Membrane electrodes can modulate the electrochemical response of redox proteins—direct electrochemistry of cytochrome c (original) (raw)
Related papers
A Biomimetic Electrode Platform for Cytochrome c Electrochemical Studies
International journal of electrochemical science
By employing a gold surface covered with the substituted mercaptopyrimidine 2-thiobarbituric acid (TBA), it was possible to prove the influence of the surface topography (through a fractal approach) and the formation of an H-bond network between the modified surface and the protein. The spontaneous adsorption of a dense monolayer of cytochrome c led to a quasi-reversible redox behavior with a high direct electron transfer rate constant (38 s -1 ),with no measurable electrocatalytic effect. The redox potential for cytochrome c in the adsorbed state has the same value to that reported for the free protein in solution. Our results suggest that TBA-covered electrodes act as a biomimetic platform that mimic the natural environment to study redox proteins without interfering with their natural behavior.
Specific ion effects on the electrochemical properties of cytochrome c
Physical Chemistry Chemical Physics, 2012
The range of salts used as supporting electrolytes in electrochemical studies of redox proteins and enzymes varies widely, with the choice of electrolyte relying on the assumption that the electrolyte used does not affect the electrochemical properties of the proteins and enzymes under investigation. Examination of the electrochemical properties of the redox protein cytochrome c (cyt c) at a 4,4'-bipyridyl modified gold electrode demonstrates that both the redox potential (E°') and the faradaic current are influenced by the nature of the electrolyte used, in a manner explained primarily by Hofmeister effects. The faradaic peak currents display an atypical trend on switching from kosmotropic to chaotropic anions, with a maximum current observed in the presence of Cl-. For a series of cations, the peak current increased in the sequence; Li + (0.34 A)<guanidinium + (0.36 A)<Na + (0.37 A)<K + (0.38 A)< Cs + (0.40 A) and for anions decreased in the sequence; Cl-(0.37 A)> Br-(0.35 A)> ClO 4-(0.35 A)> SCN-(0.31 A)> F-(0.30 A). E°' decreased by a total of 24 mV across the series F-> Cl-> Br-> ClO 4-> SCNwhereas no specific ion effect on E°' was observed for cations. Factorisation of E°' into its enthalpic and entropic components showed that while no specific trends were observed, large changes in H o' and S o' occurred with individual ions. The effect of anions on the faradaic peak current can be qualitatively explained by considering Collins' empirical rule of 'matching water affinities'. The effect of cations can not be explained by this rule. However, both anion and cation effects can be understood by taking into account the cooperative action of electrostatic and ion dispersion forces. The results demonstrate that the choice of supporting electrolyte in electrochemical investigations of redox proteins is important and emphasize that care needs to be taken in the determination and comparison of E°', H o' and S o' in different solutions.
Direct Wiring of Cytochrome c 's Heme Unit to an Electrode: Electrochemical Studies
Journal of the American Chemical Society, 2002
A novel strategy for the immobilization of cytochrome c on the surface of chemically modified electrodes is demonstrated and used to investigate the protein's electron-transfer kinetics. Mixed monolayer films of alkanethiols and ω-terminated alkanethiols (terminated with pyridine, imidazole, or nitrile groups that are able to ligate with the heme) are used to adsorb cytochrome c to the surface of gold electrodes. The use of mixed films, as opposed to pure films, allows the concentration of adsorbed cytochrome to remain dilute and ensures a higher degree of homogeneity in their environment. The adsorbed protein is studied using electrochemical methods and scanning tunneling microscopy.
Analytica Chimica Acta, 1994
A simple and effective procedure for electrode construction, based on casting a permselective membrane onto a gold electrode surface is described. A redox protein solution is entrapped between the pennselective membrane and the electrode surface. The so-mounted permselective-membrane electrode placed in an electrolyte solution is used to study horse heart cytochrome c as a test system. The measured formal potential and the pH dependence profile are in accordance with the literature data. The permselective-membrane electrode is also used to investigate the electrochemistry of cytochrome cs5r from 'Z?aiobwillusferrooxidons and the pH dependence of its formal potential. The performance of this electrode makes it very attractive for studying redox proteins present in limited amounts only.
Electrochimica Acta, 1999
Various mono-and polyheme c-type cytochromes are able to spontaneously incorporate within thin ®lms made from the ionomer poly(ester±sulfonic acid) Eastman AQ-29D acting as cation-exchange ®lms cast on carbon electrodes. AQ-®lms as evidenced from scanning electron microscopy are uniform. The electron transfer within this cation-exchange ®lm is strongly aected by the ®lm thickness. The performances of the AQ-®lms to incorporate cytochromes by varying pH are examined on the basis of electrostatic interactions which principally govern the incorporation process. From ®lm-transfer experiments, a model consisting of a two-phase ionomer coating has been developed for cytochrome c. An indirect approach based on the study of the incorporation of nonelectroactive proteins and peptides is reported. The respective abilities of AQ-29D and Na®on ®lms to incorporate/not to incorporate c-type cytochromes and other`low molar mass' species are explained by the formation of hydrated gellike AQ-®lms. #
Journal of Electroanalytical Chemistry, 1997
The majority of elecm~chemical studies on metalloproteins have reported the use of chemically modified electrodes or deliberate use of adsorbed species to obtain persistent well defined and stable voitammetric responses. This present study confirms that a diffusion controlled reduction response may be observed ibr cytochrome c at an unmodified ('bare') gold disc electrode in many electrolytes if voltammograms ate recorded immediately after the electrode is placed in contact with the solution. However. the current observed at potentials near the reversible value tbr native cytochrome c rapidly decreases in magnitude in chloride or fluoride electrolyte~ as the electrtgle contact time with the solution increases until the response is indistinguishable from that observed due to the background electrolyte. In cacodylate and phosphate buffered media, the response also decays with time, but at a much slower rate. However, in all electrolytes, a concomitant change from a peak-shaped (linear diffusion dominant) to a sigmoidal-shaped (radial diffusion dominant) response is observed as the current decreases in magnitude. The transient behaviour is explicable in terms of a 'self-blocking' model in which highly positively-charged but electroinactive cytochrome c is adsorbed on the seconds time scale and bl-cks the electrode at the reversible potential, leaving only an array of microscopically small electroactive sites available for the diffusion controlled voltammetry of native cytochrome c. Thus. the adsorption of cytochrome c effectively changes the dominant mode of mass transport tor electroactive bulk solution native cytochrome c from linear to radial diffusion as suriace blockage increases, thereby explaining both the time dependent current magnitude add the change in curve shape from peak to sigmoidal, TI. s unusual form of transient behaviour is postulated to be a consequence of the very high overall positive charges associated with both the blocking (adsorbea) and bulk solution (native) forms of cytochrome c. The proposed mechanism also rationalises how specific and nonospecific forms of interaction with the elec~rolyie lead to a highly electrolyte dependent response. © 1997 Elsevier Science S.A,
Electrochemistry of Nanozeolite-Immobilized Cytochrome c in Aqueous and Nonaqueous Solutions
Langmuir, 2010
The electrochemical properties of cytochrome c (cyt c) immobilized on multilayer nanozeolite modified electrodes have been examined in aqueous and nonaqueous solutions. Layers of Linde type-L zeolites were assembled on indium tin oxide (ITO) glass electrodes followed by adsorption of cyt c, primarily via electrostatic interactions, onto the modified ITO electrodes. The heme protein displayed a quasireversible response in aqueous solution with a redox potential of +324 mV (vs NHE), the surface coverage ( * ) increased linearly for the first four layers and then gave a nearly constant value of 200 pmol cm 2-. On immersion of the modified electrodes in 95% (v/v) nonaqueous solutions, the redox potential decreased significantly, a decrease that originated from changes in both the enthalpy and entropy of reduction. On re-immersion of the modified electrode in buffer, the faradic response immediately returned to its original value. These results demonstrate that nanozeolites have potential as stable supports for redox proteins and enzymes.