Mossbauer studies of exchange coupled cluster assemblies in biological systems

Biological systems have evolved active sites containing [4Fe-4S](2+) cluste rs covalently linked to a mononuclear Fe or Ni or to a diiron cluster. Such structures have been found in sulfite reductase, carbonmonoxide dehydrogen ases and most recently in [Fe]-hydrogenases. The link through a bridging li gand provides an exchange pathway that couples the spins of the two chromop hores. In this contribution the spin physics of these systems as viewed fro m a standpoint of Mossbauer spectroscopy is discussed.