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Journal of the American Chemical Society

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https://www.readbyqxmd.com/read/28641018/three-dimensional-imaging-of-transparent-tissues-via-metal-nanoparticle-labeling
#1
Abdullah Muhammad Syed, Shrey Sindhwani, Stefan Wilhelm, Benjamin R Kingston, Dennis S W Lee, Jennifer L Gommerman, Warren C W Chan
Chemical probes are key components of the bioimaging toolbox as they label biomolecules in cells and tissues. The new challenge in bioimaging is to design chemical probes for 3-Dimensional (3D) tissue imaging. Here, we discovered that the scattering of metal nanoparticles can provide imaging contrast in intact tissues in 3D. The nanoparticles can act as a template for chemically growing a metal layer to further enhance the scattering signal. The use of chemically-grown nanoparticles in whole tissues can amplify the scattering to produce a 1...
June 22, 2017: Journal of the American Chemical Society
https://www.readbyqxmd.com/read/28640999/common-and-potentially-prebiotic-origin-for-precursors-of-nucleotide-synthesis-and-activation
#2
Albert C Fahrenbach, Constantin Giurgiu, Chun Pong Tam, Li Li, Yayoi Hongo, Masashi Aono, Jack W Szostak
We have recently shown that 2-aminoimidazole is a superior nucleotide activating group for nonenzymatic RNA copying. Here we describe a prebiotic synthesis of 2-aminoimidazole that shares a common mechanistic pathway with that of 2-aminooxazole, a previously described key intermediate in prebiotic nucleotide synthesis. In the presence of glycolaldehyde, cyanamide, phosphate and ammonium ion, both 2-aminoimidazole and 2-aminooxazole are produced, with higher concentrations of ammonium ion and acidic pH favoring the former...
June 22, 2017: Journal of the American Chemical Society
https://www.readbyqxmd.com/read/28640639/alkaline-earth-centered-co-homologation-reduction-and-amine-carbonylation
#3
Mathew D Anker, Christos E Kefalidis, Yan Yang, Jian Fang, Michael S Hill, Mary F Mahon, Laurent Maron
Reactions of -diketiminato magnesium and calcium hydrides with 1 atmosphere of CO result in a reductive coupling process to produce the corresponding derivatives of the cis-ethenediolate dianion. Computational (DFT) analysis of this processes mediated by Ca, Sr and Ba highlight a common mechanism and a facility for the reaction that increases with increasing alkaline earth (Ae) atomic weight. Reaction of CO with PhSiH3 in the presence of the magnesium or calcium hydrides results in catalytic reduction to methylsilane and methylene silylether products respectively...
June 22, 2017: Journal of the American Chemical Society
https://www.readbyqxmd.com/read/28640637/designing-transmitter-ligands-that-mediate-energy-transfer-between-semiconductor-nanocrystals-and-molecules
#4
Zhiyuan Huang, Ming Lee Tang
Molecular control of energy transfer is an attractive proposition because it allows chemists to synthetically tweak various kinetic and thermodynamic factors. In this Perspective, we examine energy transfer between semiconductor nano-crystals (NCs) and π-conjugated molecules, focusing on the transmitter ligand at the organic-inorganic interface. Efficient transfer of triplet excitons across this interface allows photons to be directed for effective use of the entire solar spectrum. For example, a photon upconversion system composed of semiconductor NCs as sensitizers, bound organic ligands as transmitters, and molecular annihilators has the advantage of large, tunable absorption cross-sections across the visible and near infrared wavelengths...
June 22, 2017: Journal of the American Chemical Society
https://www.readbyqxmd.com/read/28640616/the-twist-of-a-silicon-silicon-double-bond-selective-anti-addition-of-hydrogen-to-an-iminodisilene
#5
Daniel Wendel, Tibor Szilvási, Christian Jandl, Shigeyoshi Inoue, Bernhard Rieger
Hydrogenation of alkenes with C=C bonds is a ubiquitous reaction in organic chemistry. However, this transformation remains unknown for heavier counterparts, disilenes with Si=Si bonds. Here we report the isolation of (Z)-diiminodisilyldisilene 2 featuring a highly trans-bent and twisted structure and the longest silicon-silicon double bond reported to date. In silico studies suggested that the Si=Si bond in 2 is described as very weak double donor-acceptor bond. We utilized the remarkable electronic and structural features of this product to achieve the first demonstration of hydrogen activation by a multiply bonded silicon compound under ambient conditions...
June 22, 2017: Journal of the American Chemical Society
https://www.readbyqxmd.com/read/28640615/reduction-of-dinitrogen-to-ammonia-catalyzed-by-molybdenum-diamido-complexes
#6
Lasantha A Wickramasinghe, Richard R Schrock, Peter Müller, Takaya Ogawa
[Ar2N3]Mo(N)(O-t-Bu) ([Ar2N3]2- = [2,6-(ArNCH2)2NC5H3]2-, where Ar = 2,6-diisopropylphenyl), which contains a conformationally rigid pyridine-based diamido ligand, can be prepared from Li2[Ar2N3] and (t-BuO)3Mo(N). [Ar2N3]Mo(N)(O-t-Bu) serves as a cata-lyst precursor for the catalytic reduction of molecular nitrogen to ammonia in diethyl ether between -78 °C and 22 °C in a batch-wise manner with CoCp*2 as the electron source and Ph2NH2OTf as the proton source. Up to ~10 equivalents of ammonia can be formed per Mo with a maximum efficiency in electrons of ~43%...
June 22, 2017: Journal of the American Chemical Society
https://www.readbyqxmd.com/read/28640613/molecular-recognition-under-interfacial-conditions-calix-4-pyrrole-based-cross-linkable-micelles-for-ion-pair-extraction
#7
Xiaodong Chi, Gretchen Marie Peters, Forrest Hammel, Chandler Brockman, Jonathan L Sessler
An anthracene-functionalized, long-tailed calix[4]pyrrole 1, containing both an anion-recognition site and cation-recognition functionality, has been synthesized and fully characterized. Upon ion-pair complexation with FeF2, receptor 1 self-assembles into multi-micelles in aqueous media. This aggregation process is ascribed to a change in polarity from non-polar to amphiphilic induced upon concurrent anion and cation complexation and permits molecular recognition-based control over chemical morphology under interfacial conditions...
June 22, 2017: Journal of the American Chemical Society
https://www.readbyqxmd.com/read/28640611/lattice-hydride-mechanism-in-electrocatalytic-co2%C3%A2-reduction-by-structurally-precise-copper-hydride-nanoclusters
#8
Qing Tang, Yongjin Lee, Dai-Ying Li, Woojun Choi, C W Liu, Dongil Lee, De-En Jiang
Copper electrocatalysts can reduce CO2 to hydrocarbons at high overpotentials. However, mechanistic understanding of CO2 reduction on nanostructured Cu catalysts has been lacking. Herein we show that the structurally precise ligand-protected Cu-hydride nanoclusters, such as Cu32H20L12 (L is a dithiophosphate ligand), offer unique selectivity for electrocatalytic CO2 reduction at low overpotentials. Our density functional theory (DFT) calculations predict that the presence of the negatively charged hydrides in the copper cluster plays a critical role in determining the selectivity of the reduction product, yielding HCOOH over CO with a lower overpotential...
June 22, 2017: Journal of the American Chemical Society
https://www.readbyqxmd.com/read/28640609/enantioselective-copper-catalyzed-arylation-driven-semi-pinacol-rearrangement-of-allylic-alcohols-with-diaryliodonium-salts
#9
Daniel H Lukamto, Matthew J Gaunt
A copper-catalyzed enantioselective arylative semi-pinacol rearrangement of allylic alcohols using diaryliodonium salts is reported. Chiral Cu(II)-bisoxazoline catalysts initiate an electrophilic alkene arylation, triggering a 1,2-alkyl migration to afford a range of non-racemic spirocyclic ketones with high yields, diastero- and enantioselectivities.
June 22, 2017: Journal of the American Chemical Society
https://www.readbyqxmd.com/read/28613857/intracellular-transfer-hydrogenation-mediated-by-unprotected-organoiridium-catalysts
#10
Sohini Bose, Anh H Ngo, Loi H Do
In the present work, we show for the first time that the conversion of aldehydes to alcohols can be achieved using "unprotected" iridium transfer hydrogenation catalysts inside living cells. The reactions were observed in real time by confocal fluorescence microscopy using a Bodipy fluorogenic substrate. We propose that the reduced cofactor nicotinamide adenine dinucleotide (NADH) is a possible hydride source inside the cell based on studies using pyruvate as a cellular redox modulator. We expect that this biocompatible reductive chemistry will be broadly useful to practitioners working at the interface of chemistry and the life sciences...
June 22, 2017: Journal of the American Chemical Society
https://www.readbyqxmd.com/read/28608682/powering-a-co2-reduction-catalyst-with-visible-light-through-multiple-sub-picosecond-electron-transfers-from-a-quantum-dot
#11
Shichen Lian, Mohamad S Kodaimati, Dmitriy S Dolzhnikov, Raul Calzada, Emily A Weiss
Photosensitization of molecular catalysts to reduce CO2 to CO is a sustainable route to storable solar fuels. Crucial to the sensitization process is highly efficient transfer of redox equivalents from sensitizer to catalyst; in systems with molecular sensitizers, this transfer is often slow because it is gated by diffusion-limited collisions between sensitizer and catalyst. This article describes the photosensitization of a meso-tetraphenylporphyrin iron(III) chloride (FeTPP) catalyst by colloidal, heavy metal-free CuInS2/ZnS quantum dots (QDs) to reduce CO2 to CO using 450 nm light...
June 22, 2017: Journal of the American Chemical Society
https://www.readbyqxmd.com/read/28604011/very-large-sized-transition-metal-dichalcogenides-monolayers-from-fast-exfoliation-by-manual-shaking
#12
Jing Peng, Jiajing Wu, Xiaoting Li, Yuan Zhou, Zhi Yu, Yuqiao Guo, Junchi Wu, Yue Lin, Zejun Li, Xiaojun Wu, Changzheng Wu, Yi Xie
For two-dimensional transition metal dichalcogenides (TMD) materials, achieving large size with high quality to provide a basis for the next generation of electronic device geometries has been a long-term need. Here, we demonstrate that, by only manual shaking within several seconds, very large-sized TMD monolayers that cover a wide range of group IVB-VIB transition metal sulfides and selenides can be efficiently harvested from intercalated single-crystal counterparts. Taking TaS2 as examples, monolayers up to unprecedented size (>100 μm) are obtained while maintaining high crystalline quality and the phase structure of the starting materials...
June 22, 2017: Journal of the American Chemical Society
https://www.readbyqxmd.com/read/28573847/nickel-sequestration-by-the-host-defense-protein-human-calprotectin
#13
Toshiki G Nakashige, Emily M Zygiel, Catherine L Drennan, Elizabeth M Nolan
The human innate immune protein calprotectin (CP, S100A8/S100A9 oligomer, calgranulin A/calgranulin B oligomer, MRP-8/MRP-14 oligomer) chelates a number of first-row transition metals, including Mn(II), Fe(II), and Zn(II), and can withhold these essential nutrients from microbes. Here we elucidate the Ni(II) coordination chemistry of human CP. We present a 2.6-Å crystal structure of Ni(II)- and Ca(II)-bound CP, which reveals that CP binds Ni(II) ions at both its transition-metal-binding sites: the His3Asp motif (site 1) and the His6 motif (site 2)...
June 22, 2017: Journal of the American Chemical Society
https://www.readbyqxmd.com/read/28557448/nonclassical-single-state-reactivity-of-an-oxo-iron-iv-complex-confined-to-triplet-pathways
#14
Claudia Kupper, Bhaskar Mondal, Joan Serrano-Plana, Iris Klawitter, Frank Neese, Miquel Costas, Shengfa Ye, Franc Meyer
C-H bond activation mediated by oxo-iron (IV) species represents the key step of many heme and nonheme O2-activating enzymes. Of crucial interest is the effect of spin state of the Fe(IV)(O) unit. Here we report the C-H activation kinetics and corresponding theoretical investigations of an exclusive tetracarbene ligated oxo-iron(IV) complex, [L(NHC)Fe(IV)(O)(MeCN)](2+) (1). Kinetic traces using substrates with bond dissociation energies (BDEs) up to 80 kcal mol(-1) show pseudo-first-order behavior and large but temperature-dependent kinetic isotope effects (KIE 32 at -40 °C)...
June 22, 2017: Journal of the American Chemical Society
https://www.readbyqxmd.com/read/28636354/rational-design-of-lithium-sulfur-battery-cathodes-based-on-experimentally-determined-maximum-active-material-thickness
#15
Michael J Klein, Gabriel M Veith, Arumugam Manthiram
Rational design of conductive carbon hosts for high energy density lithium-sulfur batteries requires an understanding of the fundamental limitations to insulating active material loading. In this work, we investigate the electrochemistry of lithium sulfide films ranging in thickness from 30 to 3500 nm. We show that films thicker than approximately 40 nm cannot be charged at local charge densities above 1 μA cm-2, and by implication, the maximum useful pore diameter is near 60 nm in a practical cathode. 'Activation' overpotentials for Li2S are identified in thicker films, resulting from polysulfide generation, but are shown not to improve the fundamental areal charge limitations...
June 21, 2017: Journal of the American Chemical Society
https://www.readbyqxmd.com/read/28636349/water-dynamics-from-the-surface-to-the-interior-of-a-supramolecular-nanostructure
#16
Julia H Ortony, Baofu Qiao, Christina J Newcomb, Timothy J Keller, Liam C Palmer, Elad Deiss-Yehiely, Monica Olvera de la Cruz, Songi Han, Samuel I Stupp
Water within and surrounding the structure of a biological system adopts context-specific dynamics that mediate virtually all of the events involved in the inner workings of a cell. These events range from protein folding and molecular recognition to the formation of hierarchical structures. Water dynamics are mediated by the chemistry and geometry of interfaces where water and biomolecules meet. Here we investigate experimentally and computationally the translational dynamics of vicinal water molecules within the volume of a supramolecular peptide nanofiber measuring 6...
June 21, 2017: Journal of the American Chemical Society
https://www.readbyqxmd.com/read/28635275/infrared-determination-of-the-protonation-state-of-a-key-histidine-residue-in-the-photosynthetic-water-oxidizing-center
#17
Shin Nakamura, Takumi Noguchi
Photosynthetic water oxidation is performed at the Mn4CaO5 cluster in photosystem II (PSII). The protonation structures of amino acid residues and water molecules around the Mn4CaO5 cluster are crucial in water oxidation reactions. In this study, we determined the protonation state of a key His residue in water oxidation, D1-H337, which is directly hydrogen bonded with the oxygen atom of the Mn4CaO5 cluster, using polarized attenuated total reflectance Fourier transform infrared (ATR-FTIR) spectroscopy. Flash-induced polarized ATR-FTIR difference spectra upon the S1→S2 transition of oriented PSII membranes showed broad negative and positive features around 2600 and 2900 cm-1, respectively, with large dichroic ratios, accompanied with several minor peaks attributable to the Fermi resonance of a His NH vibration...
June 21, 2017: Journal of the American Chemical Society
https://www.readbyqxmd.com/read/28635274/oxidation-state-dependent-binding-properties-of-the-active-site-in-a-mo-containing-formate-dehydrogenase
#18
William E Robinson, Arnau Bassegoda, Erwin Reisner, Judy Hirst
Molybdenum-containing formate dehydrogenase H from Escherichia coli (EcFDH-H) is a powerful model system for studies of the reversible reduction of CO2 to formate. However, the mechanism of FDH catalysis is currently debated, and whether the primary Mo coordination sphere remains saturated or one of the ligands dissociates to allow direct substrate binding during turnover is disputed. Here, we describe how oxidation state-dependent changes at the active site alter its inhibitor binding properties. Using protein film electrochemistry we show that formate oxidation by EcFDH-H is inhibited strongly and competitively by N3-, OCN-, SCN-, NO2- and NO3-, whereas CO2 reduction is inhibited only weakly and not competitively...
June 21, 2017: Journal of the American Chemical Society
https://www.readbyqxmd.com/read/28635273/a-direct-bandgap-copper-antimony-halide-perovskite
#19
Brenda Vargas, Estrella Ramos, Enrique Pérez-Gutiérrez, Juan C Alonso, Diego Solis-Ibarra
Since the establishment of perovskite solar cells (PSCs) there has been an intense search for alternative materials to replace lead and improve their stability towards moisture and light. As single-metal perovskite structures have yielded unsatisfactory performances, an alternative is the use of double perovskites that incorporate a combination of metals. To this day, only a handful of these compounds have been synthesized, but most of them have indirect bandgaps and/or do not have bandgaps energies well-suited for photovoltaic applications...
June 21, 2017: Journal of the American Chemical Society
https://www.readbyqxmd.com/read/28635271/emerging-chemistry-strategies-for-engineering-native-chromatin
#20
Yael David, Tom W Muir
Chromosomes present one of most challenging of all substrates for biochemical study. This is because genomic DNA is physically associated with an astonishing collection of nuclear factors, which serve to both store the nucleic acid in a stable form, but also grant access to the information it encodes when needed. Understanding this complex molecular choreography is central to the field of epigenetics. One of the great challenges in this area is to move beyond correlative type information, which is now in abundant supply, to the point where we can truly connect the dots at the molecular level...
June 21, 2017: Journal of the American Chemical Society
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