Mihaly Novak

Electrochemical reactions of cytochrome c on electrodes modified by fullerene films

Abstract C60 fullerene film modified electrodes were investigated for the electrochemical reactions of cytochrome c. It was established, that depending on the oxidation state of the fullerene films, the electrochemistry of the protein varied. The best, stablest redox reaction could be measured on partially reduced film. The response of cytochrome c was quite independent of the underlying substrate (gold or glassy carbon), indicating that the fullerene film acted as a promoter. Molecular sieve character and the possible effect of negative charges or polar groups on the surface of the films were suggested to be the reason of enhanced stability of the electrochemical response compared to bare electrodes.

Stable and reversible electrochemistry of cytochrome c on bare electrodes Part 1. Effect of ionic strength

Abstract Stable and reversible electrochemical responses of cytochrome c can be measured on bare unmodified gold and glassy carbon electrodes. It has been found that in phosphate buffers the electrochemical behaviour varies from completely irreversible to reversible on both electrodes depending on the concentration of the supporting electrolyte. The optimum phosphate concentration was found to be between 20 and 30 mM. It was also observed that the electrochemical response improved with the lifetime of the protein samples and could be destroyed by mechanical aggregation of cytochrome c molecules. The importance of oligomeric forms of cytochrome c on the electrode surfaces was emphasized; they determine the overall electrochemical behaviour.

Potential/pH equilibrium diagrams of some MeSH2O ternary systems and their interpretation from the point of view of metallic corrosion

Abstract Hydrogen sulphide and elementary sulphur can give rise to serious corrosion of metals, producing metal sulphides as main corrosion products. The stability domains of metal sulphides have been studied by the authors on the basis of potential/pH equilibrium diagrams of different metal-sulphur-water ternary systems, constructed with the method developed by Pourbaix. In this paper the domains of thermodynamic stability of the sulphides of Mg, Al, Mn, Zn, Fe, Cd, Co, Ni, Sn, Pb, Cu and Ag are presented and discussed from the point of view of corrosion. On the basis of the diagrams it can be concluded that the electromotive force of the corrosion elements is much higher in the presence of hydrogen sulphide and elementary sulphur than for metal-water binary systems, and cathodic hydrogen evolution may occur with some metals that are quite immune in binary metal-water systems. For iron, the requirements of cathodic protection are higher in the presence of hydrogen sulphide.

Electrochemistry on partially reduced fullerene films

Abstract Electrochemical studies on solution cast fullerene (C60, C70) films were carried out in aqueous solutions. It was observed that a special pretreatment of films in quinhydrone solution could provide suitable conditions to investigate the electrochemical behavior of fullerene films exclusively. It was found that fullerene films can conduct electrons to the solution phase in their partially reduced forms. They behave as diodes with pronounced current rectifying character. Results on these partially reduced layers also support conclusions on the bulk reduction of the fullerene films in aqueous media.

Stable and reversible electrochemistry of cytochrome c on bare electrodes Part II: Effects of experimental conditions

Abstract The electrochemical behaviour of cytochrome c was studied on gold and glassy carbon electrodes as a function of pH, the type of anions present in the electroyltes and temperature. It was established that the stability and the reversibility of electron transfer processes are determined by the adsorption of the protein on the electrode surface, which can be greatly influenced by factors having an effect on the double layer around the molecules. Stable electrochemistry can be observed if the conditions are suitable for the native, monomeric form of cytochrome c to be preserved on the surfaces.

Separation of faradaic and capacitive current regions in the redox transformation of poly(3-methylthiophene) with the exclusion of overoxidation processes

Abstract The electrostability of the poly(3-methylthiophene) film prepared in nitrobenzene provided the opportunity to study its redox transformations in an extended anodic potential region with the exclusion of the overoxidation. From spectroelectrochemical results a capacitive region could be separated in the highly oxidized state of the layer which exhibited a large capacitance. This pattern—assumed to be related to charge separation/redistribution within the film at high potential field connected to solvent movements—is promising from the point of view of symmetric p-type/n-type superconductors.

Photoelectrochemical behaviour of C60 films in various oxidation states

Abstract The photoelectrochemical behaviour of C 60 films, deposited on gold and glassy carbon surfaces, was studied in various oxidation states, and with various compounds in the solution phase. It was established that neutral C 60 films behave as porous intrinsic semiconductors, and they can be converted to porous n-type semiconductors upon reduction in the presence of Li + , or Na + . If the reduction was carried out in K + -, Rb + -, or Cs + -containing solutions, the reduced films were pure conductors. Depending on the size of the electroactive species in the electrolyte, both photo-oxidation and photoreduction could be observed on the semiconducting reduced films. The spectral dependence of the photocurrents was also determined, and some basic parameters of the films were established.

Redox anion doped polypyrolle films; electrochemical behaviour of polypyrrole prepared in Fe(CN)6 solution

Polypyrrole films were formed with hexacyano-ferrate (HCF) anions as exclusive dopants. It was observed that a portion of the built-in HCF displayed reversible electro-chemistry, but the majority of the doping anions are non-electroactive, while they are inside the polymers. Calculations showed that one excess positive charge on the polymer backbone was compensated by one HCF ion, thus, the entrapment of these multivalent anions was accompanied by the inclusion of a large amount of cations as well. These films were sensitive for the size of the cations present in the solution.

Photoeffect on a Cu anode during electropolishing

Abstract The photoeffect on a Cu anode was studied during electropolishing. The photoeffect consists of a thermoeffect and the actual photoresponse. The pattern of the photoresponse reveals a change in the surface layer during electropolishing as a function of the potential and hydrodynamic conditions.

Manganese-doped fullerene film electrodes

Abstract Manganese-doped C 60 fullerene films were produced on glassy carbon substrates by electrochemical reduction in aqueous solutions. It was established that manganese ions can be inserted into the fullerene lattice during the fullerene reduction initiated by potassium or sodium ions. The final reduced fullerene was mixed doped, containing either potassium and manganese, or sodium and manganese fulleride. The formation of manganese fulleride was explained by a mechanism involving ion exchange.