Geometric and Electronic Structural Contributions to Fe/O₂ Reactivity.

Area of Science:

• Biochemistry
• Bioinorganic Chemistry
• Spectroscopy

Background:

• Non-heme iron enzymes activate dioxygen using ferrous (FeII) or ferric (FeIII) centers.
• FeII active sites are often EPR inactive due to their integer spin ground state.
• Understanding these active sites and reaction intermediates is key to enzyme mechanism elucidation.

Purpose of the Study:

• To develop and apply novel spectroscopic techniques for characterizing non-heme iron enzyme active sites and intermediates.
• To gain detailed geometric and electronic structural insights into ferrous centers and their interactions during dioxygen activation.
• To elucidate the nature and reactivity of key intermediates, such as FeIII-OOH and FeIV=O, and their spin-state dependence.

Main Methods:

• Variable-Temperature Variable-Field Magnetic Circular Dichroism (VTVH MCD) spectroscopy to define electronic and geometric structures.
• Nuclear Resonance Vibrational Spectroscopy (NRVS) for precise geometric structure determination.
• Application of these methods to study enzyme mechanisms like DNA cleavage by bleomycin and substrate halogenation by dioxygenases.

Main Results:

• Established VTVH MCD as a powerful tool for characterizing high-spin ferrous active sites.
• Defined the structures of FeIII-OOH and FeIV=O intermediates involved in O2 activation.
• Demonstrated the influence of frontier molecular orbital spin states on intermediate reactivity.
• Derived experimentally validated reaction coordinates for enzymatic processes.

Conclusions:

• The developed spectroscopic methodologies provide unprecedented insight into non-heme iron enzyme mechanisms.
• Understanding intermediate structures and electronic properties is crucial for controlling enzymatic reactivity.
• These findings have implications for designing novel catalysts and therapeutic agents, such as anticancer drugs.