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Journal of the American Chemical Society

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https://www.readbyqxmd.com/read/28340300/synthesis-of-3-o-sulfated-oligosaccharides-to-understand-the-relationship-between-structures-and-functions-of-heparan-sulfate
#1
Zhangjie Wang, Po-Hung Hsieh, Yongmei Xu, David Thieker, Evangeline Juan En Chai, Shaoshuai Xie, Brian Cooley, Robert Woods, Lianli Chi, Jian Liu
The sulfation at the 3-OH position of glucosamine is an important modification in forming structural domains for heparan sulfate to enable its biological functions. Seven 3-O-sulfotransferase isoforms in the human genome are involved in the biosynthesis of 3-O-sulfated heparan sulfate. As a rare modification present in heparan sulfate, the availability of 3-O-sulfated oligosaccharides is very limited. Here, we report the use of a chemoenzymatic synthetic approach to synthesize six 3-O-sulfated oligosaccharides, including three hexasaccharides and three octasaccharides...
March 24, 2017: Journal of the American Chemical Society
https://www.readbyqxmd.com/read/28340294/a-well-defined-osmium-cupin-complex-hyperstable-artificial-osmium-peroxygenase
#2
Nobutaka Fujieda, Takumi Nakano, Yuki Taniguchi, Haruna Ichihashi, Hideki Sugimoto, Yuma Morimoto, Yosuke Nishikawa, Genji Kurisu, Shinobu Itoh
Thermally stable TM1459 cupin superfamily protein from Thermotoga maritima was repurposed as an osmium (Os) peroxygenase by metal-substitution strategy employing the metal-binding promiscuity. This novel artificial metalloenzyme bears a datively bound Os ion supported by the 4-histidine motif. The well-defined Os center is responsible for not only the catalytic activity but also the thermodynamic stability of the protein folding, leading to the robust biocatalyst (Tm ≈ 120 °C). The spectroscopic analysis and atomic resolution X-ray crystal structures of Os-bound TM1459 revealed two types of donor sets to Os center with octahedral coordination geometry...
March 24, 2017: Journal of the American Chemical Society
https://www.readbyqxmd.com/read/28339195/the-electronic-configuration-and-ligand-nature-of-five-coordinate-iron-porphyrin-carbene-complexes-an-experimental-study
#3
Yulong Liu, Wei Xu, Jing Zhang, William Fuller, Charles E Schulz, Jianfeng Li
The five coordinate iron porphyrin carbene complexes [Fe(TPP)(CCl<u>2</u>)] (TPP = tetraphenylporphyrin), [Fe(TTP)(CCl<u>2</u>)] (TTP = tetratolylporphyrin) and [Fe(TFPP)(CPh<u>2</u>)] (TFPP = tetra(pentafluorophenyl)porphin), utilizing two types of carbene ligands (CCl<u>2</u> and CPh<u>2</u>), have been investigated by single crystal X-ray, XANES (X-ray Absorption Near Edge Spectroscopy), Mössbauer, NMR and UV-vis spectros-copies. The XANES unambiguously suggested the iron(II) oxida-tion state of the complexes...
March 24, 2017: Journal of the American Chemical Society
https://www.readbyqxmd.com/read/28339188/preparation-and-characterization-of-parent-phenylphosphinidene-and-its-oxidation-to-phenyldioxophosphorane-the-elusive-phospho-rous-analogue-of-nitrobenzene
#4
Artur Mardyukov, Dominik Niedek, Peter R Schreiner
Triplet phenylphosphinidene was prepared by light-induced elimination of ethylene from the corresponding phenylphosphirane and was characterized by IR and UV/Vis spectroscopy together with matching of its spectral data with density functional theory (DFT) computations. The photolysis of phenylphosphirane in 3P-O2 doped matrices enabled the spectroscopic identification of a hitherto unknown phenyldioxophosphorane, the long elusive phosphorous analogue of nitrobenzene.
March 24, 2017: Journal of the American Chemical Society
https://www.readbyqxmd.com/read/28338315/solid-solution-alloying-of-immiscible-ru-and-cu-with-enhanced-co-oxidation-activity
#5
Bo Huang, Hirokazu Kobayashi, Tomokazu Yamamoto, Syo Matsumura, Yoshihide Nishida, Katsutoshi Sato, Katsutoshi Nagaoka, Shogo Kawaguchi, Yoshiki Kubota, Hiroshi Kitagawa
We report on novel solid-solution alloy nanoparticles (NPs) of Ru and Cu that are completely immiscible even above melting point in bulk phase. Powder X-ray diffraction, scanning transmission electron microscopy, and energy-dispersive X-ray measurements demonstrated that Ru and Cu atoms were homogeneously distributed in the alloy NPs. Ru0.5Cu0.5 NPs demonstrated higher CO oxidation activity than fcc-Ru NPs, which are known as one of the best monometallic CO oxidation catalysts.
March 24, 2017: Journal of the American Chemical Society
https://www.readbyqxmd.com/read/28335597/enantioselective-conjunctive-cross-coupling-of-bis-alkenyl-borates-a-general-synthesis-of-chiral-allylboron-reagents
#6
Emma K Edelstein, Sheila Namirembe, James P Morken
Palladium catalyzed conjunctive cross-coupling is used for the synthesis of enantioenriched allylboron reagents. This reaction employs non-symmetric bis(alkenyl)borates as substrates and appears to occur by a mechanism that involves selective activation of the less substituted alkene, followed by migration of the more substituted alkene during the course of a Pd-induced metalate rearrangement.
March 24, 2017: Journal of the American Chemical Society
https://www.readbyqxmd.com/read/28335594/skeletal-transformation-of-a-classical-fullerene-c88-into-a-non-classical-fullerene-chloride-c84cl30-bearing-quaternary-sequentially-fused-pentagons
#7
Fei Jin, Shangfeng Yang, Erhard Kemnitz, Sergej I Trojanov
A classical fullerene is composed of hexagons and pentagons only, and its stability is generally determined by the Isolated-Pentagon-Rule (IPR). Herein, high-temperature chlorination of a mixture containing a classical IPR-obeying fullerene C88 resulted in isolation and X-ray crystallographic characterization of non-IPR, non-classical (NC) fullerene chloride C84(NC2)Cl30 (1) containing two heptagons. The carbon cage in C84(NC2)Cl30 contains 14 pentagons, 12 of which form two pairs of fused pentagons and two groups of quaternary sequentially fused pentagons, which have never been observed in re-ported carbon cages...
March 24, 2017: Journal of the American Chemical Society
https://www.readbyqxmd.com/read/28324654/a-general-strategy-for-visible-light-decaging-based-on-the-quinone-trimethyl-lock
#8
David P Walton, Dennis A Dougherty
Visible-light triggered quinone trimethyl locks are reported as a general design for long-wavelength photoremovable protecting groups for alcohols and amines. Intramolecular photoreduction unmasks a reactive phenol that undergoes fast lactonization to release alcohols and amines. Model substrates are released in quantitative yield along with well-defined, colorless hydroquinone byproducts. Substituent modifications of the quinone core allow absorption from 400 to 600 nm.
March 24, 2017: Journal of the American Chemical Society
https://www.readbyqxmd.com/read/28306250/co2-selective-absorbents-in-air-reverse-lipid-bilayer-structure-forming-neutral-carbamic-acid-in-water-without-hydration
#9
Fuyuhiko Inagaki, Chiaki Matsumoto, Takashi Iwata, Chisato Mukai
Emission gas and air contain not only CO2 but also plentiful moisture, making it difficult to achieve selective CO2 absorption without hydration. To generate absorbed CO2 (wet CO2) under heating, the need for external energy to release the absorbed water has been among the most serious problems in the fields of carbon dioxide capture and storage (CCS) and direct air capture (DAC). We found that the introduction of the hydrophobic phenyl group into alkylamines of CO2 absorbents improved the absorption selectivity between CO2 and water...
March 24, 2017: Journal of the American Chemical Society
https://www.readbyqxmd.com/read/28298084/small-molecule-acceptor-based-on-the-heptacyclic-benzodi-cyclopentadithiophene-unit-for-highly-efficient-nonfullerene-organic-solar-cells
#10
Bin Kan, Huanran Feng, Xiangjian Wan, Feng Liu, Xin Ke, Yanbo Wang, Yunchuang Wang, Hongtao Zhang, Chenxi Li, Jianhui Hou, Yongsheng Chen
A new nonfullerene small molecule with acceptor-donor-acceptor (A-D-A) structure, namely, NFBDT, based on a heptacyclic benzodi(cyclopentadithiophene) (FBDT) unit using benzo[1,2-b:4,5-b']dithiophene as the core unit, was designed and synthesized. Its absorption ability, energy levels, thermal stability, as well as photovoltaic performances were fully investigated. NFBDT exhibits a low optical bandgap of 1.56 eV resulting in wide and efficient absorption that covered the range from 600 to 800 nm, and suitable energy levels as an electron acceptor...
March 24, 2017: Journal of the American Chemical Society
https://www.readbyqxmd.com/read/28292175/determining-band-edge-energies-and-morphology-dependent-stability-of-formamidinium-lead-perovskite-films-using-spectroelectrochemistry-and-photoelectron-spectroscopy
#11
R Clayton Shallcross, Yilong Zheng, S Scott Saavedra, Neal R Armstrong
We show for the first time that the frontier orbital energetics (conduction band minimum (CBM) and valence band maximum (VBM)) of device-relevant, methylammonium bromide (MABr)-doped, formamidinium lead trihalide perovskite (FA-PVSK) thin films can be characterized using UV-vis spectroelectrochemistry, which provides an additional and straightforward experimental technique for determining energy band values relative to more traditional methods based on photoelectron spectroscopy. FA-PVSK films are processed via a two-step deposition process, known to provide high efficiency solar cells, on semitransparent indium tin oxide (ITO) and titanium dioxide (TiO2) electrodes...
March 24, 2017: Journal of the American Chemical Society
https://www.readbyqxmd.com/read/28290199/unbinding-kinetics-of-a-p38-map-kinase-type-ii-inhibitor-from-metadynamics-simulations
#12
Rodrigo Casasnovas, Vittorio Limongelli, Pratyush Tiwary, Paolo Carloni, Michele Parrinello
Understanding the structural and energetic requisites of ligand binding toward its molecular target is of paramount relevance in drug design. In recent years, atomistic free energy calculations have proven to be a valid tool to complement experiments in characterizing the thermodynamic and kinetic properties of protein/ligand interaction. Here, we investigate, through a recently developed metadynamics-based protocol, the unbinding mechanism of an inhibitor of the pharmacologically relevant target p38 MAP kinase...
March 24, 2017: Journal of the American Chemical Society
https://www.readbyqxmd.com/read/28288514/reactive-pendant-mn%C3%A2-o-in-a-synthetic-structural-model-of-a-proposed-s4-state-in-the-photosynthetic-oxygen-evolving-complex
#13
Shivaiah Vaddypally, Sandeep K Kondaveeti, Santosh Karki, Megan M Van Vliet, Robert J Levis, Michael J Zdilla
The molecular mechanism of the Oxygen Evolving Center of photosystem II has been under debate for decades. One frequently cited proposal is the nucleophilic attack by water hydroxide on a pendant Mn═O moiety, though no chemical example of this reactivity at a manganese cubane cluster has been reported. We describe here the preparation, characterization, and a reactivity study of a synthetic manganese cubane cluster with a pendant manganese-oxo moiety. Reaction of this cluster with alkenes results in oxygen and hydrogen atom transfer reactions to form alcohol- and ketone-based oxygen-containing products...
March 24, 2017: Journal of the American Chemical Society
https://www.readbyqxmd.com/read/28278372/mechanistic-studies-on-rhodium-catalyzed-enantioselective-silylation-of-aryl-c-h-bonds
#14
Taegyo Lee, John F Hartwig
Several classes of enantioselective silylations of C-H bonds have been reported recently, but little mechanistic data on these processes are available. We report mechanistic studies on the rhodium-catalyzed, enantioselective silylation of aryl C-H bonds. A rhodium silyl dihydride and a rhodium norbornyl complex were prepared and determined to be interconverting catalyst resting states. Kinetic isotope effects indicated that the C-H bond cleavage step is not rate-determining, but the C-H bond cleavage and C-Si bond-forming steps together influence the enantioselectivity...
March 24, 2017: Journal of the American Chemical Society
https://www.readbyqxmd.com/read/28266843/spectroscopic-studies-of-the-chan-lam-amination-a-mechanism-inspired-solution-to-boronic-ester-reactivity
#15
Julien C Vantourout, Haralampos N Miras, Albert Isidro-Llobet, Stephen Sproules, Allan J B Watson
We report an investigation of the Chan-Lam amination reaction. A combination of spectroscopy, computational modeling, and crystallography has identified the structures of key intermediates and allowed a complete mechanistic description to be presented, including off-cycle inhibitory processes, the source of amine and organoboron reactivity issues, and the origin of competing oxidation/protodeboronation side reactions. Identification of key mechanistic events has allowed the development of a simple solution to these issues: manipulating Cu(I) → Cu(II) oxidation and exploiting three synergistic roles of boric acid has allowed the development of a general catalytic Chan-Lam amination, overcoming long-standing and unsolved amine and organoboron limitations of this valuable transformation...
March 24, 2017: Journal of the American Chemical Society
https://www.readbyqxmd.com/read/28199106/mechanistic-studies-of-the-photoinduced-quinone-trimethyl-lock-decaging-process
#16
Clinton J Regan, David P Walton, Oliver S Shafaat, Dennis A Dougherty
Mechanistic studies of a general reaction that decages a wide range of substrates on exposure to visible light are described. The reaction involves a photochemically initiated reduction of a quinone mediated by an appended thioether. After reduction, a trimethyl lock system incorporated into the quinone leads to thermal decaging. The reaction could be viewed as an electron-transfer initiated reduction of the quinone or as a hydrogen abstraction-Norrish Type II-reaction. Product analysis, kinetic isotope effects, stereochemical labeling, radical clock, and transient absorption studies support the electron transfer mechanism...
March 24, 2017: Journal of the American Chemical Society
https://www.readbyqxmd.com/read/28335592/air-and-light-stable-p4-and-as4-within-an-anion-coordination-based-tetrahedral-cage
#17
Dong Yang, Jie Zhao, Le Yu, Xiangsong Lin, Wenyao Zhang, Hongwei Ma, Adolf Gogoll, Zhibin Zhang, Yao-Yu Wang, Xiao-Juan Yang, Biao Wu
In contrast to the stable dinitrogen molecule, white phosphorus (P4) and yellow arsenic (As4) are very reactive allotropic modifications of these two heavier pnicogen elements, which has greatly hampered the study of their properties and applications. Thus the safe storage and transport of them is imperative. Supramolecular caged structures are one of the most efficient approaches for the encapsulation and stabilization of reactive species; however, their use in the P4 and As4 chemistry is very rare. In the current work, we demonstrate a new design strategy for constructing finite cages and including guests based on anion coordination chemistry...
March 23, 2017: Journal of the American Chemical Society
https://www.readbyqxmd.com/read/28335591/heteroatom-doped-perihexacene-from-a-double-helicene-precursor-on-surface-synthesis-and-properties
#18
Xiao-Ye Wang, Thomas Dienel, Marco Di Giovannantonio, Gabriela Borin Barin, Neerav Kharche, Okan Deniz, José I Urgel, Roland Widmer, Samuel Stolz, Luis Henrique De Lima, Matthias Muntwiler, Matteo Tommasini, Vincent Meunier, Pascal Ruffieux, Xinliang Feng, Roman Fasel, Klaus Müllen, Akimitsu Narita
We report on the surface-assisted synthesis and spectroscopic characterization of the hitherto longest periacene analogue with oxygen-boron-oxygen (OBO) segments along the zigzag edges, that is, a heteroatom-doped perihexacene 1. Surface-catalyzed cyclodehydrogenation successfully transformed the double helicene precursor 2, i.e. 12a,26a-dibora-12,13,26,27-tetraoxa-benzo[1,2,3-hi:4,5,6-h'i']dihexacene, into the planar perihexacene analogue 1, which was visualized by scanning tunneling microscopy (STM) and noncontact atomic force microscopy (nc-AFM)...
March 23, 2017: Journal of the American Chemical Society
https://www.readbyqxmd.com/read/28334527/alkene-carbene-isomerisation-induced-by-borane-access-to-an-asymmetrical-diborene
#19
Wei Lu, Yongxin Li, Rakesh Ganguly, Rei Kinjo
A 2,3-dihydro-1H-1,2-azaborole derivative 2 was converted to a cyclic (alkyl)(amino)carbene (cAAC) via 1,2-hydrogen migration triggered by boranes to afford cAAC-borane adducts. This procedure allowed to develop an asymmetrical diborene cAAC∙(Br)B=B(Br)∙IDip 6, which was isolated and fully characterized. The 11B NMR spectrum, X-ray diffraction analysis and computational studies indicate that π-electrons on the central B2 moiety in 6 are unequivalently distributed, and thus polarized. A complete scission of the B=B double bond in 6 was achieved by the treatment with an isonitrile, which led to the formation of a base-stabilized B,N-containing methylenecyclopropane 7...
March 23, 2017: Journal of the American Chemical Society
https://www.readbyqxmd.com/read/28333455/an-unusual-%C3%AE-carbon-hydroxylation-of-proline-promotes-active-site-maturation
#20
Vasiliki E Fadouloglou, Stavroula Balomenou, Michalis Aivaliotis, Dina Kotsifaki, Sofia Arnaouteli, Anastasia Tomatsidou, Georgios Efstathiou, Nikos Kountourakis, Sofia Miliara, Marianna Griniezaki, Aleka Tsalafouta, Spiros A Pergantis, Ivo G Boneca, Nicholas M Glykos, Vassilis Bouriotis, Michael Kokkinidis
The full extent of proline (Pro) hydroxylation has yet to be established, as it is largely unexplored in bacteria. We describe here a so far unknown Pro hydroxylation activity which occurs in active sites of polysaccharide deacetylases (PDAs) from bacterial pathogens, modifying the protein backbone at the Cα atom of a Pro residue to produce 2-hydroxyproline (2-Hyp). This process modifies with high specificity a conserved Pro, shares with the deacetylation reaction the same active site and one cata-lytic residue and utilizes molecular oxygen as source for the hydroxyl group oxygen of 2-Hyp...
March 23, 2017: Journal of the American Chemical Society
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