Oxidation Of Ferrocyanide Research Articles

Influence of a soil enzyme on iron-cyanide complex speciation and mineral adsorption

Cyanide is commonly found as ferrocyanide [Fe II(CN) 6] −4 and in the more mobile form, ferricyanide [Fe III(CN) 6] −3 in contaminated soils and sediments. Although soil minerals may influence ferrocyanide speciation, and thus mobility, the possible influence of soil enzymes has not been examined. In a series of experiments conducted under a range of soil-like conditions, laccase, a phenoloxidase enzyme derived from the fungi Trametes versicolor, was found to exert a large influence on iron-cyanide speciation and mobility. In the presence of laccase, up to 93% of ferrocyanide (36–362 ppm) was oxidized to ferricyanide within 4 h. No significant effect of pH (3.6 and 6.2) or initial ferrocyanide concentration on the extent or rate of oxidation was found and ferrocyanide oxidation did not occur in the absence of laccase. Relative to iron-cyanide–mineral systems without laccase, ferrocyanide adsorption to aluminum hydroxide and montmorillonite decreased in the presence of laccase and was similar to or somewhat greater than that of ferricyanide without laccase. Laccase-catalyzed conversion of ferrocyanide to ferricyanide was extensive though up to 33% of the enzyme was mineral-bound. These results demonstrate that soil enzymes can play a major role in ferrocyanide speciation and mobility. Biotic soil components must be considered as highly effective oxidation catalysts that may alter the mobility of metals and metal complexes in soil. Immobilized enzymes should also be considered for use in soil metal remediation efforts.

Liquid-wall mass transfer in three phase fluidized beds with cross-flow of electrolyte

Liquid-wall mass transfer coefficients were computed in a gas–liquid fluidized bed from the limiting current data obtained at the outer surface of different cross electrodes for both the cases of oxidation of ferrocyanide and reduction of ferricyanide ion. Particles of different sizes and densities were used as bed material and electrodes of five different diameters of length 44.5 mm were used. The fluid electrolyte velocities were varied from minimum fluidization velocities to well below the terminal velocities of the particles before the gas phase enters the test section. The liquid-wall mass transfer coefficient increased with increasing superficial gas velocity at a constant superficial liquid velocity upto a certain extent and reached a plateau. At constant superficial gas velocity, k L increased with increasing superficial liquid velocity. k L decreased with increase in electrode diameter. The effect of particle size on k L was found to segregate into two regions, one for d p > 4 mm and the other for d p < 4 mm. k L increased with increase in ɛ , reached a maximum and beyond an ɛ value of 0.85 showed a declining trend. The liquid-wall mass transfer coefficient data for both oxidation and reduction were correlated in terms of Coulburn factor j D , void fraction ɛ , Reynolds number based on electrode diameter Re , Froude number based on gas velocity Fr g and gas to liquid mass velocity ratio G mr .

Evanescent Wave Cavity Ring-Down Spectroscopy in a Thin-Layer Electrochemical Cell

The application of evanescent wave cavity ring-down spectroscopy (EW-CRDS) in monitoring electrogenerated species within a thin-layer electrochemical cell is demonstrated. In the proof-of-concept experiments described, ferricyanide, Fe(CN)6(3-), was produced by the transport-limited oxidation of ferrocyanide, Fe(CN)6(4-), in a thin-layer solution cell (25-250 microm) formed between an electrode and the hypotenuse of a fused-silica prism. The prism constituted one element of a high-finesse optical cavity arranged in a triangular ring geometry with light being totally internally reflected at the silica/solution interface. The cavity was pumped with the output (approximately 417 nm) of a single-mode external cavity diode laser, which was continuously scanned across the cavity modes. The presence of electrogenerated ferricyanide within the resulting evanescent field, beyond the optical interface, was detected by the enhanced loss of light trapped within the cavity, as measured by the characteristic cavity ring down. In this way, the EW-CRDS technique is sensitive to absorption in only the first few hundred nanometers of solution above the silica surface. The cavity ring-down response accompanying both cyclic voltammetric and step potential chronoamperometry experiments at a variety of electrode-surface distances is presented, and the results are shown to be well reproduced in modeling by finite element methods. The studies herein thus provide a foundation for further applications of EW-CRDS combined with electrochemistry.

Photoelectroactivity of a Hybrid System Constructed by Immobilization of Avidin onto Biotinylated TiO2 Electrodes

Immobilization of avidin onto thin film nanocrystalline TiO2 on ITO was obtained through avidin−biotin binding. In the construction of hybrid systems, dopamine was used as the TiO2 surface-active ligand, providing a conductive lead to covalently linked biotin. The assembled hybrids were characterized using electrochemical techniques of chronopotentiometry, cyclic voltammetry, and photocurrent action spectroscopy. With each layer of a biomolecule (dopamine, biotin, and avidin) attached onto the TiO2 film, an increase in overpotential (η) for the oxidation of ferrocyanide was detected by chronopotentiometric measurements. An increase in overpotential of Δη ∼ 400 mV was measured for the monolayer of avidin bonded to biotinylated electrodes. The absorption of light by semiconductor nanocrystallites results in charge separation, holes being localized on avidin. The photoinduced charge separation and oxidation of avidin yields to the dissociation of the avidin−biotin complex, promoting changes in the photoelect...

Sorption of iron‐cyanide complexes on goethite investigated in long‐term experiments

AbstractThe iron‐cyanide complexes ferrocyanide, [FeII(CN)6]4–, and ferricyanide, [FeIII(CN)6]3–, are anthropogenic contaminants in soil. We investigated their sorption on goethite, α‐FeOOH, in batch experiments in a time range from 1 d to 1 yr, their desorption by phosphate and chloride as well as their surface complexes on goethite by Fourier‐transform infrared spectroscopy (FTIR). The sorption of both complexes continued over the whole time range. Percent desorption of ferricyanide by phosphate decreased, whereas that of ferrocyanide increased until it amounted to approximately 87% for both complexes. By FTIR spectroscopy inner‐sphere complexation of both complexes on the goethite surface was indicated. With both complexes, a Berlin‐Blue‐like layer (Fe4[Fe(CN)6]3) was formed initially on the goethite surface which disappeared with increasing reaction time. After at least 30 d reaction time, ferricyanide was the only sorbed iron‐cyanide complex detected even when ferrocyanide was initially added. This resulted from slow oxidation of ferrocyanide, most probably by dissolved oxygen. Based on all results, we propose that ferricyanide forms monodentate inner‐sphere complexes on the goethite surface.

Oxidation of Ferrocyanide by Birnessite

The Fe-CN complexes ferrocyanide, [FeII(CN)6]4-, and ferricyanide, [FeIII(CN)6]3-, which are contaminants in soil and groundwater, form a redox couple, [FeII(CN)6]4- <==> [FeIII(CN)6]3- + e-, E(H) = 356 mV. We studied the oxidation of [FeII(CN)6]4- by birnessite, delta-MnIVO2, in batch experiments as influenced by [FeII(CN)6]4- concentration, pH, and reaction time. Additionally, stopped-flow experiments were carried out at five temperatures (10-30 degrees C) and four pH values (pH 4.1-5.3). In the batch experiments, [FeII(CN)6]4- was completely oxidized to [FeIII(CN)6]3-, and oxidation did neither depend on time for t > 2 min, nor on concentration (0.12-0.47 mM), nor on pH (pH 3.3-9.9). Lasting adsorption of Fe-CN complexes on the birnessite surface or precipitation of manganese ferricyanide were not detected. Manganous ions resulting from the reductive dissolution of birnessite did not precipitate as manganese oxide because an identical decrease of Mn solution concentrations was observed under air and under a N2 atmosphere. Two processes were detected by the stopped-flow experiments. The first rapid one with an activation energy of approximately 60 kJ mol(-1) was attributed to short-term adsorption and simultaneous oxidation of [FeII(CN)6]4- on the birnessite surface. The second slower process with an activation energy of approximately 20 kJ mol(-1) was attributed most probably to diffusion of the reaction product Mn2+ into the interior of the birnessite, which creates fresh reaction sites at the outer surface.

A novel dual-impedance-analysis EQCM system—investigation of bovine serum albumin adsorption on gold and platinum electrode surfaces

Both quartz crystal microbalance (QCM) impedance and electrochemical impedance spectroscopy (EIS) methods are widely used in interface studies. This paper presents details about a new strategy for simultaneous, mutual-interference-free and accurate measurements of QCM impedance and EI, through connecting a suitable capacitance in series with the piezoelectric quartz crystal (PQC) between QCM impedance and EIS measurement instruments. Combined and individual measurements of QCM impedance and EIS during silver deposition gave results comparable with each other, demonstrating the reliability of the proposed method. Bovine serum albumin (BSA) adsorption on gold and platinum electrodes in Britton–Robinson (B–R) buffers was investigated, and the Fe(CN) 6 3−/Fe(CN) 6 4− couple was used as an electrochemical probe to characterize BSA adsorption. While the reversibility of Fe(CN) 6 3−/Fe(CN) 6 4− couple on bare Au and Pt electrodes changed very slightly with decreasing solution pH from pH∼7 to pH∼2, the standard rate constant ( k s ) of this couple increased abruptly with solution pH below pH∼4.5 at a BSA-modified Au electrode, but decreased with solution pH at a BSA-modified Pt electrode. By analyzing the QCM impedance data with a modified BVD equivalent circuit and the EI data with a modified Randle's equivalent circuit, inflexion changes at pH∼4.5 were all found at pH-dependent responses of the resonant frequency, the double-layer capacitance, the capacitance of the adsorbed BSA layer, the peak-absorbance values of BSA solutions at 277.5 and 224.5 nm, and so on. It was also found that a BSA adsorption layer can effectively inhibit gold corrosion during ferrocyanide oxidation in a ferrocyanide-containing BR solution. Some preliminary explanations of these findings have been given. The proposed method is highly recommended for wider applications in surface science.

Rapid identification of viable Escherichia coli subspecies with an electrochemical screen-printed biosensor array

Rapid identification of Escherichia coli strains is an important diagnostic goal in applied medicine as well as the environmental and food sciences. This paper reports an electrochemical, screen-printed biosensor array, where selective recognition is accomplished using lectins that recognize and bind to cell-surface lipopolysaccharides and coulometric transduction exploits non-native external oxidants to monitor respiratory cycle activity in lectin-bound cells. Ten different lectins were separately immobilized onto porous membranes that feature activated surfaces (ImmunodyneABC®). Modified membranes were exposed to untreated E. coli cultures for 30 min, rinsed, and layered over the individual screen-printed carbon electrodes of the sensor array. The membranes were were incubated 5 min in a reagent solution that contained the oxidants menadione and ferricyanide as well as the respiratory substrates succinate and formate. Electrochemical oxidation of ferrocyanide for 2 min provided chronocoulometric data related to the quantities of bound cells. These screen-printed sensor arrays were used in conjunction with factor analysis for the rapid identification of four E. coli subspecies ( E. coli B, E. coli Neotype, E. coli JM105 and E. coli HB101). Systematic examination of lectin-binding patterns showed that these four E. coli subspecies are readily distinguished using only five essential lectins.

Extracellular Laccases from Cerrena unicolor 059, Cerrena unicolor 0784, and Pleurotus oastreatus 0432: A Comparative Assay

Laccases of the basidiomycetes Cerrena unicolor 059, C. unicolor 0784, and Pleurotus oastreatus 0432 were subjected to a comparative study. The enzymes were isolated as homogeneous preparations with molecular weights of 55, 56, and 57 kD, respectively. The three enzymes were found to be glycoproteins. The carbohydrate moiety of the glycoproteins included mannose, galactose, and N-acetylglucosamine. The carbohydrate moieties of the laccases from C. unicolor 059, C. unicolor 0784, and P. oastreatus 0432 accounted for 17, 23, and 24%, respectively. The pH optima of the enzymes corresponded to 4.0, 3.75, and 5.6, respectively. Thermal stability tests (carried out at 40°C) demonstrated that the laccase of C. unicolor 0784 was characterized by the highest temperature resistance (the enzyme retained 25% activity after 172 h of incubation). The values of the Michaelis constant (KM) were determined for the reactions of oxidation of pyrocatechol, hydroquinone, and potassium ferrocyanide catalyzed by the laccases of the basidiomycetes.

Oxidative Sorption Treatment To Remove Radionuclides from the Bottoms of the Leningrad Nuclear Power Plant

Treatment of the bottoms of the Leningrad Nuclear Power Plant to remove radionuclide using ferrocyanide sorbent was studied. To improve the efficiency of radionuclide sorption on the sorbent, the bottoms were subjected to a preliminary treatment involving oxidation of organic compounds and ferrocyanide precipitation. The oxidation was performed using hydrogen peroxide and potassium permanganate instead of expensive ozone. The conditions of ferrocyanide precipitation from the preliminarily oxidized bottoms and of further separation of the resulting precipitate were determined. It was found that ferrocyanide oxidation decreases the activity of the bottoms by more than two orders of magnitude.

Pyrrolidine dithiocarbamate is a potent antioxidant against hypochlorous acid-induced protein damage

The antioxidant potential of the dithiol compound pyrrolidine dithiocarbamate (PDTC) against protein damage induced by hypochlorous acid (HOCl) was investigated. The effects of PDTC were compared to those of reduced glutathione (GSH) and N-acetylcysteine (NAC). PDTC markedly and in a concentration-dependent manner inhibited HOCl-induced inactivation of α 1-antiproteinase, protein carbonyl formation on serum albumin and oxidation of human low-density lipoprotein. The direct scavenging of HOCl by PDTC was demonstrated by two quantitative methods, oxidation of ferrocyanide and chlorination of monochlorodimedon. In all assay systems, PDTC was two to three times more potent than GSH and NAC, while diethyldithiocarbamate was about as effective as PDTC. These data demonstrate that PDTC is a potent antioxidant against HOCl-induced protein oxidative damage, suggesting that PDTC might be useful in the prevention and treatment of inflammatory conditions.

Amperometric Detection of Sulfide at a Boron Doped Diamond Electrode: The Electrocatalytic Reaction of Sulfide with Ferricyanide in Aqueous Solution.

The oxidation of sulfide at a boron doped diamond (BDD) electrode has been examined and its analytical utility appraised and compared with other common electrode substrates (Pt, Au, glassy carbon). The suitability of using BDD as a sulfide sensing substrate has been assessed through examining the electrocatalytic oxidation of ferrocyanide to ferricyanide in the presence of sulfide using both cyclic voltammetry and chronoamperometry. The high oxidation potential for the direct oxidation of sulfide at a BDD electrode allows clear resolution of both the ferrocyanide wave and sulfide oxidation wave producing a distinct analytical signal at the oxidation peak potential of ferrocyanide. The procedure was applied to the recovery of a sulfide spike in sewage effluents with a recovery of 102±4.5%.

Investigation of the model compounds at 4-aminobenzoic acid modified glassy carbon electrode by scanning electrochemical microscopy

In this paper, we studied the reactions of both potassium ferricyanide and hexaammineruthenium(III) chloride at a 4-aminobenzoic acid (4-ABA) modified glassy carbon electrode (GCE) by scanning electrochemical microscopy (SECM) in different pH solutions. The surface of the modified electrode has carboxyl groups, the dissociation of which are strongly dependent upon the solution pH values. The rate constant k b of the oxidation of ferrocyanide on the modified electrode can be obtained by fitting the experimental tip current–distance ( I T– d) curves with the theoretical values. The surface p K a of the 4-ABA modified GCE was estimated from the plot of standard rate constant k ° versus the solution pH and is equal to 3.2, which is in good agreement with the reported result. The SECM approach curves for Ru(NH 3) 6 3+ both on the bare and the modified electrodes show similar diffusion control processes. These results can be explained by the electrostatic interactions between the modified electrode surface and the model compounds with different charges.

Ionic mass transfer in presence of turbulence promoters in a circular conduit

Ionic mass transfer in a circular conduit in the presence of ring promoter assembly is measured by limiting current technique using diffusion controlled electrochemical reactions (reduction of ferricyanide and oxidation of ferrocyanide). A supporting rod on which rings are mounted at equidistance is concentrically fixed in the conduit of 0.05 m I.D. to augment the mass transfer rates. Cross-sectional diameter of the ring is changed from 0.0065 m to 0.0125 m and the spacing in between the rings is varied from0.03 m and 0.15 m respectively. The improvement in mass transfer coefficients is up to 6.5. The data are correlated by the following dimensionless equation. ▪

Failure of Exogenous NADH and Cytochrome c to Support Energy-Dependent Swelling of Mitochondria

The possibility of direct oxidation of external NADH in rat liver mitochondria and of the inner membrane potential generation in this process is still not clear. In the present work, the energy-dependent swelling of mitochondria in the medium containing valinomycin and potassium acetate was measured as one of the main criteria of the proton-motive force generation by complex III, complex IV, and both complexes III and IV of the respiratory chain. Mitochondria swelling induced by external NADH oxidation was compared with that induced by succinate or ferrocyanide oxidation, or by electron transport from succinate to ferricyanide. Mitochondria swelling, nearly equal to that promoted by ferrocyanide oxidation, was observed under external NADH oxidation, but only after the outer mitochondrial membrane was ruptured as a result of the swelling-contraction cycle, caused by succinate oxidation and its subsequent inhibition. In this case, significantly accelerated intermembrane electron transport and well-detected inner membrane potential generation, in addition to mitochondria swelling, were also observed. Presented results suggest that exogenous NADH and cytochrome c do not support the inner membrane potential generation in intact rat liver mitochondria, because the external NADH–cytochrome c reductase system, oriented in the outer mitochondrial membrane toward the cytoplasm, is inaccessible for endogenous cytochrome c reduction; as well, the inner membrane cytochrome c oxidase is inaccessible for exogenous cytochrome c oxidation.

Copper- and Zinc-containing Superoxide Dismutase Can Act as a Superoxide Reductase and a Superoxide Oxidase

The copper- and zinc-containing superoxide dismutase can catalyze the oxidation of ferrocyanide by O(2) as well as the reduction of ferricyanide by O(2). Thus, it can act as a superoxide dismutase (SOD), a superoxide reductase (SOR), and a superoxide oxidase (SOO). The human manganese-containing SOD does not exert SOR or SOO activities with ferrocyanide or ferricyanide as the redox partners. It is possible that some biological reductants can take the place of ferrocyanide and can also interact with human manganese-containing superoxide dismutase, thus making the SOR activity a reality for both SODs. The consequences of this possibility vis à vis H(2)O(2) production, the overproduction of SODs, and the role of copper- and zinc-containing superoxide dismutase mutations in causing familial amyotrophic lateral sclerosis are discussed, as well as the likelihood that the biologically effective SOD mimics, as described to date, actually function as SORs.

The pro-oxidative activity of SOD and nitroxide SOD mimics.

Native Cu,Zn-SOD and synthetic SOD mimics sometimes demonstrate an apparently anomalous bell-shaped dose-response relationship when protecting various biological systems from oxidative stress. Several mechanisms have been proposed to account for such an effect, including: overproduction of H(2)O(2), peroxidative activity of SOD, and opposing roles played by O(2)(*-) in both initiation and termination of radical chain reactions. In the present study, ferrocyanide and thiols, which are susceptible to one-electron and two-electron oxidation, respectively, were subjected to a flux of superoxide in the presence and absence of SOD or SOD mimics. The results show that 1) either O(2)(*-)/HO(2)(*) or H(2)O(2) alone partially inactivates papain, whereas when combined they act synergistically; 2) nitroxide SOD mimics, but not SOD, exhibit a bell-shaped dose-response relationship in protecting papain from inactivation; 3) SOD, which at low dose inhibits superoxide-induced oxidation of ferrocyanide, loses its antioxidative effect as its concentration increases. These findings offer an additional explanation for the pro-oxidative activity of SOD and SOD mimics without invoking any dual activity of O(2)(*-) or a combined effect of SOD and H(2)O(2). The most significant outcome of an increase in SOD level is a decrease of [O(2)(*-)](steady state), rather than any notable elevation of [H(2)O(2)](steady state). As a result, the reaction kinetics of the high oxidation state of each catalyst is altered. In the presence of ultra-low [O(2)(*-)](steady state), the oxidized form of SOD [Cu(II),Zn-SOD] or SOD mimic (oxo-ammonium cation) does not react with O(2)(*-) but rather oxidizes the target molecule that it was supposed to have protected. Consequently, these catalysts exert an anti- or pro-oxidative effect depending on their concentration.

Limiting current in a redox system on a vertical electrode under conditions of natural convection

The problem of calculating the limiting current in a redox system on a vertical plane electrode under the natural convection conditions is solved. By way of example, the reaction of ferrocyanide oxidation on platinum in a solution containing a mixture of potassium ferrocyanide and ferricyanide (in excess). An equation for the effective Rayleigh number determining the limiting current is derived by Karman’s method with allowance made for the migration current of an indifferent electrolyte. Limiting currents in the electrochemical system under study are determined experimentally. The calculated and measured limiting currents are compared.

Laser Activated Voltammetry: Mass Transport, Surface Effects and Analytical Applications

The voltammetry of various well-characterized aqueous and nonaqueous electrochemical systems has been studied at platinum and gold disk electrodes under illumination from a 10 Hz pulsed Nd:YAG laser frequency doubled to operate at 532 nm. A simple Nernst diffusion layer model is established to quantify the slight enhancement in mass transport observed as a function of laser intensity in the thermoelastic region where light energy absorbed by the metal is insufficient to cause localized melting or vaporization but does lead to a partial thinning of the diffusion layer thickness through surface heating/vibration. This leads to sigmoidal shaped voltammograms whilst maintaining a clean, reproducible electrode surface. Above the ablation threshold, the minimum laser intensity required to cause electrode damage, atomic force microscopy (AFM) is used to probe the nature of the surface damage and its relationship to the laser intensity. The Nernst-diffusion model is verified by means of potential step chronoamperometric measurements in water and acetonitrile where good agreement with theory is seen for transport across a diffusion layer of a thickness corresponding to that inferred from steady-state voltammetry. Applications of the laser activation technique are illustrated by three systems found to be passivating in aqueous media; the two electron reduction of toluidine blue dye, iodide oxidation and the oxidation of ferrocyanide in the presence of the blood protein, fibrinogen. In all cases clean, reproducible and quantitative voltammetry is seen in contrast to that observed in the absence of laser activation, demonstrating the excellent surface-cleaning effects of LAV.

Arginine 177 is involved in Mn(II) binding by manganese peroxidase.

Site-directed mutations R177A and R177K in the gene encoding manganese peroxidase isozyme 1 (mnp1) from Phanerochaete chrysosporium were generated. The mutant enzymes were expressed in P. chrysosporium during primary metabolic growth under the control of the glyceraldehyde-3-phosphate dehydrogenase gene promoter, purified to homogeneity, and characterized by spectroscopic and kinetic methods. The UV-vis spectra of the ferric and oxidized states and resonance Raman spectra of the ferric state were similar to those of the wild-type enzyme, indicating that the heme environment was not significantly affected by the mutations at Arg177. Apparent K(m) values for Mn(II) were approximately 20-fold greater for the R177A and R177K MnPs than for wild-type MnP. However, the apparent K(m) values for the substrates, H(2)O(2) and ferrocyanide, and the k(cat) values for Mn(II) and ferrocyanide oxidation were similar to those of the wild-type enzyme. The second-order rate constants for compound I (MnPI) reduction of the mutant MnPs by Mn(II) were approximately 10-fold lower than for wild-type MnP. In addition, the K(D) values calculated from the first-order plots of MnP compound II (MnPII) reduction by Mn(II) for the mutant enzymes were approximately 22-fold greater than for wild-type MnP. In contrast, the first-order rate constants for MnPII reduction by Mn(II) were similar for the mutant and wild-type MnPs. Furthermore, second-order rate constants for the wild-type and mutant enzymes for MnPI formation, for MnPI reduction by bromide, and for MnPI and MnPII reduction by ferrocyanide were not significantly changed. These results indicate that both the R177A and R177K mutations specifically affect the binding of Mn, whereas the rate of electron transfer from Mn(II) to the oxidized heme apparently is not affected.