Microgravimetric monitoring of transport of cations during redox reactions of indium(III) hexacyanoferrate(III,II): Radiotracer evidence for the flux of anions in the film

We demonstrate here that, primarily, electrolyte cations but also, to some extent, anions are capable of penetrating indium hexacyanoferrate films during redox reactions. We find from electrochemical quartz crystal microbalance measurements that the electrolyte cation (K⁺) undergoes sorption and desorption during the system's reduction and oxidation, respectively. The formal potential, which has been determined from the system's well-defined voltammetric peaks recorded with the use of an ultramicroelectrode, decreases ～40 mV per decade of decreasing K⁺ concentration. The latter value is lower than the 60 mV change expected for the involvement of a cation in the reaction mechanism according to the ideal Nernstian dependence. We also demonstrate, using 35-S labelled sulfate, that anion penetrates the reduced film and its concentration markedly increases during oxidation. Careful examination of cyclic voltammetric responses of the system shows that, in addition to the well-defined peaks, capacitance-like currents appear during oxidation. During reduction anion is largely expelled from the film. This complex ionic penetration and transport in indium hexacynoferrate may be explained in terms of formation of two forms: ‘soluble’, KIn^III[Fe^II(CN)₆], and ‘insoluble’ (‘normal’), In^III₄[Fe^II(CN)₆]₃, during the electrochemical growth or potential cycling of the films. These forms would require cations and anions, respectively, to provide charge balance during reactions. Regardless of the actual mechanism, penetration of anions cannot be neglected completely in the discussion of charging of indium hexacyanoferrate.     

The complex formation of ions with a phospholipid monolayer adsorbed at an aqueous|1,2-dichloroethane interface

The complex formation of phosphatidylcholine adsorbed at a water|1,2-dichloroethane, W|DCE, interface with ions was evaluated based on the desorption behavior of lipids at the interface accompanied by an ion transfer and was confirmed by measuring voltammograms for the ion transfer facilitated by the complex formation with lipids. The desorption behavior of lipids was measured according to the Wilhelmy vertical plate method, the cell of which was improved to achieve polarization of the W|DCE interface. Voltammograms for the ion transfer at the W|DCE interface facilitated by the complex formation with lipids were recorded at a micro W|DCE interface in order to avoid the influence of convection caused by the desorption of lipids at the interface. Lipids adsorbed at the W|DCE interface showed complex formation with alkali metal ions, ${\mathrm{NH}}_4^{+}\text{,}({\mathrm{CH}}_3){\mathrm{NH}}_3^{+}\text{,}({\mathrm{CH}}_3{)}_2{\mathrm{NH}}_2^{+}\mathrm{or}({\mathrm{CH}}_3{)}_3{\mathrm{NH}}^{+}$, but not with $({\mathrm{CH}}_3{)}_4{\mathrm{N}}^{+}$ or anions such as ${\mathrm{SO}}_4^{2-}$, CH₃COO^?, Cl^?, Br^?, ${\mathrm{NO}}_3^{-}$, I^? or ${\mathrm{ClO}}_4^{-}$. Lipids also showed strong complex formation with a basic amino acid such as an arginine cation, which has two amino groups in the molecule. The strength of the complex formation with lipids was ${\mathrm{Arg}}^{+}>{\mathrm{Li}}^{+}\text{,}{\mathrm{Na}}^{+}>{\mathrm{K}}^{+}>{\mathrm{NH}}_4^{+}>{\mathrm{CH}}_3{\mathrm{NH}}_3^{+}>({\mathrm{CH}}_3{)}_2{\mathrm{NH}}_2^{+}>{\mathrm{Cs}}^{+}>({\mathrm{CH}}_3{)}_3{\mathrm{NH}}^{+}$.     

Study of antioxidant properties by voltammetry

A highly attractive, convenient and especially sensitive voltammetric approach for the study of antioxidant properties and determination of their activity is suggested in this work, where antioxidants are substances, which interrupt radical-chain oxidation processes in organic and inorganic molecules. The comparative analysis of the activity of well-known antioxidants such as ascorbic and citric acids, glucose, their compound solutions, some food products (green tea extract, apple vinegar) and pharmaceuticals (haemodesum, polyglucinum, Ringer solution) has been carried out. The character of the antioxidant influence on the oxygen electrochemical reduction has been investigated. Finally the use of these substances for prophylactic purposes has been recommended.     

Differential effects of amphetamine isomers on dopamine release in the rat striatum and nucleus accumbens core

Rationale Current medications for attention-deficit/hyperactivity disorder (ADHD) include some single isomer compounds [dextroamphetamine (d-amphetamine, dexedrine) and dexmethylphenidate (Focalin)] and some racemic compounds [methylphenidate and mixed-salts amphetamine (Adderall)]. Adderall, which contains approximately 25% l-amphetamine, has been successfully marketed as a first-line medication for ADHD. Although different clinical effects have been observed for d-amphetamine, Adderall, and benzedrine; potential psychopharmacological differences on the level of neurotransmission between d-amphetamine and l-amphetamine have not been well characterized.Objectives To evaluate potential differences in the isomers, we used the technique of high-speed chronoamperometry with Nafion-coated single carbon-fiber microelectrodes to measure amphetamine-induced release of dopamine (DA) in the striatum and nucleus accumbens core of anesthetized male Fischer 344 rats. Amphetamine solutions were locally applied by pressure ejection using micropipettes.Results The presence of l-amphetamine in the d,l-amphetamine solutions did not cause increased release of DA but did change DA release kinetics. The d,l-amphetamine-evoked signals exhibited significantly faster rise times and shorter signal decay times. This difference was also observed in the nucleus accumbens core. When l-amphetamine was locally applied, DA release was not significantly different in amplitude, and it exhibited the same rapid kinetics of d,l-amphetamine.Conclusions These data support the hypothesis that amphetamine isomers have different effects on release of DA from nerve endings. It is possible that l-amphetamine may have unique actions on the DA transporter, which is required for the effects of amphetamine on DA release from nerve terminals.     

Electron transfer between a lutetium bisphthalocyanine and Fe across liquid|liquid interfaces between water and dichlorohexane or nitrobenzene; influence of coupling with ion transfer

The electron transfer across the liquid|liquid interface between aqueous solutions (W) of Fe^III/II compounds (hexacyanoferrates, chlorides) and a (t-butyl) substituted Lu^IIIbisphthalocyanine in dichlorohexane (DCH) or nitrobenzene (NB), has been studied by voltammetry at a microinterface and by spectrophotometry. The electron transfer wave has been observed only at the W|DCH. Coupling with an ion transfer facilitates this electron transfer: the Lu^IIIbisphthalocyanine has been oxidized or reduced across the W|NB interface, depending on the ion establishing the interfacial potential.     

Electrocatalytic reduction of uranium by bacterial cytochromes: biochemical and chemical factors influencing the catalytic process

Cyclic voltammetry was used to investigate the kinetics of the electron transfer between uranium(VI) and polyheme c-type cytochromes of bacterial origin. Reduced cytochromes were oxidized by U(VI), either in homogeneous solution, or when cytochromes were entrapped by a dialysis membrane or immobilized within an ion-exchanger film. By using membrane electrode technology, several factors such as uranium complexation, pH, origin of the cytochrome and medium were examined. Results suggest that uranium(VI) reductase activity is strongly dependent upon experimental conditions. In particular, a narrow pH window and well-controlled complexation conditions are necessary to observe high electrocatalytic reduction of uranium(VI) by c-type cytochromes. It has been demonstrated that U(VI) electroreduction originates in the presence of hemin-containing groups in the partner species.     

Electrochemical determination of naltrexone on the surface of glassy carbon electrode modified with Nafion-doped carbon nanoparticles: Application to determinations in pharmaceutical and clinical preparations

A new sensitive and selective electrochemical sensor was developed for determination of naltrexone (NAL) in pharmaceutical dosage form and human plasma. Naltrexone is an opioid antagonist which is commonly used for the treatment of narcotic addiction and alcohol dependence. A voltammetric study of naltrexone has been carried out at the surface of glassy carbon electrode (GCE) modified with Nafion-doped carbon nanoparticles (CNPs). The electrochemical oxidation of naltrexone was investigated by cyclic and differential pulse voltammetric techniques. The dependence of peak currents and potentials on pH, concentration and the potential scan rate was investigated. The electrode characterization by electrochemical methods and atomic force microscopy (AFM) showed that CNPs enhanced the electroactive surface area and accelerated the rate of electron transfer. Application of the modified electrode resulted in a sensitivity enhancement of more than 20 times, relative to the bare GCE, in detection of NAL and a considerable negative shift in peak potential was achieved. Two linear dynamic ranges of 1–10 μM and 10–100 μM with a detection limit of 0.1 μM was obtained in phosphate buffer of pH = 3. Differential pulse voltammetry as a simple, rapid, sensitive and selective method was developed for the determination of NAL in dosage form and human plasma without any treatments. No electroactive interferences were found in biological fluids from the endogenous substances and additives present in capsules.     

Voltammetry of heterogeneous labile metal–macromolecular systems for any ligand-to-metal ratio: Part I. Approximate voltammetric expressions for the limiting current to obtain complexation information

We present approximate expressions and rigorous numerical simulations corresponding to the voltammetric limiting currents of a titration experiment of a heterogeneous macromolecular ligand with a metal ion under fully labile conditions. We highlight the accuracy of an approximate expression based on a polynomial expansion of the limiting current in terms of the fraction of the bound metal concentration in the bulk solution. Values of the coefficients of the polynomial expansion for macromolecular complexation are provided. The accuracy of this polynomial expression for systems exhibiting different degrees of heterogeneity together with its easy computation, suggests its application in the finding of the bulk value of the bound metal concentration from the limiting current for a given pair of total ligand and metal concentrations. Thus, straightforward calculations lead to the binding curve which can then be interpreted using the standard methods.     

Solvent-effect on the interconversion among one-, two- and four-electron reduction waves for the 18-molybdodiphosphate complex, [(P2O7)Mo18O54]4−

For the [(P₂O₇)Mo₁₈O₅₄]^4? complex, the presence of small cations such as H⁺, Li⁺ and Na⁺ caused one-electron waves to be converted into four- and two-electron waves in a complex manner. With the addition of a trace amount of H⁺, a four-electron reduction wave was obtained in solvents of weaker basicity like acetone, acetonitrile and propylene carbonate (PC); the relative permittivity did not affect the appearance of the four-electron wave. On the other hand, two-electron waves were obtained in solvents of stronger basicity like N,N-dimethylformamide (DMF), N,N-dimethylacetamide (DMA), and N-methylpyrrolidinone (NMP). With the addition of Li⁺ or Na⁺, the one-electron waves were converted into two-electron waves only in acetone, indicating that the conversion can occur in solvents of both weak basicity and low relative permittivity.     

Ion-exchange voltammetry of tris(2,2′-bipyridyl) ruthenium(II), iron(II), osmium(II) and tris(2,2′-bipyrazyl) ruthenium(II) in acetonitrile solutions at poly(ester-sulphonate) coated electrodes

Glassy carbon electrodes modified with the poly(ester-sulphonate) ionomer Kodak AQ 55 D are used and characterized in acetonitrile solutions. The potential window accessible in acetonitrile + tetrabutylammonium hexafluorophosphate extends from ?1.750 V to +1.900 V vs. an aqueous KCl saturated Ag/vbAgCl reference electrode.The electrochemical behaviour of [Ru(bpy)₃]²⁺, [Fe(bpy)₃]²⁺, [Os(bpy)₃]²⁺ and [Ru(bpz)₃]²⁺ (where bpy = 2,2′bipyridyl and bpz = 2,2′bipyrazyl) is studied at the modified electrode. All the electroactive cations are preconcentrated efficiently in the polymeric coating. In the case of bpy complexes both a one-electron oxidation as well as two one-electron steps of the stepwise reduction of the starting complex are detected at the modified electrode.In the case of [Ru(bpz)₃]²⁺, three consecutive reduction steps can be observed, while no oxidation process is observed in the direct positive scan before reaching the upper limit of the potential range accessible at the modified electrode.The relative order in the ion-exchange selectivity coefficients in acetonitrile solutions for the cations studied is evaluated by comparison with the electrochemical behaviour observed at unmodified electrodes. The possibility of gaining information on preconcentration effects for ion-exchange voltammetry in non-aqueous solvents from the Gibbs energies of transfer from water to hydrophobic media is also discussed.