Structure-Property Relationships of Fe₄ S₄ Clusters

Area of Science:

• Bioinorganic Chemistry
• Computational Chemistry
• Materials Science

Background:

• Iron-sulfur (Fe4S4) clusters are vital in biological electron transfer and catalysis.
• Understanding their electronic and structural properties is crucial for designing functional mimics.
• Previous studies highlight the sensitivity of Fe4S4 clusters to their environment.

Purpose of the Study:

• To investigate the theoretical sensitivity of Fe4S4 cluster properties to structural distortions.
• To compare model Fe4S4 clusters with those coordinated by cysteine residues.
• To analyze the influence of spin coupling and charge state on reorganization energies.

Main Methods:

• Theoretical calculations on [Fe4S4(SH)4]3-/2-/1- model clusters.
• Comparison with Fe4S4 clusters coordinated by ethyl thiolates (cysteine mimics).
• Analysis of potential energy, spin coupling, adiabatic detachment energy, and reorganization energy.

Main Results:

• Ground-state spin-coupling schemes are sensitive to hydrogen-hydrogen distances in model clusters.
• Inner-sphere reorganization energies are significantly affected by spin-coupling schemes (up to 13 kcal/mol).
• Redox couples [Fe4S4(SR)4]2-/1- exhibit lower reorganization energies (6-12 kcal/mol) than [Fe4S4(SR)4]2-/3- (14-18 kcal/mol).

Conclusions:

• Structural distortions and spin-coupling schemes critically influence Fe4S4 cluster properties.
• Reorganization energies are lower for the 2-/1- redox couple compared to the 2-/3- couple.
• Theoretical findings provide insights for interpreting experimental data on Fe4S4 clusters.