摘要:

AbstractAfter outlining the chemical features and properties which make zeolites such an important group of catalysts and sorbents, the article explains how high‐resolution solid‐state NMR with magic‐angle spinning reveals numerous new insights into their structure.29Si‐MAS‐NMR readily and quantitatively identifies five distinct Si(OAl)n(OSi)4‐nstructural groups in zeolitic frameworks (n = 0, 1,….4), corresponding to the first tetrahedral coordination shell of a silicon atom. Many catalytic and other chemical properties of zeolites are governed by the short‐range Si, Al order, the nature of which is greatly clarified by29Si‐MAS‐NMR. It is shown that, as expected from Pauling's electroneutrality principle and Loewenstein's rule, both in zeolite X and in zeolite A (with Si/Al = 1.00) there are no AlOAl linkages. In zeolite A and zeolite X with Si/Al = 1.00 there is strict alternation of Si and Al on the tetrahedral sites. Ordering models for Si/Al ratios up to 5.00 (in zeolite Y) may also be evaluated by a combination of MAS‐NMR experiments and computational procedures.29Si‐MAS‐NMR spectra reveal the presence of numerous crystallographically distinct Si(OSi)4sites in silicalite/ZSM‐5, suggesting that the correct space group for these related porosilicates is not Pnma.27Al‐MAS‐NMR clearly distinguishes tetrahedrally and octahedrally coordinated aluminum, proving that, contrary to earlier claims, Al in silicalite is tetrahedrally substituted within the framework. In combination,29Si‐ and27Al‐MAS‐NMR is a powerful tool for monitoring the course of solid‐state processes (such as ultrastabilization of synthetic faujasites) and of gas‐solid reactions (dealumination of zeolites with silicon tetrachloride vapor at elevated temperatures). They also permit the quantitative determination offrameworkSi/Al ratios in the region 1.00

ISSN:0570-0833    

DOI:10.1002/anie.198302593

出版商:Hüthig&Wepf Verlag    

年代:1983

数据来源: WILEY

摘要:

AbstractApproximately 50 years ago,Otto Warburgreceived the Nobel Prize for his fundamental work on the “Atmungsferment”. But not until the end of the fifties was it possible to isolate this complicated membrane enzyme, which is necessary for respiration and energy production in most living organisms on earth. Since then, intensive research has been performed to elucidate the mechanism of reduction of oxygen to water and the coupled translocation of protons across the membrane which is involved in ATP synthesis. Until now the results have been unsatisfactory because the four catalytic heavy‐metal redox centers are bound to proteins, the structures of which have begun to be studied only recently. In the course of this research, it was discovered that cytochrome c oxidase from bacteria contains only two or three, whereas the enzyme complex from animals contains thirteen different protein components. The present article analyzes the possible functions of the various protein subunits and, using the example of cytochrome c oxidase, shows that biochemical evolution proceeds in such a way as to increase regulatory cap

ISSN:0570-0833    

DOI:10.1002/anie.198302751

出版商:Hüthig&Wepf Verlag    

年代:1983

数据来源: WILEY

摘要:

AbstractClassical structural formulas often convey the impressiononly thoserelationships between the atoms are of importance which hold a molecule together as symbolized by the chemical bonds. However, many interactions between atoms or groups of atoms are not adequately denoted in this manner. Nevertheless, their existence can have important consequences forground state energies(cis‐difluoroethylene is more stable thantrans‐difluoroethylene),conformations(thesynform of methyl vinyl ether is more stable than theantiform),reactivities(anendocyclopropane ring in 7‐anti‐norbornyl derivatives accelerates solvolysis by a factor of 1014),UV spectra(“superposition” of the π‐systems of acridine and purine‐bonded through a four‐membered chain‐results in hypochromism),CD spectra(the inherently symmetrical but dissymmetrically perturbed chromophore of 2‐deuterionorbornadiene allows the observation of three transitions in the near UV), andESR spectra(the long‐range coupling with H‐4 in the bridgehead bicyclo[2.1.1]hex‐1‐yl radical equals 22.5 G). Since orbital interactions are involved in most intramolecular effects of this kind,photoelectron spectroscopyhas proven an informative and valua

ISSN:0570-0833    

DOI:10.1002/anie.198302831

出版商:Hüthig&Wepf Verlag    

年代:1983

数据来源: WILEY

摘要:

AbstractThe complete manuscript of this communication appears in:Angew. Chem. Suppl. 1983, 363. DOI:10.1002/anie.198303630

ISSN:0570-0833    

DOI:10.1002/anie.198303141

出版商:Hüthig&Wepf Verlag    

年代:1983

数据来源: WILEY

ISSN:0570-0833    

DOI:10.1002/anie.198303151

出版商:Hüthig&Wepf Verlag    

年代:1983

数据来源: WILEY

摘要:

AbstractThe complete manuscript of this communication appears in:Angew. Chem. Suppl. 1983, 396. DOI:10.1002/anie.198303960

ISSN:0570-0833    

DOI:10.1002/anie.198303161

出版商:Hüthig&Wepf Verlag    

年代:1983

数据来源: WILEY

摘要:

AbstractThe complete manuscript of this communication appears in:Angew. Chem. Suppl. 1983, 405. DOI:10.1002/anie.198304050

ISSN:0570-0833    

DOI:10.1002/anie.198303171

出版商:Hüthig&Wepf Verlag    

年代:1983

数据来源: WILEY

摘要:

AbstractThe complete manuscript of this communication appears in:Angew. Chem. Suppl. 1983, 307. DOI:10.1002/anie.198303070

ISSN:0570-0833    

DOI:10.1002/anie.198303181

出版商:Hüthig&Wepf Verlag    

年代:1983

数据来源: WILEY

摘要:

AbstractThe complete manuscript of this communication appears in:Angew. Chem. Suppl. 1983, 323. DOI:10.1002/anie.198303230

ISSN:0570-0833    

DOI:10.1002/anie.198303191

出版商:Hüthig&Wepf Verlag    

年代:1983

数据来源: WILEY

摘要:

AbstractThe complete manuscript of this communication appears in:Angew. Chem. Suppl. 1983, 457. DOI:10.1002/anie.198304570

ISSN:0570-0833    

DOI:10.1002/anie.198303201

出版商:Hüthig&Wepf Verlag    

年代:1983

数据来源: WILEY