Effect of the protein structure and heme iron coordination sphere on the long-range electron transfer from hematite and zinc oxide nanostructures to cytochrome c

Cytochrome c has gained increasing interest in non-biological areas because of its electronic and magnetic properties that are applicable in spintronics and energy. The chiral helicoidal structure of cytochrome c gives to this protein the property of chiral-induced spin selectivity (CISS) applicable to spintronics and energy. In a previous study, it was demonstrated that Fe2O3, structured as layers of nanowires (NWs) and nanoflakes (NFs), contrary to ZnONWs, can efficiently reduce cytochrome c heme when submitted to illumination with a sunlight simulator. The present study investigated the influence of α-helix content and heme iron axial ligands on the capacity of cytochrome c to accept electrons from Fe2O3NWs (NFs) pristine and decorated with gold nanoparticles. Microperoxidase-11 (MP-11), a heme-undecapeptide produced by cytochrome c digestion was irradiated in the presence of Fe2O3NFs. Efficient photoreduction was observed only for MP-11 with hexacoordinated heme iron. The results demonstrated that the heme coordination sphere rather than the α-helix content is crucial for the efficient long-range electron transfer from hematite to heme iron. Also, ZnO grown as nanoflowers (NFws) at room temperature was tested as a photoreduction agent, and like ZnONWs was also an inefficient photoreduction agent for cytochrome c.