Operando Spectroscopy Investigations of the Redox Reactions in Heme and Heme-Proteins

Abstract

Operando spectroscopic investigations during molecular redox processes provide unique insights into complex molecular structure and their transformations. Herein, a combination of a potentiodynamic method with spectroscopy has been employed to holistically investigate the structural transformations during Fe-redox (Fe3+Fe2+) of hemin vis á vis heme-proteins e.g. myoglobin (Mb), hemoglobin (Hb) and cytochrome-C (Cyt-C). The UV-VIS findings reveal the formation of hemozoin ( heme-dimer), which can be selectively prevented via a high concentration of strongly interacting ligands e.g. histidine (the fifth coordinating ligand in the heme-based protein). On the other hand, methionine does not prevent the formation of hemozoin. In Mb, Hb, and Cyt-C, as the fifth coordination site is occupied by histidine, hemozoin formation is inhibited. During Fe3+ Fe2+, operando circular dichroism exhibits a decrease in the initial helical component in Hb from nearly 40% to 28%, which is close to the initial helix component of Mb ( 25%), strongly indicating denaturation of protein in the redox pathway. The rate of change of the helices versus potential is almost identical for Mb and Hb, but comparatively faster than Cyt-C. In addition, the Raman bands of M-N dynamics and protein agglomeration, it is concluded that Cyt-C prefers to agglomerate in the 2+ state, whereas Mb/Hb in the 3+ state. Using the power of operando spectroscopy, the present study unearths complexities associated with molecular redox having implications in electrocatalysis, energy storage, and sensing.