyi; Bergsten, Tova M; Groves, John T

    2015-04-29

    We report a manganese-catalyzed aliphatic C-H azidation reaction that can efficiently convert secondary, tertiary, and benzylic C-H bonds to the corresponding azides. The method utilizes aqueous sodium azide solution as the azide source and can be performed under air. Besides its operational simplicity, the potential of this method for late-stage functionalization has been demonstrated by successful azidation of various bioactive molecules with yields up to 74%, including the important drugs pregabalin, memantine, and the antimalarial artemisinin. Azidation of celestolide with a chiral manganese salen catalyst afforded the azide product in 70% ee, representing a Mn-catalyzed enantioselective aliphatic C-H azidation reaction. Considering the versatile roles of organic azides in modern chemistry and the ubiquity of aliphatic C-H bonds in organic molecules, we envision that this Mn-azidation method will find wide application in organic synthesis, drug discovery, and chemical biology.

  8. Enhanced Reactivity in Dioxirane C-H Oxidations via Strain Release: A Computational and Experimental Study

    PubMed Central

    Zou, Lufeng; Paton, Robert S.; Eschenmoser, Albert; Newhouse, Timothy R.; Baran, Phil S.; Houk, K. N.

    2013-01-01

    The site- and stereo-selectivities of C-H oxidations of substituted cyclohexanes and trans-decalins by dimethyldioxirane (DMDO) were investigated computationally with quantum mechanical density functional theory (DFT). The multi-configuration CASPT2 method was employed on model systems to establish the preferred mechanism and transition state geometry. The reaction pathway involving a rebound step is established to account for the retention of stereochemistry. The oxidation of sclareolide with dioxirane reagents is reported, including the oxidation by the in situ generated tBu-TFDO, a new dioxirane that better discriminates between C-H bonds based on steric effects. The release of 1,3-diaxial strain in the transition state contributes to the site selectivity and enhanced axial reactivity for tertiary C-H bonds, a result of the lowering of distortion energy. In addition to this strain release factor, steric and inductive effects contribute to the rates of C-H oxidation by dioxiranes. PMID:23461537

  9. Characterization of nanocomposite a-C:H/Ag thin films synthesized by a hybrid deposition process

    NASA Astrophysics Data System (ADS)

    Venkatesh, M.; Taktak, S.; Meletis, E. I.

    2015-08-01

    Silver containing amorphous carbon films were deposited on Si wafer using a hybrid deposition process combining d.c. magnetron sputtering and PECVD. The concentration of Ag in the films was varied from 1.3 to 8.3 at % by changing d.c. magnetron current of Ag target. The influence of incorporated Ag in the a-C:H on the atomic bond structure of the films were investigated by XPS, FTIR, Raman, and HRTEM methods of analysis. The XPS, FTIR, and Raman studies demonstrated that as the silver concentration increased in the a-C:H, sp2 bonding content increased and a-C:H films changed to more graphitic structure. The high resolution TEM cross sectional studies revealed that crystalline Ag particles formed with a size in the range of 2-4 nm throughout an amorphous a-C:H matrix.

  10. Multidirectional Synthesis of Substituted Indazoles via Iridium-Catalyzed C-H Borylation.

    PubMed

    Sadler, Scott A; Hones, Andrew C; Roberts, Bryan; Blakemore, David; Marder, Todd B; Steel, Patrick G

    2015-05-15

    In the absence of a steric directing group, iridium-catalyzed C-H borylation of N-protected indazoles occurs rapidly and selectively at C-3 and the resulting boronate esters can be utilized in a range of downstream conversions. The functional group tolerance of the iridium-catalyzed C-H borylation reaction enables simple and efficient multidirectional syntheses of substituted indazoles to be realized.

  11. A chiral rhodium carboxamidate catalyst for enantioselective C-H amination.

    PubMed

    Zalatan, David N; Du Bois, J

    2008-07-23

    Rh2(S-nap)4, a chiral dirhodium tetracarboxamidate complex, has been developed and shown to be an effective catalyst for the asymmetric, intramolecular C-H amination of sulfamate esters. Enantiomeric excesses range from 60-99% for a collection of disparately substituted 3-arylpropylsulfamates. In addition, Rh2(S-nap)4 is found to promote chemoselective allylic C-H oxidation of unsaturated sulfamates, a property not observed with other dirhodium complexes tested to date.

  12. Cobalt-catalyzed intramolecular C-H amination with arylsulfonyl azides.

    PubMed

    Ruppel, Joshua V; Kamble, Rajesh M; Zhang, X Peter

    2007-11-08

    Cobalt complexes of porphyrins are effective catalysts for intramolecular C-H amination with arylsulfonyl azides. The cobalt-catalyzed process can proceed efficiently under mild and neutral conditions in low catalyst loading without the need of other reagents or additives, generating nitrogen gas as the only byproduct. The catalytic system can be applied to primary, secondary, and tertiary C-H bonds and is suitable for a broad range of arylsulfonyl azides, leading to high-yielding syntheses of various benzosultams.

  13. Heme Mediated STAT3 Activation in Severe Malaria

    PubMed Central

    Liu, Mingli; Amodu, Audu S.; Pitts, Sidney; Patrickson, John; Hibbert, Jacqueline M.; Battle, Monica; Ofori-Acquah, Solomon F.; Stiles, Jonathan K.

    2012-01-01

    Background The mortality of severe malaria [cerebral malaria (CM), severe malaria anemia (SMA), acute lung injury (ALI) and acute respiratory distress syndrome (ARDS)] remains high despite the availability associated with adequate treatments. Recent studies in our laboratory and others have revealed a hitherto unknown correlation between chemokine CXCL10/CXCR3, Heme/HO-1 and STAT3 and cerebral malaria severity and mortality. Although Heme/HO-1 and CXCL10/CXCR3 interactions are directly involved in the pathogenesis of CM and fatal disease, the mechanism dictating how Heme/HO-1 and CXCL10/CXCR3 are expressed and regulated under these conditions is still unknown. We therefore tested the hypothesis that these factors share common signaling pathways and may be mutually regulated. Methods We first clarified the roles of Heme/HO-1, CXCL10/CXCR3 and STAT3 in CM pathogenesis utilizing a well established experimental cerebral malaria mouse (ECM, P. berghei ANKA) model. Then, we further determined the mechanisms how STAT3 regulates HO-1 and CXCL10 as well as mutual regulation among them in CRL-2581, a murine endothelial cell line. Results The results demonstrate that (1) STAT3 is activated by P. berghei ANKA (PBA) infection in vivo and Heme in vitro. (2) Heme up-regulates HO-1 and CXCL10 production through STAT3 pathway, and regulates CXCL10 at the transcriptional level in vitro. (3) HO-1 transcription is positively regulated by CXCL10. (4) HO-1 regulates STAT3 signaling. Conclusion Our data indicate that Heme/HO-1, CXCL10/CXCR3 and STAT3 molecules as well as related signaling pathways play very important roles in the pathogenesis of severe malaria. We conclude that these factors are mutually regulated and provide new opportunities to develop potential novel therapeutic targets that could be used to supplement traditional prophylactics and treatments for malaria and improve clinical outcomes while reducing malaria mortality. Our ultimate goal is to develop novel therapies

  14. Rh(III)/Cu(II)-cocatalyzed synthesis of 1H-indazoles through C-H amidation and N-N bond formation.

    PubMed

    Yu, Da-Gang; Suri, Mamta; Glorius, Frank

    2013-06-19

    Substituted 1H-indazoles can be formed from readily available arylimidates and organo azides by Rh(III)-catalyzed C-H activation/C-N bond formation and Cu-catalyzed N-N bond formation. For the first time the N-H-imidates are demonstrated to be good directing groups in C-H activation, also capable of undergoing intramolecular N-N bond formation. The process is scalable and green, with O2 as the terminal oxidant and N2 and H2O formed as byproducts. Moreover, the products could be transformed to diverse important derivatives.

  15. Physical activity and metabolic risk among US youth: Mediation by obesity [abstract

    Technology Transfer Automated Retrieval System (TEKTRAN)

    Physical activity has been inversely associated with metabolic risk, although pediatric studies are limited. It has been hypothesized that obesity mediates this relationship. Some studies reported that waist circumference (WC) is more highly related to metabolic risk than BMI, and may be a better me...

  16. Situated Uses of ICT and Mediation of Joint Activity in a Primary Education Instructional Sequence

    ERIC Educational Resources Information Center

    Coll, Cesar; Rochera, Maria J.; Colomina, Rosa

    2010-01-01

    Introduction: From a socioconstructivist and situated perspective of teaching and learning processes, the authors analyze how one teacher and her group of 19 sixth-grade pupils use ICT. The study focuses on the way these tools mediate their activity, and evaluates the tools' potential for teaching and learning innovation. Method: A case study…

  17. Activity Theory and Technology Mediated Interaction: Cognitive Scaffolding Using Question-Based Consultation on "Facebook"

    ERIC Educational Resources Information Center

    Rambe, Patient

    2012-01-01

    Studies that employed activity theory as a theoretical lens for exploring computer-mediated interaction have not adopted social media as their object of study. However, social media provides lecturers with personalised learning environments for diagnostic and prognostic assessments of student mastery of content and deep learning. The integration…

  18. Lysozyme-mediated biomineralization of titanium-tungsten oxide hybrid nanoparticles with high photocatalytic activity.

    PubMed

    Kim, Jung Kyu; Jang, Ji-ryang; Choi, Noori; Hong, Dahyun; Nam, Chang-Hoon; Yoo, Pil J; Park, Jong Hyeok; Choe, Woo-Seok

    2014-10-21

    Titanium-tungsten oxide composites with greatly enhanced photocatalytic activity were synthesized by lysozyme-mediated biomineralization. It was shown for the first time that simple control of the onset of biomineralization could enable fine tuning of the composition and crystallinity of the composites to determine their photocatalytic performance.

  19. Mediated Effects of Perceived Competence on Youth Physical Activity and Sedentary Behavior

    ERIC Educational Resources Information Center

    Bai, Yang; Chen, Senlin; Vazou, Spyridoula; Welk, Gregory J.; Schaben, Jodee

    2015-01-01

    Purpose: This study evaluates whether physical activity (PA) and sedentary behavior (SB) are influenced by a common mediating relationship. Method: A total of 1,552 participants in 3rd to 12th grade completed an online survey that included assessments of PA at school (PAS), PA at home (PAH), and SB as well as a battery of psychosocial variables…

  20. Selective functionalisation of saturated C-H bonds with metalloporphyrin catalysts.

    PubMed

    Che, Chi-Ming; Lo, Vanessa Kar-Yan; Zhou, Cong-Ying; Huang, Jie-Sheng

    2011-04-01

    The recent surge of interest in metal-catalysed C-H bond functionalisation reactions reflects the importance of such reactions in biomimetic studies and organic synthesis. This critical review focuses on metalloporphyrin-catalysed saturated C-H bond functionalisation reported since the year 2000, including C-O, C-N and C-C bond formation via hydroxylation, amination and carbenoid insertion, respectively, together with a brief description of previous achievements in this area. Among the metalloporphyrin-catalysed reactions highlighted herein are the hydroxylation of steroids, cycloalkanes and benzylic hydrocarbons; intermolecular amination of steroids, cycloalkanes and benzylic or allylic hydrocarbons; intramolecular amination of sulfamate esters and organic azides; intermolecular carbenoid insertion into benzylic, allylic or alkane C-H bonds; and intramolecular carbenoid C-H insertion of tosylhydrazones. These metalloporphyrin-catalysed saturated C-H bond functionalisation reactions feature high regio-, diastereo- or enantioselectivity and/or high product turnover numbers. Mechanistic studies suggest the involvement of metal-oxo, -imido (or nitrene), and -carbene porphyrin complexes in the reactions. The reactivity of such metal-ligand multiple bonded species towards saturated C-H bonds, including mechanistic studies through both experimental and theoretical means, is also discussed (244 references).

  1. Modulation of Tumorigenesis by Dietary Intervention Is Not Mediated by SIRT1 Catalytic Activity

    PubMed Central

    Clark-Knowles, Katherine V.; Dewar-Darch, Danielle; Jardine, Karen E.; McBurney, Michael W.

    2014-01-01

    The protein deacetylase SIRT1 is involved in the regulation of a large number of cellular processes that are thought to be required for cancer initiation and progression. Both SIRT1 activity and tumorigenesis can be influenced by dietary fat and polyphenolics. We set out to determine whether dietary modulations of tumorigenesis are mediated by SIRT1 catalytic functions. We introduced a mammary gland tumor-inducing transgene, MMTV-PyMT, into stocks of mice bearing a H355Y point mutation in the Sirt1 gene that abolishes SIRT1 catalytic activity. Tumor latency was reduced in animals fed a high fat diet but this effect was not dependent on SIRT1 activity. Resveratrol had little effect on tumor formation except in animals heterozygous for the mutant Sirt1 gene. We conclude that the effects of these dietary interventions on tumorigenesis are not mediated by modulation of SIRT1 catalytic activity. PMID:25380034

  2. Activation of glutathione peroxidase via Nrf1 mediates genistein's protection against oxidative endothelial cell injury

    SciTech Connect

    Hernandez-Montes, Eva; Pollard, Susan E.; Vauzour, David; Jofre-Montseny, Laia; Rota, Cristina; Rimbach, Gerald; Weinberg, Peter D.; Spencer, Jeremy P.E. . E-mail: j.p.e.spencer@reading.ac.uk

    2006-08-04

    Cellular actions of isoflavones may mediate the beneficial health effects associated with high soy consumption. We have investigated protection by genistein and daidzein against oxidative stress-induced endothelial injury. Genistein but not daidzein protected endothelial cells from damage induced by oxidative stress. This protection was accompanied by decreases in intracellular glutathione levels that could be explained by the generation of glutathionyl conjugates of the oxidised genistein metabolite, 5,7,3',4'-tetrahydroxyisoflavone. Both isoflavones evoked increased protein expression of {gamma}-glutamylcysteine synthetase-heavy subunit ({gamma}-GCS-HS) and increased cytosolic accumulation and nuclear translocation of Nrf2. However, only genistein led to increases in the cytosolic accumulation and nuclear translocation of Nrf1 and the increased expression of and activity of glutathione peroxidase. These results suggest that genistein-induced protective effects depend primarily on the activation of glutathione peroxidase mediated by Nrf1 activation, and not on Nrf2 activation or increases in glutathione synthesis.

  3. Conversion of embryonic stem cells into extraembryonic lineages by CRISPR-mediated activators

    PubMed Central

    Wei, Shu; Zou, Qingjian; Lai, Sisi; Zhang, Quanjun; Li, Li; Yan, Quanmei; Zhou, Xiaoqing; Zhong, Huilin; Lai, Liangxue

    2016-01-01

    The recently emerged CRISPR/Cas9 technique has opened a new perspective on readily editing specific genes. When combined with transcription activators, it can precisely manipulate endogenous gene expression. Here, we enhanced the expression of endogenous Cdx2 and Gata6 genes by CRISPR-mediated activators, thus mouse embryonic stem cells (ESCs) were directly converted into two extraembryonic lineages, i.e., typical trophoblast stem cells (TSCs) and extraembryonic endoderm cells (XENCs), which exhibited characters of TSC or XENC derived from the blastocyst extraembryonic lineages such as cell morphology, specific gene expression, and differentiation ability in vitro and in vivo. This study demonstrates that the cell fate can be effectively manipulated by directly activating of specific endogenous gene expression with CRISPR-mediated activator. PMID:26782778

  4. A Catalytic Role for C-H/π Interactions in Base Excision Repair by Bacillus cereus DNA Glycosylase AlkD.

    PubMed

    Parsons, Zachary D; Bland, Joshua M; Mullins, Elwood A; Eichman, Brandt F

    2016-09-14

    DNA glycosylases protect genomic integrity by locating and excising aberrant nucleobases. Substrate recognition and excision usually take place in an extrahelical conformation, which is often stabilized by π-stacking interactions between the lesion nucleobase and aromatic side chains in the glycosylase active site. Bacillus cereus AlkD is the only DNA glycosylase known to catalyze base excision without extruding the damaged nucleotide from the DNA helix. Instead of contacting the nucleobase itself, the AlkD active site interacts with the lesion deoxyribose through a series of C-H/π interactions. These interactions are ubiquitous in protein structures, but evidence for their catalytic significance in enzymology is lacking. Here, we show that the C-H/π interactions between AlkD and the lesion deoxyribose participate in catalysis of glycosidic bond cleavage. This is the first demonstration of a catalytic role for C-H/π interactions as intermolecular forces important to DNA repair.

  5. Visible-Light-Driven Oxidation of Primary C-H Bonds over CdS with Dual Co-catalysts Graphene and TiO2

    NASA Astrophysics Data System (ADS)

    Yang, Min-Quan; Zhang, Yanhui; Zhang, Nan; Tang, Zi-Rong; Xu, Yi-Jun

    2013-11-01

    Selective activation of primary C-H bonds for fine chemicals synthesis is of crucial importance for the sustainable exploitation of available feedstocks. Here, we report a viable strategy to synthesize ternary GR-CdS-TiO2 composites with an intimate spatial integration and sheet-like structure, which is afforded by assembling two co-catalysts, graphene and TiO2, into the semiconductor CdS matrix with specific morphology as a visible light harvester. The GR-CdS-TiO2 composites are able to serve as a highly selective visible-light-driven photocatalyst for oxidation of saturated primary C-H bonds using benign oxygen as oxidant under ambient conditions. This work demonstrates a wide, promising scope of adopting co-catalyst strategy to design more efficient semiconductor-based photocatalyst toward selective activation of C-H bonds using solar light and molecular oxygen.

  6. The intact CFTR protein mediates ATPase rather than adenylate kinase activity.

    PubMed

    Ramjeesingh, Mohabir; Ugwu, Francisca; Stratford, Fiona L L; Huan, Ling-Jun; Li, Canhui; Bear, Christine E

    2008-06-01

    The two NBDs (nucleotide-binding domains) of ABC (ATP-binding-cassette) proteins function in a complex to mediate ATPase activity and this activity has been linked to their regulated transport activity. A similar model has been proposed for CFTR (cystic fibrosis transmembrane conductance regulator), the chloride channel defective in cystic fibrosis, wherein ATP binding and hydrolysis regulate the channel gate. Recently, it was shown that the individual NBDs isolated from CFTR primarily mediate adenylate kinase activity, raising the possibility that this activity may also contribute to gating of the CFTR channel. However, this present study shows that whereas the isolated NBDs exhibit adenylate kinase activity, the full-length purified and reconstituted CFTR protein functions as an ATPase, arguing that the enzymatic activity of the NBDs is dependent on their molecular context and appropriate domain-domain assembly. As expected, the disease-causing mutant bearing a mutation in the ABC signature motif, CFTR-G551D, exhibited a markedly reduced ATPase activity. Furthermore, mutation of the putative catalytic base in CFTR caused a reduction in ATPase activity, with the CFTR-E1371Q mutant supporting a low level of residual activity. Neither of these mutants exhibited detectable adenylate kinase activity. Together, these findings support the concept that the molecular mechanism of action of CFTR is dependent on ATP binding and hydrolysis, and that the structure of prokaryotic ABC ATPases provide a useful template for understanding their mechanism of action.

  7. Sapap3 deletion anomalously activates short-term endocannabinoid-mediated synaptic plasticity

    PubMed Central

    Chen, Meng; Wan, Yehong; Ade, Kristen; Ting, Jonathan; Feng, Guoping; Calakos, Nicole

    2011-01-01

    Retrograde synaptic signaling by endocannabinoids is a widespread mechanism for activity-dependent inhibition of synaptic strength in the brain. Although prevalent, the conditions for eliciting endocannabinoid (eCB)-mediated synaptic depression vary among brain circuits. As yet, relatively little is known about the molecular mechanisms underlying this variation, although the initial signaling events are likely dictated by postsynaptic proteins. SAPAPs are a family of postsynaptic proteins unique to excitatory synapses. Using Sapap3 knock-out (KO) mice, we find that, in the absence of SAPAP3, striatal medium spiny neuron (MSN) excitatory synapses exhibit eCB-mediated synaptic depression under conditions that do not normally activate this process. The anomalous synaptic plasticity requires type 5 metabotropic glutamate receptors (mGluR5), which are dysregulated in Sapap3 KO MSNs. Both surface expression and activity of mGluR5 are increased in Sapap3 KO MSNs, suggesting that enhanced mGluR5 activity may drive the anomalous synaptic plasticity. In direct support of this possibility, we find that, in wildtype (WT) MSNs, pharmacological enhancement of mGluR5 by a positive allosteric modulator is sufficient to reproduce the increased synaptic depression seen in Sapap3 KO MSNs. The same pharmacologic treatment, however, fails to elicit further depression in KO MSNs. Under conditions that are sufficient to engage eCB-mediated synaptic depression in WT MSNs, Sapap3 deletion does not alter the magnitude of the response. These results identify a role for SAPAP3 in the regulation of postsynaptic mGluRs and eCB-mediated synaptic plasticity. SAPAPs, through their effect on mGluR activity, may serve as regulatory molecules gating the threshold for inducing eCB-mediated synaptic plasticity. PMID:21715621

  8. Pain mediates the association between physical activity and the impact of fibromyalgia on daily function.

    PubMed

    Umeda, Masataka; Corbin, Lisa W; Maluf, Katrina S

    2015-01-01

    This study quantified the association between recreational physical activity and daily function in women with fibromyalgia, and determined if this association is mediated by symptoms of pain, depression, or body mass. Twenty-three women diagnosed with fibromyalgia participated in an observational survey study. Recreational physical activity and the impact of fibromyalgia on daily function were assessed using the sport and leisure time physical activity subscales of the Baecke Physical Activity Questionnaire (BPAQ) and the Fibromyalgia Impact Questionnaire (FIQ), respectively. Potential mediators of the association between physical activity and daily function were assessed using the Visual Analogue Scale for pain intensity (VAS-Pain), the Beck Depression Inventory (BDI), and body mass index (BMI). BPAQ was inversely associated with FIQ (R (2) = 0.20) and VAS-Pain (R (2) = 0.39). VAS-Pain was positively associated with FIQ (R (2) = 0.23). The inverse association between BPAQ and FIQ was no longer significant after controlling for VAS-Pain. BDI was positively associated with FIQ (R (2) = 0.37), whereas BMI was not. BPAQ was not significantly associated with either BDI or BMI. These results indicate that the intensity of musculoskeletal pain, rather than depressive symptoms or body mass, mediates the association between physical activity and daily function among women with fibromyalgia.

  9. PARP promoter-mediated activation of a VSG expression site promoter in insect form Trypanosoma brucei.

    PubMed

    Urményi, T P; Van der Ploeg, L H

    1995-03-25

    In trypanosomes the rRNA, PARP and VSG gene promoters mediate alpha-amanitin-resistant transcription of protein coding genes, presumably by RNA polymerase (pol) I. We compared the activity of PARP and VSG promoters integrated at one of the alleles of the largest subunit of pol II genes in insect form trypanosomes. Even though both promoters are roughly equally active in transient transformation assays in insect form trypanosomes, only the PARP promoter functioned effectively when integrated at the pol II largest subunit or other loci. Promoter activity in transient transformation assays is therefore not necessarily predictive of transcriptional activity once integrated into the trypanosome genome. The integrated fully active PARP promoter could upregulate in cis an otherwise poorly active integrated VSG promoter. The PARP promoter nucleotide sequence elements responsible for VSG promoter activation coincided with most of the important PARP promoter elements mapped previously by linker scanning mutagenesis, indicating that it is not a single unique promoter element that was responsible for VSG promoter activation. The data suggest that PARP promoter-mediated activation of the VSG promoter does not result from complementation of the VSG promoter with a single insect form-specific transcription factor whose binding site is missing from the VSG promoter and present in the PARP promoter. We favor a model in which chromatin structure at the locus is altered by the PARP promoter, allowing VSG promoter activation in insect form trypanosomes. We discuss the significance of these observations for the control of VSG promoters in insect form trypanosomes.

  10. Tumor necrosis factor gene expression is mediated by protein kinase C following activation by ionizing radiation.

    SciTech Connect

    Hallahan, D. E.; Virudachalam, S.; Sherman, M. L.; Huberman, E.; Kufe, D. W.; Weichselbaum, R. R.; Univ. of Chicago; Dana-Farber Cancer Inst.; Univ. of Chicago

    1991-01-01

    Tumor necrosis factor (TNF) production following X-irradiation has been implicated in the biological response to ionizing radiation. Protein kinase C (PKC) is suggested to participate in TNF transcriptional induction and X-ray-mediated gene expression. We therefore studied radiation-mediated TNF expression in HL-60 cells with diminished PKC activity produced by either pretreatment with protein kinase inhibitors or prolonged 12-O-tetradecanoylphorbol-13-acetate treatment. Both treatments resulted in attenuation of radiation-mediated TNF induction. Consistent with these results, we found no detectable induction of TNF expression following X-irradiation in the HL-60 variant deficient in PKC-mediated signal transduction. The rapid activation of PKC following {gamma}-irradiation was established using an in vitro assay measuring phosphorylation of a PKC specific substrate. A 4.5-fold increase in PKC activity occurred 15 to 30 s following irradiation, which declined to baseline at 60 s. Two-dimensional gel electrophoresis of phosphoproteins extracted from irradiated cells demonstrated in vivo phosphorylation of the PKC specific substrate Mr 80,000 protein at 45 s following X-irradiation. These findings indicate that signal transduction via the PKC pathway is required for the induction of TNF gene expression by ionizing radiation.

  11. Activation of sperm EGFR by light irradiation is mediated by reactive oxygen species.

    PubMed

    Shahar, Shiran; Hillman, Pnina; Lubart, Rachel; Ickowicz, Debby; Breitbart, Haim

    2014-01-01

    To acquire fertilization competence, spermatozoa must undergo several biochemical and motility changes in the female reproductive tract, collectively called capacitation. Actin polymerization and the development of hyperactivated motility (HAM) are part of the capacitation process. In a recent study, we showed that irradiation of human sperm with visible light stimulates HAM through a mechanism involving reactive-oxygen-species (ROS), Ca(2+) influx, protein kinases A (PKA), and sarcoma protein kinase (Src). Here, we showed that this effect of light on HAM is mediated by ROS-dependent activation of the epidermal growth factor receptor (EGFR). Interestingly, ROS-mediated HAM even when the EGFR was activated by EGF, the physiological ligand of EGFR. Light irradiation stimulated ROS-dependent actin polymerization, and this effect was abrogated by PBP10, a peptide which activates the actin-severing protein, gelsolin, and causes actin-depolymerization in human sperm. Light-stimulated tyrosine phosphorylation of Src-dependent gelsolin, resulting in enhanced HAM. Thus, light irradiation stimulates HAM through a mechanism involving Src-mediated actin polymerization. Light-stimulated HAM and in vitro-fertilization (IVF) rate in mouse sperm, and these effects were mediated by ROS and EGFR. In conclusion, we show here that irradiation of sperm with visible light, enhances their fertilization capacity via a mechanism requiring ROS, EGFR and HAM.

  12. Self-Management Strategies Mediate Self-Efficacy and Physical Activity

    PubMed Central

    Dishman, Rod K.; Motl, Robert W.; Sallis, James F.; Dunn, Andrea L.; Birnbaum, Amanda S.; Welk, Greg J.; Bedimo-Rung, Ariane L.; Voorhees, Carolyn C.; Jobe, Jared B.

    2008-01-01

    Background Self-efficacy theory proposes that girls who have confidence in their capability to be physically active will perceive fewer barriers to physical activity or be less influenced by them, be more likely to pursue perceived benefits of being physically active, and be more likely to enjoy physical activity. Self-efficacy is theorized also to influence physical activity through self-management strategies (e.g., thoughts, goals, plans, and acts) that support physical activity, but this idea has not been empirically tested. Methods Confirmatory factor analysis was used to test the factorial validity of a measure of self-management strategies for physical activity. Next, the construct validity of the measure was tested by examining whether self-management strategies mediated the relationship between self-efficacy and self-reported physical activity, independently of several social-cognitive variables (i.e., perceived barriers, outcome expectancy value, and enjoyment), among cross-sectional samples of 6th grade (n =309) and 8th grade (n =296) girls tested between February 14 and March 17, 2002. Data were analyzed in 2004. Results Consistent with theory, self-efficacy had direct effects on the social-cognitive variables. The primary novel finding is that self-management strategies mediated the association of self-efficacy with physical activity in both samples. Conclusions The measure of self-management strategies for physical activity yields valid scores among adolescent girls and warrants experimental study as a mediator of the influence of efficacy beliefs on physical activity. PMID:15958246

  13. Reactive oxygen species production and redox state in parthenogenetic and sperm-mediated bovine oocyte activation.

    PubMed

    Morado, S; Cetica, P; Beconi, M; Thompson, J G; Dalvit, G

    2013-05-01

    The knowledge concerning redox and reactive oxygen species (ROS)-mediated regulation of early embryo development is scarce and remains controversial. The aim of this work was to determine ROS production and redox state during early in vitro embryo development in sperm-mediated and parthenogenetic activation of bovine oocytes. Sperm-mediated oocyte activation was carried out in IVF-modified synthetic oviductal fluid (mSOF) with frozen-thawed semen. Parthenogenetic activation was performed in TALP plus ionomycin and then in IVF-mSOF with 6-dimethylaminopurine plus cytochalasin B. Embryos were cultured in IVF-mSOF. ROS and redox state were determined at each 2-h interval (7-24 h from activation) by 2',7'-dichlorodihydrofluorescein diacetate and RedoxSensor Red CC-1 fluorochromes respectively. ROS levels and redox state differed between activated and non-activated oocytes (P<0.05 by ANOVA). In sperm-activated oocytes, an increase was observed between 15 and 19 h (P<0.05). Conversely, in parthenogenetically activated oocytes, we observed a decrease at 9 h (P<0.05). In sperm-activated oocytes, ROS fluctuated throughout the 24 h, presenting peaks around 7, 19, and 24 h (P<0.05), while in parthenogenetic activation, peaks were detected at 7, 11, and 17 h (P<0.05). In the present work, we found clear distinctive metabolic patterns between normal and parthenogenetic zygotes. Oxidative activity and ROS production are an integral part of bovine zygote behavior, and defining a temporal pattern of change may be linked with developmental competence.

  14. Direct approaches to nitriles via highly efficient nitrogenation strategy through C-H or C-C bond cleavage.

    PubMed

    Wang, Teng; Jiao, Ning

    2014-04-15

    Because of the importance of nitrogen-containing compounds in chemistry and biology, organic chemists have long focused on the development of novel methodologies for their synthesis. For example, nitrogen-containing compounds show up within functional materials, as top-selling drugs, and as bioactive molecules. To synthesize these compounds in a green and sustainable way, researchers have focused on the direct functionalization of hydrocarbons via C-H or C-C bond cleavage. Although researchers have made significant progress in the direct functionalization of simple hydrocarbons, direct C-N bond formation via C-H or C-C bond cleavage remains challenging, in part because of the unstable character of some N-nucleophiles under oxidative conditions. The nitriles are versatile building blocks and precursors in organic synthesis. Recently, chemists have achieved the direct C-H cyanation with toxic cyanide salts in the presence of stoichiometric metal oxidants. In this Account, we describe recent progress made by our group in nitrile synthesis. C-H or C-C bond cleavage is a key process in our strategy, and azides or DMF serve as the nitrogen source. In these reactions, we successfully realized direct nitrile synthesis using a variety of hydrocarbon groups as nitrile precursors, including methyl, alkenyl, and alkynyl groups. We could carry out C(sp(3))-H functionalization on benzylic, allylic, and propargylic C-H bonds to produce diverse valuable synthetic nitriles. Mild oxidation of C═C double-bonds and C≡C triple-bonds also produced nitriles. The incorporation of nitrogen within the carbon skeleton typically involved the participation of azide reagents. Although some mechanistic details remain unclear, studies of these nitrogenation reactions implicate the involvement of a cation or radical intermediate, and an oxidative rearrangement of azide intermediate produced the nitrile. We also explored environmentally friendly oxidants, such as molecular oxygen, to make our

  15. RAD18-mediated ubiquitination of PCNA activates the Fanconi anemia DNA repair network.

    PubMed

    Geng, Liyi; Huntoon, Catherine J; Karnitz, Larry M

    2010-10-18

    The Fanconi anemia (FA) network is important for the repair of interstrand DNA cross-links. A key event in FA pathway activation is the monoubiquitylation of the FA complementation group I (FANCI)-FANCD2 (ID) complex by FA complementation group L (FANCL), an E3 ubiquitin ligase. In this study, we show that RAD18, another DNA damage-activated E3 ubiquitin ligase, also participates in ID complex activation by ubiquitylating proliferating cell nuclear antigen (PCNA) on Lys164, an event required for the recruitment of FANCL to chromatin. We also found that monoubiquitylated PCNA stimulates FANCL-catalyzed FANCD2 and FANCI monoubiquitylation. Collectively, these experiments identify RAD18-mediated PCNA monoubiquitination as a central hub for the mobilization of the FA pathway by promoting FANCL-mediated FANCD2 monoubiquitylation.

  16. Cognitive activity and physiological arousal: processes that mediate mood-congruent memory.

    PubMed

    Varner, L J; Ellis, H C

    1998-09-01

    This research proposes that the cognitive activity associated with the experience of an emotional state mediates the occurrence of mood-congruent processing. Two experiments examined the role of cognitive activity in selective processing of words in a mood congruence paradigm. Four induction procedures were used: a depressed-mood induction, a schema induction organized around the theme of writing a paper, an arousal induction, and a control neutral-mood induction. The memory task consisted of recalling a word list composed of negatively associated and thematically organized words. Selective processing was demonstrated in conjunction with the depressed-mood and organizational-schema induction procedures. In contrast, the arousal and neutral induction procedures did not produce selective processing of words from the list. The findings support the thesis that cognitive activity mediates the selective processing typical of mood congruence as distinct from arousal processes per se. The findings are discussed with respect to the resource allocation model and semantic network theory.

  17. UTX demethylase activity is required for satellite cell–mediated muscle regeneration

    PubMed Central

    Wang, Chaochen; Nakka, Kiran; Benyoucef, Aissa; Sebastian, Soji; Zhuang, Lenan; Chu, Alphonse; Palii, Carmen G.; Camellato, Brendan; Brand, Marjorie

    2016-01-01

    The X chromosome–encoded histone demethylase UTX (also known as KDM6A) mediates removal of repressive trimethylation of histone H3 lysine 27 (H3K27me3) to establish transcriptionally permissive chromatin. Loss of UTX in female mice is embryonic lethal. Unexpectedly, male UTX-null mice escape embryonic lethality due to expression of UTY, a paralog that lacks H3K27 demethylase activity, suggesting an enzyme-independent role for UTX in development and thereby challenging the need for active H3K27 demethylation in vivo. However, the requirement for active H3K27 demethylation in stem cell–mediated tissue regeneration remains untested. Here, we employed an inducible mouse KO that specifically ablates Utx in satellite cells (SCs) and demonstrated that active H3K27 demethylation is necessary for muscle regeneration. Loss of UTX in SCs blocked myofiber regeneration in both male and female mice. Furthermore, we demonstrated that UTX mediates muscle regeneration through its H3K27 demethylase activity, as loss of demethylase activity either by chemical inhibition or knock-in of demethylase-dead UTX resulted in defective muscle repair. Mechanistically, dissection of the muscle regenerative process revealed that the demethylase activity of UTX is required for expression of the transcription factor myogenin, which in turn drives differentiation of muscle progenitors. Thus, we have identified a critical role for the enzymatic activity of UTX in activating muscle-specific gene expression during myofiber regeneration and have revealed a physiological role for active H3K27 demethylation in vivo. PMID:26999603

  18. Inhibition of peroxisome proliferator-activated receptor (PPAR)-mediated keratinocyte differentiation by lipoxygenase inhibitors.

    PubMed Central

    Thuillier, Philippe; Brash, Alan R; Kehrer, James P; Stimmel, Julie B; Leesnitzer, Lisa M; Yang, Peiying; Newman, Robert A; Fischer, Susan M

    2002-01-01

    Lipoxygenase (LOX) metabolites from arachidonic acid and linoleic acid have been implicated in atherosclerosis, inflammation, keratinocyte differentiation and tumour progression. We previously showed that peroxisome proliferator-activated receptors (PPARs) play a role in keratinocyte differentiation and that the PPARalpha ligand 8S-hydroxyeicosatetraenoic acid is important in this process. We hypothesized that blocking LOX activity would block PPAR-mediated keratinocyte differentiation. Three LOX inhibitors, nordihydroguaiaretic acid, quercetin and morin, were studied for their effects on primary keratinocyte differentiation and PPAR activity. All three LOX inhibitors blocked calcium-induced expression of the differentiation marker keratin 1. In addition, activity of a PPAR-responsive element was inhibited in the presence of all three inhibitors, and this effect was mediated primarily through PPARalpha and PPARgamma. LOX inhibitors decreased the activity of a chimaeric PPAR-Gal4-ligand-binding domain reporter system and this effect was reversed by addition of PPAR ligands. Ligand-binding studies revealed that the LOX inhibitors bind directly to PPARs and demonstrate a novel mechanism for these inhibitors in altering PPAR-mediated gene expression. PMID:12069687

  19. DNMT1-mediated PTEN hypermethylation confers hepatic stellate cell activation and liver fibrogenesis in rats

    SciTech Connect

    Bian, Er-Bao; Huang, Cheng; Ma, Tao-Tao; Tao, Hui; Zhang, Hui; Cheng, Chang; Lv, Xiong-Wen; Li, Jun

    2012-10-01

    Hepatic stellate cell (HSC) activation is an essential event during liver fibrogenesis. Phosphatase and tension homolog deleted on chromosome 10 (PTEN), a tumor suppressor, is a negative regulator of this process. PTEN promoter hypermethylation is a major epigenetic silencing mechanism in tumors. The present study aimed to investigate whether PTEN promoter methylation was involved in HSC activation and liver fibrosis. Treatment of activated HSCs with the DNA methylation inhibitor 5-aza-2′-deoxycytidine (5-azadC) decreased aberrant hypermethylation of the PTEN gene promoter and prevented the loss of PTEN expression that occurred during HSC activation. Silencing DNA methyltransferase 1 (DNMT1) gene also decreased the PTEN gene promoter methylation and upregulated the PTEN gene expression in activated HSC-T6 cells. In addition, knockdown of DNMT1 inhibited the activation of both ERK and AKT pathways in HSC-T6 cells. These results suggest that DNMT1-mediated PTEN hypermethylation caused the loss of PTEN expression, followed by the activation of the PI3K/AKT and ERK pathways, resulting in HSC activation. Highlights: ► PTEN methylation status and loss of PTEN expression ► DNMT1 mediated PTEN hypermethylation. ► Hypermethylation of PTEN contributes to the activation of ERK and AKT pathways.

  20. Dexamethasone-induced apoptosis of osteocytic and osteoblastic cells is mediated by TAK1 activation.

    PubMed

    Ding, Heyuan; Wang, Tao; Xu, Dongli; Cha, Bingbing; Liu, Jun; Li, Yiming

    2015-05-01

    Increased apoptosis of osteoblasts and osteocytes is the main mechanism of glucocorticoid (GC)-induced osteonecrosis. In the current study, we investigated whether dexamethasone (Dex)-induced osteoblastic and osteocytic cell apoptosis is mediated through activation of transforming growth factor-β (TGF-β)-activated kinase 1 (TAK1), and whether TAK1 inhibition could promote survival opposing the deleterious effects of Dex. We found that TAK1 was activated by Dex in both osteocytic MLO-Y4 and osteoblastic OB-6 cells, which was prevented by two known anti-oxidants N-acetylcysteine (NAC) and ebselen. TAK1 inhibitors, including LYTAK1 and 5Z-7-oxozeaenol (57-OZ), inhibited Dex-induced apoptosis of MLO-Y4 and OB-6 cells. Meanwhile shRNA-mediated knockdown of TAK1 also suppressed Dex-induced damages to MLO-Y4 and OB-6 cells. On the other hand, exogenously over-expressing TAK1 enhanced Dex-induced MLO-Y4 and OB-6 cell apoptosis. At the molecular level, we found that TAK1 mediated Dex-induced pro-apoptotic Pyk2-JNK activation. Inhibition or silencing of TAK1 almost abolished Pyk2-JNK phosphorylations by Dex in MLO-Y4 and OB-6 cells. TAK1 over-expression, on the other hand, increased Dex's activity on Pyk2-JNK phosphorylations in above cells. We conclude that part of the pro-apoptotic actions of Dex on osteoblastic and osteocytic cells are mediated through TAK1 activation, and that inhibition of TAK1 might protect from GC-induced damages to osteoblasts and osteocytes.

  1. Site-selective and stereoselective functionalization of unactivated C-H bonds

    NASA Astrophysics Data System (ADS)

    Liao, Kuangbiao; Negretti, Solymar; Musaev, Djamaladdin G.; Bacsa, John; Davies, Huw M. L.

    2016-05-01

    The laboratory synthesis of complex organic molecules relies heavily on the introduction and manipulation of functional groups, such as carbon-oxygen or carbon-halogen bonds; carbon-hydrogen bonds are far less reactive and harder to functionalize selectively. The idea of C-H functionalization, in which C-H bonds are modified at will instead of the functional groups, represents a paradigm shift in the standard logic of organic synthesis. For this approach to be generally useful, effective strategies for site-selective C-H functionalization need to be developed. The most practical solutions to the site-selectivity problem rely on either intramolecular reactions or the use of directing groups within the substrate. A challenging, but potentially more flexible approach, would be to use catalyst control to determine which site in a particular substrate would be functionalized. Here we describe the use of dirhodium catalysts to achieve highly site-selective, diastereoselective and enantioselective C-H functionalization of n-alkanes and terminally substituted n-alkyl compounds. The reactions proceed in high yield, and functional groups such as halides, silanes and esters are compatible with this chemistry. These studies demonstrate that high site selectivity is possible in C-H functionalization reactions without the need for a directing or anchoring group present in the molecule.

  2. Optical properties of a-C:H thin films modified by Ti and Ag

    NASA Astrophysics Data System (ADS)

    Prikhodko, Oleg Yu.; Mikhailova, Svetlana L.; Mukhametkarimov, Ershan C.; Maksimova, Suyumbika Ya.; Manabaev, Nurlan K.; Dauthan, Kuanysh

    2016-09-01

    Structure and optical properties of amorphous diamond-like carbon (a-C: H) thin films modified with Ag, Ti and Ag + Ti metal impurities are studied. The films were prepared by ion-plasma magnetron sputtering of combined polycrystalline graphite and metal target in the mixture of Ar and CH4 gases. AFM, SEM and TEM methods show that a-C:H films are heterogeneous, nanostructured and characterized by the presence of silver nanoclusters on the surface sized 60 nm and both Ti and Ag nanoclusters with a mean size (2 ÷ 3) nm in the bulk of films. It was found that in a- C:H films as well as in a-C:H films plasma resonance absorption due to excitation of surface plasmons in silver nanoclusters in the visible region of spectrum takes place. Intensity of the resonance absorption in the a- C:H films increases with increase in concentration of silver. The results are important for produce of nanomaterials with nonlinear optical properties based on the amorphous diamond-like carbon films containing metal nanoclusters.

  3. Synthesis of heterocyclic-fused benzopyrans via the Pd(II)-catalyzed C-H alkenylation/C-O cyclization of flavones and coumarins.

    PubMed

    Kim, Yechan; Moon, Youngtaek; Kang, Dahye; Hong, Sungwoo

    2014-06-07

    An efficient and practical method for effecting a tandem C-H alkenylation/C-O cyclization has been achieved via the C-H functionalization of flavone derivatives. The synthetic utility of the one-pot sequence was demonstrated by obtaining convenient access to coumarin-annelated benzopyrans. The reaction scope for the transformation was found to be fairly broad, affording good yields of a wide range of flavone- or coumarin-fused benzopyran motifs, which are privileged structures in many biologically active compounds.

  4. A Metallacycle Fragmentation Strategy for Vinyl Transfer from Enol Carboxylates to Secondary Alcohol C-H Bonds via Osmium- or Ruthenium-Catalyzed Transfer Hydrogenation.

    PubMed

    Park, Boyoung Y; Luong, Tom; Sato, Hiroki; Krische, Michael J

    2015-06-24

    A strategy for catalytic vinyl transfer from enol carboxylates to activated secondary alcohol C-H bonds is described. Using XPhos-modified ruthenium(0) or osmium(0) complexes, enol carboxylate-carbonyl oxidative coupling forms transient β-acyloxy-oxametallacycles, which eliminate carboxylate to deliver allylic ruthenium(II) or osmium(II) alkoxides. Reduction of the metal(II) salt via hydrogen transfer from the secondary alcohol reactant releases the product of carbinol C-H vinylation and regenerates ketone and zero-valent catalyst.

  5. O-H hydrogen bonding promotes H-atom transfer from α C-H bonds for C-alkylation of alcohols.

    PubMed

    Jeffrey, Jenna L; Terrett, Jack A; MacMillan, David W C

    2015-09-25

    The efficiency and selectivity of hydrogen atom transfer from organic molecules are often difficult to control in the presence of multiple potential hydrogen atom donors and acceptors. Here, we describe the mechanistic evaluation of a mode of catalytic activation that accomplishes the highly selective photoredox α-alkylation/lactonization of alcohols with methyl acrylate via a hydrogen atom transfer mechanism. Our studies indicate a particular role of tetra-n-butylammonium phosphate in enhancing the selectivity for α C-H bonds in alcohols in the presence of allylic, benzylic, α-C=O, and α-ether C-H bonds.

  6. Activation of SAT1 engages polyamine metabolism with p53-mediated ferroptotic responses.

    PubMed

    Ou, Yang; Wang, Shang-Jui; Li, Dawei; Chu, Bo; Gu, Wei

    2016-11-01

    Although p53-mediated cell-cycle arrest, senescence, and apoptosis remain critical barriers to cancer development, the emerging role of p53 in cell metabolism, oxidative responses, and ferroptotic cell death has been a topic of great interest. Nevertheless, it is unclear how p53 orchestrates its activities in multiple metabolic pathways into tumor suppressive effects. Here, we identified the SAT1 (spermidine/spermine N(1)-acetyltransferase 1) gene as a transcription target of p53. SAT1 is a rate-limiting enzyme in polyamine catabolism critically involved in the conversion of spermidine and spermine back to putrescine. Surprisingly, we found that activation of SAT1 expression induces lipid peroxidation and sensitizes cells to undergo ferroptosis upon reactive oxygen species (ROS)-induced stress, which also leads to suppression of tumor growth in xenograft tumor models. Notably, SAT1 expression is down-regulated in human tumors, and CRISPR-cas9-mediated knockout of SAT1 expression partially abrogates p53-mediated ferroptosis. Moreover, SAT1 induction is correlated with the expression levels of arachidonate 15-lipoxygenase (ALOX15), and SAT1-induced ferroptosis is significantly abrogated in the presence of PD146176, a specific inhibitor of ALOX15. Thus, our findings uncover a metabolic target of p53 involved in ferroptotic cell death and provide insight into the regulation of polyamine metabolism and ferroptosis-mediated tumor suppression.

  7. Mediator Kinase Inhibition Further Activates Super-Enhancer Associated Genes in AML

    PubMed Central

    Nitulescu, Ioana I.; Tangpeerachaikul, Anupong; Poss, Zachary C.; Da Silva, Diogo H.; Caruso, Brittany T.; Arefolov, Alexander; Fadeyi, Olugbeminiyi; Christie, Amanda L.; Du, Karrie; Banka, Deepti; Schneider, Elisabeth V.; Jestel, Anja; Zou, Ge; Si, Chong; Ebmeier, Christopher C.; Bronson, Roderick T.; Krivtsov, Andrei V.; Myers, Andrew G.; Kohl, Nancy E.; Kung, Andrew L.; Armstrong, Scott A.; Lemieux, Madeleine E.; Taatjes, Dylan J.; Shair, Matthew D.

    2015-01-01

    Super-enhancers (SEs), which are composed of large clusters of enhancers densely loaded with the Mediator complex, transcription factors (TFs), and chromatin regulators, drive high expression of genes implicated in cell identity and disease, such as lineage-controlling TFs and oncogenes 1, 2. BRD4 and CDK7 are positive regulators of SE-mediated transcription3,4,5. In contrast, negative regulators of SE-associated genes have not been well described. Here we report that Mediator-associated kinases cyclin-dependent kinase 8 (CDK8) and CDK19 restrain increased activation of key SE-associated genes in acute myeloid leukaemia (AML) cells. We determined that the natural product cortistatin A (CA) selectively inhibited Mediator kinases, had antileukaemic activity in vitro and in vivo, and disproportionately induced upregulation of SE-associated genes in CA-sensitive AML cell lines but not in CA-insensitive cell lines. In AML cells, CA upregulated SE-associated genes with tumour suppressor and lineage-controlling functions, including the TFs CEBPA, IRF8, IRF1 and ETV6 6, 7, 8. The BRD4 inhibitor I-BET151 downregulated these SE-associated genes, yet also has antileukaemic activity. Individually increasing or decreasing expression of these TFs suppressed AML cell growth, providing evidence that leukaemia cells are sensitive to dosage of SE-associated genes. Our results demonstrate that Mediator kinases can negatively regulate SE-associated gene expression in specific cell types and can be pharmacologically targeted as a therapeutic approach to AML. PMID:26416749

  8. Torilin Inhibits Inflammation by Limiting TAK1-Mediated MAP Kinase and NF-κB Activation

    PubMed Central

    Kim, Tae-Hwan; Kwak, Yi-Seong; Kim, Na-Mi; Kim, Seung-Hyung

    2017-01-01

    Torilin, a sesquiterpene isolated from the fruits of Torilis japonica, has shown antimicrobial, anticancer, and anti-inflammatory properties. However, data on the mechanism of torilin action against inflammation is limited. This study aimed at determining the anti-inflammatory property of torilin in LPS-induced inflammation using in vitro model of inflammation. We examined torilin's effect on expression levels of inflammatory mediators and cytokines in LPS-stimulated RAW 264.7 macrophages. The involvement of NF-kB and AP-1, MAP kinases, and adaptor proteins were assessed. Torilin strongly inhibited LPS-induced NO release, iNOS, PGE2, COX-2, NF-α, IL-1β, IL-6, and GM-CSF gene and protein expressions. In addition, MAPKs were also suppressed by torilin pretreatment. Involvement of ERK1/2, P38MAPK, and JNK1/2 was further confirmed by PD98059, SB203580, and SP600125 mediated suppression of iNOS and COX-2 proteins. Furthermore, torilin attenuated NF-kB and AP-1 translocation, DNA binding, and reporter gene transcription. Interestingly, torilin inhibited TAK1 kinase activation with the subsequent suppression of MAPK-mediated JNK, p38, ERK1/2, and AP-1 (ATF-2 and c-jun) activation and IKK-mediated I-κBα degradation, p65/p50 activation, and translocation. Together, the results revealed the suppression of NF-κB and AP-1 regulated inflammatory mediator and cytokine expressions, suggesting the test compound's potential as a candidate anti-inflammatory agent. PMID:28316375

  9. Oxidative modification of caspase-9 facilitates its activation via disulfide-mediated interaction with Apaf-1.

    PubMed

    Zuo, Yong; Xiang, Binggang; Yang, Jie; Sun, Xuxu; Wang, Yumei; Cang, Hui; Yi, Jing

    2009-04-01

    Intracellular reactive oxygen species (ROS) are known to regulate apoptosis. Activation of caspase-9, the initial caspase in the mitochondrial apoptotic cascade, is closely associated with ROS, but it is unclear whether ROS regulate caspase-9 via direct oxidative modification. The present study aims to elucidate the molecular mechanisms by which ROS mediate caspase-9 activation. Our results show that the cellular oxidative state facilitates caspase-9 activation. Hydrogen peroxide treatment causes the activation of caspase-9 and apoptosis, and promotes an interaction between caspase-9 and apoptotic protease-activating factor 1 (Apaf-1) via disulfide formation. In addition, in an in vitro mitochondria-free system, the thiol-oxidant diamide promotes auto-cleavage of caspase-9 and the caspase-9/Apaf-1 interaction by facilitating the formation of disulfide-linked complexes. Finally, a point mutation at C403 of caspase-9 impairs both H(2)O(2)-promoted caspase-9 activation and interaction with Apaf-1 through the abolition of disulfide formation. The association between cytochrome c and the C403S mutant is significantly weaker than that between cytochrome c and wild-type caspase-9, indicating that oxidative modification of caspase-9 contributes to apoptosome formation under oxidative stress. Taken together, oxidative modification of caspase-9 by ROS can mediate its interaction with Apaf-1, and can thus promote its auto-cleavage and activation. This mechanism may facilitate apoptosome formation and caspase-9 activation under oxidative stress.

  10. Glucose-6-phosphate mediates activation of the carbohydrate responsive binding protein (ChREBP)

    SciTech Connect

    Li, Ming V.; Chen, Weiqin; Harmancey, Romain N.; Nuotio-Antar, Alli M.; Imamura, Minako; Saha, Pradip; Taegtmeyer, Heinrich; Chan, Lawrence

    2010-05-07

    Carbohydrate response element binding protein (ChREBP) is a Mondo family transcription factor that activates a number of glycolytic and lipogenic genes in response to glucose stimulation. We have previously reported that high glucose can activate the transcriptional activity of ChREBP independent of the protein phosphatase 2A (PP2A)-mediated increase in nuclear entry and DNA binding. Here, we found that formation of glucose-6-phosphate (G-6-P) is essential for glucose activation of ChREBP. The glucose response of GAL4-ChREBP is attenuated by D-mannoheptulose, a potent hexokinase inhibitor, as well as over-expression of glucose-6-phosphatase (G6Pase); kinetics of activation of GAL4-ChREBP can be modified by exogenously expressed GCK. Further metabolism of G-6-P through the two major glucose metabolic pathways, glycolysis and pentose-phosphate pathway, is not required for activation of ChREBP; over-expression of glucose-6-phosphate dehydrogenase (G6PD) diminishes, whereas RNAi knockdown of the enzyme enhances, the glucose response of GAL4-ChREBP, respectively. Moreover, the glucose analogue 2-deoxyglucose (2-DG), which is phosphorylated by hexokinase, but not further metabolized, effectively upregulates the transcription activity of ChREBP. In addition, over-expression of phosphofructokinase (PFK) 1 and 2, synergistically diminishes the glucose response of GAL4-ChREBP. These multiple lines of evidence support the conclusion that G-6-P mediates the activation of ChREBP.

  11. Mitogen-activated protein kinase pathways are required for melatonin-mediated defense responses in plants.

    PubMed

    Lee, Hyoung Yool; Back, Kyoungwhan

    2016-04-01

    Melatonin enhances pathogen resistance by inducing the expression of a number of plant defense-related genes. To examine whether the melatonin-mediated pathogen resistance is associated with mitogen-activated protein kinase (MAPK) cascades, Arabidopsis and tobacco leaves were treated with melatonin and investigated for MAPK activation using an antiphospho-p44/42 MAPK (Erk1/2) monoclonal antibody. Two MAPKs, MPK3 and MPK6, were activated rapidly and transiently by 1 μm melatonin treatment in Arabidopsis. Its tobacco ortholog MAPKs were also activated. The activation of MPK3 and MPK6 by 2-hydroxymelatonin and N-acetylserotonin was also observed, albeit to a lesser degree than that by melatonin. Furthermore, MAPK activation by melatonin was uncoupled from G-protein signaling, because melatonin efficiently activated two MAPKs in a G-protein β knockout mutant (agb1). Suppression of both MPK3 and MPK6 in transgenic Arabidopsis exhibited significant decreases in the induction of defense-related gene expression and pathogen resistance relative to wild-type plants. Using an array of MAP kinase kinase (MKK) knockout mutants, we found that four MKKs, namely MKK4, MKK5, MKK7, and MKK9, are responsible for the activation of MPK3 and MPK6 by melatonin, indicating that melatonin-mediated innate immunity is triggered by MAPK signaling through MKK4/5/7/9-MPK3/6 cascades.

  12. Stem cell factor-mediated activation pathways promote murine eosinophil CCL6 production and survival.

    PubMed

    Dolgachev, Vladislav; Thomas, Molly; Berlin, Aaron; Lukacs, Nicholas W

    2007-04-01

    Eosinophil activation during allergic diseases has a detrimental role in the generation of pathophysiologic responses. Stem cell factor (SCF) has recently shown an inflammatory, gene-activating role on eosinophils and contributes to the generation of pathophysiologic changes in the airways during allergic responses. The data in the present study outline the signal transduction events that are induced by SCF in eosinophils and further demonstrate that MEK-mediated signaling pathways are crucial for SCF-induced CCL6 chemokine activation and eosinophil survival. SCF-mediated eosinophil activation was demonstrated to include PI-3K activation as well as MEK/MAPK phosphorylation pathways. Subsequent analysis of CCL6 gene activation and production induced by SCF in the presence or absence of rather specific inhibitors for certain pathways demonstrated that the MEK/MAPK pathway but not the PI-3K pathway was crucial for the SCF-induced CCL6 gene activation. These same signaling pathways were shown to initiate antiapoptotic events and promote eosinophil survival, including up-regulation of BCL2 and BCL3. Altogether, SCF appears to be a potent eosinophil activation and survival factor.

  13. Exploring the plasma chemistry in microwave chemical vapor deposition of diamond from C/H/O gas mixtures.

    PubMed

    Kelly, Mark W; Richley, James C; Western, Colin M; Ashfold, Michael N R; Mankelevich, Yuri A

    2012-09-27

    Microwave (MW)-activated CH(4)/CO(2)/H(2) gas mixtures operating under conditions relevant to diamond chemical vapor deposition (i.e., X(C/Σ) = X(elem)(C)/(X(elem)(C) + X(elem)(O)) ≈ 0.5, H(2) mole fraction = 0.3, pressure, p = 150 Torr, and input power, P = 1 kW) have been explored in detail by a combination of spatially resolved absorption measurements (of CH, C(2)(a), and OH radicals and H(n = 2) atoms) within the hot plasma region and companion 2-dimensional modeling of the plasma. CO and H(2) are identified as the dominant species in the plasma core. The lower thermal conductivity of such a mixture (cf. the H(2)-rich plasmas used in most diamond chemical vapor deposition) accounts for the finding that CH(4)/CO(2)/H(2) plasmas can yield similar maximal gas temperatures and diamond growth rates at lower input powers than traditional CH(4)/H(2) plasmas. The plasma chemistry and composition is seen to switch upon changing from oxygen-rich (X(C/Σ) < 0.5) to carbon-rich (X(C/Σ) > 0.5) source gas mixtures and, by comparing CH(4)/CO(2)/H(2) (X(C/Σ) = 0.5) and CO/H(2) plasmas, to be sensitive to the choice of source gas (by virtue of the different prevailing gas activation mechanisms), in contrast to C/H process gas mixtures. CH(3) radicals are identified as the most abundant C(1)H(x) [x = 0-3] species near the growing diamond surface within the process window for successful diamond growth (X(C/Σ) ≈ 0.5-0.54) identified by Bachmann et al. (Diamond Relat. Mater.1991, 1, 1). This, and the findings of similar maximal gas temperatures (T(gas) ~2800-3000 K) and H atom mole fractions (X(H)~5-10%) to those found in MW-activated C/H plasmas, points to the prevalence of similar CH(3) radical based diamond growth mechanisms in both C/H and C/H/O plasmas.

  14. LIME acts as a transmembrane adapter mediating BCR-dependent B-cell activation.

    PubMed

    Ahn, Eunseon; Lee, Hyunsook; Yun, Yungdae

    2006-02-15

    Assembly of a signaling complex around the transmembrane adapter LAT is essential for the transmission of T-cell receptor (TCR)-mediated signaling. However, a LAT-like molecule responsible for the initial activation events in B-cell receptor (BCR) signaling has not yet been identified. Here, we show that LIME is a transmembrane adaptor required for BCR-mediated B-cell activation. LIME was found to be expressed in mouse splenic B cells. Upon BCR cross-linking, LIME was tyrosine phosphorylated by Lyn and associated with Lyn, Grb2, PLC-gamma2, and PI3K. Reduction of LIME expression by the introduction of siRNA resulted in the disruption of BCR-mediated activation of MAPK, calcium flux, NF-AT, PI3K, and NF-kappaB. Taken together, these results establish that LIME is an essential transmembrane adaptor linking BCR ligation to the downstream signaling events that lead to B-cell activation.

  15. Evaluation of antibacterial activity of plant mediated CaO nanoparticles using Cissus quadrangularis extract.

    PubMed

    Marquis, Gowdhami; Ramasamy, Balagurunathan; Banwarilal, Sarkar; Munusamy, Ayyasamy Pudukadu

    2016-02-01

    An assessment of antibacterial activity of greenly synthesized nanoparticles using aqueous stem extract of Cissus quadrangularis was carried out. The synthesized nanoparticles were characterized by UV-Vis spectroscopy, SEM, XRD, FTIR and further subjected for antibacterial activity against the pathogens Staphylococcus aureus, Escherichia coli, Klebsiella pneumoniae, Pseudomonas aeruginosa, Salmonella typhi, Shigella dysenteriae and Vibrio cholerae. The SEM photograph represents cubic and hexagonal shape of NPs about 58nm respectively whereas the XRD indicated the pure phase of the product and no impurity in peaks of well crystallized products. The FTIR spectrum of nanoparticles showed intensive peaks with blue shift indicating the crystalline and shorten the distance of crystal lattice. The plant mediated CaO nanoparticles showed maximum inhibition on E. coli followed by other strains. In MIC, the plant mediated CaO NPs possess high activity against all the test organisms whereas the CaCl2 and CaO compounds were moderately active. The approach to the synthesis of plant mediated CaO NPs has many advantages as scaled up, economic viability, etc. Application of such ecofriendly nanoparticles in bactericidal, wound healing and other medical applications makes this method potential existing for the large scale synthesis of the inorganic materials.

  16. PCSK6-mediated corin activation is essential for normal blood pressure.

    PubMed

    Chen, Shenghan; Cao, Pengxiu; Dong, Ningzheng; Peng, Jianhao; Zhang, Chunyi; Wang, Hao; Zhou, Tiantian; Yang, Junhua; Zhang, Yue; Martelli, Elizabeth E; Naga Prasad, Sathyamangla V; Miller, Rachel E; Malfait, Anne-Marie; Zhou, Yiqing; Wu, Qingyu

    2015-09-01

    Hypertension is the most common cardiovascular disease, afflicting >30% of adults. The cause of hypertension in most individuals remains unknown, suggesting that additional contributing factors have yet to be discovered. Corin is a serine protease that activates the natriuretic peptides, thereby regulating blood pressure. It is synthesized as a zymogen that is activated by proteolytic cleavage. CORIN variants and mutations impairing corin activation have been identified in people with hypertension and pre-eclampsia. To date, however, the identity of the protease that activates corin remains elusive. Here we show that proprotein convertase subtilisin/kexin-6 (PCSK6, also named PACE4; ref. 10) cleaves and activates corin. In cultured cells, we found that corin activation was inhibited by inhibitors of PCSK family proteases and by small interfering RNAs blocking PCSK6 expression. Conversely, PCSK6 overexpression enhanced corin activation. In addition, purified PCSK6 cleaved wild-type corin but not the R801A variant that lacks the conserved activation site. Pcsk6-knockout mice developed salt-sensitive hypertension, and corin activation and pro-atrial natriuretic peptide processing activity were undetectable in these mice. Moreover, we found that CORIN variants in individuals with hypertension and pre-eclampsia were defective in PCSK6-mediated activation. We also identified a PCSK6 mutation that impaired corin activation activity in a hypertensive patient. Our results indicate that PCSK6 is the long-sought corin activator and is important for sodium homeostasis and normal blood pressure.

  17. Rh(III)- and Zn(II)-Catalyzed Synthesis of Quinazoline N-Oxides via C-H Amidation-Cyclization of Oximes.

    PubMed

    Wang, Qiang; Wang, Fen; Yang, Xifa; Zhou, Xukai; Li, Xingwei

    2016-12-02

    Quinazoline N-oxides have been prepared from simple ketoximes and 1,4,2-dioxazol-5-ones via Rh(III)-catalyzed C-H activation-amidation of the ketoximes and subsequent Zn(II)-catalyzed cyclization. The substrate scope and functional group compatibility were examined. The reaction features relay catalysis by Rh(III) and Zn(II).

  18. N-Acyl Amino Acid Ligands for Ruthenium(II)-Catalyzed meta-C-H tert-Alkylation with Removable Auxiliaries.

    PubMed

    Li, Jie; Warratz, Svenja; Zell, Daniel; De Sarkar, Suman; Ishikawa, Eloisa Eriko; Ackermann, Lutz

    2015-11-04

    Acylated amino acid ligands enabled ruthenium(II)-catalyzed C-H functionalizations with excellent levels of meta-selectivity. The outstanding catalytic activity of the ruthenium(II) complexes derived from monoprotected amino acids (MPAA) set the stage for the first ruthenium-catalyzed meta-functionalizations with removable directing groups. Thereby, meta-alkylated anilines could be accessed, which are difficult to prepare by other means of direct aniline functionalizations. The robust nature of the versatile ruthenium(II)-MPAA was reflected by challenging remote C-H transformations with tertiary alkyl halides on aniline derivatives as well as on pyridyl-, pyrimidyl-, and pyrazolyl-substituted arenes. Detailed mechanistic studies provided strong support for an initial reversible C-H ruthenation, followed by a SET-type C-Hal activation through homolytic bond cleavage. Kinetic analyses confirmed this hypothesis through an unusual second-order dependence of the reaction rate on the ruthenium catalyst concentration. Overall, this report highlights the exceptional catalytic activity of ruthenium complexes derived from acylated amino acids, which should prove instrumental for C-H activation chemistry beyond remote functionalization.

  19. P(O)R2-directed Pd-catalyzed C-H functionalization of biaryl derivatives to synthesize chiral phosphorous ligands.

    PubMed

    Hu, Rong-Bin; Wang, Hong-Li; Zhang, Hong-Yu; Zhang, Heng; Ma, Yan-Na; Yang, Shang-Dong

    2014-01-01

    Chiral phosphorus ligands have been widely used in transition metal-catalyzed asymmetric reactions. Herein, we report a new synthesis approach of chiral biaryls containing a phosphorus moiety using P(O)R2-directed Pd-catalyzed C-H activation; the functionalized products are produced with good enantioselectivity.

  20. Diverse sp3 C-H functionalization through alcohol β-sulfonyloxylation

    NASA Astrophysics Data System (ADS)

    Xu, Yan; Yan, Guobing; Ren, Zhi; Dong, Guangbin

    2015-10-01

    Site-selective C-H functionalization has emerged as an attractive tool for derivatizing complex synthetic intermediates, but its use for late-stage diversification is limited by the functional groups that can be introduced, especially at unactivated sp3-hybridized positions. To overcome this, we introduce a strategy that directly installs a sulfonyloxy group at a β-C-H bond of a masked alcohol and subsequently employs nucleophilic substitution reactions to prepare various derivatives. Hydroxyl groups are widely found in bioactive molecules and are thus readily available as synthetic handles. A directing group is easily added (and subsequently removed) from the alcohols such that a formal site-selective β-C-H sulfonyloxylation of these alcohols is achieved. Substitution reactions with carbon, nitrogen, oxygen and other nucleophiles then lead to diverse functionalizations that may help to streamline the synthesis of complex analogues for drug discovery.