Iron-sulfur clusters substitution reactions

The initial 6 A-resolution X-ray work showed one of the [4Fe 4S] clusters is 15 A and the other 22 A from the preceding iron-sulfur electron acceptor, FeS-X. Discussion of the iron-sulfur center FeS-X itself will be deferred to Chapter 31, where the interaction of the FeS-X domain with PsaC (FeS-A/FeS-B) and its involvement in electron transfer to FeS-A/B will also be addressed. More recent work by the Berlin group at 4 A resolution has refined the distance measurements to 15.4 and 22.2 A, respectively. Fig. 12 (B) shows a three-dimensional model of PsaC based on low-temperature EPR measurements by Kamlowski and coworkers on PS-I single crystals. Their interpretation was made by using the bacterial ferredoxin model as a PsaC substitute in the PS-I reaction center matrix, and adjusting its orientation for the best agreement with the EPR data. The g-tensor orientation of EeS-A and FeS-B in the PS-I single crystals determines the PsaC orientation relative to the two clusters. 

Generalized ligand substitution reaction (24) proceeds with a variety of anionic ligands such as halides, thiolates, and arene oxides. Certain neutral ligands also substitute on the 6484] core, notably isonitriles and tertiary phosphines. Although nitrosyl clusters are not within the purview of this section, we note the existence of cubane-type [Fe4S4(NO)4] . Iron-sulfur-nitrosyl... 

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