Spectroelectrochemical study of the redox reaction mechanism of cytochrome c at a gold electrode in a neutral solution in the presence of 4,4'-bipyridyl as a surface modifier

Abstract

The redox reaction of cytochrome c at a gold electrode in the presence of 4,4'-bipyridyl (4-bpy) as a surface modifier was investigated spectroelectrochemically in a neutral aqueous solution. Two types of the redox processes of cytochrome c were studied in detail. One (process I) is the diffusion-controlled reaction of cytochrome c from the solution phase to the electrode surface covered by the adsorbed layer of 4-bpy, at the same formal potential as the native cytochrome c. The other (process II) involves both the reaction of cytochrome c coadsorbed with 4-bpy on the gold electrode surface and the mediated reduction of cytochrome c in the solution phase. It was found that the formal potential of cytochrome c coadsorbed with 4-bpy became more positive as the concentration of 4-bpy increased. This is probably due to the fact that the coadsorbed 4-bpy acts to reduce the degree of unfolding of adsorbed cytochrome c. Electroreflectance spectra of each of the two processes were very different. It was found that the electronic structure of the cytochrome c coadsorbed with 4-bpy was different from that of the native cytochrome c.

Direct voltammetry of cytochrome c at trace concentrations with nanoelectrode ensembles

“…3b obtained at the NEE in the presence of 4,4 0 -bipy added as promoter, shows an E 1=2 value slightly more negative than that measured in the absence of promoter. This confirms the occurrence of some (weak) interaction between cyt c and the promoter [17,18,45].…”

“…For a bare gold surface this limit is 6 20 lM, while with 4,4 0 -bipy it increases to about 80-100 lM. Cytochrome c adsorption has practically no effect on the possibility of observing electron transfer between the gold surface and the protein redox centre in the case of promoter modified electrodes [41], while it can block the electron transfer process for the bare gold surface [45,48,50]. In fact, as discussed by Niki and co-workers [48], when the adsorbed layer is not too compact, adsorbed protein molecules can even act as ''self-promoters'' for electron transfer to solution, diffusing cyt c molecules.…”

“…Niki and co-workers [45,48] showed that promoters undergo competitive adsorption with cytochrome c; the adsorbed promoter modifies the electrode surface so avoiding the adsorption/denaturation of the protein and concomitant blocking of the electrode surface. The idea that this adsorption might be reduced or eliminated by using a very diluted cytochrome c solution, prompted us to study the effective concentration dependence of such an adsorption phenomenon.…”

Template Deposition of Metals

“…These promoters are generally required to avoid adsorption/denaturation (83,102,103) of cytochrome c on the Au surface. However, such an adsorption is concentration dependent so that lowering the cytochrome c solution concentration below the adsorption limit (possible at NEEs thanks to their lower detection limit) can overcome adsorption-related problems.…”

Direct measurement of cyclic current-voltage responses of integral membrane proteins at a self-assembled lipid-bilayer-modified electrode: cytochrome f and cytochrome c oxidase.

“…It is well known that the use of direct electrochemical methods to obtain thermodynamically correct values for the redox potentials of electron-transfer proteins has proven to be rather difficult as a consequence of strong interactions between these proteins and the electrode surface, which often lead to adsorption and structural alteration (1)(2)(3)(4)(5)(6)(7). Attempts to circumvent this problem have resulted in the development of a variety of strategies for chemically modifying metal and semiconductor surfaces so as to provide an electron transfer pathway that maintains protein native structure and eliminates strong binding (1,.…”