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Journal of the American Chemical Society

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https://www.readbyqxmd.com/read/28812893/%C3%AE-sulfinyl-benzoates-as-precursors-to-li-and-mg-carbenoids-for-the-stereoselective-iterative-homologation-of-boronic-esters
#1
Giorgia Casoni, Murat Kucukdisli, James M Fordham, Matthew Burns, Eddie L Myers, Varinder K Aggarwal
The stereoselective reagent-controlled homologation of boronic esters is one of a small number of iteratable synthetic transformations that if automated could form the basis of a veritable molecule-making machine. Recently, α-stannyl triisopropylbenzoates and α-sulfinyl chlorides have emerged as useful building blocks for the iterative homologation of boronic esters. However, α-stannyl benzoates need to be prepared using stoichiometric amounts of the (+)- or (-)-enantiomer of the scarcely available and expensive diamine sparteine; also, these building blocks, together with the byproducts that are generated during homologation, are perceived as being toxic...
August 16, 2017: Journal of the American Chemical Society
https://www.readbyqxmd.com/read/28812886/room-temperature-ring-opening-of-quinoline-isoquinoline-and-pyridine-with-low-valent-titanium
#2
Seung-Yeol Baek, Takashi Kurogi, Dahye Kang, Masahiro Kamitani, Seongyeon Kwon, Douglas Solowey, Chun-Hsing Chen, Maren Pink, Patrick J Carroll, Daniel J Mindiola, Mu-Hyun Baik
The complex (PNP)Ti=CHtBu(CH2tBu) (PNP = N[2-PiPr2-4-methylphenyl]2-) dehydrogenates cyclohexane to cyclohexene by forming a transient low-valent titanium-alkyl species, [(PNP)Ti(CH2tBu)], which reacts with two equivalents of quinoline (Q) at room temperature to form H3CtBu and a Ti(IV) species where the less hindered C2=N1 bond of Q is ruptured and coupled to another equivalent of Q. The product isolated from this reaction is an imide with a tethered cycloamide group, (PNP)Ti=N[C18H13N] (1). Under photolytic conditions, intramolecular C-H bond activation across the imide-moiety in 1 occurs to form 2, and thermolysis reverses this process...
August 16, 2017: Journal of the American Chemical Society
https://www.readbyqxmd.com/read/28812350/green-solvent-processable-dopant-free-hole-transporting-materials-for-robust-and-efficient-perovskite-solar-cells
#3
Junwoo Lee, Mahdi Malekshahi Byranvand, Gyeongho Kang, Sung Y Son, Seulki Song, Guan-Woo Kim, Taiho Park
In addition to having proper energy levels and high hole mobility (μh) without the use of dopants, hole-transporting materials (HTMs) used in n-i-p-type perovskite solar cells (PSCs) should be processed using green solvents to enable environmentally friendly device fabrication. Although many HTMs have been assessed, owing to the limited solubility of HTMs in green solvents, no green-solvent-processable HTM has been reported to date. Here we report on a green-solvent-processable HTM, an asymmetric D-A polymer (asy-PBTBDT) that exhibits superior solubility even in the green solvent, 2-methylanisole, which is a known food additive...
August 16, 2017: Journal of the American Chemical Society
https://www.readbyqxmd.com/read/28810739/a-hexa-rhodium-metallopeptide-catalyst-for-site-specific-functionalization-of-natural-antibodies
#4
Jun Ohata, Zachary T Ball
Preparation of antibody-drug conjugates (ADCs), an emerging class of targeted biological hybrid agents, necessitates precise control of conjugation reactivity. Antibodies have complex multi-stranded architectures, and specific modification of natu-ral antibodies has proven quite challenging. Here, we demonstrate that cooperative activity of a multi-metallic metallopeptide enables efficient site-specific antibody functionalization, based on molecular recognition of the constant Fc region. This interplay of multiple metal centers enables introduction of an orthogonal alkyne handle into monoclonal or polyclonal antibodies from different species...
August 16, 2017: Journal of the American Chemical Society
https://www.readbyqxmd.com/read/28810738/nature-of-the-active-sites-for-co-reduction-on-copper-nanoparticles-suggestions-for-optimizing-performance
#5
Tao Cheng, Hai Xiao, William A Goddard
Recent experiments show that the grain boundaries (GBs) of copper nanoparticles (NP) lead to outstanding performance in reducing CO2 and CO to alcohol products. We report here multiscale simulations that mimic experimental synthesis conditions to predict the structure of a 10nm Cu NP (158,555 atoms). To identify active sites, we first predict the CO binding at a large number of sites and select 4 exhibiting CO binding stronger than the (211) step surface. Then, we predict the formation energy of *OCCOH intermediate as a descriptor for C-C coupling, identifying two active sites, both of which have an undercoordinated surface square site adjacent to a subsurface stacking fault...
August 16, 2017: Journal of the American Chemical Society
https://www.readbyqxmd.com/read/28792761/manganese-catalyzed-%C3%AE-olefination-of-nitriles-by-primary-alcohols
#6
Subrata Chakraborty, Uttam Kumar Das, Yehoshoa Ben-David, David Milstein
Catalytic α-olefination of nitriles using primary alcohols, via dehydrogenative coupling of alcohols with nitriles, is presented. The reaction is catalyzed by a pincer complex of an earth-abundant metal (manganese), in the absence of any additives, base, or hydrogen acceptor, liberating dihydrogen and water as the only byproducts.
August 16, 2017: Journal of the American Chemical Society
https://www.readbyqxmd.com/read/28787139/control-of-architecture-in-rhombic-dodecahedral-pt-ni-nanoframe-electrocatalysts
#7
Nigel Becknell, Yoonkook Son, Dohyung Kim, Dongguo Li, Yi Yu, Zhiqiang Niu, Teng Lei, Brian T Sneed, Karren L More, Nenad M Markovic, Vojislav R Stamenkovic, Peidong Yang
Platinum-based alloys are known to demonstrate advanced properties in electrochemical reactions that are relevant for proton exchange membrane fuel cells and electrolyzers. Further development of Pt alloy electrocatalysts relies on the design of architectures with highly active surfaces and optimized utilization of the expensive element, Pt. Here, we show that the three-dimensional Pt anisotropy of Pt-Ni rhombic dodecahedra can be tuned by controlling the ratio between Pt and Ni precursors such that either a completely hollow nanoframe or a new architecture, the excavated nanoframe, can be obtained...
August 16, 2017: Journal of the American Chemical Society
https://www.readbyqxmd.com/read/28777568/positioning-the-water-oxidation-reaction-sites-in-plasmonic-photocatalysts
#8
Shengyang Wang, Yuying Gao, Shu Miao, Taifeng Liu, Linchao Mu, Rengui Li, Fengtao Fan, Can Li
Plasmonic photocatalysis, stemming from the effective light absorbance and confinement of surface plasmons, provides a pathway to enhance solar energy conversion. Although the plasmonic hot electrons in water reduction have been extensively studied, exactly how the plasmonic hot holes participate in the water splitting reaction has not yet been well understood. In particular, where the plasmonic hot holes participate in water oxidation is still illusive. Herein, taking Au/TiO2 as a plasmonic photocatalyst prototype, we investigated the plasmonic hot holes involved in water oxidation...
August 16, 2017: Journal of the American Chemical Society
https://www.readbyqxmd.com/read/28764327/enhanced-photoluminescence-emission-and-thermal-stability-from-introduced-cation-disorder-in-phosphors
#9
Chun Che Lin, Yi-Ting Tsai, Hannah E Johnston, Mu-Huai Fang, Fengjiao Yu, Wuzong Zhou, Pamela Whitfield, Ye Li, Jing Wang, Ru-Shi Liu, J Paul Attfield
Optimizing properties of phosphors for use in white-light-emitting diodes (WLEDs) is an important materials challenge. Most phosphors have a low level of lattice disorder due to mismatch between the host and activator cations. Here we show that deliberate introduction of high levels of cation disorder leads to significant improvements in quantum efficiency, stability to thermal quenching, and emission lifetime in Sr1.98-x(Ca0.55Ba0.45)xSi5N8:Eu0.02 (x = 0-1.5) phosphors. Replacing Sr by a (Ca0.55Ba0.45) mixture with the same average radius increases cation size variance, resulting in photoluminescence emission increases of 20-26% for the x = 1...
August 16, 2017: Journal of the American Chemical Society
https://www.readbyqxmd.com/read/28756660/spectroscopy-and-dft-calculations-of-a-flavo-diiron-enzyme-implicate-new-diiron-site-structures
#10
Andrew C Weitz, Nitai Giri, Jonathan D Caranto, Donald M Kurtz, Emile L Bominaar, Michael P Hendrich
Flavo-diiron proteins (FDPs) are non-heme iron containing enzymes that are widespread in anaerobic bacteria, archaea, and protozoa, serving as the terminal components to dioxygen and nitric oxide reductive scavenging pathways in these organisms. FDPs contain a dinuclear iron active site similar to that in hemerythrin, ribonucleotide reductase, and methane monooxygenase, all of which can bind NO and O2. However, only FDP competently turns over NO to N2O. Here, EPR and Mössbauer spectroscopies allow electronic characterization of the diferric and diferrous species of FDP...
August 16, 2017: Journal of the American Chemical Society
https://www.readbyqxmd.com/read/28753024/thiocarbonyl-ylide-chemistry-enables-a-concise-synthesis-of-%C3%A2-hippolachnin-a
#11
Nils Winter, Dirk Trauner
Hippolachnin A (1) is an antifungal polyketide that bristles with ethyl groups mounted onto a caged heterotricyclic core. It has shown potent activity against Cryptococcus neoformans, a yeast that can affect immunocompromised patients as an opportunistic pathogen. Herein we describe a concise, diversifiable, and scalable synthesis of (±)-hippolachnin A (1). It features a powerful photochemical opening step, a diastereoselective addition of an ethyl cuprate and an unusual strategy to install two additional ethyl groups that makes use of a thiocarbonyl ylide generated in situ...
August 16, 2017: Journal of the American Chemical Society
https://www.readbyqxmd.com/read/28810743/layer-by-layer-molecular-assemblies-for-dye-sensitized-pho-toelectrosynthesis-cells-prepared-by-atomic-layer-deposi-tion
#12
Degao Wang, Matthew V Sheridan, Bing Shan, Byron H Farnum, Seth L Marquard, Benjamin D Sherman, Michael S Eberhart, Animesh Nayak, Christopher Dares, Atanu Das, R Morris Bullock, Thomas J Meyer
In a Dye Sensitized Photoelectrosynthesis Cell (DSPEC) the relative orientation of the catalyst and chromophore plays an important role in determining the device efficiency. Here we introduce a new, robust atomic layer deposition (ALD) procedure for the preparation of molecular chromophore-catalyst assemblies on wide bandgap semiconductors. In this procedure, solution deposited, phosphonate derivatized metal complexes on metal oxide surfaces are treated with reactive metal reagents in the gas phase by ALD to form an outer metal ion bridging group which can bind a second phosphonate containing species from solution to establish a R1-PO2-O-M-O-PO2-R2 type surface assembly...
August 15, 2017: Journal of the American Chemical Society
https://www.readbyqxmd.com/read/28810123/electrochemical-dissolution-of-iridium-and-iridium-oxide-par-ticles-in-acidic-media-transmission-electron-microscopy-electrochemical-flow-cell-coupled-to-inductively-coupled-plasma-mass-spectrometry-and-x-ray-absorption-spectros-copy-study
#13
Primož Jovanovič, Nejc Hodnik, Francisco Ruiz-Zepeda, Iztok Arcon, Barbara Jozinović, Milena Zorko, Marjan Bele, Martin Šala, Vid Simon Šelih, Samo B Hocevar, Miran Gaberscek
Iridium based particles as the most promising proton exchange membrane electrolyser electrocatalysts were investigated by transmission electron microscopy (TEM), and by coupling of electrochemical flow cell (EFC) with online inductively coupled plasma mass spectrometer (ICP-MS). Additionally, a thin-film rotating disc electrode (RDE), an identical location trans-mission and scanning electron microscopy (IL-TEM and IL-SEM) as well as an X-ray absorption spectroscopy (XAS) studies have been performed. Extremely sensitive online time-and potential-resolved electrochemical dissolution profiles revealed that iridium particles dissolved already well below oxygen evolution reaction (OER) potentials, presumably induced by iridium surface oxidation and reduction processes, also referred to as transient dissolution...
August 15, 2017: Journal of the American Chemical Society
https://www.readbyqxmd.com/read/28810120/aqueous-solvation-of-ammonia-and-ammonium-probing-hydrogen-bond-motifs-with-ft-ir-and-soft-x-ray-spectroscopy
#14
Maria Ekimova, Wilson Quevedo, Lukasz Szyc, Marcella Iannuzzi, Philippe Wernet, Michael Odelius, Erik T J Nibbering
In a multi-facetted investigation combining local soft-x-ray and vibrational spectroscopic probes with ab initio molecular dynamics simulations, hydrogen-bond interactions of two key principal amine compounds in aqueous solution, ammonia (NH3) and ammonium ion (NH4+), are quantitatively assessed in terms of electronic structure, solvation structure, and dynamics. From the x-ray measurements and from the complementary determination of the IR-active hydrogen stretching and bending modes of NH3 and NH4+ in aqueous solution, the picture emerges of a comparatively strongly hydrogen-bonded NH4+ ion via N-H donating interactions, whereas NH3 has a strong accepting hydrogen bond with one water molecule at the nitrogen lone pair but only weak N-H donating hydrogen bonds...
August 15, 2017: Journal of the American Chemical Society
https://www.readbyqxmd.com/read/28809560/recombinant-macrocyclic-lanthipeptides-incorporating-non-canonical-amino-acids
#15
Claudio Zambaldo, Xiaozhou Luo, Angad P Mehta, Peter G Schultz
Nisin is a complex lanthipeptide that has broad spectrum antibacterial activity. In efforts to broaden the structural diversity of this ribosomally synthesized lantibiotic, we now report the recombinant expression of Nisin variants that incorporate noncanonical amino acids (ncAAs) at discrete positions. This is achieved by expressing the nisA structural gene, cyclase (nisC) and dehydratase (nisB), together with an orthogonal nonsense suppressor tRNA/aminoacyl-tRNA synthetase pair in Escherichia coli. A number of ncAAs with novel chemical reactivity were genetically incorporated into NisA, including an α-chloroacetamide-containing ncAA that allowed for the expression of Nisin variants with novel macrocyclic topologies...
August 15, 2017: Journal of the American Chemical Society
https://www.readbyqxmd.com/read/28809559/on-the-influence-of-the-bridge-on-triplet-state-delocalization-in-linear-porphyrin-oligomers
#16
Sabine Richert, Bart Limburg, Harry L Anderson, Christiane R Timmel
The extent of triplet state delocalization is investigated in rigid linear zinc porphyrin oligomers as a function of interporphyrin bonding characteristics, specifically in meso-meso singly linked and β,meso,β fused structures, using electron paramagnetic resonance techniques. The results are compared with those of earlier measurements on porphyrin oligomers with alkyne linkers exhibiting different preferred conformations. It is shown that dihedral angles near 90° between the porphyrin planes in directly meso-to-meso linked porphyrin oligomers lead to localization of the photoexcited triplet state on a single porphyrin unit, whereas previous work demonstrated even delocalization over two units in meso-to-meso ethyne or butadiyne-bridged oligomers, where the preferred dihedral angles amount to roughly 30° and 0°, respectively...
August 15, 2017: Journal of the American Chemical Society
https://www.readbyqxmd.com/read/28809552/characterization-of-2-oxindole-forming-heme-enzyme-mare-expanding-the-functional-diversity-of-the-tryptophan-dioxygenase-superfamily
#17
Yuyang Zhang, Yi Zou, Nelson L Brock, Tingting Huang, Yingxia Lan, Xiaozheng Wang, Zixin Deng, Yi Tang, Shuangjun Lin
3-Substituted 2-oxindoles are important structural motifs found in many biologically active natural products and pharmaceutical lead compounds. Here, we report an enzymatic formation of the 3-substituted 2-oxindoles catalyzed by MarE in the maremycin biosynthetic pathway in Streptomyces sp. B9173. MarE is a homologue of Fe(II)/heme-dependent tryptophan 2,3-dioxygenases (TDOs). Typical TDOs usually catalyze the insertion of two oxygen atoms from O2 into an indole ring to generate N-formylkynurenine (NFK)-like products...
August 15, 2017: Journal of the American Chemical Society
https://www.readbyqxmd.com/read/28809490/electrophilic-zinc-homoenolates-synthesis-of-cyclopropylamines-from-cyclopropanols-and-amines
#18
L Reginald Mills, Luis Miguel Barrera Arbelaez, Sophie A L Rousseaux
Metal homoenolates, produced via C-C bond cleavage of cyclopropanols, have been extensively investigated as nucleophiles for the synthesis of β-substituted carbonyl derivatives. Herein, we demonstrate that zinc homoenolates can react as carbonyl-electrophiles in the presence of nucleophilic amines to yield highly valuable trans-cyclopropylamines in good yields and high diastereoselectivities. GSK2879552, a lysine demethylase 1 inhibitor currently in clinical trials for the treatment of small cell lung carcinoma, was synthesized using this strategy...
August 15, 2017: Journal of the American Chemical Society
https://www.readbyqxmd.com/read/28809485/dispersion-and-halogen-bonding-interactions-binding-of-the-axial-conformers-of-monohalo-and-%C3%A2-trans-1-2-dihalocyclohexanes-in-enantiopure-alleno-acetylenic-cages
#19
Cornelius Gropp, Tamara Husch, Nils Trapp, Markus Reiher, François Diederich
Enantiopure alleno-acetylenic cage (AAC) receptors with a resorcin[4]arene scaffold, from which four homochiral alleno-acetylenes converge to shape a cavity closed by a four-fold OH-hydrogen-bonding array, form a highly ordered porous network in the solid state. They enable the complexation and co-crystallization of otherwise non-crystalline small molecules. This paper analyzes the axial conformers of monohalo- and (±)-trans-1,2-dihalocyclohexanes, bound in the interior cavity of the AACs, on the atomic level in the solid state and in solution, accompanied by accurate calculations...
August 15, 2017: Journal of the American Chemical Society
https://www.readbyqxmd.com/read/28809102/hyper-open-shell-states-the-lowest-excited-spin-states-of-o-atom-fe2-ion-and-fef2
#20
Zoltán Varga, Pragya Verma, Donald G Truhlar
Excited spin states are important for reactivity, catalysis, and magnetic applications. This work examines the relative energies of the spin states of O atom, Fe2+ ion, and FeF2 and characterizes their excited spin states. Both single-reference and multi-reference methods are used to establish the character of the lowest singlet excited state of all three systems and the lowest triplet excited state of Fe2+ and FeF2. We find that the conventional representation of the orbital occupancies is incorrect in that the states have more unpaired electrons than the minimum number required by their total electron spin quantum number...
August 15, 2017: Journal of the American Chemical Society
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