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Journal of the American Chemical Society

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https://www.readbyqxmd.com/read/28944665/kinetic-study-of-living-ring-opening-metathesis-polymerization-with-third-generation-grubbs-catalysts
#1
Dylan J Walsh, Sii Hong Lau, Michael G Hyatt, Damien Guironnet
The rate of living ring-opening metathesis polymerization (ROMP) of N-hexyl-exo-norbornene-5,6-dicarboximide initiated by Grubbs third-generation catalyst precursors [(H2IMes)(py)2(Cl)2Ru═CHPh] and [(H2IMes)(3-Br-py)2(Cl)2Ru═CHPh] is measured to be independent of catalyst concentration. This result led to the development of a rate law describing living ROMP initiated by a Grubbs third-generation catalyst that includes an inverse first-order dependency in pyridine. Additionally, it is demonstrated that one of the two pyridines coordinated to the solid catalyst is fully dissociated in solution...
September 25, 2017: Journal of the American Chemical Society
https://www.readbyqxmd.com/read/28944664/hemiindigo-highly-bistable-photoswitching-at-the-biooptical-window
#2
Christian Petermayer, Stefan Thumser, Florian Kink, Peter Mayer, Henry Dube
Hemiindigo is a long known chromophore that absorbs in the blue part of the spectrum but has almost completely been ignored as potential photoswitch. Herein we show how the absorption of hemiindigo is shifted to the red part of the visible spectrum and how nearly perfect photoswitching can be achieved using blue or green and red light. Five derivatives were investigated giving very high isomeric yields in both switching directions, i.e. >90% E isomer after irradiation with 470 to 530 nm light and 99% Z isomer with 590 up to 680 nm light...
September 25, 2017: Journal of the American Chemical Society
https://www.readbyqxmd.com/read/28899099/accurately-modeling-the-conformational-preferences-of-nucleosides
#3
Mihai Burai Patrascu, Elise Malek-Adamian, Masad J Damha, Nicolas Moitessier
Sugar puckering of nucleosides impacts nucleic acid structures; hence their biological function. Similarly, nucleoside-based therapeutics may adopt different conformations affecting their binding affinity, DNA incorporation, and excision rates. As a result, significant efforts have been made to develop nucleoside analogues adopting specific conformations to improve bioactivity and pharmacokinetic profiles of the corresponding nucleoside-containing drugs. Understanding and ultimately predicting these conformational preferences would significantly help in the design of more effective structures...
September 25, 2017: Journal of the American Chemical Society
https://www.readbyqxmd.com/read/28875703/doubly-excited-character-or-static-correlation-of-the-reference-state-in-the-controversial-2-1-ag-state-of-trans-butadiene
#4
Yinan Shu, Donald G Truhlar
Butadiene is the simplest polyene and has long served as a model system for many chemical and spectroscopic properties. However, this small molecule has presented significant challenges to theoretical chemistry. The 2(1)Ag state, which is dark but photochemically important, is a prime source of this difficulty. Previous studies attributed the notorious difficulty in treating this state to strong double excitation character of the 2(1)Ag state, which prevents the application of linear response (LR) methods. Therefore, one would require methods with much higher computational cost, especially for the analogues of this state in longer polyenes, and consequently studies of longer polyenes are very limited...
September 25, 2017: Journal of the American Chemical Society
https://www.readbyqxmd.com/read/28853287/stress-propagation-through-biological-lipid-bilayers-in-silico
#5
Camilo Aponte-Santamaría, Jan Brunken, Frauke Gräter
Membrane tension plays various critical roles in the cell. We here asked how fast and how far localized pulses of mechanical stress dynamically propagate through biological lipid bilayers. In both coarse-grained and all-atom molecular dynamics simulations of a dipalmitoylphosphatidylcholine lipid bilayer, we observed nanometer-wide stress pulses, propagating very efficiently longitudinally at a velocity of approximately 1.4 ± 0.5 nm/ps (km/s), in close agreement with the expected speed of sound from experiments...
September 25, 2017: Journal of the American Chemical Society
https://www.readbyqxmd.com/read/28942650/lability-and-basicity-of-bipyridine-carboxylate-phosphonate-ligand-accelerate-single-site-water-oxidation-by-ruthenium-based-molecular-catalysts
#6
David W Shaffer, Yan Xie, David J Szalda, Javier J Concepcion
A critical step in creating an artificial photosynthesis system for energy storage is designing catalysts that can thrive in an assembled device. Single-site catalysts have an advantage over bimolecular catalysts because they remain effective when immobilized. Hybrid water oxidation catalysts described here, combining the features of single-site bis-phosphonate catalysts and fast bimolecular bis-carboxylate catalysts, have reached turnover frequencies over 100 s(-1), faster than both related catalysts under identical conditions...
September 24, 2017: Journal of the American Chemical Society
https://www.readbyqxmd.com/read/28942643/biomimetic-total-synthesis-of-%C3%A2-griffipavixanthone-via-a-cationic-cycloaddition-cyclization-cascade
#7
Kyle D Reichl, Michael J Smith, Min K Song, Richard Johnson, John A Porco
We report the concise, biomimetic total synthesis of the dimeric, Diels-Alder natural product griffipavixanthone from a readily accessible prenylated xanthone monomer. The key step utilizes a novel intermolecular [4+2] cycloaddition-cyclization cascade between a vinyl para-quinone methide and an in situ generated isomeric diene promoted by either Lewis or Brønsted acids. Experimental and computational studies of the reaction pathway suggest that a stepwise, cationic Diels-Alder cycloaddition is operative.
September 24, 2017: Journal of the American Chemical Society
https://www.readbyqxmd.com/read/28942639/mechanistic-basis-for-efficient-site-selective-aerobic-catalytic-turnover-in-pd-catalyzed-c-h-imidoylation-of-heterocycle-containing-molecules
#8
Stephen J Tereniak, Shannon S Stahl
A recently reported Pd-catalyzed oxidative C-H imidoylation of N-methoxybenzamides to iminoisoindolinones with tBuNC exhibits a number of unique features that have important implications for Pd-catalyzed aerobic oxidation catalysis: (1) The reaction tolerates heterocycles that commonly poison PdII oxidation catalysts. (2) The site selectivity of C-H activation is controlled by an N-methoxyamide group in the substrate rather than a suitably positioned heterocycle. (3) A Pd0 source, Pd2(dba)3 (dba = dibenzylideneacetone), is superior to Pd(OAc)2 as a precatalyst, and other PdII sources [PdCl2, Pd(TFA)2, Pd(OTf)2] are ineffective (TFA = trifluoroacetate, OTf = trifluoromethanesulfonate)...
September 24, 2017: Journal of the American Chemical Society
https://www.readbyqxmd.com/read/28942653/exploiting-diffusion-barrier-and-chemical-affinity-of-metal-organic-frameworks-for-efficient-hydrogen-isotope-separation
#9
Jin Yeong Kim, Rafael Balderas-Xicohtencatl, Linda Zhang, Sung Gu Kang, Michael Hirscher, Hyunchul Oh, Hoi Ri Moon
Deuterium plays a pivotal role in industrial and scientific research, and is irreplaceable for various applications such as isotope tracing, neutron moderation, and neutron scattering. In addition, deuterium is a key energy source for fusion reactions. Thus, the isolation of deuterium from physico-chemically almost identical isotopic mixture is a seminal challenge in modern separation technology. However, current commercial approaches suffer from extremely low separation efficiency (i.e. cryogenic distillation, selectivity of 1...
September 23, 2017: Journal of the American Chemical Society
https://www.readbyqxmd.com/read/28942647/pore-breathing-of-metal-organic-frameworks-by-environmental-transmission-electron-microscopy
#10
Lucas R Parent, Huy Pham, Joseph P Patterson, Michael S Denny, Seth M Cohen, Nathan C Gianneschi, Francesco Paesani
Metal-organic frameworks (MOFs) have emerged as an effective platform for the rational design of multifunctional materials, combining large specific surface areas with flexible, periodic frameworks that can undergo reversible structural transitions, or "breathing", upon temperature and pressure changes, and through gas adsorption/desorption processes. Although MOF breathing can be inferred from the analysis of adsorption isotherms, direct observation of the structural transitions has been lacking, and the underlying processes of framework-reorganization in individual MOF nanocrystals is largely unknown...
September 23, 2017: Journal of the American Chemical Society
https://www.readbyqxmd.com/read/28938065/in-vitro-selection-of-diversely-functionalized-aptamers
#11
Dehui Kong, Wayland Yeung, Ryan Hili
We describe the application of T4 DNA ligase-catalyzed DNA templated oligonucleotide polymerization toward the evolution of a diversely functionalized nucleic acid aptamer for human α-thrombin. Using a 256-membered ANNNN co-monomer library comprising 16 sub-libraries modi-fied with different functional groups, a highly-functionalized aptamer for thrombin was raised with a dissociation constant of 1.6 nM. The aptamer was found to be selective for thrombin, and re-quired the modifications for binding affinity...
September 22, 2017: Journal of the American Chemical Society
https://www.readbyqxmd.com/read/28937776/4-c-methoxy-2-deoxy-2-fluoro-modified-ribonucleotides-improve-metabolic-stability-and-elicit-efficient-rnai-mediated-gene-silencing
#12
Elise Malek-Adamian, Dale Guenther, Shigeo Matsuda, Saúl Martínez-Montero, Ivan Zlatev, Joel Harp, Mihai Burai Patrascu, Donald J Foster, Johans J Fakhoury, Lydia Perkins, Nicolas Moitessier, Rajar Manoharan, Nate Taneja, Anna Bisbe, Klaus Charisse, Martin A Maier, Kallanthottathil G Rajeev, Martin Egli, Muthiah Manoharan, Masad J Damha
We designed novel 4'-modified 2'-deoxy-2'-fluorouridine (2'-F U) analogues with the aim to improve nuclease resistance and potency of therapeutic siRNAs by introducing 4'-C-methoxy (4'-OMe) as the alpha (C4'α) or beta (C4'β) epimers. The C4'α epimer was synthesized by a stereoselective route in six steps; however, both α and β epimers could be obtained by a non-stereoselective approach starting from 2'-F U. (1)H-NMR analysis and computational investigation of the α-epimer revealed that the 4'-OMe imparts a conformational bias towards the North-East sugar pucker, due to intramolecular hydrogen bonding and hyperconjugation effects...
September 22, 2017: Journal of the American Chemical Society
https://www.readbyqxmd.com/read/28937775/operando-phonon-studies-of-the-protonation-mechanism-in-highly-active-hydrogen-evolution-reaction-pentlandite-catalysts
#13
Ioannis Zegkinoglou, Ali Zendegani, Ilya Sinev, Sebastian Kunze, Hemma Mistry, Hyo Sang Jeon, Jiyong Zhao, Michael Y Hu, E Ercan Alp, Stefan Piontek, Mathias Smialkowski, Ulf-Peter Apfel, Fritz Körmann, Jorg Neugebauer, Tilmann Hickel, Beatriz Roldan Cuenya
Synthetic pentlandite (Fe4.5Ni4.5S8) is a promising electrocatalyst for hydrogen evolution, demonstrating high current densities, low overpotential and remarkable stability in bulk form. The depletion of sulfur from the surface of this catalyst during the electrochemical reaction has been proposed to be beneficial for its catalytic performance, but the role of sulfur vacancies and the mechanism determining the reaction kinetics are still unknown. We have performed electrochemical operando studies of the vibrational dynamics of pentlandite under hydrogen evolution reaction conditions using 57Fe nuclear resonant inelastic X-ray scattering...
September 22, 2017: Journal of the American Chemical Society
https://www.readbyqxmd.com/read/28937758/monomeric-huntingtin-exon-1-has-similar-overall-structural-features-for-wild-type-and-pathological-polyglutamine-lengths
#14
John B Warner, Kiersten Ruff, Piau Siong Tan, Edward A Lemke, Rohit V Pappu, Hilal A Lashuel
Huntington's disease is caused by expansion of a polyglutamine (polyQ) domain within exon 1 of the huntingtin gene (Httex1). A popular hypothesis is that the Httex1 protein undergoes sharp conformational changes as the polyQ length exceeds a threshold of 36 residues. We test this hypothesis by combining novel semi-synthesis strategies with state-of-the-art single molecule Förster resonance energy transfer measurements on biologically relevant Httex1 proteins of five different polyQ lengths. Our results, integrated with atomistic simulations, negate the hypothesis of a sharp, polyQ length-dependent change in the structure of monomeric Httex1...
September 22, 2017: Journal of the American Chemical Society
https://www.readbyqxmd.com/read/28937756/direct-comparison-of-c-h-bond-amination-efficacy-through-manipulation-of-nitrogen-valence-centered-redox-imido-versus-iminyl
#15
Matthew J T Wilding, Diana A Iovan, Alexandra T Wrobel, James T Lukens, Samantha N MacMillan, Kyle M Lancaster, Theodore A Betley
Reduction of previously reported iminyl radical (ArL)FeCl(•N(C6H4-p-tBu)) (2) with potassium graphite furnished the corresponding high-spin (S = 5/2) imido (ArL)Fe(N(C6H4-p-tBu)) (3) (ArL = 5-mesityl-1,9-(2,4,6-Ph3C6H2)dipyrrin). Oxidation of the three-coordinate imido (ArL)Fe(NAd) (5) with chlorotriphenylmethane afforded (ArL)FeCl(•NAd) (6) with concomitant expulsion of Ph3C(C6H5)CPh2. The respective alkyl/aryl imido/iminyl pairs (3, 2; 5, 6) have been characterized by EPR, zero-field 57Fe Mössbauer, magnetometry, single crystal X-ray diffraction, XAS, and EXAFS for 6...
September 22, 2017: Journal of the American Chemical Society
https://www.readbyqxmd.com/read/28937220/a-fluorescence-polarization-activity-based-protein-profiling-assay-in-the-discovery-of-potent-selective-inhibitors-for-human-non-lysosomal-glucosylceramidase
#16
Daniel Lahav, Bing Liu, Richard J B H N van den Berg, Adrianus M C H van den Nieuwendijk, Tom Wennekes, Amar T Ghisaidoobe, Imogen Breen, Maria J Ferraz, Chi-Lin Kuo, Liang Wu, Paul P Geurink, Huib Ovaa, Gijsbert A van der Marel, Mario van der Stelt, Rolf G Boot, Gideon J Davies, Johannes M F G Aerts, Herman S Overkleeft
Human non-lysosomal glucosylceramidase (GBA2) is one of several enzymes that controls levels of glycolipids and whose activity is linked to several human disease states. There is a major need to design or discover selective GBA2 inhibitors both as chemical tools and as potential therapeutic agents. Here, we describe the development of a fluorescence polarization activity-based protein profiling (FluoPol-ABPP) assay for the rapid identification, from a 350+ library of iminosugars, of GBA2 inhibitors. A focused library is generated based on leads from the FluoPol-ABPP screen and assessed on GBA2 selectivity offset against the other glucosylceramide metabolizing enzymes, glucosylceramide synthase (GCS), lysosomal glucosylceramidase (GBA) and the cytosolic retaining β-glucosidase, GBA3...
September 22, 2017: Journal of the American Chemical Society
https://www.readbyqxmd.com/read/28937217/visible-light-mediated-aerobic-oxidation-of-n-alkylpyridinium-salts-under-organic-photocatalysis
#17
Yunhe Jin, Lunyu Ou, Haijun Yang, Hua Fu
Quinolones and isoquinolones exhibit diverse biological and pharmaceutical activities, and their synthesis is highly desirable under mild conditions. Here, a highly efficient and environmentally friendly visible light-mediated aerobic oxidation of readily available N-alkylpyridinium salts has been developed with Eosin Y as the organic photocatalyst and air as the terminal oxidant, and the reaction provided quinolones and isoquinolones in good yields. The method shows numerous advantages including mild and environmentally friendly conditions, high efficiency, tolerance of wide functional groups and low cost...
September 22, 2017: Journal of the American Chemical Society
https://www.readbyqxmd.com/read/28922911/enantioselective-synthesis-of-cyclobutenes-by-intermolecular-2-2-cycloaddition-with-non-c2-symmetric-digold-catalysts
#18
Cristina García-Morales, Beatrice Ranieri, Imma Escofet, Laura López-Suarez, Carla Obradors, Andrey I Konovalov, Antonio M Echavarren
The enantioselective intermolecular gold(I)-catalyzed [2+2] cycloaddition of terminal alkynes and alkenes has been achieved using non-C2-chiral Josiphos digold(I) complexes as catalysts, by the formation of the monocationic complex. This new approach has been applied to the enantioselective total synthesis of rumphellaone A.
September 22, 2017: Journal of the American Chemical Society
https://www.readbyqxmd.com/read/28901136/tren-capped-hexaphyrin-zinc-complexes-interplaying-molecular-recognition-m%C3%A3-bius-aromaticity-and-chirality
#19
Hervé Ruffin, Gildas Nyame Mendendy Boussambe, Thierry Roisnel, Vincent Dorcet, Bernard Boitrel, Stéphane Le Gac
Over the past decade, the hexaphyrin skeleton has emerged as a multifaceted frame exhibiting strong interplay between topology, aromaticity, and metal coordination, opening new research areas beyond porphyrins. However, molecular recognition with hexaphyrins has been underexplored, mainly because of the lack of general synthetic strategies leading to sophisticated molecular hosts. Here we have developed a straightforward approach for capping the heteroannulene frame with tripodal units (e.g., tris(2-aminoethyl)amine [tren]) through postsynthetic modification of a readily accessible meso-(2-aminophenyl) tris-substituted platform...
September 22, 2017: Journal of the American Chemical Society
https://www.readbyqxmd.com/read/28898056/pressure-stabilized-semiconducting-electrides-in-alkaline-earth-metal-subnitrides
#20
Yunwei Zhang, Weikang Wu, Yanchao Wang, Shengyuan A Yang, Yanming Ma
High pressure is able to modify profoundly the chemical bonding and generate new phase structures of materials with chemical and physical properties not accessible at ambient conditions. We here report an unprecedented phenomenon on the pressure-induced formation of semiconducting electrides via compression of layered alkaline-earth subnitrides Ca2N, Sr2N, and Ba2N that are conducting electrides with loosely confined electrons in the interlayer voids at ambient pressure. Our extensive first-principles swarm structure searches identified the high-pressure semiconducting electride phases of a tetragonal I4̅2d structure for Ca2N and a monoclinic Cc structure shared by Sr2N and Ba2N, both of which contain atomic-size cavities with paring electrons distributed within...
September 22, 2017: Journal of the American Chemical Society
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