REDOX THERMODYNAMICS OF CYTOCHROME-C AT THE BARE GLASSY-CARBON ELECTRODE

Investigation of the redox thermodynamics of horse heart cytochrome c at bare glassy carbon electrodes has been performed using cyclic voltammetry with a nonisothermal electrochemical cell. The thermodynamic parameters of the electron-transfer reaction of cytochrome c have been estimated in different component buffer solutions. The change DELTAS(re)-degrees in reaction center entropy and the formal potential E-degrees' (at 25-degrees-C, vs. standard hydrogen electrode (SHE)) for cytochrome c are found to be -64.1 J K-1 mol-1 and 0.251 V in phosphate buffer, -64.8 J K-1 mol-1 and 0.257 V in Tris + HCl buffer, -65.6 J K-1 mol-1 and 0.261 V in Tris+CH3COOH buffer (pH 7.0, ionic strength 100 mM). The temperature dependence of the formal potential obtained in phosphate buffer with or without NaCl in the range 5-55-degrees-C shows biphase characteristics in an alkaline solution with an intersection point at ca. 44-degrees-C or 42-degrees-C, which should be due to a structural change in the protein moiety of cytochrome c. However, in acidic and neutral solutions only a monotonic relationship between E-degrees' and temperature is observed. The effect of the buffer component on E-degrees' for cytochrome c is also discussed.

ELECTROCHEMICAL CATALYSIS AT AN ULTRAMICROELECTRODE MODIFIED WITH REDOX SPECIES

General equations of the electrocatalytic reaction at an ultramicroelectrode modified with redox species have been described according to the Andrieux Saveant model. The electrocatalytic kinetic process has been discussed for the whole set of cases, ie (R), (R + S), (SR) (SR + E), (E), (R + E), (ER), (S), (ER + S) and (S + E) limiting situations. The effect of gamma on the catalytic steady state current shows that the higher the value of gamma, the lower the catalytic current. The kinetic process shifts rapidly from R to E with increasing values of gamma. It is favorable for catalysis only when gamma is very low. Therefore, the redox species modified ultramicroelectrode with thin film is utilized for electrocatalysis, and the larger the radius of ultramicroelectrode, the higher the catalytic efficiency.

MEASUREMENT OF CATALYTIC ACTIVITY VARIATION FOR H2O2 OXIDATION AT A COBALT PORPHYRIN COATED ELECTRODE

A rapid rotation-scan method was used for the electrocatalytic oxidation of H2O2 at a cobalt protoporphyrin modified pyrolytic graphite electrode (CoPP/PG). The rate constant of H2O2 oxidation at the CoPP/PG electrode at different potentials and in different pH solutions was measured. The variation of catalytic activity with reaction charges (Q) passed through the electrode was analyzed. This provided a convenient electrochemical method to study the passivation and poisoning of catalytic sites with time.

ELECTROCHEMICAL STABILITY AND ELECTROCATALYSIS BEHAVIORS OF POLY(3-METHYLTHIOPHENE) THIN-FILM MODIFIED ELECTRODES

The Electrochemical stability of poly(3-methylthiophene) (PMT) thin film modified glassy carbon electrodes was investigated experimentally with successive cyclic voltammetry(CV) The effects of electrolyte solutions on the stability were studied. In the presence of small hydrated anions (less-than-or-equal-to 3.5nm) in the solution, the electroactivity of PMT films decreased with the characteristics of second order kinetics. In a solution with large hydrated anions (greater-than-or-equal-to 4 nm), PMT films have good stability. PMT/GO electrode can electrocatalyse the oxidation of Br- and Cl- anions, and loses its electroactivity rapidly. X-ray photoelectron spectra (XPS) have demonstrated that chlorine has bonded covalently onto the PMT structure after OV cycles in NaCl solutions.

A STUDY ABOUT PH CHEMICALLY MODIFIED ELECTRODES BASED ON AMINO-DERIVATIVES OF NAPHTHALENE

The electrochemical polymerization of amino-derivatives of naphthalene has been studied on the platinum wire electrodes. The effects of acidity of the modifying media and the potential scan rate on the cyclic voltammograms are verified. As potentiometric pH sensors, the electrodes prepared from 1-naphthylamine and 2,3-diaminonaphthalene showed performance characteristics superior to some other electrodes tested. The electrode modified with 1-naphthylamine in the optimum medium showed a nearly Nernstian response of 4.20-13.70 pH and a slope of -54.8 mV/pH, while the linear range of the electrode prepared by 2,3-diaminonaphthalene was 4.00-13.60 pH, with a slope of -52.4 mV/pH.

ELECTROCHEMICAL STUDY OF ISOPOLYOXOMETALLATES AND HETEROPOLYOXOMETALLATES FILM MODIFIED MICROELECTRODES .1. PRETREATMENT AND MODIFICATION OF THE MO80-26(4-) MODIFIED CARBON-FIBER MICROELECTRODE

In this paper the preparation of isopoly- and heteropolyoxometallates (IPA and HPA) thin film modified carbon fiber (CF) microelectrodes and the factor that influences the modification of IPA and HPA films are described. IPA and HPA film modified CF microelectrodes can all be prepared by cyclic potential scan and simple dip coating. The modified electrodes prepared are very stable and reversible in acidic solution with monolayer characteristics. The electrochemical pretreatment of CF microelectrodes plays an important role in the modification of IPA and HPA film. The absorption of IPA and HPA film on electrode surfaces has been discussed on the basis of surface conditions of the CF microelectrode and the structure of IPA and HPA.

THE IMPEDANCE STUDY OF MODIFIED PEO POLYMER ELECTROLYTE

The ultra-thin modified PEO (polyethylene oxide)-LiClO4 polymer electrolyte film (50-mu-m) was obtained by solution-casting technique. Impedance spectra were taken on the cells consisting of above PEO film electrolyte and ion-blocking or nonblocking electrodes. The ambient conductivity as high as 1.33 X 10(-4)S cm-1 could be achieved for PEO electrolyte modified by the crosslinking. It was shown that the resistance at the interface between solid polymer electrolyte and lithium electrode is growing with increasing the storage time. At high temperature, as 96-degrees-C, the ionic transport is clearly controlled by diffusion.

COBALT PORPHYRIN NAFION FILM ON CARBON MICROARRAY ELECTRODE TO MONITOR OXYGEN FOR ENZYME ANALYSIS OF GLUCOSE

A microcarbon array electrode was modified by the placement of a Nafion film containing cobalt tetramethylpyridyl phorphyrin on its surface. This electrode was applied to the analysis of solution glucose when it was further modified by the immobilization of glucose oxidase on the outermost surface of the Nafion by the cross-linking of serum albumin with glutaraldehyde. The concomitant decrease in the concentration of oxygen, as it was consumed in the enzymatic reaction of glucose with glucose oxidase, was determined by either cyclic voltammetry or a double potential step method at the porphyrin-Nafion catalytic electrode. Glucose could be determined in the range of 0.01-4 mM rapidly, without interference from substances such as ascorbate or other saccharides.

Capillary electrophoresis with boron doped diamond electrode for amperometric detection of low molecular weight biological substrate

The research work in this thesis included the sensitive and selective separation of biological substance by capillary electrophoresis with a boron doped diamond electrode for amperometric detection. Chapter 1 introduced the capillary electrophoresis and electrochemical detection. It included the different modes of capillary electrophoresis, polyelectrolyte multilayers coating for open tubular capillary electrochromatography, different modes of electrochemical detection and carbon based electrodes. Chapter 2 showed the synthesized and electropolymerized N-acetyltyramine with a negatively charged sulfobutylether-β-cyclodextrin on a boron doped diamond (BDD) electrode followed by the electropolymerzation of pyrrole to form a stable and permselective film for selective dopamine detection. For comparison, a glassy carbon (GC) electrode with a combined electropolymerized permselective film of polytyramine and polypyrrole-1-propionic acid was used for selective detection of dopamine. The detection limit of dopamine was improved from 100 nM at a GC electrode to 5 nM at a BDD electrode. Chapter 3 showed field-amplified sample stacking using a fused silica capillary coated with gold nanoparticles embedded in poly(diallyldimethylammonium) chloride, which has been investigated for the electrophoretic separation of indoxyl sulphate, homovanillic acid and vanillylmandelic acid. The detection limit of the three analytes obtained by using a boron doped diamond electrode was around 75 nM, which was significantly below their normal physiological levels in biological fluids. This combined separation and detection scheme was applied to the direct analysis of these analytes and other interfereing chemicals including uric and ascorbic acids in urine samples without off-line sample treatment or preconcentration. Chapter 4 showed the selective detection of Pseudomonas Quinolone Signal, PQS for quorum sensing from its precursor HHQ, using a simply boron doped diamond electrode. Furthermore, by combining poly(diallyldimethylammonium) chloride modified fused silica capillary with a BDD electrode for amperometric detection, PQS was separated from HHQ and other analogues. The detection limit of PQS was as low as 65 nM. Different P. aeruginosa mutant strains were studied. Chapter 5 showed the separation of aminothiols by layer-by-layer coating of silica capillary with a boron doped diamond electrode. The capillary was layer-by-layer coated with the polycation poly(diallyldimethylammonium) chloride and negatively charged silica nanoparticles. All the aminothiols was separated and detected using a BDD electrode in an acidic electrolyte. It was a novel scheme for the separation and detection of glutathione reduced and oxidized forms, which is important for estimated overstressed level in the human system.

Plasma chloriding of thin-film silver - A novel process in silver-silver chloride reference electrode fabrication

Silver thin films were modified using a novel plasma modification process for the development of thin-film silver-silver chloride reference electrodes. The surface, physical, and electrochemical properties of these electrodes were investigated by atomic force microscopy, thickness and resistivity measurement techniques, as well as impedance spectroscopy and potentiometry. After plasma treatment, thin-film growth was observed and the electrodes, in general, exhibited low interface impedance and a roughened surface. Evidence of a complex surface reorganization was found. Correlating plasma conditions with film properties suggested that increasing pressure and exposure duration increased species availability, therefore governing the reaction rates, while input power appeared to influence the type of surface chemical reactions. Results also indicated that Ar/Cl-2 mixtures should be employed rather than pure chlorine plasmas. (C) 2002 The Electrochemical Society.

Resonance Raman and surface-enhanced resonance Raman studies of polymer-modified electrodes which mimic heme enzymes

Iron-5,10,15,20-tetraphenylporphyrin (FeTPP) has been incorporated into films of a coordinating hydrogel polymer support medium, poly(gamma-ethyl-L-glutamate) (PEG) functionalised with imidazole pendant arms (PEG-Im), and studied in situ on silver electrodes using a combination of both resonance Raman (RR) and surface-enhanced resonance Raman (SERR) spectroscopy. The SERR spectra give information on the portion of the film close to the electrode surface while RR spectra probe the

Identification of CO adsorbed at Ru and Pt sites on a polycrystalline Pt/Ru electrode and the observation of their oxidation and free interchange under open circuit conditions

The spontaneous oxidation of CO adsorbates on a Pt electrode modified by Ru under open circuit (OC) conditions in perchloric acid solution has been followed, for the first time, using in situ FTIR spectroscopy, and the dynamics of the surface processes taking place have been elucidated. The IR data show that adsorbed CO present on both the Ru and Pt domains and can be oxidized by the oxygen-containing adlayer on the Ru in a chemical process to produce CO under OC conditions. There is a free exchange of CO is between the Ru and Pt sites. Oxidation of CO may take place at the edges of the Ru islands, but CO is transfer, at least on the time scale of these experiments, allows the two different populations to maintain equilibrium. Oxidation is limited in this region by the rate of supply of oxygen to die surface of the catalyst. A mechanism is postulated to explain the observed behavior.

Electrocatalytic activity of Ru-modified Pt(111) electrodes toward CO oxidation

The electrochemical deposition of Ru on Pt(111) electrodes has been investigated by electron diffraction, Auger spectroscopy, and cyclic voltammetry in a closed UHV transfer system. At small coverages Ru formed a monatomic commensurate layer, at higher coverage mostly small islands with a bilayer height were detected. When the Pt was almost completely covered by Ru, three-dimensional clusters developed. The island structure of Ru changed upon electrooxidation of CO, reflecting an enhanced mobility of Ru. Adsorption and electrooxidation of CO have been studied on such Ru-modified Pt(111) electrodes using cyclic voltammetry and in situ FTIR spectroscopy. Compared to the pure metals, the Ru-CO bond is weakened, the Pt-CO bond strengthened on the modified electrodes. The catalytic activity of the Ru/Pt(111) electrode toward CO adlayer oxidation is higher than that of pure Ru and a PtRu alloy (50:50). It is concluded that the electrooxidation of CO takes place preferentially at the Ru islands, while CO adsorbed on Pt migrates to them. © 1999 American Chemical Society.

In situ FTIRS investigations of surface processes of Rh electrode - Novel observation of geminal adsorbates of carbon monoxide on Rh electrode in acid solution

With the help of in situ multi-step FTIR Spectroscopy, two types of adsorbed geminal CO have been observed for the first time at an electrochemically modified Rh electrode. A doublet band of two broad peaks at 2166 and 2112cm is assigned to geminal CO on Rh surface oxide (or hydroxide) produced by the electrochemical modification process, and a doublet band of two peaks near 2103 and 2033cm is ascribed to geminal CO on surface clusters of Rh formed by reduction of Rh surface oxide. Based on the evolution of FTIR spectra with the electrode potential, the surface processes of a Rh electrode, subjected to a potential cycling treatment at 1.5Vs between -0.275 and 2.4V for 2min, have been elucidated. The present results at the solid/liquid electrochemical interface were compared with those obtained at the solid/gas interface, and consistent conclusions were achieved.