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Contents
4 From Small Molecules to Complex Systems: A Survey
of Chemical and Biological Applications of the Mössbauer Effect . . . 173
Volker Schünemann
4.1 Iron Centers in Chemical Complexes and Biomolecules:
Structural Overview, Biological Relevance and Physical
Properties . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 174
4.2 Spectroscopic Techniques to Investigate Iron Centers
in Chemistry and Biology Based on the Mössbauer Effect:
Strategy and Requirements . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 177
4.2.1 Sample Requirements for Conventional Mössbauer
Spectroscopy and Synchrotron Based Techniques . . . . . . . . 178
4.2.2 Spectral Analysis: Thin Absorber Approximation
and Transmission Integral . . . . . . . . . . . . . . . . . . . . . . . . . . . . 180
4.2.3 Mössbauer Spectroscopy of Iron in Molecules: The
Spin Hamiltonian Concept . . . . . . . . . . . . . . . . . . . . . . . . . . . 181
4.2.4 Calculation of Mössbauer Parameters with Quantum
Chemical Methods . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 186
4.2.5 Calculation of Iron Ligand Modes in Chemical
Complexes and Proteins . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 188
4.3 Exploring Spin States in Iron(II) Containing Compounds . . . . . . . . 188
4.3.1 Thermal Spin Crossover (SCO) and Mössbauer
Spectroscopy . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 188
4.3.2 Light Induced Excited Spin State Trapping (LIESST) . . . . 190
4.3.3 Exploration of Iron Ligand Modes by Synchrotron
Based Nuclear Inelastic Scattering (NIS) . . . . . . . . . . . . . . . 194
4.4 Electronic and Vibrational Properties of a Heme Protein:
The NO Transporter Protein Nitrophorin . . . . . . . . . . . . . . . . . . . . . . 196
4.4.1 Probing Small Ligand Binding to Nitrophorin
with Mössbauer Spectroscopy . . . . . . . . . . . . . . . . . . . . . . . . 197
4.4.2 Investigation of Vibrational Properties
of Nitrophorins . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 200
4.4.3 Calculation of Mössbauer Parameters of Nitrophorins
Using DFT Based Methods to Proof Structural
Models of Heme Centers . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 202
4.5 Investigation of Iron-Sulfur Proteins . . . . . . . . . . . . . . . . . . . . . . . . . 204
4.5.1 Identification of Fe–S-Centers by Mössbauer
Spectroscopy . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 205
4.5.2 Exploration of the Unusual 4Fe–4S Center
of the LytB Protein . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 209
4.5.3 In Vivo Mössbauer Spectroscopy of Iron-Sulfur
Proteins Inside E. Coli Cells . . . . . . . . . . . . . . . . . . . . . . . . . . 211
4.6 Future Applications of the Mössbauer Effect in Chemistry
and Biology . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 212
4.7 Summary . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 215
References . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 216