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https://www.readbyqxmd.com/read/28437020/deactivation-of-a-cobalt-catalyst-for-water-reduction-via-valence-tautomerism
#1
Claudio N Verani, Habib Baydoun, Shivnath Mazumder, H Bernhard Schlegel
The activity of the water reduction catalyst [CoIII(L1)(pyr)2]PF6 (1), where (L1)-2 is a bis-amido pyridine ligand and pyr is pyrrolidine, is investigated. Catalyst 1 has an overpotential of 0.54 V and a high observed TOF of 23 min-1, albeit for a relatively short time. Considering the significant activity of 1 and aiming to improve catalyst design, a detailed structural and electronic study is performed to understand the mechanisms of deactivation. Experimental and theoretical evidence support that the metal-reduced [CoI(L1)]- is in tautomeric equilibrium with the ligand-reduced [CoII(L1●)]- species...
April 24, 2017: Chemistry: a European Journal
https://www.readbyqxmd.com/read/28437015/one-step-solution-phase-growth-of-transition-metal-dichalcogenide-thin-films-directly-on-solid-substrates
#2
Anupam Giri, Heeseung Yang, Kalianan Thiyagarajan, Woosun Jang, Jae Min Myoung, Ranbir Singh, Aloysius Soon, Kilwon Cho, Unyong Jeong
Ultrathin transition metal dichalcogenides (TMDs) have exotic electronic properties. With success in easy synthesis of high quality TMD thin films, the potential applications will become more viable in electronics, optics, energy storage, and catalysis. Synthesis of TMD thin films has been mostly performed in vacuum or by thermolysis. So far, there is no solution phase synthesis to produce large-area thin films directly on target substrates. Here, this paper reports a one-step quick synthesis (within 45-90 s) of TMD thin films (MoS2 , WS2 , MoSe2 , WSe2 , etc...
April 24, 2017: Advanced Materials
https://www.readbyqxmd.com/read/28436668/cycloisomerization-between-aryl-enol-ether-and-silylalkynes-under-ruthenium-hydride-catalysis-synthesis-of-2-3-disubstituted-benzofurans
#3
Shohei Ohno, Kohei Takamoto, Hiromichi Fujioka, Mitsuhiro Arisawa
Metal-catalyzed cycloisomerization reactions of 1,n-enynes have become conceptually and chemically attractive processes in the search for atom economy, which is a key subject of current research. However, metal-catalyzed cycloisomerization between aryl enol ether and silylalkynes has not been developed. The ruthenium hydride complex catalyzed cycloisomerization between aryl enol ether and silylalkynes is reported to give benzofurans having useful functional groups, vinyl and trimethylsilylmethyl, on the 2- and 3-positions, respectively...
April 24, 2017: Organic Letters
https://www.readbyqxmd.com/read/28436649/multi-arm-junctions-for-dynamic-dna-nanotechnology
#4
Shohei Kotani, William L Hughes
Non-enzymatic catalytic substrates have been engineered using toehold-mediated DNA strand displacement, and their programmable applications range from medical diagnosis to molecular computation. However, the complexity, stability, scalability, and sensitivity of those systems are plagued by network leakage. A novel way to suppress leakage is to increase its energy barrier through four-way branch migration. Presented here, we designed multi-arm junction substrates that simultaneously exploit four-way branch migration, with a high-energy barrier to minimize leakage, and three-way branch migration, with a low energy barrier to maximize catalysis...
April 24, 2017: Journal of the American Chemical Society
https://www.readbyqxmd.com/read/28436644/ultrathin-tio2-b-nanosheets-as-the-inductive-agent-for-transfering-h2o2-into-superoxide-radicals
#5
Zhen Wei, Di Liu, Weiqin Wei, Xianjie Chen, Qiang Han, Wenqing Yao, Xinguo Ma, Yongfa Zhu
Reflux method to synthesis ultrathin polycrystalline TiO2(B) nanosheets (NS) which is assembled by single crystals, and further stacked into nanoflowers structure. Based on the theoretical calculations and experiments, H2O2 can easily substitute the ethylene glycol adsorded on the surface of TiO2(B) NS, forming H2O2-NS due to the lower adsorption energy and the unique structural features of ultrathin TiO2(B) nanosheets. TiO2(B) NS and H2O2 system can be accelerated to generat superoxide radicals under heat or light and thus exhibits a great degradation property on dye molecules, the total organic carbon (TOC) removal rate was 6 times higher than H2O2 alone...
April 24, 2017: ACS Applied Materials & Interfaces
https://www.readbyqxmd.com/read/28436556/theoretical-evidence-for-bond-stretch-isomerism-in-grubbs-olefin-metathesis
#6
Premaja R Remya, Cherumuttathu H Suresh
A comprehensive density functional theory study on the dissociative and associative mechanisms of Grubbs first and second generation olefin metathesis catalysis reveals that ruthenacyclobutane intermediate (RuCB) observed in the Chauvin mechanism is not unique as it can change to a non-metathetic ruthenacyclobutane (RuCB') via the phenomenon of bond stretch isomerism (BSI). RuCB and RuCB' differ mainly in RuCα , RuCβ , and Cα Cβ bond lengths of the metallacycle. RuCB is metathesis active due to the agostic type bonding-assisted simultaneous activation of both Cα Cβ bonds, giving hypercoordinate character to Cβ whereas an absence of such bonding interactions in RuCB' leads to typical CC single bond distances and metathesis inactivity...
April 24, 2017: Journal of Computational Chemistry
https://www.readbyqxmd.com/read/28436523/mechanistic-insights-into-the-selective-cyclization-of-indolines-with-alkynes-and-alkenes-to-produce-six-and-seven-membered-1-7-fused-indolines-via-rh-iii-catalysis-a-theoretical-study
#7
Lingli Han, Xinyu Zhang, Xingdong Wang, Fengyue Zhao, Shaojing Liu, Tao Liu
The coupling reaction mechanisms of the Rh(iii)-catalyzed redox-neutral C7-selective aryl C-H functionalization of indolines with alkynes and alkenes have been theoretically investigated with the aid of the density functional theory (DFT) calculations. Our calculation results indicate that the active catalyst in this system is the cationic species [Cp*Rh(OAc)](+) (2cat) instead of the neutral species Cp*Rh(OAc)2 (1cat). The origin of forming different products associated with using different coupling partners was also rationalized in detail...
April 24, 2017: Organic & Biomolecular Chemistry
https://www.readbyqxmd.com/read/28436495/electrochemistry-mass-spectrometry-for-mechanism-study-of-oxygen-reduction-at-water-oil-interface
#8
Shu-Juan Liu, Zheng-Wei Yu, Liang Qiao, Bao-Hong Liu
Electrochemistry methods have been widely employed in the development of renewable energy, and involved in various processes, e.g. water splitting and oxygen reduction. Remarkable progress notwithstanding, there are still many challenges in further optimization of catalysts to achieve high performance. For this purpose, an in-depth understanding of reaction mechanism is needed. In this study, an electrochemistry-mass spectrometry method based on a Y-shaped dual-channel microchip as electrochemical cell and ionization device was demonstrated...
April 24, 2017: Scientific Reports
https://www.readbyqxmd.com/read/28436076/unclicking-the-click-metal-assisted-mechanochemical-cycloreversion-of-triazoles-is-possible
#9
Martin Krupička, Przemyslaw Dopieralski, Dominik Marx
The mechanochemical cycloreversion of 1,2,3-triazole compounds, which serve as unusually stable building blocks in materials and biomolecular chemistry as a result of mild "click chemistry", remains puzzling. We show that the hitherto discussed straight-forward retro-click mechanism of the 1,4-disubstituted isomer, even if Cu(I) catalyzed, can be ruled out in view of more favorable activation free energies of destructive pathways. In stark contrast, the 1,5-regioiomer can undergo cycloreversion under rather mild mechanochemical conditions owing to its favorable response to the external force in conjunction with standard Ru(II) catalysis...
April 24, 2017: Angewandte Chemie
https://www.readbyqxmd.com/read/28435960/meteorite-impacts-on-ancient-oceans-opened-up-multiple-nh3-production-pathways
#10
Kohei Shimamura, Fuyuki Shimojo, Aiichiro Nakano, Shigenori Tanaka
A recent series of shock experiments by Nakazawa et al. starting in 2005 (e.g. [Nakazawa et al., Earth Planet. Sci. Lett., 2005, 235, 356]) suggested that meteorite impacts on ancient oceans would have yielded a considerable amount of NH3 to the early Earth from atmospheric N2 and oceanic H2O through reduction by meteoritic iron. To clarify the mechanisms, we imitated the impact events by performing multi-scale shock technique-based ab initio molecular dynamics in the framework of density functional theory in combination with multi-scale shock technique (MSST) simulations...
April 24, 2017: Physical Chemistry Chemical Physics: PCCP
https://www.readbyqxmd.com/read/28435946/faraday-discussions-meeting-catalysis-for-fuels
#11
Nico Fischer, Simon A Kondrat, Mzamo Shozi
Welcome to Africa was the motto when after more than 100 years the flag ship conference series of the Royal Society of Chemistry, the Faraday Discussions was hosted for the first time on the African Continent. Under the fitting topic 'Catalysis for Fuels' over 120 delegates followed the invitation by the conference chair Prof. Graham Hutchings FRS (Cardiff Catalysis Institute), his organizing committee and the co-organizing DST-NRF Centre of Excellence in Catalysis c*change (). In the presentations of 21 invited speakers and 59 posters, cutting edge research in the field of catalysis for fuels, designing new catalysts for synthetic fuels, hydrocarbon conversion in the production of synthetic fuels and novel photocatalysis was presented over the two-day meeting...
April 24, 2017: Chemical Communications: Chem Comm
https://www.readbyqxmd.com/read/28435869/a-dynamic-hydrophobic-core-orchestrates-allostery-in-protein-kinases
#12
Jonggul Kim, Lalima G Ahuja, Fa-An Chao, Youlin Xia, Christopher L McClendon, Alexandr P Kornev, Susan S Taylor, Gianluigi Veglia
Eukaryotic protein kinases (EPKs) constitute a class of allosteric switches that mediate a myriad of signaling events. It has been postulated that EPKs' active and inactive states depend on the structural architecture of their hydrophobic cores, organized around two highly conserved spines: C-spine and R-spine. How the spines orchestrate the transition of the enzyme between catalytically uncommitted and committed states remains elusive. Using relaxation dispersion nuclear magnetic resonance spectroscopy, we found that the hydrophobic core of the catalytic subunit of protein kinase A, a prototypical and ubiquitous EPK, moves synchronously to poise the C subunit for catalysis in response to binding adenosine 5'-triphosphate...
April 2017: Science Advances
https://www.readbyqxmd.com/read/28435179/real-time-measurement-of-size-resolved-elemental-composition-ratio-for-flame-synthesized-composite-nanoparticle-aggregates-using-a-tandem-smps-icp-oes
#13
Nathan Reed, Jiaxi Fang, Sanmathi Chavalmane, Pratim Biswas
Composite nanoparticles find application in catalysis, drug delivery, and energy storage and require increasingly fine control of their physical properties and composition. While composite nanoparticles have been widely synthesized and characterized, little work has systematically correlated the initial concentration of precursors and the final composition of flame synthesized composite nanoparticles. This relationship is explored in a diffusion flame aerosol reactor by coupling a scanning mobility particle sizer (SMPS) with an inductively coupled plasma optical emission spectrometer (ICP-OES)...
2017: Aerosol Science and Technology: the Journal of the American Association for Aerosol Research
https://www.readbyqxmd.com/read/28433497/clostridium-difficile-toxin-glucosyltransferase-domains-in-complex-with-a-non-hydrolyzable-udp-glucose-analogue
#14
Joseph W Alvin, D Borden Lacy
Clostridium difficile is the leading cause of hospital-acquired diarrhea and pseudomembranous colitis worldwide. The organism produces two homologous toxins, TcdA and TcdB, which enter and disrupt host cell function by glucosylating and thereby inactivating key signalling molecules within the host. As a toxin-mediated disease, there has been a significant interest in identifying small molecule inhibitors of the toxins' glucosyltransferase activities. This study was initiated as part of an effort to identify the mode of inhibition for a small molecule inhibitor of glucosyltransferase activity called apigenin...
April 19, 2017: Journal of Structural Biology
https://www.readbyqxmd.com/read/28430422/gauging-donor-acceptor-properties-and-redox-stability-of-chelating-click-derived-triazoles-and-triazolylidenes-a-case-study-with-rhenium-i-complexes
#15
Lisa Suntrup, Sinja Klenk, Johannes Klein, Sebastian Sobottka, Biprajit Sarkar
Bidentate ligands containing at least one triazole or triazolylidene (mesoionic carbene, MIC) unit are extremely popular in contemporary chemistry. One reason for their popularity is the similarities as well as differences in the donor/acceptor properties that these ligands display in comparison to their pyridine or other N-heterocyclic carbene counterparts. We present here seven rhenium(I) carbonyl complexes where the bidentate ligands contain combinations of pyridine/triazole/triazolylidene. These are the first examples of rhenium(I) complexes with bidentate 1,2,3-triazol-5-ylidene-containing ligands...
April 21, 2017: Inorganic Chemistry
https://www.readbyqxmd.com/read/28430280/potassium-complexes-supported-by-monoanionic-tetradentate-amino-phenolate-ligands-synthesis-structure-and-catalysis-in-the-ring-opening-polymerization-of-rac-lactide
#16
Chenhui Yao, Yang Yang, Shaoan Xu, Haiyan Ma
A series of potassium complexes bearing monoanionic tetradentate amino-phenolate ligands, [LK]2 (L = {(2-R(1))C6H4CH2N[(CH2)2R(2)]CH2(4-R(4)-6-R(3))C6H2O-}, R(1) = NMe2, R(2) = NEt2, R(3) = CPh3, R(4) = Me (1); R(1) = R(2) = NEt2, R(3) = CPh3, R(4) = Me (2); R(1) = NMe2, R(2) = NEt2, R(3) = R(4) = cumyl (4); R(1) = R(2) = OMe, R(3) = (t)Bu, R(4) = Me (6); L = (2-NMe2)C6H4CH2N[[CH2-(S)-1-butylpyrrolidinyl]CH2(4-Me-6-CPh3)C6H2O-] (3)), have been synthesized via reactions of KN(SiMe3)2 and 1 equiv. of the corresponding aminophenols...
April 21, 2017: Dalton Transactions: An International Journal of Inorganic Chemistry
https://www.readbyqxmd.com/read/28430274/high-throughput-and-ultratrace-naked-eye-colorimetric-detection-of-au-3-based-on-the-gold-amalgam-stimulated-peroxidase-mimetic-activity-in-aqueous-solutions
#17
Shouting Zhang, Zhuoyue Zhang, Tiansheng Wang, Dongxu Zhang, Xuemei Li, Zhonghua Xue, Duoliang Shan, Xiaoquan Lu
Herein, we present a catalysis-based, label-free, and efficient strategy for a rapid, high-throughput, highly selective and ultrasensitive naked-eye colorimetric assay of Au(3+) in aqueous solutions, based on the gold amalgam-stimulated peroxidase mimetic activity.
April 21, 2017: Chemical Communications: Chem Comm
https://www.readbyqxmd.com/read/28430203/photoredox-activation-of-carbon-dioxide-for-amino-acid-synthesis-in-continuous-flow
#18
Hyowon Seo, Matthew H Katcher, Timothy F Jamison
Although carbon dioxide (CO2) is highly abundant, its low reactivity has limited its use in chemical synthesis. In particular, methods for carbon-carbon bond formation generally rely on two-electron mechanisms for CO2 activation and require highly activated reaction partners. Alternatively, radical pathways accessed via photoredox catalysis could provide new reactivity under milder conditions. Here we demonstrate the direct coupling of CO2 and amines via the single-electron reduction of CO2 for the photoredox-catalysed continuous flow synthesis of α-amino acids...
May 2017: Nature Chemistry
https://www.readbyqxmd.com/read/28429712/electron-transport-and-visible-light-absorption-in-a-plasmonic-photocatalyst-based-on-strontium-niobate
#19
D Y Wan, Y L Zhao, Y Cai, T C Asmara, Z Huang, J Q Chen, J Hong, S M Yin, C T Nelson, M R Motapothula, B X Yan, D Xiang, X Chi, H Zheng, W Chen, R Xu, Ariando, A Rusydi, A M Minor, M B H Breese, M Sherburne, M Asta, Q-H Xu, T Venkatesan
Semiconductor compounds are widely used for photocatalytic hydrogen production applications, where photogenerated electron-hole pairs are exploited to induce catalysis. Recently, powders of a metallic oxide (Sr1-xNbO3, 0.03<x<0.20) were reported to show competitive photocatalytic efficiencies under visible light, which was attributed to interband absorption. This discovery expanded the range of materials available for optimized performance as photocatalysts. Here we study epitaxial thin films of SrNbO3+δ and find that their bandgaps are ∼4...
April 19, 2017: Nature Communications
https://www.readbyqxmd.com/read/28429580/metal-ion-coupled-consecutive-photoinduced-electron-transfer-generates-strong-reduction-potentials-from-visible-light
#20
Andreas Meyer, Tomas Slanina, Alexander Heckel, Burkhard König
Metal ions can have beneficial effects on photoinduced electron transfer. Merging such metal-ion coupled electron transfer (MCET) with consecutive photoinduced electron transfer (conPET) enables the one-electron reduction of chlorobenzene with blue light in the presence of diisopropylethylamine as electron donor. The presence of the metal ions extends the substrate scope of the photoredox catalysis to extreme reduction potentials (beyond -3 V vs SCE).
April 21, 2017: Chemistry: a European Journal
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