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    Ruthenium(II)-catalysed remote C-H alkylations as a versatile platform to meta-decorated arenes. 

    Li, Jie; Korvorapun, Korkit; De Sarkar, Suman; Rogge, Torben; Burns, David J.; Warratz, Svenja; Ackermann, Lutz
    Nature communications 2017-06-09; 8: Art. 15430
    The full control of positional selectivity is of prime importance in C-H activation technology. Chelation assistance served as the stimulus for the development of a plethora of ortho-selective arene functionalizations. In sharp contrast, meta-selective C-H functionalizations continue to be scarce, with all ruthenium-catalysed transformations currently requiring difficult to remove or modify nitrogen-containing heterocycles. Herein, we describe a unifying concept to access a wealth of meta-decorated arenes by a unique arene ligand effect in proximity-induced ruthenium(II) C-H activation catalysis. The transformative nature of our strategy is mirrored by providing a step-economical entry to a range of meta-substituted arenes, including ketones, acids, amines and phenols-key structural motifs in crop protection, material sciences, medicinal chemistry and pharmaceutical industries.
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    In Search of the Reason for the Breathing Effect of MIL53 Metal-Organic Framework: An ab Initio Multiconfigurational Study 

    Weser, Oskar; Veryazov, Valera
    Frontiers in Chemistry 2017; 5: Art. 111
    Multiconfigurational methods are applied to study electronic properties and structural changes in the highly flexible metal-organic framework MIL53(Cr). Via calculated bending potentials of angles, that change the most during phase transition, it is verified that the high flexibility of this material is not a question about special electronic properties in the coordination chemistry, but about overall linking of the framework. The complex posseses a demanding electronic structure with delocalized spin density, antifferomagnetic coupling and high multi-state character requiring multiconfigurational methods. Calculated properties are in good agreement with known experimental values confirming our chosen methods.
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    Membrane tension increases fusion efficiency of model membranes in the presence of SNAREs. 

    Kliesch, Torben-Tobias; Dietz, Jörn; Turco, Laura; Halder, Partho; Polo, Elena; Tarantola, Marco; Jahn, Reinhard; Janshoff, Andreas
    Scientific reports 2017-09-21; 7(1): Art. 12070
    The large gap in time scales between membrane fusion occurring in biological systems during neurotransmitter release and fusion observed between model membranes has provoked speculations over a large number of possible factors that might explain this discrepancy. One possible reason is an elevated lateral membrane tension present in the presynaptic membrane. We investigated the tension-dependency of fusion using model membranes equipped with a minimal fusion machinery consisting of syntaxin 1, synaptobrevin and SNAP 25. Two different strategies were realized; one based on supported bilayers and the other one employing sessile giant liposomes. In the first approach, isolated patches of planar bilayers derived from giant unilamellar vesicles containing syntaxin 1 and preassembled SNAP 25 (ΔN-complex) were deposited on a dilatable PDMS sheet. In a second approach, lateral membrane tension was controlled through the adhesion of intact giant unilamellar vesicles on a functionalized surface. In both approaches fusion efficiency increases considerably with lateral tension and we identified a threshold tension of 3.4 mN m(-1), at which the number of fusion events is increased substantially.
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    Iron L2,3-Edge X-ray Absorption and X-ray Magnetic Circular Dichroism Studies of Molecular Iron Complexes with Relevance to the FeMoco and FeVco Active Sites of Nitrogenase 

    Kowalska, Joanna K.; Nayyar, Brahamjot; Rees, Julian A.; Schiewer, Christine E.; Lee, Sonny C.; Kovacs, Julie A.; Meyer, Franc; Weyhermüller, Thomas; Otero, Edwige; DeBeer, Serena
    Inorganic Chemistry 2017; 56(14) p.8147-8158
    Herein, a systematic study of a series of molecular iron model complexes has been carried out using Fe L2,3-edge X-ray absorption (XAS) and X-ray magnetic circular dichroism (XMCD) spectroscopies. This series spans iron complexes of increasing complexity, starting from ferric and ferrous tetrachlorides ([FeCl4]−/2–), to ferric and ferrous tetrathiolates ([Fe(SR)4]−/2–), to diferric and mixed-valent iron–sulfur complexes [Fe2S2R4]2–/3–. This test set of compounds is used to evaluate the sensitivity of both Fe L2,3-edge XAS and XMCD spectroscopy to oxidation state and ligation changes. It is demonstrated that the energy shift and intensity of the L2,3-edge XAS spectra depends on both the oxidation state and covalency of the system; however, the quantitative information that can be extracted from these data is limited. On the other hand, analysis of the Fe XMCD shows distinct changes in the intensity at both L3 and L2 edges, depending on the oxidation state of the system. It is also demonstrated that the XMCD intensity is modulated by the covalency of the system. For mononuclear systems, the experimental data are correlated with atomic multiplet calculations in order to provide insights into the experimental observations. Finally, XMCD is applied to the tetranuclear heterometal–iron–sulfur clusters [MFe3S4]3+/2+ (M = Mo, V), which serve as structural analogues of the FeMoco and FeVco active sites of nitrogenase. It is demonstrated that the XMCD data can be utilized to obtain information on the oxidation state distribution in complex clusters that is not readily accessible for the Fe L2,3-edge XAS data alone. The advantages of XMCD relative to standard K-edge and L2,3-edge XAS are highlighted. This study provides an important foundation for future XMCD studies on complex (bio)inorganic systems.
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    Accurate Neural Network Description of Surface Phonons in Reactive Gas–Surface Dynamics: N 2 + Ru(0001) 

    Shakouri, Khosrow; Behler, Jörg; Meyer, Jörg; Kroes, Geert-Jan
    The Journal of Physical Chemistry Letters 2017; 8(10) p.2131-2136
    Ab initio molecular dynamics (AIMD) simulations enable the accurate description of reactive molecule-surface scattering especially if energy transfer involving surface phonons is important. However, presently, the computational expense of AIMD rules out its application to systems where reaction probabilities are smaller than about 1%. Here we show that this problem can be overcome by a high-dimensional neural network fit of the molecule-surface interaction potential, which also incorporates the dependence on phonons by taking into account all degrees of freedom of the surface explicitly. As shown for N2 + Ru(0001), which is a prototypical case for highly activated dissociative chemisorption, the method allows an accurate description of the coupling of molecular and surface atom motion and accurately accounts for vibrational properties of the employed slab model of Ru(0001). The neural network potential allows reaction probabilities as low as 10-5 to be computed, showing good agreement with experimental results.
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    Identifying the first folded alkylbenzene via ultraviolet, infrared, and Raman spectroscopy of pentylbenzene through decylbenzene 

    Hewett, Daniel M.; Bocklitz, Sebastian; Tabor, Daniel P.; Sibert III, Edwin L.; Suhm, Martin A.; Zwier, Timothy S.
    Chemical Science 2017; 2017(8) p.5305-5318
    The conformational preferences of pentyl- through decylbenzene are studied under jet-cooled conditions in the gas phase. Laser-induced fluorescence excitation spectra, fluorescence-dip infrared spectra in the alkyl CH stretch region, and Raman spectra are combined to provide assignments for the observed conformers. Density functional theory calculations at the B3LYP-D3BJ/def2TZVP level of theory provide relative energies and normal mode vibrations that serve as inputs for an anharmonic local mode theory introduced in earlier work on alkylbenzenes with n = 2–4. This model explicitly includes anharmonic mixing of the CH stretch modes with the overtones of scissors/bend modes of the CH2 and CH3 groups in the alkyl chain, and is used to assign and interpret the single-conformation IR spectra. In octylbenzene, a pair of LIF transitions shifted −92 and −78 cm−1 from the all-trans electronic origin have unique alkyl CH stretch transitions that are fit by the local model to a g1g3g4 conformation in which the alkyl chain folds back over the aromatic ring π cloud. Its calculated energy is only 1.0 kJ mol−1 above the all-trans global minimum. This fold is at an alkyl chain length less than half that of the pure alkanes (n = 18), consistent with a smaller energy cost for the g1 dihedral and the increased dispersive interaction of the chain with the π cloud. Local site frequencies for the entire set of conformers from the local mode model show ‘edge effects’ that raise the site frequencies of CH2(1) and CH2(2) due to the phenyl ring and CH2(n − 1) due to the methyl group. The g1g3g4 conformer also shows local sites shifted up in frequency at CH2(3) and CH2(6) due to interaction with the π cloud.
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    Tuning Selectivity of Fluorescent Carbon Nanotube-Based Neurotransmitter Sensors. 

    Mann, Florian A.; Herrmann, Niklas; Meyer, Daniel; Kruss, Sebastian
    Sensors (Basel, Switzerland) 2017-06-28; 17(7): Art. 1521
    Detection of neurotransmitters is an analytical challenge and essential to understand neuronal networks in the brain and associated diseases. However, most methods do not provide sufficient spatial, temporal, or chemical resolution. Near-infrared (NIR) fluorescent single-walled carbon nanotubes (SWCNTs) have been used as building blocks for sensors/probes that detect catecholamine neurotransmitters, including dopamine. This approach provides a high spatial and temporal resolution, but it is not understood if these sensors are able to distinguish dopamine from similar catecholamine neurotransmitters, such as epinephrine or norepinephrine. In this work, the organic phase (DNA sequence) around SWCNTs was varied to create sensors with different selectivity and sensitivity for catecholamine neurotransmitters. Most DNA-functionalized SWCNTs responded to catecholamine neurotransmitters, but both dissociation constants (Kd) and limits of detection were highly dependent on functionalization (sequence). Kd values span a range of 2.3 nM (SWCNT-(GC)15 + norepinephrine) to 9.4 μM (SWCNT-(AT)15 + dopamine) and limits of detection are mostly in the single-digit nM regime. Additionally, sensors of different SWCNT chirality show different fluorescence increases. Moreover, certain sensors (e.g., SWCNT-(GT)10) distinguish between different catecholamines, such as dopamine and norepinephrine at low concentrations (50 nM). These results show that SWCNTs functionalized with certain DNA sequences are able to discriminate between catecholamine neurotransmitters or to detect them in the presence of interfering substances of similar structure. Such sensors will be useful to measure and study neurotransmitter signaling in complex biological settings.
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    Cooperativity in Alcohol–Nitrogen Complexes: Understanding Cryomatrices through Slit Jet Expansions 

    Oswald, Sönke; Wallrabe, Mareike; Suhm, Martin A.
    The Journal of Physical Chemistry A 2017; 121(18) p.3411-3422
    FTIR spectroscopy of supersonic expansions is used to characterize alcohol dimers with one, two, and several nitrogen molecules attached to them. The nitrogen coating causes progressive spectral downshifts of the OH stretching fundamentals which are related to and explain matrix isolation shifts. Comparison of methanol, tert-butyl alcohol and ethanol as well as deuteration of methanol assist in the assignment. Alcohol monomers and trimers are significantly more resistant to nitrogen coating due to a lack of cooperativity and dangling bonds, respectively. In the case of ethanol, the role of conformational isomerism and combination bands is further elucidated. The experimental findings help rationalize the anomalously small OH stretching dimerization shift of methanol in the gas phase, in comparison to that of tert-butyl alcohol.
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    Catalytic Synthesis of N-Heterocycles via Direct C(sp3)–H Amination Using an Air-Stable Iron(III) Species with a Redox-Active Ligand 

    Bagh, Bidraha; Broere, Daniël L. J.; Sinha, Vivek; Kuijpers, Petrus F.; van Leest, Nicolaas P.; de Bruin, Bas; Demeshko, Serhiy; Siegler, Maxime A.; van der Vlugt, Jarl Ivar
    Journal of the American Chemical Society 2017; 139 p.1520-5126
    Coordination of FeCl3 to the redox-active pyridine−aminophenol ligand NNOH2 in the presence of base and under aerobic conditions generates FeCl2(NNOISQ) (1), featuring high-spin FeIII and an NNOISQ radical ligand. The complex has an overall S = 2 spin state, as deduced from experimental and computational data. The ligand-centered radical couples antiferromagnetically with the Fe center. Readily available, well-defined, and air-stable 1 catalyzes the challenging intramolecular direct C(sp3)−H amination of unactivated organic azides to generate a range of saturated N-heterocycles with the highest turnover number (TON) (1 mol% of 1, 12 h, TON = 62; 0.1 mol% of 1, 7 days, TON = 620) reported to date. The catalyst is easily recycled without noticeable loss of catalytic activity. A detailed kinetic study for C(sp3)−H amination of 1-azido-4-phenylbutane (S1) revealed zero order in the azide substrate and first order in both the catalyst and Boc2O. A cationic iron complex, generated from the neutral precatalyst upon reaction with Boc2O, is proposed as the catalytically active species.
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    Aptamers provide superior stainings of cellular receptors studied under super-resolution microscopy 

    Gomes de Castro, Maria Angela; Höbartner, Claudia; Opazo, Felipe
    PLOS ONE 2017; 12(2): Art. e0173050
    Continuous improvements in imaging techniques are challenging biologists to search for more accurate methods to label cellular elements. This is particularly relevant for diffraction-unlimited fluorescence imaging, where the perceived resolution is affected by the size of the affinity probes. This is evident when antibodies, which are 10–15 nm in size, are used. Previously it has been suggested that RNA aptamers (~3 nm) can be used to detect cellular proteins under super-resolution imaging. However, a direct comparison between several aptamers and antibodies is needed, to clearly show the advantages and/or disadvantages of the different probes. Here we have conducted such a comparative study, by testing several aptamers and antibodies using stimulated emission depletion microscopy (STED). We have targeted three membrane receptors, EGFR, ErbB2 and Epha2, which are relevant to human health, and recycle between plasma membrane and intracellular organelles. Our results suggest that the aptamers can reveal more epitopes than most antibodies, thus providing a denser labeling of the stained structures. Moreover, this improves the overall quality of the information that can be extracted from the images. We conclude that aptamers could become useful fluorescent labeling tools for light microscopy and super-resolution imaging, and that their development for novel targets is imperative.
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    Electronic and Magnetic Nano Phase Separation in Cobaltates La2−x Sr x CoO4 

    Li, Z. W.; Drees, Y.; Ricci, A.; Lamago, D.; Piovano, A.; Rotter, M.; Schmidt, W.; Sobolev, O.; Rütt, U.; Gutowski, O.; et al.
    Sprung, M.Castellan, J. P.Tjeng, L. H.Komarek, A. C.
    Journal of Superconductivity and Novel Magnetism 2015; 29(3) p.727-731
    The single-layer perovskite cobaltates have attracted enormous attention due to the recent observation of hour-glass shaped magnetic excitation spectra which resemble the ones of the famous high-temperature superconducting cuprates. Here, we present an overview of our most recent studies of the spin and charge correlations in floating-zone grown cobaltate single crystals. We find that frustration and a novel kind of electronic and magnetic nano phase separation are intimately connected to the appearance of the hour-glass shaped spin excitation spectra. We also point out the difference between nano phase separation and conventional phase separation.
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    Vaccinia Virus Immunomodulator A46: A Lipid and Protein-Binding Scaffold for Sequestering Host TIR-Domain Proteins 

    Fedosyuk, Sofiya; Bezerra, Gustavo Arruda; Radakovics, Katharina; Smith, Terry K.; Sammito, Massimo; Bobik, Nina; Round, Adam; Ten Eyck, Lynn F.; Djinović-Carugo, Kristina; Usón, Isabel; et al.
    Skern, Tim
    PLOS Pathogens 2016; 12(12): Art. e1006079
    Vaccinia virus interferes with early events of the activation pathway of the transcriptional factor NF-kB by binding to numerous host TIR-domain containing adaptor proteins. We have previously determined the X-ray structure of the A46 C-terminal domain; however, the structure and function of the A46 N-terminal domain and its relationship to the C-terminal domain have remained unclear. Here, we biophysically characterize residues 1±83 of the N-terminal domain of A46 and present the X-ray structure at 1.55 Å. Crystallographic phases were obtained by a recently developed ab initio method entitled ARCIMBOLDO_BORGES that employs tertiary structure libraries extracted from the Protein Data Bank; data analysis revealed an all β-sheet structure. This is the first such structure solved by this method which should be applicable to any protein composed entirely of β-sheets. The A46(1±83) structure itself is a β-sandwich containing a co-purified molecule of myristic acid inside a hydrophobic pocket and represents a previously unknown lipid-binding fold. Mass spectrometry analysis confirmed the presence of long-chain fatty acids in both N-terminal and full-length A46; mutation of the hydrophobic pocket reduced the lipid content. Using a combination of high resolution X-ray structures of the N- and C-terminal domains and SAXS analysis of full-length protein A46(1±240), we present here a structural model of A46 in a tetrameric assembly. Integrating affinity measurements and structural data, we propose how A46 simultaneously interferes with several TIR-domain containing proteins to inhibit NF-κB activation and postulate that A46 employs a bipartite binding arrangement to sequester the host immune adaptors TRAM and MyD88.
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    Water oxidation mediated by ruthenium oxide nanoparticles supported on siliceous mesocellular foam 

    Gustafson, Karl P. J.; Shatskiy, Andrey; Verho, Oscar; Kärkäs, Markus D.; Schluschass, Bastian; Tai, Cheuk-Wai; Åkermark, Björn; Bäckvall, Jan-Erling; Johnston, Eric V.
    Catal. Sci. Technol. 2017; 7(1) p.293-299
    Artificial photosynthesis is an attractive strategy for converting solar energy into fuel. In this context, development of catalysts for oxidation of water to molecular oxygen remains a critical bottleneck. Herein, we describe the preparation of a well-defined nanostructured RuO2 catalyst, which is able to carry out the oxidation of water both chemically and photochemically. The developed heterogeneous RuO2 nanocatalyst was found to be highly active, exceeding the performance of most known heterogeneous water oxidation catalysts when driven by chemical or photogenerated oxidants.
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    Reaction cross sections and thermal rate constant for Cl− + CH 3 Br → ClCH 3+ Br− from J-dependent quantum scattering calculations 

    Hennig, Carsten; Schmatz, Stefan
    Phys. Chem. Chem. Phys. 2016; 18(29) p.19668-19675
    Employing dimensionality-reduced time-independent quantum scattering theory and summation over all possible total angular momentum states, initial-state selected reaction cross sections for the exothermic gas-phase bimolecular nucleophilic substitution (SN2) reaction Cl + CH3Br - ClCH3 + Br have been calculated. The carbon–halogen bonds and the rotation of the methyl halides are taken into account. In agreement with previous calculations for J = 0, initial rotational motion of CH3Br decreases the reaction probability and consequently the cross sections. The experimentally obtained thermal rate constant for 300 K is reproduced within the experimental error. For lower temperatures, it is calculated to be below the experimental values but shows the same strong increase for T - 0.
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    Metal-catalyzed direct alkylations of (hetero)arenes via C–H bond cleavages with unactivated alkyl halides 

    Ackermann, Lutz
    Chemical Communications 2010; 46(27)
    Significant progress has been made in direct alkylations of (hetero)arenes with unactivated alkyl halides. Thus, C–H bond functionalizations were accomplished with b-hydrogen-containing alkyl halides in the presence of palladium, nickel or ruthenium catalysts under basic reaction conditions. A valuable asset of these methodologies is represented by their excellent regio- and chemoselectivities, along with remarkable mild reaction conditions, rendering this approach an attractive alternative to traditional alkylation strategies.
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    Ruthenium-catalyzed oxidative C–H alkenylation of aryl carbamates 

    Li, Jie; Kornhaaß, Christoph; Ackermann, Lutz
    Chemical Communications 2012; 48(92)
    A cationic ruthenium(II) catalyst enabled highly efficient oxidative alkenylations of electron-rich arenes bearing removable, weakly coordinating carbamates, and allowed for cross-dehydrogenative C–H bond functionalization in an aerobic manner.
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    C–H nitrogenation and oxygenation by ruthenium catalysis 

    Thirunavukkarasu, Vedhagiri S.; Kozhushkov, Sergei I.; Ackermann, Lutz
    Chem. Commun. 2014; 50(1) p.29-39
    Remarkable recent progress has been accomplished in direct C–H functionalizations for the formation of C–N and C–O bonds through the use of readily accessible ruthenium catalysts. Particularly, ruthenium(II) complexes allowed for challenging direct C(sp2)–H hydroxylation of arenes. These catalysts set the stage for step-economical C–H functionalization with electron-rich as well as electron-deficient (hetero)arenes and, therefore, provided versatile access to diversely decorated phenols. While a number of synthetically useful protocols for ruthenium-catalyzed C(sp3)–H bond nitrogenation have been elaborated, the analogous transformations of more stable C(sp2)–H bonds were very recently achieved.
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    Ruthenium-catalyzed ortho-C–H halogenations of benzamides 

    Wang, Lianhui; Ackermann, Lutz
    Chem. Commun. 2014; 50(9) p.1083-1085
    [Ru3(CO)12] and AgO2C(1-Ad) enabled the first ruthenium-catalyzed intermolecular halogenations of arenes via C–H activation. Thereby, brominations and iodinations of electron-rich and electron-deficient benzamides were achieved in a highly selective fashion.
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    C–H arylations of 1,2,3-triazoles by reusable heterogeneous palladium catalysts in biomass-derived γ-valerolactone 

    Tian, Xu; Yang, Fanzhi; Rasina, Dace; Bauer, Michaela; Warratz, Svenja; Ferlin, Francesco; Vaccaro, Luigi; Ackermann, Lutz
    Chem. Commun. 2016; 52(63) p.9777-9780
    C–H arylations were accomplished with a user-friendly heterogeneous palladium catalyst in the biomass-derived c-valerolactone (GVL) as an environmentally-benign reaction medium. The userfriendly protocol was characterized by ample substrate scope and high functional group tolerance in the C–H arylation of 1,2,3- triazoles, and the palladium catalyst could be recycled and reused in the C–H activation process.
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    Heterogeneous palladium-catalysed Catellani reaction in biomass-derived γ-valerolactone 

    Rasina, Dace; Kahler-Quesada, Arianna; Ziarelli, Simone; Warratz, Svenja; Cao, Hui; Santoro, Stefano; Ackermann, Lutz; Vaccaro, Luigi
    Green Chem. 2016; 18(18) p.5025-5030
    Herein, we report the unprecedented use of a heterogeneous palladium catalyst for the step-economical Catellani reaction. The substrate scope with encapsulated Pd(OAc)2 (Pd EnCat™ 30) or Pd/Al2O3 proved to be broad, while the renewable biomass-derived γ-valerolactone (GVL) was identified as an effective reaction medium. Mechanistic studies highlighted the possible heterogeneous nature of the Pd/Al2O3 catalyst, while showing that the reaction performed in the presence of Pd EnCat™ 30 is most likely catalysed by leached homogeneous palladium species. The heterogeneous Pd/Al2O3 catalyst can be easily recovered at the end of the reaction and efficiently reused in consecutive reaction runs.
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