Tetranuclear iron-sulfur clusters

Tetranuclear iron-sulfur clusters of the type [Fe4S4(SR)4]2, where R = CH2C6H5 and C6H5, were found138 to catalyze the reduction of C02 in DMF solutions. Controlled-potential electrolyses were carried out in a C02-saturated 0.1 M tetrabutylammonium tetrafluoroborate (TBAT)-DMF solution at a mercury pool cathode. In the absence of a catalyst, C02 was substantially reduced only at potentials more negative than -2.4 V versus SCE, while in the presence of a cluster, the reduction took place at around -1.7 V thus, potential shift of ca. 0.7 V was achieved. The products were analyzed by means of gas chromatography and isotachophoresis. Without a catalyst, oxalate was the main product, and addition of small amounts of water to the DMF solution favored formate production, whereas in the presence of the catalyst, formate was produced predominantly even in a dry DMF solution. This result was interpreted in terms of indirect reduction of C02, proceeding by electron transfer from the reduced cluster to C02 in the bulk... 

Salerno, J. C., Ohnishi, T., Lim, J., and King, T. E. (1976). Tetranuclear and binuclear iron-sulfur clusters in succinate dehydrogenase A method of iron quantitation by formation of paramagnetic complexes. Biochem. Biophys. Res. Commun. 73, 833-839. 

Tetranuclear iron-sulfur clusters are key relay stations in the electron flow in photosynthesis. Photosystem I comprises three subunits, PsaA, PsaB and PsaC. The latter contains two [Fe4S4] centres FA and FB. The core subunits PsaA and B, respectively, house a [Fe4S4] centre denoted FX in addition to other, organic cofactors. The role of this latter cluster was probed in preparations partially devoid of PsaC. It was concluded from the results that FX has a major role in controlling the electron transport through PS I.236 Since the final acceptor of the electrons in PS I is a ferredoxin with a [Fe2S2] cluster it was of interest to study a... 

Glaser T, Rose K, Shadle SE, Hedman B, Hodgson , Solomon El (2001) S -edge X-ray absorption studies of tetranuclear iron-sulfur clusters p-sulfide bonding and its contribution to electron delocalization. J Am Chem Soc 123 442-454... 

Several other tetranuclear iron-sulfur cluster compounds of general formula [Fc4S4X4]" ", in which X is a non-thiolate terminal ligand, have been studied in some detail. These include systems in which X = Cl, NO and dithiolene. The structure of the dianion [Fe4S4Cl4] " has been... 

Iron-sulfur cluster compounds, 1203 dinuclear, 235 electrochemistry, 236 hexanuclear, 241 mononuclear, 235 tetranuclear, 238 trinuclear, 237 Isomerization iridium catalysts, 1158... 

Iron-sulfur-nitrosyl complexes (continued) from tetranuclear precursors, 32 343 tellurium analogs, 32 350 tetrairon complexes, N NMR spectroscopy, 32 365 x-ray crystallography [Fe(NO)(S2CNR2)2 and related clusters, 32 359-361... 

An interesting new tetranuclear iron hybrid cluster protein (HCP) has been observed and characterized from two sulfate reducing bacteria. Combined X-ray diffraction and EPR data showed that it contains both oxygen and sulfur bridges between the iron ions. The nature of the cluster was found to be independent of the presence or absence of oxygen in the sample preparation.247... 

It is instructive, in this context, to compare the case of assembly of both nitrosylated iron sulfur tetranuclear clusters and the related clusters with pendant thiolate groups (13), with the laborious and stepwise initial synthesis (38) of cubane C8H8 this comparison is, of course, simply one between thermodynamically controlled processes, in the case of the iron sulfur systems, and kinetically controlled reactions for C8H8 synthesis. 

Tetranuclear Iron-Sulfur and Iron-Selenium Clusters 33... 

Fig. 17.2. Scheme of energy levels (a) in the iron-sulfur tetranuclear cluster and scheme of electron peculation of the highest orbitals (b). When the charge of the cluster changes by the addition or elimination of an electron, the cluster system can add or donate one to two electrons without a substantial change in ener and configuration. Therefore, it is characterized as a system with the great electron capacity (I.B. Bersuker). 

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