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21.
Tanja Vidaković-Koch Tamara Miličić Luka A. Živković Hoon Seng Chan Ulrike Krewer Menka Petkovska 《Current Opinion in Electrochemistry》2021
The nonlinear frequency response analysis (NFRA) can be seen as an extension of electrochemical impedance spectroscopy. NFRA gives a full and detailed representation of the system response and can establish a connection between model parameters and the experimentally observed phenomena. In this article, different theoretical NFRA approaches and the most recent application examples are discussed. A simple electrochemical example is used to showcase the benefits and disadvantages of analyzing the system response by using different approaches. In addition, it was shown how to extract experimental harmonic values and analyze them. 相似文献
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S. Jakobs Ulrike Schulz Angela Duparré Norbert Kaiser 《Analytical and bioanalytical chemistry》1997,358(1-2):242-244
SiO2 protective coatings have been deposited on polycarbonate substrates by plasma ion assisted deposition. The influence of ion energy on the water permeability and the surface topography of the coatings was studied by infrared spectroscopy and atomic force microscopy. Coatings deposited at sufficiently high ion energies show a barrier effect against moisture uptake and considerably reduced film roughness. Both effects are attributed to an increase of the packing densities of the coatings. 相似文献
23.
Marcus B. Kindervater Katherine M. Marczenko Ulrike Werner‐Zwanziger Saurabh S. Chitnis 《Angewandte Chemie (Weinheim an der Bergstrasse, Germany)》2019,131(23):7932-7937
Reaction of a tethered triamine ligand with Bi(NMe2)3 gives a Bi triamide, for which a BiI electronic structure is shown to be most appropriate. The T‐shaped geometry at bismuth provides the first structural model for edge inversion in bismuthines and the only example of a planar geometry for pnictogen triamides. Analogous phosphorus compounds exhibit a distorted pyramidal geometry because of different Bi?N and P?N bond polarities. Although considerable BiI character is indicated for the title Bi triamide, it exhibits reactivity similar to BiIII electrophiles, and expresses either a vacant or a filled p orbital at Bi, as evidenced by coordination of either pyridine N‐oxide or W(CO)5. The product of the former shows evidence of coordination‐induced oxidation state change at bismuth. 相似文献
24.
Rei Tomifuji Prof. Takuya Kurahashi Prof. Seijiro Matsubara 《Chemistry (Weinheim an der Bergstrasse, Germany)》2019,25(38):8987-8991
The development and use of a multiple-activation catalyst with ion-paired Lewis acid and Brønsted acid in an asymmetric aza-Diels–Alder reaction of simple dienes (non-Danishefsky-type electron-rich dienes) was achieved by utilizing the [FeBr2]+[FeBr4]− combination prepared in situ from FeBr3 and chiral phosphoric acid. Synergistic effects of the highly active ion-paired Lewis acid [FeBr2]+[FeBr4]− and a chiral Brønsted acid are important for promoting the reaction with high turnover frequency and high enantioselectivity. The multiple-activation catalyst system was confirmed using synchrotron-based X-ray absorption fine structure measurements, and theoretical studies. This study reveals that the developed catalyst promoted the reaction not only by the interaction offered by the ion-paired Lewis acid and the Brønsted acid but also noncovalent interactions. 相似文献
25.
Heller B Sundermann B Buschmann H Drexler HJ You J Holzgrabe U Heller E Oehme G 《The Journal of organic chemistry》2002,67(13):4414-4422
The photocatalyzed [2 + 2 + 2]-cycloaddition of nitriles with 2 equiv of acetylene to 2-pyridines can be carried out under mild conditions and represents a valuable extension to common synthetical methods. For the ideal wavelength range (350-500 nm), lamps as well as sunlight can be used. Working at room temperature and in organic solvents such as toluene or hexane as well as in water gives satisfying results in many cases. However, it is also possible to vary the solvent and the reaction temperature of the photocatalyzed synthesis and to choose, with respect to the specific substrate, specific requirements for this particular reaction and general requirements of the method. This simple and selective method derives its potential mainly from the large variety of applicable nitriles. Suitable substrates include (functionalized) aliphatic and aromatic nitriles as well as cyanamides derived from secondary amines. 相似文献
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Development and application of a simple routine method for the determination of selenium in serum by octopole reaction system ICPMS 总被引:1,自引:0,他引:1
The aim of the study was to develop an inductively coupled plasma mass spectrometry (ICPMS) method for robust and simple routine determination of selenium in serum. Polyatomic interferences on 76Se, 77Se, and 78Se were removed by applying an octopole reaction system ICPMS with the reaction cell pressurized with H2 gas. We developed a novel simple optimization routine for the H2 gas flow based on a signal-to-noise ratio (SNR) calculation of the selenium signal measured in a single selenium standard. The optimum H2 flow was 2.9 mL min–1. The selenium content in serum was determined after a 50-fold dilution with 0.16 M HNO3 and quantified by using addition calibration and gallium as an internal standard. The method detection limit was 0.10 g L–1 for 76Se and 78Se and 0.13 g L–1 for 77Se. Human serum samples from a case-control study investigating if selenium was associated with risk of colorectal adenoma were analyzed. The average selenium concentration for the control group (n=768) was 137.1 g L–1 and the range was 73.4–305.5 g L–1. The within-batch repeatability (a batch is ten samples) estimated from 182 replicate analyses was 6.3% coefficient of variation (CV), whereas the between-batch repeatability was 7.4% CV estimated from 361 replicates between batches. The method accuracy was evaluated by analysis of a human serum certified reference material (Seronorm Serum level II, Sero A/S, Norway). There was a fairly good agreement between the measured average of 145±3 g L–1 (n=36) and the certified value of 136±9 g L–1. In addition the method was successfully applied for analysis of zinc serum concentrations without further optimization. For the Seronorm certified reference material a value of 911±75 g L–1 (n=31) for zinc was obtained, which corresponds well to the certified zinc value of 920±60 g L–1. 相似文献
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Peptides bearing an acryloyl residue at their N‐terminus were coupled with various C‐glycosides in an equimolar ratio via cross‐metathesis. The newly formed olefin was obtained with high E/Z selectivity in satisfying to high yields with low homodimerization of the starting materials. The posttranslational cross‐metathesis approach was shown to be suitable for the combinatorial synthesis of a small library of C‐glycopeptides. 相似文献