摘要:

AbstractUp to the present time hemoglobin has enjoyed pride of place among the objects of study in molecular biology. Investigations on this molecule have culminated in the complete description of its atomic structure in various functional states and point the way for future research on other biopolymers. However, more than just a knowledge of the anatomy of this protein is required before we can make quantitative predictions about its function.

ISSN:0570-0833    

DOI:10.1002/anie.197106631

出版商:Hüthig&Wepf Verlag    

年代:1971

数据来源: WILEY

摘要:

AbstractAs a result of the development of pulse Fourier transform NMR spectroscopy13C resonance has become accepted as a means of elucidating the structures of organic compounds having the natural13C abundance. Assignment of the signals is facilitated by broad‐band and off resonance proton decoupling and by knowledge of longitudinal relaxation times. The pulse Fourier technique, which is more sensitive and faster than conventional NMR spectroscopy because of multi‐channel excitation, allows13C measurements within a short time even on dilute samples of high molecular weight compounds without prior enrichment in

ISSN:0570-0833    

DOI:10.1002/anie.197106731

出版商:Hüthig&Wepf Verlag    

年代:1971

数据来源: WILEY

摘要:

AbstractMolecules rearrange by regular and irregular processes. The former occur with preservation of bonds and coordination numbers while the latter involve rupture and reformation of bonds via states possessing different coordination numbers. For molecules with skeletons that carry n ligands both processes can be represented by permutation operators belonging to the symmetrical group Sn. These operators are obtained from the descriptors of the particular molecules in a simple manner; the conceivable reaction mechanisms correspond to the skeletal symmetry subclasses of Sn. Regular rearrangements—e.g. of phosphorane derivatives with a monocentric skeleton, including their analogs, or of ethane derivatives with a dicentric skeleton—all submit themselves to classification based upon skeletal non‐rigidity. Flexible molecular skeletons are representable by a collection of rigid skeletal models which can be interconverted by deformations of bond angles and/or some form of internal rotation. To accomplish mechanistic understanding of these regular processes, it is useful to represent the symmetries of the rigid skeletal models and the existent ligand equivalencies by subgroups of Snand consider the dependence of the skeletal flexibility upon the given ligand set. This procedure is based on the ideas of Polya and Longuet‐Higgins. The former introduced separation of permutational molecular symmetry into skeletal symmetry and ligand set symmetry, which, combined with the total molecular symmetry concept developed by Longuet‐Higgins for the treatment of non‐rigid symmetric molecules, yield the foundation for the following classification of regular pentacoordinate rearrangements and related processes. It will be shown that with the given quantum chemical properties of the pentacoordinate phosphorus bond system, including participation of the P3dorbital set, not only the BPR‘2’mechanism but also single and multiple TR[2]processes must be considered in the interpretation of the observed phenomena. Although some experimental observations can be interpreted by either of the two mechanisms, and certain other regular rearrangements can be explained only by invoking the TR mechanism, no regular processes are known, as yet, that can be explained solely by th

ISSN:0570-0833    

DOI:10.1002/anie.197106871

出版商:Hüthig&Wepf Verlag    

年代:1971

数据来源: WILEY

摘要:

AbstractThe factors influencing the chemical isomer shift, quadrupole splitting and hyperfine magnetic interactions, are briefly summarized and applications to solid state systems reviewed. New results on the disordered rutile phases Fe2MgF6, FeMg2F6, and FeCoNiF2, and on the trirutile phase Li+Fe2+Fe3+F6are presented to illustrate the power of the Mössbauer technique in probing details of oxidation states, site symmetries and magnetic ordering. An extensive study on the nonstoichiometric wüstite phase Fe1−xO is also reported and analyzed in terms of diffusion broadening at high temperatures and defect clustering in quenched samples; the production of essentially stoichiometric FeO by annealing is also discussed. Recent results on the application of large external magnetic fields to diamagnetic compounds of tin are reviewed and results of a Mössbauer investigation of lunar samples returned by the Apollo 11 and 12 missions are discu

ISSN:0570-0833    

DOI:10.1002/anie.197107161

出版商:Hüthig&Wepf Verlag    

年代:1971

数据来源: WILEY

ISSN:0570-0833    

DOI:10.1002/anie.197107252

出版商:Hüthig&Wepf Verlag    

年代:1971

数据来源: WILEY

ISSN:0570-0833    

DOI:10.1002/anie.197107261

出版商:Hüthig&Wepf Verlag    

年代:1971

数据来源: WILEY

ISSN:0570-0833    

DOI:10.1002/anie.197107271

出版商:Hüthig&Wepf Verlag    

年代:1971

数据来源: WILEY

ISSN:0570-0833    

DOI:10.1002/anie.197107281

出版商:Hüthig&Wepf Verlag    

年代:1971

数据来源: WILEY

ISSN:0570-0833    

DOI:10.1002/anie.197107291

出版商:Hüthig&Wepf Verlag    

年代:1971

数据来源: WILEY

ISSN:0570-0833    

DOI:10.1002/anie.197107301

出版商:Hüthig&Wepf Verlag    

年代:1971

数据来源: WILEY