Photo-induced Electron Transfer from Hematite and Zinc Oxide Nanostructures to Cytochrome C: Systems Applicable to Spintronics

Cytochrome c is a protein covalently bound to the iron protoporphyrin IX (heme) with electronic and magnetic properties applicable in spintronics and energy. The cytochrome c protein chain is folded in a chiral structure (a-helix) that is responsible for the chiral-induced spin selectivity (CISS) applicable to spintronics and energy. The helicoidal structure of cytochrome c is associated to a redox center, a Fe(III) porphyrin, that can accept electrons from the conduction band of semiconductors to be converted to the Fe(II) form. Considering a possible connection between redox reactions of cytochrome c with its spin selectivity property and stability, the present study focused on the processes that modulate the photo-induced electron transfer from semiconductors to Fe(III) porphyrin of cytochrome c. Two semiconductors, ZnO and Fe ₂ O ₃ , structured as layers of nanowires (NWs) and nanoflakes (NFs), named as ZnONWs and Fe ₂ O ₃ NWs(NFs), vertically grown on different substrates, were studied. Under illumination with a sunlight simulator, the Fe ₂ O ₃ NWs(NFs) efficiently converted Fe(III) cytochrome c to the Fe(II) state, while ZnONWs promoted oxidative damages on the protein. Decoration of Fe ₂ O ₃ NWs(NFs) with gold nanoparticles impaired cytochrome c photoreduction. The analysis of the pro-oxidant species produced by ZnONWs and Fe ₂ O ₃ NWs(NFs) revealed that the high production of hydrogen peroxide by ZnO material was the main responsible for the inefficient cytochrome c reduction. Hydrogen peroxide production by ZnO resulted from superoxide ion disproportionation rather than from hydroxyl radical produced by water splitting and, consequently, was not influenced by cytochrome c spin filtering as demonstrated for the photoelectrochemical systems.