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  • 101
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    American Association for the Advancement of Science (AAAS)
    In: Science
    Publication Date: 2018-12-21
    Keywords: Chemistry
    Print ISSN: 0036-8075
    Electronic ISSN: 1095-9203
    Topics: Biology , Chemistry and Pharmacology , Geosciences , Computer Science , Medicine , Natural Sciences in General , Physics
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  • 102
    Publication Date: 2018-12-21
    Description: Single-molecule magnets (SMMs) containing only one metal center may represent the lower size limit for molecule-based magnetic information storage materials. Their current drawback is that all SMMs require liquid-helium cooling to show magnetic memory effects. We now report a chemical strategy to access the dysprosium metallocene cation [(Cp i Pr5 )Dy(Cp*)] + (Cp i Pr5 , penta-iso-propylcyclopentadienyl; Cp *, pentamethylcyclopentadienyl), which displays magnetic hysteresis above liquid-nitrogen temperatures. An effective energy barrier to reversal of the magnetization of U eff = 1541 wave number is also measured. The magnetic blocking temperature of T B = 80 kelvin for this cation overcomes an essential barrier toward the development of nanomagnet devices that function at practical temperatures.
    Keywords: Chemistry
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  • 103
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    American Association for the Advancement of Science (AAAS)
    In: Science
    Publication Date: 2018-10-19
    Keywords: Chemistry
    Print ISSN: 0036-8075
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    Topics: Biology , Chemistry and Pharmacology , Geosciences , Computer Science , Medicine , Natural Sciences in General , Physics
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  • 104
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    American Association for the Advancement of Science (AAAS)
    In: Science
    Publication Date: 2018-10-19
    Description: The development of highly reactive and stereoselective catalytic systems is required not only to improve existing synthetic methods but also to invent distinct chemical reactions. Herein, a homogenized combination of nickel-based Lewis acid–surfactant-combined catalysts and single-walled carbon nanotubes is shown to exhibit substantial activity in water. In addition to the enhanced reactivity, stereoselective performance and long-term stability were demonstrated in asymmetric conjugate addition reactions of aldoximes to furnish chiral nitrones in high yields with excellent selectivities. The practical and straightforward application of the designed catalysts in water provides an expedient, environmentally benign, and highly efficient pathway to access optically active compounds.
    Keywords: Chemistry
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  • 105
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    American Association for the Advancement of Science (AAAS)
    In: Science
    Publication Date: 2018-11-02
    Keywords: Chemistry
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  • 106
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    American Association for the Advancement of Science (AAAS)
    In: Science
    Publication Date: 2018-12-14
    Keywords: Chemistry
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  • 107
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    American Association for the Advancement of Science (AAAS)
    In: Science
    Publication Date: 2018-10-26
    Keywords: Chemistry
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  • 108
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    American Association for the Advancement of Science (AAAS)
    In: Science
    Publication Date: 2018-11-02
    Description: Exploration of intermediates that enable chemoselective cycloaddition reactions and expeditious construction of fused- or bridged-ring systems is a continuous challenge for organic synthesis. As an intermediate of interest, the oxyallyl cation has been harnessed to synthesize architectures containing seven-membered rings via (4+3) cycloaddition. However, its potential to access five-membered skeletons is underdeveloped, largely due to the thermally forbidden (3+2) pathway. Here, the combination of a tailored precursor and a Pd(0) catalyst generates a Pd-oxyallyl intermediate that cyclizes with conjugated dienes to produce a diverse array of tetrahydrofuran skeletons. The cycloaddition overrides conventional (4+3) selectivity by proceeding through a stepwise pathway involving a Pd-allyl transfer and ring closure sequence. Subsequent treatment of the (3+2) adducts with a palladium catalyst converts the heterocycles to the carbocyclic cyclopentanones.
    Keywords: Chemistry
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  • 109
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    American Association for the Advancement of Science (AAAS)
    In: Science
    Publication Date: 2018-11-16
    Keywords: Chemistry
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  • 110
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    American Association for the Advancement of Science (AAAS)
    In: Science
    Publication Date: 2018-08-10
    Keywords: Chemistry
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  • 111
    Publication Date: 2018-08-10
    Description: Understanding the practical limitations of chemical reactions is critically important for efficiently planning the synthesis of compounds in pharmaceutical, agrochemical, and specialty chemical research and development. However, literature reports of the scope of new reactions are often cursory and biased toward successful results, severely limiting the ability to predict reaction outcomes for untested substrates. We herein illustrate strategies for carrying out large-scale surveys of chemical reactivity by using a material-sparing nanomole-scale automated synthesis platform with greatly expanded synthetic scope combined with ultrahigh-throughput matrix-assisted laser desorption/ionization–time-of-flight mass spectrometry (MALDI-TOF MS).
    Keywords: Chemistry
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  • 112
    Publication Date: 2018-08-24
    Description: Researchers around the world have observed the formation of molecularly ordered structures of unknown origin on the surface of titanium dioxide (TiO 2 ) photocatalysts exposed to air and solution. Using a combination of atomic-scale microscopy and spectroscopy, we show that TiO 2 selectively adsorbs atmospheric carboxylic acids that are typically present in parts-per-billion concentrations while effectively repelling other adsorbates, such as alcohols, that are present in much higher concentrations. The high affinity of the surface for carboxylic acids is attributed to their bidentate binding. These self-assembled monolayers have the unusual property of being both hydrophobic and highly water-soluble, which may contribute to the self-cleaning properties of TiO 2 . This finding is relevant to TiO 2 photocatalysis, because the self-assembled carboxylate monolayers block the undercoordinated surface cation sites typically implicated in photocatalysis.
    Keywords: Chemistry
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  • 113
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    American Association for the Advancement of Science (AAAS)
    In: Science
    Publication Date: 2018-08-31
    Keywords: Chemistry
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  • 114
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    American Association for the Advancement of Science (AAAS)
    In: Science
    Publication Date: 2018-08-31
    Keywords: Chemistry
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  • 115
    Publication Date: 2018-08-31
    Description: The alkaline earth metals calcium (Ca), strontium (Sr), and barium (Ba) typically engage in chemical bonding as classical main-group elements through their n s and n p valence orbitals, where n is the principal quantum number. Here we report the isolation and spectroscopic characterization of eight-coordinate carbonyl complexes M(CO) 8 (where M = Ca, Sr, or Ba) in a low-temperature neon matrix. Analysis of the electronic structure of these cubic O h -symmetric complexes reveals that the metal–carbon monoxide (CO) bonds arise mainly from [M(d )] -〉 (CO) 8 backdonation, which explains the strong observed red shift of the C-O stretching frequencies. The corresponding radical cation complexes were also prepared in gas phase and characterized by mass-selected infrared photodissociation spectroscopy, confirming adherence to the 18-electron rule more conventionally associated with transition metal chemistry.
    Keywords: Chemistry
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  • 116
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    American Association for the Advancement of Science (AAAS)
    In: Science
    Publication Date: 2018-09-07
    Keywords: Chemistry
    Print ISSN: 0036-8075
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  • 117
    Publication Date: 2018-09-07
    Description: Mystery surrounds the transition from gas-phase hydrocarbon precursors to terrestrial soot and interstellar dust, which are carbonaceous particles formed under similar conditions. Although polycyclic aromatic hydrocarbons (PAHs) are known precursors to high-temperature carbonaceous-particle formation, the molecular pathways that initiate particle formation are unknown. We present experimental and theoretical evidence for rapid molecular clustering–reaction pathways involving radicals with extended conjugation. These radicals react with other hydrocarbon species to form covalently bound complexes that promote further growth and clustering by regenerating resonance-stabilized radicals through low-barrier hydrogen-abstraction and hydrogen-ejection reactions. Such radical–chain reaction pathways may lead to covalently bound clusters of PAHs and other hydrocarbons that would otherwise be too small to condense at high temperatures, thus providing the key mechanistic steps for rapid particle formation and surface growth by hydrocarbon chemisorption.
    Keywords: Chemistry
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  • 118
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    American Association for the Advancement of Science (AAAS)
    In: Science
    Publication Date: 2018-09-14
    Keywords: Chemistry
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  • 119
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    American Association for the Advancement of Science (AAAS)
    In: Science
    Publication Date: 2018-04-27
    Keywords: Chemistry
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  • 120
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    American Association for the Advancement of Science (AAAS)
    In: Science
    Publication Date: 2018-04-27
    Keywords: Chemistry
    Print ISSN: 0036-8075
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  • 121
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    American Association for the Advancement of Science (AAAS)
    In: Science
    Publication Date: 2018-04-27
    Description: Basic heteroarenes are a ubiquitous feature of pharmaceuticals and bioactive molecules, and Minisci-type additions of radical nucleophiles are a leading method for their elaboration. Despite many Minisci-type protocols that result in the formation of stereocenters, exerting control over the absolute stereochemistry at these centers remains an unmet challenge. We report a process for addition of prochiral radicals, generated from amino acid derivatives, to pyridines and quinolines. Our method offers excellent control of both enantioselectivity and regioselectivity. An enantiopure chiral Brønsted acid catalyst serves both to activate the substrate and induce asymmetry, while an iridium photocatalyst mediates the required electron transfer processes. We anticipate that this method will expedite access to enantioenriched small-molecule building blocks bearing versatile basic heterocycles.
    Keywords: Chemistry
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  • 122
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    American Association for the Advancement of Science (AAAS)
    In: Science
    Publication Date: 2018-05-25
    Keywords: Chemistry
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  • 123
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    American Association for the Advancement of Science (AAAS)
    In: Science
    Publication Date: 2018-05-25
    Keywords: Chemistry
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  • 124
    Publication Date: 2018-10-26
    Description: Primary amines are essential constituents of biologically active molecules and versatile intermediates in the synthesis of drugs and agrochemicals. However, their preparation from easily accessible alkenes remains challenging. Here, we report a general strategy to access primary amines from alkenes through an operationally simple iron-catalyzed aminochlorination reaction. A stable hydroxylamine derivative and benign sodium chloride act as the respective nitrogen and chlorine sources. The reaction proceeds at room temperature under air; tolerates a large scope of aliphatic and conjugated alkenes, including densely functionalized substrates; and provides excellent anti-Markovnikov regioselectivity with respect to the amino group. The reactivity of the 2-chloroalkylamine products, an understudied class of amphoteric molecules, enables facile access to linear or branched aliphatic amines, aziridines, aminonitriles, azido amines, and homoallylic amines.
    Keywords: Chemistry
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  • 125
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    American Association for the Advancement of Science (AAAS)
    In: Science
    Publication Date: 2018-11-09
    Keywords: Chemistry
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  • 126
    Publication Date: 2018-11-09
    Description: Despite the enormous potential for the use of stereospecific cross-coupling reactions to rationally manipulate the three-dimensional structure of organic molecules, the factors that control the transfer of stereochemistry in these reactions remain poorly understood. Here we report a mechanistic and synthetic investigation into the use of enantioenriched alkylboron nucleophiles in stereospecific Pd-catalyzed Suzuki cross-coupling reactions. By developing a suite of molecular descriptors of phosphine ligands, we could apply predictive statistical models to select or design distinct ligands that respectively promoted stereoinvertive and stereoretentive cross-coupling reactions. Stereodefined branched structures were thereby accessed through the predictable manipulation of absolute stereochemistry, and a general model for the mechanism of alkylboron transmetallation was proposed.
    Keywords: Chemistry
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  • 127
    Publication Date: 2018-11-16
    Description: Heterobiaryls composed of pyridine and diazine rings are key components of pharmaceuticals and are often central to pharmacological function. We present an alternative approach to metal-catalyzed cross-coupling to make heterobiaryls using contractive phosphorus C–C couplings, also termed phosphorus ligand coupling reactions. The process starts by regioselective phosphorus substitution of the C–H bonds para to nitrogen in two successive heterocycles; ligand coupling is then triggered via acidic alcohol solutions to form the heterobiaryl bond. Mechanistic studies imply that ligand coupling is an asynchronous process involving migration of one heterocycle to the ipso position of the other around a central pentacoordinate P(V) atom. The strategy can be applied to complex drug-like molecules containing multiple reactive sites and polar functional groups, and also enables convergent coupling of drug fragments and late-stage heteroarylation of pharmaceuticals.
    Keywords: Chemistry
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  • 128
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    American Association for the Advancement of Science (AAAS)
    In: Science
    Publication Date: 2018-07-06
    Keywords: Chemistry
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  • 129
    Publication Date: 2018-07-06
    Description: Conical intersections play a critical role in excited-state dynamics of polyatomic molecules because they govern the reaction pathways of many nonadiabatic processes. However, ultrafast probes have lacked sufficient spatial resolution to image wave-packet trajectories through these intersections directly. Here, we present the simultaneous experimental characterization of one-photon and two-photon excitation channels in isolated CF 3 I molecules using ultrafast gas-phase electron diffraction. In the two-photon channel, we have mapped out the real-space trajectories of a coherent nuclear wave packet, which bifurcates onto two potential energy surfaces when passing through a conical intersection. In the one-photon channel, we have resolved excitation of both the umbrella and the breathing vibrational modes in the CF 3 fragment in multiple nuclear dimensions. These findings benchmark and validate ab initio nonadiabatic dynamics calculations.
    Keywords: Chemistry
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  • 130
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    American Association for the Advancement of Science (AAAS)
    In: Science
    Publication Date: 2018-07-13
    Keywords: Chemistry
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  • 131
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    American Association for the Advancement of Science (AAAS)
    In: Science
    Publication Date: 2018-06-22
    Keywords: Chemistry
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  • 132
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    American Association for the Advancement of Science (AAAS)
    In: Science
    Publication Date: 2018-04-13
    Keywords: Chemistry
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  • 133
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    American Association for the Advancement of Science (AAAS)
    In: Science
    Publication Date: 2018-05-04
    Keywords: Chemistry
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  • 134
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    American Association for the Advancement of Science (AAAS)
    In: Science
    Publication Date: 2018-05-11
    Keywords: Chemistry
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  • 135
    Publication Date: 2018-05-11
    Description: Common anionic nucleophiles such as those derived from inorganic salts have not been used for enantioselective catalysis because of their insolubility. Here, we report that merging hydrogen bonding and phase-transfer catalysis provides an effective mode of activation for nucleophiles that are insoluble in organic solvents. This catalytic manifold relies on hydrogen bonding complexation to render nucleophiles soluble and reactive, while simultaneously inducing asymmetry in the ensuing transformation. We demonstrate the concept using a chiral bis-urea catalyst to form a tridentate hydrogen bonding complex with fluoride from its cesium salt, thereby enabling highly efficient enantioselective ring opening of episulfonium ion. This fluorination method is synthetically valuable considering the scarcity of alternative protocols and points the way to wider application of the catalytic approach with diverse anionic nucleophiles.
    Keywords: Chemistry
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  • 136
    Publication Date: 2018-05-18
    Description: Carbon dioxide (CO 2 ) electroreduction could provide a useful source of ethylene, but low conversion efficiency, low production rates, and low catalyst stability limit current systems. Here we report that a copper electrocatalyst at an abrupt reaction interface in an alkaline electrolyte reduces CO 2 to ethylene with 70% faradaic efficiency at a potential of –0.55 volts versus a reversible hydrogen electrode (RHE). Hydroxide ions on or near the copper surface lower the CO 2 reduction and carbon monoxide (CO)–CO coupling activation energy barriers; as a result, onset of ethylene evolution at –0.165 volts versus an RHE in 10 molar potassium hydroxide occurs almost simultaneously with CO production. Operational stability was enhanced via the introduction of a polymer-based gas diffusion layer that sandwiches the reaction interface between separate hydrophobic and conductive supports, providing constant ethylene selectivity for an initial 150 operating hours.
    Keywords: Chemistry
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  • 137
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    American Association for the Advancement of Science (AAAS)
    In: Science
    Publication Date: 2018-05-25
    Keywords: Chemistry
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  • 138
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    American Association for the Advancement of Science (AAAS)
    In: Science
    Publication Date: 2018-03-23
    Description: White phosphorus, generated in the legacy thermal process for phosphate rock upgrading, has long been the key industrial intermediate for the synthesis of phosphorus-containing chemicals, including herbicides, flame-retardants, catalyst ligands, battery electrolytes, pharmaceuticals, and detergents. In contrast, phosphate fertilizers are made on a much larger scale from phosphoric acid, obtained by treating phosphate rock with sulfuric acid. Dehydration of phosphoric acid using sodium chloride gives trimetaphosphate, and here we report that trichlorosilane, primarily used for the production of high-purity silicon, reduces trimetaphosphate to the previously unknown bis(trichlorosilyl)phosphide anion. This anion offers an entry point to value-added organophosphorus chemicals such as primary and secondary alkyl phosphines, and thus to organophosphinates, and can also be used to prepare phosphine gas and the hexafluorophosphate anion, all previously available only downstream from white phosphorus.
    Keywords: Chemistry
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  • 139
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    American Association for the Advancement of Science (AAAS)
    In: Science
    Publication Date: 2018-04-06
    Keywords: Chemistry
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  • 140
    Publication Date: 2018-04-06
    Description: Cross-coupling chemistry is widely applied to carbon-carbon bond formation in the synthesis of medicines, agrochemicals, and other functional materials. Recently, single-electron–induced variants of this reaction class have proven particularly useful in the formation of C(sp 2 )–C(sp 3 ) linkages, although certain compound classes have remained a challenge. Here, we report the use of sulfones to activate the alkyl coupling partner in nickel-catalyzed radical cross-coupling with aryl zinc reagents. This method’s tolerance of fluoroalkyl substituents proved particularly advantageous for the streamlined preparation of pharmaceutically oriented fluorinated scaffolds that previously required multiple steps, toxic reagents, and nonmodular retrosynthetic blueprints. Five specific sulfone reagents facilitate the rapid assembly of a vast set of compounds, many of which contain challenging fluorination patterns.
    Keywords: Chemistry
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  • 141
    Publication Date: 2018-05-04
    Description: Plasmon-induced chemical reactions of molecules adsorbed on metal nanostructures are attracting increased attention for photocatalytic reactions. However, the mechanism remains controversial because of the difficulty of direct observation of the chemical reactions in the plasmonic field, which is strongly localized near the metal surface. We used a scanning tunneling microscope (STM) to achieve real-space and real-time observation of a plasmon-induced chemical reaction at the single-molecule level. A single dimethyl disulfide molecule on silver and copper surfaces was dissociated by the optically excited plasmon at the STM junction. The STM study combined with theoretical calculations shows that this plasmon-induced chemical reaction occurred by a direct intramolecular excitation mechanism.
    Keywords: Chemistry
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  • 142
    Publication Date: 2018-05-25
    Description: Identifying catalyst activation modes that exploit one-electron chemistry and overcome associated deactivation pathways will be transformative for developing first-row transition metal catalysts with performance equal or, ideally, superior to precious metals. Here we describe a zinc-activation method compatible with high-throughput reaction discovery that identified scores of cobalt-phosphine combinations for the asymmetric hydrogenation of functionalized alkenes. An optimized catalyst prepared from ( R , R )-Ph-BPE {Ph-BPE, 1,2-bis[(2 R ,5 R )-2,5-diphenylphospholano]ethane} and cobalt chloride [CoCl 2 ·6H 2 O] exhibited high activity and enantioselectivity in protic media and enabled the asymmetric synthesis of the epilepsy medication levetiracetam at 200-gram scale with 0.08 mole % catalyst loading. Stoichiometric studies established that the cobalt (II) catalyst precursor ( R , R )-Ph-BPECoCl 2 underwent ligand displacement by methanol, and zinc promoted facile one-electron reduction to cobalt (I), which more stably bound the phosphine.
    Keywords: Chemistry
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  • 143
    Publication Date: 2018-06-01
    Description: Transition metal–catalyzed arene functionalization has been widely used for molecular synthesis over the past century. In this arena, copper catalysis has long been considered a privileged platform due to the propensity of high-valent copper to undergo reductive elimination with a wide variety of coupling fragments. However, the sluggish nature of oxidative addition has limited copper’s capacity to broadly facilitate haloarene coupling protocols. Here, we demonstrate that this copper oxidative addition problem can be overcome with an aryl radical–capture mechanism, wherein the aryl radical is generated through a silyl radical halogen abstraction. This strategy was applied to a general trifluoromethylation of aryl bromides through dual copper-photoredox catalysis. Mechanistic studies support the formation of an open-shell aryl species.
    Keywords: Chemistry
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  • 144
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    American Association for the Advancement of Science (AAAS)
    In: Science
    Publication Date: 2018-05-18
    Keywords: Chemistry
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  • 145
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    American Association for the Advancement of Science (AAAS)
    In: Science
    Publication Date: 2018-06-01
    Keywords: Chemistry
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  • 146
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    American Association for the Advancement of Science (AAAS)
    In: Science
    Publication Date: 2018-03-23
    Keywords: Chemistry
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    Topics: Biology , Chemistry and Pharmacology , Geosciences , Computer Science , Medicine , Natural Sciences in General , Physics
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  • 147
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    American Association for the Advancement of Science (AAAS)
    In: Science
    Publication Date: 2018-03-23
    Keywords: Chemistry
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    Topics: Biology , Chemistry and Pharmacology , Geosciences , Computer Science , Medicine , Natural Sciences in General , Physics
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  • 148
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    American Association for the Advancement of Science (AAAS)
    In: Science
    Publication Date: 2018-03-30
    Keywords: Chemistry
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  • 149
    Publication Date: 2018-03-30
    Description: The activation of olefins for asymmetric chemical synthesis traditionally relies on transition metal catalysts. In contrast, biological enzymes with Brønsted acidic sites of appropriate strength can protonate olefins and thereby generate carbocations that ultimately react to form natural products. Although chemists have recently designed chiral Brønsted acid catalysts to activate imines and carbonyl compounds, mimicking these enzymes to protonate simple olefins that then engage in asymmetric catalytic reactions has remained a substantial synthetic challenge. Here, we show that a class of confined and strong chiral Brønsted acids enables the catalytic asymmetric intramolecular hydroalkoxylation of unbiased olefins. The methodology gives rapid access to biologically active 1,1-disubstituted tetrahydrofurans, including (–)-Boivinianin A.
    Keywords: Chemistry
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  • 150
    Publication Date: 2018-04-13
    Description: Machine learning methods are becoming integral to scientific inquiry in numerous disciplines. We demonstrated that machine learning can be used to predict the performance of a synthetic reaction in multidimensional chemical space using data obtained via high-throughput experimentation. We created scripts to compute and extract atomic, molecular, and vibrational descriptors for the components of a palladium-catalyzed Buchwald-Hartwig cross-coupling of aryl halides with 4-methylaniline in the presence of various potentially inhibitory additives. Using these descriptors as inputs and reaction yield as output, we showed that a random forest algorithm provides significantly improved predictive performance over linear regression analysis. The random forest model was also successfully applied to sparse training sets and out-of-sample prediction, suggesting its value in facilitating adoption of synthetic methodology.
    Keywords: Chemistry
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  • 151
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    American Association for the Advancement of Science (AAAS)
    In: Science
    Publication Date: 2018-06-22
    Keywords: Chemistry
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  • 152
    Publication Date: 2018-06-29
    Description: Chiral amines are widely used as catalysts in asymmetric synthesis to activate carbonyl groups for α-functionalization. Carbonyl catalysis reverses that strategy by using a carbonyl group to activate a primary amine. Inspired by biological carbonyl catalysis, which is exemplified by reactions of pyridoxal-dependent enzymes, we developed an N-quaternized pyridoxal catalyst for the asymmetric Mannich reaction of glycinate with aryl N -diphenylphosphinyl imines. The catalyst exhibits high activity and stereoselectivity, likely enabled by enzyme-like cooperative bifunctional activation of the substrates. Our work demonstrates the catalytic utility of the pyridoxal moiety in asymmetric catalysis.
    Keywords: Chemistry
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  • 153
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    American Association for the Advancement of Science (AAAS)
    In: Science
    Publication Date: 2018-07-13
    Keywords: Chemistry
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    Topics: Biology , Chemistry and Pharmacology , Geosciences , Computer Science , Medicine , Natural Sciences in General , Physics
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  • 154
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    American Association for the Advancement of Science (AAAS)
    In: Science
    Publication Date: 2018-07-13
    Description: Deconstructive functionalizations involving scission of carbon-carbon double bonds are well established. In contrast, unstrained C(sp 3 )–C(sp 3 ) bond cleavage and functionalization have less precedent. Here we report the use of deconstructive fluorination to access mono- and difluorinated amine derivatives by C(sp 3 )–C(sp 3 ) bond cleavage in saturated nitrogen heterocycles such as piperidines and pyrrolidines. Silver-mediated ring-opening fluorination using Selectfluor highlights a strategy for cyclic amine functionalization and late-stage skeletal diversification, establishing cyclic amines as synthons for amino alkyl radicals and providing synthetic routes to valuable building blocks.
    Keywords: Chemistry
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  • 155
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    American Association for the Advancement of Science (AAAS)
    In: Science
    Publication Date: 2018-07-20
    Keywords: Chemistry
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  • 156
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    American Association for the Advancement of Science (AAAS)
    In: Science
    Publication Date: 2018-07-06
    Keywords: Chemistry
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  • 157
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    American Association for the Advancement of Science (AAAS)
    In: Science
    Publication Date: 2018-07-06
    Description: Transformation of simple precursors into structurally complex cyclobutanes, present in many biologically important natural products and pharmaceuticals, is of considerable interest in medicinal chemistry. Starting from 1,3-enynes and ethylene, both exceptionally inexpensive starting materials, we report a cobalt-catalyzed route to vinylcyclobutenes, as well as the further enantioselective addition of ethylene to these products to form complex cyclobutanes with all-carbon quaternary centers. These reactions can proceed in discrete stages or in a tandem fashion to achieve three highly selective carbon-carbon bond formations in one pot using a single chiral cobalt catalyst.
    Keywords: Chemistry
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  • 158
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    American Association for the Advancement of Science (AAAS)
    In: Science
    Publication Date: 2018-07-27
    Keywords: Chemistry
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  • 159
    Publication Date: 2018-02-23
    Description: Currently, the only compounds known to support fixation and functionalization of dinitrogen (N 2 ) under nonmatrix conditions are based on metals. Here we present the observation of N 2 binding and reduction by a nonmetal, specifically a dicoordinate borylene. Depending on the reaction conditions under which potassium graphite is introduced as a reductant, N 2 binding to two borylene units results in either neutral (B 2 N 2 ) or dianionic ([B 2 N 2 ] 2– ) products that can be interconverted by respective exposure to further reductant or to air. The 15 N isotopologues of the neutral and dianionic molecules were prepared with 15 N-labeled dinitrogen, allowing observation of the nitrogen nuclei by 15 N nuclear magnetic resonance spectroscopy. Protonation of the dianionic compound with distilled water furnishes a diradical product with a central hydrazido B 2 N 2 H 2 unit. All three products were characterized spectroscopically and crystallographically.
    Keywords: Chemistry
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  • 160
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    American Association for the Advancement of Science (AAAS)
    In: Science
    Publication Date: 2018-02-23
    Keywords: Chemistry
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    Topics: Biology , Chemistry and Pharmacology , Geosciences , Computer Science , Medicine , Natural Sciences in General , Physics
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  • 161
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    American Association for the Advancement of Science (AAAS)
    In: Science
    Publication Date: 2018-01-19
    Keywords: Chemistry
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  • 162
    Publication Date: 2018-01-19
    Description: Chemical manufacturing is often done at large facilities that require a sizable capital investment and then produce key compounds for a finite period. We present an approach to the manufacturing of fine chemicals and pharmaceuticals in a self-contained plastic reactionware device. The device was designed and constructed by using a chemical to computer-automated design (ChemCAD) approach that enables the translation of traditional bench-scale synthesis into a platform-independent digital code. This in turn guides production of a three-dimensional printed device that encloses the entire synthetic route internally via simple operations. We demonstrate the approach for the -aminobutyric acid receptor agonist, (±)-baclofen, establishing a concept that paves the way for the local manufacture of drugs outside of specialist facilities.
    Keywords: Chemistry
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  • 163
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    American Association for the Advancement of Science (AAAS)
    In: Science
    Publication Date: 2018-01-26
    Keywords: Chemistry
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  • 164
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    American Association for the Advancement of Science (AAAS)
    In: Science
    Publication Date: 2018-01-26
    Keywords: Chemistry
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  • 165
    Publication Date: 2018-01-26
    Description: The scarcity of complex intermediates in pharmaceutical research motivates the pursuit of reaction optimization protocols on submilligram scales. We report here the development of an automated flow-based synthesis platform, designed from commercially available components, that integrates both rapid nanomole-scale reaction screening and micromole-scale synthesis into a single modular unit. This system was validated by exploring a diverse range of reaction variables in a Suzuki-Miyaura coupling on nanomole scale at elevated temperatures, generating liquid chromatography–mass spectrometry data points for 5760 reactions at a rate of 〉1500 reactions per 24 hours. Through multiple injections of the same segment, the system directly produced micromole quantities of desired material. The optimal conditions were also replicated in traditional flow and batch mode at 50- to 200-milligram scale to provide good to excellent yields.
    Keywords: Chemistry
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  • 166
    Publication Date: 2018-01-26
    Description: Since the discovery by Ullmann and Bielecki in 1901, reductive dimerization (or homocoupling) of aryl halides has been extensively exploited for the generation of a range of biaryl-based functional molecules. In contrast to the single-point connection in these products, edge-sharing fused aromatic systems have not generally been accessible from simple aryl halides via annulation cascades. Here we report a single-step synthesis of fused aromatics with a triphenylene core by the palladium-catalyzed annulative dimerization of structurally and functionally diverse chlorophenylenes through double carbon-hydrogen bond activation. The partially fused polyaromatics can be transformed into fully fused, small graphene nanoribbons, which are otherwise difficult to synthesize. This simple, yet powerful, method allows access to functional -systems of interest in optoelectronics research.
    Keywords: Chemistry
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  • 167
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    American Association for the Advancement of Science (AAAS)
    In: Science
    Publication Date: 2018-08-24
    Keywords: Chemistry
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  • 168
    Publication Date: 2018-08-24
    Description: Lithium-oxygen (Li-O 2 ) batteries have attracted much attention owing to the high theoretical energy density afforded by the two-electron reduction of O 2 to lithium peroxide (Li 2 O 2 ). We report an inorganic-electrolyte Li-O 2 cell that cycles at an elevated temperature via highly reversible four-electron redox to form crystalline lithium oxide (Li 2 O). It relies on a bifunctional metal oxide host that catalyzes O–O bond cleavage on discharge, yielding a high capacity of 11 milliampere-hours per square centimeter, and O 2 evolution on charge with very low overpotential. Online mass spectrometry and chemical quantification confirm that oxidation of Li 2 O involves transfer of exactly 4 e – /O 2 . This work shows that Li-O 2 electrochemistry is not intrinsically limited once problems of electrolyte, superoxide, and cathode host are overcome and that coulombic efficiency close to 100% can be achieved.
    Keywords: Chemistry
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  • 169
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    American Association for the Advancement of Science (AAAS)
    In: Science
    Publication Date: 2018-09-14
    Keywords: Chemistry
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  • 170
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    American Association for the Advancement of Science (AAAS)
    In: Science
    Publication Date: 2018-09-21
    Keywords: Chemistry
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  • 171
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    American Association for the Advancement of Science (AAAS)
    In: Science
    Publication Date: 2018-09-21
    Keywords: Chemistry
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  • 172
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    American Association for the Advancement of Science (AAAS)
    In: Science
    Publication Date: 2018-10-12
    Keywords: Chemistry
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  • 173
    Publication Date: 2018-03-06
    Description: Intramolecular insertion of metal nitrenes into carbon-hydrogen bonds to form -lactam rings has traditionally been hindered by competing isocyanate formation. We report the application of theory and mechanism studies to optimize a class of pentamethylcyclopentadienyl iridium(III) catalysts for suppression of this competing pathway. Modulation of the stereoelectronic properties of the auxiliary bidentate ligands to be more electron-donating was suggested by density functional theory calculations to lower the C–H insertion barrier favoring the desired reaction. These catalysts transform a wide range of 1,4,2-dioxazol-5-ones, carbonylnitrene precursors easily accessible from carboxylic acids, into the corresponding -lactams via sp 3 and sp 2 C–H amidation with exceptional selectivity. The power of this method was further demonstrated by the successful late-stage functionalization of amino acid derivatives and other bioactive molecules.
    Keywords: Chemistry
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  • 174
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    American Association for the Advancement of Science (AAAS)
    In: Science
    Publication Date: 2018-03-06
    Keywords: Chemistry
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  • 175
    Publication Date: 2018-03-16
    Description: Single adatoms are expected to participate in many processes occurring at solid surfaces, such as the growth of graphene on metals. We demonstrate, both experimentally and theoretically, the catalytic role played by single metal adatoms during the technologically relevant process of graphene growth on nickel (Ni). The catalytic action of individual Ni atoms at the edges of a growing graphene flake was directly captured by scanning tunneling microscopy imaging at the millisecond time scale, while force field molecular dynamics and density functional theory calculations rationalize the experimental observations. Our results unveil the mechanism governing the activity of a single-atom catalyst at work.
    Keywords: Chemistry
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  • 176
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    American Association for the Advancement of Science (AAAS)
    In: Science
    Publication Date: 2018-03-16
    Description: Zhang et al . (Reports, 27 January 2017, p. 374) reported synthesis of a cyclo -N 5 – ion putatively stabilized in a solid-state salt by hydrogen bonding from surrounding counterions. We performed theoretical calculations suggesting that HN 5 would be favored over the anion in the reported pentazolate salt via proton transfer.
    Keywords: Chemistry
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  • 177
    Publication Date: 2018-03-16
    Description: Huang and Xu argue that the cyclo -N 5 – ion in (N 5 ) 6 (H 3 O) 3 (NH 4 ) 4 Cl we described in our report is theoretically unfavorable and is instead protonated. Their conclusion is invalid, as they use an improper method to assess the proton transfer in a solid crystal structure. We present an in-depth experimental and theoretical analysis of (N 5 ) 6 (H 3 O) 3 (NH 4 ) 4 Cl that supports the results in the original paper.
    Keywords: Chemistry
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  • 178
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    American Association for the Advancement of Science (AAAS)
    In: Science
    Publication Date: 2018-02-23
    Keywords: Chemistry
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    Topics: Biology , Chemistry and Pharmacology , Geosciences , Computer Science , Medicine , Natural Sciences in General , Physics
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  • 179
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    American Association for the Advancement of Science (AAAS)
    In: Science
    Publication Date: 2018-02-23
    Keywords: Chemistry
    Print ISSN: 0036-8075
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    Topics: Biology , Chemistry and Pharmacology , Geosciences , Computer Science , Medicine , Natural Sciences in General , Physics
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  • 180
    Publication Date: 2021-05-19
    Description: Status of fish consumption was analyzed by completing the 295 questionnaires in all 22 metropolitan regions of Tehran from different households in 2008. After reviewing the descriptive and statistics analysis along with the non-parametric statistics, the fish consumption per capita was extracted through formulas. The average and mode of purchasing of each household occurs 11 times per year with 5.1 Kg in each time. Considering the higher fish consumption growth rate in Iran, the sequence of interest in all kinds of protein is as follows: poultry, mutton, beef, Trout, wild fishes and Chinese carps. The highest interest of households to buy fish more than other protein resources is due to the nutrient value of it. An average of 33.2% purchasing is dedicated to the farmed fish. 59% of purchasers are interested to buy packed up fish products and pay attention to the label of nutrient values on the product package. Fish consumption per capita is 13.3 Kg, which is divided to 6.4 kg for farmed fishes, 5.8 Kg for wild fishes and 1.1 Kg for canned fish. The higher consumption per capita of Tehran citizens in comparison with other people from other cities, who are living in Tehran, is because of their tendency and freshness of farmed fishes. In contrast, the consumption of canned and wild fishes among people of littoral regions who live in Tehran is higher than others.
    Description: Published
    Keywords: Fish consumption per capita ; Fish ; Consumption ; Per capita ; Fisheries
    Repository Name: AquaDocs
    Type: Journal Contribution , Refereed
    Format: pp.546-556
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  • 181
    Publication Date: 2021-05-19
    Description: The purpose of the present research was to identify and rank the effective environmental (background) indices on OE process in Mazandaran Fisheries Organization. In terms of data collection, the method used in this study was the descriptive-survey method and in terms of research purposes, it was an applied research. Statistical population included experts and leading experts of Mazandaran fisheries organization in 2014. After literature review, the effective environmental (background) indices on OE were identified. Data were collected using Delphi and paired comparisons questionnaires, and analyzed using fuzzy Delphi method and FAHP. The results showed that the effective environmental (background) indices on OE, in order of priority, were the economic environments, legal-political environment, social-cultural environment, technological environment, administrative environment and international environment.
    Description: Published
    Keywords: Development ; Economic ; Environmental ; Organizational Entrepreneurship ; Fuzzy Delphi ; Fuzzy AHP ; Mazandaran Fisheries Organization ; Entrepreneurship ; Fisheries ; Explanation ; Ranking ; Factors
    Repository Name: AquaDocs
    Type: Journal Contribution , Refereed
    Format: pp.125-138
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  • 182
    Publication Date: 2021-05-19
    Description: Creating a database of affiliated laboratories of the institute is organized with the aim of integrating information related to laboratories of research centers and their subsidiaries. The main objective of conducting this project in this stage is to upgrade it, establish and running one software system based on up-to-date technology of networking. For this purpose organizing the centers database, a periodic report on various aspects can be done which help for implementing appropriate monitoring and management .Among the sectors that are designed and upgraded for this system include : Portal, bank of information, advanced possibilities for inputting data, searching and reporting on laboratory.The advantages of this precise and updated reports can be collected easily from the general information of research institutes and centers, reports of the number of lab experts with different educational levels in affiliated centers, awareness of numbers and status of the chemical materials in the laboratories of each center, and the significant and important point is about economizing equipment, chemical materials and on time calibration.
    Description: Published
    Keywords: Bank of information ; Laboratories ; Research institute ; Network ; Data ; Fisheries
    Repository Name: AquaDocs
    Type: Journal Contribution , Refereed
    Format: pp.149-153
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  • 183
    Publication Date: 2021-05-19
    Description: Caspian Sea, Persian Gulf and the natural aquatic environment, made Iran’s geo-strategic and socioeconomic situation of the fisheries and aquaculture sector unique. This sector in the three areas of “ecotourism”, “food production” and “social behavior” play a crucial role in achieving Iran's Vision Policy of 1404 goals. However, Iran's valuable position in ornamental fish farming industry has been less attention and several issues challenged its development trend. Markazi is one of the leading provinces in this industry. So the main purposes of research were to identify current situation and providing development strategies. This study was descriptive and data were collected by survey method. The Statistical population was ornamental fish’s Producers and experts in Markazi province which due to limit number, census sampling was applied. The main tool for gathering information was questionnaire which its face validity confirmed through educational specialist and expert’s viewpoint. Also, the reliability of research tool was evaluated by Coronbach Alfa Test. The results showed that "Employment and income" and "Interest in breeding ornamental fish" were two main reasons to attract practitioners to this industry. The respondents considered the current situation ornamental fish industry, undesirable (Score 1.17 out of 5). Factor analysis showed that five factors named; "Corporate management and food resources", "management of extension and informing about authentic breeding principles", "Care Management and Insurance", "imported fish quality management" and "technical and financial support" have explained about 80% of the variance of the current situation and barriers to the development of ornamental fish industry in Markazi Province. The most important strategies to reduce facing problem in mentioned industry were development priority belonged ornamental fish industry trade system and development of specialized human resources training.
    Description: Published
    Keywords: Ornamental fish industry ; ِDevelopment ; Ornamental ; Fish ; Industry ; Fisheries ; Aquaculture ; Quality
    Repository Name: AquaDocs
    Type: Journal Contribution , Refereed
    Format: pp.133-148
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  • 184
    Publication Date: 2021-05-19
    Description: Debido a la disminución de las poblaciones de Panulirus argus a nivel nacional, y al conocimiento limitado sobre su estado actual en la región noroccidental de Cuba, se realizó la evaluación de la pesquería de langosta en esta zona. Se aplicó un Modelo Dinámico de Biomasa basado en series de captura (t) y esfuerzo pesquero (días pesca) por temporadas de pesca entre 1955-2015. El modelo mostró buen ajuste a los datos de captura (R2 = 0,74). Los parámetros estimados fueron: coeficiente de capturabilidad (q = 6,08 x 10-5), tasa intrínseca de crecimiento de la población (r = 0,18) y capacidad de carga del ambiente (K = 5 621 t). La captura máxima sostenible (CMS) obtenida fue de 251 t con un esfuerzo (fCMS) de 1 469 días pesca, una tasa de mortalidad por pesca (FCMS) de 0,089 y una biomasa (BCMS) de 2 811 t. A partir de 2012 se observó un incremento en la captura por unidad de esfuerzo, lo cual puede reflejar una cierta recuperación de la abundancia de la especie, ya que la biomasa presenta una tendencia creciente desde 2005 aunque todavía se encuentra por debajo del límite de sostenibilidad (BCMS), por lo que el recurso se califica como agotado. Los resultados de la tasa de mortalidad por pesca (F) muestran que existieron niveles elevados de explotación en los períodos 1966-1978, 1982-1992 y 1994-2005, que contribuyeron con la disminución de la biomasa por debajo de su nivel sostenible desde 1972. Sin embargo, en los últimos años se observa una reducción de F por debajo del límite de FCMS, y por lo tanto la pesquería no se encuentra bajo efectos de sobrepesca desde 2005.
    Description: Due to the declining populations of Panulirus argus nation wide, and the limited knowledge about its current status in the northwestern region of Cuba, an assessment of the spiny lobster fishery in this area was conducted. A biomass dynamic model was applied, based on catch series (t) and fishing effort (fishing days) by fishing seasons between years 1955-2015.The model showed good fit to the data catch (R2 = 0,74).The estimated parameters were: catchability coefficient (q = 6,08 x 10-5), population growth intrinsic rate (r = 0,18) and environment carrying capacity (K = 5 621 t). The maximum sustainable yield (MSY) obtained was 251 t, with an effort (fMSY) of 1 469 fishing days, a fishing mortality rate (FMSY) of 0.089 and a biomass (BMSY) of 2811 t. From 2012 an increase in catch per unit effort was observed, which may reflect a recovery in the abundance of the species. The biomass also shows a rebuilding from 2005, but remains depleted below the limit of BMSY. The fishing mortality rate (F) was high in the periods 1966-1978, 1982-1992 and 1994-2005, which contributed to the decline of the biomass below its sustainable level since 1972. In recent years F decreased bellow FMSY and therefore there is not overfishing since 2005.
    Description: Published
    Keywords: Langosta ; Modelo dinámico de biomasa ; Panulirus argus ; Pesquería ; Región noroccidental ; Lobster ; Biomass dynamic model ; Fisheries ; Northwestern region
    Repository Name: AquaDocs
    Type: Journal Contribution , Refereed
    Format: pp.24-29
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  • 185
    Publication Date: 2021-05-19
    Description: Thunnus tonggol is one of the most important large pelagic fish species in Hormuzgan province waters. Nominal catch of T. tonggol in 2010 was 32405 tones comprising 65% of total catch of large pelagic fishes. For sustainable exploitation of the resources of this fish, we need to identify its fishing pattern, maximum constant yield and recruitment pattern. Hence, length and weight data were collected randomly from 6 major artisanal fish-landing sites Hassineh, Kong, Bandar Abbas, Salakh, Sirik and Jask in Hormuzgan province, starting in April 2010 over one year. Growth parameters L∞ and K were estimated at 112.23cm 0.3 and (1/year), respectively. Hence, the natural mortality was calculated at 0.43 (1/year) and the maximum constant yield was computed at 11880 tones. Length-weight power relationship, W= aFLb , was W= 3×10-05FL2.82 that showed T. tonggol have isometric growth. Fishing pattern indicated that almost 85% of the catch was under the size at first maturity. Maximum recruitment pattern was in November with average fork length being 27cm. For optimum exploitation of T. tonggol stocks, we suggest two approaches including fishing ban in the maximum recruitment time and gear (Drift gillnet) modification.
    Description: Published
    Keywords: Mackerels ; Thunnus tonggol ; MCY ; Fishing ; Pattern ; Fisheries ; Fish ; Fish stocks
    Repository Name: AquaDocs
    Type: Journal Contribution , Refereed
    Format: pp.129-138
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  • 186
    Publication Date: 2021-05-19
    Description: Published
    Keywords: Establishment ; Streblospio gynobranchiata ; Cerastoderma glaucum ; Fish cage culture ; Structure ; Macrobenthic ; Invertebrate ; Population ; Culture ; Fish ; Biomass ; Abundance ; Feeding ; Fisheries
    Repository Name: AquaDocs
    Type: Journal Contribution , Refereed
    Format: pp.23-40
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  • 187
    Publication Date: 2022-05-25
    Description: Despite an absence of freshwater exploitation, the adult salmon run in the Matamek River, Quebec, declined during 1975-1980 to 〈23% of the level thought to occur there prior to 1967. Returns in 1979 and 1980 of adults tagged as smolts were 1.0% and 0.9%, respectively. Numbers of emigrating smolts and their corresponding adult returns are not significantly correlated, although we observed a trend towards more salmon (2 sea year fish) returning with larger numbers of migrating smolts. Since 1967 there is noted a decrease in the age at which returning adults smolted and females appear to now constitute a larger percentage of returning grilse and salmon. These, and other changes in life history characteristics, appear to be caused solely by commercial exploitation.
    Description: Prepared by the Woods Hole Oceanographic Institution and the Department of Recreation, Fish and Game of the Province of Quebec.
    Keywords: Atlantic salmon ; Fish populations ; Atlantic salmon ; Fisheries
    Repository Name: Woods Hole Open Access Server
    Type: Technical Report
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  • 188
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    Unknown
    Massachusetts Institute of Technology and Woods Hole Oceanographic Institution
    Publication Date: 2022-05-25
    Description: Submitted in partial fulfillment of the requirements for the degree of Doctor of Philosophy at the Massachusetts Institute of Technology and the Woods Hole Oceanographic Institution June 2017
    Description: This thesis documents the origin, distribution, and fate of methane and several of its isotopic forms on Earth. Using observational, experimental, and theoretical approaches, I illustrate how the relative abundances of 12CH4, 13CH4, 12CH3D, and 13CH3D record the formation, transport, and breakdown of methane in selected settings. Chapter 2 reports precise determinations of 13CH3D, a “clumped” isotopologue of methane, in samples collected from various settings representing many of the major sources and reservoirs of methane on Earth. The results show that the information encoded by the abundance of 13CH3D enables differentiation of methane generated by microbial, thermogenic, and abiogenic processes. A strong correlation between clumped- and hydrogen-isotope signatures in microbial methane is identified and quantitatively linked to the availability of H2 and the reversibility of microbially-mediated methanogenesis in the environment. Determination of 13CH3D in combination with hydrogen-isotope ratios of methane and water provides a sensitive indicator of the extent of C–H bond equilibration, enables fingerprinting of methane-generating mechanisms, and in some cases, supplies direct constraints for locating the waters from which migrated gases were sourced. Chapter 3 applies this concept to constrain the origin of methane in hydrothermal fluids from sediment-poor vent fields hosted in mafic and ultramafic rocks on slow- and ultraslow-spreading mid-ocean ridges. The data support a hypogene model whereby methane forms abiotically within plutonic rocks of the oceanic crust at temperatures above ca. 300 C during respeciation of magmatic volatiles, and is subsequently extracted during active, convective hydrothermal circulation. Chapter 4 presents the results of culture experiments in which methane is oxidized in the presence of O2 by the bacterium Methylococcus capsulatus strain Bath. The results show that the clumped isotopologue abundances of partially-oxidized methane can be predicted from knowledge of 13C/12C and D/H isotope fractionation factors alone.
    Description: The research activities documented in this thesis were made possible by grants to my advisor from the U.S. National Science Foundation (NSF award EAR-1250394), the National Aeronautics and Space Administration (NASA) Astrobiology Institute (NAI, University of Colorado, Boulder, CAN 7 under Cooperative Agreement NNA15BB02A), the Department of Energy (DOE, Small Business Innovation Research program, contract DE-SC0004575), the Alfred P. Sloan Foundation via the Deep Carbon Observatory, and a Shell Graduate Fellowship through the MIT Energy Initiative. I completed the bulk of the work in this thesis while being supported by a National Defense Science and Engineering Graduate (NDSEG) Fellowship awarded through the Office of Naval Research of the U.S. Department of Defense. The StanleyW.Watson Fellowship Fund provided support during my first summer term at WHOI.The Charles M. Vest Presidential Fellowship at MIT supported me in the first year of my Ph.D. studies. I received additional support that year through NSF award EAR-1159318 (to S. Ono and T. Bosak) and theWalter & Adel Hohenstein Graduate Fellowship of Phi Kappa Phi. The MIT Earth Resources Laboratory and PAOC Houghton Fund funded my attendance at several conferences.
    Keywords: Methane ; Chemistry ; Isotopes ; Oxidation
    Repository Name: Woods Hole Open Access Server
    Type: Thesis
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  • 189
    Publication Date: 2022-05-25
    Description: The United States Congressional Serial Set contains a wide variety of historical documents relating to natural resources and their history in the United States. It is an excellent resource for those researching historical data concerning fisheries, from extant species and ecology to economic issues. Information on resources outside the United States is also available due to the U.S. history of explorations and expansions. Charts, maps and tables are found within many of the papers and reports. There are also numerous scientific illustrations.
    Keywords: Fisheries ; fisheries data ; historical account ; United States government data ; United States Serial Set
    Repository Name: Woods Hole Open Access Server
    Type: Article
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  • 190
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    Unknown
    University of Tehran , Kish International Campus | Iran, Kish Island
    Publication Date: 2021-05-19
    Description: Unpublished
    Keywords: Lutjanus ehrenbergii ; Fish ; Fisheries
    Repository Name: AquaDocs
    Type: Images/Video , Non Refereed
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  • 191
    Publication Date: 2021-05-19
    Description: The Deepwater Horizon accident and oil spill in the Gulf of Mexico from the Macondo well began on April 20, 2010. Oil flowed into the Gulf for 87 days until the well was capped on July 15, 2010, and declared sealed on September 19, 2010. The United States (USA) Government initially estimated that a total oil discharge into the Gulf of 4.9 million barrels (210 million U.S. gallons) resulted from the spill; however, the estimate was challenged in litigation, reduced to 3.19 million barrels by a trial court, and remains in dispute. A massive cleanup, restoration, and research program followed and continues to the present, mostly funded by BP Exploration & Production Inc. (BP).
    Description: Published
    Keywords: Deepwater Horizon Oil Rig ; Pollution effects ; Fish ; Fisheries ; Oil spills ; Marine mammals ; Birds ; Turtles ; Diseases
    Repository Name: AquaDocs
    Type: Book/Monograph/Conference Proceedings , Refereed
    Format: lxv, pp.869-1757
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  • 192
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    Unknown
    University of Tehran , Kish International Campus | Iran, Kish Island
    Publication Date: 2021-05-19
    Description: Unpublished
    Keywords: Ecsenius pulcher ; Blenny ; Fish ; Fisheries ; Coral reef ; Benthic
    Repository Name: AquaDocs
    Type: Images/Video , Non Refereed
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  • 193
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    Unknown
    Universidade Estadual de Maringá. Departamento de Biologia. Programa de Pós-Graduação em Ecologia de Ambientes Aquáticos Continentais.
    Publication Date: 2022-07-12
    Description: The promotion of mega-constructions, as reservoirs of Itaipu and Yacyretá, are based in ideas of development and progress. However, the report showed by the World Commission on Dams (WCD) in November of 2000, made responsible to the big reservoirs, the projects on Sustainable Regional Development (SRD), as generating of social and environmental damages. Thus, the main goal of the present study is to investigate the social and cultural transformations in the communities of the islanders and riparian people from Ituzaingó and Porto Rico with the constructions of the hydroelectric power plants of Itaipu (Brazil), Porto Primavera (Brazil) and Yacyretá (Argentina). Are analyzed many factors that allowed the built of those reservoirs and their principal actors. Also, the contradictions more visible verified in the social community and environmental of Ituzaingó and Porto Rico. The three reservoirs are located on the Paraná River basin, because the exploration of there hidroelectrical potential and promote of development of the different regions. Although, the reservoirs of Itaipu and Yacyretá, as projects of DRS, not allowed better social conditions for the traditional communities of Porto Rico and Ituzaingó, and they were made loose their significance when they are compare with the damages caused. In the other hand, its main beneficiaries are the multilateral financiers agencies and the economical trusts with distant headquarters from the south of Brazil and the northeast of Argentina.
    Description: A aceitação e promoção de megaobras, como as barragens de Itaipu e Yacyretá, são baseadas em idéias de desenvolvimento e de progresso. Contudo, o informe apresentado pela Comissão Mundial de Represas (CMR) em novembro de 2000, responsabilizou às grandes represas, os projetos de Desenvolvimento Regional Sustentável (DRS) por excelência, como geradoras de uma série de danos sociais e ambientais. Destarte, o objetivo do presente trabalho foi o estudo das transformações sociais ocorridas nas comunidades de ilhéus e ribeirinhos de Ituzaingó e Porto Rico a partir das mudanças na paisagem ecológica decorrentes das construções das usinas hidrelétricas de Itaipu (Brasil), Porto Primavera (Brasil) e Yacyretá (Argentina). Com essa finalidade foram analisados alguns dos fatores que possibilitaram a concretização desses projetos assim como a identificação dos seus principais protagonistas. O trabalho também contemplou o resgate das vozes dos pescadores-lavradores da região. As três usinas assentam-se sobre o rio Paraná com o propósito de explorar o seu potencial hidrelétrico e estimular o desenvolvimento das respectivas regiões. Porém, as represas de Itaipu, Porto Primavera e Yacyretá, como projetos de DRS, não promoveram, até hoje, melhoras significativas para as comunidades tradicionais de Porto Rico e Ituzaingó. O desenvolvimento alcançado perde toda importância quando comparado aos prejuízos ocasionados. Paradoxalmente, os seus principais beneficiários são as agências financiadoras multilaterais e os consórcios econômicos com sedes distantes do sul brasileiro e do nordeste argentino.
    Description: PhD
    Keywords: Hydroelectric ; Impact environment ; Fisheries ; Paraná River ; Environment police ; Ciências Ambientais ; Brazil ; Comunidades ; Pescadores ; Política ambiental ; Exclusão social ; Ecologia humana ; Usinas hidrelétricas ; Impacto socioambiental ; Human ecology ; Brasil ; Comunity ; Paraná, Rio
    Repository Name: AquaDocs
    Type: Thesis/Dissertation
    Format: 137pp.
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  • 194
    Publication Date: 2022-05-26
    Description: This report represents a first step at considering the potential for the use of market-based incentives to aid in the resolution of fishery bycatch problems. Market-based incentives have several advantages over more traditional command-and-control approaches, including cost-effective allocations of environmental controls; incentives for firms to seek technological solutions; flexibility; returns to the public for the use of its resources; and lower administrative costs in some cases. Notwithstanding these advantages and with several notable exceptions, market-based incentives are almost never employed in the management of fishery bycatch problems. There may be several reasons why this is the case, including significant distributional effects, high costs of monitoring and enforcement, difficulties in educating consumers about product attributes, administrative and transactions costs, or merely oversight. We consider this report to be an "advanced outline" of the issues surrounding the consideration of market-based incentives. We begin first by developing in Section 2 a definition of bycatch, including a "typology" of bycatch types. Next, we compile available public information on bycatch in U.S. fisheries, as defined by target species, location, and gear type (Section 3 and Appendix 1). We then review, in Section 4, two potentially relevant strands of literature, the economic theory of multispecies fisheries and studies from other social sciences of how small-scale fisheries deal with problems of bycatch. In Section 5, we describe, in general, the kinds of market-based policy instruments that may be of use in managing bycatch problems. Following this evaluation, we identify and discuss, as case studies; three priority fisheries: th~ northeastern groundfish fishery; the Gulf of Mexico shrimp fishery; and the eastern tropical Pacific yellowfin tuna fishery (Section 6). Finally, in Section 7, we outline approaches to identifying appropriate policy instruments, including a qualitative comparison of market-based approaches, an examination of the effect of specific types of uncertainty on the choice between taxes and ITQs, and the development of a "proposal" for a bycatch management "policy package." This section concludes with a proposal for a set of priority market-based approaches to bycatch management in the three cases discussed in Section 6.
    Description: NOAA Contract No. 50-DGNF-5-00172
    Keywords: Bycatch ; Fisheries
    Repository Name: Woods Hole Open Access Server
    Type: Working Paper
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  • 195
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    Unknown
    Massachusetts Institute of Technology and Woods Hole Oceanographic Institution
    Publication Date: 2022-05-26
    Description: Submitted in partial fulfillment of the requirements for the degree of Doctor of Philosophy at the Massachusetts Institute of Technology and the Woods Hole Oceanographic Institution February 2017
    Description: Salt marshes are physically, chemically, and biologically dynamic environments found globally at temperate latitudes. Tidal creeks and marshtop ponds may expand at the expense of productive grass-covered marsh platform. It is therefore important to understand the present magnitude and drivers of production and respiration in these submerged environments in order to evaluate the future role of salt marshes as a carbon sink. This thesis describes new methods to apply the triple oxygen isotope tracer of photosynthetic production in a salt marsh. Additionally, noble gases are applied to constrain air-water exchange processes which affect metabolism tracers. These stable, natural abundance tracers complement traditional techniques for measuring metabolism. In particular, they highlight the potential importance of daytime oxygen sinks besides aerobic respiration, such as rising bubbles. In tidal creeks, increasing nutrients may increase both production and respiration, without any apparent change in the net metabolism. In ponds, daytime production and respiration are also tightly coupled, but there is high background respiration regardless of changes in daytime production. Both tidal creeks and ponds have higher respiration rates and lower production rates than the marsh platform, suggesting that expansion of these submerged environments could limit the ability of salt marshes to sequester carbon.
    Description: Financial support for my doctoral research was provided by the United States Department of Defense through the National Defense Science and Engineering Graduate Fellowship Program, the National Science Foundation under grant OCE-1233678, and the Woods Hole Oceanographic Institution (WHOI) under grants from the WHOI Coastal Ocean Institute, Ocean and Climate Change Institute, and Ocean Life Institute. WHOI Academic Programs Office also provided funding support for research, through the Ocean Ventures Fund, and for my stipend, as graduate research assistantships including an assistantship from the United States Geological Survey administered by WHOI.
    Keywords: Marshes ; Chemistry ; Metabolism ; Knorr (Ship : 1970-) Cruise KN210-04
    Repository Name: Woods Hole Open Access Server
    Type: Thesis
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  • 196
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    American Association for the Advancement of Science (AAAS)
    In: Science
    Publication Date: 2017-08-11
    Description: Vicinal diamines are a common structural motif in bioactive natural products, therapeutic agents, and molecular catalysts, motivating the continuing development of efficient, selective, and sustainable technologies for their preparation. We report an operationally simple and environmentally friendly protocol that converts alkenes and sodium azide—both readily available feedstocks—to 1,2-diazides. Powered by electricity and catalyzed by Earth-abundant manganese, this transformation proceeds under mild conditions and exhibits exceptional substrate generality and functional group compatibility. Using standard protocols, the resultant 1,2-diazides can be smoothly reduced to vicinal diamines in a single step, with high chemoselectivity. Mechanistic studies are consistent with metal-mediated azidyl radical transfer as the predominant pathway, enabling dual carbon-nitrogen bond formation.
    Keywords: Chemistry
    Print ISSN: 0036-8075
    Electronic ISSN: 1095-9203
    Topics: Biology , Chemistry and Pharmacology , Geosciences , Computer Science , Medicine , Natural Sciences in General , Physics
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  • 197
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    American Association for the Advancement of Science (AAAS)
    In: Science
    Publication Date: 2017-08-18
    Keywords: Chemistry
    Print ISSN: 0036-8075
    Electronic ISSN: 1095-9203
    Topics: Biology , Chemistry and Pharmacology , Geosciences , Computer Science , Medicine , Natural Sciences in General , Physics
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  • 198
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    American Association for the Advancement of Science (AAAS)
    In: Science
    Publication Date: 2017-08-18
    Keywords: Chemistry
    Print ISSN: 0036-8075
    Electronic ISSN: 1095-9203
    Topics: Biology , Chemistry and Pharmacology , Geosciences , Computer Science , Medicine , Natural Sciences in General , Physics
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  • 199
    Publication Date: 2017-08-18
    Description: In methanogenic archaea, the carbon dioxide (CO 2 ) fixation and methane-forming steps are linked through the heterodisulfide reductase (HdrABC)–[NiFe]-hydrogenase (MvhAGD) complex that uses flavin-based electron bifurcation to reduce ferredoxin and the heterodisulfide of coenzymes M and B. Here, we present the structure of the native heterododecameric HdrABC-MvhAGD complex at 2.15-angstrom resolution. HdrB contains two noncubane [4Fe-4S] clusters composed of fused [3Fe-4S]-[2Fe-2S] units sharing 1 iron (Fe) and 1 sulfur (S), which were coordinated at the CCG motifs. Soaking experiments showed that the heterodisulfide is clamped between the two noncubane [4Fe-4S] clusters and homolytically cleaved, forming coenzyme M and B bound to each iron. Coenzymes are consecutively released upon one-by-one electron transfer. The HdrABC-MvhAGD atomic model serves as a structural template for numerous HdrABC homologs involved in diverse microbial metabolic pathways.
    Keywords: Chemistry
    Print ISSN: 0036-8075
    Electronic ISSN: 1095-9203
    Topics: Biology , Chemistry and Pharmacology , Geosciences , Computer Science , Medicine , Natural Sciences in General , Physics
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  • 200
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    American Association for the Advancement of Science (AAAS)
    In: Science
    Publication Date: 2017-08-25
    Keywords: Chemistry
    Print ISSN: 0036-8075
    Electronic ISSN: 1095-9203
    Topics: Biology , Chemistry and Pharmacology , Geosciences , Computer Science , Medicine , Natural Sciences in General , Physics
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