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Gold catalysis

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https://www.readbyqxmd.com/read/29137161/constructing-asymmetric-polyion-complex-vesicles-via-template-assembling-strategy-formulation-control-and-tunable-permeability
#1
Junbo Li, Lijuan Liang, Ju Liang, Wenlan Wu, Huiyun Zhou, Jinwu Guo
A strategy for constructing polyion complex vesicles (PICsomes) with asymmetric structure is described. Poly(methylacrylic acid)-block-poly(N-isopropylacrylamide) modified gold nanoparticles (PMAA-b-PNIPAm-@-Au NPs) were prepared and then assembled with poly(ethylene glycol)-block-poly[1-methyl-3-(2-methacryloyloxy propylimidazolium bromine)] (PEG-b-PMMPImB) via polyion complex of PMMA and PMMPImB. After removing the Au NPs template, asymmetric PICsomes composed of a PNIPAm inner-shell, PIC wall, and PEG outer-corona were obtained...
November 13, 2017: Nanomaterials
https://www.readbyqxmd.com/read/29131927/direct-evidence-for-the-origin-of-bis-gold-intermediates-probing-gold-catalysis-with-mass-spectrometry
#2
Mei Lu, Yijin Su, Pengyi Zhao, Xiaohan Ye, Yi Cai, Xiaodong Shi, Eric Masson, Fengyao Li, J Larry Campbell, Hao Chen
Gold-catalyzed alkyne hydration was studied using in-situ reacting mass spectrometry (MS) technology. By monitoring the reaction process in solution under different conditions (regular and very diluted catalyst concentrations, different pHs) and examining the reaction occurrence in the early reaction stage (1-2 ms after mixing) with MS, we collected a series of experimental evidence to support that the bisgold complex is a key reaction intermediate. Furthermore, both experimental and computational studies confirmed that the σ,π-bisgold complexes are not active intermediate toward nucleophilic addition...
November 13, 2017: Chemistry: a European Journal
https://www.readbyqxmd.com/read/29131220/highly-regioselective-gold-catalyzed-formal-hydration-of-propargylic-gem-difluorides
#3
Jean-Denys Hamel, Tatsuru Hayashi, Mélissa Cloutier, Paul R Savoie, Olivier Thibeault, Meggan Beaudoin, Jean-François Paquin
Herein, we report a highly regioselective gold-catalyzed formal hydration of propargylic gem-difluorides. Not only does this transformation provide access to versatile fluorinated building blocks that were difficult or hardly possible to access beforehand, but it also represents a rare case of a highly regioselective gold-catalyzed hydroalkoxylation of internal alkynes and puts forward the utility of the difluoromethylene unit as a directing group in catalysis.
November 13, 2017: Organic & Biomolecular Chemistry
https://www.readbyqxmd.com/read/29115710/pmo-immobilized-au-i-nhc-complexes-heterogeneous-catalysts-for-sustainable-processes
#4
Pascal van der Voort, Els De Canck, Fady Nahra, Kevin Bevernaege, Sofie Vanden Broeck, Judith Ouwehand, Diederick Maes, Steven P Nolan
A stable Periodic Mesoporous Organosilica (PMO) with accessible sulfonic acid functionalities is prepared via a one-pot-synthesis and is used as solid support for highly active catalysts, consisting of gold(I)-N-heterocyclic carbene (NHC) complexes. The gold complexes are successfully immobilized on the nanoporous hybrid material via a straightforward acid-base reaction with the corresponding [Au(OH)(NHC)] synthon. This catalyst design strategy results in a boomerang-type catalyst, allowing the active species to detach from the surface to perform the catalysis and then to recombine with the solid after all the starting material is consumed...
November 8, 2017: Chemphyschem: a European Journal of Chemical Physics and Physical Chemistry
https://www.readbyqxmd.com/read/29115312/plasmonic-support-mediated-activation-of-1-nm-platinum-clusters-for-catalysis
#5
S Wieghold, L Nienhaus, F L Knoller, F F Schweinberger, J J Shepherd, J W Lyding, U Heiz, M Gruebele, F Esch
Nanometer-sized metal clusters are prime candidates for photoactivated catalysis, based on their unique tunable optical and electronic properties, combined with a large surface-to-volume ratio. Due to the very small optical cross sections of such nanoclusters, support-mediated plasmonic activation could potentially make activation more efficient. Our support is a semi-transparent gold film, optimized to work in a back-illumination geometry. It has a surface plasmon resonance excitable in the 510-540 nm wavelength range...
November 8, 2017: Physical Chemistry Chemical Physics: PCCP
https://www.readbyqxmd.com/read/29112816/surface-composition-and-crystallinity-of-coalescing-silver-gold-nanoparticles
#6
Eirini Goudeli, Sotiris E Pratsinis
Bimetallic nanoparticles exhibit catalytic, optical, electronic, and magnetic synergy between their constituent metals. Typically, that synergy is traced to the domain structure and surface characteristics of such particles. Here these characteristics of coalescing Ag-Au nanoparticles of various initial sizes and morphologies (segregated or alloys) are investigated by atomistic molecular dynamics (MD) at different temperatures. Silver atoms exhibit increased mobility over Au and occupy gradually the surface of the coalesced (or sintered) bimetallic particle, consistent with scanning electron microscopy and selective O2 chemisorption experiments for heterogeneous catalysis of ethylene oxidation...
November 13, 2017: ACS Nano
https://www.readbyqxmd.com/read/29105856/rapid-iododeboronation-with-and-without-gold-catalysis-application-to-radiolabelling-of-arenes
#7
Stacey Webster, Kerry M O'Rourke, Conor Fletcher, Sally Pimlott, Andrew Sutherland, Ai-Lan Lee
Radiopharmaceuticals incorporating radioactive iodine in combination with SPECT imaging play a key role in nuclear medicine, with applications in drug development and disease diagnosis. Despite this importance, there are relatively few general methods for incorporating radioiodine into small molecules. Here we describe a rapid, air- and moisture-stable ipso-iododeboronation procedure using NIS, in the non-toxic and green solvent dimethyl carbonate. The fast reaction and mild conditions of the gold-catalysed method led to the development of a highly efficient process for radiolabelling of arenes, which constitutes the first example of an application of homogenous gold catalysis to selective radiosynthesis...
November 6, 2017: Chemistry: a European Journal
https://www.readbyqxmd.com/read/29104992/fluorescence-resonance-energy-transfer-fret-for-the-verification-of-dual-gold-catalysis
#8
O Halter, H Plenio
Fluorescence resonance energy transfer (FRET) in appropriately tagged NHC-gold complexes can be utilized to in situ observe the formation of digold species, which are known to be catalytically relevant intermediates in various gold catalyzed reactions.
November 16, 2017: Chemical Communications: Chem Comm
https://www.readbyqxmd.com/read/29098472/synthesis-and-co-oxidation-activity-of-1d-mixed-binary-oxide-ceo2-lao-x-supported-gold-catalysts
#9
Huanhuan Yu, Siyuan Zhong, Baolin Zhu, Weiping Huang, Shoumin Zhang
One-dimensional (1D) Ce-La nanorods with different La contents (Ce and La in the molar ratio of 1:0, 3:1, 1:1, 1:3, and 0:1) were synthesized by hydrothermal process. Au/Ce-La nanorod catalysts were obtained by a modified deposition-precipitation method. The samples were characterized by N2 adsorption-desorption (BET), ICP, X-ray diffraction (XRD), SEM, TEM, EDX, X-ray photoelectron spectroscopy (XPS), UV-vis diffuse reflectance spectroscopy (UV-vis DRS), and temperature-programmed reduction (H2-TPR). It revealed that La existed as LaO x in the 1D nanorods...
November 2, 2017: Nanoscale Research Letters
https://www.readbyqxmd.com/read/29091910/calculation-extinction-cross-sections-and-molar-attenuation-coefficient-of-small-gold-nanoparticles-and-experimental-observation-of-their-uv-vis-spectral-properties
#10
Junqi Tang, Kunpeng Gao, Quanhong Ou, Xuewen Fu, Shi-Qing Man, Jie Guo, Yingkai Liu
Gold nanoparticles (AuNPs) have been researched extensively, such as applied in various biosensors, biomedical imaging and diagnosis, catalysis and physico-chemical analysis. These applications usually required to know the nanoparticle size or concentration. Researchers have been studying a simply and quick way to estimate the concentration or size of nanoparticles from their optical spectra and SPR feature for several years. The extinction cross-sections and the molar attenuation coefficient were one of the key parameters...
October 20, 2017: Spectrochimica Acta. Part A, Molecular and Biomolecular Spectroscopy
https://www.readbyqxmd.com/read/29089478/direct-observation-of-the-nanoscale-kirkendall-effect-during-galvanic-replacement-reactions
#11
See Wee Chee, Shu Fen Tan, Zhaslan Baraissov, Michel Bosman, Utkur Mirsaidov
Galvanic replacement (GR) is a simple and widely used approach to synthesize hollow nanostructures for applications in catalysis, plasmonics, and biomedical research. The reaction is driven by the difference in electrochemical potential between two metals in a solution. However, transient stages of this reaction are not fully understood. Here, we show using liquid cell transmission electron microscopy that silver (Ag) nanocubes become hollow via the nucleation, growth, and coalescence of voids inside the nanocubes, as they undergo GR with gold (Au) ions at different temperatures...
October 31, 2017: Nature Communications
https://www.readbyqxmd.com/read/29071202/an-electrochemical-aptasensor-using-coaxial-capillary-with-magnetic-nanoparticle-urease-catalysis-and-pcb-electrode-for-rapid-and-sensitive-detection-of-escherichia-coli-o157-h7
#12
Lei Wang, Fengchun Huang, Gaozhe Cai, Lan Yao, Huilin Zhang, Jianhan Lin
The continuous outbreaks of foodborne diseases have drawn public attentions to food safety. Early screening of foodborne pathogens is crucial to prevent and control of foodborne diseases. In this study, a novel electrochemical aptasensor was developed for rapid and sensitive detection of E. coli O157:H7 using the coaxial capillary with immune magnetic nanoparticles (MNPs) for specific separation of the target bacteria, the urease with urea for amplification of the impedance signals, and the PCB gold electrode for measurement of the impedance change...
2017: Nanotheranostics
https://www.readbyqxmd.com/read/29058906/predicting-counterion-effects-using-a-gold-affinity-index-and-a-hydrogen-bonding-basicity-index
#13
Zhichao Lu, Junbin Han, Otome E Okoromoba, Naoto Shimizu, Hideki Amii, Cláudio F Tormena, Gerald B Hammond, Bo Xu
We have developed a gold affinity index and hydrogen bonding basicity index for counterions and have used these indexes to forecast their reactivity in cationic gold catalysis.
October 23, 2017: Organic Letters
https://www.readbyqxmd.com/read/29058889/remote-cooperative-group-strategy-enables-ligands-for-accelerative-asymmetric-gold-catalysis
#14
Zhixun Wang, Corrado Nicolini, Cedric Hervieu, Yuk-Fai Wong, Giuseppe Zanoni, Liming Zhang
An accelerative asymmetric gold catalysis is achieved for the first time via chiral ligand metal cooperation. An asymmetrically positioned remote amide group in the designed chiral binaphthyl-based ligand plays the essential role of a general base catalyst and selectively accelerates the cyclizations of 4-allen-1-ols into one prochiral allene face. The reactions are mostly highly enantioselective with achiral substrates, and due to the accelerated nature of the catalysis catalyst loadings as low as 100 ppm are allowed...
November 7, 2017: Journal of the American Chemical Society
https://www.readbyqxmd.com/read/29038430/two-dimensional-metallic-tantalum-disulfide-as-a-hydrogen-evolution-catalyst
#15
Jianping Shi, Xina Wang, Shuai Zhang, Lingfeng Xiao, Yahuan Huan, Yue Gong, Zhepeng Zhang, Yuanchang Li, Xiebo Zhou, Min Hong, Qiyi Fang, Qing Zhang, Xinfeng Liu, Lin Gu, Zhongfan Liu, Yanfeng Zhang
Two-dimensional metallic transition metal dichalcogenides are emerging as prototypes for uncovering fundamental physical phenomena, such as superconductivity and charge-density waves, as well as for engineering-related applications. However, the batch production of such envisioned transition metal dichalcogenides remains challenging, which has hindered the aforementioned explorations. Herein, we fabricate thickness-tunable tantalum disulfide flakes and centimetre-sized ultrathin films on an electrode material of gold foil via a facile chemical vapour deposition route...
October 16, 2017: Nature Communications
https://www.readbyqxmd.com/read/29035053/designed-bifunctional-phosphine-ligand-enabled-gold-catalyzed-isomerizations-of-ynamides-and-allenamides-stereoselective-and-regioselective-formation-of-1-amido-1-3-dienes
#16
Xingguang Li, Zhixun Wang, Xu Ma, Pei-Nian Liu, Liming Zhang
By using designed biphenyl-2-ylphosphines functionalized with a remote basic groups as ligands, N-alkynyl-o-nosylamides are directly converted to (1E,3E)-1-amido-1,3-dienes with excellent diastereoselectivities under gold catalysis. With allenamides as substrates, the gold-catalyzed isomerizations are high yielding and applicable to a broad substrate scope including various nitrogen protecting groups and exhibit unprecedented (3E)-selectivities for the distal C-C double bond and good regioselectivities. Combining this gold catalysis with one-pot Diels-Alder reactions leads to rapid assembly of valuable bicyclic compounds...
October 16, 2017: Organic Letters
https://www.readbyqxmd.com/read/29024556/synthesis-of-metal-nanoparticles-in-metal-phenolic-networks-catalytic-and-antimicrobial-applications-of-coated-textiles
#17
Gyeongwon Yun, Shuaijun Pan, Ting-Yi Wang, Junling Guo, Joseph J Richardson, Frank Caruso
The synthesis of metal nanoparticle (NP)-coated textiles (nanotextiles) is achieved by a dipping process in water without toxic chemicals or complicated synthetic procedures. By taking advantage of the unique nature of tannic acid, metal-phenolic network-coated textiles serve as reducing and stabilizing sites for the generation of metal nanoparticles of controllable size. The textiles can be decorated with various metal nanoparticles, including palladium, silver, or gold, and exhibit properties derived from the presence of the metal nanoparticles, for example, catalytic activity in water (>96% over five cycles using palladium nanoparticles) and antibacterial activity against Gram-negative bacteria (inhibition of Escherichia coli using silver nanoparticles) that outperforms a commercial bandage...
October 12, 2017: Advanced Healthcare Materials
https://www.readbyqxmd.com/read/29022942/facile-synthesis-of-gold-nanomaterials-with-unusual-crystal-structures
#18
Zhanxi Fan, Xiao Huang, Ye Chen, Wei Huang, Hua Zhang
Gold (Au) nanomaterials have attracted wide research attention, owing to their high chemical stability, promising catalytic properties, excellent biocompatibility, unique electronic structure and outstanding localized surface plasmon resonance (LSPR) absorption properties; all of which are closely related to their size and shape. Recently, crystal-phase-controlled synthesis of noble metal nanomaterials has emerged as a promising strategy to tune their physicochemical properties. This protocol describes the detailed experimental procedures for the crystal-phase-controlled syntheses of Au nanomaterials with unusual crystal structures under mild conditions...
November 2017: Nature Protocols
https://www.readbyqxmd.com/read/29022633/in-site-encapsulating-gold-nanowires-into-hemin-coupled-protein-scaffolds-through-biomimetic-assembly-towards-the-nanocomposites-with-strong-catalysis-electrocatalysis-and-fluorescence-properties
#19
Shuai Li, Liyan Zhang, Yao Jiang, Shuyun Zhu, Xiaoxia Lv, Zhiqiang Duan, Hua Wang
An efficient and green biomimetic assembly protocol was developed for the fabrication of multifunctional nanocomposites by mimicking the configuration of natural protein enzymes. Bovine serum albumin (BSA) as the protein model was first split to produce the disassembled BSA (dBSA) of linear polymer and then coupled with catalytic Hemin (Hem). The yielded dBSA-Hem scaffolds were utilized to in-site encapsulate gold nanoclusters (AuNCs) through biominerization, yielding the dBSA-Hem-AuNCs. It was discovered that the nanocomposites could display the well-defined composition and spheric morphology...
October 26, 2017: Nanoscale
https://www.readbyqxmd.com/read/29019658/resonance-enhancement-of-nonlinear-optical-scattering-in-monolayer-protected-gold-clusters
#20
Stefan Knoppe, Thierry Verbiest
Monolayer-protected metal clusters (MPCs) have recently gained significant research interest, since they are promising candidates for various applications in bioimaging and catalysis. Besides this, MPCs promise to aid in understanding the evolution of the metallic state from bottom-up principles. MPCs can be prepared with atomic precision, and their nonscalable properties (indicating molecule-like behavior) have been studied with a variety of techniques both theoretically and experimentally. Here, we present spectrally resolved second-order nonlinear optical scattering experiments on thiolate-protected gold clusters (Au130(SR)50, Au144(SR)60, and Au500(SR)120)...
October 16, 2017: Journal of the American Chemical Society
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