Dr. Lukas Kaltschnee  Dr. Anil P. Jagtap  Dr. Jeffrey McCormick  Dr. Shawn Wagner  Prof. Dr. Louis-S. Bouchard  Prof. Dr. Marcel Utz  Prof. Dr. Christian Griesinger  Dr. Stefan Glöggler 《Chemistry (Weinheim an der Bergstrasse, Germany)》2019,25(47):11031-11035

NMR offers many possibilities in chemical analysis, structural investigations, and medical diagnostics. Although it is broadly used, one of NMR spectroscopies main drawbacks is low sensitivity. Hyperpolarization techniques enhance NMR signals by more than four orders of magnitude allowing the design of new contrast agents. Parahydrogen induced polarization that utilizes the para-hydrogen's singlet state to create enhanced signals is of particular interest since it allows to produce molecular imaging agents within seconds. Herein, we present a strategy for signal enhancement of the carbonyl ¹³C in amino acids by using parahydrogen, as demonstrated for glycine and alanine. Importantly, the hyperpolarization step is carried out in water and chemically unmodified canonical amino acids are obtained. Our approach thus offers a high degree of biocompatibility, which is crucial for further application. The rapid sample hyperpolarization (within seconds) may enable the continuous production of biologically useful probes, such as metabolic contrast agents or probes for structural biology.  相似文献   

    

Daniela. S. Mattes  Bettina Streit  Dhaka R. Bhandari  Juliane Greifenstein  Tobias C. Foertsch  Stephan W. Münch  Barbara Ridder  Clemens v. Bojni i&#x;‐Kninski  Alexander Nesterov‐Mueller  Bernhard Spengler  Ute Schepers  Stefan Brse  Felix F. Loeffler  Frank Breitling 《Macromolecular rapid communications》2019,40(6)

Here, the combinatorial synthesis of molecule arrays via a laser‐assisted process is reported. Laser‐transferred polymer nanolayers with embedded monomers, activators, or bases can be reliably stacked on top of each other, spot‐by‐spot, to synthesize molecule arrays. These various chemicals in the nanometer‐thin layers are mixed by heat or solvent vapor, inducing coupling reactions. As an example, peptoid arrays with a density of 10 000 spots per cm² with the sub‐monomer or monomer method are generated. Moreover, successful reactions spot‐by‐spot are verified by laser‐transferring MALDI‐matrix (Matrix‐assisted laser desorption/ionization) followed by MALDI mass spectrometry imaging.  相似文献   

    

Raluca‐Ioana Stefan‐van&#x;Staden  Mariana Mincu  Jacobus Frederick van&#x;Staden 《Electroanalysis》2019,31(7):1342-1347

Two stochastic microsensors based on immobilization of the complex between protoporphyrin IX and cobalt on nanographene paste and on the reduced graphene oxide paste were proposed for the simultaneous identification and quantification of bisphenols A (BPA), F (BPF) and Z (BPZ) from water samples. The signatures obtained for the BPA, BPF, and BFZ when both stochastic microsensors were used shown that the microsensors can be used for the discrimination between the three bisphenols in water samples. Very low limits of determination were obtained for the three bisphenols: 1fmol/L for BPA and BPF when the microsensor based on the immobilization of the complex between protoporphyrin IX and cobalt on nanographene paste was used, and 10fmol/L for BPZ when the microsensor based on the immobilization of the complex between protoporphyrin IX and cobalt on reduced graphene oxide paste was used. The linear concentration ranges covered by the proposed stochastic microsensors were: between 10^?15 and 10^?5 mol/L for BPA, between 10^?15 and 10^?7 mol/L for BPF, and between 10^?13 and 10^?10 mol/L for BPZ. The recoveries of the bisphenols in water samples were higher than 99.50 %, with RSD values lower than 1.00 %.  相似文献   

    

Dragos Mutruc  Alexis Goulet‐Hanssens  Sam Fairman  Sebastian Wahl  Annett Zimathies  Christopher Knie  Stefan Hecht 《Angewandte Chemie (International ed. in English)》2019,58(37)

  相似文献   

    

Yann K. Petit  Christian Leypold  Nika Mahne  Elonore Mourad  Lukas Schafzahl  Christian Slugovc  Sergey M. Borisov  Stefan A. Freunberger 《Angewandte Chemie (International ed. in English)》2019,58(20):6535-6539

Singlet oxygen (¹O₂) causes a major fraction of the parasitic chemistry during the cycling of non‐aqueous alkali metal‐O₂ batteries and also contributes to interfacial reactivity of transition‐metal oxide intercalation compounds. We introduce DABCOnium, the mono alkylated form of 1,4‐diazabicyclo[2.2.2]octane (DABCO), as an efficient ¹O₂ quencher with an unusually high oxidative stability of ca. 4.2 V vs. Li/Li⁺. Previous quenchers are strongly Lewis basic amines with too low oxidative stability. DABCOnium is an ionic liquid, non‐volatile, highly soluble in the electrolyte, stable against superoxide and peroxide, and compatible with lithium metal. The electrochemical stability covers the required range for metal–O₂ batteries and greatly reduces ¹O₂ related parasitic chemistry as demonstrated for the Li–O₂ cell.  相似文献   

    

Aulbach  Stefan  Falk  Michael  Fuller  Timo 《Annals of the Institute of Statistical Mathematics》2019,71(3):599-626

Annals of the Institute of Statistical Mathematics - A multivariate distribution function F is in the max-domain of attraction of an extreme value distribution if and only if this is true for the...  相似文献   

    

Stefan Knoche  Dr. Maurice Heid  Niklas Gora  Dominik Ohlig  Prof. Dr. Alfons Drochner  Prof. Dr. Christian Hess  Prof. Dr. Bastian Etzold  Prof. Dr. Herbert Vogel 《ChemCatChem》2019,11(14):3242-3252

Gas phase oxidation of acrolein to acrylic acid on hydrothermally prepared Mo/V/W mixed oxides was investigated by isotopic labeling of acrolein. In this context, perdeuterated acrolein was synthesized for the first time and subsequently used for mechanistic studies. A clear kinetic isotopic effect (KIE) is observed referring to the α-hydrogen-abstraction as the rate-determining step in the selective acrolein oxidation. Furthermore, no change in the selectivity patterns is observed due to the perdeuteration, which confirms that the α-hydrogen-abstraction also acts as the rate-limiting step in the total oxidation of acrolein. Based on these KIE studies combined with additional experiments including D₂O-SSITKA and temperature-programmed desorption, a detailed reaction mechanism for acrolein oxidation is proposed.  相似文献   

    

Dr. Vanessa M. Vasconcelos  Dr. Carlos Ponce-de-León  Prof. Stefan M. Rosiwal  Prof. Marcos R. V. Lanza 《ChemElectroChem》2019,6(13):3516-3524

Reactive Blue 19 (RB-19) dye has a low fixation efficiency, a long half-life and high toxicity. It is easily loss during the cleaning of textiles and can remain in the environment for a long time, causing serious environmental problems if not removed. This study reports the degradation of RB-19 by: 1) direct electrochemical degradation with boron-doped diamond (BDD) electrodes and 2) combined processes using BDD and reticulated vitreous carbon (RVC) electrodes that generate H₂O₂. The direct degradation uses different current densities and concentrations. High currents densities, longer electrolysis times and low volumetric flow rates favour RB-19 degradation, removing total colour and 100 % TOC after 5 and 60 min, respectively. At a current density of 41 mA cm⁻² and a volumetric flow rate of 20 dm³ h⁻¹, the energy consumption to degrade 20 mg dm⁻³ of RB-19 was 279 kWh kg⁻¹. The TOC removal of RB-19 dye combining BDD and RVC at a current density of 41 mA cm⁻² was below 72 % after 90 min and the energy consumption increased to 612 kWh kg⁻¹. The higher energy consumption observed during the combined process suggests that the direct degradation process at low volumetric flow rates is more efficient than the combined process.  相似文献   

    

Sebastian Schenk  Eva Maria Zollner  Oliver Krahn  Berit Schreck  Ren Hammer  Stefan Frster  Wolf Widdra 《Acta Crystallographica. Section A, Foundations and Advances》2019,75(2):307-313

The atomically resolved real‐space structure of a long‐range‐ordered dodecagonal quasicrystal is determined based on scanning tunnelling microscopy. For the BaTiO₃‐derived oxide quasicrystal which spontaneously forms on a Pt(111) surface, 8100 atomic positions have been determined and are compared with an ideal Niizeki–Gähler tiling. Although the Niizeki–Gähler tiling has a complex three‐element structure, the abundance of the triangle, square and rhomb tiling elements in the experimental data closely resembles the ideal frequencies. Similarly, the frequencies of all possible next‐neighbour tiling combinations are, within the experimental uncertainty, identical to the ideal tiling. The angular and orientational distributions of all individual tiling elements show the characteristics of the dodecagonal quasicrystal. In contrast, the analysis of the orientation of characteristic and more complex tiling combinations indicates the partial decomposition of the quasicrystal into small patches with locally reduced symmetry. These, however, preserve the long‐range quasicrystal coherence. The symmetry reduction from dodecagonal to sixfold is assigned to local interaction with the threefold substrate. It leads to atomic flips which preserve the number of quasicrystal tiling elements.  相似文献   

    

Stefan Lffler  Stefan Sack  Thomas Schachinger 《Acta Crystallographica. Section A, Foundations and Advances》2019,75(6):902-910

This work studies the elastic scattering behavior of electron vortices when propagating through amorphous samples. A formulation of the multislice approach in cylindrical coordinates is used to theoretically investigate the redistribution of intensity between different angular momentum components due to scattering. To corroborate and elaborate on our theoretical results, extensive numerical simulations are performed on three model systems (Si₃N₄, Fe_0.8B_0.2, Pt) for a wide variety of experimental parameters to quantify the purity of the vortices, the net angular momentum transfer, and the variability of the results with respect to the random relative position between the electron beam and the scattering atoms. These results will help scientists to further improve the creation of electron vortices and enhance applications involving them.  相似文献