Mössbauer Spectroscopy

For metallobiomolecules that contain iron (Fe), this technique provides a powerful means of identifying the spin state, oxidation state, and site symmetry of the Fe site. As a "satellite" facility, this technique is accessible to collaborators studying Fe proteins [Vincent Huynh, Emory].

Acronyms, synonyms

• Recoilless Nuclear Resonance Absorption

Measured physical quantities

• Hyperfine interactions between the ⁵⁷Fe nucleus and its surrounding electrons

Information available

• Intrinsic oxidation and spin states of iron sites
• Electronic properties of iron centers
• Relative concentrations of distinct iron sites
• Qualitative ligand environment (coordination number, ligand type)

Information NOT available, limitations

• Only applicable to iron complexes
• Difficult on spectroscopically dilute samples with natural abundance Fe

Examples of questions that can be answered

• What is the oxidation state of this iron site?
• What is the detailed electronic description of this iron site?
• How many iron atoms are in this metal cluster?
• To which iron atoms do substrate and inhibitors bind?
• What are the intermediates and kinetics of the catalytic reaction involving this iron site?

Major advantages

• The technique is sensitive only to iron and can detect all iron present in the sample

Major disadvantages

• Cannot detect metals other than iron
• Usually requires ⁵⁷Fe enrichment

Sample constraints

• Concentration for each distinct ⁵⁷Fe site should be greater than or equal to 0.5 mM
• Sample volume is ca. 0.35 - 0.45 mL
• Avoid high concentrations of relatively heavy atoms such as Na, Cl and Ca