Biological systems nitrogenases

Of particular interest are those complexes which serve as model compounds for biological systems such as the active center of the MoFe protein in nitrogenase.107 These complexes will be discussed in detail in the relevant chapters. It should be noted here, however, that WS2- is a non-innocent ligand, and thus complexes such as [Co(WS4)2]" (n = 2,3)108>109 and [Fe(WS4)2]" (n = 2, 3) can easily be prepared.110,111,112 In addition, some unusual complexes have been synthesized with WS2- as ligands. One such example is [Fe3W3S12]4 which contains the Fe3(/r3-S)2 center as depicted in Figure 11. 

Eady, R.R. 1990. Vanadium nitrogenases. In Vanadium in biological systems. N.D. Chasteen (Ed.), Kluwer Academic Publishers, Dordrecht, pp. 99-127. 

Eady, R.R. 1995. Vanadium nitrogenases of Azotobacter. Metal Ions in Biological Systems 31 363 -05. 

Applications to specific biological systems containing vanadium will be addressed in some detail in the context of the respective subsections of Chapter 4 on naturally occurring vanadium compounds vanadium in sea squirts (e.g. Figure 4.3), vanadate-dependent haloperoxidases (e.g. Table 4.5) and vanadium nitrogenases (e.g. Table 4.8). The central messages, including key references, are briefly summarised here. 

Eady RR (1990) Vanadium nitrogenases. In Chasteen ND, ed. Vanadium in Biological Systems, pp. 99—127. Kluwer Dordrecht, Netherlands. 

Eady RR (1995) Vanadium nitrogenases of Azoto-bacter. In Sigel H and Sigel A, eds. Metal Ions in Biological Systems, Vanadium and its Role in Life, pp. 363-405. Marcel Dekker, Inc, New York, Basel, Hong Kong. 

In biological systems Mo is present as the Fe/Mo cofactor of the nitrogenase enzymes (2) and of the multitude of oxidoreductases (3). In the latter the common molybdopterin cofactor (4), in addition to a dithiolene functionalized pyranopterin (5) ligand (Fig. 1), contains terminal oxo ligands and in the case of xanthine oxidase both oxo and thio ligands. Some aspects of molybdenum sulfur chemistry discussed in this work may be relevant to the biosynthesis of the molybdopterin cofactor and the function of xanthine oxidase (6). 

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