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131.
Dr. Dinar Abdullin Nico Fleck Christoph Klein Philipp Brehm Sebastian Spicher Prof. Dr. Arne Lützen Prof. Dr. Stefan Grimme Prof. Dr. Olav Schiemann 《Chemistry (Weinheim an der Bergstrasse, Germany)》2019,25(10):2586-2596
Iron(III) porphyrins have the propensity to form μ2-oxo-dimers, the structures of which resemble two wheels on an axle. Whereas their crystal structure is known, their solution structure and internal dynamics is not. In the present work, the structure and dynamics of such dimers were studied by means of electron paramagnetic resonance (EPR) spectroscopy and quantum chemistry based molecular dynamics (MD) simulations by using the semiempirical tight-binding method (GFN-xTB). To enable EPR investigation of the dimers, a nitroxide was attached to each of the tetraphenylporphyrin cores through a linear and a bent linker. The inter-nitroxide distance distributions within the dimers were determined by continuous-wave (cw)-EPR and pulsed electron–electron double resonance (PELDOR or DEER) experiments and, with the help of MD, interpreted in terms of the rotation of the porphyrin planes with respect to each other around the Fe–O–Fe axis. It was found that such rotation is restricted to the four registers defined by the phenyl substituents. Within the registers, the rotation angle swings between 30° and 60° in the proximal and between 125° and 145° in the distal register. With EPR, all four angles were found to be equally populated, whereas the 30° and 145° angles are strongly favored to the expense of the 60° and 125° angles in the MD simulation. In either case, the internal dynamics of these dimers thus resemble the motion of a step motor. 相似文献
132.
133.
Dr. Yasuyuki Nakamura Dr. Bastian Ebeling Dr. Arne Wolpers Dr. Vincent Monteil Dr. Franck D'Agosto Prof. Dr. Shigeru Yamago 《Angewandte Chemie (International ed. in English)》2018,57(1):305-309
The first successfully controlled radical polymerization (CRP) of ethylene is reported using several organotellurium chain‐transfer agents (CTAs) under mild conditions (70 °C, 200 bar of ethylene) within the concept of organotellurium‐mediated radical polymerization (TERP). In contrast to preceding works on CRPs of ethylene applying reversible addition–fragmentation chain‐transfer (RAFT), the TERP system provided a high livingness and chain‐end functionalization of polyethylene chains. Molar‐mass distributions with dispersities between 1.3 and 2.1 were obtained up to average molar masses of 5000 g mol?1. As in the RAFT system, the high reactivity of the growing polyethylenyl radical led to an inherent side reaction. For the presented TERP systems, however, this side reaction did not result in dead chains, while it could even be effectively suppressed by a good choice of the CTA. 相似文献
134.
135.
We compute the André–Quillen (or Harrison) cohomology of an affine toric variety. The best results are obtained either in the general case for the first three cohomology groups, or in the case of isolated singularities for all cohomology groups, respectively. 相似文献
136.
Arne Jensen 《Arkiv f?r Matematik》1998,36(2):363-377
Results are obtained on the scattering theory for the Schrödinger equation $i\partial _t u(t,x) = - \Delta _x u(t,x) + V(t,x)u(t,x) + F(u(t,x))$ in spacesL r (R;L q (R d )) for a certain range ofr, q, the so-called space-time scattering. In the linear case (i.e.F≡)) the relation with usual configuration space scattering is established. 相似文献
137.
Lie M Barnholt Klepper K Nilsen O Fjellvåg H Kjekshus A 《Dalton transactions (Cambridge, England : 2003)》2008,(2):253-259
Thin films of iron cobalt oxides with spinel-type structure are made by the atomic layer deposition (ALD) technique using Fe(thd)3 (Hthd = 2,2,6,6-tetramethylheptane-3,5-dione), Co(thd)2, and ozone as precursors. Pulse parameters for ALD-type growth are established and such growth can be achieved at deposition temperatures between 185 and 310 degrees C. Films have been deposited on amorphous soda-lime glass and single-crystalline substrates of Si(100), MgO(100), and alpha-Al2O3(001) which all provide crystalline films, but with various orientations and crystallite sizes. Application of an external magnetic field during the film growth does not influence film growth characteristics (growth rate, crystallinity, topography etc.). Magnetization data are reported for phase-pure films of spinel-type structure with composition Fe2CoO4. 相似文献
138.
Vincent Weigelt Dr. Sarah Vogl Dr. Johannes Schmidt Prof. Arne Thomas 《Angewandte Chemie (International ed. in English)》2023,62(39):e202307818
The Wittig reaction is a key step in industrial processes to synthesise large quantities of vitamin A and various other important chemicals that are used in daily life. This article presents a pathway to achieve the Wittig reaction in a solid network. A highly porous triphenylphosphine-based polymer was applied as a solid Wittig reagent that undergoes, in a multi-step cycle, in total six post-synthetic modifications. This allowed for regeneration of the solid Wittig reagent and reuse for the same reaction cycle. Of particular industrial relevance is that the newly developed material also enables a simple way of separating the product by filtration. Therefore, additional costly and difficult separation and purification steps are no longer needed. 相似文献
139.
Prasenjit Das Jérôme Roeser Arne Thomas 《Angewandte Chemie (International ed. in English)》2023,62(29):e202304349
A chemically stable 2D microporous COF ( PMCR-1 ) was synthesized via the multicomponent Povarov reaction. PMCR-1 exhibits a remarkable and long-term stable photocatalytic H2O2 production rate (60 h) from pure and sea water under visible light. The H2O2 production is markedly enhanced when benzyl alcohol (BA) is added as reductant, which is also due to a strong π–π interaction of BA with dangling phenyl moieties in the COF pores introduced by the multicomponent Povarov reaction. Motivated by the concomitant BA oxidation to benzaldehyde during H2O2 formation, the photocatalytic oxidation of various organic substrates such as benzyl amine and methyl sulfide derivatives was investigated. It is shown that the well-defined micropores of PMCR-1 enable size-selective photocatalytic oxidation. 相似文献
140.
Bojdys MJ Müller JO Antonietti M Thomas A 《Chemistry (Weinheim an der Bergstrasse, Germany)》2008,14(27):8177-8182
Herein we report the synthesis of a crystalline graphitic carbon nitride, or g-C(3)N(4), obtained from the temperature-induced condensation of dicyandiamide (NH(2)C(=NH)NHCN) by using a salt melt of lithium chloride and potassium chloride as the solvent. The proposed crystal structure of this g-C(3)N(4) species is based on sheets of hexagonally arranged s-heptazine (C(6)N(7)) units that are held together by covalent bonds between C and N atoms which are stacked in a graphitic, staggered fashion, as corroborated by powder X-ray diffractometry and high-resolution transmission electron microscopy. 相似文献