ISSN:0570-0833    

DOI:10.1002/anie.199400031

出版商:Hüthig&Wepf Verlag    

年代:1994

数据来源: WILEY

摘要:

AbstractOne can view plants as a reference library of compounds waiting to be searched by a chemist who is looking for a particular property. Taxol, a complex polyoxygenated diterpene isolated from the Pacific Yew,Taxus brevifolia, was discovered during extensive screening of plant materials for antineoplastic agents during the late 1960s. Over the last two decades, interest in and research related to taxol has slowly grown to the point that the popular press now seems poised to scoop each new development. What was once an obscure compound, of interest only to the most masochistic of synthetic chemists and an equally small number of cellular biologists, has become one of the few organic compounds, which, like benzene and aspirin, is recognizable by name to the average citizen. In parallel, the scientific study of taxol has blossomed. Physicians are currently studying its effects on nearly every known neoplasm. Biologists are using taxol to study the mechanisms of cell function by observing the effects of its interactions with the cellular skeletal systems. Synthetic chemists, absorbed by the molecule's unique and sensitive structure and functionality, are exploring seemingly every available pathway for its synthesis. Indeed, the demand for taxol has risen so in the last five years that alternative sources to the extraction ofT. brevifoliaare being vigorously pursued. Because of the rapidly expanding scope of research in the multifaceted study of taxol, those who are interested in the field may find acquisition of a reasonable base of knowledge an arduous task. For this reason, this account attempts to bring together, for the first time, in a cogent overview the chemistry and biology of this unique molecule.

ISSN:0570-0833    

DOI:10.1002/anie.199400151

出版商:Hüthig&Wepf Verlag    

年代:1994

数据来源: WILEY

摘要:

AbstractAlthough the effect on which X‐ray absorption spectroscopy (EXAFS spectroscopy) is based has been known for about 70 years, up until about 20 years ago it had not found any application. The reasons for this were on the one hand the shortage of efficient X‐ray sources, and on the other hand the lack of a suitable theoretical description. With the advent of synchrotron radiation the situation has changed completely. Today, EXAFS spectroscopy is applied to a variety of very different problems and used more and more frequently to answer chemical questions. The extraordinary behavior of EXAFS spectroscopy that allows the determination of local structures in almost any mixture, independent of the sample's physical state as well as element‐specifically with high sensitivity, carries with it the danger that the amount of the obtainable structural information will be overestimated. A realistic estimate of the capability of EXAFS spectroscopy has in the meantime been achieved for crystalline materials, but not for amorphous materials. In this case the viewpoints range from complete rejection to overinterpretation of the EXAFS spectrum. In this article an attempt is made to show how EXAFS spectroscopy can be applied in the investigation of noncrystalline materials. First, the measurement techniques, data analysis procedures, and the simulation of EXAFS spectra are explained. Starting with the simplest systems, the amorphous metals and nonmetals, and using representative but not necessarily current examples, an explanation is given of the structural information provided by EXAFS spectroscopy, of how the local environment about the two components can be determined in binary systems, and of how even the crystallization process and structural changes can be investigated in chemical reactions. Thereafter, EXAFS studies on solutions, molecular liquids, and melts are presented. The final section is concerned with typical applications of EXAFS spectroscopy, the investigation of homogeneous and heterogeneous catalysts as well as the elucidation of active sites in en

ISSN:0570-0833    

DOI:10.1002/anie.199400451

出版商:Hüthig&Wepf Verlag    

年代:1994

数据来源: WILEY

ISSN:0570-0833    

DOI:10.1002/anie.199400671

出版商:Hüthig&Wepf Verlag    

年代:1994

数据来源: WILEY

ISSN:0570-0833    

DOI:10.1002/anie.199400691

出版商:Hüthig&Wepf Verlag    

年代:1994

数据来源: WILEY

ISSN:0570-0833    

DOI:10.1002/anie.199400731

出版商:Hüthig&Wepf Verlag    

年代:1994

数据来源: WILEY

ISSN:0570-0833    

DOI:10.1002/anie.199400751

出版商:Hüthig&Wepf Verlag    

年代:1994

数据来源: WILEY

ISSN:0570-0833    

DOI:10.1002/anie.199400771

出版商:Hüthig&Wepf Verlag    

年代:1994

数据来源: WILEY

ISSN:0570-0833    

DOI:10.1002/anie.199400801

出版商:Hüthig&Wepf Verlag    

年代:1994

数据来源: WILEY

ISSN:0570-0833    

DOI:10.1002/anie.199400821

出版商:Hüthig&Wepf Verlag    

年代:1994

数据来源: WILEY