General characteristics of the copper-based mercury film electrode

The optimum conditions for the preparation, storage, conditioning and renewal of copper-based mercury film electrodes (CBMFEs) are given. The voltammetric results obtained at these electrodes are compared with the predictions of the theory of cyclic and stripping voltammetry at the mercury film electrode, as well as with the results obtained at the silver-based and the platinum-based mercury film electrodes. The advantage of a CBMFE is prolonged life-time, whereas the disadvantages ar the decreased range of usable positive potentials and the possibility of interfering reactions of the electrodeposited metals with the copper substrate or copper dissolved in the mercury phase. The presence of copper has no essential influence on the behaviour of lead and thallium; it affects the behaviour of zinc markedly and that of cadmium and indium slightly. The conditions allowing the minimization of the harmful action of copper on the behaviour of cadmium and indium have been found.     

Optimization of CuW alloy electrodeposition towards high-tungsten content

With the help of the factorial design of experiments, optimization of the deposition of the CuW alloy was successfully done. The important deposition parameters were identified as pH, current density, and—the most important one—copper ion concentration. All of them were examined in their wide ranges. Under optimal conditions, in a citrate bath, with copper ion concentration of 1.0 mM, at current density of −100 mA cm⁻² and at pH ca. 8.3, the alloy layer had the highest tungsten content (circa 30 wt.%), satisfactory adhesion and a smooth and crackless morphology. The structure of the electrodeposited alloy can be described as an amorphous solid solution of Cu in W with built-in Cu nanocrystals.

     

Electroanalytical and spectroscopic procedures for examination of interactions between double stranded DNA and intercalating drugs

A method is presented for the electroanalytical characterization of interactions of dsDNA with a drug, under conditions that both agents are dissolved in the phosphate buffer solution and both are electroactive. Normal pulse, square wave, differential pulse, and cyclic voltammetries were employed in the measurements of the drug and dsDNA oxidation signals at carbon electrodes. UV–Vis spectroscopy was used as a non-electrochemical method to support the electroanalytical data. An anticancer drug, C-1311 (5-diethylaminoethyl-amino-8-hydroxyimidazoacridinone), has been selected for the examination. Normal pulse voltammetry was particularly useful in showing that under the conditions employed neither dsDNA nor the drug were adsorbed at the electrode surface. Necessary conditions for the appearance of the well-defined dsDNA voltammetric signal (guanine peak) are: rigorous chemical and biological purity in the cell and appropriate purity of DNA. An analysis of the obtained results confirmed that there were two modes of interaction between C-1311 and dsDNA: by intercalation and electrostatically. In the presence of excess NaCl the electrostatic interactions deteriorate. The binding constants (K ₁ and K ₂, respectively) and the number (n) of nucleic base pairs (bp) and the number (m) of phosphate groups (pg) interacting with one molecule of drug have been determined. For strong interactions (intercalation) the values of the binding constant, K ₁, and the binding-site size, n, equal 3.7 × 10⁴ M⁻¹ and 2.1, respectively. For the weak electrostatic interactions the K ₂ and m parameters equal 0.28 × 10⁴ M⁻¹ and 4.7. The intercalation process is rather slow and its rate (the conditions of pseudo-first-order reaction) was estimated to equal 7 × 10⁻⁴ s⁻¹. The possibility of independent determination of both interacting agents was very useful in the study. Figure Intercalation of C-1311 into a dsDNA fragment     

Activity changes of glassy carbon electrodes caused by their exposure to OH• radicals

GC electrodes were exposed to Fenton solutions. The surface changes produced by the OH^? radicals of these solution were inspected using SEM, XPS, Raman spectroscopy and electrochemistry. The OH^? radicals caused erosion and roughening of the surface, selective oxidation and dissolution of sp² carbon, and reduction of the number of nucleation sites for silver deposition.     

Increase in rate of electrodeposition and in Ni(II) concentration in the bath as a way to control grain size of amorphous/nanocrystalline Ni-W alloys

Calculations based on the equilibria involved have been carried out to find the conditions of the highest possible solubility of Ni(II) in an ammonia-citrate bath for the electrodeposition of amorphous/nanocrystalline Ni-W alloys. The appropriate increase in the concentration of citrate, followed by the corresponding increase in the concentration of Ni(II), has led, under the conditions of constant current, to the increase in the efficiency of the electrodeposition and therefore the rate of electrodeposition by 3.2 times. The amorphous alloys obtained in solutions of different Ni(II) concentrations had different sizes of nanocrystals (15–100 ?), as determined from X-ray diffractograms, and different alloy compositions (10–19.5 at% of W), but were of similar high hardness. Electronic Publication     

Fe-N-C catalysts for oxygen electroreduction under external magnetic fields:Reduction of magnetic O2 to nonmagnetic H2O

An extensive analysis of iron-nitrogen-carbon(Fe-N-C)electrocatalysts synthesis and activity is presented concerning synthesis conditions such as initial Fe content,pyrolysis temperature and atmosphere(inert N₂,reducing NH₃,oxidizing Cl₂ and their sequential combinations)and the influence of an external magnetic field on their performance in oxygen reduction reaction(ORR).Thermosetting porous polymers doped with FeCl₃ were utilized as the Fe-N-C catalysts precursors.The pyrolysis temperature was varied within a 700-900℃range.The temperature and atmosphere of pyrolysis strongly affect the porosity and compositi on of the resultant Fe-N-C catalysts,while the in itial amount of Fe precursor shows much weaker impact.Pyrolysis under NH₃ yields materials similar to those pyrolyzed under an inert atmosphere(N₂).In contrast,pyrolysis under Cl₂ yields carbon of peculiar character with highly disordered structure and extensive microporosity.The application of a static external magnetic field strongly enhances the ORR process(herein studied in an alkaline environment)and the enhancement correlates with the Fe content in the Fe-N-C catalysts.The Fe-N-C materials containing ferromagnetic iron phase embedded in N-doped microporous carbon constitute attractive catalysts for magnetic field-aided anion exchange membrane fuel cell technology.     

Substantial Influence of Temperature on Anchoring of Gold‐Nanoparticle Monolayer for Performance of DNA Biosensors

This paper presents a way of modification of crystalline gold surface with a high quality layer of gold nanoparticles (Au NPs) via self‐assembled dithiol. The application of additional Au NPs monolayer prepared at various temperatures was tested with three types of biosensors previously described in the literature. The examined DNA biosensors differed by the detection method and the way of the immobilization of DNA probe at the modified gold electrode surface. For the immobilization of DNA probe in the sensing layer either the formation of SAM or the affinity binding (biotin – sterptavidin) or covalent attachment were used. The necessary condition of successful preparation of a perfect such monolayer is the preparation temperature of 4 °C. The preparation of Au NPs layers at higher than 4 °C temperatures leads to poor repeatability and unsatisfactory precision of the measurements. The application of the perfect Au monolayer lowers the detection limit (circa by 10 to 100 times) for all tested DNA biosensors.     

Metal ion-driven synthesis of polyaniline composite doped with metallic nanocrystals at the boundary of two immiscible liquids

In this work, silver and gold–polyaniline composite materials were chemically synthesized at the nitrobenzene/water interface. Aniline (monomer) was dissolved in nitrobenzene and the oxidizing agent (either silver (I) or gold (III)) was dissolved in water. Metals, which were formed during the reaction were in nano- and microcrystalline forms and were partially embedded in the polymer. The forms of gold and silver crystallites found in the synthesized composites differed significantly. The rate of growth of the PANI-Ag and -Au composites and their morphologies depended on concentration of the reagents in both phases. The average size of the gold crystals was smaller compared to silver and was in the range of 20–25 nm. The obtained composite materials were characterized by cyclic voltammetry, scanning electron microscopy, and Raman spectroscopy. The pernigraniline species of polyaniline dominated in the entire volume of the PANI-Au composite and in parts of the PANI-Ag material located at the aqueous solution side, while partially oxidized emeraldine was the main component of PANI-Ag at the organic phase side.     

Microscopic observation of the crystalline form of poly(<Emphasis Type="Italic">o</Emphasis>-methoxyaniline) on a membrane electrode

We describe electrochemical and microscopic (SEM) studies on the electrochemical polymerization of poly(o-methoxyaniline). The crystalline form of the polymer was obtained. The poly(o-methoxyaniline) crystals are formed on a membrane electrode from an acidic solution of the monomer. It is suggested that the pores of the membrane work as nuclear crystallization points.Contribution to the 3rd Baltic Conference on Electrochemistry, Gdansk-Sobieszewo, Poland, 23–26 April 2003Dedicated to the memory of Harry B. Mark, Jr. (28 February 1934–3 March 2003)