Speciation 98: Abstracts
Dieter Rehder
Institut für Anorganische und Angewandte Chemie, Universität Hamburg, D-20146 Hamburg (Germany)
Vanadium is an essential constituent of two enzymes (nitrogenase, haloperoxidase) and a low-molecular weight compound, amavadin, found in Amanita mushrooms. It further is accumulated by sea squirts and fan worms. Vanadate also interacts with a variety of enzymes, and the greater part of this interaction results in the inhibition of phosphorylation enzymes, which is due to the comparability of vanadate and phosphate, or the inhibition of enzymes with cysteinyl in their active sites as a result of the redox-activity of VV and VIV. The insulin-mimetic action of many vanadium compounds is related to this kind of interaction.
We have modelled the binding of vanadium to protein side-chain function such as provided by tyrosinate, serinate, aspartate, glutamate, cysteinate, methionine and histidine. Complexes were synthesised which constitute ligand sets containing phenolate, alkoxide, carboxylate, thiolate, thioether and enamine functions. Several of these complexes are depicted in the Figure. The solid state investigations have been supplemented by solution studies of the vanadate-dipeptide and the vanadate-nucleoside systems. Some of the structural models also exhibit functional similarities with the enzymes, and are related to in vitro applications. Examples are the oxidation of thioethers (to sulfoxides), of thiolates (to disulphides), the reductive protonation of dinitrogen and alkynes, and the reductive C-C coupling of isonitriles, reactions which are catalysed by vanadium complexes resembling the active centres in vanadium-nitrogenase and vanadate-dependent haloperoxidases.
The relevance of catecholatovanadium complexes for the accumulation of vanadium by sea squirts, and the possible transport and protection of oligovanadates by ionophores is also addressed.
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