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Journal of the American Chemical Society

Jiajia Ma, Anthony R Rosales, Xiaoqiang Huang, Klaus Harms, Radostan Riedel, Olaf Wiest, Eric Meggers
We report a visible-light-activated asymmetric β-C(sp(3))-H functionalization of 2-acyl imidazoles and 2-acylpyridines with 1,2-dicarbonyl compounds (typically α-ketoesters) catalyzed by a tailored stereogenic-at-rhodium Lewis acid catalyst. The C-C bond formation products are obtained in high yields (up to 99%) and with excellent stereoselectivities (up to >20:1 dr and up to >99% ee). Experimental and computational studies support a mechanism in which a photoactivated Rh-enolate transfers a single electron to the 1,2-dicarbonyl compound followed by proton transfer and a subsequent stereocontrolled radical-radical recombination...
November 21, 2017: Journal of the American Chemical Society
Matthias Westphal, Michael Andreas Schafroth, Roman Sarott, Michael Imhof, Christian Bold, Philipp Leippe, Amey Dhopeshwarkar, Jessica Grandner, Vsevolod Katritch, Ken Mackie, Dirk Trauner, Erick M Carreira, James Allen Frank
The cannabinoid receptor 1 (CB1) is an inhibitory G protein-coupled receptor abundantly expressed in the central nerv-ous system. It has rich pharmacology and largely accounts for the recreational use of cannabis. We describe efficient asymmetric syntheses of four photoswitchable Δ(9)-tetrahydrocannabinol derivatives (azo-THCs) from a central building block 3-Br-THC. Using electrophysiology and a FRET-based cAMP assay, two compounds are identified as potent CB1 agonists that change their effect upon illumination...
November 21, 2017: Journal of the American Chemical Society
Heekyoung Choi, Kang Jin Cho, Hyowon Seo, Junho Ahn, Jinying Liu, Shim Sung Lee, Hyungjun Kim, Chuanliang Feng, Jong Hwa Jung
Transfer and inversion of supramolecular chirality from chiral ca-lix[4]arene analogs (3D and 3L) with an alanine moiety to an achi-ral bipyridine derivative (1) with glycine moieties in a co-assembled hydrogel are demonstrated. Molecular chirality of 3D and 3L could transfer supramolecular chirality to an achiral bipyridine derivative 1. Moreover, the addition of 0.6 equiv. of 3D or 3L to 1 induced the supramolecular chirality inversion of 1. More interestingly, the 2D-sheet structure of the co-assembled hydrogels formed with 0...
November 21, 2017: Journal of the American Chemical Society
Yun-Fang Yang, Peiyuan Yu, Kendall N Houk
The mechanisms of Diels-Alder reactions between 1,2,3-triazines and enamines have been explored with density functional theory computations. The focus of this work is on the origins of the different reactivities and mechanisms induced by substituents and by hexafluoroisopropanol (HFIP) solvent. These inverse electron-demand Diels-Alder reactions of triazines have wide applications in bioorthogonal chemistry and natural product synthesis. Both concerted and stepwise cycloadditions are predicted, depending on the nature of substituents and solvents...
November 21, 2017: Journal of the American Chemical Society
Amit Kumar Mandal, James R Diers, Dariusz M Niedzwiedzki, Gongfang Hu, Rui Liu, Eric J Alexy, Jonathan S Lindsey, David F Bocian, Dewey Holten
Three sets of tetrapyrrole-chromophore arrays have been examined that exhibit panchromatic absorption across large portions of the near-ultraviolet (NUV) to near-infrared (NIR) spectrum along with favorable excited-state properties for use in solar-energy conversion. The arrays vary the tetrapyrrole (porphyrin, chlorin, bacteriochlorin), chromophore (boron-dipyrrin, perylene, terrylene), and attachment sites (meso-position, β-pyrrole position). In all, seven dyads, one triad, and nine benchmarks in toluene and benzonitrile were studied using steady-state and time-resolved absorption and fluorescence spectroscopy...
November 21, 2017: Journal of the American Chemical Society
Zhengxing Qin, Katie A Cychosz, Georgian Melinte, Hussein El Siblani, Jean-Pierre Gilson, Matthias Thommes, Christian Fernandez, Svetlana Mintova, Ovidiu Ersen, Valentin Valtchev
Zeolites are widely used in industrial processes, mostly as catalysts or adsorbents. Increasing their micropore volume could further improve their already exceptional catalytic and separation performances. We report a tunable extraction of zeolite framework cations (Si, Al) on a faujasite-type zeolite, the archetype of molecular sieves with cages and the most widely used as a catalyst and sorbent; this results in ca. 10% higher micropore volume with limited impact on its thermal stability. This increased micropore volume results from the opening of some of the small (sodalite) cages, otherwise inaccessible to most molecules...
November 21, 2017: Journal of the American Chemical Society
Chunguang Zhu, Zhiyuan Zhao, Huajie Chen, Liping Zheng, Xiaolin Li, Jinyang Chen, Yanming Sun, Feng Liu, Yunlong Guo, Yunqi Liu
We report a regioregular bis-pyridal[2,1,3]-thiadiazole (BPT) acceptor strategy to construct the first ambipolar pyridal[2,1,3]thiadiazole-based semiconducting polymer (PBPTV). The use of BPT unit enables PBPTV to achieve high electron affinity, low LUMO level, and extended π-conjugation. All these factors provide PBPTV with encouraging hole and electron mobilities up to 6.87 and 8.49 cm2 V-1 s-1, respectively. Our work demonstrates that the BPT unit is a promising building block for designing high-performance electron-transporting semiconductors in organic electronics...
November 21, 2017: Journal of the American Chemical Society
Santiago Rodríguez-Jiménez, Mingrui Yang, Ian Stewart, Anna L Garden, Sally Brooker
A simple method, using density functional theory (DFT), of predicting spin state in advance of synthesis is reported. Specifically, an excellent correlation is observed between the switching temperatures (T1/2) in CDCl3 solution of five spin crossover (SCO)-active [FeII(Lazine)2(NCBH3)2] complex-es and the DFT calculated (and the observed) 15N NMR chemical shift (δNA) of the five different azine-substituted 1,2,4-triazole ligands employed, Lazine = 4-(4-methylphenyl)-3-phenyl-5-(azine)-1,2,4-triazole, where azine = pyridine, pyridazine, 4-pyrimidine, pyrazine and 2-pyrimidine...
November 21, 2017: Journal of the American Chemical Society
Xue-Sen Hou, Guo-Long Zhu, Li-Jun Ren, Zihan Huang, Rui-Bin Zhang, Goran Ungar, Li-Tang Yan, Wei Wang
Honeycomb structure endows graphene with extraordinary properties. But could a honeycomb monolayer superlattice also be gen-erated via self-assembly of colloids or nanoparticles? Here we report the construction of mono- and multilayer molecular films with honeycomb structure that can be regarded as self-assembled artificial graphene (SAAG). We construct fan-shaped molecular building blocks by covalently connecting two kinds of clusters, one polyoxometalate (POM) and four polyhedral oligomeric silsesquioxanes (POSS)...
November 21, 2017: Journal of the American Chemical Society
Ting Wu, Rupam Mukherjee, Olga S Ovchinnikova, Liam Collins, Mahshid Ahmadi, Wei Lu, Nam-Goo Kang, Jimmy W Mays, Stephen Jesse, David Mandrus, Bin Hu
Hybrid perovskites, as emerging multifunctional semiconductors, have demonstrated dual electronic/ionic conduction properties. We report a metal/ion interaction induced p-i-n junction across slightly n-type doped MAPbI3 single crystals with Au/MAPbI3/Ag configuration based on interface dependent Seebeck effect, Hall effect and time-of-flight secondary ion mass spectrometry analysis. The organic cations (MA(+)) interact with Au atoms, forming positively charged coordination complexes at Au/MAPbI3 interface, whereas iodine anions (I(-)) can react with Ag contacts, leading to interfacial ionic polarization...
November 21, 2017: Journal of the American Chemical Society
Rebecca A Scheidt, Gergely F Samu, Csaba Janáky, Prashant V Kamat
The charging of a mesoscopic TiO2 layer in a metal halide perovskite solar cell can influence the overall power conversion efficiency. By employing CsPbBr3 films deposited on a mesoscopic TiO2 film, we have succeeded in probing the influence of electrochemical bias on the charge carrier recombination process. The transient absorption spectroscopy experiments conducted at different applied potentials indicate a decrease in the charge carrier lifetimes of CsPbBr3 as we increase the potential from -0.6 to +0.6 V vs Ag/AgCl...
November 21, 2017: Journal of the American Chemical Society
Maha Abdelrasoul, Komala Ponniah, Alice Mao, Meghan S Warden, Wessam Elhefnawy, Yaohang Li, Steven M Pascal
Tyrosine phosphorylation plays an important role in many cellular and intercellular processes including signal transduction, subcellular localization, and regulation of enzymatic activity. In 1999, Blom et al., using the limited number of protein data bank (PDB) structures available at that time, reported that the side chain structures of phosphorylated tyrosine (pY) are partitioned into two conserved conformational clusters ( Blom, N.; Gammeltoft, S.; Brunak, S. J. Mol. Biol. 1999 , 294 , 1351 - 1362 ). We have used the spectral clustering algorithm to cluster the increasingly growing number of protein structures with pY sites, and have found that the pY residues cluster into three distinct side chain conformations...
November 21, 2017: Journal of the American Chemical Society
Noam I Saper, John F Hartwig
Recent interest in the valorization of lignin has led to reactions involving the cleavage of strong aromatic C-O bonds. However, few experimental mechanistic studies of these reactions have been published. We report detailed mechanistic analysis of the hydrogenolysis of diaryl ethers catalyzed by the combination of Ni(COD)2 (COD = 1,5-cyclooctadiene) and an N-heterocyclic carbene (NHC). Experiments on the catalytic reaction indicated that NaOt-Bu was necessary for catalysis, but kinetic analysis showed that the base is not involved in the rate-limiting C-O bond cleavage...
November 21, 2017: Journal of the American Chemical Society
Cláudio M Nunes, Igor Reva, Sebastian Kozuch, Robert J McMahon, Rui Fausto
The slippery potential energy surface of aryl nitrenes has revealed unexpected and fascinating reactions. To explore such a challenging surface, one powerful approach is to use a combination of a cryogenic matrix environment and a tunable narrowband radiation source. In this way, we discovered the heavy-atom tunneling reaction involving spontaneous ring expansion of a fused-ring benzazirine into a seven-membered ring cyclic ketenimine. The benzazirine was generated in situ by the photochemistry of protium and deuterated triplet 2-formylphenylnitrene isolated in an argon matrix...
November 21, 2017: Journal of the American Chemical Society
Meng S Choy, Mark Swingle, Brandon D'Arcy, Kevin Abney, Scott F Rusin, Arminja N Kettenbach, Rebecca Page, Richard E Honkanen, Wolfgang Peti
Selective inhibitors for each serine/threonine phosphatase (PPP) are essential to investigate the biological actions of PPPs and to guide drug development. Although multiple organisms (cyanobacteria, dinoflagellates, beetles, etc.) produce natural toxins that bind and inhibit the active sites of PPPs, they are largely non-selective, typically inhibiting one or more family members with equal potencies. Thus, the use of these toxins as chemical tools to study the relationship between individual PPPs and their biological substrates, and how disruptions in these relationships contributes to human disease, is severely limited...
November 20, 2017: Journal of the American Chemical Society
Edward P Booker, Tudor H Thomas, Claudio Quarti, Michael R Stanton, Cameron D Dashwood, Alexander J Gillett, Johannes M Richter, Andrew J Pearson, Nathaniel J L K Davis, Henning Sirringhaus, Michael B Price, Neil C Greenham, David Beljonne, Siân E Dutton, Felix Deschler
We investigate the origin of the broadband visible emission in layered hybrid lead-halide perovskites and its connection with structural and photophysical properties. We study <001> oriented thin films of hexylammonium (HA) lead iodide, (C6H16N)2PbI4, and dodecylammonium (DA) lead iodide, (C12H28N)2PbI4 by combining first-principles simulations with time-resolved photoluminescence, steady-state absorption and X-ray diffraction measurements on cooling from 300 K to 4 K. Ultrafast transient absorption and photoluminescence measurements are used to track the formation and recombination of emissive states...
November 20, 2017: Journal of the American Chemical Society
Mingoo Jin, Tim S Chung, Tomohiro Seki, Hajime Ito, Miguel A Garcia-Garibay
Here we present a structural design aimed at the control of phosphorescence emission as the result of changes in molecular rotation in a crystalline material. The proposed strategy includes the use of aurophilic interactions, both as a crystal engineering tool and as sensitive emission probe, and the use of a dumbbell-shaped architecture intended to create a low packing density region that permits the rotation of a central phenylene. Molecular rotor 1 with of a central 1,4-diethynylphenylene rotator linked to two gold(I) triphenylphosphane complexes was prepared and its structure confirmed by single crystal X-ray diffraction (XRD), which revealed chains mediated by dimeric aurophilic interactions...
November 20, 2017: Journal of the American Chemical Society
Teresa Bartholomeyzik, Robert Pendrill, Richard Lihammar, Tuo Jiang, Göran Widmalm, Jan-E Bäckvall
Pd-catalyzed C-C bond-forming reactions under oxidative conditions constitute a class of important and widely used synthetic proto¬cols. This article describes a mechanistic investigation of the arylating carbocyclization of allenynes using boronic acids and focuses on the correlation between reaction conditions and product selectivity. Isotope effects confirm that either allenic or propargylic C-H activation, respectively, occurs directly after substrate binding. With an excess of H2O, a triene product is selectively formed via allenic C-H activation...
November 20, 2017: Journal of the American Chemical Society
Jun Guo, Yin Zhang, Lin Shi, Yanfei Zhu, Megersa Feyissa Mideksa, Ke Hou, Wenshi Zhao, Dawei Wang, Meiting Zhao, Xiaofei Zhang, Jiawei Lv, Jianqi Zhang, Xiaoli Wang, Zhiyong Tang
Hetero-nanostructures featured with both strong plasmon absorption and high catalytic activity are believed to be ideal platforms to realize efficient light-driven catalysis. However, in reality it remains great challenge to acquire high performance catalysis in such hetero-nanostructures due to poor generation and transfer of plamson-induced hot electrons. In this report, we demonstrate that Au nanorod@Pd superstructures (Au@Pd SSs), where the ordered Pd nanoarrays are precisely grown on Au nanorod surfaces via solution-based seed-mediated approach, would be an excellent solution for this challenge...
November 20, 2017: Journal of the American Chemical Society
Pei Liu, Vincent Grenier, Wootack Hong, Vikram R Muller, Evan W Miller
We present a method to target voltage-sensitive fluorescent dyes to specified cells using an enzyme-catalyzed fluorogenic reaction on cell surfaces. The dye/enzyme hybrids are composed of a photoinduced electron transfer (PeT)-based fluorescent voltage indicator and a complementary enzyme expressed on the cell surface. Action of the exogenous enzyme on the dye results in fluorogenic activation of the dye, enabling fast voltage imaging in defined neurons with sensitivity surpassing those of purely genetically encoded approaches...
November 20, 2017: Journal of the American Chemical Society
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