High-speed Cyclic Voltammetry Research Articles

Electron transfer kinetics of methylviologen included in 4-sulfonatocalix[n]arenes at glassy carbon electrode; adiabaticity and activation energy

Quasi-reversible single electron transfer (ET) kinetics of methylviologen partly-included at the rim of 4-sulfonatocalix[n]arenes (n = 4,6 and 8) has been investigated in aqueous solution. ET rates were measured by Nicholson method with relatively large potential scan rates (0.9 V/s < v < 50 V/s). ET proceeded adiabatically on the direct collision between the MV+/MV2+ and the electrode surface. The host-guest binding equilibrium at the activation state was not established under the high-speed cyclic voltammetry condition. The non-equilibrium stabilization energy was independent of the size of the cavitands. The activation energy of ET under the partly-included condition was 70–80% of that without any inclusion.

QUANTITATIVE RAPID IDENTIFICATION OF ANTIGENS AND ANTIBODIES

In this paper we describe our method of high-speed cyclic voltammetry for rapid identification of microbial antigens and antibodies. Quantitative detection of complementary antibodies and antigens carried out by developed biosensor systems. They contain recognizing a biologically active intermediate phase.Measurement of cyclic current-voltage characteristics (CCVC) was performed using a computerized potentiodynamic complex. Recorded triad potential - E, current - j, time - t. From CCVC determined cteor = f(ceks) dependence. Their analysis revealed that for all the interfaces, containing, as the recognition phase, the antibody or antigen Staphylococcus aureus (S. aureus) correlation coefficient r2 between theoretical and experimental concentrations did not exceed the range 0,960 ÷ 0,996.The developed method has allowed to increase the accuracy and reproducibility of measurements and made it possible to identify the species of microorganisms in a shorter period of time, which in many cases is critical.

Long-Range Electronic Coupling between Ferrocene and Gold in Alkanethiolate-based Monolayers on Electrodes

High-speed cyclic voltammetry was used to measure rates for ferrocene oxidation/reduction in a series of self-assembled monolayers formed by coadsorption of N-(mercaptoalkyl)ferrocenecarboxamide ((C5H5)Fe(C5H4)CONH(CH2)nSH where n = 7−10, and 15) with mercapto alcohol (HO(CH2)n+1SH where n = 7−10, and 15) on gold. Standard electron-transfer rate constants were obtained as a function of chain length and from these rate constants, a β value (describing the exponential decay of rate with adsorbate chain length) of 1.1 methylene-1 or 0.85 A-1 was obtained. The rate data were also used to estimate coupling factors, |VAB|, describing the long-range electronic coupling between the immobilized ferrocene groups and the underlying gold electrode. Electronic coupling factors varied from a low of 0.06 cm-1 for the long-chain monolayer (18 bonds in the pathway linking ferrocene to the electrode) to a high of 6.5 cm-1 for the short-chain monolayer (10 bonds linking ferrocene to the electrode). The latter value is in go...

The electrochemical oxidation of 2-phenyl-1,2-benzisoselenazol-3(2H) -one and its derivatives. A study of the electrode process in dried acetonitrile at conventional electrodes and microelectrodes

The electrochemical oxidation of 2-phenyl-1,2-benzisoselenazol-3(2H)-one and several of its derivatives was investigated in dried acetonitrile by conventional and microelectrode techniques. The unsubstituted benzisoselenazolone ( 1a) as well as its derivatives substituted in position 4′ by methyl ( 1b) and methoxy ( 1c) groups are oxidized by controlled potential electrolysis into their selenoxides ( 2a–c). The intermediary cation radicals (CRs), eventually stabilized in the medium by addition of a water scavenger (trifluoroacetic anhydride, 1%), were detected by high-speed cyclic voltammetry at potential scan rates up to 30 kV s −1. The corresponding reaction mechanism is of an ECE-type, in which the chemical step consists of the hydrolysis of the formed CR by residual water. A comparison with its sulphur analogues, 2-phenyl-1,2-benzisothiazol-3(2H)-ones ( 3), showed that the selenium CRs are three orders of magnitude more reactive towards residual water then their sulphur analogues. Similar studies of benzisoselenazolones substituted on the N-aryl ring by electro-donating groups, 2-(3,4-dimethoxyphenyl)- ( 1d), 2-(3,4-methylenedioxyphenyl)- ( 1e) and 2-(4-dimethylaminophenyl)-1,2-benzisoselenazolone ( 1f), gave rise to no selenoxide formation, although intermediary CRs were detected at potential scan rates below 30 V s −1.

Electrochemical studies of iron(III) Schiff base complexes—II. Dimeric μ-OXO[Fe III(N 2O 2)] 2O complexes

The electrochemical reduction of μ-oxo bridged Fe III dimers (L)FeOFe(L), where L is a Schiff base, has been investigated in aprotic solvents by cyclic voltammetry and coulometry with UV-vis spectroscopy. Three complexes deriving from Schiff base ligands with N 2O 2 environments are described. The reduction of (L)Fe IIIOFe III(L) occurs at a potential around −1 V/SCE and releases the monomeric Fe II(L) complex. A mechanism is proposed using high speed cyclic voltammetry. The reduction pattern is affected by dioxygen through the high reactivity of Fe II(L). These μ-oxo bridged Fe III dimers (L)FeOFe(L) can also be cleaved by Cl − addition and yield the monomeric Fe III(L) complexes. Finally, the FeO bond is not so strong because it cleaves either by electrochemical reduction or by chemical addition of Cl −.

High-speed cyclic voltammetry

High-speed cyclic voltammetry

Measurement of nanomolar dopamine diffusion using low-noise perfluorinated ionomer coated carbon fiber microelectrodes and high-speed cyclic voltammetry.

Several improvements in the fabrication and use of carbon fiber voltammetric microelectrodes (CFVMs) are described. These procedures did not involve oxidative treatment, but resulted in sensitivities and selectivities approaching those of treated CFVMs, without the inherent slow response times associated with the latter electrodes. To accomplish this we reduced CFVM noise by (1) improving the adhesive seal between the 8 microns o.d. carbon fiber and the glass insulation using vacuum, (2) snapping rather than cutting or beveling the fiber to be flush with the glass, and (3) using a concentrated electrolyte solution to make electrical contact with the fiber. System noise was reduced by digital smoothing and signal averaging. Selectivity of the CFVMs for dopamine over ascorbate was enhanced to better than 2000:1 by coating with Naflon, a perfluorinated cation exchange polymer, using a low (+0.5 V vs Ag/AgCl) electroplating potential. This low voltage also prevented electrode surface oxidation. To demonstrate the performance of our CFVMs, we used them in conjunction with high-speed cyclic voltammetry to accurately measure the diffusion coefficient of iontophoretically released dopamine at concentrations as low as 35 nM over distances of less than 200 microns in agarose gel.

Accommodation of rat nigrostriatal dopamine neurones to high frequency electrical stimulation of the median forebrain bundle: in vivo voltammetric data.

The frequency response of nigrostriatal neurones to electrical stimulation of the median forebrain bundle was investigated in vivo using high-speed cyclic voltammetry to measure the evoked striatal dopamine overflow. It was found that the nerves could follow 25-50 Hz stimulation for at least 10 s, whereas the neurones were unable to respond to high frequencies (100-200 Hz) for more than 1-3 s. Accommodation, due to incomplete re-equilibration of ionic fluxes between successive stimuli, provides a possible explanation for these findings.

Sub-second striatal dopamine release measured by in vivo voltammetry

High speed cyclic voltammetry was used to measure electrically stimulated striatal dopamine release in vivo with 25 mc time resolution. Dopamine release after 1 s stimulations was readily detectable and could be manipulated by drugs known to influence dopaminergic neurones. Using data-average dopamine release could be detected following stimulus trains as short as 100 ms. The use of carbon fibre microelectrodes gave a spatial resolution better than 5 μm.

The influence of stimulus parameters on the potentiation of striatal dopamine release by metoclopramide: in vivo voltammetric data.

Carbon fibre microelectrodes were implanted acutely into the striatum of chloral hydrate-anaesthetised rats to measure the dopamine released by electrical stimulation of the ipsilateral nigrostriatal pathway. High speed cyclic voltammetry was used throughout. The effects of metoclopramide and of different stimulation parameters (frequency and duration) were investigated. Using a 10 s stimulus train, it was found that frequencies less than 25 Hz evoked little measurable dopamine release. Maximum release occurred at 50-62.5 Hz. Metoclopramide (2.5-20 mg/kg i.p.) increased stimulated dopamine release in a dose-dependent fashion. The effect of metoclopramide (10 mg/kg) was investigated in detail at 25, 37.5 and 50 Hz stimulation frequency and at 2.5, 5.0 and 10.0 s after the onset of stimulation. Metoclopramide, at all stimulation frequencies, caused the largest percentage elevation of release at 2.5 s of stimulation. The results indicate that prolonged stimulation can deplete the releasable pool of dopamine and mask the effects of dopamine receptor blockade.

Measurement of stimulated dopamine release in the rat by in vivo voltammetry: The influence of stimulus duration on drug responses

High-speed cyclic voltammetry at carbon fibre microelectrodes was used to monitor stimulated striatal dopamine (DA) release in the anaesthetised rat. The effects of metoclopramide, chlorpromazine, benztropine and dexamphetamine on DA release after 1 s and 10 s stimulations were investigated. The antagonists enhanced DA release most clearly with 1 s stimuli. Benztropine had no effect on DA release with the 10 s stimulations, but elevated release after 1 s trains. Dexamphetamine reduced release with 10 s stimuli but enhanced release after 1 s trains. The results are discussed in terms of neuronal DA uptake and releasable DA pool size.

In vivo voltammetric characterization of low affinity striatal dopamine uptake: Drug inhibition profile and relation to dopaminergic innervation density

Electrical stimulation of the median forebrain bundle evoked dopamine release in the ipsilateral striatum which was monitored with high-speed cyclic voltammetry. After stimulation, the extracellular concentration of dopamine fell due to uptake in a biphasic manner, showing zero-order and first-order components. The zero-order phase corresponded to a V max of 42.8 ± 1.8nmol/min/g tissue. The uptake system could be blocked by d-amphetamine, methylphenidate and nomifensine, but not by benztropine, amfonelic acid or mazindol. The density of uptake sites showed a correlation with the density of striatal dopamine innervation.

Ascorbic acid does not modulate stimulated dopamine release: In vivo voltammetric data in the rat

Electrical stimulation of the nigrostriatal pathway released dopamine (DA) in the striatum of the anaesthetized rat. The level of DA released by 10-s stimulus trains was measured by high-speed cyclic voltammetry. Metoclopramide (10 mg/kg) increased DA release by ∼20%. Apomorphine (1.76 mg/kg) caused a ∼40% decrease in release which was blocked by metoclopramide. Ascorbate (1.76 g/kg) had no effect on stimulated DA release. Furthermore, pretreatment of rats with ascorbate trebled the striatal extracellular ascorbate level, but failed to modify the effects of metoclopramide and apomorphine on DA release. We conclude that ascorbate has no effect on the presynaptic autoreceptors that modulate striatal DA release in vivo.

A Voltammetric Investigation of AC Corrosion Phenomena at an Aluminum Electrode in Hydrochloric Acid

Abstract The electrochemical behavior of Al in HCl has been studied by cyclic voltammetry, square-wave chronoamperometry, and square-wave chronopotentiometry. High speed cyclic voltammetry was studied thoroughly, and the effects of temperature, HCl concentration, potential sweep rate, and cathodic potential limit were examined. Relevant parameters that can be determined from the cyclic voltammetric i-V curve include the breakdown and protection potentials for Al, the onset potential for hydrogen evolution, and the magnitude of the anodic and cathodic currents. The degree of passivity, which is reflected in the anodic breakdown potential and the magnitude of the anodic current, decreased with increasing solution temperature and HCl concentration, and increased with higher sweep rates. The nature of the Al passivation that occurs during the cathodic half-cycle depends on the cathodic potential limit. These processes and their relationship to the voltammetric curves are discussed in detail.

Regional differences in extracellular ascorbic acid levels in the rat brain determined by high speed cyclic voltammetry

High speed cyclic voltammetry was used in combination with pressure ejection of ascorbate oxidase for the determination of extracellular ascorbic acid within the brain of the anaesthetized rat. Large variations in absolute levels of ascorbate were found between animals although distribution patterns showed a good degree of reproducibility. Ascorbate levels in the white matter of the corpus callosum were found to be higher than in adjacent areas of grey matter (striatum and cortex).