Items 1-20 of 536

    • Journal Article

      Accurate Probabilities for Highly Activated Reaction of Polyatomic Molecules on Surfaces Using a High-Dimensional Neural Network Potential: CHD 3 + Cu(111) 

      Gerrits, N.; Shakouri, Khosrow; Behler, Jörg; Kroes, Geert-Jan
      The Journal of Physical Chemistry Letters 2019; 10(8) p.1763-1768
      An accurate description of reactive scattering of molecules on metal surfaces often requires the modeling of energy transfer between the molecule and the surface phonons. Although ab initio molecular dynamics (AIMD) can describe this energy transfer, AIMD is at present untractable for reactions with reaction probabilities smaller than 1%. Here, we show that it is possible to use a neural network potential to describe a polyatomic molecule reacting on a mobile metal surface with considerably reduced computational effort compared to AIMD. The highly activated reaction of CHD3 on Cu(111) is used as a test case for this method. It is observed that the reaction probability is influenced considerably by dynamical effects such as the bobsled effect and surface recoil. A special dynamical effect for CHD3 + Cu(111) is that a higher vibrational efficacy is obtained for two quanta in the CH stretch mode than for a single quantum.
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    • Journal Article

      Photochemically Driven Reverse Water-Gas Shift at Ambient Conditions mediated by a Nickel Pincer Complex 

      Schneck, Felix; Schendzielorz, Florian; Hatami, Nareh; Finger, Markus; Würtele, Christian; Schneider, Sven
      Angewandte Chemie International Edition 2018; 57(44) p.14482-14487
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    • Journal Article

      A Ruthenium Hydrido Dinitrogen Core Conserved across Multielectron/Multiproton Changes to the Pincer Ligand Backbone 

      Bruch, Quinton J.; Lindley, Brian M.; Askevold, Bjorn; Schneider, Sven; Miller, Alexander J. M.
      Inorganic Chemistry 2018; 57(4) p.1964-1975
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    • Journal Article

      Four- and Five-Coordinate Osmium(IV) Nitrides and Imides: Circumventing the “Nitrido Wall” 

      Abbenseth, Josh; Bete, Sarah C.; Finger, Markus; Volkmann, Christian; Würtele, Christian; Schneider, Sven
      Organometallics 2017; 37(5) p.802-811
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    • Journal Article

      Magnetoelastic hybrid excitations in CeAuAl3 

      Čermák, Petr; Schneidewind, Astrid; Liu, Benqiong; Koza, Michael Marek; Franz, Christian; Schönmann, Rudolf; Sobolev, Oleg; Pfleiderer, Christian
      Proceedings of the National Academy of Sciences 2019; 116(14) p.6695-6700
      Nearly a century of research has established the Born–Oppenheimer approximation as a cornerstone of condensed-matter systems, stating that the motion of the atomic nuclei and electrons may be treated separately. Interactions beyond the Born–Oppenheimer approximation are at the heart of magneto-elastic functionalities and instabilities. We report comprehensive neutron spectroscopy and ab initio phonon calculations of the coupling between phonons, CEF-split localized 4f electron states, and conduction electrons in the paramagnetic regime of CeAuAl3, an archetypal Kondo lattice compound. We identify two distinct magneto-elastic hybrid excitations that form even though all coupling constants are small. First, we find a CEF–phonon bound state reminiscent of the vibronic bound state (VBS) observed in other materials. However, in contrast to an abundance of optical phonons, so far believed to be essential for a VBS, the VBS in CeAuAl3 arises from a comparatively low density of states of acoustic phonons. Second, we find a pronounced anticrossing of the CEF excitations with acoustic phonons at zero magnetic field not observed before. Remarkably, both magneto-elastic excitations are well developed despite considerable damping of the CEFs that arises dominantly by the conduction electrons. Taking together the weak coupling with the simultaneous existence of a distinct VBS and anticrossing in the same material in the presence of damping suggests strongly that similarly well-developed magneto-elastic hybrid excitations must be abundant in a wide range of materials. In turn, our study of the excitation spectra of CeAuAl3 identifies a tractable point of reference in the search for magneto-elastic functionalities and instabilities.
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    • Journal Article

      High-resolution experimental and computational electrophysiology reveals weak β-lactam binding events in the porin PorB 

      Bartsch, Annika; Llabrés, Salomé; Pein, Florian; Kattner, Christof; Schön, Markus; Diehn, Manuel; Tanabe, Mikio; Munk, Axel; Zachariae, Ulrich; Steinem, Claudia
      Scientific Reports 2019; 9(1): Art. 1264
      The permeation of most antibiotics through the outer membrane of Gram-negative bacteria occurs through porin channels. To design drugs with increased activity against Gram-negative bacteria in the face of the antibiotic resistance crisis, the strict constraints on the physicochemical properties of the permeants imposed by these channels must be better understood. Here we show that a combination of high-resolution electrophysiology, new noise-filtering analysis protocols and atomistic biomolecular simulations reveals weak binding events between the β-lactam antibiotic ampicillin and the porin PorB from the pathogenic bacterium Neisseria meningitidis. In particular, an asymmetry often seen in the electrophysiological characteristics of ligand-bound channels is utilised to characterise the binding site and molecular interactions in detail, based on the principles of electro-osmotic flow through the channel. Our results provide a rationale for the determinants that govern the binding and permeation of zwitterionic antibiotics in porin channels.
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    • Journal Article

      Air-Stable Secondary Phosphine Oxides for Nickel-Catalyzed Cross-Couplings of Aryl Ethers by C–O Activation 

      Ghorai, Debasish; Loup, Joachim; Zanoni, Giuseppe; Ackermann, Lutz
      Synlett 2019; 30(04) p.429-432
      Air- and moisture-stable secondary phosphine oxides (SPOs) enabled nickel-catalyzed Kumada–Corriu cross-couplings of various arylmethyl ethers at room temperature by challenging C–O activation.
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    • Journal Article

      Di- and Tetrairon(III) μ-Oxido Complexes of an N3S-Donor Ligand: Catalyst Precursors for Alkene Oxidations 

      Das, Biswanath; Al-Hunaiti, Afnan; Sánchez-Eguía, Brenda N.; Zeglio, Erica; Demeshko, Serhiy; Dechert, Sebastian; Braunger, Steffen; Haukka, Matti; Repo, Timo; Castillo, Ivan; et al.
      Nordlander, Ebbe
      Frontiers in Chemistry 2019; 7 p.97-97
      The new di- and tetranuclear Fe(III) μ-oxido complexes [Fe4(μ-O)4(PTEBIA)4](CF3SO3)4(CH3CN)2] (1a), [Fe2(μ-O)Cl2(PTEBIA)2](CF3SO3)2 (1b), and [Fe2(μ-O)(HCOO)2(PTEBIA)2](ClO4)2 (MeOH) (2) were prepared from the sulfur-containing ligand (2-((2,4-dimethylphenyl)thio)-N,N-bis ((1-methyl-benzimidazol-2-yl)methyl)ethanamine (PTEBIA). The tetrairon complex 1a features four μ-oxido bridges, while in dinuclear 1b, the sulfur moiety of the ligand occupies one of the six coordination sites of each Fe(III) ion with a long Fe-S distance of 2.814(6) Å. In 2, two Fe(III) centers are bridged by one oxido and two formate units, the latter likely formed by methanol oxidation. Complexes 1a and 1b show broad sulfur-to-iron charge transfer bands around 400-430 nm at room temperature, consistent with mononuclear structures featuring Fe-S interactions. In contrast, acetonitrile solutions of 2 display a sulfur-to-iron charge transfer band only at low temperature (228 K) upon addition of H2O2/CH3COOH, with an absorption maximum at 410 nm. Homogeneous oxidative catalytic activity was observed for 1a and 1b using H2O2 as oxidant, but with low product selectivity. High valent iron-oxo intermediates could not be detected by UV-vis spectroscopy or ESI mass spectrometry. Rather, evidence suggest preferential ligand oxidation, in line with the relatively low selectivity and catalytic activity observed in the reactions.
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    • Journal Article

      Rational Design of Chiral Selenium-π-Acid Catalysts 

      Krätzschmar, Felix; Ortgies, Stefan; Willing, Robert; Breder, Alexander
      Catalysts 2019; 9(2): Art. 153
      A series of unprecedented chiral selenium- -acid catalysts for the asymmetric, oxidative functionalization of alkenes has been developed. In total, eleven different chiral dihydrodiselenocine and (di-)alkoxyphenyl (di)selenide motifs have been synthesized in a concise, modal, and straightforward fashion. Commercially available, non-racemic alcohols have been predominantly used as chiral building blocks for the facile assembly of the selenium- -acid catalysts. These species have been exemplarily applied to the enantioselective intermolecular imidation and intramolecular acyloxylation of two olefins using N-fluorobenzenesulfonimide (NFSI) and ambient air, respectively, as terminal oxidants. In part, the catalysts provide very good yields of up to 99% and enantiomeric ratios of up to 83.5:16.5 under aerobic conditions.
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    • Journal Article

      Serum and Serum Albumin Inhibit in vitro Formation of Neutrophil Extracellular Traps (NETs) 

      Neubert, Elsa; Senger-Sander, Susanne N.; Manzke, Veit S.; Busse, Julia; Polo, Elena; Scheidmann, Sophie E. F.; Schön, Michael P.; Kruss, Sebastian; Erpenbeck, Luise
      Frontiers in Immunology 2019; 10: Art. 12
      The formation of neutrophil extracellular traps (NETs) is an immune defense mechanism of neutrophilic granulocytes. Moreover, it is also involved in the pathogenesis of autoimmune, inflammatory, and neoplastic diseases. For that reason, the process of NET formation (NETosis) is subject of intense ongoing research. In vitro approaches to quantify NET formation are commonly used and involve neutrophil stimulation with various activators such as phorbol 12-myristate 13-acetate (PMA), lipopolysaccharides (LPS), or calcium ionophores (CaI). However, the experimental conditions of these experiments, particularly the media and media supplements employed by different research groups, vary considerably, rendering comparisons of results difficult. Here, we present the first standardized investigation of the influence of different media supplements on NET formation in vitro. The addition of heat-inactivated (hi) fetal calf serum (FCS), 0.5% human serum albumin (HSA), or 0.5% bovine serum albumin (BSA) efficiently prevented NET formation of human neutrophils following stimulation with LPS and CaI, but not after stimulation with PMA. Thus, serum components such as HSA, BSA and hiFCS (at concentrations typically found in the literature) inhibit NET formation to different degrees, depending on the NETosis inducer used. In contrast, in murine neutrophils, NETosis was inhibited by FCS and BSA, regardless of the inducer employed. This shows that mouse and human neutrophils have different susceptibilities toward the inhibition of NETosis by albumin or serum components. Furthermore, we provide experimental evidence that albumin inhibits NETosis by scavenging activators such as LPS. We also put our results into the context of media supplements most commonly used in NET research. In experiments with human neutrophils, either FCS (0.5-10%), heat-inactivated (hiFCS, 0.1-10%) or human serum albumin (HSA, 0.05-2%) was commonly added to the medium. For murine neutrophils, serum-free medium was used in most cases for stimulation with LPS and CaI, reflecting the different sensitivities of human and murine neutrophils to media supplements. Thus, the choice of media supplements greatly determines the outcome of experiments on NET-formation, which must be taken into account in NETosis research.
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    • Journal Article

      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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    • Journal Article

      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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    • Journal Article

      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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    • Journal Article

      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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    • Journal Article

      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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    • Journal Article

      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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    • Journal Article

      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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    • Journal Article

      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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    • Journal Article

      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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    • Journal Article

      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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