Electron Transfer between Surface-Confined Cytochrome c and an N-Acetylcysteine-Modified Gold Electrode

Abstract

Cytochrome c (cyt c) was adsorbed on N-acetylcysteine (NAC)-modified gold electrodes via electrostatic interaction. The cyt c layer exhibited reversible and stable electrochemical redox transformation in 0.01 M phosphate butter, pH 7.4, where the heterogeneous electron transfer (ET) constant k‘het was measured by three techniques: cyclic voltammetry at high sweep rates (CV), electrochemical impedance (EI), and electroreflectance (ER) spectroscopy. In addition, k‘het was also determined from combining sets of simultaneous electrochemical impedance (EI) and electroreflectance (ER) measurements in a new impedance model in which a constant-phase element was used. The negligible shift (−0.023 mV) in the formal potential from the solution value, and the close agreement of the measured distribution around the CV peaks (full-width voltage at half-peak-height, E fwhh = 97 mV) with the theoretical value of 90.6 mV, suggested that the immobilized cyt c is retained at the electrode in the native state. Apparent k‘het values, as determined by each method separately, were as follows: (k‘CV = 920 ± 280 s-1 by CV, k‘EI = 660 ± 200 s-1 by EI, and k‘ER = 2100 ± 300 s-1 by ER as interpreted using previously published methods. ,, In the combined EI/ER measurements, k‘ER was found to increase linearly with the frequency of the ac modulating current and spanned a range from about 400 to 800 s-1, which is close to the interprotein electron-transfer rate constant (800 s-1) measured between cyt c and one of its natural redox partners, cytochrome c peroxidase. It is concluded that further attempts to reconcile these discrepancies in k‘het determinations will require more detailed descriptions of the interfacial elements in the impedance models.

Electron-Transfer Rate in Potential-Modulated Redox Reactions with Electro-Active Optical Waveguides

“…Spectroelectrochemical techniques are particularly useful to mitigate those difficulties by focusing solely on the faradaic process and avoiding the strong non-faradaic electrical background. [10][11][12][13][14][15][16][17][18][19][20][21][22] Based on spectroscopic optical changes that typically accompany a redox event, it is usually possible to select the wavelength of a probing light beam to uniquely capture the optical changes associated with the faradaic process and is immune to the presence and motion of background ions in the electric double layer.…”

Direct electrochemistry of cytochrome c on electrodeposited nickel oxide nanoparticles

“…Many reports have described the electrochemistry of cytochrome c in terms of modifier-electrode and modifier-protein interactions [14][15][16][17][18]. Many promoters, like some small organic compounds [19,20], amino acids together with some derived molecules [21,22], small peptides [23] and conductive polymers [24], have been found to promote the direct electrochemistry of cytochrome c on the electrode surface.…”

Amperometric Detection of Superoxide Dismutase at Cytochrome c-Immobilized Electrodes: Xanthine Oxidase and Ascorbate Oxidase Incorporated Biopolymer Membrane for in-vivo Analysis

“…The E o′ of Au/cyt c, -0.01 V, is equal to those reported for cyt c adsorbed or covalently-bound to the COOH-terminated Au-alkanethiolate layers. [26][27][28] The faradaic charge Qp c associated with the cathodic wave of cyt c was 0.69 µC cm -2 (taking the real surface area of the Au electrode into account) independent of υ in the range of 20 to 500 mV s -1 ; the Γ of cyt c was determined to be 7.2 × 10 -12 mol cm -2 . The determined Γ value of cyt c is a little higher than the theoretical monolayer surface coverage value of cyt c, 6.8 × 10 -12 mol cm -2 , calculated using the unit cell dimensions of cyt c (5.83, 5.83 and 4.18 nm) and the area of a cyt c molecule (2400 Å 2 ).…”