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Chemical Science

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https://www.readbyqxmd.com/read/30009016/annulation-cascade-of-arylnitriles-with-alkynes-to-stable-delocalized-pah-carbocations-via-intramolecular-rhodium-migration
#1
Jiangliang Yin, Fulin Zhou, Lei Zhu, Mufan Yang, Yu Lan, Jingsong You
Herein, we propose the conception of heteroatom-promoted delocalization of the positive charge of an oxonium ion and thus develop a highly efficient rhodium(iii)-catalyzed hydration and three fold C-H activation/annulation cascade of arylnitriles with alkynes, affording a structurally diverse family of delocalized polycyclic aromatic hydrocarbon (PAH) carbocations. DFT calculations demonstrate that the positive charge mostly locates around the C1 atom and is partly delocalized by ambient N, O1 and C5 atoms...
June 28, 2018: Chemical Science
https://www.readbyqxmd.com/read/30009015/highly-stable-and-porous-porphyrin-based-zirconium-and-hafnium-phosphonates-electron-crystallography-as-an-important-tool-for-structure-elucidation
#2
Timo Rhauderwiek, Haishuang Zhao, Patrick Hirschle, Markus Döblinger, Bart Bueken, Helge Reinsch, Dirk De Vos, Stefan Wuttke, Ute Kolb, Norbert Stock
The Ni-metallated porphyrin-based tetraphosphonic acid (Ni-tetra(4-phosphonophenyl)porphyrin, Ni-H8 TPPP) was used for the synthesis of highly porous metal phosphonates containing the tetravalent cations Zr4+ and Hf4+ . The compounds were thoroughly characterized regarding their sorption properties towards N2 and H2 O as well as thermal and chemical stability. During the synthesis optimization the reaction time could be substantially decreased under stirring from 24 to 3 h in glass vials. M-CAU-30, [M2 (Ni-H2 TPPP)(OH/F)2 ]·H2 O (M = Zr, Hf) shows exceptionally high specific surface areas for metal phosphonates of a BET = 1070 and 1030 m2 g-1 for Zr- and Hf-CAU-30, respectively, which are very close/correspond to the theoretical values of 1180 and 1030 m2 g-1 ...
June 28, 2018: Chemical Science
https://www.readbyqxmd.com/read/30009014/versatile-in-situ-synthesis-of-mno-2-nanolayers-on-upconversion-nanoparticles-and-their-application-in-activatable-fluorescence-and-mri-imaging
#3
Yuan Wu, Dan Li, Fang Zhou, Hao Liang, Yuan Liu, Weijia Hou, Quan Yuan, Xiaobing Zhang, Weihong Tan
We have developed a simple and versatile strategy for in situ growth of MnO2 on the surfaces of oleic acid-capped hydrophobic upconversion nanoparticles (UCNPs) by optimizing the component concentrations in the Lemieux-von Rudloff reagent. The oxidation time was shortened by a factor of two compared to that of the reported method. This oxidation process has no obvious adverse effects on the phases of UCNPs. STEM, X-ray photoelectron spectroscopy (XPS), Fourier transform infrared (FTIR) and energy-dispersive X-ray analysis (EDX) characterization demonstrated the successful growth of MnO2 on the surfaces of UCNPs...
June 28, 2018: Chemical Science
https://www.readbyqxmd.com/read/30009013/reversible-mechanofluorochromism-of-aniline-terminated-phenylene-ethynylenes
#4
Seth A Sharber, Kuo-Chih Shih, Arielle Mann, Fanny Frausto, Terry E Haas, Mu-Ping Nieh, Samuel W Thomas
Seven three-ring phenylene-ethynylene (PE) structural analogs, differing only in the lengths of alkyl chains on terminal aniline substituents, show 50-62 nm bathochromic shifts in emission maxima in response to mechanical force (mechanofluorochromism, MC). These shifts are fully reversible with heat or solvent fuming. Shearing of these solids yields a transition from green-emitting crystalline phases to orange-emitting amorphous phases as established by differential scanning calorimetry and X-ray diffraction...
June 28, 2018: Chemical Science
https://www.readbyqxmd.com/read/30009012/sustainable-p-type-copper-selenide-solar-material-with-ultra-large-absorption-coefficient
#5
Erica M Chen, Logan Williams, Alan Olvera, Cheng Zhang, Mingfei Zhang, Guangsha Shi, John T Heron, Liang Qi, L Jay Guo, Emmanouil Kioupakis, Pierre F P Poudeu
Earth-abundant solar absorber materials with large optical absorption coefficients in the visible enable the fabrication of low-cost high-efficiency single and multi-junction thin-film solar cells. Here, we report a new p-type semiconductor, Cu4 TiSe4 (CTSe), featuring indirect (1.15 eV) and direct (1.34 eV) band gaps in the optimal range for solar absorber materials. CTSe crystallizes in a new noncentrosymmetric cubic structure (space group F 4[combining macron]3 c ) in which CuSe4 tetrahedra share edges and corners to form octahedral anionic clusters, [Cu4 Se4 ]4- , which in turn share corners to build the three-dimensional framework, with Ti4+ ions located at tetrahedral interstices within the channels...
June 28, 2018: Chemical Science
https://www.readbyqxmd.com/read/30009011/core-shell-patterning-of-synthetic-hydrogels-via-interfacial-bioorthogonal-chemistry-for-spatial-control-of-stem-cell-behavior
#6
K T Dicker, J Song, A C Moore, H Zhang, Y Li, D L Burris, X Jia, J M Fox
A new technique is described for the patterning of cell-guidance cues in synthetic extracellular matrices (ECM) for tissue engineering applications. Using s -tetrazine modified hyaluronic acid (HA), bis- trans -cyclooctene (TCO) crosslinkers and monofunctional TCO conjugates, interfacial bioorthogonal crosslinking was used to covalently functionalize hydrogels as they were synthesized at the liquid-gel interface. Through temporally controlled introduction of TCO conjugates during the crosslinking process, the enzymatic degradability, cell adhesivity, and mechanical properties of the synthetic microenvironment can be tuned with spatial precision...
June 28, 2018: Chemical Science
https://www.readbyqxmd.com/read/30009010/modular-access-to-functionalized-5-8-5-fused-ring-systems-via-a-photoinduced-cycloisomerization-reaction
#7
Anna E Salvati, James A Law, Josue Liriano, James H Frederich
A 5-8-5 carbocyclic ring system forms the core of over 30 distinct natural products. Several members of this family have gained attention for their diverse activity in cell culture. In these cases, biological function is mediated by the arrangement of substituents around a conserved 5-8-5 nucleus. Despite the potential applications of this privileged substructure in medicinal chemistry, modular strategies for its assembly are underdeveloped. Herein, we describe a cycloisomerization reaction that forms the 5-8-5 framework directly...
June 28, 2018: Chemical Science
https://www.readbyqxmd.com/read/30009009/an-ultrasensitive-polydopamine-bi-functionalized-sers-immunoassay-for-exosome-based-diagnosis-and-classification-of-pancreatic-cancer
#8
Teng-Da Li, Ren Zhang, Hui Chen, Zhi-Peng Huang, Xin Ye, Hui Wang, An-Mei Deng, Ji-Lie Kong
Early diagnosis and metastasis monitoring for pancreatic cancer are extremely difficult due to a lack of sensitive liquid biopsy methods and reliable biomarkers. Herein, we developed easy-to-prepare and effective polydopamine-modified immunocapture substrates and an ultrathin polydopamine-encapsulated antibody-reporter-Ag(shell)-Au(core) multilayer (PEARL) Surface-Enhanced Raman Scattering (SERS) nano-tag with a quantitative signal of the Raman reporter at 1072 cm-1 , which achieved ultrasensitive and specific detection of pancreatic cancer-derived exosomes with a detection limit of only one exosome in 2 μL of sample solution (approximately 9 × 10-19 mol L-1 )...
June 28, 2018: Chemical Science
https://www.readbyqxmd.com/read/30009008/an-n-heterocyclic-carbene-ligand-promotes-highly-selective-alkyne-semihydrogenation-with-copper-nanoparticles-supported-on-passivated-silica
#9
Nicolas Kaeffer, Hsueh-Ju Liu, Hung-Kun Lo, Alexey Fedorov, Christophe Copéret
We report a surface organometallic route that generates copper nanoparticles (NPs) on a silica support while simultaneously passivating the silica surface with trimethylsiloxy groups. The material is active for the catalytic semihydrogenation of phenylalkyl-, dialkyl- and diaryl-alkynes and displays high chemo- and stereoselectivity at full alkyne conversion to corresponding ( Z )-olefins in the presence of an N-heterocyclic carbene (NHC) ligand. Solid-state NMR spectroscopy using the NHC ligand 13 C-labeled at the carbenic carbon reveals a genuine coordination of the carbene to Cu NPs...
June 28, 2018: Chemical Science
https://www.readbyqxmd.com/read/30009007/reagent-dictated-site-selectivity-in-intermolecular-aliphatic-c-h-functionalizations-using-nitrogen-centered-radicals
#10
Anthony M Carestia, Davide Ravelli, Erik J Alexanian
The site selectivities of intermolecular, aliphatic C-H bond functionalizations are central to the value of these transformations. While the scope of these reactions continues to expand, the site selectivities remain largely dictated by the inherent reactivity of the substrate C-H bonds. Herein, we introduce reagent-dictated site selectivity to intermolecular aliphatic C-H functionalizations using nitrogen-centered amidyl radicals. Simple modifications of the amide lead to high levels of site selectivity in intermolecular C-H functionalizations across a range of simple and complex substrates...
June 28, 2018: Chemical Science
https://www.readbyqxmd.com/read/30009006/single-and-double-activation-of-acetone-by-isolobal-b-triple-bond-length-as-m-dash-n-and-b-triple-bond-length-as-m-dash-b-triple-bonds
#11
Julian Böhnke, Tobias Brückner, Alexander Hermann, Oscar F González-Belman, Merle Arrowsmith, J Oscar C Jiménez-Halla, Holger Braunschweig
B[triple bond, length as m-dash]N and B[triple bond, length as m-dash]B triple bonds induce C-H activation of acetone to yield a (2-propenyloxy)aminoborane and an unsymmetrical 1-(2-propenyloxy)-2-hydrodiborene, respectively. DFT calculations showed that, despite their stark electronic differences, both the B[triple bond, length as m-dash]N and B[triple bond, length as m-dash]B triple bonds activate acetone via a similar coordination-deprotonation mechanism. In contrast, the reaction of acetone with a cAAC-supported diboracumulene yielded a unique 1,2,3-oxadiborole, which according to DFT calculations also proceeds via an unsymmetrical diborene, followed by intramolecular hydride migration and a second C-H activation of the enolate ligand...
June 28, 2018: Chemical Science
https://www.readbyqxmd.com/read/30009005/engineering-of-a-near-infrared-fluorescent-probe-for-real-time-simultaneous-visualization-of-intracellular-hypoxia-and-induced-mitophagy
#12
Yongchao Liu, Lili Teng, Lanlan Chen, Hongchang Ma, Hong-Wen Liu, Xiao-Bing Zhang
Mitophagy induced by hypoxia plays an important role in regulating cellular homeostasis via the removal of dysfunctional mitochondria in the lysosomal degradation pathway, which results in physiological changes in the mitochondria, such as the pH, polarity and viscosity. However, the lack of an effective method for imaging of both the hypoxic microenvironment and the resulting variable mitochondria limits the visualization of hypoxia-induced mitophagy. Based on the specific mitochondrial pH changes during the hypoxia-induced mitophagy process, we have reported a near-infrared fluorescent probe (NIR-HMA) for real-time simultaneous visualization of the hypoxic microenvironment and the subsequent mitophagy process in live cells...
June 28, 2018: Chemical Science
https://www.readbyqxmd.com/read/30009004/catalysis-by-design-development-of-a-bifunctional-water-splitting-catalyst-through-an-operando-measurement-directed-optimization-cycle
#13
Nikolay Kornienko, Nina Heidary, Giannantonio Cibin, Erwin Reisner
A critical challenge in energy research is the development of earth abundant and cost-effective materials that catalyze the electrochemical splitting of water into hydrogen and oxygen at high rates and low overpotentials. Key to addressing this issue lies not only in the synthesis of new materials, but also in the elucidation of their active sites, their structure under operating conditions and ultimately, extraction of the structure-function relationships used to spearhead the next generation of catalyst development...
June 28, 2018: Chemical Science
https://www.readbyqxmd.com/read/30009003/product-oriented-chemical-surface-modification-of-a-levansucrase-sacb-via-an-ene-type-reaction
#14
Maria Elena Ortiz-Soto, Julia Ertl, Jürgen Mut, Juliane Adelmann, Thien Anh Le, Junwen Shan, Jörg Teßmar, Andreas Schlosser, Bernd Engels, Jürgen Seibel
Carbohydrate processing enzymes are sophisticated tools of living systems that have evolved to execute specific reactions on sugars. Here we present for the first time the site-selective chemical modification of exposed tyrosine residues in SacB, a levansucrase from Bacillus megaterium ( Bm -LS) for enzyme engineering purposes via an ene-type reaction. Bm -LS is unable to sustain the synthesis of high molecular weight (HMW) levan (a fructose polymer) due to protein-oligosaccharide dissociation events occurring at an early stage during polymer elongation...
June 28, 2018: Chemical Science
https://www.readbyqxmd.com/read/29997886/synthesis-and-applications-of-highly-functionalized-1-halo-3-substituted-bicyclo-1-1-1-pentanes
#15
Dimitri F J Caputo, Carlos Arroniz, Alexander B Dürr, James J Mousseau, Antonia F Stepan, Steven J Mansfield, Edward A Anderson
Bicyclo[1.1.1]pentanes (BCPs) are important bioisosteres of 1,4-disubstituted arenes, tert -butyl and acetylenic groups that can impart physicochemical benefits on drug candidates. Here we describe the synthesis of BCPs bearing carbon and halogen substituents under exceptionally mild reaction conditions, via triethylborane-initiated atom-transfer radical addition ring-opening of tricyclo[1.1.1.01,3 ]pentane (TCP) with alkyl halides. This chemistry displays broad substrate scope and functional group tolerance, enabling application to BCP analogues of biologically-relevant targets such as peptides, nucleosides, and pharmaceuticals...
June 21, 2018: Chemical Science
https://www.readbyqxmd.com/read/29997885/carboxylate-directed-c-h-allylation-with-allyl-alcohols-or-ethers
#16
Xiao-Qiang Hu, Zhiyong Hu, A Stefania Trita, Guodong Zhang, Lukas J Gooßen
A [Ru( p -cymene)Cl2 ]2 catalyst activates allyl alcohols and ethers for the regioselective ortho -C-H allylation of aromatic and heteroaromatic carboxylates. The reaction is orthogonal to most C-H functionalisations with allyl alcohols in that allyl arenes rather than carbonyl compounds are obtained. A wide range of substrates are thus smoothly transformed to allylarenes at 50 °C in phosphate-buffered 2,2,2-trichloroethanol. The reaction concept combines the use of abundant reagents and directing groups in a sustainable, waste-minimised method for C-C bond formation...
June 21, 2018: Chemical Science
https://www.readbyqxmd.com/read/29997884/copper-catalyzed-enantioselective-1-2-borylation-of-1-3-dienes
#17
Yangbin Liu, Daniele Fiorito, Clément Mazet
A highly enantioselective Cu-catalyzed borylation of 2-substituted 1,3-dienes is reported. The use of a chiral phosphanamine ligand is essential in achieving high chemo-, regio-, diastereo- and enantioselectivity. It provides access to a variety of homoallylic boronates in consistently high yield and enantiomeric excess with 2-aryl and 2-heteroaryl 1,3-dienes as well as sterically demanding 2-alkyl 1,3-dienes. Preliminary investigations based on a non-linear effect study point to a mechanism involving more than one metal center...
June 21, 2018: Chemical Science
https://www.readbyqxmd.com/read/29997883/directed-nickel-catalyzed-1-2-dialkylation-of-alkenyl-carbonyl-compounds
#18
Joseph Derosa, Vincent A van der Puyl, Van T Tran, Mingyu Liu, Keary M Engle
A nickel-catalyzed conjunctive cross-coupling of non-conjugated alkenes, alkyl halides, and alkylzinc reagents is reported. Regioselectivity is controlled by chelation of a removable bidentate 8-aminoquinoline directing group. Under optimized conditions, a wide range of 1,2-dialkylated products can be accessed in moderate to excellent yields. To the best of our knowledge, this report represents the first example of three-component 1,2-dialkylation of non-conjugated alkenes to introduce differentiated alkyl fragments...
June 21, 2018: Chemical Science
https://www.readbyqxmd.com/read/29997882/mechanically-triggered-reversible-stepwise-tricolor-switching-and-thermochromism-of-anthracene-o-carborane-dyad
#19
Xueyan Wu, Jixi Guo, Yali Cao, Jianzhang Zhao, Wei Jia, Yi Chen, Dianzeng Jia
A novel single organic molecule-carborane conjugate, CAN , was synthesized in a high yield via a modified nickel-catalyzed cross-coupling reaction incorporating an anthracene unit and an o -carborane moiety. CAN exhibits multiple functions of tricolored mechanochromism and mechanically triggered thermochromism. The fluorescence could be switched from blue to bright yellow then to pink by grinding. The robust and reversible thermochromic process was triggered by the mechanical force. The locally excited (LE) state emission, intermolecular excimer formation and twisted intermolecular charge transfer (TICT) are the primary origins of this tricolor switching property...
June 21, 2018: Chemical Science
https://www.readbyqxmd.com/read/29997881/the-morphology-and-surface-charge-dependent-cellular-uptake-efficiency-of-upconversion-nanostructures-revealed-by-single-particle-optical-microscopy
#20
Di Zhang, Lin Wei, Meile Zhong, Lehui Xiao, Hung-Wing Li, Jianfang Wang
The cellular uptake efficiency of nanostructures has been demonstrated to be highly dependent on the surface charge, size and shape although the cellular internalization process is still far from being well-understood. In this work, a series of NaYF4 :Yb3+ , Er3+ upconversion nanoparticles (UCNPs) with different morphologies and surface coatings were prepared to explore the influence of surface charge and morphology on the cellular internalization process with single-particle fluorescence microscopy. It is found that the higher the surface charge and larger the surface-to-volume ratio of the nanoparticles, the more efficient the cellular uptake will be...
June 21, 2018: Chemical Science
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