59,386 results match your criteria Journal of the American Chemical Society [Journal]


A Large Family of Synthetic Two-Dimensional Metal Hydrides.

J Am Chem Soc 2019 Apr 25. Epub 2019 Apr 25.

Synthetic two-dimensional (2D) materials without layered bulk allotropes are approaching a new frontier of materials flatland, one with properties richer than those of graphene-like materials. This is the case even as only a few chemical elements and blends have shown synthetic 2D forms. While hydrogen and metals are earth-abundant and form numerous compounds, rarely are 2D materials with only robust metal-hydrogen bonds. Read More

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http://dx.doi.org/10.1021/jacs.9b02279DOI Listing

Elucidation of the Reaction Mechanism for High-Temperature Water-Gas Shift over an Industrial-type Copper-Chromium-Iron Oxide Cata-lyst.

J Am Chem Soc 2019 Apr 25. Epub 2019 Apr 25.

The water-gas shift (WGS) reaction is of paramount importance for the chemical industry, as it constitutes, coupled with me-thane reforming, the main industrial route to produce hydrogen. Copper-Chromium-Iron oxide-based catalysts have been wide-ly used for the high-temperature WGS reaction industrially. The WGS reaction mechanism by the CuCrFeOx catalyst has been debated for years, mainly between a 'redox' mechanism involving the participation of atomic oxygen from the catalyst and an 'associative' mechanism proceeding via a surface formate-like intermediate. Read More

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http://dx.doi.org/10.1021/jacs.9b03516DOI Listing

A Molecular Photoelectrode for Water Oxidation Inspired by Photosystem II.

J Am Chem Soc 2019 Apr 25. Epub 2019 Apr 25.

In artificial photosynthesis, the sun drives water splitting into H and O or converts CO into a useful form of carbon. In most schemes, water oxidation is typically the limiting half-reaction. Here, we introduce a molecular approach to the design of a photoanode that incorporates an electron acceptor, a sensitizer, an electron donor, and a water oxidation catalyst in a single molecular assembly. Read More

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http://pubs.acs.org/doi/10.1021/jacs.9b02548
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http://dx.doi.org/10.1021/jacs.9b02548DOI Listing
April 2019
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Synergy of Single-Atom Ni and Ru Sites on CeO for Dry Reforming of CH.

J Am Chem Soc 2019 Apr 25. Epub 2019 Apr 25.

School of Chemistry and Chemical Engineering , The Queen's University , Belfast BT9 5AG , U.K.

Heterogeneous catalysis performs on specific sites of a catalyst surface even if specific sites of many catalysts during catalysis could not be identified readily. Design of a catalyst by managing catalytic sites on an atomic scale is significant for tuning catalytic performance and offering high activity and selectivity at a relatively low temperature. Here, we report a synergy effect of two sets of single-atom sites (Ni and Ru) anchored on the surface of a CeO nanorod, CeNiRuO. Read More

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http://dx.doi.org/10.1021/jacs.8b10910DOI Listing

Dicyclopenta[4,3,2,1-ghi:4',3',2',1'-pqr]perylene: A Bowl-shaped Fragment of Fullerene C70 with Global Anti-aromaticity.

J Am Chem Soc 2019 Apr 25. Epub 2019 Apr 25.

Solution-phase synthesis of buckybowls remains a big challenge and there are limited reports on the fragments of C70. Herein, we report a new basic subunit of C70 with C2v symmetry, the dicyclopenta[4,3,2,1-ghi:4',3',2',1'-pqr]perylene (2CP-Per). Its aryl-substituted derivative 2CP-Per-Ar was synthesized and shows a bowl-shaped geometry according to X-ray crystallographic analysis. Read More

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http://dx.doi.org/10.1021/jacs.9b03169DOI Listing

Cationic Co(I)-Intermediates for Hydrofunctionalization Reactions: Regio- and Enantioselective Cobalt-Catalyzed 1,2-Hydroboration of 1,3-Dienes.

J Am Chem Soc 2019 Apr 25. Epub 2019 Apr 25.

Department of Chemistry and Biochemistry , The Ohio State University , 100 West 18th Avenue , Columbus , Ohio 43210 , United States.

Much of the recent work on catalytic hydroboration of alkenes has focused on simple alkenes and styrene derivatives with few examples of reactions of 1,3-dienes, which have been reported to undergo mostly 1,4-additions to give allylic boronates. We find that reduced cobalt catalysts generated from 1,n- bis-diphenylphosphinoalkane complexes [PhP-(CH) -PPh]CoX; n = 1-5) or from (2-oxazolinyl)phenyldiarylphosphine complexes [(G-PHOX)CoX] (G = 4-substituent on oxazoline ring) effect selective 1,2-, 1,4-, or 4,3-additions of pinacolborane (HBPin) to a variety of 1,3-dienes depending on the ligands chosen. Conditions have been found to optimize the 1,2-additions. Read More

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http://dx.doi.org/10.1021/jacs.8b13812DOI Listing

Hydrogen-Bonding and Hydrophobic Groups Contribute Equally to the Binding of Hyperactive Antifreeze and Ice Nucleating Proteins to Ice.

J Am Chem Soc 2019 Apr 25. Epub 2019 Apr 25.

Hyperactive insect antifreeze proteins and bacterial ice-nucleating proteins are arguably the most potent ice-binding molecules in nature. These highly effective proteins bind ice through amphiphilic ice-binding sites based on arrays of threonine residues. It remains poorly understood how hydrophilic and hydrophobic groups of the binding site contribute to the ice affinity of proteins. Read More

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http://dx.doi.org/10.1021/jacs.9b02248DOI Listing

Comparison of the structures and mechanisms of the pistol and hammerhead ribozymes.

J Am Chem Soc 2019 Apr 24. Epub 2019 Apr 24.

Comparison of the secondary and three-dimensional structures of the hammerhead and pistol ribozymes reveal many close similarities, so in this work we have asked if they are mechanistically identical. We have determined a new crystal structure of the pistol ribozyme, and have shown that G40 acts as general base in the cleavage reaction. The conformation in the active site ensures an in-line attack of the O2' nucleophile, and the conformation at the scissile phosphate and the position of the general base are closely similar to those in the hammerhead ribozyme. Read More

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http://dx.doi.org/10.1021/jacs.9b02141DOI Listing

Probing Size and Substrate Effects on the Hydrogen Evolution Reaction by Single Isolated Pt Atoms, Atomic Clusters, and Nanoparticles.

J Am Chem Soc 2019 Apr 24. Epub 2019 Apr 24.

Center for Electrochemistry, Department of Chemistry , The University of Texas at Austin , Austin , Texas 78712 , United States.

We report the catalytic activity of a single, isolated Pt deposit on Bi and Pb supports to probe the size and substrate effects on the electrochemical hydrogen evolution reaction (HER). Deposits were made electrolytically by an atom-by-atom method in a controlled plating; we prepared an individual Pt deposit on Bi and Pb ultramicroelectrodes (UMEs) such as a single isolated atom, clusters containing one to five Pt atoms, and nanoparticles to about 10 nm radius. A steady-state voltammogram on the single Pt deposits is observed by electrocatalytic amplification of the HER, with a negligible contribution by the HER at the substrate UME. Read More

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http://dx.doi.org/10.1021/jacs.8b13366DOI Listing

CO and CO/H Conversion to Methoxide by a Uranium(IV) Hydride.

J Am Chem Soc 2019 Apr 24. Epub 2019 Apr 24.

Institut des Sciences et Ingénierie Chimiques , Ecole Polytechnique Fédérale de Lausanne (EPFL) , CH-1015 Lausanne , Switzerland.

Here we show that a scaffold combining siloxide ligands and a bridging oxide allows the synthesis and characterization of the stable dinuclear uranium(IV) hydride complex [K{[U(OSi(O Bu))](μ-O)(μ-H)}], 2, which displays high reductive reactivity. The dinuclear bis-hydride 2 effects the reductive coupling of acetonitrile by hydride transfer to yield [K{[U(OSi(O Bu))](μ-O)(μ-κ-NC(CH)NCHCH)}], 3. Under ambient conditions, the reaction of 2 with CO affords the oxomethylene reduction product [K{[U(OSi(O Bu))](μ-CHO)(μ-O)}], 4, that can further add H to afford the methoxide hydride complex [K{[U(OSi(O Bu))](μ-OCH)(μ-O)(μ-H)}], 5, from which methanol is released in water. Read More

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http://dx.doi.org/10.1021/jacs.9b02235DOI Listing

The Total Synthesis of (+)-Arborisidine.

J Am Chem Soc 2019 Apr 21. Epub 2019 Apr 21.

The first total synthesis of arborisidine, a unique Kopsia indole alkaloid possessing a fully substituted cyclohexanone ring system with two quaternary carbons, has been achieved in 7 steps in racemic format from tryptamine and 9 steps in asymmetric format from D-tryptophan methyl ester. Key elements of the design include a carefully orchestrated decyanation protocol to finalize the asymmetric formation of an aza-quaternary center challenging to access in optically active format via direct Pictet-Spengler cyclizations with tryptamine, a metal-promoted 6- endo-dig cyclization of an enyne to establish the second core quaternary center, and regiospecific functionalizations of the resultant complex diene to finalize the target structure. The distinct and efficient nature of the developed solution is highlighted by several unsuccessful approaches and unexpected rearrangements. Read More

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http://dx.doi.org/10.1021/jacs.9b03248DOI Listing

A Direct-Bandgap 2D Silver-Bismuth Iodide Double Perovskite: The Structure-Directing Influence of an Oligothiophene Spacer Cation.

J Am Chem Soc 2019 Apr 23. Epub 2019 Apr 23.

Three-dimensional (3D) hybrid organic-inorganic lead halide perovskites (HOIPs) feature remarkable optoelectronic properties for solar energy conversion but suffer from long-standing issues of environmental stability and lead-toxicity. Associated two-dimensional (2D) analogs are garnering increasing interest due to superior chemical stability, structural diversity and broader property tunability. Towards lead-free 2D HOIPs, double perovskites (DPs) with mixed valent dual metals are attractive but remain unexplored beyond a recent 2D Ag-Bi bromide DP with n-butylammonium spacer cations. Read More

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http://dx.doi.org/10.1021/jacs.9b02909DOI Listing

Kinetic Control of Interpenetration in Fe-Biphenyl-4,4'-Dicarboxylate Metal-Organic Frameworks by Coordination and Oxidation Modulation.

J Am Chem Soc 2019 Apr 24. Epub 2019 Apr 24.

Phase control in the self-assembly of metal-organic frameworks (MOFs) is often a case of trial and error; judicious control over a number of synthetic variables is required to select the desired topology and control features such as interpenetration and defectivity. Herein, we present a comprehensive investigation of self-assembly in the Fe-biphenyl-4,4'-dicarboxylate system, demonstrating that coordination modulation can reliably tune between the kinetic product, non-interpenetrated MIL-88D(Fe), and the thermodynamic product, two-fold interpenetrated MIL-126(Fe). Density functional theory simulations reveal that correlated disorder of the terminal anions on the metal clusters results in hydrogen-bonding between adjacent nets in the interpenetrated phase and is the thermodynamic driving force for its formation. Read More

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http://dx.doi.org/10.1021/jacs.9b03269DOI Listing

Solid state ionics of hybrid halide perovskites.

J Am Chem Soc 2019 Apr 18. Epub 2019 Apr 18.

Many exciting "anomalies" affecting long-time and low-frequency phenomena in the photo-active halide perovskites that are presently in the focus of the field of photovoltaics turn out to be rather expected from the point of view of Solid State Ionics. This paper discusses such issues based on the mixed conducting nature of these materials, and indicates how the Solid State Ionics toolbox can be used to condition and potentially improve these solids. In addition to equilibrium bulk properties, interfacial effects and light effects on the mixed conductivity are considered. Read More

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http://dx.doi.org/10.1021/jacs.8b13594DOI Listing

A "Superaerophobic" Nickel Phosphide Nanoarray Catalyst for Efficient Hydrogen Evolution at Ultra-High Current Densities.

J Am Chem Soc 2019 Apr 22. Epub 2019 Apr 22.

The design of highly efficient non-noble metal electrocatalysts for large-scale hydrogen production remains an ongoing challenge. We report here a Ni2P nanoarray catalyst grown on a commercial Ni foam substrate, which demonstrates an outstanding electrocatalytic activity and stability in basic electrolyte. The high catalytic activity can be attributed to the favorable electron transfer, superior intrinsic activity and the intimate connection between the nanoarrays and their substrate. Read More

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http://dx.doi.org/10.1021/jacs.9b02527DOI Listing

Unexpectedly Strong Chiral Amplification of Chiral/Achiral and Chiral/Chiral Copolymers of Biphenylylacetylenes and Further Enhancement/Inversion and Memory of the Macromolecular Helicity.

J Am Chem Soc 2019 Apr 22. Epub 2019 Apr 22.

We report an unexpectedly strong amplification of the macromolecular helicity in dynamic helical copolymers of chi-ral/achiral and chiral/chiral (R/S) biphenylylacetylenes in which the chiral residues are remote from the biphenyl pendants and further from the main chains. The copolymers consisting of 20 mol% chiral monomers and chiral monomers of 20% enanti-omeric excess (ee) showed a full induced circular dichroism (ICD) as intense as that of the chiral homopolymer. In contrast, an analogous poly(phenylacetylene) bearing the identical chiral residue (100% ee) showed no circular dichroism (CD) in the polymer backbone, indicating the critical role of the biphenyl moieties in the observed high chiral amplification. Read More

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http://dx.doi.org/10.1021/jacs.9b02904DOI Listing

Visible-Light-Driven Tunable Molecular Motors Based on Oxindole.

J Am Chem Soc 2019 Apr 25. Epub 2019 Apr 25.

Stratingh Institute for Chemistry , University of Groningen , Nijenborgh 4 , 9747 AG , Groningen , The Netherlands.

Molecular rotary motors based on oxindole which can be driven by visible light are presented. This novel class of motors can be easily synthesized via a Knoevenagel condensation, and the choice of different upper halves allows for the facile tuning of their rotational speed. The four-step rotational cycle was explored using DFT calculations, and the expected photochemical and thermal isomerization behavior was confirmed by NMR, UV/vis, and CD spectroscopy. Read More

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http://dx.doi.org/10.1021/jacs.9b03237DOI Listing

Mechanical Unfolding and Thermal Refolding of Single-Chain Nanoparticles Using Ligand-Metal Bonds.

J Am Chem Soc 2019 Apr 24. Epub 2019 Apr 24.

Covalent macromolecules tend to fragment under mechanical stress through the mechanochemical scission of covalent bonds in the backbone. However, linear polymers that have been intramolecularly collapsed by covalent bonds show greater mechanochemical stability compared to other thermoplastics. Here, Rhodium-π bonds are used for intramolecular collapse in order to show that mechanical stress can be removed from the polymer backbone and focused on weaker intramolecular cross-links, leading to polymer unfolding instead of mechanochemical events at the backbone. Read More

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http://dx.doi.org/10.1021/jacs.9b01960DOI Listing

Ligand-Mediated Band Engineering in Bottom-Up Assembled SnTe Nanocomposites for Thermoelectric Energy Conversion.

J Am Chem Soc 2019 Apr 19. Epub 2019 Apr 19.

The bottom-up assembly of colloidal nanocrystals is a versatile methodology to produce composite nanomaterials with precisely tuned electronic properties. Beyond the synthetic control over crystal domain size, shape, crystal phase and composition, solution-processed nanocrystals allow exquisite surface engineering. This provides additional means to modulate the nanomaterial characteristics and particularly its electronic transport properties. Read More

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http://dx.doi.org/10.1021/jacs.9b01394DOI Listing

14.7% Efficiency Organic Photovoltaic Cells Enabled by Active Materials with a Large Electrostatic Potential Difference.

J Am Chem Soc 2019 Apr 22. Epub 2019 Apr 22.

Although significant improvements have been achieved for organic photovoltaic cells (OPVs), the top-performing devices still show far behind power conversion efficiencies than the commercialized solar cells. One of the main reasons is the large driving force required for separating electron-hole pairs. Here, we demonstrate an efficiency of 14. Read More

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http://dx.doi.org/10.1021/jacs.8b12937DOI Listing

Tuning the Circumference of Six-Porphyrin Nanorings.

J Am Chem Soc 2019 Apr 24. Epub 2019 Apr 24.

Most macrocycles are made from a simple repeat unit, resulting in high symmetry. Breaking this symmetry allows fine tuning of the circumference, providing better control of the host-guest behavior and electronic structure. Here we present the template-directed synthesis of two unsymmetrical cyclic porphyrin hexamers with both ethyne (C2) and butadiyne (C4) links, and we compare these nanorings with the symmetrical analogues with six ethyne or six butadiyne links. Read More

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http://dx.doi.org/10.1021/jacs.9b02965DOI Listing

Nickel-Catalyzed Decarboxylation of Aryl Carbamates for Converting Phenols into Aromatic Amines.

J Am Chem Soc 2019 Apr 21. Epub 2019 Apr 21.

Herein, we describe a new catalytic approach to accessing aromatic amines from an abundant feedstock, namely phenols. The most reliable catalytic method for converting phenols to aromatic amines uses an activating group, such as a trifluoromethane sulfonyl group. However, this activating group is eliminated as a leaving group during the amination process, resulting in significant waste. Read More

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http://dx.doi.org/10.1021/jacs.9b02751DOI Listing

Valence Engineering via Selective Atomic Substitution on Tetrahedral Sites in Spinel Oxide for Highly Enhanced Oxygen Evolution Catalysis.

J Am Chem Soc 2019 Apr 22. Epub 2019 Apr 22.

A major challenge which prohibits the practical application of single/double-transition metal (3d-M) oxides as oxygen evolution reaction (OER) catalysts is the high overpotentials during the electrochemical process. Herein, our theoretical calculation shows that Fe will be more energetically favorable in the tetrahedral site than Ni and Co, which can further regulate their electronic structure of binary NiCo spinel oxides for optimal adsorption energies of OER intermediates and improved electronic conductivity, and hence boost their OER performance. X-ray absorption spectroscopy study on the as-synthesized NiCoFe oxide catalysts indicates that Fe preferentially dopes into tetrahedral sites of the lattice, which induces high proportions of Ni and Co on the octahedral sites (the active sites in OER). Read More

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http://dx.doi.org/10.1021/jacs.8b13701DOI Listing

Self-Assembly of Anionic Polyoxometalate-Organic Architectures Based on Lacunary Phosphomolybdates and Pyridyl Ligands.

J Am Chem Soc 2019 Apr 23. Epub 2019 Apr 23.

Department of Applied Chemistry, School of Engineering , The University of Tokyo , 7-3-1 Hongo , Bunkyo-ku, Tokyo 113-8656 , Japan.

The development of novel systems for metal-organic architectures is an attractive research field because they are fascinating materials with unexplored functions. Lacunary polyoxometalates (POMs) offer structurally well-defined coordination sites with various coordination directions and numbers in addition to the designable properties; thus, lacunary POMs are ideal building blocks for inorganic-organic architectures. However, their utilization is currently limited by their low stability and difficulty in controlling the reactivity. Read More

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http://dx.doi.org/10.1021/jacs.9b02541DOI Listing

Approach to a Substituted Heptamethine Cyanine Chain by the Ring Opening of Zincke Salts.

J Am Chem Soc 2019 Apr 23. Epub 2019 Apr 23.

Department of Chemistry and RECETOX , Masaryk University , Kamenice 5, 625 00 Brno , Czech Republic.

Cyanine dyes play an indispensable and central role in modern fluorescence-based biological techniques. Despite their importance and widespread use, the current synthesis methods of heptamethine chain modification are restricted to coupling reactions and nucleophilic substitution at the meso position in the chain. Herein, we report the direct transformation of Zincke salts to cyanine dyes under mild conditions, accompanied by the incorporation of a substituted pyridine residue into the heptamethine scaffold. Read More

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http://dx.doi.org/10.1021/jacs.9b02537DOI Listing

meta-Selective C-H Borylation of Benzamides and Pyridines by an Iridium-Lewis Acid Bifunctional Catalyst.

J Am Chem Soc 2019 Apr 21. Epub 2019 Apr 21.

We report herein the iridium-catalyzed meta-selective C-H borylation of benzamides by using a newly designed a 2,2'-bipyridine (bpy) ligand bearing an alkylaluminum biphenoxide moiety. We also demonstrate the iridium-catalyzed C3-selective C-H borylation of pyridine with a 1,10-phenanthroline (Phen) ligand bearing an alkylborane moiety. It is proposed that the Lewis acid-base interaction between the Lewis acid moiety and the aminocarbonyl group or the sp2-hybridized nitrogen atom accelerates the reaction and controls the site-selectivity. Read More

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http://dx.doi.org/10.1021/jacs.9b03138DOI Listing

Pyridine-based PCP-Ruthenium Complexes: Unusual Structures and Metal-Ligand Cooperation.

J Am Chem Soc 2019 Apr 19. Epub 2019 Apr 19.

Metal-ligand cooperation (MLC) by dearomatization/aromatization provides a unique way for bond activation, which has led to the discovery of various acceptorless dehydrogenative coupling reactions. However, most of the studies are based on pincer complexes with a central nitrogen donor. Aiming at exploration of the possibility of MLC by PCP-type pincer complexes, we report herein the synthesis, characterization, structure and reactivity of pyridine-based PCP-Ru complexes. Read More

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http://dx.doi.org/10.1021/jacs.9b02669DOI Listing

Metal-Organic Framework Nanoparticle-Assisted Cryopreservation of Red Blood Cells.

J Am Chem Soc 2019 Apr 23. Epub 2019 Apr 23.

The development of hybrid nanomaterials mimicking antifreeze proteins that can modulate/inhibit the growth of ice crystals for cell/tissue cryopreservation has attracted increasing interests. Herein, we describe the first utilization of zirconium (Zr)-based metal-organic framework (MOF) nanoparticles (NPs) with well-defined surface chemistries for the cryopreservation of red blood cells (RBCs) without the need of any (toxic) organic solvents. Distinguishing features of this cryoprotective approach include the exceptional water stability, low hemolytic activity, and the long periodic arrangement of organic linkers on the surface of MOF NPs which provide the precise spacing of hydrogen donors to recognize and match the ice crystal planes. Read More

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http://pubs.acs.org/doi/10.1021/jacs.9b00992
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http://dx.doi.org/10.1021/jacs.9b00992DOI Listing
April 2019
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Alternating Copolymerization of Inorganic Nanoparticles.

J Am Chem Soc 2019 Apr 24. Epub 2019 Apr 24.

Nanoparticle self-assembly has emerged as an indispensable tool in designing structured materials with a wide range of ap-plications, but quantitatively predicting the assembly process and structures still remains challenging. Drawing inspirations from the toolbox of molecular reactions and behaviors is of utmost importance in further advancement of principles and theories for assembling nanoparticles at length scale orders of magnitude larger. Here we represent a general paradigm for the predictive self-assembly of binary inorganic nanoparticles into linear nanostructures in periodic sequence by expanding horizon of alternating copolymerization at molecular level to nanoscale colloidal systems. Read More

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http://dx.doi.org/10.1021/jacs.9b02316DOI Listing

Cobalt-Catalyzed Intermolecular Hydrofunctionalization of Alkenes: Evidence for a Bimetallic Pathway.

J Am Chem Soc 2019 Apr 23. Epub 2019 Apr 23.

A functional group tolerant cobalt-catalyzed method for the intermolecular hydrofunctionalization of alkenes with oxygen- and nitrogen-based nucleophiles is reported. This protocol features a strategic use of hypervalent iodine(III) reagents that enables a mechanistic shift from conventional cobalt-hydride catalysis. Key evidence was found supporting a unique bimetallic-mediated rate-limiting step involving two distinct cobalt(III) species, from which a new carbon-heteroatom bond is formed. Read More

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http://dx.doi.org/10.1021/jacs.9b01857DOI Listing

Discovery, X-ray Crystallography and Antiviral Activity of Allosteric Inhibitors of Flavivirus NS2B-NS3 Protease.

J Am Chem Soc 2019 Apr 23. Epub 2019 Apr 23.

Flaviviruses, including dengue, West Nile and recently emerged Zika virus, are important human pathogens, but there are no drugs to prevent or treat these viral infections. The highly conserved Flavivirus NS2B-NS3 protease is essential for viral replication and therefore a drug target. Compound screening followed by medicinal chemistry yielded a series of drug-like, broadly active inhibitors of Flavivirus proteases with IC as low as 120 nM. Read More

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http://dx.doi.org/10.1021/jacs.9b02505DOI Listing

Unexpected Precatalyst σ-Ligand Effects in Phenoxyimine Zr-Catalyzed Ethylene/1-Octene Copolymerizations.

J Am Chem Soc 2019 Apr 24. Epub 2019 Apr 24.

Recent decades have witnessed intense research efforts aimed at developing new homogeneous olefin polymerization catalysts, with a primary focus on metal-Cl or metal -hydrocarbyl precursors. Curiously, metal-NR2 precursors have received far less attention. In this contribution, the Zr-amido complex FI2ZrX2 (FI = 2,4-di-tert-butyl-6-((isobutylimino)methyl)phenolate, X = NMe2) is found to exhibit high ethylene polymerization activity and relatively high 1-octene co-enchainment selectivity (up to 7. Read More

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http://dx.doi.org/10.1021/jacs.9b01445DOI Listing

Porous Crystalline Olefin-Linked Covalent Organic Frameworks.

J Am Chem Soc 2019 Apr 23. Epub 2019 Apr 23.

Department of Chemistry , University of California-Berkeley ; Materials Sciences Division, Lawrence Berkeley National Laboratory; and Kavli Energy NanoSciences Institute, Berkeley , California 94720 , United States.

The first unsubstituted olefin-linked covalent organic framework, termed COF-701, was made by linking 2,4,6-trimethyl-1,3,5-triazine (TMT) and 4,4'-biphenyldicarbaldehyde (BPDA) through Aldol condensation. Formation of the unsubstituted olefin (-CH═CH-) linkage upon reticulation is confirmed by Fourier transform infrared (FT-IR) spectroscopy and solid-state C cross-polarization magic angle spinning (CP-MAS) NMR spectroscopy of the framework and of its C-isotope-labeled analogue. COF-701 is found to be porous (1715 m g) and to retain its composition and crystallinity under both strongly acidic and basic conditions. Read More

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http://dx.doi.org/10.1021/jacs.9b02848DOI Listing

Inducing Disorder in Order: Hierarchically Porous Covalent Organic Framework Nanostructures for Rapid Removal of Persistent Organic Pollutants.

J Am Chem Soc 2019 Apr 21. Epub 2019 Apr 21.

The key factor responsible for fast diffusion and mass transfer through a porous material is the availability of a widely open pore-interior having complete accessibility from their surface. But, due to their highly stacked nature, ordered two dimen-sional (2D) materials fail to find real-world applicability, as it is difficult to take advantage of their complete structure, espe-cially the inner cores. In this regard, three dimensional (3D) nano-structures constructed from layered two dimensional crys-tallites could prove advantageous. Read More

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http://dx.doi.org/10.1021/jacs.9b02706DOI Listing

Bioinspired Thiophosphorodichloridate Reagents for Chemoselective Histidine Bioconjugation.

J Am Chem Soc 2019 Apr 24. Epub 2019 Apr 24.

Department of Chemistry , University of California , Berkeley , California 94720 , United States.

Site-selective bioconjugation to native protein residues is a powerful tool for protein functionalization, with cysteine and lysine side chains being the most common points for attachment owing to their high nucleophilicity. We now report a strategy for histidine modification using thiophosphorodichloridate reagents that mimic post-translational histidine phosphorylation, enabling fast and selective labeling of protein histidines under mild conditions where various payloads can be introduced via copper-assisted alkyne-azide cycloaddition (CuAAC) chemistry. We establish that these reagents are particularly effective at covalent modification of His-tags, which are common motifs to facilitate protein purification, as illustrated by selective attachment of polyarginine cargoes to enhance the uptake of proteins into living cells. Read More

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http://dx.doi.org/10.1021/jacs.8b11912DOI Listing

Probing inhomogeneous diffusion in the microenvironments of phase-separated polymers under confinement.

J Am Chem Soc 2019 Apr 24. Epub 2019 Apr 24.

Biopolymer condensates formed by liquid-liquid phase separation of proteins and nucleic acids have been recently discovered to be prevalent in biology. These dynamic condensates behave like biochemical reaction vessels but little is known about their structural organization and biophysical properties, which are likely related to condensate size. Thus, it is critical that we study them on scales found in vivo. Read More

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http://pubs.acs.org/doi/10.1021/jacs.8b13349
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http://dx.doi.org/10.1021/jacs.8b13349DOI Listing
April 2019
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Computer-Guided Discovery of a pH-Responsive Organic Photocatalyst and Application for pH and Light Dual-Gated Polymerization.

J Am Chem Soc 2019 Apr 22. Epub 2019 Apr 22.

In this work, we adopted a fully computer-guided strategy in discovering an efficient pH-switchable organic photocatalyst (OPC), unprecedentedly turning colorless at pH 5 and recovering strong visible-light absorption and photoactivity at pH 7. This is the first example of an OPC design fully guided by comprehensive density functional theory (DFT) studies covering electrostatic, electrochemical, and photophysical predictions. Characterization of the designed OPC after synthesis confirmed the computational predictions. Read More

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http://dx.doi.org/10.1021/jacs.9b01096DOI Listing

Benzo-Fused Periacenes or Double Helicenes? Different Cyclodehydrogenation Pathways on Surface and in Solution.

J Am Chem Soc 2019 Apr 23. Epub 2019 Apr 23.

Institute of Functional Nano & Soft Materials (FUNSOM), Jiangsu Key Laboratory for Carbon-Based Functional Materials and Devices, Joint International Research Laboratory of Carbon-Based Functional Materials and Devices , Soochow University , Suzhou 215123 , China.

Controlling the regioselectivity of C-H activation in unimolecular reactions is of great significance for the rational synthesis of functional graphene nanostructures, which are called nanographenes. Here, we demonstrate that the adsorption of tetranaphthyl- p-terphenyl precursors on metal surfaces can completely change the cyclodehydrogenation route and lead to obtaining planar benzo-fused perihexacenes rather than double [7]helicenes during solution synthesis. The course of the on-surface planarization reactions is monitored using scanning probe microscopy, which unambiguously reveals the formation of dibenzoperihexacenes and the structures of reaction intermediates. Read More

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http://dx.doi.org/10.1021/jacs.9b01267DOI Listing

Catalytic C-H Amination Mediated by Dipyrrin Cobalt Imidos.

J Am Chem Soc 2019 Apr 23. Epub 2019 Apr 23.

Reduction of (ArL)Co(II)Br (ArL = 5-mesityl-1,9-(2,4,6-Ph3C6H2)dipyrrin) with potassium graphite afforded the novel Co(I) synthon (ArL)Co. Treatment of (ArL)Co with a stoichiometric amount of various alkyl azides (N3R) furnished three-coordinate Co(III) alkyl imidos (ArL)Co(NR) as confirmed by single crystal X-ray diffraction (R: CMe2Bu, CMe2(CH2)2CHMe2). The exclusive formation of four-coordinate cobalt tetrazido complexes (ArL)Co(κ2-N4R2) was observed upon addition of excess azide, inhibiting any subsequent C-H amination. Read More

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http://dx.doi.org/10.1021/jacs.9b01262DOI Listing

Proximity-Induced Cooperative Polymerization in "Hinged" Helical Polypeptides.

J Am Chem Soc 2019 Apr 23. Epub 2019 Apr 23.

Cooperative interactions and transitions are amongst the most im-portant strategies utilized by biological systems to regulate a variety of physical and chemical processes. We report herein an auto-accelerated, rapid cooperative polymerization of N-carboxyanhydrides (NCAs) with initiators structurally as simple as linear aliphatic diamines for the synthesis of polypeptides. The polymerization initiated by diamines proceeds via the formation of "hinged" polypeptides - two blocks of helical chains connected head-to-head by the diamine molecules in the polymerization solution. Read More

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http://dx.doi.org/10.1021/jacs.9b02298DOI Listing

Defined Merocyanine Dye Stacks from a Dimer up to an Octamer by Spacer-Encoded Self-Assembly Approach.

J Am Chem Soc 2019 Apr 23. Epub 2019 Apr 23.

Institut für Organische Chemie , Universität Würzburg , Am Hubland , 97074 Würzburg , Germany.

A series of well-defined chromophore stacks is obtained upon self-assembly of merocyanine and bis(merocyanine) dyes in nonpolar solvents. Careful design of the spacer moieties linking the dipolar chromophores within the bis(merocyanine) dyes allows one to direct the dipole-dipole interaction driven aggregation into stacks of desired size from dimer up to octamer. The spacer-encoded self-assembly process was investigated by UV/vis absorption spectroscopy showing an increase of the hypsochromic shift with increasing stack size. Read More

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http://dx.doi.org/10.1021/jacs.9b01835DOI Listing

Thermodynamic Hydricity of [FeFe]-Hydrogenases.

Authors:
Eric S Wiedner

J Am Chem Soc 2019 Apr 19. Epub 2019 Apr 19.

After remaining elusive for many years, terminal hydride states have now been identified in several native and mutant [FeFe]-hydrogenases. In this Perspective, hydride states of [FeFe]-hydrogenases are considered on the basis of hydricity, a thermodynamic parameter that has been instrumental for the rational design of synthetic molecular catalysts. Importantly, it is shown how the hydricity of [FeFe]-hydrogenases can inspire future research efforts in both the study of hydrogenases and the design of molecular catalysts. Read More

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http://dx.doi.org/10.1021/jacs.8b13084DOI Listing

Visible-Light-Controlled Ruthenium-Catalyzed Olefin Metathesis.

J Am Chem Soc 2019 Apr 22. Epub 2019 Apr 22.

Department of Chemistry , Columbia University , New York , New York 10027 , United States.

Olefin metathesis is now one of the most efficient ways to create new carbon-carbon bonds. While most efforts focused on the development of ever-more efficient catalysts, a particular attention has recently been devoted to developing latent metathesis catalysts, inactive species that need an external stimulus to become active. This furnishes an increased control over the reaction which is crucial for applications in materials science. Read More

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http://dx.doi.org/10.1021/jacs.8b13663DOI Listing

Endogenous ROS-Triggered Morphology Transformation for Enhanced Cooperative Interaction with Mitochondria.

J Am Chem Soc 2019 Apr 22. Epub 2019 Apr 22.

The morphology controlled molecular assemblies play vital roles in biological systems. Here we present endogenous reactive oxygen species (ROS)-triggered morphology transformation of polymer-peptide conjugates (PPCs) for cooperative interaction with mitochondria, exhibiting high tumor therapeutic efficacy. The PPCs are composed of i) a β-sheet-forming peptide KLVFF conjugated with poly (ethylene glycol) through ROS-cleavable thioketal, ii) a mitochondria-targeting cytotoxic peptide KLAK and iii) a polyvinyl alcohol backbone. Read More

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http://dx.doi.org/10.1021/jacs.8b07727DOI Listing

Synthesis of an undecasaccharide featuring an oligomannosidic heptasaccharide and a bacterial Kdo-lipid A backbone for eliciting neutralizing antibodies to mammalian oligomannose on the HIV-1 envelope spike.

J Am Chem Soc 2019 Apr 22. Epub 2019 Apr 22.

Lipooligosaccharides (LOS) from the bacterium Rhizobium radiobacter Rv3 are structurally related to antigenic mammalian oligomannoses on the HIV-1 envelope glycoprotein spike that are targets for broadly neutralizing anti-bodies. Here, we prepared a hybrid structure of viral and bacterial epitopes as part of a vaccine design strategy to elicit oligomannose-specific HIV-neutralizing antibodies using glycoconjugates based on the Rv3 LOS structure. Starting from a Kdo2GlcNAc2 tetrasaccharide precursor, a central orthogonally protected mannose trichloroacetimidate donor was coupled to OH-5 of the innermost Kdo residue. Read More

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http://dx.doi.org/10.1021/jacs.9b02872DOI Listing

Counter Cations Affect Transport in Aqueous Hydroxide Solutions with Ion Specificity.

J Am Chem Soc 2019 Apr 22. Epub 2019 Apr 22.

Department of Chemistry and Biochemistry , University of Notre Dame , Notre Dame , Indiana 46556 , United States.

The anomalously high mobility of hydroxide and hydronium ions in aqueous solutions is related to proton transfer and structural diffusion. The role of counterions in these solutions, however, is often considered to be negligible. Herein, we explore the impact of alkali metal counter cations on hydroxide solvation and mobility. Read More

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http://pubs.acs.org/doi/10.1021/jacs.8b13458
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http://dx.doi.org/10.1021/jacs.8b13458DOI Listing
April 2019
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Optical Control of Cardiac Function with a Photoswitchable Muscarinic Agonist.

J Am Chem Soc 2019 Apr 22. Epub 2019 Apr 22.

Light-triggered reversible modulation of physiological functions offers the promise of enabling on-demand spatiotemporally controlled therapeutic interventions. Optogenetics has been successfully implemented in the heart, but significant barriers to its use in the clinic remain, such as the need for genetic transfection. Herein, we present a method to modulate cardiac function with light through a photoswitchable compound and without genetic manipulation. Read More

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http://dx.doi.org/10.1021/jacs.9b03505DOI Listing

Post-assembly Modification of Phosphine Cages Controls Host-Guest Behavior.

J Am Chem Soc 2019 Apr 22. Epub 2019 Apr 22.

Department of Chemistry , University of Cambridge , Lensfield Road , Cambridge CB2 1EW , United Kingdom.

We report the design, synthesis, and post-assembly modification of a new phosphine-paneled supramolecular cage framework, the anion binding ability of which can be modified rationally through selective post-assembly functionalization. The parent phosphine-paneled cage can be modified in situ through oxidation, methylation, or auration. These covalent and coordinative modifications to the exterior of the cage strongly influence the guest-binding properties of the host. Read More

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http://dx.doi.org/10.1021/jacs.9b02604DOI Listing

Efficient Long-Range, Directional Energy Transfer through DNA-Templated Dye Aggregates.

J Am Chem Soc 2019 Apr 23. Epub 2019 Apr 23.

Center for Molecular Design and Biomimetics at the Biodesign Institute , Arizona State University , Tempe , Arizona 85287 , United States.

The benzothiazole cyanine dye K21 forms dye aggregates on double-stranded DNA (dsDNA) templates. These aggregates exhibit a red-shifted absorption band, enhanced fluorescence emission, and an increased fluorescence lifetime, all indicating strong excitonic coupling among the dye molecules. K21 aggregate formation on dsDNA is only weakly sequence dependent, providing a flexible approach that is adaptable to many different DNA nanostructures. Read More

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http://dx.doi.org/10.1021/jacs.9b01548DOI Listing