The nature of Fe–O<sub>2</sub> bond of oxyheme complexes

Abstract

<p indent="0mm">Dioxygen (O₂) is one of the most important diatomic molecules in the nature and life. In spite of a long history of study on the interactions of dioxygen with the oxygen-carrying and -storing heme complexes, there are a number of scientific debates concerning the geometric, electronic, and biophysical properties. These issues include the geometry of the bound dioxygen, the perplexing nature of the (diamagnetic) electronic structure, the dynamics of the Fe–O₂ group in the heme environment, the relative orientation of the bound dioxygen with respect to the plane of the <italic>trans</italic>-histidine, and the unusual and intriguing features of Mössbauer properties. Herein, we propose two strategies on the design and synthesis of new oxyheme models—hydrogen bonding (H-bonding) and covalent-bond axial ligand. H-bonding extensively exists in protein environment and is crucial for the oxyheme functions. Covalent-bond axial ligand could change the orientation, basicity of proximal histidine and thus charge donation to the iron, which finally tuning the Fe–O₂ bond strength. These structural modifications of oxyheme pocket could control and/or change the dioxygen motions and dynamic disorder, providing new insights into the electronic and geometric structures of Fe–O₂ bond. In addition, our previous experience on oxyhemes studies indicated that dioxygen motions are strongly related to the thermal situation. Hence the temperature-dependent single-crystal characterization, which will give vivo pictures on the dioxygen dynamic motions, is necessary. The new research will shed light on the studies of the nature of Fe–O₂ bond, which will enrich the bioinorganic theories and are important for the biologically functional material research.