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Gold catalysis

Zhengnan Shen, Hani Mobarak, Wei Li, Göran Widmalm, Biao Yu
The β-(1-2)-linked 6-deoxy-L-altropyranose di- to penta-saccharides 2-5, relevant to the O-antigen of the infectious Yersinia enterocolitica O:3, were synthesized for the first time. The challenging 1,2-cis-altropyranosyl linkage was assembled effectively via glycosylation with 2-O-benzyl-3,4-di-O-benzoyl-6-deoxy-L-altropyranosyl ortho-hexynylbenzoate (7) under the catalysis of PPh3AuNTf2. NMR and molecular modeling studies showed that the pentasaccharide (5) adopted a left-handed helical conformation.
February 23, 2017: Journal of Organic Chemistry
Kasper Planeta Kepp
Gold plays a major role in nanochemistry, catalysis, and electrochemistry. Accordingly, hundreds of studies apply density functionals to study chemical bonding with gold, yet there is no systematic attempt to assess the accuracy of these methods applied to gold. This paper reports a benchmark against 51 experimental bond enthalpies of AuX systems and seven additional polyatomic and cationic molecules. 12 density functionals were tested, covering meta functionals, hybrids with variable HF exchange, double-hybrid, dispersion-corrected and non-hybrid GGA functionals...
February 17, 2017: Journal of Physical Chemistry. A
Kazuki Tsubokura, Kenward K H Vong, Ambara R Pradipta, Akihiro Ogura, Sayaka Urano, Tsuyoshi Tahara, Satoshi Nozaki, Hirotaka Onoe, Yoichi Nakao, Regina Sibgatullina, Almira Kurbangalieva, Yasuyoshi Watanabe, Katsunori Tanaka
Metal complex catalysis within biological systems is largely limited to cell and bacterial systems. In this work, a glycoalbumin-Au(III) complex was designed and developed that enables organ-specific, localized propargyl ester amidation with nearby proteins within live mice. The targeted reactivity can be imaged through the use of Cy7.5- and TAMRA-linked propargyl ester based fluorescent probes. This targeting system could enable the exploitation of other metal catalysis strategies for biomedical and clinical applications...
February 15, 2017: Angewandte Chemie
Yen-Chun Lee, Sumersing Patil, Christopher Golz, Carsten Strohmann, Slava Ziegler, Kamal Kumar, Herbert Waldmann
The selective transformation of different starting materials by different metal catalysts under individually optimized reaction conditions to structurally different intermediates and products is a powerful approach to generate diverse molecular scaffolds. In a more unified albeit synthetically challenging strategy, common starting materials would be exposed to a common metal catalysis, leading to a common intermediate and giving rise to different scaffolds by tuning the reactivity of the metal catalyst through different ligands...
February 14, 2017: Nature Communications
John R Finnegan, Jessica Gwyther, Ian Manners
Patch works! Patchy block copolymer micelles with a corona consisting of two chemically different patches have been designed for the selective binding of catalytically active nanoparticles. The fabrication of nonwoven supports by electrospinning was combined with crystallization-driven self-assembly for precise control over micelle formation to prepare a new recyclable catalyst platform.
February 10, 2017: Angewandte Chemie
Daksh Agarwal, Carlos Aspetti, Matteo Cargnello, Mingliang Ren, Jinkyoung Yoo, Christopher B Murray, Ritesh Agarwal
The field of plasmonics has attracted considerable attention in recent years because of potential applications in various fields such as nanophotonics, photovoltaics, energy conversion, catalysis and therapeutics. It is becoming increasing clear that intrinsic high losses associated with plasmons can be utilized to create new device concepts to harvest the generated heat. It is therefore important to design cavities, which can harvest optical excitations efficiently to generate heat. We report a highly engineered nanowire cavity, which utilizes a high dielectric silicon core with a thin plasmonic film (Au) to create an effective metallic cavity to strongly confine light, which when coupled with localized surface plasmons in the nanoparticles of the thin metal film produces exceptionally high temperatures upon laser irradiation...
February 6, 2017: Nano Letters
Jian-Fang Cui, Hok-Ming Ko, Ka-Pan Shing, Jie-Ren Deng, Nathanael Chun-Him Lai, Man-Kin Wong
Unprecedented stable BINOL/gold(III) complexes, adopting a novel C,O-chelation mode, were synthesized by a modular approach through combination of 1,1'-binaphthalene-2,2'-diols (BINOLs) and cyclometalated gold(III) dichloride complexes [(C^N)AuCl2 ]. X-ray crystallographic analysis revealed that the bidentate BINOL ligands tautomerized and bonded to the Au(III) atom through C,O-chelation to form a five-membered ring instead of the conventional O,O'-chelation giving a seven-membered ring. These gold(III) complexes catalyzed acetalization/cycloisomerization and carboalkoxylation of ortho-alkynylbenzaldehydes with trialkyl orthoformates...
February 6, 2017: Angewandte Chemie
Khwaja Salahuddin Siddiqi, Azamal Husen
For biosynthesis of gold nanoparticles different parts of a plant are used as they contain metabolites such as alkaloids, flavonoids, phenols, terpenoids, alcohols, sugars and proteins which act as reducing agents to produce nanoparticles. They also act as capping agent and stabilizer for them. They are used in medicine, agriculture and many other technologies. The attention is therefore focussed on all plant species which have either aroma or colour in their leaves, flowers or roots for the synthesis of nanoparticles because they all contain such chemicals which reduce the metal ions to metal nanoparticles...
March 2017: Journal of Trace Elements in Medicine and Biology
Pei Zuo, Lan Jiang, Xin Li, Bo Li, Yongda Xu, Xuesong Shi, Peng Ran, Tianbao Ma, Dawei Li, Liangti Qu, Yongfeng Lu, Costas P Grigoropoulos
Edge-active site control of MoS2 is crucial for applications such as chemical catalysis, synthesis of functional composites, and biochemical sensing. This work presents a novel nonthermal method to simultaneously tune surface chemical (edge-active sites) and physical (surface periodic micro/nano structures) properties of MoS2 using temporally shaped femtosecond pulses, through which shape-controlled gold nanoparticles are in situ and self-assembly grown on MoS2 surfaces to form Au-MoS2 hybrids. The edge-active sites with unbound sulfurs of laser-treated MoS2 drive the reduction of gold nanoparticles, while the surface periodic structures of laser-treated MoS2 assist the shape-controllable growth of gold nanoparticles...
February 3, 2017: ACS Applied Materials & Interfaces
Simona Neri, Sergio Garcia Martin, Cristian Pezzato, Leonard J Prins
The activity of a gold nanoparticle-based catalyst can be reversibly up- and down-regulated by light. Light is used to switch a small molecule between cis- and trans-isomers, which inhibits the catalytic activity of the nanoparticles to different extent. The system is functional in aqueous buffer, which paves the way for integrating the system in biological networks.
January 26, 2017: Journal of the American Chemical Society
Fu-Min Liao, Zhong-Yan Cao, Jin-Sheng Yu, Jian Zhou
We report a highly stereoselective synthesis of all-carbon or fluorinated tetrasubstituted alkenes from diazo reagents and fluorinated enol silyl ethers, using C-F bond as a synthetic handle. Cationic Au(I) catalysis plays a key role in this reaction. Remarkable fluorine effects on the reactivity and selectivity was also observed.
January 18, 2017: Angewandte Chemie
Courtney A Smith, Stephen E Motika, Lukasz Wojtas, Xiaodong Shi
An intermolecular condensation of alkynols and terminal alkynes is reported. Using IPrAuNTf2, an efficient Au-catalyzed cyclization-alkynylation strategy furnishes (2-arylalkynyl) cyclic ethers in moderate to excellent yields (up to 94%). This strategy is extended to the synthesis of functionalized 2,3-dihydrooxepines via the sequential Au-catalyzed ring expansion of the cyclic ether substrates.
February 16, 2017: Chemical Communications: Chem Comm
Kang Liu, Yanru Bu, Yuanhui Zheng, Xuchuan Jiang, Aibing Yu, Huanting Wang
Gold nanorods (AuNRs) are versatile materials due to their broadly tunable optical properties associated with their anisotropic feature. Conventional seed-mediated synthesis is, however, not only limited by the operational complexity and over-sensitivity towards subtle changes of experimental conditions but also suffers from low yield (≈15 %). A facile seedless method is reported to overcome these challenges. Monodispersed AuNRs with high yield (≈100 %) and highly adjustable longitudinal surface plasmon resonance (LSPR) are reproducibly synthesized...
January 10, 2017: Chemistry: a European Journal
Lucia Mora-Tamez, Vicente Esquivel-Peña, Ana Lilia Ocampo, Eduardo Rodríguez de San Miguel, Daniel Grande, Josefina de Gyves
A polymeric membrane-supported catalyst with immobilized gold nanoparticles (AuNPs) was prepared through the extraction and in-situ reduction of gold(III) salts in a one-step strategy. Polymeric inclusion membranes (PIMs) and polymeric nanoporous membranes (PNMs) were tested as different membrane support systems. Transport experiments indicated that PIMs composed of cellulose triacetate, 2-nitrophenyloctyl ether, and an aliphatic tertiary amine (Adogen® 364 or Alamine® 336) were the most efficient supports for Au(III) extraction...
January 7, 2017: ChemSusChem
Jun-Gang Wang, Xin Hua, Meng Li, Yi-Tao Long
Polydopamine functionalized plasmonic nanocomposites with well-distributed catalytically active small gold nanoislands around large gold core were fabricated without using any chemical reductant or surfactant. The optical properties, surface molecular structures, and ensemble catalytic activity of the gold nanocomposites were investigated by time-of-flight secondary ion mass spectrometry and UV-vis spectroscopy, respectively. Moreover, the considerable catalytic activity of the nanocomposites toward 4-nitrophenol reduction was real time monitored by dark-field spectroscopy techniques at the single-nanoparticle level avoiding averaging effects in bulk systems...
January 13, 2017: ACS Applied Materials & Interfaces
Jungjoon Kim, Wook Jeong, Young Ho Rhee
A flexible synthetic method toward highly substituted tetrahydropyran is reported. The key transformation involves atom-efficient sequential metal catalysis consisting of Pd-catalyzed addition of homopropargylic alcohols to alkoxyallene and the subsequent gold(I)-catalyzed cycloisomerization. Notably, this method gives access to both 2,6-cis- and 2,6-trans-tetrahydropyrans possessing diverse substitution patterns.
December 22, 2016: Organic Letters
Felix W W Hartrampf, Takayuki Furukawa, Dirk Trauner
An enantioselective total synthesis of the Lycopodium alkaloid lycoposerramine R is presented. It relies on a base-mediated cyclization that resembles the Conia-ene reaction of ynones and gold-catalyzed variants thereof. Thus, hydrindanones and other functionalized ring systems bearing an exocyclic alkene can be rapidly accessed at room temperature without noble metal catalysis or substrate preactivation.
December 21, 2016: Angewandte Chemie
Aslam C Shaikh, Dnyanesh S Ranade, Pattuparambil R Rajamohanan, Prasad P Kulkarni, Nitin T Patil
Oxidative intramolecular 1,2-amino-oxygenation reactions, combining gold(I)/gold(III) catalysis, is reported. The reaction provides efficient access to a structurally unique ionic pyridinium-oxazole dyad with tunable emission wavelengths. The application of these fluorophores as potential biomarkers has been investigated.
December 21, 2016: Angewandte Chemie
Jun Li, Lili Lin, Bowen Hu, Pengfei Zhou, Tianyu Huang, Xiaohua Liu, Xiaoming Feng
A highly efficient asymmetric cascade reaction between alkynyl esters and allylic alcohols has been realized. Key to success was the combination of a hydroalkoxylation reaction catalyzed by a π-acidic gold(I) complex with a Claisen rearrangement catalyzed by a chiral Lewis acidic N,N'-dioxide-nickel(II) complex. A range of acyclic α-allyl β-keto esters were synthesized in high yields (up to 99 %) with good diastereoselectivities (up to 97:3) and excellent enantioselectivities (up to 99 % ee) under mild reaction conditions...
December 20, 2016: Angewandte Chemie
Geoffroy Hervé Lonca, Ciputra Tejo, Hui Ling Chan, Shunsuke Chiba, Fabien Gagosz
Denitrogenative 6-endo-dig azide-yne cyclization of α-propargyloxy-β-haloalkylazides was enabled by gold catalysis, thus providing 2H-1,3-oxazines. This rare cyclization mode in gold-catalyzed reactions of azide-yne substrates was demonstrated to be facilitated and controlled by electronic and resonance effects of the alkyne substituents. Molecular transformations of the as-prepared 2H-1,3-oxazines were also investigated.
December 19, 2016: Chemical Communications: Chem Comm
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