Pierre Bianco

Correlations studies between structural and redox properties of cytochromes C3

Individual redox potential values are determined for different cytochromes c3. These polyhaemic cytochromes can be divided into two groups: one characterized by only one marked reduction step, the other one giving at least two well-marked reduction steps corresponding to redox potential values ranging from - 0.120 to - 0.400 V. Correlations between potential values and structural data are discussed.

Current—potential responses for a tetrahemic protein: a method of determining the individual half-wave potentials of cytochrome c3 from desulfovibrio desulfuricans strain Norway

Abstract A tetrahemic protein, cytochrome c 3 from Desulfovibrio desulfuricans strain Norway, is studied by differential pulse polarography and linear sweep voltammetry at hanging mercury electrode. A graphical subtractive method applied to the current-potential curves is described and the four individual redox potentials are determined. Both series of experiments lead to two fit sets of values corresponding to reversible electrode processes. The relationship between these redox potentials and the structural data is discussed.

Modification of the gold electrode for the electrochemical study of cytochrome c

Abstract The modification of the gold electrode by some nitrogen hetero-cycles is used for electrochemically studying cytochrome c. Fifteen molecules are tested, but only six are active. The prominent characteristics of the active molecules are defined, and the competition between cytochrome c, 4,4′-bipyridine, 1,2-bis(4-puridyl)ethylene and aldrithiol-4 for the adsorption at the gold electrode has been studied in particular.

A permselective-membrane electrode for the electrochemical study of redox proteins. Application to cytochrome C552 from Thiobacillus ferrooxidans

Abstract 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 permselective 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 c552 from Thiobacillus ferrooxidans 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.

Study of cytochromes c3 from Desulfovibrio vulgaris (Hildenborough) and Desulfovibrio desulfuricans (Norway) by differential pulse polarography and spectroelectrochemical method

(1) Cytochromes c3 from Desulfovibrio vulgaris (Hildenborough strain) and Desulfovibrio desulfuricans (Norway strain) have been studied by differential pulse polarography and spectroelectrochemical method. Both cytochromes exhibit two reduction potential values Eh approximately --0.25 and --0.34 V (D. vulgaris), Eh approximately --0.16 and --0.34 V (D. desulfuricans). (2) Titrations by dithionite and controlled potential electrolysis coupled with polarography and spectrophotometry suggest that in both cases electronic exchanges are rapid.

Voltammetric Studies of the Behavior of Carbon Black during Phenol Oxidation on Ti/Pt Electrodes

Oxidation of phenol on platinum electrodes rapidly leads to the formation of a passivating film on the surface of these electrodes. Studies of cyclic voltammetry and chronoamperometry combined with high-performance liquid chromatography (HPLC) analyses have shown that the presence of carbon black avoids these phenomena of passivation and thus allows the complete mineralization of phenol. The nature of carbon black and the pH value are two important factors which are studied here. VULCAN XC-72 R, an intrinsic p-type semiconductor, having a large specific area, showed all its efficiency when cyclic voltammetry experiments were carried out in an acid medium (pH 2.2). HPLC analyses revealed the appearance of several by-products such as hydroquinone and benzoquinone, and maleic and fumaric acids.

Electrocatalytic Hydrogen‐Evolution at the Pyrolytic Graphite Electrode in the Presence of Hydrogenase

The electrocatalytic hydrogen-evolution at the pyrolytic graphite electrode has been studied by cyclic voltammetry. This reaction has been achieved for solutions containing the redox protein Desulfovibrio vulgaris (Hildenborough) hydrogenase and a polycationic species poly-L-lysine. The effect of several parameters (concentrations, molecular weight of poly-L-lysine) on the electrocatalytic reaction has been investigated. Using small-overpotential conditions it has been shown that this electrode has the hydrogen-electrode function. Its stability has been examined using cyclic voltammetry and impedance measurements

Electrochemical properties of pyrolytic graphite electrodes modified through adsorbed proteins

Abstract The adsorption of various proteins at the PG electrode has been studied electrochemically using the film transfer technique. When the transfer is performed into probe systems such as Fe(CN) 3− 4− 6 or spinach ferredoxin, three possibilities exist: inhibition, no effect, promotion. The different factors which may govern the properties of these modified electrodes have been examined: the pH of the solution investigated, the pH at which the PG electrode was treated, the polarization of the PG electrode, the coadsorption of two proteins. A special attention has been drawn on the promotion of slow electrochemical systems such as ferredoxins or flavodoxins when using the PG electrode modified by adsorbed Desulfovibrio vulgaris cytochrome c3. A pattern of behaviour has been proposed by taking into account several factors: coulombic interactions, hydrophobicity, the effect of electric field on adsorbed molecules.

Control of the electron transfer reactions between c-type cytochromes and lipid-modified electrodes

The electron transfer reactions between a lipid-modified pyrolytic graphite (PG) electrode and four c-type cytochromes (monoheme cytochrome c and cytochrome c553 from Desulfovibrio vulgaris Hildenborough, tetraheme cytochromes c3 from D. vulgaris Hildenborough and D. desulfuricans Norway) have been studied by cyclic and square-wave voltammetry. No signal was detected at the PG electrode simply coated with a mixed layer of phosphatidylcholine (PC) and cholesterol (CH). The peaks corresponding to the reduction—reoxidation of cytochrome c553 were restored by doping the lipid layer with laurate anions (LA). In the case of cytochrome c, a rapid electron transfer reaction has been observed at the (PCCH + LA)-modified PG electrode, accompanied by the progressive incorporation of protein molecules. By studying the effect of pH on the cv peak heights, it has been shown that the profiles for the four cytochromes depend on the protonation of the laurate anions and the protonation—deprotonation of protein species. The results support the electrostatic nature of the interactions between the cytochrome and the lipid layer but other factors (eg hydrophobic effects) are not excluded.

Immobilization of glucose oxidase on carbon electrodes

Abstract The procedures tor glucose oxidase immobilization based on simple adsorption on pyrolytic graphite or on covalent attachment on glassy carbon using the carbodiimide activation method are compared. The catalytic current produced in the enzymatic oxidation of glucose is non-persistent when using the pyrolytic graphite electrode modified by the adsorption of glucose oxidase. In the case of glassy carbon electrodes, the successive steps (polishing, oxidation, activation, enzyme immobilization and detection) of the experimental procedure have been examined using electrochemical (cyclic and differential pulse voltammetry, controlled-potential amperometry) techniques. The influence of several parameters (incubation time, concentration, pH, temperature) on the electrode response has been investigated.