ChemInform Abstract: The Smallest “Aurophilic Species”.

ChemInform is a weekly Abstracting Service, delivering concise information at a glance that was extracted from about 200 leading journals. To access a ChemInform Abstract of an article which was published elsewhere, please select a “Full Text” option. The original article is trackable via the “References” option.     

The “Nickel Effect”

Whereas the reaction of ethylene and triethylaluminum under pressure at 100°C yields trialkylaluminum compounds having long alkyl chains, the presence of small amounts of nickel salts induces the formation of butene. The discovery of this “nickel effect” represents the starting point for the development of the Ziegler catalysts. Comparatively little was formerly known about the nature and the mode of action of the catalytically active nickel species. A basis for the elucidation of the effect was provided by studies on the reduction of nickel compounds by organoaluminum compounds, on the occurrence and existence of nickel hydrides, and on interactions between nickel(0) and Lewis acids as well as organic compounds of main group metals. The most significant result of these studies is the recognition that multicenter bonding systems involving trialkylaluminum compounds and nickel atoms are involved. These react further with complex bonded ethylene in what is probably a concerted manner.     

Structure and Evolution of the “Atmungsferment” Cytochrome c Oxidase

Approximately 50 years ago, Otto Warburg received 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 capacity.