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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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    Role of the transmembrane domain in SNARE protein mediated membrane fusion: peptide nucleic acid/peptide model systems 

    Wehland, Jan-Dirk; Lygina, Antonina S.; Kumar, Pawan; Guha, Samit; Hubrich, Barbara E.; Jahn, Reinhard; Diederichsen, Ulf
    Mol. BioSyst. 2016; 12(9) p.2770-2776
    Fusion of synaptic vesicles with the presynaptic plasma membrane is mediated by Soluble NSF (N-ethylmaleimide-sensitive factor) Attachment Protein Receptor proteins also known as SNAREs. The backbone of this essential process is the assembly of SNAREs from opposite membranes into tight four helix bundles forcing membranes in close proximity. With model systems resembling SNAREs with reduced complexity we aim to understand how these proteins work at the molecular level. Here, peptide nucleic acids (PNAs) are used as excellent candidates for mimicking the SNARE recognition motif by forming well-characterized duplex structures. Hybridization between complementary PNA strands anchored in liposomes through native transmembrane domains (TMDs) induces the merger of the outer leaflets of the participating vesicles but not of the inner leaflets. A series of PNA/peptide hybrids differing in the length of TMDs and charges at the C-terminal end is presented. Interestingly, mixing of both outer and inner leaflets is seen for TMDs containing an amide in place of the natural carboxylic acid at the C-terminal end. Charged side chains at the C-terminal end of the TMDs are shown to have a negative impact on the mixing of liposomes. The length of the TMDs is vital for fusion as with the use of shortened TMDs, fusion was completely prevented.
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    Diffusion of single molecular and macromolecular probes during the free radical bulk polymerization of MMA – towards a better understanding of the Trommsdorff effect on a molecular level 

    Nölle, Jan Martin; Primpke, Sebastian; Müllen, Klaus; Vana, Philipp; Wöll, Dominik
    Polym. Chem. 2016; 7(24) p.4100-4105
    Free radical bulk polymerizations exhibit complex kinetics due to the viscosity increase during the polymerization process. Especially the termination rate constant can be strongly influenced by the mobility of polymer chains in the polymerization mixture. As a consequence an autoacceleration period, the so-called Trommsdorff effect, can be observed often. In order to investigate this behaviour on a nanoscopic scale, we directly visualized the mobility of molecules and macromolecules in polymerizing MMA solutions using a combination of highly sensitive fluorescence correlation spectroscopy and widefield fluorescence microscopy. For this purpose, rather monodisperse PMMA chains were synthesized by RAFT polymerization and fluorescence-labelled with perylenediimide derivatives. The behaviour of the different fluorescent probes could be related to their size and flexibility. Our studies show that diffusional heterogeneities must be accounted for when modeling bulk polymerization.
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    Ruthenium(ii)-catalyzed C–H functionalizations on benzoic acids with aryl, alkenyl and alkynyl halides by weak-O-coordination 

    Mei, Ruhuai; Zhu, Cuiju; Ackermann, Lutz
    Chem. Commun. 2016; 52(89) p.13171-13174
    C–H arylations of weakly coordinating benzoic acids were achieved by versatile ruthenium(II) catalysis with ample substrate scope. Thus, user-friendly ruthenium(II) biscarboxylate complexes modified with tricyclohexylphosphine enabled C–H functionalizations with aryl electrophiles. The unique versatility of the ruthenium(II) catalysis manifold was reflected by facilitating effective C–H activations with aryl, alkenyl and alkynyl halides.
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    C–H carboxylation of heteroarenes with ambient CO 2 

    Fenner, Sabine; Ackermann, Lutz
    Green Chem. 2016; 18(13) p.3804-3807
    The C–H carboxylation of heteroarenes was achieved under transition metal-free reaction conditions with naturally abundant CO2 as the C1 source at relatively low temperature. The C–H carboxylation was mediated by KOt-Bu at atmospheric pressure of CO2, and thereby provided atom- and step-economical access to various heteroaromatic carboxylic acid derivatives.
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    Heterogeneous catalytic approaches in C–H activation reactions 

    Santoro, Stefano; Kozhushkov, Sergei I.; Ackermann, Lutz; Vaccaro, Luigi
    Green Chem. 2016; 18(12) p.3471-3493
    Despite the undisputed advances and progress in metal-catalyzed C–H functionalizations, this atomeconomical approach had thus far largely been developed with the aid of various metal catalysts that were operative in a homogeneous fashion. While thereby major progress was accomplished, these catalytic systems featured notable disadvantages, such as low catalyst recyclability. This review summarizes the development of user-friendly, recyclable and easily separable heterogeneous catalysts for C–H activation. This strategy was characterized by a remarkably broad substrate scope, considerable levels of chemo- and site-selectivities and proved applicable to C–C as well as C–heteroatom formation processes. Thus, recyclable catalysts were established for arylations, hydroarylations, alkenylations, acylations, nitrogenations, oxygenations, or halogenations, among others. The rapid recent progress in selective heterogeneous C–H functionalizations during the last decade until December 2015 is reviewed.
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    Exposing elusive cationic magnesium–chloro aggregates in aluminate complexes through donor control 

    Brouillet, Etienne V.; Kennedy, Alan R.; Koszinowski, Konrad; McLellan, Ross; Mulvey, Robert E.; Robertson, Stuart D.
    Dalton Trans. 2016; 45(13) p.5590-5597
    The cationic magnesium moiety of magnesium organohaloaluminate complexes, relevant to rechargeable Mg battery electrolytes, typically takes the thermodynamically favourable dinuclear [Mg2Cl3]+ form in the solid-state. We now report that judicious choice of Lewis donor allows the deliberate synthesis and isolation of the hitherto only postulated mononuclear [MgCl]+ and trinuclear [Mg3Cl5]+ modifications, forming a comparable series with a common aluminate anion [(Dipp)(Me3Si)NAlCl3]−. By pre-forming the Al–N bond prior to introduction of the Mg source, a consistently reproducible protocol is reported. Usage of the green solvent 2-methyltetrahydrofuran in place of THF in the context of Mg/Al battery electrolyte type complexes is also promoted.
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