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Journal of the American Chemical Society

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https://www.readbyqxmd.com/read/28719738/an-activator-blocker-pair-provides-a-controllable-on-off-switch-for-a-ketosteroid-isomerase-active-site-mutant
#1
Vandana Lamba, Filip Yabukarski, Daniel Herschlag
Control of enzyme activity is fundamental to biology and represents a long-term goal in bioengineering and precision therapeutics. While several powerful molecular strategies have been developed, limitations remain in their generalizability and dynamic range. We demonstrate a control mechanism via separate small molecules that turn on the enzyme (activator) and turn off the activation (blocker). We show that a pocket created near the active site base of the enzyme ketosteriod isomerase (KSI) allows efficient and saturable base rescue when the enzyme's natural general base is removed...
July 18, 2017: Journal of the American Chemical Society
https://www.readbyqxmd.com/read/28719199/giant-pbse-cdse-cdse-quantum-dots-crystal-structure-limited-ultrastable-near-infrared-photoluminescence-from-single-nanocrystals
#2
Christina J Hanson, Nicolai F Hartmann, Ajay Singh, Xuedan Ma, William J I DeBenedetti, Joanna L Casson, John K Grey, Yves J Chabal, Anton V Malko, Milan Sykora, Andrei Piryatinski, Han Htoon, Jennifer A Hollingsworth
Toward a truly photostable PbSe quantum dot (QD) we apply the thick-shell or "giant" QD structural motif to this notoriously environmentally sensitive nanocrystal system. Namely, using a sequential application of two shell-growth techniques-partial-cation exchange and successive ionic layer adsorption and reaction (SILAR)-we are able to overcoat the PbSe QDs with sufficiently thick CdSe shells to impart new single-QD-level photostability as evidenced by suppression of both photobleaching and blinking behavior...
July 18, 2017: Journal of the American Chemical Society
https://www.readbyqxmd.com/read/28719198/biomimetic-platinum-promoted-polyene-polycyclizations-influence-of-alkene-substitution-and-pre-cyclization-conformations
#3
Christina McCulley, Michael J Geier, Brandi M Hudson, Michel R Gagné, Dean J Tantillo
Results of kinetic experiments and quantum chemical computations on a series of platinum-promoted polycyclization reactions are described. Analysis of these results reveal a reactivity model that reaches beyond the energetics of the cascade itself, incorporating an ensemble of pre-cyclization conformations of the platinum-alkene reactant complex, only a subset of which are productive for bi- (or larger) cyclization and lead to products. Similarities and differences between this scenario, including reaction coordinates for polycyclization, for platinum- and enzyme-promoted polycyclization are highlighted...
July 18, 2017: Journal of the American Chemical Society
https://www.readbyqxmd.com/read/28719197/enabling-the-cross-coupling-of-tertiary-organoboron-nucleophiles-through-radical-mediated-alkyl-transfer
#4
David N Primer, Gary A Molander
The construction of quaternary centers is a common challenge in the synthesis of complex materials and natural products. Current cross-coupling strategies that can be generalized for setting these centers are sparse and, when known, are typically predicated on the use of reactive organometallic reagents. To address this shortcoming a new, photoredox-Ni dual catalytic strategy for the cross-coupling of tertiary organoboron reagents with aryl halides is reported. In addition to details on the cross-coupling scope and limitations, full screening efforts and mechanistic experiments are communicated...
July 18, 2017: Journal of the American Chemical Society
https://www.readbyqxmd.com/read/28719195/fluorinated-boronic-acid-appended-pyridinium-salts-and-19f-nmr-spectroscopy-for-diol-sensing
#5
Jörg Axthelm, Sven H C Askes, Martin Elstner, Upendar Reddy Gandra, Helmar Görls, Peter Bellstedt, Alexander Schiller
The identification and discrimination of diols is of fundamental importance in medical diagnostics, such as measuring the contents of glucose in the urine of diabetes patients. Diol sensors are often based on fluorophore-appended boronic acids, but these severely lack discrimination power and their response is one-dimensional. As an alternative strategy, we present the use of fluorinated boronic acid-appended pyridinium salts in combination with 19F NMR spectroscopy. A pool of 59 (bio)analytes was screened, containing monosaccharides, phosphorylated and N-acetylated sugars, polyols, carboxylic acids, nucleotides and amines...
July 18, 2017: Journal of the American Chemical Society
https://www.readbyqxmd.com/read/28719192/precise-molecular-design-of-high-tc-3d-organic-inorganic-perovskite-ferroelectric-mehdabco-rbi3-mehdabco-n-methyl-1-4-diazabi-cyclo-2-2-2-octane
#6
Wan-Ying Zhang, Yuan-Yuan Tang, Peng-Fei Li, Ping-Ping Shi, Wei-Qiang Liao, Da-Wei Fu, Heng-Yun Ye, Yi Zhang, Ren-Gen Xiong
With the flourishing development of (CH3NH3)PbI3, three-dimensional (3D) organic-inorganic perovskites with unique structure-property flexibility have become a worldwide focus. However, they still face great challenges in effec-tively inducing ferroelectricity. Despite the typical 3D perovskite structure and the ability of dabco to trigger phase transition, unfortunately [H2dabco]RbCl3 (dabco = 1,4-diazabicyclo[2.2.2]octane) adopts a nonpolar crystal structure without ferroelectricity. Within larger RbI3 framework, we assemble N-methyl-dabco gained by reducing the molecular symmetry of dabco into a new 3D organic-inorganic perovskite...
July 18, 2017: Journal of the American Chemical Society
https://www.readbyqxmd.com/read/28718644/general-and-direct-method-for-preparing-oligonucleotide-functionalized-metal-organic-framework-nanoparticles
#7
Shunzhi Wang, C Michael McGuirk, Michael B Ross, Shuya Wang, Pengcheng Chen, Hang Xing, Yuan Liu, Chad A Mirkin
Metal-organic frameworks (MOFs) are a class of modular, crystalline, and porous materials that hold promise for storage and transport of chemical cargoes. Though MOFs have been studied in bulk forms, ways of deliberately manipulating the external surface functionality of MOF nanoparticles are less developed. A generalizable approach to modify their surfaces would allow one to impart chemical functionality onto the particle surface that is independent of the bulk MOF structure. Moreover, the use of a chemically programmable ligand, such as DNA, would allow for the manipulation of interparticle interactions...
July 18, 2017: Journal of the American Chemical Society
https://www.readbyqxmd.com/read/28718642/predictive-model-for-site-selective-aryl-and-heteroaryl-c-h-functionalization-via-organic-photoredox-catalysis
#8
Kaila A Margrey, Joshua B McManus, Simone Bonazzi, Frederic Zecri, David A Nicewicz
Direct C-H functionalization of aromatic compounds is a useful synthetic strategy that has garnered much attention due to its application to pharmaceuticals, agrochemicals, and late stage functionalization reactions on complex molecules. Based on previous methods disclosed by our lab, we sought to develop a predictive model for site selectivity and extend this aryl functionalization chemistry to a selected set of heteroaromatic systems commonly used in the pharmaceutical industry. Using electron density calculations, we were able to predict site selectivity of direct C-H functionalization in a number of heterocycles and identify general trends observed across heterocycle classes...
July 18, 2017: Journal of the American Chemical Society
https://www.readbyqxmd.com/read/28718640/smi2-h2o-n-reductions-of-electron-rich-enamines-by-concerted-proton-coupled-electron-transfer
#9
Scott S Kolmar, James M Mayer
Samarium diiodide in the presence of water and THF (SmI2(H2O)n) has in recent years become a versatile and useful reagent, mainly for reducing carbonyl-type substrates. This work reports the reduction of several enamines by SmI2(H2O)n. Mechanistic experiments implicate a concerted proton-coupled electron transfer (PCET) pathway, based on various evidence against initial outer-sphere electron transfer, proton transfer or substrate coordination. A thermochemical analysis indicates that the C-H bond formed in the rate determining step has a bond dissociation free energy (BDFE) of ~32 kcal mol-1...
July 18, 2017: Journal of the American Chemical Society
https://www.readbyqxmd.com/read/28702995/extreme-conductance-suppression-in-molecular-siloxanes
#10
Haixing Li, Marc H Garner, Timothy A Su, Anders Jensen, Michael S Inkpen, Michael L Steigerwald, Latha Venkataraman, Gemma C Solomon, Colin Nuckolls
Single-molecule conductance studies have traditionally focused on creating highly conducting molecular wires. However, progress in nanoscale electronics demands insulators just as it needs conductors. Here we describe the single-molecule length-dependent conductance properties of the classic silicon dioxide insulator. We synthesize molecular wires consisting of Si-O repeat units and measure their conductance through the scanning tunneling microscope-based break-junction method. These molecules yield conductance lower than alkanes of the same length and the largest length-dependent conductance decay of any molecular systems measured to date...
July 18, 2017: Journal of the American Chemical Society
https://www.readbyqxmd.com/read/28700224/cu-catalyzed-hydrocarbonylative-c-c-coupling-of-terminal-alkynes-with-alkyl-iodides
#11
Li-Jie Cheng, Neal P Mankad
A Cu-catalyzed hydrocarbonylative C-C coupling of terminal alkynes with unactivated alkyl iodides has been developed, enabling highly chemo- and regioselective synthesis of unsymmetrical dialkyl ketones. A variety of functional groups are tolerated, and both primary and secondary alkyl iodides react well. An autotandem sequence of two Cu-catalyzed processes is proposed: first hydrocarbonylative coupling of the alkyne and the alkyl iodide, followed by reduction of the intermediate unsaturated ketone to the saturated product...
July 18, 2017: Journal of the American Chemical Society
https://www.readbyqxmd.com/read/28683546/mesoporous-tungsten-oxides-with-crystalline-framework-for-highly-sensitive-and-selective-detection-of-foodborne-pathogens
#12
Yongheng Zhu, Yong Zhao, Junhao Ma, Xiaowei Cheng, Jing Xie, Pengcheng Xu, Haiquan Liu, Hongping Liu, Haijiao Zhang, Minghong Wu, Ahmed A Elzatahry, Abdulaziz Alghamdi, Yonghui Deng, Dongyuan Zhao
Foodborne pathogens like Listeria monocytogenes can cause various illnesses and pose a serious threat to public health. They produce species-specific microbial volatile organic compounds, i.e., the biomarkers, making it possible to indirectly measure microbial contamination in foodstuff. Herein, highly ordered mesoporous tungsten oxides with high surface areas and tunable pores have been synthesized and used as sensing materials to achieve an exceptionally sensitive and selective detection of trace Listeria monocytogenes...
July 18, 2017: Journal of the American Chemical Society
https://www.readbyqxmd.com/read/28682634/pressure-effects-on-structure-and-optical-properties-in-cesium-lead-bromide-perovskite-nanocrystals
#13
Guanjun Xiao, Ye Cao, Guangyu Qi, Lingrui Wang, Chuang Liu, Zhiwei Ma, Xinyi Yang, Yongming Sui, Weitao Zheng, Bo Zou
Metal halide perovskites (MHPs) are gaining increasing interest because of their extraordinary performance in optoelectronic devices and solar cells. However, developing an effective strategy for achieving the band-gap engineering of MHPs that will satisfy the practical applications remains a great challenge. In this study, high pressure is introduced to tailor the optical and structural properties of MHP-based cesium lead bromide nanocrystals (CsPbBr3 NCs), which exhibit excellent thermodynamic stability. Both the pressure-dependent steady-state photoluminescence and absorption spectra experience a stark discontinuity at ∼1...
July 18, 2017: Journal of the American Chemical Society
https://www.readbyqxmd.com/read/28682611/forbidden-chemistry-two-photon-pathway-in-2-2-cycloaddition-of-maleimides
#14
Mikhail V Tsurkan, Christiane Jungnickel, Michael Schlierf, Carsten Werner
Two-photon excitation provides high spatial resolution in three dimensions of the corresponding chemical or physical processes, allowing submicrometer structuring in stereolithography and three-dimensional (3D) microfabrication. While studying two-photon structuring applications, we observed an undescribed phenomenon in photochemistry that dictates reactivity of maleimide groups in two-photon mode. A low-absorbance transition formerly ignored in classical photochemistry has been found for maleimides. This transition was assigned to symmetry-breaking donor-acceptor complex formation, which revealed a formally forbidden pathway in [2+2] cycloaddition reactions of maleimide moieties...
July 18, 2017: Journal of the American Chemical Society
https://www.readbyqxmd.com/read/28682606/on-surface-synthesis-of-sandwich-molecular-nanowires-on-graphene
#15
Felix Huttmann, Nicolas Schleheck, Nicolae Atodiresei, Thomas Michely
We demonstrate a new synthesis route for the growth of organometallic sandwich molecular nanowires, taking the example of Eu-cyclooctatetraene (EuCot), a predicted ferromagnetic semiconductor. We employ simultaneous exposure of Cot molecules and Eu vapor in ultrahigh vacuum to an inert substrate, such as graphene. Using a Cot excess under temperature conditions of a finite residence time of the molecule, the reactand diffusion confined to two dimensions results in a clean product of ultralong wires. In situ scanning tunneling microscopy reveals not only their molecular structure but also a rich and intriguing growth morphology...
July 18, 2017: Journal of the American Chemical Society
https://www.readbyqxmd.com/read/28678494/photoelectron-transfer-dissociation-reveals-surprising-favorability-of-zwitterionic-states-in-large-gaseous-peptides-and-proteins
#16
James Bonner, Yana A Lyon, Christopher Nellessen, Ryan R Julian
Structural characterization of proteins in the gas phase is becoming increasingly popular, highlighting the need for a greater understanding of how proteins behave in the absence of solvent. It is clear that charged residues exert significant influence over structures in the gas phase due to strong Coulombic and hydrogen-bonding interactions. The net charge for a gaseous ion is easily identified by mass spectrometry, but the presence of zwitterionic pairs or salt bridges has previously been more difficult to detect...
July 18, 2017: Journal of the American Chemical Society
https://www.readbyqxmd.com/read/28675700/conjugated-trimeric-scaffolds-accessible-from-indolyne-cyclotrimerizations-synthesis-structures-and-electronic-properties
#17
Janice B Lin, Tejas K Shah, Adam E Goetz, Neil K Garg, K N Houk
We report the design and synthesis of a new class of indole-based conjugated trimers. The targeted compounds are accessed from in situ generated, highly reactive indolyne intermediates using Pd-catalyzed cyclotrimerization reactions. By harnessing three indolyne isomers, six isomeric indole trimers are accessible, none of which have been previously synthesized. Using computational analysis, we describe the structural and photophysical properties of these unique compounds. This study showcases the use of indolynes in transition metal-catalyzed reactions, while providing access to a new class of conjugated trimers, including highly bent heteroaromatic compounds...
July 18, 2017: Journal of the American Chemical Society
https://www.readbyqxmd.com/read/28665606/large-area-co-assembly-of-nanowires-for-flexible-transparent-smart-windows
#18
Jin-Long Wang, Yi-Ruo Lu, Hui-Hui Li, Jian-Wei Liu, Shu-Hong Yu
Electrochromic devices with controllable color switching, low cost, and energy-saving advantages have been widely used as smart windows, rear-view car mirrors, displays, and so on. However, the devices are seriously limited for flexible electronics as they are traditionally fabricated on indium tin oxide (ITO) substrates which will lose their conductivity after bending cycles (the resistance significantly changed from 200 Ω to 6.56 MΩ when the bending radius was 1.2 cm). Herein, we report a new route for large area coassembly of nanowires (NWs), resulting in the formation of multilayer ordered nanowire (NW) networks with tunable conductivity (7-40 Ω/sq) and transmittance (58-86% at 550 nm) for fabrication of flexible transparent electrochromic devices, showing good stability of electrochromic switching behaviors...
July 18, 2017: Journal of the American Chemical Society
https://www.readbyqxmd.com/read/28715214/exploiting-carbonyl-groups-to-control-intermolecular-rhodium-catalyzed-alkene-and-alkyne-hydroacylation
#19
Thomas J Coxon, Maitane Fernández, James Barwick-Silk, Alasdair I McKay, Louisa E Britton, Andrew S Weller, Michael C Willis
Readily available β-carbonyl-substituted aldehydes are shown to be exceptional substrates for Rh-catalyzed intermolecular alkene and alkyne hydroacylation reactions. By using cationic rhodium catalysts incorporating bisphosphine ligands, efficient and selective reactions are achieved for β-amido, β-ester, and β-keto aldehyde substrates, providing a range of synthetically useful 1,3-dicarbonyl products in excellent yields. A correspondingly broad selection of alkenes and alkynes can be employed. For alkyne substrates, the use of a catalyst incorporating the Ampaphos ligand triggers a regioselectivity switch, allowing both linear and branched isomers to be prepared with high selectivity in an efficient manner...
July 17, 2017: Journal of the American Chemical Society
https://www.readbyqxmd.com/read/28715211/alternating-sequence-controlled-copolymer-synthesis-of-%C3%AE-hydroxy-acids-via-syndioselective-ring-opening-polymerization-of-o-carboxyanhydrides-using-zirconium-hafnium-alkoxide-initiators
#20
Yangyang Sun, Zhaowei Jia, Changjuan Chen, Yong Cong, Xiaoyang Mao, Jincai Wu
The ring-opening polymerization (ROP) of O-carboxyanhydrides (OCAs) can give diverse poly(α-hydroxy acid)s (PAHAs) with different functional groups because of easy modification of the side group of OCAs, which can extend applications of PAHAs widely. The stereoselective polymerization of O-carboxyanhydrides and further sequence controlled alternating copolymerization of OCAs were still big challenges until now for lack of suitable catalysts/initiators. In this work, a highly syndioselective ROP of OCAs system as the first stereoselective example in this area is reported using zirconium/hafnium alkoxides as initiators with the highest Pr- value up to 0...
July 17, 2017: Journal of the American Chemical Society
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