摘要:

AbstractThe cycloadditions of 3‐hydroxy‐1‐methylpyridinium betaines with electron‐deficient olefins have been extended to a variety of 1‐substituents in place of methyl. Application of resonance theory and later of quantum chemical methods led to rationalization of preceding results and prediction of new reactions. Thermal additions of 2π‐ and 6π‐electron addends at the 2,6‐positions and of 4π‐electron addends at the 2,4‐positions are described. The cycloadducts are highly interesting potential syn

ISSN:0570-0833    

DOI:10.1002/anie.197600011

出版商:Hüthig&Wepf Verlag    

年代:1976

数据来源: WILEY

摘要:

AbstractCertain polyenic substances havingtransolefinic bonds in a 1,5 relationship can be induced to undergo stereospecific, non‐enzymic, cationic cyclization to give polycyclic products with all‐trans(“natural”) configuration. These transformations appear to mimic in principle the biogenetic conversion of squalene into polycyclic triterpenoids. Acetal and allylic alcohol functions are effective initiators for these cyclizations, and methylacetylenic end groups are particularly useful terminators since they lead to five‐membered rings. Thus a tetraenic acetal having no chiral centers has been converted in a single step into a tetracyclic product having seven such centers. The process is highly stereoselective, giving only two of 64 possible racemates. Systems have also been developed for effecting the total synthesis of the steroid nucleus in a single step starting from a substrate containing only one ring. The mechanism of these biomimetic cyclizations and also that of their enzymic counterparts is still unknown, but the balance of the evidence favors a synchronou

ISSN:0570-0833    

DOI:10.1002/anie.197600091

出版商:Hüthig&Wepf Verlag    

年代:1976

数据来源: WILEY

摘要:

AbstractApart from the long known visual pigments, another retinal protein complex exists in nature,viz.bacteriorhodopsin from halobacteria. In contrast to the visual pigments such as the rhodopsins, which act as light sensors in the eye, bacteriorhodopsin actually transforms light energy. This energy conversion is connected with the asymmetric incorporation of bacteriorhodopsin in the lattice structure of the purple membrane which forms patches on the cell surface of halobacteria. Alongside the chlorophyll system, the purple membrane system represents the second light energy conversion principle to be discovered in living nature. Bacteriorhodopsin acts as a light‐driven proton pump or as the main component of such a pump system. Absorption of light triggers off a cycle of reactions coupled with the spatially oriented uptake and release of a proton. In the intact cell an electrochemical gradient is thus built up across the cell membrane of the bacterium in which part of the absorbed light energy is stored and which is not dependent upon redox processes as in the case of respiration or photosynthesis. This electrochemical gradient can supply the energy required for ATP synthesis in the cell; a reversible proton‐translocating ATPase serves as catalyst sys

ISSN:0570-0833    

DOI:10.1002/anie.197600171

出版商:Hüthig&Wepf Verlag    

年代:1976

数据来源: WILEY

摘要:

AbstractCouched in the often confusing term “Fourier Spectroscopy” is the combined exploitation of a fundamental physical concept, a simple mathematical principle, and use of modern data technology. Introduction of this relatively young method into instrument technology has given great impetus to nuclear magnetic resonance and infrared spectroscopy. The infrared spectroscopic investigation of low frequency molecular vibrations has especially profited; in this connection one speaks of far infrared (FIR) Fourier Spectroscopy, which has opened up numerous interesting applications in organic, inorganic, and physical chemis

ISSN:0570-0833    

DOI:10.1002/anie.197600251

出版商:Hüthig&Wepf Verlag    

年代:1976

数据来源: WILEY

ISSN:0570-0833    

DOI:10.1002/anie.197600392

出版商:Hüthig&Wepf Verlag    

年代:1976

数据来源: WILEY

ISSN:0570-0833    

DOI:10.1002/anie.197600401

出版商:Hüthig&Wepf Verlag    

年代:1976

数据来源: WILEY

ISSN:0570-0833    

DOI:10.1002/anie.197600411

出版商:Hüthig&Wepf Verlag    

年代:1976

数据来源: WILEY

ISSN:0570-0833    

DOI:10.1002/anie.197600421

出版商:Hüthig&Wepf Verlag    

年代:1976

数据来源: WILEY

ISSN:0570-0833    

DOI:10.1002/anie.197600431

出版商:Hüthig&Wepf Verlag    

年代:1976

数据来源: WILEY

ISSN:0570-0833    

DOI:10.1002/anie.197600441

出版商:Hüthig&Wepf Verlag    

年代:1976

数据来源: WILEY