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Journal of the American Chemical Society

Li Chen, Nathchar Naowarojna, Heng Song, Shu Wang, Jianyun Wang, Zixin Deng, Changming Zhao, Pinghua Liu
Ovothiol is a histidine thiol derivative. The biosynthesis of ovothiol involves an extremely efficient trans-sulfuration strategy. The non-heme iron enzyme OvoA catalyzed oxidative coupling be-tween cysteine and histidine is one of the key steps. Besides catalyzing the oxidative coupling between cysteine and histidine, OvoA also catalyzes the oxi-dation of cysteine to cysteine sulfinic acid (cysteine dioxygenase activity). Thus far, very little mecha-nistic information is available for OvoA-catalysis. In this report, we measured the kinetic isotope effect (KIE) in OvoA-catalysis using the isotopically sensitive branching method...
March 15, 2018: Journal of the American Chemical Society
Johannes Diesel, Anastasiia M Finogenova, Nicolai Cramer
Annulated pyridones are an important scaffold found in many biologically active compounds. A Ni(0)-catalyzed C-H functionalization of 2- and 4-pyridone is disclosed, providing access to annulated pyridones via enantioselective intramolecular olefin hydroarylation. Key to the success of the transformation was the development of a sterically hindered and tunable N-heterocyclic carbene ligand resembling a chiral version of IPr. This ligand allows for mild reaction temperatures, and leads to the annulated pyridones in excellent yields and enantioselectivities...
March 15, 2018: Journal of the American Chemical Society
Jonathan L Kuo, Chris Lorenc, Janine M Abuyuan, Jack R Norton
Radical cyclizations are most often achieved in the presence of a radical initiator and Bu3 SnH, but environmental considerations demand that alternative reagents be developed - ones that can serve as a synthetic equivalents to the hydrogen atom. We have revisited [CpV(CO)3 H]- , a known replacement for Bu3 SnH, and found that it can be used catalytically under H2 in the presence of a base. We have carried out the tin-free and catalytic radical cyclization of alkyl iodide substrates. The reactions are atom-efficient and the conditions are mild, with broad tolerance for functional groups...
March 15, 2018: Journal of the American Chemical Society
Jinxu Gao, Adelphe Mfuh, Yuka Amako, Christina M Woo
Many therapeutics elicit cell-type specific polypharmacology that is executed by a network of molecular recognition events between a small molecule and the whole proteome. However, measurement of the structures that underpin the molecular associations between the proteome and even common therapeutics, such as the nonsteroidal anti-inflammatory drugs (NSAIDs), is limited by the inability to map the small molecule interactome. To address this gap, we developed a platform termed small molecule interactome mapping by photoaffinity labeling (SIM-PAL) and applied it to the in cellulo direct characterization of specific NSAID binding sites...
March 15, 2018: Journal of the American Chemical Society
Qing Li, Biao Yang, Jonas Björk, Qigang Zhong, Huanxin Ju, Junjie Zhang, Nan Cao, Ziliang Shi, Haiming Zhang, Daniel Ebeling, Andre Schirmeisen, Junfa Zhu, Lifeng Chi
Hierarchical control of chemical reactions is being considered as one of the most ambitious and challenging topics in modern organic chemistry. In this study, we have realized the one-by-one scission of the X-H bonds (X=N and C) of aromatic amines in a controlled fashion on the Cu(111) surface. Each dehydrogenation reaction leads to certain metal-organic supramolecular structures, which were monitored in single-bond resolution via scanning tunneling microscopy and non-contact atomic force microscopy. Moreover, the reaction pathways were elucidated from X-ray photoelectron spectroscopy measurements and density functional theory calculations...
March 15, 2018: Journal of the American Chemical Society
Kuikun Yang, Yijing Liu, Yi Liu, Qian Zhang, Chuncai Kong, Chenglin Yi, Zijian Zhou, Zhantong Wang, Guofeng Zhang, Yang Zhang, Niveen M Khashab, Xiaoyuan Chen, Zhihong Nie
This article describes the fabrication of nanosized magneto-vesicles (MVs) comprising tunable layers of densely-packed superparamagnetic iron oxide nanoparticles (SPIONs) in membranes via cooperative assembly of polymer-tethered SPIONs and free poly(styrene)-b-poly(acrylic acid) (PS-b-PAA). The membrane thickness of MVs could be well controlled from 9.8 to 93.2 nm by varying the weight ratio of PS-b-PAA to SPIONs. The increase in membrane thickness was accompanied with the transition from monolayer MVs, to double-layered MVs and to multilayered MVs (MuMVs)...
March 15, 2018: Journal of the American Chemical Society
Andy A Thomas, Andrew F Zahrt, Connor P Delaney, Scott E Denmark
The Suzuki-Miyaura reaction is the most practiced palladium-catalyzed, cross-coupling reaction because of its broad applicability, low toxicity of the metal (B), and the wide variety of commercially available boron substrates. A wide variety of boronic acids and esters, each with different properties, have been developed for this process. Despite the popularity of the Suzuki-Miyaura reaction, the precise manner in which the organic fragment is transferred from boron to palladium has remained elusive for these reagents...
March 15, 2018: Journal of the American Chemical Society
Teklab Gebregiworgis, Christopher Boyd Marshall, Tadateru Nishikawa, Nikolina Radulovich, María-José Sandi, Zhenhao Fang, Robert Rottapel, Ming-Sound Tsao, Mitsuhiko Ikura
Small GTPases (sGTPases) are critical switch-like regulators that mediate several important cellular functions and are often mutated in human cancers. They are activated by guanine nucleotide exchange factors (GEFs), which specifically catalyze the exchange of GTP for GDP. GEFs coordinate signaling networks in normal cells, and are frequently deregulated in cancers. sGTPase signaling pathways are complex and interconnected; however, most GEF assays do not reveal such complexity. In this communication, we describe the development of a unique real-time NMR-based multiplexed GEF assay that employs distinct isotopic labeling schemes for each sGTPase protein to enable simultaneous observation of six proteins of interest...
March 15, 2018: Journal of the American Chemical Society
Jan Paulo T Zaragoza, Maxime A Siegler, David P Goldberg
High-valent metal-hydroxide species are invoked as critical intermediates in both catalytic, metal-mediated O2 activation (e.g., by Fe porphyrin in Cytochrome P450) and O2 production (e.g., by the Mn cluster in Photosystem II). However, well-characterized mononuclear MIV (OH) complexes remain a rarity. Herein we describe the synthesis of MnIV (OH)(ttppc) (3) (ttppc = tris(2,4,6-triphenylphenyl) corrole), which has been characterized by X-ray diffraction (XRD). The large steric encumbrance of the ttppc ligand allowed for isolation of 3...
March 15, 2018: Journal of the American Chemical Society
Hiroki Yokoi, Satoru Hiroto, Hiroshi Shinokubo
The reversible formation of σ-bonds between organic radicals has been widely investigated. However, reports on the formation of σ-dimers from delocalized π-radical cations are scarce. Herein, we report the reversible σ-dimerization behavior of a bowl-shaped π-radical cation generated from a nitrogen-embedded buckybowl, both in the crystalline state and in solution. The detailed structure of the σ-dimer in the crystalline state was determined by a single-crystal X-ray diffraction analysis. The monomeric radical cation exists predominantly in solution at room temperature, while dimerization of the radical cations occurs through carbon-carbon σ-bond formation upon reducing the temperature...
March 15, 2018: Journal of the American Chemical Society
Erika Virmani, Julian M Rotter, Andre Mähringer, Tobias von Zons, Adelheid Godt, Thomas Bein, Stefan Wuttke, Dana D Medina
Controlled on-surface film growth of porous and crystalline frameworks is a central requisite for incorporating these materials into functional platforms and operational devices. Here, we present the synthesis of thin zirconium-based metal-organic framework (MOF) films by vapor-assisted conversion (VAC). We established protocols adequate for the growth of UiO-66, UiO-66(NH2 ), UiO-67, and UiO-68(NH2 ) as well as the porous interpenetrated Zr-organic framework (PPPP-PIZOF-1) as highly oriented thin films. Through the VAC approach, precursors in a cast solution layer on a bare gold substrate are reacting to form a porous continuous MOF film, oriented along the [111] crystal axis by an exposure to a solvent vapor under elevated temperatures of 100 °C and 3 h reaction times...
March 15, 2018: Journal of the American Chemical Society
Ganhua Xie, Pei Li, Zhiju Zhao, Zhongpeng Zhu, Xiang-Yu Kong, Zhen Zhang, Kai Xiao, Liping Wen, Lei Jiang
Water wetting behavior in nano-confined environments plays an important role in mass transport and signal trans-mission of organisms. It is valuable and challengeable to investigate how water behaves in such a nanometer-scale with external stimuli, in particular with electric field and light. Unfortunately, the mechanism of hydrophobic reaction inside the nano-spaces is still obscure and lacks of experimental supporting for the current electric-field- or photo-responsive nanochannels which suffer from fragility or monofunctionality...
March 15, 2018: Journal of the American Chemical Society
Zongbi Bao, Danyan Xie, Ganggang Chang, Hui Wu, Liangying Li, Wei Zhou, Hailong Wang, Zhiguo Zhang, Huabin Xing, Qiwei Yang, Michael J Zaworotko, Qilong Ren, Banglin Chen
Research on HOFs has been developed for quite a long time; however, those with both established permanent porosities and functional properties are extremely rare due to weak hydrogen-bonding interactions among molecular organic linkers which are much more fragile and difficult to stabilize. Herein, through judiciously combining the superiority of both the moderately stable coordination bonds in MOFs and hydrogen bonds, we have realized a microporous hydrogen-bonded organometallic framework HOF-21, which not only shows permanent porosity but also exhibits highly selective separation performance of C2H2/C2H4 at room temperature...
March 14, 2018: Journal of the American Chemical Society
Lindsay M Repka, Kenton J Hetrick, See Hyun Chee, Wilfred A van der Donk
The dehydratase NisB performs stepwise tRNAGlu -dependent glutamylation of Ser/Thr residues and subsequent glutamate elimination to effect eight dehydrations in the biosynthesis of the antibacterial peptide nisin. Its substrate, NisA, bears a C-terminal core peptide that is modified and an N-terminal leader peptide (LP) that is not modified but that is required for efficient dehydration. To elucidate the mechanism of LP-NisB interactions during dehydration, we engineered a disulfide that covalently links the NisA LP to NisB...
March 14, 2018: Journal of the American Chemical Society
Liang Zhang, David August, Jiankang Zhong, George F S Whitehead, Inigo J Vitorica-Yrezabal, David A Leigh
We report the two-step synthesis of a molecular trefoil knot in 90 % overall yield through the self-assembly of a twelve-component trimeric circular zinc helicate followed by ring closing metathesis of six pendant alkene chains. Both the trimeric circular helicate intermediate and the resulting trefoil knot were characterized by NMR spectroscopy, mass spectrometry and X-ray crystallography.
March 14, 2018: Journal of the American Chemical Society
D Matthew Peacock, Quan Jiang, Patrick S Hanley, Thomas R Cundari, John F Hartwig
We report the formation of phosphine-ligated alkylpalladium(II) amido complexes that undergo reductive elimination to form alkyl-nitrogen bonds and a combined experimental and computational investigation of the factors controlling the rates of these reactions. The free-energy barriers to reductive elimination from t-Bu3P-ligated complexes were significantly lower (ca. 3 kcal/mol) than those previously reported from NHC-ligated complexes. The rates of reactions from complexes containing a series of electronically and sterically varied anilido ligands showed that the reductive elimination is slower from complexes of less electron-rich or more sterically-hindered anilido ligands than from those contain-ing more electron rich and less hindered anilido ligands...
March 14, 2018: Journal of the American Chemical Society
Elizabeth S Ryland, Ming-Fu Lin, Max A Verkamp, Kaili Zhang, Kristin Benke, Michaela Carlson, Josh Vura-Weis
Iron porphyrins are the active sites of many natural and artificial catalysts, and their photoinduced dynamics have been described as either relaxation into a vibrationally hot ground state or as a cascade through metal-centered states. In this work, we directly probe the metal center of iron(III) tetraphenyl porphyrin chloride (FeTPPCl) using femtosecond M2,3 -edge x-ray absorption near-edge structure (XANES) spectroscopy. Photoexcitation at 400 nm produces a (π, π*) state that evolves in 70 fs to an iron(II) ligand-to-metal charge transfer (LMCT) state...
March 14, 2018: Journal of the American Chemical Society
Christoph Helling, Christoph Wölper, Stephan Schulz
Cp*AsCl2 (Cp* = C5Me5) reacts with one equivalent of LGa (L = HC[C(Me)N(2,6-i-Pr2C6H3)]2) with formation of L(Cl)GaAs(Cl)Cp* 1, whereas the reaction with two equivalents of LGa yielded gallaarsene LGaAsCp* 2 containing a Ga=As double bond and (η1-Ga(Cp*)L(η2-GaL)(μ-As3) 3. 2 and 3 were structural-ly characterized by single crystal X-ray diffraction and the π-bonding contribution in 2 was analyzed by temperature-dependent 1H NMR spectroscopy (9.65 kcal mol-1) and by quantum mechani-cal computation.
March 14, 2018: Journal of the American Chemical Society
Georgina Shillito, Thomas B J Hall, Dan Preston, Philipp Traber, Lingjun Wu, Katherine Reynolds, Raphael Horvath, Xue Zhong Sun, Nigel T Lucas, James D Crowley, Michael W George, Stephan Kupfer, Keith C Gordon
The ground and excited state photophysical properties of a series of fac-[Re(L)(CO)3 (α-diimine)]n+ complexes, where L = Br- , Cl- , 4-dimethylaminopyridine (dmap) and pyridine (py) have been extensively studied utilizing numerous electronic and vibrational spectroscopic techniques in conjunction with a suite of quantum computational methods. The α-diimine ligand consists of 1,10-phenanthroline with the highly electron donating triphenylamine (TPA) appended in the 5 position. This gives rise to intra-ligand charge-transfer (ILCT) states lying lower in energy than the conventional metal-to-ligand charge-transfer (MLCT) state, the energies of which are red and blue-shifted, respectively, as the ancillary ligand, L becomes more electron withdrawing...
March 14, 2018: Journal of the American Chemical Society
Yanpeng Zhu, Zeming Xia, Zeying Cai, Ziyong Yuan, Nianqiang Jiang, Tao Li, Yonggen Wang, Xiaoyu Guo, Zhihao Li, Shuang Ma, Dingyong Zhong, Yang Li, Jiaobing Wang
We report the synthesis and characterization of two hexapole [7]helicenes (H7Hs). Single crystal X-ray diffraction unambiguously confirms the molecular structure. H7H absorbs light, with distinct Cotton effect, from ultraviolet to the near infrared (λmax = 618 nm). Cyclic voltammetry reveals nine reversible redox states, consecutively from -2 to +6. These chiroptical and electronic properties of H7H are inaccessible from helicene's small homologues.
March 14, 2018: Journal of the American Chemical Society
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