Electrochemical Study of the Self-exchange between Viologen-thiol Self assembled Monolayers and Alkanethiol Gold Electrodes

The preparation and cyclic voltammetric behaviors of self assembled monolayers (SAMs) containing electroactive viologen group have been investigated. Treatment of this viologen SAM with solutions of alkanethiols remits in replacing the electroactive third, shifting negatively its formal potentials and decreasing its heterogeneous elixtron transfer constants along with the immersion time. The aim of the work is to understand the exchange regularity of the mixed SANK on gold electrode surface.

A novel method of electrodepositing highly dispersed nano palladium particles on glassy carbon electrode

The volumetric behavior of a chloride complex of palladium was studied at a glassy carbon electrode (GCE). The Pd-IV complex existing on the GCE surface was found, which was proposed to form an octahedral surface complex through coordination to the oxygen atom of an oxygen functional group on the pretreated GCE surface. The ferri/ferrocyanide redox couple was used as a probe to examine the activity of the GCE. X-ray photoelectron spectroscopy provided the evidence of the surface complex existing on the GCE. Highly dispersed Pd particles can be obtained when the surface complexes were reduced electrochemically to Pd atoms. The Pd particles obtained in this way were in nanometer scale and exhibit high catalytic activity towards the oxidation of hydrazine. (C) 1997 Elsevier Science Ltd.

Abnormal IR spectra of CO adsorbed on the surface of glass carbon electrode modified with polypyrrole film with platinum microparticles

Abnormal IR spectra of CO adsorbed at the surface of glass carbon electrode modified with polypyrrole film with Pt microparticles are reported.

Self-assembled monolayers of thiols on gold electrodes for bioelectrochemistry and biosensors

Monolayers of biological compounds including redox proteins and enzymes, and phospholipids have been immobilized on a gold electrode surface through self-assembling. These proteins and enzymes, such as cytochrome c, cytochrome c oxidase and horseradish peroxidase (HRP), immobilized covalently to the self-assembled monolayers (SAMs) of 3-mercaptopropionic acid on a gold electrode, communicate directly electrons with the electrode surface without mediators and keep their physiological activities. The electron transfer of HRP with the gold electrode can also be mediated by the alkanethiol SAMs with electroactive group viologens on the gold electrode surface. All these direct electrochemistries of proteins and enzymes might offer an opportunity to build a third generation of biosensors without mediators for analytes, such as H2O2, glucose and cholesterol. Monensin and valinomycin have been incorporated into the bilayers on the gold electrode consisting of the SAMs of alkanethiol and a lipid monolayer, which have high selectivity for monovalent ions, and the resulting Na+ or K+ sensor has a wide linear range and high stability. These self-assembly systems provide a good mimetic model for studying the physiological function of a membrane and its associated enzyme. (C) 1997 Elsevier Science S.A.

Organic phase enzyme electrodes based on organohydrogel

A dimethylformamide-polyhydroxyl cellulose organo-hydrogel has been prepared, and its applications for enzyme immobilization in construction of organic phase biosensors have been exploited. With horseradish peroxidase, tyrosinase, and bilirubin oxidase immobilized in the organohydrogel, enzyme electrodes can be operated in various situations, including aqueous buffer, oil/water mixtures, and anhydrous organic solvents, and even in dimethylformamide, to determine analytes of different solubilities, e.g., organic peroxides, phenolic compounds and bilirubin. Biosensing has no restrictions in terms of measuring media and solubilities of analytes.

Direct electron transfer to cytochrome c oxidase in self-assembled monolayers on gold electrodes

The monolayer of cytochrome c oxidase maintaining physiological activity and attached covalently to the self-assembled monolayers of 3-mercaptopropionic acid (MPA) on a gold electrode was obtained. The results of cyclic voltammetry show that direct electron transfer between cytochrome c oxidase and the electrode surface is a fast and diffusionless process. MPA has a dual role as both electrode modifier and the bridging molecule which: keeps cytochrome c oxidase at an appropriate orientation without denaturation and enables direct electron transfer between the protein and the modified electrode. Immobilized cytochrome c oxidase exhibits biphasic phenomena between the concentration of the electrolyte and the normal potentials; meanwhile its electrochemical behavior is also influenced by the buffer components. The quasi-reversible electron transfer process of cytochrome c oxidase with formal potential 385 mV vs. SHE in 5mM phosphate buffer solution (pH 6.4) corresponds to the redox reaction of cyt a(3) in cytochrome c oxidase, and the heterogeneous electron transfer rate constant obtained is 1.56 s(-1). By cyclic voltammetry measurements, it was observed that oxidation and reduction of cytochrome c in solution were catalyzed by the immobilized cytochrome c oxidase. This cytochrome c oxidase/MPA/Au system provides a good mimetic model to study the physiological functions of membrane-associated enzymes and hopefully to build a third-generation biosensor without using a mediator.

Electrochemical behaviour of TCNQ on platinum supported BLMs

The electrochemical behaviour of TCNQ modified S-BLM has been investigated through capacitor measurement and cyclic voltammetry (CV) which shows the surface wave behaviour of the TCNQ redox form. The voltammetry CV has shown different pairs peak at different scan rates and a possible explanation is provided.

In situ external reflection FTIR spectroelectrochemical investigation of poly(o-phenylenediamine) film coated on a platinum electrode

The electrochemically deposited poly(o-phenylenediamine) film on a Pt electrode has been investigated utilizing in situ external reflection FTIR spectroelectrochemistry technique. The prepared ladder polymer film is found to be partially ring-opened. The dopant ClO4- is evidenced to orient in such a way that more than one oxygen atom attach to the charge sites of the polymer. This suggests that positive charges of oxidized polymer are partially delocalized over the whole chains. The proton movement observed during the oxidation reaction is associated with the solvated MeCN molecule. It is proposed that the proton diffusion, dissolvation and protonation of the film may be essential to the electrochemical reduction reaction of the film. Copyright (C) 1996 Elsevier Science Ltd.

The direct electrochemistry of cytochrome c at the nanometer-sized rare earth element oxide particle-modified gold electrodes

The direct electrochemistry of cytochrome c was studied at nanometer-sized rare earth element dioxide particle-modified gold electrodes. It was demonstrated that rare earth element oxides can accelerate the electrochemical reaction of cytochrome c and the reversibility of the electrochemical reaction of cytochrome c was related to the size of rare earth element oxide particles.

Scanning tunneling microscopy characterization of electrode materials in electrochemistry

Ex situ and in situ STM characterization of the electrode materials, including HOPG, GC, Au, Pt and other electrodes, is briefly surveyed and critically evaluated. The relationship between the electrode activity and surface microtopography is discussed.

A comparison of electrocatalytic ability of various mediators adsorbed onto paraffin impregnated graphite electrodes for oxidation of reduced nicotinamide coenzymes

Twelve mediators have been modified by adsorption onto the paraffin impregnated graphite electrodes (IGE). The resulting electrodes exhibit electrocatalytic activity of different degrees towards oxidation of 1,4-dihydronicotinamide adenine dinucleotide (NADH). The electrocatalytic ability of the chemically modified electrode (CME) depends mainly on the formal potential and molecular structure of mediator. The formation of the charge transfer complex between NADH and adsorbed mediator has been demonstrated by the experiments using a rotating disk electrode. An electrocatalytic scheme obeying Michaelis-Menten kinetics has been confirmed, and some kinetic parameters were estimated. The solution pH influences markedly the electrocatalytic activity of the modified electrode. Various possible reasons are discussed.

Dynamic spectroelectrochemical measurement for the conformational transition of cytochrome c induced by bromopyrogal red

The conformational transition of horse heart cytochrome c induced by bromopyrogal red (BPR) in very low concentration has been firstly investigated by dynamic spectroelectrochemical technique, both at the BPR adsorbed platinum gauze electrode and at a bare platinum gauze electrode in a solution containing BPR. The effect of BPR on the structure of cytochrome c was studied by UV-visible and Fourier transform IR spectroscopy. The unfolded cytochrome c behaves simply as an electron transfer protein with a formal potential of -142 mV vs. a normal hydrogen electrode. The difference between the formal potentials of the native and unfolded cytochrome c is coupled to a difference in conformational energy of the two states of about 40 kJ mol(-1), which agrees well with the result reported. The stability and slow refolding of the unfolded cytochrome c are discussed.

ELECTROACTIVE COATINGS OF DICYANO-BIS(1,10-PHENANTHROLINE)IRON(II) ATTACHED TO NAFION POLYMER FILM-MODIFIED ELECTRODES VIA ADSORPTION

A dicyano-bis(1,10-phenanthroline)iron(II) modified elecrode was prepared. The voltammetric and the spectroelectrochemical behavior of this electrode were investigated. The influence of pH and the amount of Nafion and dicyano-bis(1,10-phenanthroline) iron(II) (DBPI) used in the electrode preparation on the electrochemical behavior is presented.

ELECTROCATALYTIC OXIDATION AND ION-CHROMATOGRAPHIC DETECTION OF BR-, I-, SO32-, S2O32- AND SCN- AT A PLATINUM PARTICLE-BASED GLASSY-CARBON MODIFIED ELECTRODE

A modified method for dispersing platinum particles on a glassy carbon (GC) electrode was investigated. The ultramicro Pt particle-modified electrode obtained exhibited high catalytic stability and activity towards the oxidation of some halide ions (Br-, I-) and inorganic sulfur species (S2O32-, SO32- and SCN-). These anions were separated and detected by using ion chromatography and electrochemical detection via this novel dispersed Pt particles-GC working electrode. The detection limits were 20 ng/ml for Br-, 1.0 ng/ml for I-, 10 ng/ml for SO32- and 4.0 ng/ml for SCN-. This method was employed for the analysis of industrial and environmental waste waters.