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Journal of the American Chemical Society

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https://www.readbyqxmd.com/read/28548850/highly-enantioselective-copper-and-iron-catalyzed-intramolecular-cyclopropanation-of-indoles
#1
Huan Xu, Li Yi-Pan, Yan Cai, Guo-Peng Wang, Shou-Fei Zhu, Qi-Lin Zhou
We report the first intramolecular enantioselective cyclopropa-nation of indoles, which was accomplished in good to high yield (up to 94%) with excellent enantioselectivity (up to >99.9% ee) by using copper or iron complexes of chiral spiro bisoxa-zolines as catalysts. This reaction is a straightforward, efficient method for constructing polycyclic compounds with an all-carbon quaternary chiral center at the 3-position of the indole skeleton, a core structure shared by numerous natural products and bioactive compounds...
May 26, 2017: Journal of the American Chemical Society
https://www.readbyqxmd.com/read/28548849/de-risking-the-cu-mediated-18f-fluorination-of-heterocyclic-pet-radioligands
#2
Nicholas Taylor, Enrico Emer, Sean Preshlock, Michael Schedler, Matthew Tredwell, Stefan Verhoog, Joël Mercier, Christophe Genicot, Veronique Emilie Gouverneur
Molecules labeled with fluorine 18 (18F) are used in positron emission tomography to visualize, characterize and measure biological processes in the body. Despite recent advances in the incorporation of 18F onto arenes, the development of general and efficient approaches to label radioligands necessary for drug discovery programs remains a significant task. This full account describes a de-risking approach towards the radiosynthesis of heterocyclic PET radioligands using the copper-mediated 18F fluorination of aryl boron reagents with 18F-fluoride as a model reaction...
May 26, 2017: Journal of the American Chemical Society
https://www.readbyqxmd.com/read/28548827/dynamic-disorder-and-electronic-structures-of-electron-precise-dianionic-diboranes-insights-from-solid-state-multinuclear-magnetic-resonance-spectroscopy
#3
Y T Angel Wong, Johannes Landmann, Maik Finze, David L Bryce
The J(11B, 11B) coupling constants of various salts of the electron-precise hexacyanodiborane(6) dianion, [B2(CN)6]2-, were obtained using 11B double-quantum filtered (DQF) J-resolved solid-state nuclear magnetic resonance (SSNMR) spectroscopy. Our results show that the magnitude of the DQF J splitting is influenced by both the crystallo-graphic symmetry of the system and the presence of dynamics. The splittings are amplified by a factor of 3 as compared to the corresponding theoretical J coupling constants for cases where 1) there is an absence of dynamics but the boron pairs are crystallographically equivalent, or 2) the boron pairs are crystallographically inequivalent but are rendered magnetically equivalent on the timescale of the experiment due to dynamic disorder, which was identified by 11B and 13C SSNMR experiments...
May 26, 2017: Journal of the American Chemical Society
https://www.readbyqxmd.com/read/28548500/the-photochemical-hexadehydro-diels-alder-hv-hdda-reaction
#4
Feng Xu, Xiao Xiao, Thomas R Hoye
We demonstrate that the hexadehydro-Diels-Alder cycloisomerization reaction to produce reactive benzyne derivatives can be initiated photochemically. As with the thermal variant of the HDDA process, the reactive intermediates are formed in the absence of reagents or the resulting byproducts required for the generation of benzynes by traditional methods. This photo-HDDA (or hv-HDDA) reaction occurs at much lower temperatures (including even at -70 °C) than the thermal HDDA, but the benzynes produced behave in the same fashion with respect to their trapping reactions, suggesting that they are of the same electronic state...
May 26, 2017: Journal of the American Chemical Society
https://www.readbyqxmd.com/read/28548496/alkylated-selenophene-based-ladder-type-monomers-via-a-facile-route-for-high-performance-thin-film-transistor-applications
#5
Zhuping Fei, Yang Han, Eliot Gann, Thomas Hodsden, Anthony Chesman, Christopher R McNeill, Thomas D Anthopoulos, Martin Heeney
We report the synthesis of two new selenophene containing ladder-type monomers, cyclopentadiselenophene (CDS) and indacenodiselenophene (IDSe), via a twofold and fourfold Pd catalyzed coupling with a 1,1-diborylmethane derivative. Co-polymers with benzothiadiazole (BT) were prepared in high yield by Suzuki polymerization to afford co-polymers which exhibited excellent solubility in a range of non-chlorinated solvents. The CDS co-polymer exhibited a band gap of just 1.18 eV, which is amongst the lowest reported for donor-acceptor polymers...
May 26, 2017: Journal of the American Chemical Society
https://www.readbyqxmd.com/read/28547991/enhancing-enantiomeric-separation-with-strain-the-case-of-serine-on-cu-531
#6
Yonghui Wang, Sha Yang, Miguel Fuentes-Cabrera, Shuang Li, Wei Liu
Serine has two enantiomers, D and L, which exhibit identical physical and chemical properties but have dramatically different physiological effects. For the pharmaceutical industry, it is thus very important to be able to separate both enantiomers. Using density-functional theory with an accurate treatment of the van der Waals interactions, here we study the enantioselectivity of the (531) surfaces of Cu, Ag, Au, and Pd. Among these surfaces, it is found that Cu(531) is the more efficient one for energetically separating serine enantiomers...
May 26, 2017: Journal of the American Chemical Society
https://www.readbyqxmd.com/read/28538099/iodide-selective-synthetic-ion-channels-based-on-shape-persistent-organic-cages
#7
Bahiru Punja Benke, Pulakesh Aich, Younghoon Kim, Kyung Lock Kim, Md Rumum Rohman, Soonsang Hong, In-Chul Hwang, Eun Hui Lee, Joon Ho Roh, Kimoon Kim
We report here a synthetic ion channel developed from a shape-persistent porphyrin-based covalent organic cage. The cage was synthesized by employing a synthetically economical dynamic covalent chemistry (DCC) approach. The organic cage selectively transports biologically relevant iodide ions over other inorganic anions by a dehydration-driven, channel mechanism as evidenced by vesicle-based fluorescence assays and planar lipid bilayer-based single channel recordings. Furthermore, the organic cage appears to facilitate iodide transport across the membrane of a living cell, suggesting that the cage could be useful as a biological tool that may replace defective iodide channels in living systems...
May 26, 2017: Journal of the American Chemical Society
https://www.readbyqxmd.com/read/28541698/a-sensitive-phonon-based-probe-for-structure-identification-of-1t-mote2
#8
Lin Zhou, Shengxi Huang, Yuki Tatsumi, Lijun Wu, Huaihong Guo, Yaqing Bie, Keiji Ueno, Teng Yang, Yimei Zhu, Jing Kong, Riichiro Saito, Mildred S Dresselhaus
In this work, by combining transmission electron microscopy and polarized Raman spectroscopy for the 1T' MoTe2 flakes with different thicknesses, we found that the polarization dependence of Raman intensity is given as a function of excitation laser wavelength, phonon symmetry and phonon frequency, but has weak dependence on the flake thickness from few-layer to multilayer. In addition, the frequency of Raman peaks and the relative Raman intensity are sensitive to flake thickness, which manifests Raman spectroscopy as an effective probe for thickness of 1T' MoTe2...
May 25, 2017: Journal of the American Chemical Society
https://www.readbyqxmd.com/read/28541696/reversible-redox-activity-in-multicomponent-metal-organic-frameworks-constructed-from-trinuclear-copper-pyrazolate-building-blocks
#9
Binbin Tu, Qingqing Pang, Huoshu Xu, Xiaomin Li, Yulin Wang, Zhen Ma, Linhong Weng, Qiaowei Li
Inorganic functionalization of metal-organic frameworks (MOFs), such as incorporating multiple inorganic building blocks with distinct metals into one structure and further modulating the metal charges, endows the porous materials with significant properties towards their applications in catalysis. In this report, by exploring the role of 4-pyrazolecarboxylic acid (H2PyC) in the formation of trinuclear copper pyrazolate as a metalloligand in situ, four new MOFs with multiple components in order were constructed through one-pot synthesis...
May 25, 2017: Journal of the American Chemical Society
https://www.readbyqxmd.com/read/28541692/stable-chloro-and-bromoxenate-cage-anions-x3-xeo3-3-3-and-x4-xeo3-4-4-x-cl-or-br
#10
James T Goettel, Veit Haensch, Gary J Schrobilgen
The number of isolable compounds which contain different noble-gas-element bonds is limited for xenon and even more so for krypton. Examples of Xe-Cl bonds are rare and prior to this work, no definitive evidence for a Xe-Br bonded compound existed. The syntheses, isolation, and characterization of the first compounds to contain Xe-Br bonds and their chlorine analogues are described in the present work. The reactions of XeO3 with [N(CH3)4]Br and [N(C2H5)4]Br have provided two bromoxenate salts, [N(C2H5)4][Br3(XeO3)3] and [N(CH3)4][Br4(XeO3)4], in which the cage anions have Xe-Br bond lengths that range from 3...
May 25, 2017: Journal of the American Chemical Society
https://www.readbyqxmd.com/read/28541687/bicyclic-alkyl-amino-carbenes-bicaacs-stable-carbenes-more-ambiphilic-than-caacs
#11
Eder Tomás-Mendivil, Max M Hansmann, Cory M Weinstein, Rodolphe Jazzar, Mohand Melaimi, Guy Bertrand
A straightforward strategy allows for the synthesis of storable bicyclic (alkyl)(amino)carbenes (BICAACs), which feature enhanced σ-donating and π-accepting properties compared to monocyclic (alkyl)(amino)carbenes (CAACs). Due to the bicyclo[2.2.2]octane skeleton, the steric environment around the carbene center is different from that of CAACs, and similar to that observed in classical NHCs. The different electronic properties of BICAACs as compared to CAACs allow for ligand exchange reactions not only at a metal center, but also at main group elements...
May 25, 2017: Journal of the American Chemical Society
https://www.readbyqxmd.com/read/28541686/general-oriented-formation-of-carbon-nanotubes-from-metal-organic-frameworks
#12
Jiashen Meng, Chaojiang Niu, Linhan Xu, Jiantao Li, Xiong Liu, Xuanpeng Wang, Yuzhu Wu, Xiaoming Xu, Wenyi Chen, Qi Li, Zi-Zhong Zhu, Dongyuan Zhao, Liqiang Mai
Carbon nanotubes (CNTs) are of great interest for many potential applications because of their extraordinary electronic, mechanical and structural properties. However, issues of chaotic staking, high cost and high energy dissipation in the synthesis of CNTs remain to be resolved. Here we develop a facile, general and high-yield strategy for the oriented formation of CNTs from metal-organic frameworks (MOFs) through a low-temperature (as low as 430 °C) pyrolysis process. The selected MOF crystals act as a single precursor for both nanocatalysts and carbon sources...
May 25, 2017: Journal of the American Chemical Society
https://www.readbyqxmd.com/read/28541671/cage-walking-vertex-differentiation-by-palladium-catalyzed-isomerization-of-b-9-bromo-meta-carborane
#13
Rafal Miroslaw Dziedzic, Joshua L Martin, Jonathan C Axtell, Liban M A Saleh, Ta-Chung Ong, Yun-Fang Yang, Marco S Messina, Arnold L Rheingold, Kendall N Houk, Alexander M Spokoyny
We report the first observed Pd-catalyzed isomerization (cage-walking) of 9-bromo-meta-carborane during Pd-catalyzed cross-coupling which enables formation of B-O and B-N bonds at all boron vertices (B(2), B(4), B(5), and B(9)) of meta-carborane. Experimental and theoretical studies suggest this isomerization mechanism is strongly influenced by the steric crowding at the Pd catalyst by either a biaryl phosphine ligand and/or substrate. Ultimately, this "cage-walking" process provides a unique pathway to preferentially introduce functional groups at the B(2) vertex using B(9)-bromo-meta-carborane as the sole starting material through substrate control...
May 25, 2017: Journal of the American Chemical Society
https://www.readbyqxmd.com/read/28541038/conical-ionic-amphiphiles-endowed-with-micellization-ability-but-lacking-air-and-oil-water-interfacial-activity
#14
Hirohisa Nitta, Koji Harano, Mayuko Isomura, Ellen H G Backus, Mischa Bonn, Eiichi Nakamura
Micellization in water and reduction of the surface tension of water interfaces with air and oil are two archetypical properties of surfactants, caused by self-aggregation and Gibbs monolayer formation at the interfaces, respectively. We present here a new type of amphiphiles that possess a conical shape consisting of a hydrophobic apex and five ionic termini at its base of the cone. The conical shape and the high charge density cooperatively impede the monolayer formation at the interfaces, and hence prevent foaming and emulsification...
May 25, 2017: Journal of the American Chemical Society
https://www.readbyqxmd.com/read/28539043/achieving-remarkable-activity-and-durability-towards-oxygen-reduction-reaction-based-on-ultrathin-rh-doped-pt-nanowires
#15
Hongwen Huang, Kan Li, Zhao Chen, Laihao Luo, Yuqian Gu, Dongyan Zhang, Chao Ma, Rui Si, Jinlong Yang, Zhenmeng Peng, Jie Zeng
The research of active and sustainable electrocatalysts towards oxygen reduction reaction (ORR) is of great importance for industrial application of fuel cells. Here, we report a remarkable ORR catalyst with both excellent mass activity and durability based on sub-2-nm thick Rh-doped Pt nanowires, which combines the merits of high utilization efficiency of Pt atoms, anisotropic one-dimensional nanostructure, and doping of Rh atoms. Compared with commercial Pt/C catalyst, the Rh-doped Pt nanowires/C catalyst shows a 7...
May 25, 2017: Journal of the American Chemical Society
https://www.readbyqxmd.com/read/28502167/transient-porosity-in-densely-packed-crystalline-carbazole-p-diethynylphenylene-carbazole-rotors-co2-and-acetone-sorption-properties
#16
Andrés Aguilar-Granda, Salvador Pérez-Estrada, Elı Sánchez-González, J Raziel Álvarez, Joelis Rodríguez-Hernández, Mario Rodríguez, Arian E Roa, Simón Hernández-Ortega, Ilich A Ibarra, Braulio Rodríguez-Molina
We report for the first time the high sorption properties of a molecular rotor with no permanent voids or channels in its crystal structure. Such crystalline phase originates from THF, DCM, or the irreversible desolvation of entrapped benzene molecules. From these, the benzene in its solvate form acts as rotation stopper, as supported by dynamic characterization using solid-state (2)H NMR experiments. In the solvent-free form, the diffusion of small quantities of iodine vapors caused a significant change in the intramolecular rotation, increasing the known activation energy to rotation from 8...
May 25, 2017: Journal of the American Chemical Society
https://www.readbyqxmd.com/read/28493679/light-induced-fluorescence-modulation-of-quantum-dot-crystal-violet-conjugates-stochastic-off-on-off-cycles-for-multicolor-patterning-and-super-resolution
#17
Sungwook Jung, Joonhyuck Park, Jiwon Bang, Jae-Yeol Kim, Cheolhee Kim, Yongmoon Jeon, Seung Hwan Lee, Ho Jin, Sukyung Choi, Bomi Kim, Woo Jin Lee, Chan-Gi Pack, Jong-Bong Lee, Nam Ki Lee, Sungjee Kim
Photoswitching or modulation of quantum dots (QDs) can be promising for many fields that include display, memory, and super-resolution imaging. However, such modulations have mostly relied on photomodulations of conjugated molecules in QD vicinity, which typically require high power of high energy photons at UV. We report a visible light-induced facile modulation route for QD-dye conjugates. QD crystal violets conjugates (QD-CVs) were prepared and the crystal violet (CV) molecules on QD quenched the fluorescence efficiently...
May 25, 2017: Journal of the American Chemical Society
https://www.readbyqxmd.com/read/28539042/ruthenium-catalyzed-cycloisomerization-of-2-alkynylanilides-synthesis-of-3-substituted-indoles-by-1-2-carbon-migration
#18
Takuma Watanabe, Yuichiro Mutoh, Shinichi Saito
We developed ruthenium-catalyzed cycloisomerization of alkynylanilides which gave 3-substituted indoles in high yields. The reaction proceeded via the disubstituted vinylidene ruthenium complex which was formed by the 1,2-carbon migration.
May 24, 2017: Journal of the American Chemical Society
https://www.readbyqxmd.com/read/28538098/two-dimensional-metal-organic-framework-nanosheets-as-an-enzyme-inhibitor-modulation-of-the-%C3%AE-chymotrypsin-activity
#19
Ming Xu, Shuai Yuan, Xin-Yu Chen, Yu-Jie Chang, Gregory Steven Day, Zhi-Yuan Gu, Hong-Cai Zhou
Two-dimensional metal-organic framework (MOF) nanosheets are utilized as effective enzyme inhibitors, providing an in-spiring means to enhance the control of cellular processes as well as improve our understanding of the surface chemistry between MOFs and enzymes. In this paper, we demonstrated that the activity of α-Chymotrypsin (ChT) can be effectively inhibited with 96.9% inhibition by the 2-D Cu(bpy)2(OTf)2 nanosheets, while the other Zn2(bim)4 nanosheets show no significant inhibition effect towards ChT...
May 24, 2017: Journal of the American Chemical Society
https://www.readbyqxmd.com/read/28538096/location-of-the-substrate-binding-site-of-the-cytochrome-bo3-ubiquinol-oxidase-from-escherichia-coli
#20
Sylvia K Choi, Lici Schurig-Briccio, Ziqiao Ding, Sangjin Hong, Chang Sun, Robert B Gennis
Cytochrome bo3 is a respiratory proton-pumping oxygen reductase that is a member of the heme-copper superfamily that utilizes ubiquinol-8 (Q8H2) as a substrate. The current consensus model has Q8H2 oxidized at a low affinity site (QL), passing electrons to a tightly bound quinone cofactor at a high affinity site (QH site) that stabilizes the one-electron reduced ubisemiquinone, facilitating the transfer of electrons to the redox active metal centers where O2 is reduced to water. The current work shows that the Q8 bound to the QH site is more dynamic than previously thought...
May 24, 2017: Journal of the American Chemical Society
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