In-situ FTIR spectroelectrochemical study of chromium hexacyanoferrate on glassy carbon electrode

Chromium hexacyanoferrate (CrHCF) modified grassy carbon electrode (GC) in different electrolytes was studied by cyclic voltammetry and in situ FTIR spectroelectrochemistry. The results indicate that the behavior of CrHCF firm can be understood in term of two structures: Cr1/3Cr(III)Fe(II)(CN), and MCr(III)Fe(II)(CN)(6). Besides,the film exists in amorphous state: the outer layer is porous film, while the inner layer is relatively compact. According to the electrochemical reaction of CrHCF, the lattice can contract and expand with the cations' diffusion.

Electrochemistry of heteropolyanions in coulombically linked self-assembled monolayers

A composite film containing heteropolyanion was fabricated on gold by attaching the Keggin-type heteropolyanion, PMo12O403- on a 4-aminothiophenol SAM via Au-S bonding. Reflection FTIR, cyclic voltammetry and XPS were used for the characterization of the composite film. Reflection FTIR studies indicate that there is some Coulombic interaction between PMo12O403- and the surface amino group in the composite film, which greatly improves the film stability and prevents effectively the destructive intermolecular aggregation. The composite him shows three reversible redox couples within the pH range pH less than or equal to 7.0, attributed to three two-electron and two-proton electrochemical reduction-oxidation processes of PMo12O403-. Compared with PMo12O403- in the solution, the PMo12O403- of the composite film electrode can exist in a larger pH range, and shows smaller peak-to-peak separation, and more reversible reaction kinetics. Moreover, the composite him obtained shows a good catalytic activity for the reduction of BrO3-. (C) 1998 Elsevier Science S.A. All rights reserved.

In-situ microscopic FTIR spectroelectrochemical study of the reduction of K3Fe(CN)(6) in polymer electrolyte

Cyclic voltammetry and in-situ microscopic FTIR spectroelectrochemistry were used for the electrochemical and vibrational characterizations of the reduction process of K3Fe (CN)(6) in polyethylene glycol(PEG) with LiClO4 as supporting electrolyte at a Pt microelectrode. The rate of electron transfer is a function of the concentration of the supporting electrolyte. The redox potentials and cyclic voltammetric currents vary with Li/O molar ratio. The bl-situ spectroelectrochemistry shows that the infrared spectra are influenced by the concentration of LiClO4. The bridging cyanide groups with a structure Fe-I-C drop N ... Fe-I-C drop N are formed during the reduction process of K3Fe (CN)(6). There may be an activated complex between the Lif cation and the complex anion.

Microelectrode voltammetric measurement of heterogeneous electron transfer rate constants for reduction of 7,7,8 ',8 '-tetracyanoquinodimethane in polymer electrolytes

This paper presents a microelectrode voltammetric determination of heterogeneous electron transfer rate constants (k(s)) and diffusion coefficients (D) of 7,7,8',8 '-tetracyanoquinodimethane (TCNQ) in polyelectrolytes. The diffusion coefficients are estimated using cyclic voltammetry under linear diffusion conditions, and the heterogeneous electron transfer rate constants are obtained under mixed linear and radial diffusion in the polyelectrolyte. k(s) and D increase with increasing temperature, and the activation barriers of the electrode reaction for reduction of TCNQ are obtained. On the other hand, the dependencies of D and k(s) of TCNQ on the size and charge of the counterion are compared in the polyelectrolyte. (C) 1998 Elsevier Science Ltd. All rights reserved.

Amperometric glucose biosensor based on sol-gel organic-inorganic hybrid material

A new type of sol-gel organic-inorganic hybrid material was developed and used for the production of biosensors. This material is composed of silica sol and a grafting copolymer of poly(vinyl alcohol) with 4-vinylpyridine. It prevents the cracking of conventional sol-gel-derived glasses and eliminates the swelling of the hydrogel. The optimum composition of the hybrid material was first examined, and then glucose oxidase was immobilized in this matrix to demonstrate its application. The characteristics of the biosensor were studied by cyclic voltammetry and chronoamperometry. The biosensor exhibited a series of good properties: high sensitivity (600 nA mmol(-1)L(-1)), short response time (11 s) and remarkable long-term stability in storage (at least 5 months). In addition, the characteristics of the second-generation biosensor with the use of tetrathiafulvalene as a mediator mere discussed.

Probe beam deflection study on electrochemically controlled release of 5-fluorouracil

In this paper, the polypyrrole (PPy) film modified electrodes are used as an electroreleasing reservoir. The electrochemically controlled release of 5-fluorouracil (5-FU) from a PPy film modified electrode to aqueous electrolytes is studied by the in situ probe beam deflection (PBD) method combined with cyclic voltammetry (CV) and chronoamperometry (CA). The PBD results reveal that the release of 5-FU from PPy film depends on the electrochemical redox process of the PPy film electrode. The released amount is controlled by the reduction potential and is proportional to the thickness of the film. The exchange of 5-FU anions with Cl- on an open circuit is slow on the time scale of minutes, but the release of 5-FU anions can proceed quickly at -0.6 V (vs Ag/AgCl). The amount of released 5-FU decreases with the time that the PPy film is soaked in aqueous solution. (C) 1998 Elsevier Science Ltd. All rights reserved.

Paint-freeze method to form self-assembled alkanethiol/phospholipid bilayers on gold

A paint-freeze method for preparing self-assembled alkanethiol/phospholipid bilayers on a gold surface has been described (by cyclic voltammetry, a.c impedance, polarized FTIR-ATR) to be well-ordered and packed, stable, solvent-free bilayers. The lipid order parameter was 0.67, calculated from the dichroic ratio, consistent with a well-ordered lipid film in which the methylene groups have segmental flexibility and are disordered to a degree which is typical for a lipid bilayer in the liquid-crystalline phase. Such a supported membrane provides a useful way for studies in biophysics, physiology and electrochemistry.

The electrochemical behaviour of soluble polyimides

The electrochemical behaviour of five soluble polyimides was studied in organic solution using cyclic voltammetry. The relationship between the electrochemical behaviour and the molecular structure was discussed, It was found that the colours of polyimides can be changed due to the electrochemical redox reactions.

Catalytic oxidation of cyclohexene to cyclohexanone by a triple system in acidic aqueous acetonitrile medium

The catalytic oxidation of cyclohexene to cyclohexanone using Pd(OAc)(2)/HQ/FePc was investigated in an acidic aqueous solution of acetonitrile. The role of each component of this system in the oxidation of cyclohexene was explored by means of UV-VIS, IR, XPS spectroscopy and. cyclic voltammetry, respectively. Based on the experimental results, the mechanism of the oxidation of cyclohexene catalyzed by Pd(OAc)(2)/HQ/FePc was elucidated.

Self-assembly of the pre-formed inclusion complexes between cyclodextrins and alkanethiols on gold electrodes

A new kind of self-assembled monolayer (SAM) formed in aqueous solution through the pre-formed inclusion complexes (abbreviated CD . C-n) between alpha-, beta-cyclodextrins (CDs) and alkanethiols (CH3(CH2)(n-1)SH, n = 10, 14 and 18) was prepared successfully on gold electrodes. High-resolution H-1 NMR was used to confirm the formation of CD . C-n. X-ray photoelectron spectroscopy, cyclic voltammetry and chronoamperometry were used to characterize the resulting SAMs (denoted as M-CD . Cn). It was found that M-CD . Cn were more stable against repeated potential cycling in 0.5 M H2SO4 than SAMs of CH3(CH2)(n-1)SH (denoted as M-Cn), with a relative sequence of Mbeta-CD . Cn > Malpha-CD . Cn > M-Cn. In addition, an order of blocking the electron transfer between gold electrodes and redox couples (both Fe(CN)(6)(3-) and Ru(NH3)(6)(3+)) in solution, M-CD . C10 > M-CD . C14 > M-CD . C18, was observed. A plausible explanation is provided to elucidate some of the observations. (C) 1997 Elsevier Science S.A.

Electrochemical quartz crystal microbalance study for vanadium hexacyanoferrates: monitoring of film growth and ion effects during redox reactions

An electrochemical quartz crystal microbalance was employed to monitor directly the growth of vanadium hexacyanoferrate (VHF) films on platinum substrates during electrodeposition and interfacial coagulation in the solution containing sulfuric acid electrolyte, vanadium(IV) and hexacyanoferrate(III). Mass changes of the gold/crystal working electrode were correlated with cyclic voltammetry data. Effects of cations (NH4+, Li+, Na+ and K+), anions (SO42- and NO3-) and solvent during redox reactions of the films were studied. The results show that cations were incorporated into the film during reduction and expelled from the film during oxidation. Solvent also participates in VHF electrochemistry, and its role cannot be neglected. Anions play no role in VHF electrochemistry. (C) 1997 Elsevier Science S.A.

In situ FTIR spectroelectrochemistry of a microarray electrode

A thin-layer microdisk array electrode (TLMDAE) was designed for in situ reflectance FTIR spectroelectrochemical studies. A theoretical estimation, cyclic voltammetry, chronoamperometry and in situ IR measurements demonstrate that this novel design of array electrode results in advantages such as reduced ohmic potential drop, small cell constant and facility for diffusional exchange between thin layer and bulk solution. It has been suggested that the enhanced edge diffusion on the TLMDAE leads to a reduced accumulation of species in the thin layer. (C) 1997 Elsevier Science S.A.

Hydrazines probe of interaction of horseradish peroxidase with cryo-hydrogel

The interaction between horseradish peroxidase (HRP) and the cryo-hydrogel was probed by using hydrazines which show high specificity of the reaction of the edge in the prosthetic heme of horseradish peroxidase. For comparison, the interaction of hydrazine with the horseradish peroxidase adsorbed on graphite electrode was also carried out by using steady-state response of the enzyme electrode and cyclic voltammetry. In order to obtain a proper explanation of the kinetic parameters for the enzymatic reaction, the theoretical expressions of I-max and K-M' in the Michaelis-Menten equation for the experimental system were provided. (C) 1997 Elsevier Science B.V.

Axial coordination effects of pyridine on the electrochemistry of (TPP)Co in 1,2-dichloroethane solution

The electrochemistry of (TPP)Co in the presence of pyridine was investigated in dichloroethane solution by cyclic voltammetry. With the addition of pyridine to the solution, the reduction peaks of the axial complex compounds, (TPP)Co(III)(Py) and (TPP)Co(III)(Py)(2) were observed. It was found that the reduction peak of Co(II)/Co(I) shifted to about -1.20V (SCE) with the increase of added pyridine. The new reduction peak may be attributed to the direct reduction of the axially complex (TPP)Co(II)(Py).

Spontaneous assembly of the inclusion complexes of viologen-attached alkanethiols and alpha-, beta-cyclodestrin on gold electrode

Electroactive self-assembled monolayers (SAMs) with well-defined electrochemical responses were prepared by spontaneous assembly of the inclusion complexes (CD/C8VComegaSH) of viologen-attached alkanethiols (C8VComegaSH) and alpha- and beta-cyclodextrin (CD). They were characterized by X-ray photoelectron spectroscopy and cyclic voltammetry. The results demonstrate that the chemisorption process of CD/C8VComegaSH on gold substrate occurs through S-Au bonds, and that the redox sites in SAMs of CD/C8VComegaSH are in a much more uniform environment than those in SAMs of C8VComegaSH.