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排序方式: 共有236条查询结果,搜索用时 15 毫秒
11.
Dr. Daniel Brodbeck Dr. Sonia Álvarez-Barcia Dr. Jan Meisner Dr. Florian Broghammer Julian Klepp Dr. Delphine Garnier Dr. Wolfgang Frey Prof. Dr. Johannes Kästner Prof. Dr. René Peters 《Chemistry (Weinheim an der Bergstrasse, Germany)》2019,25(6):1515-1524
Asymmetric 1,2-additions of cyanide yield enantioenriched cyanohydrins as versatile chiral building blocks. Next to HCN, volatile organic cyanide sources are usually used. Among them, cyanoformates are more attractive on technical scale than TMSCN for cost reasons, but catalytic productivity is usually lower. Here, the development of a new strategy for cyanations is described, in which this activity disadvantage is overcome. A Lewis acidic Al center cooperates with an aprotic onium moiety within a remarkably robust bifunctional Al–F–salen complex. This allowed for unprecedented turnover numbers of up to 104. DFT studies suggest an unexpected unique trimolecular pathway in which the ammonium bound cyanide attacks the aldehyde, which itself is activated by the carbonyl group of the cyanoformate binding to the Al center. In addition, a novel practical carboxycyanation method was developed that makes use of KCN as the sole cyanide source. The use of a pyrocarbonate as carboxylating reagent provided the best results. 相似文献
12.
R.J. Panlener R.N. Blumenthal J.E. Garnier 《Journal of Physics and Chemistry of Solids》1975,36(11):1213-1222
Thermogravimetric measurements were performed on nonstoichiometric CeO2?x in the temperature range 750–1500°C and from oxygen pressures of 10?2 to 10?26 atm. From this data the deviation from stoichiometry x = x(T, Po2) was determined. The thermodynamic quantities Δo2 and Δo2 were calculated in the region 0.001? x ? 0.3 and found to be independent of temperature.In the composition region 0.001< x < 0.006, the variation of Δo2 with x is consistent with a defect model involving randomly distributed doubly ionized oxygen vacancies. The experimental dependence of x and σ (electrical conductivity) is shown to be consistent with this model as Δo2 (≈ -10 eV) exhibits a slight dependence on x. It is postulated that the variation in Δo2 may result from lattice parameter increases with x, while the defects remain essentially randomly distributed.In the composition region 0.006 < x < 0.1, x ∝ with 1 < n < 5, and in the region 0.1 < x < 0.3, x ∝ with n increasing rapidly with x to n? 30. This behavior is believed to result from increasing defect interaction with increasing departures from stoichiometry. It is interesting to note that the ordered phase observed by Bevan and Kordis between CeO1·72 and CeO1·70 was not observed in this study at temperatures between 1300° and 1500°C. 相似文献
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The binding of d- and l-tryptophan molecules to bovine serum albumin (BSA) protein has been studied using liquid chromatography and ultrafiltration in the pH range from 7 to 11. A hydrophobic interaction between tryptophan and BSA has been observed at pH 7.0 on BSA grafted chromatographic column. However, this interaction is negligible at higher pH for which the interaction to the stereospecific site was predominant. For both grafted and free proteins, the complexation mechanism was a competitive binding of d- and l-enantiomers on a single site. The apparent complexation constants for both d- and l-tryptophan show a maximum in the pH range 9-10. The variations of the apparent complexation constants versus pH were the result of the protonation of both the amino acid and a single site of the protein assuming that the complexation occurs between the zwitter-ionic amino acid form and the unprotonated BSA site. The apparent pK(BSA) is slightly shifted from 8.3 for grafted BSA protein to 9.4 for free BSA protein. This shift is presumably as a result of the different protein conformation. 相似文献
15.
Cyclopropanols 5, 6 and 2 with substituent groups (-CH2OH, -CH2OTs, -CH2Br) in the 1-position, and oxaspiropentane 8, have been prepared from methylenecyclopropane. Cyclopropanols with vinyl groups in the 1-position (1-vinyl 12, 1-cyclopentenyl 13 and 1-cyclohexenyl 14) and 1-cyclopropylcyclopropanol 20 have been prepared from 1, 3-dichloroacetone.Each of the compounds readily undergoes ring expansion to the corresponding cyclobutanones. The reaction provides a simple route to cyclobutanones, the parent ketone itself being easily obtained from oxaspiropentane 8. 相似文献
16.
E. F. Schwier C. Monney N. Mariotti Z. Vydrovà M. García-Fernández C. Didiot M. G. Garnier P. Aebi 《The European Physical Journal B - Condensed Matter and Complex Systems》2011,81(4):399-403
We explore the interplay between the elastic scattering of photoelectrons and the surface core level shifts with regard to
the determination of core level binding energies in Au(111) and Cu3Au(100). We find that an artificial shift is created in the binding energies of the Au 4f core levels, that exhibits a dependence on the emission angle, as well as on the spectral intensity of the core level emission
itself. Using a simple model, we are able to reproduce the angular dependence of the shift and relate it to the anisotropy
in the electron emission from the bulk layers. Our results demonstrate that interpretation of variation of the binding energy
of core-levels should be conducted
with great care and must take into account the possible influence of artificial shifts induced by elastic scattering. 相似文献
17.
René Garnier 《Annali di Matematica Pura ed Applicata》1962,58(1):1-34
Résumé Soit Γ un quadrilatère variable, dont deux c?tés opposés A2A3, A1A4 sont dans les plans x3=c, x3=−c. Quand c tend vers0, Γ tend vers un quadrilatèreΓ
0 présentant un point double, A0. Le travail étudie la représentation conforme sur le demi-plan R(ix)<0 (ou sur le cercle - unité) de la surface minimale
∑ passant par Γ. Il montre (§ I) que si les affixes x de A1, A2, A4 sont 0, 1, ∞, l'affixe de A3 sera ɛ−2, où ɛ tend vers 0 avec c. Il étudie (§ II) l'allure pour ɛ tendant vers 0 des intégrales canoniques de l'équation linéaire
du problème. La forme de la relation entre ɛ et c est indiquée au no 19; on montre que dans la région de striction ɛ |x| reste borné et que la surface ∑ y est assimilable à une surface minimale
simple: la surface de vis à filet carré. La représentation conforme de l'une des deux régions de ∑ qui tendent à se séparer
l'une de l'autre tend à envahir tout le demi-plan (ou tout le cercle-unité). Les représentations conformes de ∑ pour c>0 et
c<0 ne sont pas analytiquement distinctes (n0 20). A titre d'exemple, on étudie (n0 21) le cas où ∑ possède un axe de symétrie.
A M. Enrico Bompiani pour son Jubilé scientifique 相似文献
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19.
We present new results for the time reversal of weakly nonlinear pulses traveling in a random dissipative environment. Also we describe a new theory for calculating the eddy viscosity for weakly nonlinear waves propagating over a random surface. The turbulent viscosity is calculated from first principles, namely, without imposing any stress-strain hypothesis. A viscous shallow water model is considered and its effective viscosity characterized. We also show that weakly nonlinear waves can still be time reversed under weak dissipation. Incoherently scattered signals are recompressed, both for time reversal in transmission as well as in reflection. Under the weakly nonlinear, weakly dissipative regime, dissipation only affects the refocused pulse profile regarding its amplitude, but its shape is not corrupted. Numerical experiments are presented. 相似文献
20.
We have performed a series of measurements to study the low temperature dynamics of an interacting magnetic nanoparticle system. The results obtained demonstrate striking memory effects in the dc magnetization and magnetic relaxation that support the existence of a spin-glass-like phase in interacting magnetic nanoparticles. Moreover, we observe an asymmetric response with respect to temperature change that supports a hierarchical picture, rather than the droplet model discussed in other works on nanoparticle systems. 相似文献