Spin-inversion mechanisms in O₂ binding to a model heme complex revisited by density function theory calculations

Area of Science:

• Computational Chemistry
• Quantum Chemistry
• Biophysical Chemistry

Background:

• Heme proteins are crucial in biological processes, involving oxygen binding.
• Understanding spin-inversion mechanisms is key to elucidating these processes at a molecular level.

Purpose of the Study:

• Investigate spin-inversion mechanisms during oxygen binding to a model Fe(II)-porphyrin-imidazole complex.
• Characterize spin-inversion structures and dynamics using advanced computational methods.

Main Methods:

• Density-functional theory (DFT) calculations were employed.
• The mixed-spin Hamiltonian method was used to locate spin-inversion structures.
• On-the-fly Born-Oppenheimer molecular dynamics simulations were performed.

Main Results:

• Nine spin-inversion structures were optimized for various spin multiplicities (singlet-triplet, singlet-quintet, triplet-quintet, quintet-septet).
• Singlet-triplet inversion occurs at short Fe-O distances, while singlet-quintet and quintet-septet occur at longer distances.
• Both narrow and broad crossing models are implicated in O2 binding to the heme complex.

Conclusions:

• The study provides detailed insights into the spin-inversion pathways in O2-heme interactions.
• Computational dynamics reveal correlations between reaction coordinates and spin-inversion dynamics.
• Findings contribute to a deeper understanding of electron spin states in metalloporphyrin systems.