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71.
Sandra Mller Stefan Barwe Justus Masa Daniela Wintrich Sabine Seisel Helmut Baltruschat Wolfgang Schuhmann 《Angewandte Chemie (International ed. in English)》2020,59(4):1585-1589
Carbon corrosion at high anodic potentials is a major source of instability, especially in acidic electrolytes and impairs the long‐term functionality of electrodes. In‐depth investigation of carbon corrosion in alkaline environment by means of differential electrochemical mass spectrometry (DEMS) is prevented by the conversion of CO2 into CO32?. We report the adaptation of a DEMS system for online CO2 detection as the product of carbon corrosion in alkaline electrolytes. A new cell design allows for in situ acidification of the electrolyte to release initially dissolved CO32? as CO2 in front of the DEMS membrane and its subsequent detection by mass spectrometry. DEMS studies of a carbon‐supported nickel boride (NixB/C) catalyst and Vulcan XC 72 at high anodic potentials suggest protection of carbon in the presence of highly active oxygen evolution electrocatalysts. Most importantly, carbon corrosion is decreased in alkaline solution. 相似文献
72.
Zechao Yang Lukas Fromm Tim Sander Julian Gebhardt Tobias A. Schaub Andreas Grling Milan Kivala Sabine Maier 《Angewandte Chemie (International ed. in English)》2020,59(24):9549-9555
Demonstrated here is a supramolecular approach to fabricate highly ordered monolayered hydrogen‐ and halogen‐bonded graphyne‐like two‐dimensional (2D) materials from triethynyltriazine derivatives on Au(111) and Ag(111). The 2D networks are stabilized by N???H?C(sp) bonds and N???Br?C(sp) bonds to the triazine core. The structural properties and the binding energies of the supramolecular graphynes have been investigated by scanning tunneling microscopy in combination with density‐functional theory calculations. It is revealed that the N???Br?C(sp) bonds lead to significantly stronger bonded networks compared to the hydrogen‐bonded networks. A systematic analysis of the binding energies of triethynyltriazine and triethynylbenzene derivatives further demonstrates that the X3‐synthon, which is commonly observed for bromobenzene derivatives, is weaker than the X6‐synthon for our bromotriethynyl derivatives. 相似文献
73.
Susanne Bhr Sabine Brinkmann‐Chen Marc Garcia‐Borrs John M. Roberts Dimitris E. Katsoulis K. N. Houk Frances H. Arnold 《Angewandte Chemie (International ed. in English)》2020,59(36):15507-15511
Compared to the biological world's rich chemistry for functionalizing carbon, enzymatic transformations of the heavier homologue silicon are rare. We report that a wild‐type cytochrome P450 monooxygenase (P450BM3 from Bacillus megaterium, CYP102A1) has promiscuous activity for oxidation of hydrosilanes to give silanols. Directed evolution was applied to enhance this non‐native activity and create a highly efficient catalyst for selective silane oxidation under mild conditions with oxygen as the terminal oxidant. The evolved enzyme leaves C?H bonds present in the silane substrates untouched, and this biotransformation does not lead to disiloxane formation, a common problem in silanol syntheses. Computational studies reveal that catalysis proceeds through hydrogen atom abstraction followed by radical rebound, as observed in the native C?H hydroxylation mechanism of the P450 enzyme. This enzymatic silane oxidation extends nature's impressive catalytic repertoire. 相似文献
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Ballardini R Balzani V Clemente-León M Credi A Gandolfi MT Ishow E Perkins J Stoddart JF Tseng HR Wenger S 《Journal of the American Chemical Society》2002,124(43):12786-12795
We have designed, synthesized, and investigated a self-assembling supramolecular system which mimics, at a molecular level, the function performed by a macroscopic electrical extension cable. The system is made up of three components, 12+, 2-H3+, and 3. Component 12+ consists of two moieties: a [Ru(bpy)3]2+ unit, which plays the role of an electron donor under light excitation, and a DB24C8 crown ether, which fulfills the function of a socket. The wire-type component 2-H3+ is also composed of two moieties, a secondary dialkylammonium-ion center and a bipyridinium unit, which thread into the DB24C8 crown-ether socket of 12+ and the 1/5DN38C10 crown-ether socket 3, respectively. The photochemical, photophysical, and electrochemical properties of the three separated components, of the 12+ superset 2-H3+ and 2-H3+ subset 3 dyads, and of the 12+ superset 2-H3+ subset 3 triad have been investigated in CH2Cl2 solution containing 2% MeCN. Reversible connection/disconnection of the two plug/socket systems can be controlled independently by acid/base and redox stimulation. The behavior of the various different dyads and triad has been monitored by light absorption and emission spectroscopies, as well as by electrochemical techniques. In the fully connected 12+ superset 2-H3+ subset 3 triad, light excitation of the [Ru(bpy)3]2+ unit of component 12+ is followed by electron transfer (k = 2.8 x 108 s-1) to the bipyridinium unit of component 2-H3+, which is plugged into component 3. Possible schemes to obtain improved molecular-level electrical extension cables are discussed. 相似文献