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Journal of the American Chemical Society

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https://www.readbyqxmd.com/read/29786426/influence-of-enzyme-quantity-and-distribution-on-the-self-propulsion-of-non-janus-urease-powered-micromotors
#1
Tania Patiño, Natalia Feiner-Gracia, Xavier Arque, Albert Miguel-López, Anita Jannasch, Tom Stumpp, Erik Schäffer, Lorenzo Albertazzi, Samuel Sanchez
The use of enzyme catalysis to power micro and nanomachines offers unique features such as biocompatibility, versatili-ty and fuel bioavailability. Yet, the key parameters underlying the motion behavior of enzyme-powered motors are not completely understood. Here, we investigate the role of enzyme distribution and quantity on the generation of active mo-tion. Two different micromotor architectures based on either polystyrene (PS) or polystyrene coated with a rough silicon dioxide shell (PS@SiO2) were explored...
May 22, 2018: Journal of the American Chemical Society
https://www.readbyqxmd.com/read/29782169/indium-catalysts-for-low-pressure-co-2-epoxide-ring-opening-copolymerization-evidence-for-a-mononuclear-mechanism
#2
Arnaud Thevenon, Anish Cyriac, Dominic Myers, Andrew J P White, Christopher B Durr, Charlotte K Williams
The alternating copolymerization of CO2 /epoxides is a useful means to incorporate high levels of carbon dioxide into polymers. The reaction is generally proposed to occur by bimetallic or bicomponent pathways. Here, the first indium catalysts are presented, which are proposed to operate by a distinct mononuclear pathway. The most active and selective catalysts are phosphasalen complexes, which feature ligands comprising two iminophosphoranes linked to sterically hindered ortho-phenolates. The catalysts are active at 1 bar pressure of carbon dioxide and are most effective without any cocatalyst...
May 21, 2018: Journal of the American Chemical Society
https://www.readbyqxmd.com/read/29782155/a-narrow-gap-semiconducting-germanium-allotrope-from-the-oxidation-of-a-layered-zintl-phase-in-ionic-liquids
#3
Zhongjia Tang, Alexander P Litvinchuk, Melissa Gooch, Arnold M Guloy
A metastable germanium allotrope, Ge(oP32), was synthe-sized as polycrystalline powders and single crystals from the mild-oxidation/delithiation of Li7Ge12 in ionic liquids. Its crystal structure, from single crystal X-ray diffraction (P bcm, a = 8.1527(4) Å, b = 11.7572(5) Å, c = 7.7617(4) Å), features a complex covalent network of 4-bonded Ge, resulting from a well-ordered topotactic oxidative condensation of [Ge12 ]7- layers. It is a diamagnetic semiconductor (Eg = 0.33 eV), and transforms exothermically and irreversibly to α-Ge at 363 °C...
May 21, 2018: Journal of the American Chemical Society
https://www.readbyqxmd.com/read/29782154/miclip-mapseq-a-substrate-identification-approach-for-radical-sam-rna-methylating-enzymes
#4
Vanja Stojković, Tongyue Chu, Gabriel Therizols, David E Weinberg, Danica Galonić Fujimori
Although present across bacteria, the large family of radical SAM RNA methylating enzymes is largely uncharacterized. Escherichia coli RlmN, the founding member of the family, methylates an adenosine in 23S rRNA and several tRNAs to yield 2-methyladenosine (m2A). However, varied RNA substrate specificity among RlmN enzymes, combined with the ability of certain family members to generate 8-methyladenosine (m8A), makes functional predictions across this family challenging. Here, we present a method for unbiased substrate identification that exploits highly efficient, mechanism-based crosslinking between the enzyme and its RNA substrates...
May 21, 2018: Journal of the American Chemical Society
https://www.readbyqxmd.com/read/29782153/temperature-responsive-fluorescent-organoplatinum-ii-metallacycles
#5
Jian-Hong Tang, Yue Sun, Zhong-Liang Gong, Zhong-Yu Li, Zhixuan Zhou, Heng Wang, Xiaopeng Li, Manik Lal Saha, Yu-Wu Zhong, Peter J Stang
The synthesis, characterization, and temperature-responsive properties of two fluorescent organoplatinum(II) metallacycles are reported. Metallacycles M1 and M2 were prepared via the coordination-driven self-assembly of a 120o triarylamine ligand L1 and a 120o diplatinum(II) acceptor Pt-1 or 180o diplatinum(II) acceptor Pt-2, respectively. M1 and M2 are hexagonal metallacycles, comprising of three or six freely rotating anthracene pendants on their periphery, respectively. In response to the temperature variation between 20 and 60 oC, the ligand displays irregular emission changes, whereas both metallacycles show reversible absorption and emission spectral changes in THF...
May 21, 2018: Journal of the American Chemical Society
https://www.readbyqxmd.com/read/29781616/cobalt-catalyzed-regioselective-olefin-isomerization-under-kinetic-control
#6
Xufang Liu, Wei Zhang, Yujie Wang, Ze-Xin Zhang, Lei Jiao, Qiang Liu
Olefin isomerization is a significant transformation in organic synthesis, which provides a convenient synthetic route for internal olefins and remote functionalization processes. The selectivity of an olefin isomerization process is often thermodynamically controlled. Thus, to achieve selectivity under kinetic control is very challenging. Herein, we report a novel cobalt-catalyzed regioselective olefin isomerization reaction. By taking the advantage of fine-tunable NNP-pincer ligand structures, this catalytic system features high kinetic control of regioselectivity...
May 21, 2018: Journal of the American Chemical Society
https://www.readbyqxmd.com/read/29781615/superconductivity-of-rocksalt-structure-lao-epitaxial-thin-film
#7
Kenichi Kaminaga, Daichi Oka, Tetsuya Hasegawa, Tomoteru Fukumura
We report superconducting transition in LaO epitaxial thin film with the onset of superconducting transition temperature ( Tc ) at around 5 K. The Tc is the highest among lanthanum monochalcogenides opposite to the chemical trend of their Tc : 0.84, 1.02, and 1.48 K for La X ( X = S, Se, Te), respectively. The carrier control resulted in a dome-shaped Tc as a function of electron carrier density. In addition, the Tc was significantly sensitive to epitaxial strain in spite of its highly symmetric crystal structure...
May 21, 2018: Journal of the American Chemical Society
https://www.readbyqxmd.com/read/29781613/rational-design-of-the-first-lead-tin-fluorooxoborates-mb2o3f2-m-pb-sn-containing-flexible-two-dimensional-b6o12f6-%C3%A2-single-layers-with-widely-divergent-second-harmonic-generation-effects
#8
Min Luo, Fei Liang, Yunxia Song, Dan Zhao, Ning Ye, Zheshuai Lin
Molecular engineering design is a productive strategy on atomic-scale to optimize crystal structure and develop new-functional materials. Herein, the first lead/tin fluorooxoborates, MB2O3F2 (M=Pb, Sn), were rationally designed by employing the nonlinear optical crystal Sr2Be2B2O7 (SBBO) as a parent model. Compared with the rigid [Be6B6O15]∞ double layers in SBBO, MB2O3F2 have flexible two-dimensional [B6O12F6]∞ single layer, which not only keeps the NLO-favorable layered structure but also overcomes the structural instability issues of SBBO...
May 21, 2018: Journal of the American Chemical Society
https://www.readbyqxmd.com/read/29781611/organocatalytic-enantioselective-construction-of-axially-chiral-sulfone-containing-styrenes
#9
Shiqi Jia, Zhili Chen, Nan Zhang, Yu Tan, Yidong Liu, Jun Deng, Hailong Yan
We describe herein an organocatalytic enantioselective approach for the construction of axially chiral sulfone-containing styrenes. Various axially chiral sulfone-containing styrenes compounds were prepared with excellent enantioselectivities (up to >99% ee) and almost complete E/Z-selectivities (>99% E/Z). Furthermore, the axially chiral sulfone-containing styrenes could be easily converted into phosphonic acid, S/P ligand, which could be potentially used as organocatalysts or ligands in asymmetric catalysis...
May 21, 2018: Journal of the American Chemical Society
https://www.readbyqxmd.com/read/29781605/arylruthenium-iii-porphyrin-catalyzed-c-h-oxidation-and-epoxidation-at-room-temperature-and-ru-v-por-o-ph-intermediate-by-spectroscopic-analysis-and-density-functional-theory-calculations
#10
Ka-Pan Shing, Bei Cao, Yungen Liu, Hung Kay Lee, Ming-De Li, David Lee Phillips, Xiao-Yong Chang, Chi-Ming Che
The development of highly active and selective metal catalysts for efficient oxidation of hydrocarbons and identification of the reactive intermediates in the oxidation catalysis are long-standing challenges. In the rapid hydrocarbon oxidation catalyzed by ruthenium(IV) and -(III) porphyrins, the putative Ru(V)-oxo intermediates remain elusive. Herein we report that arylruthenium(III) porphyrins are highly active catalysts for hydrocarbon oxidation. Using catalyst [RuIII (TDCPP)(Ph)(OEt2 )] (H2 TDCPP = 5,10,15,20-tetrakis(2,6-dichlorophenyl)porphyrin), the oxidation of C-H bonds of various hydrocarbons with oxidant m-CPBA at room temperature gave alcohols/ketones in up to 99% yield within 1 h; use of [ n Bu4 N]IO4 as a mild alternative oxidant avoided formation of lactone from cyclic ketone in C-H oxidation, and the catalytic epoxidation with up to 99% yield and high selectivity (no aldehydes as side product) was accomplished within 5 min...
May 21, 2018: Journal of the American Chemical Society
https://www.readbyqxmd.com/read/29781604/correction-to-a-strategy-for-the-convergent-and-stereoselective-assembly-of-polycyclic-molecules
#11
Emily E Robinson, Regan J Thomson
No abstract text is available yet for this article.
May 21, 2018: Journal of the American Chemical Society
https://www.readbyqxmd.com/read/29781270/hash-mark-shaped-azaacene-tetramers-with-axial-chirality
#12
Yuki Inoue, Daisuke Sakamaki, Yusuke Tsutsui, Masayuki Gon, Yoshiki Chujo, Shu Seki
The tetramers of azapentacene derivatives with unique hash mark (#)-shaped structures were prepared in a quite facile manner. The #-shaped tetramers are optically active because of possessing extended biaryl skeletons, and the structure of the tetramer composed of four dihydrodiazapentacene (DHDAP) units (1) was investigated as the first example of this kind of molecule. The tetramer 1 showed characteristic chiroptical properties reflecting its orthogonally arranged quadruple DHDAP moieties, as well as redox activity...
May 21, 2018: Journal of the American Chemical Society
https://www.readbyqxmd.com/read/29779380/pt-decorated-composition-tunable-pd-fe-pd-c-core-shell-nanoparticles-with-enhanced-electrocatalytic-activity-towards-the-oxygen-reduction-reaction
#13
Yin Xiong, Yao Yang, Francis J DiSalvo, Héctor D Abruña
Design of electrocatalysts with both a high-Pt-utilization efficiency and enhanced electrochemical activity is still the key challenge in the development of proton exchange membrane fuel cells. In the present work, Pd-Fe/C bimetallic nanoparticles (NPs) with an optimal Fe composition and decorated with Pt are introduced as promising catalysts towards the oxygen reduction reaction. These bimetallic nanoparticles have a Pd-Fe@Pd core-shell structure with a surface Pt decoration as established through the use of electron energy loss spectroscopy (EELS) and energy-dispersive X-ray (EDX) spectroscopy...
May 21, 2018: Journal of the American Chemical Society
https://www.readbyqxmd.com/read/29779379/phase-segregation-in-potassium-doped-lead-halide-perovskites-from-39k-solid-state-nmr-at-21-1-t
#14
Dominik J Kubicki, Daniel Prochowicz, Albert Hofstetter, Shaik Mohammed Zakeeruddin, Michael Grätzel, Lyndon Emsley
Organic-inorganic lead halide perovskites are a promising family of light absorbers for a new generation of solar cells, with reported efficiencies currently exceeding 22%. A common problem of solar cells fabricated using these materials is that their efficiency depends on their cycling history, an effect known as current-voltage (J-V) hysteresis. Potassium doping has recently emerged as a universal way to overcome this adverse phenomenon. While the atomistic origins of J-V hysteresis are still not fully understood, it is essential to rationalize the atomic-level effect of protocols that lead to its suppression...
May 21, 2018: Journal of the American Chemical Society
https://www.readbyqxmd.com/read/29779370/observation-of-interpenetration-isomerism-in-covalent-organic-frameworks
#15
Tianqiong Ma, Jian Li, Jing Niu, Lei Zhang, Ahmed S Etman, Cong Lin, Dier Shi, Pohua Chen, Lihua Li, Xin Du, Junliang Sun, Wei Wang
We report herein the first example of interpenetration isomerism in covalent organic frameworks (COFs). As a well-known three-dimensional (3D) COF, COF-300 have been synthesized and characterized by the Yaghi group in 2009 as a 5-fold interpenetrated diamond structure ( dia-c5 topology). We found that adding an ageing process prior to the reported synthetic procedure afforded the formation of an inter-penetration isomer, dia-c7 COF-300. The 7-fold interpenetrated diamond structure of this new isomer was identified by powder X-ray diffraction (PXRD) and rotation electron diffraction (RED) analyses...
May 21, 2018: Journal of the American Chemical Society
https://www.readbyqxmd.com/read/29779378/bandgap-engineering-of-graphene-nanoribbons-by-control-over-structural-distortion
#16
Yunbin Hu, Peng Xie, Marzio De Corato, Alice Ruini, Shen Zhao, Felix Meggendorfer, Lasse Arnt Straasø, Loic Rondin, Patrick Simon, Juan Li, Jonathan J Finley, Michael Ryan Hansen, Jean-Sébastien Lauret, Elisa Molinari, Xinliang Feng, Johannes V Barth, Carlos-Andres Palma, Deborah Prezzi, Klaus Müllen, Akimitsu Narita
Amongst organic electronic materials, graphene nanoribbons (GNRs) offer extraordinary versatility as next-generation semiconducting materials for nanoelectronics and optoelectronics due to their tunable properties, including charge-carrier mobility, optical absorption and electronic bandgap, which are uniquely defined by their chemical structures. Although planar GNRs have been predominantly considered until now, non-planarity can be an additional parameter to modulate their property without changing the aromatic core...
May 19, 2018: Journal of the American Chemical Society
https://www.readbyqxmd.com/read/29775321/direct-ortho-c-h-aminoalkylation-of-2-substituted-pyridine-derivatives-catalyzed-by-yttrium-complexes-with-n-n-diarylethylenediamido-ligands
#17
Abhinanda Kundu, Mariko Inoue, Haruki Nagae, Hayato Tsurugi, Kazushi Mashima
A mixed ligated amidoyttrium complex, Y(NBn2 )(L1)(THF)2 (8, L1 = N,N'-bis(2,6-diisopropylphenyl)ethylenediamine), served as a catalyst for addition of the ortho-pyridyl C(sp2 )-H bond of 2-substituted pyridines to non-activated imines; complex 8 showed superior catalytic performance compared with Y[N(SiMe3 )2 ]3 (1) and Y[N(SiMe3 )2 ]2 (NBn2 )(THF) (2). Concerning the reaction mechanism, we conducted a stoichiometric reaction of an alkylyttrium complex, Y(CH2 SiMe3 )(L1)(THF)2 (7), with 2-ethylpyridine (4e), giving a mixture of (η3 -pyridylmethyl)yttrium complex 9 and (η2 -pyridyl)yttrium complex 10 along with elimination of SiMe4 ...
May 18, 2018: Journal of the American Chemical Society
https://www.readbyqxmd.com/read/29775301/enantioselective-synthesis-of-anti-1-2-diamines-by-cu-catalyzed-reductive-couplings-of-azadienes-with-aldimines-and-ketimines
#18
Xinxin Shao, Kangnan Li, Steven J Malcolmson
Here we report highly efficient and chemoselective azadiene-imine reductive couplings catalyzed by (Ph-BPE)Cu-H that afford anti-1,2-diamines. In all cases, reactions take place with either aldimine or ketimine electrophiles to deliver a single diastereomer of product in >95:5 er. The products' diamines are easily differentiable, facilitating down-stream synthesis.
May 18, 2018: Journal of the American Chemical Society
https://www.readbyqxmd.com/read/29775299/viologen-based-rotaxanes-from-dibenzo-30-crown-10
#19
Hanlie R Wessels, Carla Slebodnick, Harry W Gibson
Three [2]rotaxanes (4, 7 and 12) and one [3]rotaxane (8) were synthesized based on the dibenzo-30-crown-10/viologen binding motif. To the best of our knowledge, these are the first rotaxanes formed from dibenzo-30-crown-10 and viologens. The rotaxanes were all characterized by 1 H NMR, 13 C NMR, and HRMS. An X-ray crystal structure of one of the [2]rotaxanes (7) was obtained. This work demonstrates for the first time that dibenzo-30-crown-10 does form pseudorotaxane complexes with viologens in solution.
May 18, 2018: Journal of the American Chemical Society
https://www.readbyqxmd.com/read/29775298/a-family-of-bodipy-photocages-cleaved-by-single-photons-of-visible-near-ir-light
#20
Julie A Peterson, Chamari Wijesooriya, Elizabeth J Gehrmann, Kaitlyn M Mahoney, Pratik P Goswami, Toshia R Albright, Aleem Syed, Andrew S Dutton, Emily A Smith, Arthur H Winter
Photocages are light-sensitive chemical protecting groups that provide external control over when, where, and how much of a biological substrate is activated in cells using targeted light irradiation. Regrettably, most popular photocages (e.g. o-nitrobenzyl groups) absorb cell-damaging ultraviolet wavelengths. A challenge with achieving longer wavelength bond-breaking photochemistry is that long-wavelength-absorbing chromophores have shorter excited state lifetimes and diminished excited state energies. However, here we report the synthesis of a family of BODIPY-derived photocages with tunable absorptions across the visible/near-IR that release chemical cargo under irradiation...
May 18, 2018: Journal of the American Chemical Society
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