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ACS Catalysis

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https://www.readbyqxmd.com/read/29109904/visible-light-photocatalytic-decarboxylation-of-%C3%AE-%C3%AE-unsaturated-carboxylic-acids-facile-access-to-stereoselective-difluoromethylated-styrenes-in-batch-and-flow
#1
Xiao-Jing Wei, Wout Boon, Volker Hessel, Timothy Noël
The development of synthetic methodologies which provide access to both stereoisomers of α,β-disubstituted olefins is a challenging undertaking. Herein, we describe the development of an operationally simple and stereoselective synthesis of difluoromethylated styrenes via a visible-light photocatalytic decarboxylation strategy using fac-Ir(ppy)3 as the photocatalyst. Meta- and para-substituted cinnamic acids provide the expected E-isomer. In contrast, ortho-substituted cinnamic acids yield selectively the less stable Z-product, whereas the E-isomer can be obtained via continuous-flow processing through accurate control of the reaction time...
October 6, 2017: ACS Catalysis
https://www.readbyqxmd.com/read/29104813/photocatalytic-indole-diels-alder-cycloadditions-mediated-by-heterogeneous-platinum-modified-titanium-dioxide
#2
Spencer P Pitre, Juan C Scaiano, Tehshik P Yoon
Indole alkaloids represent an important class of molecules, with many naturally occurring derivatives possessing significant biological activity. One area that requires further development in the synthesis of indole derivatives is the Diels-Alder reaction. In this work, we expand on our previously developed heterogeneous protocol for the [4+2] cycloaddition of indoles and electron-rich dienes mediated by platinum nanoparticles supported on titanium dioxide semiconductor particles (Pt(0.2%)@TiO2) with visible-light irradiation...
October 6, 2017: ACS Catalysis
https://www.readbyqxmd.com/read/29038742/methylene-c-sp-3-h-arylation-of-aliphatic-ketones-using-a-transient-directing-group
#3
Kai Hong, Hojoon Park, Jin-Quan Yu
Palladium-catalyzed methylene β-C(sp(3))-H arylation of aliphatic ketones using a transient directing group is developed. The use of α-benzyl β-alanine directing group that forms a six-membered chelation with palladium is crucial for promoting the methylene C(sp(3))-H bond activation.
October 6, 2017: ACS Catalysis
https://www.readbyqxmd.com/read/29034122/methanol-on-anatase-tio2-101-mechanistic-insights-into-photocatalysis
#4
Martin Setvin, Xiao Shi, Jan Hulva, Thomas Simschitz, Gareth S Parkinson, Michael Schmid, Cristiana Di Valentin, Annabella Selloni, Ulrike Diebold
The photoactivity of methanol adsorbed on the anatase TiO2 (101) surface was studied by a combination of scanning tunneling microscopy (STM), temperature-programmed desorption (TPD), X-ray photoemission spectroscopy (XPS), and density functional theory (DFT) calculations. Isolated methanol molecules adsorbed at the anatase (101) surface show a negligible photoactivity. Two ways of methanol activation were found. First, methoxy groups formed by reaction of methanol with coadsorbed O2 molecules or terminal OH groups are photoactive, and they turn into formaldehyde upon UV illumination...
October 6, 2017: ACS Catalysis
https://www.readbyqxmd.com/read/29034121/atomically-dispersed-pd-o-species-on-ceo2-111-as-highly-active-sites-for-low-temperature-co-oxidation
#5
Giulia Spezzati, Yaqiong Su, Jan P Hofmann, Angelica D Benavidez, Andrew T DeLaRiva, Jay McCabe, Abhaya K Datye, Emiel J M Hensen
Ceria-supported Pd is a promising heterogeneous catalyst for CO oxidation relevant to environmental cleanup reactions. Pd loaded onto a nanorod form of ceria exposing predominantly (111) facets is already active at 50 °C. Here we report a combination of CO-FTIR spectroscopy and theoretical calculations that allows assigning different forms of Pd on the CeO2(111) surface during reaction conditions. Single Pd atoms stabilized in the form of PdO and PdO2 in a CO/O2 atmosphere participate in a catalytic cycle involving very low activation barriers for CO oxidation...
October 6, 2017: ACS Catalysis
https://www.readbyqxmd.com/read/29034120/modulating-the-external-facets-of-functional-nanocrystals-enabled-by-two-dimensional-oxide-crystal-templates
#6
Huiyu Yuan, Kai Han, David Dubbink, Guido Mul, Johan E Ten Elshof
The nature of the external crystal facets is critical to control the (photo)catalytic properties. Two-dimensional materials can expose only one type of crystal facet among zero-dimensional (0D), one-dimensional (1D), and two-dimensional (2D) materials. Controllable tuning of the nature of the external crystal facets of 2D materials is highly desirable but very challenging. Here, we show that 2D particles with the desirable crystal facet for high-performance photocatalytic H2 generation can be obtained by using 2D metal oxide materials (i...
October 6, 2017: ACS Catalysis
https://www.readbyqxmd.com/read/29034119/chloride-tolerant-gold-i-catalyzed-regioselective-hydrochlorination-of-alkynes
#7
Rene Ebule, Shengzong Liang, Gerald B Hammond, Bo Xu
We have developed a highly regioselective homogeneous gold(I)-catalyzed anti-hydrochlorination of unactivated alkynes at room temperature. We have overcome the incompatibility between conventional cationic gold catalysts and chloride by using a hydrogen-bonding activation of the Au-Cl bond. This approach is scalable, exhibits excellent functional group tolerance, and can be conducted in open air.
October 6, 2017: ACS Catalysis
https://www.readbyqxmd.com/read/28966841/s-o-ligand-promoted-palladium-catalyzed-c-h-functionalization-reactions-of-nondirected-arenes
#8
Kananat Naksomboon, Carolina Valderas, Melania Gómez-Martínez, Yolanda Álvarez-Casao, M Ángeles Fernández-Ibáñez
Pd(II)-catalyzed C-H functionalization of nondirected arenes has been realized using an inexpensive and easily accessible type of bidentate S,O-ligand. The catalytic system shows high efficiency in the C-H olefination reaction of electron-rich and electron-poor arenes. This methodology is operationally simple, scalable, and can be used in late-stage functionalization of complex molecules. The broad applicability of this catalyst has been showcased in other transformations such as Pd(II)-catalyzed C-H acetoxylation and allylation reactions...
September 1, 2017: ACS Catalysis
https://www.readbyqxmd.com/read/28966840/structural-basis-of-catalysis-in-the-bacterial-monoterpene-synthases-linalool-synthase-and-1-8-cineole-synthase
#9
Vijaykumar Karuppiah, Kara E Ranaghan, Nicole G H Leferink, Linus O Johannissen, Muralidharan Shanmugam, Aisling Ní Cheallaigh, Nathan J Bennett, Lewis J Kearsey, Eriko Takano, John M Gardiner, Marc W van der Kamp, Sam Hay, Adrian J Mulholland, David Leys, Nigel S Scrutton
Terpenoids form the largest and stereochemically most diverse class of natural products, and there is considerable interest in producing these by biocatalysis with whole cells or purified enzymes, and by metabolic engineering. The monoterpenes are an important class of terpenes and are industrially important as flavors and fragrances. We report here structures for the recently discovered Streptomyces clavuligerus monoterpene synthases linalool synthase (bLinS) and 1,8-cineole synthase (bCinS), and we show that these are active biocatalysts for monoterpene production using biocatalysis and metabolic engineering platforms...
September 1, 2017: ACS Catalysis
https://www.readbyqxmd.com/read/28966839/catalyzed-bimolecular-reactions-in-responsive-nanoreactors
#10
Rafael Roa, Won Kyu Kim, Matej Kanduč, Joachim Dzubiella, Stefano Angioletti-Uberti
We describe a general theory for surface-catalyzed bimolecular reactions in responsive nanoreactors, catalytically active nanoparticles coated by a stimuli-responsive "gating" shell, whose permeability controls the activity of the process. We address two archetypal scenarios encountered in this system: the first, where two species diffusing from a bulk solution react at the catalyst's surface, and the second, where only one of the reactants diffuses from the bulk while the other is produced at the nanoparticle surface, e...
September 1, 2017: ACS Catalysis
https://www.readbyqxmd.com/read/28944089/superior-stability-of-au-sio2-compared-to-au-tio2-catalysts-for-the-selective-hydrogenation-of-butadiene
#11
Nazila Masoud, Laurent Delannoy, Herrick Schaink, Ad van der Eerden, Jan Willem de Rijk, Tiago A G Silva, Dipanjan Banerjee, Johannes D Meeldijk, Krijn P de Jong, Catherine Louis, Petra E de Jongh
Supported gold nanoparticles are highly selective catalysts for a range of both liquid-phase and gas-phase hydrogenation reactions. However, little is known about their stability during gas-phase catalysis and the influence of the support thereon. We report on the activity, selectivity, and stability of 2-4 nm Au nanoparticulate catalysts, supported on either TiO2 or SiO2, for the hydrogenation of 0.3% butadiene in the presence of 30% propene. Direct comparison of the stability of the Au catalysts was possible as they were prepared via the same method but on different supports...
September 1, 2017: ACS Catalysis
https://www.readbyqxmd.com/read/28932620/distinct-roles-of-catalytic-cysteine-and-histidine-in-the-protease-and-ligase-mechanisms-of-human-legumain-as-revealed-by-dft-based-qm-mm-simulations
#12
Brigitta Elsässer, Florian B Zauner, Johann Messner, Wai Tuck Soh, Elfriede Dall, Hans Brandstetter
The cysteine protease enzyme legumain hydrolyzes peptide bonds with high specificity after asparagine and under more acidic conditions after aspartic acid [Baker E. N.J. Mol. Biol.1980, 141, 441-484; Baker E. N.; J. Mol. Biol.1977, 111, 207-210; Drenth J.; Biochemistry1976, 15, 3731-3738; Menard R.; J. Cell. Biochem.1994, 137; Polgar L.Eur. J. Biochem.1978, 88, 513-521; Storer A. C.; Methods Enzymol.1994, 244, 486-500. Remarkably, legumain additionally exhibits ligase activity that prevails at pH > 5.5. The atomic reaction mechanisms including their pH dependence are only partly understood...
September 1, 2017: ACS Catalysis
https://www.readbyqxmd.com/read/28824823/influence-of-the-reaction-temperature-on-the-nature-of-the-active-and-deactivating-species-during-methanol-to-olefins-conversion-over-h-sapo-34
#13
E Borodina, H Sharbini Harun Kamaluddin, F Meirer, M Mokhtar, A M Asiri, S A Al-Thabaiti, S N Basahel, J Ruiz-Martinez, B M Weckhuysen
The selectivity toward lower olefins during the methanol-to-olefins conversion over H-SAPO-34 at reaction temperatures between 573 and 773 K has been studied with a combination of operando UV-vis diffuse reflectance spectroscopy and online gas chromatography. It was found that the selectivity toward propylene increases in the temperature range of 573-623 K, while it decreases in the temperature range of 623-773 K. The high degree of incorporation of olefins, mainly propylene, into the hydrocarbon pool affects the product selectivity at lower reaction temperatures...
August 4, 2017: ACS Catalysis
https://www.readbyqxmd.com/read/28824822/rationalizing-acid-zeolite-performance-on-the-nanoscale-by-correlative-fluorescence-and-electron-microscopy
#14
Jordi Van Loon, Kris P F Janssen, Thomas Franklin, Alexey V Kubarev, Julian A Steele, Elke Debroye, Eric Breynaert, Johan A Martens, Maarten B J Roeffaers
The performance of zeolites as solid acid catalysts is strongly influenced by the accessibility of active sites. However, synthetic zeolites typically grow as complex aggregates of small nanocrystallites rather than perfect single crystals. The structural complexity must therefore play a decisive role in zeolite catalyst applicability. Traditional tools for the characterization of heterogeneous catalysts are unable to directly relate nanometer-scale structural properties to the corresponding catalytic performance...
August 4, 2017: ACS Catalysis
https://www.readbyqxmd.com/read/28824821/mild-and-regioselective-pd-oac-2-catalyzed-c-h-arylation-of-tryptophans-by-arn2-x-promoted-by-tosic-acid
#15
Alan J Reay, L Anders Hammarback, Joshua T W Bray, Thomas Sheridan, David Turnbull, Adrian C Whitwood, Ian J S Fairlamb
A regioselective Pd-mediated C-H bond arylation methodology for tryptophans, utilizing stable aryldiazonium salts, affords C2-arylated tryptophan derivatives, in several cases quantitatively. The reactions proceed in air, without base, and at room temperature in EtOAc. The synthetic methodology has been evaluated and compared against other tryptophan derivative arylation methods using the CHEM21 green chemistry toolkit. The behavior of the Pd catalyst species has been probed in preliminary mechanistic studies, which indicate that the reaction is operating homogeneously, although Pd nanoparticles are formed during substrate turnover...
August 4, 2017: ACS Catalysis
https://www.readbyqxmd.com/read/28824820/promoted-iron-nanocrystals-obtained-via-ligand-exchange-as-active-and-selective-catalysts-for-synthesis-gas-conversion
#16
Marianna Casavola, Jingxiu Xie, Johannes D Meeldijk, Nynke A Krans, Andrey Goryachev, Jan P Hofmann, A Iulian Dugulan, Krijn P de Jong
Colloidal synthesis routes have been recently used to fabricate heterogeneous catalysts with more controllable and homogeneous properties. Herein a method was developed to modify the surface composition of colloidal nanocrystal catalysts and to purposely introduce specific atoms via ligands and change the catalyst reactivity. Organic ligands adsorbed on the surface of iron oxide catalysts were exchanged with inorganic species such as Na2S, not only to provide an active surface but also to introduce controlled amounts of Na and S acting as promoters for the catalytic process...
August 4, 2017: ACS Catalysis
https://www.readbyqxmd.com/read/28804677/haloselective-cross-coupling-via-ni-photoredox-dual-catalysis
#17
Kingson Lin, Rebecca J Wiles, Christopher B Kelly, Geraint H M Davies, Gary A Molander
The chemoselective functionalization of polyfunctional aryl linchpins is crucial for rapid diversification. Although well-explored for Csp(2) and Csp nucleophiles, the chemoselective introduction of Csp(3) groups remains notoriously difficult and is virtually undocumented using Ni catalysts. To fill this methodological gap, a "haloselective" cross-coupling process of arenes bearing two halogens, I and Br, using ammonium alkylbis(catecholato)silicates, has been developed. Utilizing Ni/photoredox dual catalysis, Csp(3) -Csp(2) bonds can be forged selectively at the iodine-bearing carbon of bromo(iodo)arenes...
August 4, 2017: ACS Catalysis
https://www.readbyqxmd.com/read/28989810/carbon-support-surface-effects-in-the-gold-catalyzed-oxidation-of-5-hydroxymethylfurfural
#18
Baira Donoeva, Nazila Masoud, Petra E de Jongh
Oxidation of 5-hydroxymethylfurfural into 2,5-furandicarboxylic acid is an important transformation for the production of bio-based polymers. Carbon-supported gold catalysts hold great promise for this transformation. Here we demonstrate that the activity, selectivity, and stability of the carbon-supported gold nanoparticles in the oxidation of 5-hydroxymethylfurfural strongly depend on the surface properties of the carbon support. Gold nanoparticles supported on basic carbon materials with a low density of functional groups demonstrate higher activity in 5-hydroxymethylfurfural oxidation (TOFAu up to 1195 h(-1)), higher selectivity to 2,5-furandicarboxylic acid, and better stability in comparison to gold nanoparticles supported on carbon materials with acidic surface groups...
July 7, 2017: ACS Catalysis
https://www.readbyqxmd.com/read/28890842/catalytic-mechanisms-for-cofactor-free-oxidase-catalyzed-reactions-reaction-pathways-of-uricase-catalyzed-oxidation-and-hydration-of-uric-acid
#19
Donghui Wei, Xiaoqin Huang, Yan Qiao, Jingjing Rao, Lu Wang, Fei Liao, Chang-Guo Zhan
First-principles quantum mechanical/molecular mechanical (QM/MM)-free energy calculations have been performed to uncover how uricase catalyzes metabolic reactions of uric acid (UA), demonstrating that the entire reaction process of UA in uricase consists of two stages-oxidation followed by hydration. The oxidation consists of four steps: (1) chemical transformation from 8-hydroxyxythine to an anionic radical via a proton transfer along with an electron transfer, which is different from the previously proposed electron-transfer mechanism that involves a dianion intermediate (UA(2-)) during the catalytic reaction process; (2) proton transfer to the O2(-) anion (radical); (3) diradical recombination to form a peroxo intermediate; (4) dissociation of H2O2 to generate the dehydrourate...
July 7, 2017: ACS Catalysis
https://www.readbyqxmd.com/read/28713644/kinetic-modeling-of-the-nickel-catalyzed-esterification-of-amides
#20
Nicholas A Weires, Daniel D Caspi, Neil K Garg
Nickel-catalyzed coupling reactions provide exciting tools in chemical synthesis. However, most methodologies in this area require high catalyst loadings, which commonly range from 10-20 mol % nickel. Through an academic-industrial collaboration, we demonstrate that kinetic modeling can be used strategically to overcome this problem, specifically within the context of the Ni-catalyzed conversion of amides to esters. The successful application of this methodology to a multigram-scale coupling, using only 0...
July 7, 2017: ACS Catalysis
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