Iron-sulfur clusters—new features in enzymes and synthetic models

Mössbauer spectroscopy is very important for the characterization of iron sulfur clusters in biological and synthetic molecules. The electric and magnetic hyperfine parameters obtained for 57Fe provide valuable information about the electronic structure of the different iron sites occurring in Fe:S clusters. Although known since more than four decades, research in this field is very active, revealing unexpected functions, structures and redox states. In this overview, new aspects of double exchange and vibronic coupling in a structurally well-characterized two-iron model compound are discussed, the electronic structure of extremely reduced clusters with all iron in ferrous or even in iron(I) state is elucidated, and an exciting new type of cubane cluster occurring in oxygen-insensitive hydrogenases is presented. The latter cluster involves structural changes during function and it supports more than one redox transition, which may be essential for oxygen protection of the enzymes.