From Small Molecules to Complex Systems: A Survey of Chemical and Biological Applications of the Mössbauer Effect

Abstract

Mossbauer spectroscopy and synchrotron based nuclear resonance scattering are ideal tools to investigate electronic and dynamic properties of iron centers in chemical and biological systems. These methods have reached a level of sophistication during the last decades so that it is now possible to hunt for particular functional active iron sites even in very complex systems like iron based heterogeneous catalysts or even in some cases in biological cells. This book chapter will try to give a comprehensive overview of what can be achieved by using experimental techniques using the Mossbauer effect when combining different evaluation strategies like e.g. relatively straight forward analysis using lorentzian lines or hyperfine field distributions and more sophisticated investigations of paramagnetic iron sites by means of the spin Hamiltonian formalism. In addition the possibilities of synchrotron techniques based on the Mossbauer effect like nuclear forward and nuclear inelastic scattering will be shown. Special emphasis lies also on the sample requirements and on theoretical methods like quantum chemical density functional theory which nowadays is also available coupled with molecular mechanic shells which enables the treatment of very large systems like iron proteins. In addition to laboratory-based Mossbauer spectroscopy recent progress using synchrotron based nuclear inelastic scattering (NIS) to detect iron based vibrational modes in iron proteins and chemical systems will be described. In combination with quantum mechanical calculations for example, the iron ligand modes of NO transporter proteins have been explored. Via NIS it has been possible to detect iron ligand modes in powders and single crystals, but also in thin solid films of iron(II) based spin crossover (SCO) compounds. In addition, nuclear forward scattering (NFS) has been applied to monitor the spin switch between the S = 0 and S = 2 state of SCO microstructures. Furthermore, recent work on polynuclear iron(II) SCO compounds, iron based catalysts as well as biological cells will be discussed.