ISBN: 978-83-60043-10-3 - eurobic9

Eurobic9, 2-6 September, 2008, Wrocław, Poland
SL1. Temperature Dependent Electrochemistry of Analogous Models for
Molybdenum and Tungsten Enzymes
C. Schulzke
Institut fuer Anorganische Chemie, Georg-August-Universitaet Goettingen, Tammannstr. 4, 37077, Goettingen,
Germany,
e-mail: carola.schulzke@chem.uni-goettingen.de
Molybdopterin containing enzymes are important components of almost any known organism. They catalyse the
Oxo transfer as a two-electron redox process and are involved in the C, N and S metabolisms. Every enzyme of
this kind is either a reductase or an oxidase and they show very diverse substrate specifities. In most cases the
active site metal is molybdenum. Not so in the thermophillic and hyperthermophillic microorganisms which
utilise tungsten. As reasons for this distribution several issues are discussed in the literature (evolution, metal
supply, stability, redox potentials [1-5]) but a final conclusion is still to be drawn. If the redox potentials play a
vital role for the enzymes` choice of metal, this could be due to different temperature dependencies of
molybdenum and tungsten compounds. To evaluate this hypothesis we investigated known[5-10] and new pairs
of analogous molybdenum and tungsten complexes (with and without dithiolene ligands) with temperature
dependent voltammetry methods. The results show that there appears to be indeed a fundamental difference in
the redox potentials behaviour with changing temperatures. This may be an indication that the evolutionary
change from tungsten to molybdenum took not place only because of the better availability of molybdenum
under mesophillic conditions but also because it provides more stable redox potentials[10].
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[10] C. Schulzke, Dalton Trans. 2005, 713.
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