57Fe-Mössbauer spectroscopy and basic interpretation of Mössbauer parameters

Mössbauer spectroscopy with 57Fe is a tool for the investigation of iron in all types of materials, including biological tissue and metalloenzymes. The technique is based on resonant absorption of γ-radiation by the 57Fe nuclei in the sample, and the desired chemical information is derived from hyperfine interactions, which arise from electric and magnetic field at the nuclei due to charge and spin in the valence shell of the Mössbauer atoms. The measurements require recoilless γ-emission and absorption (Mössbauer effect), which occurs in solids and frozen samples. The physical principles are introduced with regard to practical aspects. Fundamental interpretations of Mössbauer parameters are provided in terms of ligand field descriptions of the electronic structure of iron complexes. Applications of the method in bioinorganic chemistry are demonstrated with a number of selected examples, dealing with nonheme and heme enzymes and high-valent reaction intermediates related to activation of small molecules.