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101.
Spontaneous Metal‐Free Transfer Hydrogenation of Iminoboranes with Ammonia Borane and Amine Boranes
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Lena Winner Dr. William C. Ewing Prof. K. Geetharani Dr. Theresa Dellermann Brian Jouppi Dr. Thomas Kupfer Dr. Marius Schäfer Prof. Dr. Holger Braunschweig 《Angewandte Chemie (International ed. in English)》2018,57(38):12275-12279
The first spontaneous, metal‐free, room‐temperature hydrogen transfer from ammonia borane to an iminoborane is reported. Mechanistic studies of the reaction indicate a concerted transfer of H+ and H? from donor to acceptor with an activation energy far below those of comparable concerted transfer hydrogenations. This reaction was employed in the syntheses and isolation of new B,N‐disubstituted aminoboranes, a comparatively rare subset within the aminoborane family. This successful transfer hydrogenation to a highly dehydrogenated BN system may serve as a starting point for the design of new systems capable of reversible dehydrogenation/rehydrogenation. 相似文献
102.
Lena Trojer 《Journal of Analytical and Applied Pyrolysis》1981,2(4):353-359
Hydrogen was identified as a product of the pyrolysis of polygyrene, especially at high pyrolysis temperatures. With a high interface temperature of the Pyroprobe foil pyrolyser and a high pyrolysis temperature, almost 100% of the pyrolysed polymer could be accounted for. It is then assumed that hydrogen (up to 26%) produces a corresponding amount of carbon, which remains on the foil. 相似文献
103.
Spores ofClostridium acetobutylicum were immobilized in calcium alginate. An active gel preparation was obtained after outgrowth of the spores to vegetative
cells within the gel matrix. A 100 mL column containing the immobilized cells was used for continuous production. At steady-state
conditions the productivity of butanol was 67 g/L reactor volume/day. 相似文献
104.
Pieraccini S Ferrarini A Gottarelli G Lena S Masiero S Spada GP 《The Journal of organic chemistry》2005,70(20):8009-8016
[Chemical reaction: See text] The circular dichroism spectra and the twisting ability of a series of 2-aryl-4,5-dimethyl-1,3-dioxolanes used as dopants in nematic solvents have been related to their absolute configuration. Whereas the circular dichroism (CD) spectra are deeply affected by the substituents present in the aromatic ring, which in several cases cause sign inversion, the helical twisting power beta is only marginally influenced. The values of beta also seem not very sensitive to the rotamer population around the aromatic ring; this indicates the predominant importance of the chiral dioxolane ring in determining the cholesteric induction. These facts can be explained by the different nature of the two observables: in CD, the chirality is read by the absorbing chromophore and is deeply influenced even by small changes of this group. In cholesteric induction we are dealing instead with chiral solute-solvent interactions that determine a twist in the solvent. In light of the present and previous results, this process seems predominantly determined by short-range interactions, which are modulated by the molecular shape. From a practical point of view, a configurational correlation using CD for the present series of compounds seems problematic, while the values of beta are nicely correlated to the absolute configurations. Calculations with the surface chirality method predict well the sign and order of magnitude of beta and their limited sensitivity to the phenyl substituents and rotamer population. 相似文献
105.
106.
The dielectric spectra of the glass former, m-fluoroaniline (m-FA), at ambient pressure show the presence of a secondary relaxation, which was identified in the literature as the universal Johari-Goldstein (JG) beta relaxation. However, published elastic neutron scattering and simulation data [D. Morineau, C. Alba-Simionesco, M. C. Bellisent-Funel, and M. F. Lauthie, Europhys. Lett. 43, 195 (1998); D. Morineau and C. Alba-Simionesco, J. Chem. Phys. 109, 8494 (1998)] showed the presence of hydrogen-bond-induced clusters of limited size in m-FA at ambient pressure and temperature of the dielectric measurements. The observed secondary relaxation may originate from the hydrogen-bond-induced clusters. If so, it should not be identified with the JG beta relaxation that involves essentially all parts of the molecule and has certain characteristics [K. L. Ngai and M. Paluch, J. Chem. Phys. 120, 857 (2004)], but then arises the question of where is the supposedly universal JG beta relaxation in m-FA. To gain a better understanding and resolving the problem, we perform dielectric measurements at elevated pressures and temperatures to suppress the hydrogen-bond-induced clusters and find significant changes in the dielectric spectra. The secondary relaxation observed at ambient pressure in m-FA is suppressed, indicating that indeed it originates from the hydrogen-bond-induced clusters. The spectra of m-FA are transformed at high temperature and pressure to become similar to that of toluene. The new secondary relaxation that emerges in the spectra has properties of a genuine JG relaxation like in toluene. 相似文献
107.
Yashima M Falk LK Palmqvist AE Holmberg K 《Journal of colloid and interface science》2003,268(2):348-356
Mixtures of nanosized platinum and palladium particles have been prepared by reduction of salt-containing microemulsion droplets using hydrazine as the reducing agent. To avoid possible negative effects of the presence of sulfur compounds during the preparation the microemulsion was made using the sulfur-free nonionic polyoxyethylene 4 lauryl ether surfactant. Transmission electron microscopy showed that the as-prepared mixtures contained crystalline platinum particles of fairly homogeneous size (20 to 40 nm) with adsorbed amorphous palladium particles 2 to 5 nm in size. Catalyst samples were prepared by depositing the nanoparticles on a gamma-Al(2)O(3) support followed by heating in air at 600 degrees C. Alloyed particles of platinum and palladium with sizes ranging from 5 to 80 nm were obtained during the heating. The majority of the particles had the fcc structure and their compositional range was dependent upon the Pt:Pd molar ratio of the microemulsion. A catalyst prepared from a microemulsion with a 20:80 Pt:Pd molar ratio showed the highest catalytic activity for CO oxidation, while pure platinum and palladium catalysts showed higher sulfur resistance. These results differ from the performance of conventional wet-impregnated catalysts, where a 50:50 Pt:Pd molar ratio resulted in the highest catalytic activity as well as the highest sulfur resistance. 相似文献
108.
Dr. Palraj Kalimuthu Prof. Lena J. Daumann Dr. Arjan Pol Prof. Huub J. M. Op den Camp Prof. Paul V. Bernhardt 《Chemistry (Weinheim an der Bergstrasse, Germany)》2019,25(37):8760-8768
We report the first electrochemical study of a lanthanoid-dependent methanol dehydrogenase (Eu-MDH) from the acidophilic verrucomicrobial methanotroph Methylacidiphilum fumariolicum SolV with its own physiological cytochrome cGJ electron acceptor. Eu-MDH harbours a redox active 2,7,9-tricarboxypyrroloquinoline quinone (PQQ) cofactor which is non-covalently bound but coordinates trivalent lanthanoid elements including Eu3+. Eu-MDH and the cytochrome were co-adsorbed with the biopolymer chitosan and cast onto a mercaptoundecanol (MU) monolayer modified Au working electrode. Cyclic voltammetry of cytochrome cGJ reveals a well-defined quasi-reversible FeIII/II redox couple at +255 mV vs. NHE at pH 7.5 and this response is pH independent. The reversible one-electron response of the cytochrome cGJ transforms into a sigmoidal catalytic wave in the presence of Eu-MDH and its substrates (methanol or formaldehyde). The catalytic current was pH-dependent and pH 7.3 was found to be optimal. Kinetic parameters (pH dependence, activation energy) obtained by electrochemistry show the same trends as those obtained from an artificial phenazine ethosulfate/dichlorophenol indophenol assay. 相似文献
109.
Dipl.-Phys. Lena Scherthan Rouven F. Pfleger Dr. Hendrik Auerbach Dipl.-Phys. Tim Hochdörffer Dr. Juliusz A. Wolny Dr. Wenli Bi Dr. Jiyong Zhao Dr. Michael Y. Hu Dr. E. Ercan Alp Dr. Christopher E. Anson Prof. Rolf Diller Prof. Annie K. Powell Prof. Volker Schünemann 《Angewandte Chemie (Weinheim an der Bergstrasse, Germany)》2020,132(23):8902-8907
110.