Iron-sulfur complexes

Molybdenum hexafluoride. 3,1412 Molybdenum-iron-sulfur complexes, 4,241 Molybdenum oxide amino acid formation prebiotic systems, 6, 872 Molybdenum storage protein microorganisms, 6, 681 Molybdenum telluride, 3, 1431 Molybdenum tetraalkoxides physical properties, 2, 347 Molybdenum tribromide, 3,1330 Molybdenum trichloride, 3,1330 Molybdenum trifluoride, 3, 1330 Molybdenum trihalides, 3, 1330 bond lengths, 3, 1330 magnetic moments, 3,1330 preparation, 3,1330 properties, 3, 1330 structure, 3,1330 Molybdenum triiodide, 3,1330 Molybdenum trioxide complexes, 3, 1379 Molybdenum triselenide, 3, 143)... 

Fig. 46. Schematic structure of the iron-sulfur complex in two-iron ferredoxin and adrenodoxin. (Adapted from Ref. 267)...

Carrell, H. L., dusker, J. P., Job, R., and Bruice, T. C. (1977). A synthetic tetranuclear iron-sulfur complex with ionized side chains The crystal structure of (Fe4S4(S(CH2)aCOO)4) -(Na5-N(C4H9)4) -5C6H9NO./. Am. Chem. Soc. 99, 3683-3690. 

The recent discovery that a class of electron mediating proteins, the ferredoxins (Sec. IVE2), characteristically contain two or more iron atoms bridged by sulfur atoms has stimulated interest in polynuclear iron-sulfur complexes. It seems appropriate therefore to review here what little is known about such species. 

The acidity of these proteins implies that the amino acids which occur in areas of the sequence with a preponderance of glutamic acid, aspartic acid and glutamine will not be free to ligate to the iron-sulfur complex, as they will be drawn out to the periphery of the protein conformation. Thus, consideration of the similarities in the Mossbauer spectra and inspection of the amino acid sequences and composition (170, 171) imply that cysteine is the most probable ligand to the iron-sulfur complex, and that the structure shown in Fig. 15 is valid. 

We investigated (82) two iron sulfur complexes with diazene (di-imide) as the sixth ligand, [Fe(NHS4)(N2H2)] = 1 (N2H2) and [Fe(S4)PR3 (N2H2)] = 2(N2H2)(Fig.3). 

Smith MC, Barclay JE, Cramer SP, Davies SC, Gu W-W, Hughes DL, Longhurst S, Evans DJ (2002) Nickel-iron-sulfur complexes approaching structural analogues of the active sites of NiFe-hydrogenase and carbon monoxide dehydrogenase/acetyl-CoA synthase. Dalton Trans. 2641-2647... 

Sellmann, D., Utz, J., Blum, N., and Heinemann, F. W. (1999) On the function of nitrogenase FeMo cofactors and competitive catalysts chemical principles, structural blue-prints, and the relevance of iron sulfur complexes for N2 fixation, Coord. Chem. Rev. 190-192, 607-627. 

Coenzyme Q passes electrons through iron-sulfur complexes to cytochromes b and ch which transfer the electrons to cytochrome c. In the ferric Fe3+ state, the heme iron can accept one electron and be reduced to the ferrous state Fe2+. Since the cytochromes carry one electron at a time, two molecules on each cytochrome complex are reduced for every molecule of NADH that is oxidized. The electron transfer from coenzyme Q to cytochrome c produces energy, which pumps protons across the inner mitochondrial membrane. The proton gradient produces one ATP for every coenzyme Q-hydrogen that transfers two electrons to cytochrome c. Electrons from FADH2, produced by reactions such as the oxidation of succinate to fumarate, enter the electron transfer chain at the coenzyme Q level. 

Newton, W. E. et al. Molybdenum-iron-sulfur complexes and their relevance to the molybdenum site of nitrogenase, in Ref. 23, p. 30... 

There is a large body of knowledge on the coordination chemistry of iron-sulfur complexes and iron clusters particularly directed at the modeling and nnderstanding of the action of nonheme proteins whose active sites contain iron-sulfur units. These topics are discussed in detail elsewhere in this Encyclopedia here, the emphasis is on the basic coordination chemistry. 

Dinuclear and tetranuclear complexes are also suitable starting materials, and much of the synthetic and substitutional chemistry of these species reflects the ability of the systems to sustain monomeric solvated dinitrosyl species such as [Fe(NO)2(solvent)2]+ or [Fe(NO)2(SR)(solvent)]. The latter tend to be formed in solvents having poor and the former in ones having good tt-acceptor capabilities. A review of nitrosyl complexes of iron-sulfur complexes is available. 

R. K. Thauer and P. Schonbeit, Iron-Sulfur Complexes of Ferredoxin as a Storage Form of Iron in Clostridium pasteurianum, in Tron-Sulfur Proteins , ed. T. G. Spiro, Wiley, New York, 1982, p. 329. 

W. A. Eaton and W. Lovenberg, The Iron-Sulfur Complex in Rubredoxin, in Iron Sulfur Proteins , ed. W. Lovenberg, Academic Press, New York, 1973, Vol. 12, p. 131. 

Figure 17.12. Binding of Citrate to the Iron-Sulfur Complex of Aconitase. A 4Fe-4S iron-sulfur cluster is a component of the active site of aconitase. One of the iron atoms of the cluster binds to the carboxylate and hydroxyl groups of citrate.

The electron carriers in the respiratory assembly of the inner mitochondrial membrane are quinones, flavins, iron-sulfur complexes, heme groups of cytochromes, and copper ions. Electrons from NADH are transferred to the FMN prosthetic group of NADH-Q oxidoreductase (Complex I), the first of four complexes. This oxidoreductase also contains Fe-S centers. The electrons emerge in QH2, the reduced form of ubiquinone (Q). The citric acid cycle enzyme succinate dehydrogenase is a component of the succinate-Q reductase complex (Complex II), which donates electrons from FADH2 to Q to form QH2.This highly mobile hydrophobic carrier transfers its electrons to Q-cytochrome c oxidoreductase (Complex III), a complex that contains cytochromes h and c j and an Fe-S center. This complex reduces cytochrome c, a water-soluble peripheral membrane protein. Cytochrome c, like Q, is a mobile carrier of electrons, which it then transfers to cytochrome c oxidase (Complex IV). This complex contains cytochromes a and a 3 and three copper ions. A heme iron ion and a copper ion in this oxidase transfer electrons to O2, the ultimate acceptor, to form H2O. 

Plastoquinone in turn is a reductant for excited P700 of photosystem PS I, which operates similarly to the system PS II and has a reduction potential sufficient for an electron transfer to the iron-sulfur complex of ferredoxin and finally to NADP , producing NADP -H,. 

Iron-iron bonds exist in carbonyl and nitrosyl derivatives, but these are not considered in this section. Properties consistent with Fe-Fe interactions in other systems are dominated by sulfur donor ligands. The presence of Fe-Fe bonds is not unambiguous, with sulfur bridges invariably accompanying short metal-metal separations. Synthetic routes to polynuclear iron-sulfur complexes are presented for completeness without implying the cluster bonding scheme. 

Steel, stainless steel, and copper-free steel alloys are the preferred materials of construction for mercaptan service. In particular, stainless steel should be used for any vessel or line that is to be open and exposed to air frequently. Aluminum is also suitable for mercaptan use provided the pressure rating of aluminum equipment or piping is sufficient to meet the pressure requirements of the application. Iron or carbon steel is less acceptable than stainless steels or aluminum although it can be used if appropriate measures are taken to condition the iron or carbon steel equipment before putting it into service. Allowing a small amount of mercaptan to stand in it for a period of time and subsequently keeping the equipment under a dry, inert atmosphere can prevent corrosion of the equipment. The hazard in using iron or carbon steel is the formation of iron-sulfur complexes, which are pyrophoric... 

Binding of citrate to the iron—sulfur complex of aconitase Figure 17.12... 

Many investigators have searched the mineral world for possible catalysts of biogenic reactions. Suggestive results have been obtained with metal ions, zinc for example (Lohrmann et al., 1980), clays (Cairns-Smith, 1982 Ferris, 1998), double-layer metal hydroxide minerals (Pitsch et al., 1995), pyrite (Wachtershauser, 1998), and iron-sulfur complexes (Cammack, 1983 Wachtershauser, 1998). To what extent such materials may have been crucial to the origin of life on earth is, however, not known. In addition, doubts have often been expressed that mineral catalysts could, alone, have sufficed to launch life. 

Manganese(VI) complexes, 109-111 Manganese(VII) complexes, 109-111 Marcasite, 1240 Mercury compounds ruthenium complexes, 280 Mesoperrhenates, 198 Mesoporphyrin iron complexes, 1266 Methemerythrin, 254 Molybdenum-iron-sulfur complexes, 241 MOssbauer spectroscopy iron, 1181... 

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