An in situ infrared spectroscopic study of imidazole films on copper electrodes1

Organic films electrodeposited on a copper electrode from basic solutions containing imidazole were investigated by two different in situ infrared spectroscopic techniques: real-time polarization modulation and static linear polarization reflection absorption spectroscopy. The spectra indicate that as the electrode potential is made more positive, the amount of imidazole bound to the electrode surface increases. The coating on the electrode is found to consist mainly of copper(I) imidazolate with either a random or perpendicular orientation to the polycrystalline surface. No change in orientation of the imidazole ring is seen with the variation in potential. The infrared data from both reflection techniques indicates that before the Cu(0)/Cu(I) onset the film is formed at the solution metal oxide/hydroxide interface and at potentials above this, ≥?0.54 V, a more compact film forms closer to the metal surface.     

Electrochemistry of glucose oxidase immobilized on carbon nanotubes noncovalently functionalized by multihydroxyl and multicarboxyl groups

In this paper we have described that multi-walled carbon nanotubes (MWNTs) can be homogeneously dispersed and solubilized in water using non-covalent functionalization. These soluble MWNTs were then used for the immobilization of glucose oxidase (GOx) on glassy carbon electrode. Scanning electron microscopy is used to investigate the nanoscale structure of the film formed by the functionalized MWNTs. Electrochemical measurements were conducted to reveal the electroactivity of the GOx on the MWNT modified electrode. The functionalized MWNTs served as a network carrier for GOx as well as a conductor, enhancing greatly the response current. The GOx immobilized in this way retained its bioelectrocatalytic activity for the oxidation of glucose.     

A theoretical study of the electrochemical reduction of oxygen1

Multi-dimensional potential energy surfaces have been constructed for the experimentally found most probable rate-determining step in electroreduction of oxygen on Pt(111) and Pt(100) using a combination of experimental data in Morse functions and ASED-MO (a semi-empirical quantum mechanical technique). The minimum energy path for the reaction has been extracted by Euler's single step method. In agreement with the position of Schmickler [W. Schmickler, Interfacial Electrochemistry, Oxford University Press, 1996] for atom transfer reactions, the Marcus continuum model (in which the Gibbs energy is related to rearrangements among the solvent molecules by means of quadratic expressions) has been avoided. Instead the interaction of the proton with the librating solvent molecules in its environments is described by model considerations (ion–dipole and ion–ion induced dipole interactions). A treatment of non-adiabacity has been made by means of Landau–Zener formalism and the quantum properties of the proton are taken into account using an Eckart barrier for the calculation of tunneling. On this basis, the kinetic parameters, e.g. the activation energies, entropies of activation, the symmetry factors and reaction rates of the model reaction, have been calculated.     

Sensitive electrochemical detection of hydroquinone with carbon ionogel electrode based on BMIMPF6

An ionic liquid (IL) 1-butyl-3-methylimidazolium hexafluorophosphate (BMIMPF₆) based carbon ionogel electrode (CIE) was fabricated for the sensitive voltammetric sensing of hydroquinone (HQ) in this paper. Due to the specific characteristics of the prepared working electrode, HQ exhibited an enhanced electrochemical response on CIE with a pair of well-defined redox peaks appeared in pH 2.5 phosphate buffer solution. The electrochemical behaviors of HQ on CIE were investigated by different electrochemical methods such as cyclic voltammetry and differential pulse voltammetry with the electrochemical parameters calculated. Under the optimal conditions the oxidation peak currents exhibited good linear relationship with the HQ concentration in the range from 0.13 to 100.0 μmol L⁻¹ with the detection limit of 0.07 μmol L⁻¹ (3σ). The CIE showed separated electrochemical response to HQ and catechol in the mixture solution. The proposed method was successfully applied to HQ detection in artificial wastewater with the recovery in the range from 98.9% to 102.0%.     

The kinetics of mercury nucleation from Hg22+ and Hg2+ solutions on vitreous carbon electrodes

The kinetics of the electrochemical nucleation of Hg onto vitreous carbon were studied from analysis of potentiostatic current transients obtained at different overpotentials in Hg₂²⁺ and Hg²⁺ solutions. Similar sizes of critical nuclei and number densities of sites on the surface were found for nucleation of Hg from both solutions, indicating, in agreement with nucleation theory, that the rates of nucleation are controlled by surface energies and deposit–substrate interactions. Saturation number densities of nuclei were deduced from the kinetic analysis, and their relationship with those obtained from direct observation of the electrode surface is discussed. It was found that at low overpotentials, the nuclei deposited from both solutions were uniformly distributed on the electrode surface, whereas their distribution was affected by inhibition of the nucleation rates close to already established nuclei at high overpotentials. This inhibition was enhanced during deposition from Hg²⁺ solution.     

Underpotential deposition of lead on Pt(111) in the presence of bromide: RRDPt(111)E and X-ray scattering studies1

The underpotential deposition (upd) of Pb onto Pt(111) in solution containing Br^? was examined by classical RRD_Pt(111)E electrochemical methods in combination with in situ surface X-ray scattering measurements. The results show that Pb upd onto Pt(111) in the presence of bromide is a competitive process with the total amount of Pb deposited at underpotential being only ca. 0.51±5% ML, less than the amount needed to form a close-packed monolayer, 0.63 ML (1 ML equals 1 Pb atom per Pt surface atom). Deposition of Pb adatoms is accompanied by desorption of about one-half of the bromide adsorbed on the Pt surface at higher potentials, leaving co-adsorbed bromide both in and on-top-of the adlayer. In the potential region where the ratio of co-adsorbed species is close to one (E≈0 V) there is the slow formation (over a period of ca. 2 h) of an ordered surface alloy, which has a p(2×2) unit cell. No other ordered structures of Pb are observed in the underpotential region. © 1997 Elsevier Science S.A.     

Scanning electrochemical microscopy (SECM) of facilitated ion transfer at the liquid|liquid interface1

A new mode of the scanning electrochemical microscope (SECM) operation is presented. A micropipette-based electrode is used as an amperometric microprobe (tip). The tip current is produced by facilitated transfer of ions from the aqueous solution inside the pipette into the organic solvent, e.g., the transfer of K⁺ into 1,2-dichloroethane (DCE) assisted by dibenzo-18-crown-6 (DB18C6). A positive feedback current is observed when the tip approaches the water|DCE interface due to the transfer of potassium into the aqueous layer and regeneration of DB18C6 species. Good agreement with the SECM theory can be demonstrated. Negative feedback is observed when the tip approaches a glass insulator. The dependence of the SECM response on the shape of the liquid meniscus formed at the micropipette tip is discussed. The technique developed can be used for studies of ion transfer processes at the liquid|liquid and liquid|membrane interfaces and for high resolution electrochemical imaging.     

Resonance frequency measurements in vivo and related surface properties of magnesium-incorporated, micropatterned and magnesium-incorporated TiUnite®, Osseotite®, SLA® and TiOblast® implants

Objective: To investigate implant stability using resonance frequency measurements of topographically changed and/or surface chemistry‐modified implants in rabbit bone. Material and methods: Six groups of microstructured, screw‐shaped titanium implants: two oxidized, cation‐incorporated experimental implants [Mg implants and MgMp implants with micropatterned thread flanges (80–150 μm wide and 60–70 μm deep)] and four commercially available clinical implants (TiUnite^®, Osseotite^®, SLA^®, and TiOblast^®) were installed in 10 rabbit tibia for 6 weeks. The surface properties of the implants were characterized in detail using several analytical techniques. Implant stability was measured using a resonance frequency analyzer (Osstell^?). Results: Surface characterization of the implants revealed microstructured, moderately rough implant surfaces varying 0.7–1.4 μm in S_a (mean height deviation), but with clear differences in surface chemistry. After 6 weeks, all implants showed statistically significantly higher increases in implant stability. When compared with one another, MgMp implants showed the most significant mean implant stability quotient (ISQ) value relative to the others (P≤0.016). In terms of increment (ΔISQ) in implant stability, MgMp implants showed a significantly greater value as compared with Osseotite^® (P≤0.005), TiOblast^® (P≤0.005), TiUnite^® (P≤0.005), SLA^® (P≤0.007), and Mg implants (P≤0.012). In addition, transducer direction dependence of resonance frequency analysis (RFA) measurements was observed such that the differences in the mean ISQ values between longitudinal and perpendicular measurements were significant at implant placement (P≤0.004) and after 6 weeks (P≤0). Conclusion: The present study found that implant surface properties influence RFA measurements of implant stability. Surface chemistry‐modified titanium implants showed higher mean ISQ values than did topographically changed implants. In particular, cation (magnesium)‐incorporated micropatterns in MgMp implants may play a primary role in ΔISQ.     

Electrochemical polymerization of aniline and toluidines on a thermally prepared Pt electrode1

The polymerization of aniline (AN) and toluidines (o-toluidine (OTO)/m-toluidine (MTO)) was performed electrochemically on a Pt-coated titanium electrode in 1.0 M HCl using cyclic voltammetry. The results showed that the rate of polymerization was strongly dependent upon the type of monomer employed. The polymerization rate of these monomers on a Pt-coated electrode is in the order: AN>OTO>MTO. A kinetic expression for the autoacceleration process in the electrochemical polymerization of these aniline derivatives is expressed as v=k[p][M]+k′[M] in which k′, k, [M] and [p] are the initiation (nucleation process) rate constant, the rate constant when the polymer is deposited on the electrode, monomer concentration, and the total amount of polymer, respectively. The ratios of k′/k are 6.64×10^?6, 3.23×10^?6 and 3.15×10^?6, respectively, for AN, OTO and MTO polymerization. The polymerization rate of these aniline derivatives is reduced with agitation of the monomeric solution. The experimental results of E_1/2 for the first redox process showed that the AN–OTO or AN–MTO comonomer system generated true copolymers rather than the mixture of the corresponding homopolymers. The polymerization rates of these aniline derivatives on three different electrodes are in the order: IrO₂>RuO₂>Pt-coated electrode.     

Electrochemical catalysis in microemulsions. Dynamics and organic synthesis1

Microemulsions are clear microheterogeneous fluids made from water, oil, and surfactant. They provide cheaper and less toxic alternatives to organic solvents. In this paper, we review progress in understanding reaction dynamics and designing mediated electrochemical syntheses in microemulsions. Rates of mediated electrochemical reactions in conductive microemulsions can be enhanced by preconcentration of reactants in a dynamic film on the electrode surface, or more generally by controlling the formal potential of the mediator in the fluid. The electrode|fluid interface in microemulsions probably consists of a dynamic layer of surfactant molecules packed more loosely on the electrode than in aqueous micellar solutions. Microemulsions afforded good yields of carbon–carbon addition products in reactions mediated by the cobalt complex vitamin B₁₂. Excellent stereoselective control in microemulsions made with the cationic surfactant cetyltrimethylammonium bromide was demonstrated for the catalytic cyclization of 2-(4-bromobutyl)-2-cyclohexen-1-one to 1-decalone. Electrochemical synthesis in microemulsions may be a viable future approach to environmentally friendly methods of producing organic chemicals.     

A new SO2 gas sensor based on an Mg2+ conducting solid electrolyte

A new SO₂ gas sensor based upon a magnesium ion conducting solid electrolyte MgZr₄(PO₄)₆ (MZP) and a Na₂SO₄ auxiliary electrode has been fabricated and tested. Electromotive force (emf) results with variation in the SO₂ and the O₂ partial pressures at various temperatures from 873 to 1023 K are presented. The results have shown that the response to SO₂ is rapid and the measured emf of the sensor is found to vary linearly as a function of the logarithm of the partial pressure of SO₂. As MZP does not react with SO₂, both electrodes of the sensor can be exposed to the same atmosphere containing SO₂ and thus there is neither any need for sealing the electrode compartment nor using any semi-permeable membranes.     

Novel water-borne polyurethane based electrolytes for lithium batteries—(I) tailor-made polymer1

In the light of the polyethylene oxide (PEO) structure, various polymer electrolytes based on tailor-made polyurethane (PU) were prepared and investigated by alternating current (ac) impedance. Equivalent circuits and schematic structures were proposed to describe the conductive behavior of these electrolytes. The impedance results show that water-borne polyurethane (WPU) film, impregnated with propylene carbonate (PC), has a conductivity of 2.83×10^?5 S cm^?1 at 80°C. With the addition of salt and solvent, WPU-based electrolyte exhibits a conductivity of 4.68×10^?4 S cm^?1 at 25°C. It is promising to use our tailor-made WPU as a polymer electrolyte for lithium batteries.     

Scanning electrochemical microscopy: theory and experiment for the positive feedback mode with unequal diffusion coefficients of the redox mediator couple1

Theory for the chronoamperometric positive feedback mode of the scanning electrochemical microscope (SECM) is extended to include the situation where the oxidised and reduced forms of the redox mediator couple have arbitrary diffusion coefficients. Under typical positive feedback conditions, the solution initially contains a redox-active species, R, along with excess supporting electrolyte. The potential of the tip ultramicroelectrode (UME), positioned close to an interface of interest, is adjusted to a value where R is electrolysed to produce species O at a diffusion-controlled rate. O diffuses away from the tip towards the interface, where the reverse redox reaction occurs leading to the production, and diffusional feedback of R for electrolysis at the tip electrode. When positive feedback measurements are carried out under diffusion-controlled chronoamperometric conditions, the form of the normalised current–time behaviour, at a particular tip to interface distance, is found to be sensitive to the ratio of the diffusion coefficients of the O/R couple. As a steady-state is established, the normalised current becomes independent of the diffusion coefficient ratio and depends only on the tip to interface distance. Experimental measurements on the chronoamperometric oxidation of ferrocene (Fc) in acetonitrile solution at a Pt tip UME positioned close to a Pt substrate electrode, provide support for the theoretical predictions and demonstrate that the diffusion coefficient ratio can readily be determined from SECM chronoamperometry. Although Fc and Fc⁺ are often assumed to have the same diffusion coefficients, steady-state and chronoamperometric measurements at a conventional UME yield a value of 2.0×10^?5 cm² s^?1 for the diffusion coefficient of Fc, while SECM chronoamperometry indicates that the diffusion coefficient of Fc⁺ is 1.6×10^?5 cm² s^?1.     

Multi-technique study of the anodic degradation of polyaniline films1

Polyaniline (PANI) films, formed by potential cycling methods on Au electrodes in sulfuric acid solutions, were anodically degraded with time at ca. 1 V versus RHE. Ellipsometric and cyclic voltammetric data suggest that colored species are formed within the film, perhaps containing quinone endgroups, and the bulk of the film dissolves uniformly creating greater porosity. This model of film degradation has been supported by transmission electron microscopy (TEM) studies of cross-sectional samples of PANI films. Both TEM and ellipsometry also showed that the PANI film is not delaminated, and is very resistant to anodic dissolution/degradation. Concurrent in situ mass measurements suggest that, in the early stages of film degradation, some regions of the film become electrochemically inactive, although the nature of the charge compensation mechanism of the PANI redox reaction remains unaltered. When no further film degradation can be accomplished, the mass data show that a substantial quantity of largely inactive film material is still present on the electrode surface. Furthermore, the change in the redox potential and the invariant charge compensation stoichiometry suggests that, although the final degraded film is a different material from the newly formed PANI film, only those portions of the film that have PANI characteristics are electrochemically active.     

High frequency dielectric studies of hydrated Nafion?1

This study reports high frequency dielectric measurements (0.045–30 GHz) on Nafion® 117 at various states of hydration. A novel technique to measure the broad band frequency dependent real and imaginary parts of the relative permittivity is described. The basic experimental configuration and numerical data analysis are reported along with a discussion of several difficulties encountered and experimental validation of the method. The preliminary results show a strong dependence of the dielectric constant of the Nafion® 117 membrane with water content. The dielectric constant for all hydrated membrane samples was observed to be constant over the initial part of the frequency span, ranging from a maximum of 20 in the samples with 13 waters per sulfonate to a minimum of four in very dry samples. The results reflect the decreasing polar environment of the water at low water contents as well as the increasing extent of binding of the water at the fixed ionic site at low water content. A ‘roll off’ in the dielectric constant, the extent of which was dependent on water content, was observed also in the frequency spectrum. Several possible origins for this ‘roll-off’, including real effects of dipolar relaxations occurring in the hydrated polymers and experimental effects due to the similarity of the wavelength of radiation to the sample dimensions are discussed. Finally, the conductivity of the membranes at various water contents and at frequencies below 5 GHz was extracted from the loss factor spectra. These values agreed well with previous conductivity measurements (obtained at lower frequencies) suggesting that no relaxations are observed in the intervening frequency range (roughly 5–50 MHz).     

Mechanism of the catalysis by Alcaligenes eutrophus H16 hydrogenase of direct electrochemical reduction of NAD+

The mechanism of direct electrochemical reduction of NAD⁺ into NADH catalysed by Alcaligenes eutrophus H16 hydrogenase was analysed in thin layer electrochemical cells with platinum and carbon electrodes. Two phases can be distinguished in the catalytic reaction occurring on platinum electrodes. In the potential range from approximately ?0.620 to ?0.675 V (SCE) direct electron transfer occurred via the diaphorase-like dimer of the hydrogenase. Below ?0.69 V versus SCE the hydrogenase used hydrogen species adsorbed onto the platinum electrode, but no molecular hydrogen was required for this second catalytic phase. The mechanism was quite similar to those which had been previously determined for Rhodococcus opacus hydrogenase. This confirmed the very great similarity of the two enzymes, even if the maximum NAD⁺ reduction rate of 0.36 mM min^?1 obtained here remains lower than those reached with R. opacus hydrogenase in a previous study. Careful analysis of the experimental data obtained on a carbon electrode led to the conclusion that no direct electron transfer was observed on this material under the operating conditions used. On the other hand, the voltammetric experiments performed on a carbon electrode in a thin layer cell showed clearly the occurrence of a catalytic current due to the hydrogenase-catalysed reduction of NAD⁺ by molecular hydrogen. This may be a useful tool for further analysis of the hydrogenase kinetics.     

The effect of FIV infection on CD4+ and CD8+ counts in periradicular lesions

AIM: The purpose of this study was to elucidate whether a decrease/increase in T-cell populations is present in the development of periradicular disease in the immunocompromised feline model. METHODOLOGY: Eight cats were immunosuppressed with steroids prior to infection with feline immunodeficiency virus (FIV). Another eight cats, age and sex matched littermates, were monitored and tested at equivalent periods of time and served as uninoculated, seronegative controls. Periradicular lesions were induced using local bacterial inoculations into the pulp of the canine teeth and assessed after one- and four-week periods, corresponding to the acute and chronic stages of the periradicular disease. Block sections were obtained and specimens were prepared for H & E and immunohistochemical staining for CD4+ and CD8+ receptors. Cells were quantified using a computer imaging system and data analysed using generalized estimating equation (GEE) regression models. RESULTS: Significantly lower CD4+ counts and CD4+/ CD8+ ratios were observed at all time periods in the periradicular region of the FIV group (P = 0.0006). No significant difference in CD8+ counts was observed between the two groups. In both groups there was a significant difference in the CD4+ counts between one week and baseline, and 1 week and 4 weeks. There was no significant difference between baseline and 4 weeks for either group. CONCLUSION: FIV infection reflected decreased CD4+ counts at the periradicular level, however, inflammation and progression of the lesion, appeared to be comparable to the non-immunocompromised controls.     

Quantitative studies of the inhibitory effect of perchlorate on the concentration of 36ClO4−125I− and 99mTcO4− in salivary glands of male and female mice

[³⁶Cl]-Perchlorate, [¹²⁵I]-iodide and [^99mTc]-pertechnetate were concentrated in the mouse submandibular salivary gland in the order ${}^{36}\text{ClO}{}_4{}^{\mathrm{?}}\text{=}{}^{\mathrm{99m}}\text{TcO}{}_4{}^{\mathrm{?}}\text{>}{}^{125}\text{I}{}_{\mathrm{?}}$. Gland plasma ($\text{G}\text{P}$) concentration ratios for ³⁶ClO₄^? and ^99mTcO₄^? rose to a maximum of 12 compared to a value of five for ¹²⁵I^?. In the case of all the anions studied, a significantly higher concentration was observed in male compared to female mice. This anion concentration difference between the sexes was of the same order for ³⁶ClO₄^? and ^99mTcO₄^? and was smaller in the case of ¹²⁵I^?. Results suggest that ³⁶ClO₄^? is concentrated in the duct cells of the salivary gland. The serum perchlorate levels required to decrease the $\text{(G}\text{P)}$ ratio to 1 varied for the different anions and was in the order ${}^{\mathrm{99m}}\text{TcO}{}_4{}^{\mathrm{?}}\text{>}{}^{36}\text{ClO}{}_4{}^{\mathrm{?}}\text{>}{}^{125}\text{I}{}^{\mathrm{?}}$. The concentration of perchlorate required to inhibit the concentrating mechanisms for the three anions was greater in males than females. The lowest dose of ClO₄^? used (0.28 μ-equiv./kg) was such that it did not inhibit ¹²⁵I^?or ^99mTcO₄^? uptake in either sex. With a dose of 1.43 μ-equiv./kg, the ClO₄^? concentrating mechanisms for ¹²⁵I^? and ^99mTcO₄^? were inhibited in the female but not in the male.