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    Analysis of Energy Dissipation Channels in a Benchmark System of Activated Dissociation: N2 on Ru(0001). 

    Shakouri, Khosrow; Behler, Jörg; Meyer, Jörg; Kroes, Geert-Jan
    The Journal of Physical Chemistry. C, Nanomaterials and Interfaces 2018; 122(41) p.23470-23480
    The excitation of electron-hole pairs in reactive scattering of molecules at metal surfaces often affects the physical and dynamical observables of interest, including the reaction probability. Here, we study the influence of electron-hole pair excitation on the dissociative chemisorption of N2 on Ru(0001) using the local density friction approximation method. The effect of surface atom motion has also been taken into account by a high-dimensional neural network potential. Our nonadiabatic molecular dynamics simulations with electronic friction show that the reaction of N2 is more strongly affected by the energy transfer to surface phonons than by the energy loss to electron-hole pairs. The discrepancy between the computed reaction probabilities and experimental results is within the experimental error both with and without friction; however, the incorporation of electron-hole pairs yields somewhat better agreement with experiments, especially at high collision energies. We also calculate the vibrational efficacy for the N2 + Ru(0001) reaction and demonstrate that the N2 reaction is more enhanced by exciting the molecular vibrations than by adding an equivalent amount of energy into translation.
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    Chromatin swelling drives neutrophil extracellular trap release 

    Neubert, Elsa; Meyer, Daniel; Rocca, Francesco; Günay, Gökhan; Kwaczala-Tessmann, Anja; Grandke, Julia; Senger-Sander, Susanne; Geisler, Claudia; Egner, Alexander; Schön, Michael P.; et al.
    Erpenbeck, LuiseKruss, Sebastian
    Nature Communications 2018; 9(1): Art. 3767
    Neutrophilic granulocytes are able to release their own DNA as neutrophil extracellular traps (NETs) to capture and eliminate pathogens. DNA expulsion (NETosis) has also been documented for other cells and organisms, thus highlighting the evolutionary conservation of this process. Moreover, dysregulated NETosis has been implicated in many diseases, including cancer and inflammatory disorders. During NETosis, neutrophils undergo dynamic and dramatic alterations of their cellular as well as sub-cellular morphology whose biophysical basis is poorly understood. Here we investigate NETosis in real-time on the single-cell level using fluorescence and atomic force microscopy. Our results show that NETosis is highly organized into three distinct phases with a clear point of no return defined by chromatin status. Entropic chromatin swelling is the major physical driving force that causes cell morphology changes and the rupture of both nuclear envelope and plasma membrane. Through its material properties, chromatin thus directly orchestrates this complex biological process.
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    Dinitrogen Splitting Coupled to Protonation 

    Silantyev, Gleb A.; Förster, Moritz; Schluschaß, Bastian; Abbenseth, Josh; Würtele, Christian; Volkmann, Christian; Holthausen, Max C.; Schneider, Sven
    Angewandte Chemie International Edition 2017; 56(21) p.5872-5876
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    A Square-Planar Osmium(II) Complex 

    Abbenseth, Josh; Diefenbach, Martin; Bete, Sarah C.; Würtele, Christian; Volkmann, Christian; Demeshko, Serhiy; Holthausen, Max C.; Schneider, Sven
    Chemical Communications 2017; 53(40) p.5511-5514
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    Chemical Non-Innocence of an Aliphatic PNP Pincer Ligand 

    Schneck, Felix; Finger, Markus; Tromp, Moniek; Schneider, Sven
    Chemistry - A European Journal 2016; 23(1) p.33-37
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    A Terminal Osmium(IV) Nitride: Ammonia Formation and Ambiphilic Reactivity 

    Schendzielorz, Florian S.; Finger, Markus; Volkmann, Christian; Würtele, Christian; Schneider, Sven
    Angewandte Chemie International Edition 2016; 55(38) p.11417-11420
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    Conversion of Dinitrogen into Acetonitrile under Ambient Conditions 

    Klopsch, Isabel; Kinauer, Markus; Finger, Markus; Würtele, Christian; Schneider, Sven
    Angewandte Chemie International Edition 2016; 55(15) p.4786-4789
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    Polyethylene-Grafted Gold and Silver Nanoparticles Using Catalyzed Chain Growth (CCG) 

    Wagner, Jannik; Peng, Wentao; Vana, Philipp
    Polymers 2018; 10(4): Art. 407
    We report an efficient synthesis route for the formation of gold/silver-core–PE-shell nanohybrids in a simple self-assembly approach using PE with strong aurophilicity and argentophilicity, via thiol- and trithiocarbonate terminated moieties. This united the unique properties of polyethylene (PE) with gold and silver nanoparticles, using the well-defined end-group design of PE. These nanocomposites showed a similar solubility as PE, as confirmed by dynamic light scattering, and could be fully incorporated into a polyethylene matrix with different particle contents, as visualized by transmission electron microscopy. Using UV/vis-spectroscopy, we observed reversible, thermoresponsive aggregation/deaggregation properties in the nanohybrids, validating the strong and effective anchoring of PE on gold/silver surfaces.
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    The elusive abnormal CO2 insertion enabled by metal-ligand cooperative photochemical selectivity inversion 

    Schneck, Felix; Ahrens, Jennifer; Finger, Markus; Stückl, A. Claudia; Würtele, Christian; Schwarzer, Dirk; Schneider, Sven
    Nature Communications 2018; 9(1) p.1-8: Art. 1161
    Direct hydrogenation of CO2 to CO, the reverse water-gas shift reaction, is an attractive route to CO2 utilization. However, the use of molecular catalysts is impeded by the general reactivity of metal hydrides with CO2. Insertion into M-H bonds results in formates (MO(O)CH), whereas the abnormal insertion to the hydroxycarbonyl isomer (MC(O)OH), which is the key intermediate for CO-selective catalysis, has never been directly observed. We here report that the selectivity of CO2 insertion into a Ni-H bond can be inverted from normal to abnormal insertion upon switching from thermal to photochemical conditions. Mechanistic examination for abnormal insertion indicates photochemical N-H reductive elimination as the pivotal step that leads to an umpolung of the hydride ligand. This study conceptually introduces metal-ligand cooperation for selectivity control in photochemical transformations.
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    A Square-Planar Osmium(II) Complex 

    Abbenseth, Josh; Diefenbach, Martin; Bete, Sarah C.; Würtele, Christian; Volkmann, Christian; Demeshko, Serhiy; Holthausen, Max C.; Schneider, Sven
    Chemical Communications 2017; 53(40) p.5511-5514
    Reduction of the pincer complex [OsIIICl2(PNP)] (PNP = N(CHCHPtBu2)2) affords the isolation and full characterization of an osmium(II) complex with square-planar coordination geometry, i.e. [OsIICl(PNP)]. Spectroscopic, structural and magnetic data in combination with multireference computations indicate strong temperature independent paramagnetism, which arises from an energetically well separated ground state that mixes with excited states through spin-orbit coupling.
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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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    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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