Ferrocyanide Ions Research Articles

Coupling microcalorimeter with electrochemical instruments for thermoelectrochemical research

A measurement system that couples a commercial microcalorimeter with usual electrochemical instruments was established for electrochemical calorimetry of electrode reactions. Apparent enthalpy change of anodic oxidation of ferrocyanide ion to ferricyanide ion and apparent enthalpy change of cathodic reduction of hydrogen ion to hydrogen gas were determined with this system. The difference between the apparent enthalpy change and the value calculated with conventional thermodynamic data of aqueous ions was found to be a constant at a given temperature. This system can further be used to determine unknown standard enthalpy changes of electrode reactions.

Long-time and short-time investigation of the electrode interface through electrochemical impedance measurements. Application to adsorption of human serum albumin onto glassy carbon rotating disc electrode

Abstract Two methods were used to investigate the adsorption of a human protein onto glassy carbon under well-defined conditions, i.e. in 0.1 M phosphate buffer (pH = 7.4), at T = 25°C, in the presence of equimolar (5 × 10−4 M) ferricyanide + ferrocyanide ions as steady-state indicator, with a three-electrode potentiostatic system at a bias potential of −0.67 V (SCE), under the laminar shear flow obtained by a carbon disc electrode rotated at 700 rev min−1. The protein concentration was 1 g dm−3. With the long-time method, the behaviour of the interface in its entirely was studied through the time-evolution of the impedance diagrams over a wide frequency range (sine-wave perturbation from 40 mHz to 10 kHz). With the short-time method, the time-evolution of the double-layer capacitance was determined at only one frequency, starting from the imaginary part of the impedance, on the basis of the well-known interface equivalent circuit without diffusion. However, investigation of the whole interface shoed that diffusion was actually indicated and the double-layer capacitance exhibited a fractional power-law (constant phase element) and was therefore frequency-dependent. The contribution of the characteristic electrical parameters of the interface in the overall impedance was determined. Use of the two methods justified the choice of the frequency value in the second method and showed the necessity of performing complete investigations of the interface over a wide frequency range before any capacitance measurements.

Hemodynamic study of the anterior communicating artery.

The anterior communicating artery (ACoA) is a site of predilection for intracranial saccular aneurysms causing subarachnoid hemorrhage. ACoA aneurysms are frequently associated with an asymmetrical circle of Willis. In such cases, the ACoA is probably exposed to high hemodynamic stress caused by a considerable shunt flow across the ACoA to the distal segment of the contralateral anterior cerebral artery (ACA). In the present study, the flow pattern and flow-induced shear stress in the ACoA complex that may initiate aneurysmal lesions were studied under steady and pulsatile flow conditions. Flow visualization was studied with dye injection and birefringent flow visualization in symmetrical and asymmetrical models of various sizes of ACoA. The distribution of wall shear stress was measured using an electrochemical method based on a diffusion-controlled reaction of ferricyanide ion to ferrocyanide ion at a platinum electrode embedded in the wall of the ACoA model. With equal flow rate (Reynolds number 150 to 600), vortical flow was formed in the mouth of the ACoA, and no cross flow through the ACoA was observed. The wall shear stress on the mid-wall of the ACoA was almost zero. However, as soon as the flow rate became unequal, a cross flow through the ACoA was observed. The stagnation point also appeared at the medial junction of the ACoA and ACA. The wall shear stress increased to a very high level at the wall of the ACoA and around the stagnation point. Geometric changes from the symmetrical to the asymmetrical ACoA develop higher shear stress on the ACoA than critical values and the stagnation point at the ACoA junction. A combination of these hemodynamic factors is considered to play an important role in initiation of aneurysm.

Oxidation of Ferrous and Ferrocyanide Ions by Peroxyl Radicals

Alkylperoxyl and arylperoxyl radicals were produced by pulse radiolysis in aqueous solutions, and their reactions with ferrous and ferrocyanide ions were studied by kinetic spectrophotometry. Oxidation of Fe(CN)64- took place with rate constants that varied from <1 × 105 to 5 × 107 L mol-1 s-1, depending on the electron-withdrawing effects of the substituents on the peroxyl radical and presumably reflecting variations in reduction potential of the peroxyl radical, as expected for outer-sphere electron transfer. Oxidation of Feaq2+, on the other hand, took place by an inner-sphere mechanism controlled by the rate of dissociative interchange of the water ligand. The rate constants were nearly the same for all the peroxyl radicals examined (k = (0.5−1.1) × 106 L mol-1 s-1) and involved the formation of a transient intermediate, RO2-Fe3+, which later decomposed to yield Feaq3+. The decomposition was accelerated by H+ and by Fe2+. The proposed mechanism is a modification of a previously suggested reaction scheme.

Electrochemical Rectification at a Monolayer-Modified Electrode

An electrochemical current rectifier based on a ferrocene-monolayer-modified electrode in contact with an electrolyte solution containing sodium hexacyanoferrate(II) (sodium ferrocyanide) was constructed and evaluated. Rectification was accomplished via mediated ferrocyanide oxidation by electrogenerated ferricenium in monolayers of (10-mercapto-N-decyl)ferrocenecarboxamide with dodecanethiol and (7-mercapto-N-heptyl)ferrocenecarboxamide with nonanethiol on gold electrodes. The reverse reaction of ferricyanide reduction by immobilized ferrocene is thermodynamically disfavored, thereby providing the basis for rectification. A model proposed to describe the rectification process is reminiscent of earlier treatments of electron-transfer mediation at electrodes modified with redox polymers, with the important difference that, in the present system, long-range electron transfer across the monolayer replaces electron hopping through the polymer layer as a possible rate-limiting step. Steady-state current−voltage curves corresponding to mediated ferrocyanide oxidation were recorded and analyzed using the proposed model to give values for k0, the standard rate constant for electrochemical oxidation/reduction of immobilized ferrocene groups, and kcross, the rate constant for reaction of ferricenium ions in the monolayer with ferrocyanide ions in solution. Mean k0 values of 2700 ± 1000 s-1 for the (10-mercapto-N-decyl)ferrocenecarboxamide/dodecanethiol system and 90 000 ± 60 000 s-1 for the (7-mercapto-N-heptyl)ferrocenecarboxamide/nonanethiol system obtained by analysis of steady-state current−voltage data are to be compared with values of 1400 and 51 000 s-1 for the same systems obtained by the fast-scan cyclic voltammetry method. The kcross value of 1.1 × 108 M-1 s-1 obtained from analysis of steady-state current−voltage data for the (10-mercapto-N-decyl)ferrocenecarboxamide/dodecanethiol system is in good agreement with a value calculated using the Marcus expression with literature values for the electron self-exchange rate constants for ferrocene/ferricenium and ferrocyanide/ferricyanide, indicating that the reactivity of ferricenium ions in the monolayer is similar to that expected for ferricenium in free solution.

Ferrocyanide-Templated Resins Prepared by Surface Template Polymerization.

The ferrocyanide-templated resin was prepared by the “surface template polymerization method”, using ferrocyanide ion as a template, oleylamine as a functional surfactant monomer and divinylbenzene as a matrix-forming monomer. Decyltrimethylammonium chloride (DTAC; quarternary ammonium salt) was found to be suitable as an auxiliary surfactant, when preparing the templated resin: DTAC stabilized the emulsion and was easily removed from the resin by washing with alkaline solution after the polymerization. The templated resin adsorbed ferrocyanide ions about 2 times as much as the non-templated resin. Although the structure of the complex between ferrocyanide and amino groups on the resin surface remains for further study, we found preparation conditions of the anion-templated resin using oleylamine and DTAC.

Effects of pulsating magnetic fields on electrolytic mass transfer around cylindrical cathodes.

The influence of pulsating magnetic fields on mass transfer was studied experimentally in the electroreduction of ferrocyanide ions around an inclined cylindrical cathode under diffusion-controlled conditions. The mass transfer rate is increased by applying the pulsating magnetic field as well as the static one. The time-averaged enhancement of the mass transfer rate is dependent markedly on duty cycle (ON-time ratio), peak magnetic flux density of the applied pulsating magnetic fields in a range of 20 to 200 mHz, and slightly on its frequency. The mass transfer coefficient was correlated well by two types of non-dimensional regression equations with and without a duty-cycle factor, by using the “magneto-diffusion factor” to express the contribution of the applied magnetic flux density.

Adsorption of ferrocyanide and ferricyanide ions at the aluminum oxide‐solution interface

The adsorption of complex ions (ferrocyanide (Fe(CN)4‐ 6) and ferricyanide (Fe(CN)3‐ 6) by aluminum oxide has been investigated at three initial concentrations of complex ions with varying both concentration of background electrolyte and solution pH. In this study, the triple‐layer model has been sucessfully used to simulate ferrocyanide and ferricyanide adsorption on aluminum oxide surface. Evidence for direct coordination of complex ion to the aluminum oxide has been obtained by IR investigation. The results indicate that ferrocyanide is in association with aluminum oxide surface through the outer‐sphere complexation. The ferricyanide, at neutral and alkaline condition (pH > 5), is favor to the outer‐sphere complexation with that surface, but inner‐sphere reaction plays a major role in this interfacial interation at acidic conditions (pH < 5).

Rate constants for reactions of iodine atoms in solution

AbstractLaser flash photolysis (at 248 or 308 nm) or aryl iodides in water or water/methanol solutions produces iodine atoms and phenyl radicals. Iodine atoms react rapidly with added I− to form I2− but do not react rapidly with O2 (k ⩽ 107 L mol−1 s−1). Iodine atoms oxidize phenols to phenoxyl radicals, with rate constants that vary from 1.6 × 107 L mol−1 s−1 for phenol to about 6 × 109 L mol−1 s−1 for 4‐methoxyphenol and hydroquinone. Ascorbate and a Vitamin E analogue are also oxidized very rapidly. N‐Methylindole is oxidized by I atoms to its radical cation with a diffusion‐controlled rate constant, 1.9 × 1010 L mol−1 s−1. Iodine atoms also oxidize sulfite and ferrocyanide ions rapidly but do not add to double bonds. The phenyl radicals, produced along with the I atoms, react with O2 to give phenylperoxyl radicals, which react with phenols much more slowly than I atoms. © 1995 John Wiley &amp; Sons, Inc.

The effect of light on the thermodynamic equilibrium in the formation of the complex between viologen and the ferrocyanide ion

The formation of the complex betweenN,N′-dibutyl-4,4′-dipyridilium dibromide and potassium ferrocyanide was studied in aqueous solutions. The charge transfer band was observed and the composition of the complex between the dipyridilium dication and the ferrocyanide ion (1∶1) was established. The irradiation (λ ≤ 350 nm) of deaerated solutions in the absorption region of individual components results in a shift of the thermodynamic equilibrium towards complex formationvia the intermediate formation of an exciplex. Since the absorption maximum of the complex is located in the visible region (λ = 528 nm), its reversible formation and decomposition are accompanied by reversible coloring of the solution,i.e., the system is photochromic.

Electrochemical Behaviors of Impermeable Carbon Electrodes Using Graphite/Carbon Composite

An impermeable carbon electrode was developed as a new electrochemical detector. The electrode made of graphite/glassy carbon composite (30/70 weight ratio) was prepared by the Plastic Formed Carbon (PFC) method. The microstructure of the surface of the PFC electrode was observed by scanning electron microscopy. The impermeability and the electrochemical behavior of the electrode, in comparison with HOPG, were evaluated by cyclic voltammetry in solution of 18 M sulfuric acid. The SEM observation and the cyclic voltammetry suggest that the disk plane and the cylindrical plane of PFC electrode have similar microstructure and similar pattern of cyclic voltammograms of ferro-/ferri-cyanide ions in solution of potassium chloride to those of the edge plane and the basal plane of the HOPG, respectively. The potential window on the PFC electrode was + 1.6V to -1.3V in 1 M sulfuric acid solution (vs. SCE), and this potential range corresponds to that on a glassy carbon electrode. A peak current in a redox reaction of ferrocyanide and ferricyanide was proportional to the concentration of ferrocyanide and ferricyanide ions. No change was observed in the pattern of the cyclic voltammogram of ferro-/ferri-cyanide ion response in potassium chloride solution on the PFC electrode after 100 -day immersion of the electrode. The PFC electrode showed a stable response of the surface reaction, and the reproducibility was good. Although the anode peak, which corresponds to the formation of the first-stage graphite intercalation compound, was found in the CV curves, repeated-cycle experiment indicated that the surface of the PFC electrode was almost as impermeable as glassy carbon.

Orientational effects in the infrared spectrum of the double layer material, magnesium aluminum hydroxide ferrocyanide

The infrared spectrum of the title compound, examined in a KBr disc, contains two strong overlapping bands in the CN stretching region. In oriented samples of the same material, examined with light traveling along the c axis, the sharper of of these bands is absent. This is in accord with a model in which the octahedral ferrocyanide ions are oriented with their individual 3-fold axes parallel to the c axis. The results suggest a general method for determining the orientation of intercalated and exchanged species in layered hosts.

A symptotic analysis of canards in the EOE equations and the role of the inflection line

The Edblom–Orbán–Epstein (EOE) reaction, involving iodate, sulphite and ferrocyanide ions may have oscillations in a continuous stirred tank reactor. A simplification of a 10-variable model, including two state variables, was analysed numerically by Peng et al. ( Phil. Trans. R. Soc. Lond . A337, 275 (1991)). They found that within a very small range of the inflow concentration, the amplitude of of the oscillations varied drastically. Such behaviour is well understood in singular perturbations systems, where it is known as a canard explosion . Apparently, the EOE equations do not belong to this class. We show that the two-dimensional EOE equations can be recast as a singular perturbation problem. An asymptotic expansion of the the canard point is obtained, with very good agreement with the numerical results of Peng et al . To deal with the canard explosion in systems which are not of singular perturbation type, Peng et al . introduce a new definition of the canard point, based on change of curvature of the limit cycle. We discuss the new definition, and show that it may essentially agree with the definition based on a singular perturbation approach, but is much less fit for analytical computations. We show that the discontinuous canard transition suggested by Peng et al . violates a continuity theorem in the theory of ordinary differential equations.

137Cs sorption on granular inorganic ion-exchangers based on titanium and zirconium hydroxophosphates

We have studied the sorption properties of some granular inorganic ion-exchangers synthesized by gel technology, such as titanium and zirconium hydroxophosphates (THP, ZHP), titanium and zirconium molybdophosphates and titanium and zirconium phosphate-ferrocyanides. A high selectivity of THP and ZHP modified with ferrocyanide and molybdate ions to137Cs has been found. The possibility of applying inorganic sorbents for the purification of cesium-137 contaminated foodstuff is illustrated on the examples of fish treatment.

Fourier transform SERS studies of the chemisorption of ferricyanide on gold electrode surfaces

Surface enhanced Raman spectroscopy (SERS) studies of ferricyanide and ferrocyanide ions at gold electrodes show that in solutions containing 0.1 M Cs +, ferricyanide ions are adsorbed, but not ferrocyanide. The strength of the interaction with the surface is such that the electrode can be removed from the solution without loss of the SERS signal. This chemisorbed layer is also observed from solutions containing Li + ions. The implications for the mechanism of the heterogeneous electron transfer reaction are discussed.

Sodium nitroprusside blocks NMDA receptors via formation of ferrocyanide ions.

The effects of a nitric oxide (NO) donor, sodium nitroprusside (SNP), on N-methyl-D-aspartate (NMDA) receptors were assessed by optical measurements of intracellular calcium concentration ([Ca2+]i) and patch-clamp techniques in cultured central neurons. SNP selectively blocked NMDA-mediated currents and increases in [Ca2+]i. SNP inhibited the binding of [3H]-CGS 19755. The blockade of NMDA responses by SNP was prevented by CPP or APV which are selective competitive NMDA receptor antagonists. These effects were not necessarily mediated by NO, since they were mimicked by ferrocyanide ions, the NO companion photolysis product of SNP.

Measurement of Peroxide Value in Edible Oils and Fats, and in Foods by Rapid Coulometry

Rapid coulometry was developed for the rapid and sensitive measurement of peroxide value (POV) of edible oils and fats, and foods by using a carbon felt electrode with ferrocyanide ion as a mediator. The reaction mechanism is as follows: 1) iodine is formed by the reaction of iodide ion and peroxide in the sample, 2) the reaction of iodine and ferrocyanide ion produces ferricyanide ion, and 3) ferricyanide ion is electrochemically reduced within 25 sec at the working electrode, which is maintained at -0.4V vs. the counter electrode.It was possible to conduct 25 repeated injections of 5μl of sample solution. A linear relationship between charge and concentration of iodine was observed over the range of 5×10-5×10-2M which corresponded to a POV range of 1.3-446. The analytical results obtained by rapid coulometry were in good agreement with those by iodometry.

PH Oscillation in the closed system of H2O2–Fe(CN)64––acetonitrile–water

Regular pH oscillations with small amplitude are observed during the decomposition of hydrogen peroxide in the presence of ferrocyanide ions in an unbuffered mixture of water–acetonitrile under closed conditions in the dark.

Redox electrode for monitoring oxidase-catalyzed reactions

A new approach to the measurement of hydrogen peroxide is described in this report. Redox potentiomet~c electrodes have been used to monitor dehydrogenasecatalyzed reactions [1,2]. By including diaphorase and a redox couple (ferricyanide and ferrocyanide ions) in the reaction medium, the production of NADH becomes detectable with a redox electrode [l]. In the presence of diaphorase NADH reduces ferricyanide ion to ferrocyanide ion. The change in the ferroand ferricyanide concentration ratio alters the redox potential. A similar approach can be adapted for the measurement of hydrogen peroxide in the oxidase-catalyzed reactions. Hydrogen peroxide oxidizes ferrocyanide ion to ferricyanide ion with peroxidase as a catalyst.

A luminescence quenching study on the localization problem of tris(2,2'-bipyridyl)ruthenium(2+) in micelles and hemimicelles

Quenching studies on the luminescence emission of Ru(bpy){sub 3}{sup 2+} with ferrocyanide ion, 9-methylanthracene, and doxylstearic acids have been carried out in hemimicellar and micellar aggregates to gain insight into the location of this Raman and luminescence probe. Ru(bpy){sub 3}{sup 2+} is bound to a more nonpolar hemimicellar hydrophobic region as evidenced from the observed larger Stokes shift in this case than in the case of a micellar environment. Stern-Volmer constants for the doxylstearic acid quenching of Ru(bpy){sub 3}{sup 2+} luminescence in micelles indicated that the optical electron in the MLCT state of the probe molecule resides in a bipyridyl ring which appears to be close to position 7 of the stearic acid chain.