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排序方式: 共有199条查询结果,搜索用时 15 毫秒
1.
Dr. Agnes Kütt Prof. Dr. Gunnar Jeschke Dr. Lauri Toom Dr. Jaak Nerut Prof. Christopher A. Reed 《Chemistry (Weinheim an der Bergstrasse, Germany)》2020,26(41):8871-8874
Hydride abstraction from diarylamines with the trityl ion is explored in an attempt to generate a stable diarylnitrenium ion, Ar2N+. Sequential H-atom abstraction reactions ensue. The first H-atom abstraction leads to intensely colored aminium radical cations, Ar2NH.+, some of which are quite stable. However, most undergo a second H-atom abstraction leading to ammonium ions, Ar2NH2+. In the absence of a ready source of H-atoms, a unique self-abstraction reaction occurs when Ar=Me5C6, leading to a novel iminium radical cation, Ar=N.+Ar, which decays via a second self H-atom abstraction reaction to give a stable iminium ion, Ar=N+HAr. These products differ substantially from those derived via photochemically produced diarylnitrenium ions. 相似文献
2.
Dr. Michael Georg Hoesl M. Sc. Stefan Oehm Dr. Patrick Durkin Dr. Elise Darmon Dr. Lauri Peil Dr. Hans‐Rudolf Aerni Prof. Dr. Juri Rappsilber Prof. Dr. Jesse Rinehart Prof. Dr. David Leach Prof. Dr. Dieter Söll Prof. Dr. Nediljko Budisa 《Angewandte Chemie (International ed. in English)》2015,54(34):10030-10034
We have changed the amino acid set of the genetic code of Escherichia coli by evolving cultures capable of growing on the synthetic noncanonical amino acid L ‐β‐(thieno[3,2‐b]pyrrolyl)alanine ([3,2]Tpa) as a sole surrogate for the canonical amino acid L ‐tryptophan (Trp). A long‐term cultivation experiment in defined synthetic media resulted in the evolution of cells capable of surviving Trp→[3,2]Tpa substitutions in their proteomes in response to the 20 899 TGG codons of the E. coli W3110 genome. These evolved bacteria with new‐to‐nature amino acid composition showed robust growth in the complete absence of Trp. Our experimental results illustrate an approach for the evolution of synthetic cells with alternative biochemical building blocks. 相似文献
3.
We show that by cutting off the vertices and then the edges of neighborly cubical polytopes, one obtains simple 4-dimensional polytopes with n vertices such that all separators of the graph have size at least Ω(n/log3/2 n). This disproves a conjecture by Kalai from 1991/2004. 相似文献
4.
An efficient and general approach for the synthesis of amphiphilic 1,2-amino alcohols is reported. The use of N-benzyl protecting groups is essential for obtaining good yields when opening a long-chain terminal epoxide with an amine. 相似文献
5.
6.
Experimental study of the multiple scattering effect on the flow velocity profiles measured in Intralipid phantoms by DOCT 总被引:1,自引:0,他引:1
Time domain Doppler Optical Coherence Tomography (DOCT) technique was applied to measure flow velocity profiles in highly
scattering media. We analyzed the distortions of the measured velocity profiles of the 1% Intralipid solution flow embedded
into the scattering medium at different embedding depths. For this purpose a tissue phantom consisting of a plain glass capillary
(inner diameter 0.3 mm) embedded into a slab of Intralipid solution mimicking human skin was designed. The measured flow velocity
profiles and behavior of distortions caused by multiple scattering are shown. 相似文献
7.
8.
Charly Mayeux Peeter Burk Jean-Francois Gal Ivari Kaljurand Ilmar Koppel Ivo Leito Lauri Sikk 《Journal of the American Society for Mass Spectrometry》2014,25(11):1962-1973
According to high level calculations, the upper part of the previously published FT-ICR lithium cation basicity (LiCB at 373 K) scale appeared to be biased by a systematic downward shift. The purpose of this work was to determine the source of this systematic difference. New experimental LiCB values at 373 K have been measured for 31 ligands by proton-transfer equilibrium techniques, ranging from tetrahydrofuran (137.2 kJ mol?1) to 1,2-dimethoxyethane (202.7 kJ mol?1). The relative basicities (ΔLiCB) were included in a single self-consistent ladder anchored to the absolute LiCB value of pyridine (146.7 kJ mol?1). This new LiCB scale exhibits a good agreement with theoretical values obtained at G2(MP2) level. By means of kinetic modeling, it was also shown that equilibrium measurements can be performed in spite of the formation of Li+ bound dimers. The key feature for achieving accurate equilibrium measurements is the ion trapping time. The potential causes of discrepancies between the new data and previous experimental measurements were analyzed. It was concluded that the disagreement essentially finds its origin in the estimation of temperature and the calibration of Cook’s kinetic method. Graphical Abstract
? 相似文献
9.
Birgit Maaten Lauri Loo Alar Konist Andres Siirde 《Journal of Thermal Analysis and Calorimetry》2018,131(3):2087-2091
Four oil shale samples with different amounts of organic and mineral matter were analysed through non-isothermal thermogravimetric analysis using a heating rate of 50 °C min?1 in nitrogen. The goal of the paper is to study the supposed catalytic effect of the indigenous and removed minerals. The samples contained 30, 49, 70 and 90% of organic matter, respectively. X-ray diffraction analysis was used to identify the minerals in the samples. Thermal analysis experiments were carried out up to temperatures of 850 °C in pyrolysis conditions. The mass loss data were used to study the variations in the conversion profiles of the organic matter depending on the content of the mineral matter. The obtained data and the comparison of the sample composition show that the effect of the mineral matter amount on the course of the pyrolysis processes is insignificant. 相似文献
10.
The preparation and H2S sensing potential of thick‐films of a mixed oxide, Fe2O3? Fe2(MoO4)3, were investigated. A Fourier‐transform infrared (FTIR) study confirmed the existence of sulfur species at the surface after the interaction of H2S gas with the mixed oxide. The starting material, β‐FeMoO4, was synthesized by a solvothermal method, followed by supercritical drying. Heat treatment of this material (oxidation) above 500 °C resulted in the formation of Fe2O3? Fe2(MoO4)3 mixed oxide, where Fe2O3 was a by‐product. An increase in the conductivity of the films in the presence of H2S gas (concentration range 1–20 ppm in air) was observed with the simultaneous formation of water and sulfide ions at 225 °C. An improvement of the H2S sensing potential is obtained, using an intermediate short heat treatment at higher temperature (500 °C) in the beginning of recovery (desorption) phase. This intermediate high temperature, used before every expected exposure to H2S gas, may contribute the formation of an initial surface coverage of O2?. 相似文献