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Journal of the American Chemical Society

Hongwei Fan, Alexander Mundstock, Armin Feldhoff, Alexander Knebel, Jiahui Gu, Hong Meng, Jürgen Caro
Covalent organic frameworks (COFs) have been proposed as alternative candidates for molecular sieving membranes due to their chemical stability. However, developing COF membranes with narrowed apertures close to the size of common gas molecules is a crucial task for selective gas separation. Herein, we demonstrate a new type of a two-dimensional layered-stacking COF-COF composite membrane in bilayer geometry synthesized on a porous support by successively regulating the growth of imine-based COF-LZU1 and azine-based ACOF-1 layers via a temperature-swing solvothermal approach...
July 20, 2018: Journal of the American Chemical Society
Bonnie Choi, Kihong Lee, Anastasia Voevodin, Jue Wang, Michael L Steigerwald, Patrick Batail, Xiaoyang Zhu, Xavier Roy
Surfaces play a key role in determining material properties, and their importance is further magnified in the two-dimensional (2D) limit. Though monolayers are entirely composed of surfaces, there is no chemical approach to covalently address them without breaking intralayer bond. Here, we describe a 2D semiconductor that offers two unique features among 2D materials: structural hierarchy within the monolayer and surface reactive sites that enable functionalization. The 2D semiconductor is composed of a single layer of strongly interconnected Re6 Se8 clusters arranged in an oblique lattice capped by substitutionally labile Cl atoms...
July 19, 2018: Journal of the American Chemical Society
Hana Bunzen, Felicitas Kolbe, Andreas Kalytta-Mewes, German Sastre, Eike Brunner, Dirk Volkmer
One of the main problems of gas storage in porous materials is that many molecules of interest adsorb too weakly to be retained effectively. To enhance gas storage in metal-organic frameworks (MOFs), we propose to use kinetic trapping, i.e. a process where the guest gas is captured in the voids at loading conditions and not released immediately at normal conditions. In this approach, the diffusion-limiting pore size and the framework flexibility have to be matched to the gas, requiring flexible pore apertures to be smaller than the van der Waals diameter of the trapped guest...
July 19, 2018: Journal of the American Chemical Society
Jan G Vos, Tim A Wezendonk, Adriaan Jeremiasse, Marc T M Koper
The oxygen evolution reaction (OER) and chlorine evolution reaction (CER) are electrochemical processes with high relevance to water splitting for (solar) energy conversion and industrial production of commodity chemicals, respectively. Carrying out the two reactions separately is challenging, since the catalytic intermediates are linked by scaling relations. Optimizing the efficiency of OER over CER in acidic media has proven especially difficult. In this regard, we have investigated the OER vs. CER selectivity of manganese oxide (MnOx), a known OER catalyst...
July 19, 2018: Journal of the American Chemical Society
Simon Grélaud, Phillippa Cooper, Lyman J Feron, John F Bower
Tertiary benzylic stereocenters are accessed in high enantioselectivity by Ir-catalyzed branch selective addition of anilide ortho-C-H bonds across styrenes and α-olefins. Mechanistic studies indicate that the stereocenter generating step is reversible.
July 19, 2018: Journal of the American Chemical Society
Jun Nishida, John P Breen, Kurt P Lindquist, Daiki Umeyama, Hemamala I Karunadasa, Michael D Fayer
The dynamically flexible lattices in lead-halide perovskites may play important roles in extending carrier recombination lifetime in 3D perovskite solar-cell absorbers and in exciton self-trapping in 2D perovskite white-light phosphors. Two-dimensional infrared (2D IR) spectroscopy was applied to study a recently reported Pb-I-SCN layered perovskite. The Pb-I-SCN perovskite was spin-coated on a SiO2 surface as a thin film, with a thickness of ~100 nm, where the S12CN‒ anions were isotopically diluted with the ratio of S12CN:S13CN=5:95 or 1:99 to avoid vibrational coupling and excitation transfer between adjacent SCN‒ anions...
July 19, 2018: Journal of the American Chemical Society
Jake L Greenfield, Emrys W Evans, Daniele Di Nuzzo, Marco Di Antonio, Richard H Friend, Jonathan R Nitschke
Self-assembled helical polymers hold great promise as new functional materials, where helical handedness controls useful properties such as circularly-polarized light emission or electron spin. The technique of subcomponent self-assembly can generate helical polymers from readily-prepared monomers. Here we present three distinct strategies to achieve chiral induction for double-helical metallopolymers prepared via subcomponent self-assembly. Kinetic and thermodynamic models were developed to describe the polymer growth mechanisms and quantify the strength of chiral induction, respectively...
July 19, 2018: Journal of the American Chemical Society
Brian F Fisher, Seong Ho Hong, Samuel H Gellman
A thiol-thioester exchange system has been used to measure the propensities of diverse β-amino acid residues to participate in an α-helix-like conformation. These measurements depend on formation of a parallel coiled-coil tertiary structure when two peptide segments become linked by thioester formation. One peptide segment contains a "guest" site that accommodates diverse β residues and is distal to the coiled-coil interface. We find that helix propensity is influenced by side chain placement within the β residue [β3 (side chain adjacent to nitrogen) slightly favored relative to β2 (side chain adjacent to carbonyl)]...
July 19, 2018: Journal of the American Chemical Society
Andrea Baschieri, Luca Valgimigli, Simone Gabbanini, Gino DiLabio, Eduardo Romero-Montalvo, Riccardo Amorati
We report a novel co-antioxidant system based on TEMPO (2,2,6,6-tetramethylpiperidine-1-oxyl) that, in biologically-relevant model systems, rapidly converts chain-carrying alkylperoxyl radicals to HOO•. Extremely efficient quenching of HOO• by TEMPO blocks the oxidative chain. Rate constants in chlorobenzene were measured to be 1.1×10^9 M‒1s‒1 for the reductive reaction TEMPO + HOO• → TEMPOH + O2 and 5.0×10^7 M‒1s‒1 for the oxidative reaction TEMPOH + HOO• → TEMPO + H2O2. These rate constants are significantly higher than that associated with the reaction of HOO• with alpha-tocopherol, Nature's best lipid soluble antioxidant (k = 1...
July 19, 2018: Journal of the American Chemical Society
Ruizi Peng, Xiaofang Zheng, Yifan Lyu, Liujun Xu, Xiao-Bing Zhang, Guoliang Ke, Qiaoling Liu, Changjun You, Shuangyan Huan, Weihong Tan
Among the vast number of recognition molecules, DNA ap-tamers generated from cell-SELEX exhibit unique properties for identifying cell membrane biomarkers, in particular pro-tein receptors on cancer cells. To integrate all recognition and computing modules within a single structure, a three-dimensional (3D) DNA-based logic gate nanomachine was constructed to target overexpressed cancer cell biomarkers with bispecific recognition. Thus, when the Boolean opera-tor "AND" returns a true value, it is followed by an "ON" signal when the specific cell type is presented...
July 18, 2018: Journal of the American Chemical Society
James M Cabrera, Johannes Tauber, Wandi Zhang, Ming Xiang, Michael J Krische
Enantioselectivity increases with increasing carbonyl electrophilicity in 2-propanol-mediated reductive couplings of aldehydes with branched aryl-substituted allylic acetates to form products of carbonyl anti-(α-aryl)allylation. This unusual phenomenon is caused by aldehyde coordination to diastereomeric kinetic vs thermodynamic carbonyl binding sites that deliver enantiomeric products. Exploiting this effect, anti-diastereo- and enantioselective (α-aryl)allylations of fluoral hydrate and difluoroacetaldehyde ethyl hemiacetal were developed...
July 18, 2018: Journal of the American Chemical Society
Jeffrey W Slater, Sean C Marguet, Haleigh A Monaco, Hannah S Shafaat
Well-defined molecular systems for catalytic hydrogen production that are robust, easily generated, and active under mild aqueous conditions remain underdeveloped. Nickel-substituted rubredoxin (NiRd) is one such system, featuring a tetrathiolate coordination environment around the nickel center that is identical to the native [NiFe] hydrogenases and demonstrating hydrogenase-like proton reduction activity. However, until now, the catalytic mechanism has remained elusive. In this work, we have combined quantitative protein film electrochemistry with optical and vibrational spectroscopy, density functional theory calculations, and molecular dynamics simulations to interrogate the mechanism of H2 evolution by NiRd...
July 18, 2018: Journal of the American Chemical Society
Ming Xu, Siyu Yao, Deming Rao, Yiming Niu, Ning Liu, Mi Peng, Peng Zhai, Yi Man, Li-Rong Zheng, Bin Wang, Bingsen Zhang, Ding Ma, Min Wei
The mechanism on interfacial synergistic catalysis for supported metal catalysts has long been explored and investigated in several important heterogeneous catalytic processes (e.g., water-gas shift (WGS) reaction). The modulation of metal-support interactions imposes a substantial influence on activity and selectivity of catalytic reaction, as a result of the geometric/electronic structure of interfacial sites. Although great efforts have validated the key role of interfacial sites in WGS over metal catalysts supported on reducible oxides, direct evidence at the atomic level is lacking and the mechanism of interfacial synergistic catalysis is still ambiguous...
July 17, 2018: Journal of the American Chemical Society
Daniel R Dempsey, Hanjie Jiang, Jay H Kalin, Zan Chen, Philip A Cole
N-hydroxysuccinimide (NHS)-esters are widely used to label proteins non-selectively on free amino groups. Such broad labeling can be disadvantageous because it can interfere with protein structure or function and because stoichiometry is poorly controlled. Here we describe a simple method to transform NHS-esters into site-specific protein labeling on N-terminal Cys residues. MESNA addition converts NHS-esters to chemoselective thioesters for N-Cys modification. This labeling strategy was applied to clarify mechanistic fea-tures of the ubiquitin E3 ligase WWP2 including its in-teraction with one of its substrate, the tumor suppressor PTEN, as well as its autoubiquitination molecularity...
July 17, 2018: Journal of the American Chemical Society
Nadezhda V Korovina, Jimmy Joy, Xintian Feng, Cassidy Feltenberger, Anna I Krylov, Stephen E Bradforth, Mark E Thompson
Separation of triplet excitons produced by singlet fission is crucial for efficient application of singlet fission materials. While earlier works explored the first step of singlet fission - the formation of the correlated triplet pair state, the focus of recent studies has been on understanding the second step of singlet fission - the formation of independent triplets from the correlated pair state. We present the synthesis and excited state dynamics of meta- and para-bis(ethynyltetracenyl)benzene dimers that are analogues to the ortho-bis(ethynyltetracenyl)benzene dimer reported by our groups previously...
July 17, 2018: Journal of the American Chemical Society
Stephen Boulton, Rajeevan Selvaratnam, Jean-Paul Blondeau, Frank Lezoualc'h, Giuseppe Melacini
Classical uncompetitive inhibitors are potent pharmacological modulators of enzyme function. Since they selectively target enzyme-substrate complexes (E:S), their inhibitory potency is amplified by increasing substrate concentrations. Recently, an unconventional uncompetitive inhibitor, called CE3F4R, was discovered for the exchange protein activated by cAMP isoform 1 (EPAC1). Unlike conventional uncompetitive inhibitors, CE3F4R is uncompetitive with respect to an allosteric effector, cAMP, as opposed to the substrate (i...
July 17, 2018: Journal of the American Chemical Society
Bin Li, Zengyin Chao, Chunyu Li, Zhenhua Gu
A Cu-catalyzed enantioselective desymmetrizing ring-opening reaction of six-membered cyclic diaryliodonium salts with carboxylic acids or thioacids is reported for the facile access to chiral diarylmethanes. A Cu/[cyclopropyl bis(oxazoline)] catalyst well discriminates two C-I bonds of prochiral cyclic diaryliodonium salts. A stereochemical model was proposed to rationalize the stereochemical outcome on the basis of the crystal structure of cyclic diaryliodonium salt.
July 17, 2018: Journal of the American Chemical Society
Laura Rodriguez-Pérez, Javier Ramos-Soriano, Alfonso Pérez-Sánchez, Beatriz M Illescas, Antonio Muñoz, Joanna Luczkowiak, Fatima Lasala, Javier Rojo, Rafael Delgado, Nazario Martín
SWCNTs, MWCNTs and SWCNHs have been employed as virus mimicking nanocarbon platforms for the multivalent presentation of carbohydrates in an artificial Ebola virus infection model assay. These carbon nanoforms have been chemically modified by the covalent attachment of glycodendrons and glycofullerenes using the CuAAC "click chemis-try" approach. This modification dramatically increases the water solubility of these structurally different nanocarbons. Their efficiency to block DC-SIGN mediated viral infection by an artificial Ebola virus has been tested in a cellu-lar experimental assay finding that glycoconjugates based on MWCNTs functionalized with glycofullerenes are potent inhibitors of viral infection...
July 17, 2018: Journal of the American Chemical Society
Bo Qiao, Graham M Leverick, Wei Zhao, Amar H Flood, Jeremiah A Johnson, Yang Shao-Horn
Achieving high ionic conductivity in lithium-ion battery (LIB) electrolytes requires dissociation of Li-salts; however, though the generation of free Li+ from salt dissociation is advantageous, the presence of freely diffusing anions may reduce the Li+ transference number. The use of supramolecular anion recognition to regulate and modify ion-pairing and diffusion of anions in battery electrolytes is yet to be deeply understood. Herein, we demonstrate that addition of a selective and strong PF6 - -binding macrocycle to a solution of LiPF6 in low dielectric media leads to enhanced ion pair dissociation and an increased Li+ transference number...
July 17, 2018: Journal of the American Chemical Society
Juan Canoura, ZongWen Wang, Haixiang Yu, Obtin Alkhamis, FengFu Fu, Yi Xiao
The binding of small molecules to double-stranded DNA can modulate its susceptibility to digestion by exonucleases. Here, we show that the digestion of aptamers by exonuclease III can likewise be inhibited upon binding of small-molecule targets, and exploit this finding for the first time to achieve sensitive, label-free small-molecule detection. This approach does not require any sequence engineering and employs pre-folded aptamers which have higher target-binding affinities than structure-switching aptamers widely used in current small-molecule detecting assays...
July 16, 2018: Journal of the American Chemical Society
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