Model biological iron-sulfur cluster

If one applies the same procedure to Figure 1.10B, an iron-sulfur cluster often used as a model for those in biological systems, the same magic number of 60 would be obtained. Cluster magic numbers would occur as 48 e for a triangular clusters, 60 e for tetrahedral, 72 e for trigonal bipyramidal, 74 e for square pyramidal, 86 e for octahedral, 90 e for trigonal prisms, and 120 e for cubic structures. 

This section is organized as follows we first start with a discussion of the electrochemical behavior of the Roussin-type synthetic iron- sulfur clusters for their historic importance and as an interesting introduction to poly iron-sulfur centers redox chemistry. Then we review iron-sulfur centers in proteins and artificial models in the order of increasing iron content. Finally, biological iron-sulfur centers and artificial models directly linked to other inorganic centers, the so-called bridged molecular assemblies, are considered. 

Iron-sulfur proteins belong to the class of electron-transport proteins [29]. They contain an iron sulfur cluster, e.g. [4Fe-4S], which shuttles between different oxidation states. The structure of the cluster is quite consistent among a series of these proteins, but their redox potentials vary widely. Synthetic models of iron-sulfur proteins have been designed [30] to investigate the factors that determine the reduction potential of the core and to mimic other biologically... 

Synchrotron-based nuclear resonance methods have revealed the vibrational dynamics of the iron atom in numerous systems, including alloys, amorphous materials, nanomaterials, and materials under high pressure. The above-mentioned selectivity for the probe nucleus is particularly valuable for biological macromolecules, which may contain many thousands of atoms, but a localized active site is often the true center of interest. Since its availability, NRVS has been applied to study the vibrational dynamics of Fe in proteins, porphyrin model compounds, " and iron-sulfur clusters. It is shown that NRVS can provide frequencies, amplitudes, and directions for Fe vibrations in the samples. It helps to clarify mode assignments in vibrational spectra and reveals many important vibrational modes of Fe that cannot be seen by other methods. In particular, NRVS reveals low-frequency motions of the Fe down to below 100 cm that control biological reactions. The applications presented here use Fe as the probe nucleus, but the principle applies to other Mossbauer isotopes such as " Sn, Kr, Ni, and Zn if appropriate sources are available. 

Iron-sulfur clusters are important and much investigated because they serve as models for iron-sulfur proteins, which constitute a large and significant group of biologically active substances. These substances are probably fundamental for all forms of life. They are important for such processes as the uptake and evolution of hydrogen, nitrogen fixation, ATP formation, electron transfer, and the like. 

The first successful model system for an iron-sulfur protein was an analogue of the Fe4S4 system, i.e., the system with the largest presently established biological Fe cluster. The reactions used to synthesize the cluster shown in Figure... 

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