Moessbauer studies of exchange coupled cluster assemblies in biological systems

Biological systems have evolved active sites containing [4Fe-4S]2+ clusters covalently linked to a mononuclear Fe or Ni or to a diiron cluster. Such structures have been found in sulfite reductase, carbonmonoxide dehydrogenases and most recently in [Fe]-hydrogenases. The link through a bridging ligand provides an exchange pathway that couples the spins of the two chromophores. In this contribution the spin physics of these systems as viewed from a standpoint of Moessbauer spectroscopy is discussed