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.

STUDIES ON INTERFACIAL PHENOMENA OF POLYCRYSTALLINE HG1-XCDXTE THIN-FILM ELECTRODE POLYSULFIDE REDOX SOLUTION

Electrode capacitance and photocurrent spectra of electrodeposited polycrystalline Hg1-xCdxTe thin films of varying (1-x) were measured in polysulfide redox solution, hence the flatband potentional PHI(fb) and the bandgap E(g) of Hg1-xCdxTe thin films obtained. It was of interest to find out that only the location of conduction band E(c) shifts negatively with increasing (1-x) while the valence band E(v), is almost constant. The experimental open circuit photovoltage V0 is smaller than theoretical value V(max) calculated through flatband potential PHI(fb), therefore there is a possibility of promoting the experimental open circuit photovoltage.

ELECTROCATALYSIS AT A MICRODISK ELECTRODE MODIFIED WITH A REDOX SPECIES

The current equation of the electrocatalytic reaction at a microdisk electrode modified with redox species has been described and verified experimentally. There exists a linear relationship between plateau limiting current and the radius of the microdisk electrode for a catalytic process. The influence of the dimensions of the microdisk electrode on catalytic efficiency is discussed. The polyvinylferrocene (PVFc)-modified microdisk electrode prepared by the coating method was taken as a typical example, on which the electrocatalytic oxidation of ascorbic acid could be studied. The catalytic reaction rate constants were determined as an average value of 1.5 X 10(-7) cm3/mol s by this method, and are consistent with those obtained at a conventional electrode.

ELECTROCATALYSIS OF POLYPYRROLE-METHYLENE BLUE FILM MODIFIED ELECTRODE FOR DIRECT REDOX REACTION OF CYTOCHROME-C

The electron transfer process of hemeproteins on the electrode surface is considered a promising subject in the area of bioelectrochemistry. Electrochemists believe that electron transfer between electroactive proteins and electrode surface might be expected to simulate the electron transfer between proteins. This research provides information about the electron transfer mechanism in biological system. Cytochrome c is a typical electron transferring protein,

Redox cycling of Ni-YSZ anode investigated by TPR technique

Effect of redox cycling on a Ni-YSZ anode prepared from 50 wt.% NiO and 50 wt.% YSZ was investigated by using temperature-programmed reduction (TPR), XRD and SEM techniques. XRD results showed that NiO was formed during re-oxidation. Both the XRD and TPR results depicted that the conversion of nickel to NiO depended on the re-oxidation temperature. The oxidation of Ni to NiO occurred quickly in the initial several minutes and then reached a quasi equilibrium. The TPR profiles tracing the redox cycling showed that it brought continuous changes in the NiO micro-structure at 800 degrees C, whereas at 600 degrees C it had only little effects on the reduction of NiO. Re-oxidation resulted in the formation of spongy aggregates of NiO crystallites. Redox cycling at 800 degrees C led to a continuous decrease in the primary crystallite size of NiO and a high dispersion of the Ni particles. A continuous expansion of the slice sample was observed in both of the oxidized and reduced states during the redox cycling at 800 degrees C, whereas this process did not occur during the redox cycling at 600 degrees C. (c) 2005 Elsevier B.V All rights reserved.

Effect of Fe impurity on the optical loss of Nd-doped phosphate laser glass

The optical loss coefficient at 1053-nm wavelength, influenced by Fe ions in N31-type Nd-doped phosphate laser glass, was determined precisely and analyzed in detail. It is found that the optical loss coefficient per unit of Fe concentration (cm^(-1)/ppmw) increases with Fe concentration in the range of 0---300 ppmw, but it approaches a constant as the Fe concentration is larger than 300 ppmw. Such a concentration effect is due to a shift in the redox equilibrium between Fe3+ and Fe2+ ions in the glass. The effect of oxygen pressure, temperature, and variable valence states of other metal ions in glass samples on the optical loss is also discussed.