Abstract
Multi-walled carbon nanotube (MWCNT)-modified electrodes can promote the direct electron transfer (DET) of cytochrome c (Cyt c). There are several possible mechanisms that explain the DET of Cyt c. In this study, several experimental methods, including Fourier transform infrared spectroscopy, circular dichroism, ultraviolet-visible absorption spectroscopy, and electron paramagnetic resonance spectroscopy were utilized to investigate the conformational changes of Cyt c induced by MWCNTs. The DET mechanism was demonstrated at various nano-levels: secondary structure, spatial orientation, and spin state. In the presence of MWCNTs, the secondary structure of Cyt c changes, which exposes the active site, then, the orientation of the heme is optimized, revolving the exposed active center to the optimum spatial orientation for DET; and finally, a transition of spin states is induced, providing relatively high energy and a more open microenvironment for electron transfer. These changes at different nano-levels are closely connected and form a complex process that promotes the electron transfer of Cyt c.
Highlights
Cytochrome c (Cyt c) is a water-soluble heme protein with a prosthetic iron porphyrin group
This paper aims to investigate the direct electron transfer (DET) mechanism of Cyt c induced by electron mediators at different levels
As shown in Figure 1(A), a pair of well-defined redox peaks appeared at the Multi-walled carbon nanotube (MWCNT)-modified glassy carbon (GC) electrode with the formal potential of 46 mV, which is almost in agreement with the reported formal potential of Cyt c on SWCNTs [13]
Summary
Cytochrome c (Cyt c) is a water-soluble heme protein with a prosthetic iron porphyrin group. The redox center of Cyt c is deeply embedded in the protein, and the protein is denatured upon adsorption onto a bare electrode surface, resulting in extremely slow electron-transfer kinetics and a poor response. To overcome these problems and promote fast electron transfer, electron mediators, such as Santa Barbara Amorphous (SBA-15), gold nanostructures, and carbon nanotubes (CNTs), have been used with Cyt c to modify substrate electrodes [4–8]. DET between Cyt c and electrodes has been observed with the help of the electron mediators
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