Nitrogen fixation Molybdenum

Keywords Dinitrogen complexes, Organo-nitrogen compounds, Nitrogen fixation, Molybdenum complexes, Tungsten complexes... 

Molybdenum is an essential element for several enzymes important in plant and animal metabolism. It has a unique role in nitrogenase, an enzyme that converts molecular nitrogen into ammonia in nitrogen fixation. Molybdenum enzymes provide the key steps in the fixation of nitrogen by microorganisms and its utilization by higher plants (Table 1). 

Soil Nutrient. Molybdenum has been widely used to increase crop productivity in many soils woddwide (see Fertilizers). It is the heaviest element needed for plant productivity and stimulates both nitrogen fixation and nitrate reduction (51,52). The effects are particularly significant in leguminous crops, where symbiotic bacteria responsible for nitrogen fixation provide the principal nitrogen input to the plant. Molybdenum deficiency is usually more prominent in acidic soils, where Mo(VI) is less soluble and more easily reduced to insoluble, and hence unavailable, forms. Above pH 7, the soluble anionic, and hence available, molybdate ion is the principal species. 

Finally, in 1797, the Frenchman L. N. Vauquelin discovered the oxide of a new element in a Siberian mineral, now known as crocoite (PbCr04), and in the following year isolated the metal itself by charcoal reduction. This was subsequently named chromium (Greek xpco ia, chroma, colour) because of the variety of colours found in its compounds. Since their discoveries the metals and their compounds have become vitally important in many industries and, as one of the biologically active transition elements, molybdenum has been the subject of a great deal of attention in recent years, especially in the field of nitrogen fixation (p. 1035). 

In animal metabolism, oxomolybdoenzymes catalyse a number of oxidation processes. These oxidases contain Mo coordinated to terminal O and S atoms, and their action appears to involve loss of an O or S atom along with reduction to Mo or Mo". It is, however, the role of molybdenum in nitrogen fixation which has received most attention. 

NEW DEVELOPMENTS IN SYNTHETIC NITROGEN FIXATION WITH MOLYBDENUM AND TUNGSTEN PHOSPHINE COMPLEXES1 ... 

Hidai, M. (1999) Chemical nitrogen fixation by molybdenum and tungsten complexes, Coord. Chem. Rev., 185-186, 99-108. 

Hille, R. (2005) Molybdenum-containing hydroxylases, Arch. Biochem. Biophys., 433, 107-116. Howard, J.B. and Rees, D.C. (2006) How many metals does it take to fix N2 A mechanistic overview of biological nitrogen fixation, Proc. Natl. Acad. Sci. U.S.A., 103, 17088-17093. Knowles, J.R. (1991) Enzyme catalysis not different, just better, Nature, 350, 121-124. 

Structural basis of biological nitrogen fixation, Phil. Trans. R. Soc., 363, 971-984. Schrock, R.R. (2005) Catalytic reduction of dinitrogen to ammonia at a single molybdenum center,... 

Marino R, Howarth RW, Chan F, Cole JJ, Likens GE (2003) Sulfate inhibition of molybdenum-dependent nitrogen fixation by planktonic cyanobacteria under seawater conditions a non-reversible effect. Hydrobiol 500 277-293... 

MgATP hydrolysis and, 47 189-191 nitrogenase complex, 47 186-189 substrates, 47 192-202 molybdenum iron proteins, 47 161, 166-174, 176-183, 191-192 structure, 47 162-164, 166-170 nitrogen fixation role, 36 78 in nitrogen fixation systems, 27 265-266 noncomplementary reactions with Sn", 10 215... 

The electrosynthesis of hydride complexes directly from molecular hydrogen at atmospheric pressure by reduction of Mo(II) and W(II) tertiary phosphine precursors in moderate yield has been described as also the electrosynthesis of trihydride complexes of these metals by reduction of M(IV) dihydride precursors [101,102]. Hydrogen evolution at the active site of molybdenum nitrogenases [103] is intimately linked with biological nitrogen fixation and the electrochemistry of certain well-defined mononuclear molybdenum and tungsten hydrido species has been discussed in this context [104,105]. 

New Developments in Synthetic Nitrogen Fixation with Molybdenum and Tungsten Phosphine Complexes Ameli Dreher, Gerald Stephan and Felix Tuczek... 

---