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Gold catalysis

Siyam M Ansar, Saptarshi Chakraborty, Christopher L Kitchens
Mercaptoundecanoic acid (MUA) functionalized gold nanoparticles (AuNP-MUA) were synthesized and demonstrated to possess pH-triggered aggregation and re-dispersion, as well as the capability of phase transfer between aqueous and organic phases in response to changes in pH. The pH of aggregation for AuNP-MUA is consistent with the pKa of MUA (pH ~4) in solution, while AuNP-MUA phase transition between aqueous and organic phases occurs at pH ~9. The ion pair formation between the amine group in octadecylamine (ODA), the carboxylate group in MUA, and the hydrophobic alkyl chain of ODA facilitates the phase transfer of AuNP-MUA into an organic medium...
May 17, 2018: Nanomaterials
Cristian Vidal, María Tomás-Gamasa, Paolo Destito, Fernando López, José L Mascareñas
The viability of building artificial metabolic pathways within a cell will depend on our ability to design biocompatible and orthogonal catalysts capable of achieving non-natural transformations. In this context, transition metal complexes offer unique possibilities to develop catalytic reactions that do not occur in nature. However, translating the potential of metal catalysts to living cells poses numerous challenges associated to their biocompatibility, and their stability and reactivity in crowded aqueous environments...
May 15, 2018: Nature Communications
Xuejiao Yang, Yuefei Wang, Wei Qi, Jiaxing Zhang, Liwei Zhang, Renliang Huang, Rongxin Su, Zhimin He
The photo-induced reconfigurable assembly of nanostructures via the simultaneous noncovalent and covalent polymerization of a functional ferrocene-tyrosine (Fc-Y) molecule is reported. The Fc-Y monomers can directly self-assemble into nanospheres with a smooth surface driven by noncovalent interactions. By covalent photo-crosslinking of the Fc-Y monomers, the nanospheres transform spontaneously into hollow vesicles composed of hierarchically ordered lamellar structures. It is worth noting that the formed nanostructures exhibit both reducing property for in situ mineralization of gold nanoparticles with tunable biocatalytic behavior, and the redox activity for superior energy storage capacity...
May 14, 2018: Small
Alex Plajer, Lukas Ahrens, Marcel Wieteck, Danilo M Lustosa, Rasool BabaAhmadi, Brian Yates, Alireza Ariafard, Matthias Rudolph, Frank Rominger, A Stephen K Hashmi
An unprecedented, often almost quantitative access to tricyclic aromatic compounds by dual gold catalysis was developed. This synthetic route expands the scope of benzofulvene derivatives through a C(sp2)-H bond insertion in easily available starting materials. The insertion takes place with an exclusive chemoselectivity with respect to the competing aromatic C-H positions. A bidirectional synthesis with two competing ortho-aryl C,H bonds in the selectivity-determining step also shows perfect selectivity; this result is explained by a computational investigation of the two conceivable intermediates...
May 14, 2018: Chemistry: a European Journal
Navnath D Rode, Issam Abdalghani, Antonio Arcadi, Massimiliano Aschi, Marco Chiarini, Fabio Marinelli
β-2-aminophenyl)-α,β-ynones afforded 3-unsubstituted 2-acylindoles in good yields in the presence of 20 mol% of AgOTf under MW heating. The use CuOTf as catalyst resulted in a similar reaction outcome, generally with a lower efficiency. This transformation represents the first example of 5-endo-dig cyclization of 2-alkynylanilines bearing an acyl group linked to the triple bond. By contrast with the previously reported gold-catalyzed reaction of β-2-aminophenyl)-α,β-ynones, that resulted in the formation of dibenzo[1,5]diazocines through a sequential process triggered by an intermolecular hydroamination, a selective intramolecular anti-Michael hydroamination was observed in the present study by mean of silver/copper catalysis...
May 14, 2018: Journal of Organic Chemistry
Youngsoo Kim, Jeremy G Smith, Prashant K Jain
Multi-electron redox reactions, although central to artificial photosynthesis, are kinetically sluggish. Amidst the search for synthetic catalysts for such processes, plasmonic nanoparticles have been found to catalyse multi-electron reduction of CO2 under visible light. This example motivates the need for a general, insight-driven framework for plasmonic catalysis of such multi-electron chemistry. Here, we elucidate the principles underlying the extraction of multiple redox equivalents from a plasmonic photocatalyst...
May 7, 2018: Nature Chemistry
Akbar Samadi, Henrik Klingberg, Liselotte Jauffred, Andreas Kjær, Poul Martin Bendix, Lene B Oddershede
Absorption of near infrared (NIR) light by metallic nanoparticles can cause extreme heating and is of interest for instance in cancer treatment since NIR light has a relatively large penetration depth into biological tissue. Here, we quantify the extraordinary thermoplasmonic properties of platinum nanoparticles and demonstrate their efficiency in photothermal cancer therapy. Although platinum nanoparticles are extensively used for catalysis, they are much overlooked in a biological context. Via direct measurements based on a biological matrix we show that individual irradiated platinum nanoparticles with diameters of 50-70 nm can easily reach surface temperatures up to 900 K...
May 2, 2018: Nanoscale
Ian McCue, Joshua Stuckner, Mitsu Murayama, Michael J Demkowicz
One way of expediting materials development is to decrease the need for new experiments by making greater use of published literature. Here, we use data mining and automated image analysis to gather new insights on nanoporous gold (NPG) without conducting additional experiments or simulations. NPG is a three-dimensional porous network that has found applications in catalysis, sensing, and actuation. We assemble and analyze published images from among thousands of publications on NPG. These images allow us to infer a quantitative description of NPG coarsening as a function of time and temperature, including the coarsening exponent and activation energy...
April 30, 2018: Scientific Reports
Shengrong Liao, Alessio Porta, Xinpeng Cheng, Xu Ma, Giuseppe Zanoni, Liming Zhang
Using our previously designed biphenyl-2-ylphosphine L2 featuring a remote tertiary amino group as an enabling ligand, we have developed the first gold-catalyzed intermolecular hydroalkenylation of alkynes. Synthetically valuable conjugated dienyl alcohols are formed in moderate to good yields. A range of alkenyltrifluoroborates are allowed as the alkenyl donor, and no erosion of alkene geometry and/or the propargylic configuration are detected. DFT calculations confirm the critical role of the remote basic group as a general base catalyst in promoting this novel gold catalysis in good efficiency...
April 27, 2018: Angewandte Chemie
Chongning Li, Libing Wang, Yanghe Luo, Aihui Liang, Guiqing Wen, Zhiliang Jiang
Fullerene exhibited strong catalysis of the redox reaction between HAuCl₄ and trisodium citrate to form gold nanoplasmon with a strong surface-enhanced Raman scattering (SERS) effect at 1615 cm−1 in the presence of Vitoria blue B molecule probes. When fullerene increased, the SERS peak enhanced linearly due to formation of more AuNPs as substrate. Upon addition of Ba2+ , Ba2+ ions adsorb on the fullerene surface to inhibit the catalysis of fullerene that caused the SERS peak decreasing. Analyte SO₄2− combined with Ba2+ to form stable BaSO₄ precipitate to release free fullerene that the catalysis recovered, and the SERS intensity increased linearly...
April 26, 2018: Nanomaterials
Alexander Schlimm, Nadja Stucke, Benedikt Maria Flöser, Talina Rusch, Jan Krahmer, Thomas Strunskus, Christian Näther, Olaf Magnussen, Felix Tuczek
Activating small molecules with transition metal complexes adsorbed on metallic surfaces is a novel approach combining aspects of homogeneous and heterogeneous catalysis. In order to study the influence of an Au(111) substrate on the activation of the small molecule ligand carbon monoxide a molybdenum triscarbonyl complex containing a PN3P pincer ligand is synthesized and investigated in the bulk, in solution and adsorbed on an Au(111) surface. Via a platform approach a perpendicular orientation of the molybdenum complex is achieved and confirmed by IRRAS and NEXAFS...
April 25, 2018: Chemistry: a European Journal
Alec H Christian, Zachary L Niemeyer, Matthew S Sigman, F Dean Toste
Herein, we report the integration of simple linear regressions with gold(I) catalysis to interrogate the influence of phosphine structure on metal-catalyzed organic transformations. We demonstrate that observed product ratios in [4 + 3]/[4 + 2] cycloisomerization processes are influenced by both steric and electronic properties of the phosphine, which can be represented by the Au-Cl distance. In contrast, the observed selectivity of a similar [2 + 3]/[2 + 2] cycloisomerization is governed by L/B1, a steric parameter...
June 2, 2017: ACS Catalysis
Bo Weng, Kang-Qiang Lu, Zichao Tang, Hao Ming Chen, Yi-Jun Xu
Recently, loading ligand-protected gold (Au) clusters as visible light photosensitizers onto various supports for photoredox catalysis has attracted considerable attention. However, the efficient control of long-term photostability of Au clusters on the metal-support interface remains challenging. Herein, we report a simple and efficient method for enhancing the photostability of glutathione-protected Au clusters (Au GSH clusters) loaded on the surface of SiO2 sphere by utilizing multifunctional branched poly-ethylenimine (BPEI) as a surface charge modifying, reducing and stabilizing agent...
April 18, 2018: Nature Communications
Matěj Velický, William R Hendren, Gavin Eugene Donnelly, Joel Michael Katzen, Robert M Bowman, Fumin Huang
Metals have been increasingly used as substrates in devices based on two-dimensional (2D) materials. However, the high reflectivity of bulk metals results in low optical contrast (<3%) and therefore poor visibility of transparent mono- and few-layer 2D materials on these surfaces. Here we demonstrate that by engineering the complex reflectivity of a purpose-designed multilayer heterostructure composed of thin Au films (2 - 8 nm) on SiO<sub>2</sub>/Si substrate, the optical contrast of graphene and graphene oxide (GO) can be significantly enhanced in comparison to bulk Au, up to about 3 and 5 times, respectively...
April 17, 2018: Nanotechnology
Koichiro Saito, Tetsu Tatsuma
The chirality of materials results in a wide variety of advanced technologies including image display, data storage, light management including negative refraction, and enantioselective catalysis and sensing. Here, we introduce chirality to plasmonic nanostructures by using circularly polarized light as the sole chiral source for the first time. Gold nanocuboids as precursors on a semiconductor were irradiated with circularly polarized light to localize electric fields at specific corners of the cuboids depending on the handedness of light and deposited dielectric moieties as electron oscillation boosters by the localized electric field...
April 17, 2018: Nano Letters
Xiaodong Shi, Jin Wang, Shuyao Zhang, Lukasz Wojtas, Novruz Akhmedov, Hao Chen, Chang Xu
A possible gold redox-catalyzed stereoselective thioallylation of alkynes was achieved. The reaction was accomplished with high efficiency (as low as 0.1% catalyst loading, up to 99% yield) and broad substrate scope (various alkynes, inter- and intramolecular fashion). The gold(I) catalyst acts as both pi-acid for alkyne activation and redox catalyst for Au(I/III) coupling, while the in-situ generated sulfonium cation functions as a mild oxidant. This novel methodology provides an exciting system for gold redox catalysis without the need of a strong oxidant...
April 16, 2018: Angewandte Chemie
Meng-Meng Xu, Hai-Qing Wang, Yu-Jia Mao, Guang-Jian Mei, Shu-Liang Wang, Feng Shi
A catalytic aymmetric α-arylation of aldehydes using 2-indolylmethanols as arylation reagents has been established. This reaction was enabled by a cooperative catalytic system consisting of a gold complex, a Brønsted acid and a chiral amine, which have a synergistic effect in the reaction process. By using this strategy, a series of α-arylation products of aldehydes were generated in overall acceptable yields and good enantioselectivities (up to 69%, 91:9 er). The control experiments demonstrated that the addition of PPh3AuCl as a gold complex was helpful to improve the yield, and trifluoroacetic acid as a Brønsted acid played a crucial role in the reaction by promoting the generation of carbocation and chiral enamine intermediates, which are two key intermediates of the aymmetric α-arylation reaction...
April 12, 2018: Journal of Organic Chemistry
Kai Liu, Guangyang Xu, Jiangtao Sun
An unprecedented dearomatization of indoles with diazoesters has been developed via cationic gold(i) catalysis. The functionalization selectively occurs at the C3-position to deliver methylene indole derivatives in good yields with excellent Z -selectivity, demonstrating unusual reactivity and selectivity compared with other noble metal catalysis. Importantly, simply followed by silica gel adsorption, an unprecedented metal-free aerobic oxidation occurs for indoles bearing N-electron donating substituents, providing a novel and efficient approach towards 3-substituted indolin-2-ones with a newly formed quaternary stereocenter in excellent stereoselectivity...
January 21, 2018: Chemical Science
Sarah A Lindley, Jason K Cooper, Mauricio D Rojas-Andrade, Victoria Fung, Conor J Leahy, Shaowei Chen, Jin Z Zhang
In principle, the diameter and surface plasmon resonance (SPR) frequency of hollow metal nanostructures can be independently adjusted, allowing the formation of targeted photoactivated structures of specific size and optical functionality. Although tunable SPRs have been reported for various systems, the shift in SPR is usually concomitant with a change in particle size. As such, more advanced tunability, including constant diameter with varying SPR or constant SPR with varying diameter, has not been properly achieved experimentally...
April 6, 2018: ACS Applied Materials & Interfaces
Yu-Bin Bai, Zaigang Luo, Yuguang Wang, Jin-Ming Gao, Liming Zhang
The [2+2] cycloaddition is a versatile strategy for the synthesis of strained cyclobutenes of high synthetic value. In this study, two efficient intermolecular [2+2] cycloadditions between two different types of chloroalkynes and unactivated alkene are realized with gold catalysis. Of significance is that the reaction works with challenging mono-substituted unac-tivated alkenes, which is unprecedented in gold catalysis and scarcely documented in other metal-catalyzed/promoted reactions; moreover, the reaction exhibits excellent regioselectivities, which are much better than those reported in litera-ture...
April 4, 2018: Journal of the American Chemical Society
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