James T. Huneke

Structural Studies of Molybdenum Complexes

Molybdenum-containing enzymes are vitally important in nitrogen uptake, nitrogen metabolism and several biochemical reactions.1,2 The detailed coordination environment about the molybdenum atoms of such enzymes is still unknown because no molybdoenzyme has had its structure determined by x-ray crystallography. However, the molybdenum centers of several enzymes have been probed directly by electron paramagnetic resonance (EPR) spectroscopy1 and by x-ray absorption spectroscopy (EXAFS).3–5 Comparison of the spectral data from enzymes with spectral data from coordination compounds suggests that sulfur atoms are coordinated to molybdenum in the enzymes. EXAFS data from xanthine oxidase4 and sulfite oxidase5 in their oxidized forms also indicate the presence of terminal oxo groups attached to the molybdenum. In order to effectively interpret the spectral results from enzymes, it is important to have available a series of compounds whose stoichiometry and stereochemistry have been definitively established by x-ray structure determination. Of particular interest are compounds of sulfur donor ligands and oxomolybdenum(V) species.