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171.
Sudipta Ponra Jianping Yang Haibo Wu Wangchuk Rabten Pher G. Andersson 《Chemical science》2020,11(41):11189
We have developed a simple protocol for the preparation of 1,2-fluorohydrin by asymmetric hydrogenation of fluorinated allylic alcohols using an efficient azabicyclo thiazole-phosphine iridium complex. The iridium-catalyzed asymmetric synthesis of chiral 1,2-fluorohydrin molecules was carried out at ambient temperature with operational simplicity, and scalability. This method was compatible with various aromatic, aliphatic, and heterocyclic fluorinated compounds as well as a variety of polyfluorinated compounds, providing the corresponding products in excellent yields and enantioselectivities.We have developed a simple protocol for the preparation of 1,2-fluorohydrin by asymmetric hydrogenation of fluorinated allylic alcohols using an efficient azabicyclo thiazole-phosphine iridium complex. 相似文献
172.
Markus Jarvid Anette Johansson Jonas M. Bjuggren Harald Wutzel Villgot Englund Stanislaw Gubanski Christian Müller Mats R. Andersson 《Journal of Polymer Science.Polymer Physics》2014,52(16):1047-1054
The synthesis and physico‐chemical properties of seven benzil‐type voltage stabilizers are reported. The benzil core is substituted with alkyl chains of different length that are linked to the benzil core via an ester, ether, or tertiary amine group. All additives can be melt‐processed with low‐density polyethylene (LDPE). Fourier‐transform infrared spectroscopy confirms that benzil compounds are not affected by the LDPE cross‐linking reaction induced by dicumyl peroxide. Moreover, a combination of gel content measurements, thermal analysis, and small‐angle X‐ray scattering indicates that the presence of benzil voltage stabilizers does not significantly alter the microstructure of cross‐linked polyethylene (XLPE). Electrical tree inhibition experiments under high‐voltage alternating current conditions show that all investigated additives substantially enhance the dielectric strength of the insulating material at a concentration of only 10 mmol kg?1. The highest improvement in dielectric strength, of more than 70% with respect to reference XLPE, is obtained with voltage stabilizers, which carry short (methyl) side chains that are linked to the benzil core via an ester or tertiary amine group. © 2014 Wiley Periodicals, Inc. J. Polym. Sci., Part B: Polym. Phys. 2014 , 52, 1047–1054 相似文献
173.
174.
Andersson PU Ryding MJ Sekiguchi O Uggerud E 《Physical chemistry chemical physics : PCCP》2008,10(40):6127-6134
Hydrogen/deuterium exchange in reactions of H3O(+)(H2O)n and NH4(+)(H2O)n (1 < or = n < or = 30) with D2O has been studied experimentally at center-of-mass collisions energies of < or = 0.2 eV. For a given cluster size, the cross-sections for H3O(+)(H2O)n and NH4(+)(H2O)n are similar, indicating a structural resemblance and energetics of binding. For protonated pure water clusters, H3O(+)(H2O)n, reacting with D2O the main H/D exchange mechanism is found to be proton catalyzed. In addition the H/D scrambling becomes close to statistically randomized for the larger clusters. For NH4(+)(H2O)n clusters reacting with D2O, the main mechanism is a D2O/H2O swap reaction. The lifetimes of H3O(+)(H2O)n clusters have been estimated using RRKM theory and a plateau in lifetime vs. cluster size is found already at n = 10. 相似文献
175.
This study concerns the technique electric field-assisted capillary liquid chromatography. In this technique, an electric field is applied over the separation capillary in order to provide an additional selectivity. In this technique, the electric field is applied in-line in the separation capillary and here the electric current is the factor limiting the magnitude of applied electric field. The influence of Joule heating and other factors on the current in such systems has been investigated. The temperature in the capillary was first measured within a standard CE set-up, as function of effect per unit of length. Then the same cooling system was applied to an in-line set-up, to replicate the conditions between the two systems, and thus the temperature. Thus Joule heating effects could then be calculated within the in-line system. It was found that for systems applying an electric field in line, the direct influence from Joule heating was only relatively small. The pH in the capillary was measured in the in-line set-up using cresol red/TRIS solutions as pH probe. Significant changes in pH were observed and the results suggested that electrolysis of water is the dominant electrode reaction in the in-line system. In summary, the observed conductivity change in in-line systems was found to be mainly due to the pH change by hydrolysis of water, but primarily not due the temperature change in the capillary column. 相似文献
176.
Costa EV Pinheiro ML de Souza AD Dos Santos AG Campos FR Ferreira AG Barison A 《Magnetic resonance in chemistry : MRC》2008,46(1):69-74
Using modern NMR techniques, including 1H--13C and 1H--15N heteronuclear correlation experiments, the complete and unambiguous 1H, 13C, and 15N NMR chemical shift assignments of annomontine, methoxyannomontine, and N-hydroxyannomontine pyrimidine-beta-carboline alkaloids were performed. All 1H--1H scalar coupling constants and signal multiplicities were determined, and all nOe observations were also included. 相似文献
177.
Andersson J Li S Lincoln P Andréasson J 《Journal of the American Chemical Society》2008,130(36):11836-11837
The dramatically different DNA-binding properties of the two isomeric forms of a photochromic spiropyran have been demonstrated, enabling photoswitched DNA binding. The closed, UV-absorbing form shows no signs of interaction with DNA. Upon UV exposure the spiropyran is isomerized to the open form that binds to DNA by intercalation. The process is fully reversible as the corresponding dissociation process is induced by visible light. 相似文献
178.
Andreas Andersson 《Letters in Mathematical Physics》2016,106(10):1397-1414
For a unital completely positive map \({\Phi}\) (“quantum channel”) governing the time propagation of a quantum system, the Stinespring representation gives an enlarged system evolving unitarily. We argue that the Stinespring representations of each power \({\Phi^m}\) of the single map together encode the structure of the original quantum channel and provide an interaction-dependent model for the bath. The same bath model gives a “classical limit” at infinite time \({m\to\infty}\) in the form of a noncommutative “manifold” determined by the channel. In this way, a simplified analysis of the system can be performed by making the large-m approximation. These constructions are based on a noncommutative generalization of Berezin quantization. The latter is shown to involve very fundamental aspects of quantum-information theory, which are thereby put in a completely new light. 相似文献
179.
Melander C Andersson E Axelsson S Gorton L 《Analytical and bioanalytical chemistry》2007,387(7):2585-2593
A novel method for detection of reducing ends of sugars is proposed, based on the use of as the oxidant in combination with amperometric detection and flow injection analysis (FIA). The method is very sensitive,
giving values of <10 μM for the limit of detection for a series of mono- and oligosaccharides. Samples can be analysed every
30 s, and injection can be made fully automated, making it possible to perform on-line analysis of polysaccharide samples
subjected to hydrolysis. Three methylcelluloses (MC) of different qualities were hydrolysed with three different glucanases,
and the concentrations of reducing ends prior to, during and after hydrolysis were determined. Differences were observed between
the results obtained using different combinations of enzymes and MCs, which revealed different selectivities of the various
enzymes for the different substrates. One MC was also hydrolysed and analysed in real-time for three hours. The method proposed
is superior to many of the standard methods used today, which require manual labour and have a lower sensitivity.
Figure Set-up used for the instrumentation in the FIA system with automated injection. A pump delivers the reaction solution to the
autosampler, where the samples are injected; the sample and solution react in a temperature-controlled random coil and the
response is detected using an amperometric detection cell 相似文献
180.
Crude oil analysis has long been an inspiration for the development of analytical techniques. Especially mass spectrometry
has flourished as a result of the challenge these extremely complex problems offer. Here an overview of different analytical
methods is presented that shows different ways to analyze volatile and nonvolatile crude oil components. Focus has been placed
on the use of mass spectrometry and especially the new developments that have been introduced using the emerging technique
of Fourier transform ion cyclotron resonance mass spectrometry. These studies are examples of how far the development of analytical
methods has come for the task of studying such complex problems. 相似文献