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91.
Nicolaou MG Wolfe JL Schowen RL Borchardt RT 《The Journal of organic chemistry》1996,61(19):6633-6638
The chemical stability studies of amides of 3-(3',6'-dioxo-2',4'-dimethyl-1',4'-cyclohexadienyl)-3,3-dimethylpropionic acid (Qa) [Qop(a-j)] were conducted in order to determine the utility of this redox-sensitive system as a potential prodrug promoiety or redox-sensitive protecting group in organic synthesis. This study showed that quinone propionic amides of aniline derivatives [Qop(a-d)] underwent rapid degradation in mildly acidic conditions (pH 4.5-6.0) to yield degradation products resulting from the intramolecular 1,2- or 1,4- conjugate addition of the amide nitrogen to the quinone ring. This conjugate addition was found to be specific base-catalyzed and independent of the para substituent on the aromatic ring of the amine. The predominant route of degradation yielded a five-membered ring spirolactam. By altering the nature of the amine component of the amide, these degradation reactions were prevented. Amides of Qa other than those of the aniline type [Qop(e-j)] were found to be substantially more stable and were thus proposed as the more suitable candidates for this potential redox-sensitive prodrug system and redox-sensitive protecting group for amines and alcohols in organic synthesis. 相似文献
92.
En Zhang Natalia Fulik Guang‐Ping Hao Han‐Yue Zhang Katsumi Kaneko Lars Borchardt Eike Brunner Stefan Kaskel 《Angewandte Chemie (Weinheim an der Bergstrasse, Germany)》2019,131(37):13194-13199
A new asymmetric capacitor concept is proposed providing high energy storage capacity for only one charging direction. Size‐selective microporous carbons (w<0.9 nm) with narrow pore size distribution are demonstrated to exclusively electrosorb small anions (BF4?) but size‐exclude larger cations (TBA+ or TPA+), while the counter electrode, an ordered mesoporous carbon (w>2 nm), gives access to both ions. This architecture exclusively charges in one direction with high rectification ratios (RR=12), representing a novel capacitive analogue of semiconductor‐based diodes (“CAPode”). By precise pore size control of microporous carbons (0.6 nm, 0.8 nm and 1.0 nm) combined with an ordered mesoporous counter electrode (CMK‐3, 4.8 nm) electrolyte cation sieving and unidirectional charging is demonstrated by analyzing the device charge‐discharge response and monitoring individual electrodes of the device via in situ NMR spectroscopy. 相似文献
93.
Christian G. Vogt Sven Grtz Stipe Lukin Ivan Halasz Martin Etter Jack D. Evans Lars Borchardt 《Angewandte Chemie (International ed. in English)》2019,58(52):18942-18947
The milling ball is the catalyst. We introduce a palladium‐catalyzed reaction inside a ball mill, which makes catalyst powders, ligands, and solvents obsolete. We present a facile and highly sustainable synthesis concept for palladium‐catalyzed C?C coupling reactions, exemplarily showcased for the Suzuki polymerization of 4‐bromo or 4‐iodophenylboronic acid giving poly(para‐phenylene). Surprisingly, we observe one of the highest degrees of polymerization (199) reported so far. 相似文献
94.
95.
A counterexample to an algorithm of Dien (1988) for solving a minimization problem with a quasiconcave objective function and both linear and a reverse-convex constraint shows that this algorithm needn't lead to a solution of the given problem. 相似文献
96.
We report on 18O tracer diffusion experiments and model calculations for the study of cation vacancy migration in oxide crystals. The model takes advantage of the electrostatic coupling forces between anion and cation defects that allow the evolution of the cation vacancy profile to be observed by anion tracer experiments. Applied to SrTiO3, the ambipolar diffusion of strontium vacancies with H(A)=3.5 eV was found to be the dominant reequilibration mechanism of the cation sublattice. This result is in contrast to earlier studies proposing the formation of SrO intergrowth phases. 相似文献
97.
Zhiqing He Günter Borchardt Wolfgang Wegener 《Fresenius' Journal of Analytical Chemistry》1994,348(4):264-268
Summary Despite recent progress in instrument design the surface analysis of poorly conducting materials by modern techniques operating with either primary and/or secondary charged particles always leads to an accumulation of electric charges on the bombarded surface. In materials with an appreciable ionic conductivity the resultant electric field will induce the migration of mobile species and will therefore modify elemental concentration profiles. As an illustration of this problem we present a phenomenological study of an ionic model material which contains only one mobile species (e.g. sodium or hydrogen in oxide glasses at room temperature). A simultaneous numerical solution of the diffusion equation and of Poisson's equation permits to calculate the electric field and the ionic charge carrier concentration profiles in the near surface region of the material as a function of time. Although material ablation by sputtering is not yet taken into account, this approach gives useful insights into what happens in the near surface region of an ionic conductor on analysing it by SIMS or related techniques which also produce shallow charged layers on the surface of the target. On the other hand, the results are also applicable to plasma based treatments of glass surfaces currently applied in PVD coating processes.Presented at the 7th Working Conference on Applied Surface Analysis at Jülich (Germany), June 22–25, 1992 [Other lectures and posters in Fresenius' J Anal Chem (1993): 346:1–3] 相似文献
98.
99.
T. Richter G. H. Frischat G. Borchardt und S. Scherrer 《Fresenius' Journal of Analytical Chemistry》1987,329(2-3):323-326
Summary The hydration of silicate glasses results in the formation of a layer which is depleted in alkali oxides. It is still unknown which of the species H+, H3O+ or H2O diffuses into the glass. In order to clarify the exchange mechanism in particular for reaction times less than 1 h, specimens of a model glass were leached in H2O, D2O, H2
18O and D2
18O. The hydrated layers were analyzed by means of NPB-SIMS, a method using neutral atoms as primary particles. The results indicate significant deviations from long-term leaching kinetics. From the 18O depth profiles it is clear that an oxygen species interdiffuses with sodium ions. 相似文献
100.