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Chemical Science

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https://www.readbyqxmd.com/read/28058105/c-h-functionalization-of-amines-with-aryl-halides-by-nickel-photoredox-catalysis
#1
Derek T Ahneman, Abigail G Doyle
We describe the functionalization of α-amino C-H bonds with aryl halides using a combination of nickel and photoredox catalysis. This direct C-H, C-X coupling uses inexpensive and readily available starting materials to generate benzylic amines, an important class of bioactive molecules. Mechanistically, this method features the direct arylation of α-amino radicals mediated by a nickel catalyst. This reactivity is demonstrated for a range of aryl halides and N-aryl amines, with orthogonal scope to existing C-H activation and photoredox methodologies...
December 1, 2016: Chemical Science
https://www.readbyqxmd.com/read/28042468/achieving-nano-gold-stability-through-rational-design
#2
Dean H Barrett, Michael S Scurrell, Cristiane B Rodella, Beatriz Diaz, David G Billing, Paul J Franklyn
When Au is subdivided to the nanoscale its reactivity changes from an inert nature to one of incredible reactivity which is not replicated by other catalysts. When dispersed onto metal oxides such as TiO2, nano-Au has shown high reactivities for a multitude of reduction and oxidation reactions of industrial importance with potential and current uses such as, CO oxidation, NO x reduction, purification of hydrogen for fuel cells, water gas shift reactions, abatement of volatile organic compounds (VOC's) as well as pollution and emission control systems such as autocatalysts...
November 18, 2016: Chemical Science
https://www.readbyqxmd.com/read/28042467/a-protein-dye-hybrid-system-as-a-narrow-range-tunable-intracellular-ph-sensor
#3
Palapuravan Anees, Karivachery V Sudheesh, Purushothaman Jayamurthy, Arunkumar R Chandrika, Ramakrishnapillai V Omkumar, Ayyappanpillai Ajayaghosh
Accurate monitoring of pH variations inside cells is important for the early diagnosis of diseases such as cancer. Even though a variety of different pH sensors are available, construction of a custom-made sensor array for measuring minute variations in a narrow biological pH window, using easily available constituents, is a challenge. Here we report two-component hybrid sensors derived from a protein and organic dye nanoparticles whose sensitivity range can be tuned by choosing different ratios of the components, to monitor the minute pH variations in a given system...
November 18, 2016: Chemical Science
https://www.readbyqxmd.com/read/28042466/a-multicomponent-approach-for-the-preparation-of-homoallylic-alcohols
#4
Jian-Siang Poh, Shing-Hing Lau, Iain G Dykes, Duc N Tran, Claudio Battilocchio, Steven V Ley
Here we report the in situ generation of transient allylic boronic species, by reacting TMSCHN2 and E-vinyl boronic acids, followed by their subsequent trapping with aldehydes as electrophiles to yield homoallylic alcohols. This metal-free reaction was initially discovered by the use of a flow chemistry approach to generate a variety of homoallylic alcohols in a straightforward fashion and then transferred to a batch protocol.
November 18, 2016: Chemical Science
https://www.readbyqxmd.com/read/28042465/photocatalyst-size-controls-electron-and-energy-transfer-selectable-e-z-isomer-synthesis-via-c-f-alkenylation
#5
A Singh, C J Fennell, J D Weaver
Photocatalytic alkene synthesis can involve electron and energy transfer processes. The structure of the photocatalyst can be used to control the rate of the energy transfer, providing a mechanistic handle over the two processes. Jointly considering catalyst volume and emissive energy provides a highly sensitive strategy for predicting which mechanistic pathway will dominate. This model was developed en route to a photocatalytic Caryl-F alkenylation reaction of alkynes and highly-fluorinated arenes as partners...
November 18, 2016: Chemical Science
https://www.readbyqxmd.com/read/28042464/reactive-oxygen-species-in-iridium-based-oer-catalysts
#6
Verena Pfeifer, Travis E Jones, Sabine Wrabetz, Cyriac Massué, Juan J Velasco Vélez, Rosa Arrigo, Michael Scherzer, Simone Piccinin, Michael Hävecker, Axel Knop-Gericke, Robert Schlögl
Tremendous effort has been devoted towards elucidating the fundamental reasons for the higher activity of hydrated amorphous Ir(III/IV) oxyhydroxides (IrO x ) in the oxygen evolution reaction (OER) in comparison with their crystalline counterpart, rutile-type IrO2, by focusing on the metal oxidation state. Here we demonstrate that, through an analogy to photosystem II, the nature of this reactive species is not solely a property of the metal but is intimately tied to the electronic structure of oxygen. We use a combination of synchrotron-based X-ray photoemission and absorption spectroscopies, ab initio calculations, and microcalorimetry to show that holes in the O 2p states in amorphous IrO x give rise to a weakly bound oxygen that is extremely susceptible to nucleophilic attack, reacting stoichiometrically with CO already at room temperature...
November 18, 2016: Chemical Science
https://www.readbyqxmd.com/read/28042463/correction-design-principles-of-spectroscopic-probes-for-biological-applications
#7
Jin Zhou, Huimin Ma
Correction for 'Design principles of spectroscopic probes for biological applications' by Jin Zhou et al., Chem. Sci., 2016, DOI: 10.1039/c6sc02500e.
October 19, 2016: Chemical Science
https://www.readbyqxmd.com/read/28042462/correction-a-universal-chemical-potential-for-sulfur-vapours
#8
Adam J Jackson, Davide Tiana, Aron Walsh
Correction for 'A universal chemical potential for sulfur vapours' by Adam J. Jackson et al., Chem. Sci., 2016, 7, 1082-1092.
October 19, 2016: Chemical Science
https://www.readbyqxmd.com/read/28042461/correction-photoredox-mediated-minisci-c-h-alkylation-of-n-heteroarenes-using-boronic-acids-and-hypervalent-iodine
#9
Guo-Xing Li, Cristian A Morales-Rivera, Yaxin Wang, Fang Gao, Gang He, Peng Liu, Gong Chen
Correction for 'Photoredox-mediated Minisci C-H alkylation of N-heteroarenes using boronic acids and hypervalent iodine' by Guo-Xing Li et al., Chem. Sci., 2016, DOI: ; 10.1039/c6sc02653b.
October 19, 2016: Chemical Science
https://www.readbyqxmd.com/read/28042460/asperterpenes-a-and-b-two-unprecedented-meroterpenoids-from-aspergillus-terreus-with-bace1-inhibitory-activities
#10
Changxing Qi, Jian Bao, Jianping Wang, Hucheng Zhu, Yongbo Xue, Xiaochuan Wang, Hua Li, Weiguang Sun, Weixi Gao, Yongji Lai, Jian-Guo Chen, Yonghui Zhang
Asperterpenes A (1) and B (2), two 3,5-dimethylorsellinic acid-based meroterpenoids that contain a unique β-oriented Me-21 with an unprecedented 1,2,5-trimethyl-4,9-dioxobicyclo[3.3.1]non-2-ene-3-carboxylic acid moiety, were obtained from Aspergillus terreus in very limited amounts of 3.6 mg and 1.8 mg, respectively. The absolute structure of 1 was determined using X-ray diffraction. Because of the low yield of 1, a comprehensive characterization of the BACE1 inhibitory activities of 1 was completed via molecular biological, cell and animal studies guided by in silico target confirmation (ISTC)...
October 19, 2016: Chemical Science
https://www.readbyqxmd.com/read/28042459/precision-targeted-ruthenium-ii-luminophores-highly-effective-probes-for-cell-imaging-by-stimulated-emission-depletion-sted-microscopy
#11
Aisling Byrne, Christopher S Burke, Tia E Keyes
Fluorescence microscopy has undergone a dramatic evolution over the past two decades with development of super-resolution far-field microscopy methods that break the light diffraction limited resolution of conventional microscopy, offering unprecedented opportunity to interrogate cellular processes at the nanoscale. However, these methods make special demands of the luminescent agents used for contrast and development of probes suited to super-resolution fluorescent methods is still relatively in its infancy...
October 19, 2016: Chemical Science
https://www.readbyqxmd.com/read/27928494/synthetically-tuneable-biomimetic-artificial-photosynthetic-reaction-centres-that-closely-resemble-the-natural-system-in-purple-bacteria
#12
Sai-Ho Lee, Iain M Blake, Allan G Larsen, James A McDonald, Kei Ohkubo, Shunichi Fukuzumi, Jeffrey R Reimers, Maxwell J Crossley
Porphyrin-based photosynthetic reaction centre (PRC) mimics, ZnPQ-Q2HP-C60 and MP2Q-Q2HP-C60 (M = Zn or 2H), designed to have a similar special-pair electron donor and similar charge-separation distances, redox processes and photochemical reaction rates to those in the natural PRC from purple bacteria, have been synthesised and extensive photochemical studies performed. Mechanisms of electron-transfer reactions are fully investigated using femtosecond and nanosecond transient absorption spectroscopy. In benzonitrile, all models show picosecond-timescale charge-separations and the final singlet charge-separations with the microsecond-timescale...
October 19, 2016: Chemical Science
https://www.readbyqxmd.com/read/27928493/putting-an-ultrahigh-concentration-of-amine-groups-into-a-metal-organic-framework-for-co2-capture-at-low-pressures
#13
Pei-Qin Liao, Xun-Wei Chen, Si-Yang Liu, Xu-Yu Li, Yan-Tong Xu, Minni Tang, Zebao Rui, Hongbing Ji, Jie-Peng Zhang, Xiao-Ming Chen
Tremendous efforts have been devoted to increasing the CO2 capture performance of porous materials, especially for low CO2 concentration environments. Here, we report that hydrazine can be used as a diamine short enough to functionalize the small-pore metal-organic framework [Mg2(dobdc)] (H4dobdc = 2,5-dihydroxyl-1,4-benzenedicarboxylic acid). By virtue of the ultrahigh concentration of free amine groups (6.01 mmol g(-1) or 7.08 mmol cm(-3)) capable of reversible carbamic acid formation, the new material [Mg2(dobdc)(N2H4)1...
October 19, 2016: Chemical Science
https://www.readbyqxmd.com/read/27928492/trigonal-antiprismatic-co-ii-single-molecule-magnets-with-large-uniaxial-anisotropies-importance-of-raman-and-tunneling-mechanisms
#14
Yuan-Zhu Zhang, Silvia Gómez-Coca, Andrew J Brown, Mohamed R Saber, Xuan Zhang, Kim R Dunbar
The air-stable mononuclear Co(ii) compounds [Co(II)(Tpm)2][ClO4]2 (1, Tpm = tris(pyrazol-1-yl)methane), [Co(II)(Tpm)2][BPh4]2·2MeCN (2) with trigonal antiprismatic geometry (trigonally elongated octahedral geometry) are reported. Magnetic and theoretical studies reveal that the complexes exhibit single-molecule magnet behavior with uniaxial anisotropy and a huge energy difference between ground and first excited Karmers' doublets (∼200 cm(-1)). Under applied DC fields, compounds 1 and 2 exhibit frequency and temperature dependence of the imaginary susceptibility...
October 19, 2016: Chemical Science
https://www.readbyqxmd.com/read/27928491/thermally-controlling-the-singlet-triplet-energy-gap-of-a-diradical-in-the-solid-state
#15
Yuanting Su, Xingyong Wang, Lei Wang, Zaichao Zhang, Xinping Wang, You Song, Philip P Power
Diradicals, molecules with two unpaired electrons, are reactive intermediates that play an important role in many fields. Their defining feature is the energy difference between their singlet and triplet states, which provides direct information on the extent of their electron exchange interactions. Such knowledge is essential for understanding their diradical character, which is controllable internally by modification of the electronic and steric properties of the substituents. We now report that the energy gap of a diradical in the solid state can also be controlled by an external stimulus...
October 19, 2016: Chemical Science
https://www.readbyqxmd.com/read/27746892/asymmetric-synthesis-of-chiral-%C3%AE-alkynyl-carbonyl-and-sulfonyl-derivatives-via-sequential-palladium-and-copper-catalysis
#16
Barry M Trost, James T Masters, Benjamin R Taft, Jean-Philip Lumb
We present a full account detailing the development of a sequential catalysis strategy for the synthesis of chiral β-alkynyl carbonyl and sulfonyl derivatives. A palladium-catalyzed cross coupling of terminal alkyne donors with acetylenic ester, ketone, and sulfone acceptors generates stereodefined enynes in high yield. These compounds are engaged in an unprecedented, regio- and enantioselective copper-catalyzed conjugate reduction. The process exhibits a high functional group tolerance, and this enables the synthesis of a broad range of chiral products from simple, readily available alkyne precursors...
September 16, 2016: Chemical Science
https://www.readbyqxmd.com/read/27746891/a-low-spin-manganese-iv-nitride-single-molecule-magnet
#17
Mei Ding, George E Cutsail, Daniel Aravena, Martín Amoza, Mathieu Rouzières, Pierre Dechambenoit, Yaroslav Losovyj, Maren Pink, Eliseo Ruiz, Rodolphe Clérac, Jeremy M Smith
Structural, spectroscopic and magnetic methods have been used to characterize the tris(carbene)borate compound PhB(MesIm)3Mn≡N as a four-coordinate manganese(IV) complex with a low spin (S = 1/2) configuration. The slow relaxation of the magnetization in this complex, i.e. its single-molecule magnet (SMM) properties, is revealed under an applied dc field. Multireference quantum mechanical calculations indicate that this SMM behavior originates from an anisotropic ground doublet stabilized by spin-orbit coupling...
September 1, 2016: Chemical Science
https://www.readbyqxmd.com/read/27617079/controlling-amphiphilic-copolymer-self-assembly-morphologies-based-on-macrocycle-anion-recognition-and-nucleotide-induced-payload-release
#18
Xiaofan Ji, Hu Wang, Yang Li, Danyu Xia, Hao Li, Guping Tang, Jonathan L Sessler, Feihe Huang
We report here a new approach to creating diversiform copolymer-derived self-assembly morphologies that relies on macrocycle/anion recognition in aqueous media. This approach exploits the anion binding features of a water-soluble form of the so-called 'Texas-sized' molecular box. When this tetracationic receptor is added to an aqueous solution of an amphiphilic copolymer bearing tethered carboxylate anion substituents, binding occurs to form a macrocycle/polymer complex. As the concentration of the box-like receptor increases, the relative hydrophilic fraction of the copolymer complex likewise increases...
September 1, 2016: Chemical Science
https://www.readbyqxmd.com/read/27547299/correlating-drug-target-kinetics-and-in-vivo-pharmacodynamics-long-residence-time-inhibitors-of-the-fabi-enoyl-acp-reductase
#19
Fereidoon Daryaee, Andrew Chang, Johannes Schiebel, Yang Lu, Zhuo Zhang, Kanishk Kapilashrami, Stephen G Walker, Caroline Kisker, Christoph A Sotriffer, Stewart L Fisher, Peter J Tonge
Drug-target kinetics enable time-dependent changes in target engagement to be quantified as a function of drug concentration. When coupled to drug pharmacokinetics (PK), drug-target kinetics can thus be used to predict in vivo pharmacodynamics (PD). Previously we described a mechanistic PK/PD model that successfully predicted the antibacterial activity of an LpxC inhibitor in a model of Pseudomonas aeruginosa infection. In the present work we demonstrate that the same approach can be used to predict the in vivo activity of an enoyl-ACP reductase (FabI) inhibitor in a model of methicillin-resistant Staphylococcus aureus (MRSA) infection...
September 1, 2016: Chemical Science
https://www.readbyqxmd.com/read/27708751/dual-mode-of-cell-death-upon-the-photo-irradiation-of-a-ru-ii-polypyridyl-complex-in-interphase-or-mitosis
#20
Vanessa Pierroz, Riccardo Rubbiani, Christian Gentili, Malay Patra, Cristina Mari, Gilles Gasser, Stefano Ferrari
Photodynamic therapy (PDT) is an attractive, complementary medical technique to chemotherapy. Among the different photosensitizers (PSs) employed, Ru(ii) polypyridyl complexes were found to be valid substitutes to porphyrin-based or phthalocyanine-based PSs. Here, we confirm that one such complex, namely [Ru(bipy)2-dppz-7-methoxy][PF6]2 (Ru65), which localizes in the nucleus of various cancer and normal cells, displays cytotoxicity only upon UV-A irradiation. Importantly, we disclose the molecular mechanism of the UV-A mediated cytotoxic action of Ru65...
August 16, 2016: Chemical Science
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