Voltammetry and electrocatalytic properties of cobalt (1,4,8,12-tetraazacyclopentadecane) in aqueous solution

Summary The spectrochemical, electrochemical and electrocatalytic properties of Co[15]aneN₄ ([15]aneN₄ = 1,4,8,12-tetraazacyclopentadecane) have been investigated. The results show that, in aqueous solution, this compound mainly exists as three species whose axial coordination positions are occupied by water and/or hydroxy ligands; it is marginal whether other substrates such as Cl^– and NO _inf3 ^sup– interact with the central ion in acid-base solutions. The approximate Pourbaix diagram of Co^III/II[15]ane N₄ was determined. There is an electrochemically-induced isomerization between two trans conformational isomers of the Co[15]aneN₄ complexes in acid and netural solutions. The Co[15]aneN₄ complex has electrocatalytic properties for reduction of nitrate and nitrite only in strong alkaline solution.     

Chitosan-mediated and spatially selective electrodeposition of nanoscale particles

Nanoscale particles offer a variety of interesting properties, and there is growing interest in their assembly into higher ordered structures. We report that the pH-responsive aminopolysaccharide chitosan can mediate the electrodeposition of model nanoparticles. Chitosan is known to electrodeposit at the cathode surface in response to a high localized pH. To demonstrate that chitosan can mediate nanoparticle deposition, we suspended fluorescently labeled latex nanoparticles (100 nm diameter spheres) in a chitosan solution (1%) and performed electrodeposition (0.05 mA/cm2 for several minutes). Results demonstrate that chitosan is required for nanoparticle electrodeposition; chitosan confers spatial selectivity to electrodeposition; and nanoparticles distribute throughout the electrodeposited chitosan film. Additionally, we observed that the deposited films reversibly swell upon rehydration. This work indicates that chitosan provides a simple means to assemble nanoparticles at addressable locations and provides further evidence that stimuli-responsive biological materials may facilitate fabrication at the microscale.     

A Substituted Tetraazaporphyrinogen as an Electroactive Component for a Polymeric Membrane Anion-Selective Electrode

A novel anion-selective electrode has been prepared by usingtetraazaporphyrinogen as the electroactive component and o-nitrophenyloctylether as the plasticizer. The electrode exhibits almost Nernstian responsecharacteristics for Pic^-, ReO ₄ ^- ,SCN^-, ClO ₄ ^- and TPB^-. The linearresponse ranges towards the above-mentioned anions are 10^-6 10^-2, 10^-5 10^-2,10^-5 10^-2, 10^-5 10^-1, and 10^-5 10^-2mol/Land the corresponding slopes are -56.8, -57.1, -56.3, -56.1, and -59.9mV/decade with correlation coefficients of -0.99978, -0.99987, -0.99999,-0.99998, and -0.99998, respectively. The electrode shows an anti-Hofmeisterselectivity sequence: Pic^- > SCN^- >ReO ₄ ^- > ClO ₄ ^- > I^- >Br^- > BF ₄ ^- > Sal^->NO ₃ ^- > Cl^-. The unusual responsemechanism of the novel anion-selective electrode was investigated byexperimental observations and calculation with the MNDO method. Theelectrode was used as a TPB^- and a Pic^-sensitiveelectrode, respectively, and applied to the assay of levamisolehydrochloride tablets by potentiometric titration and Gran's methods. Theresults obtained are in excellent agreement with that determined by thestandard pharmacopoeia method based on nonaqueous titration.     

Sorption and desorption of radiostrontium on powdered bentonite: Effect of pH and fulvic acid

The effect of pH and fulvic acid on the sorption of Sr on bentonite was investigated by using batch experiments. The sorption and desorption isotherms of Sr on bentonite were determined at room temperature, at pH 6.0±0.2 and in presence of 0.1M NaCl. It was found that the sorption of Sr is independent at pH<8, and then increases slightly with increasing pH. Fulvic acid increases the sorption of Sr significantly on bentonite at low pH, but decreases the sorption of Sr at pH>8. The sorption of Sr on bentonite can be described by a reversible sorption process and the sorption mechanism consists mainly of ion exchange. This revised version was published online in July 2006 with corrections to the Cover Date.     

Generalized on-shell renormalization of heavy quarks

A generalized on-shell (GOS) renormalization scheme of QCD is developed to evaluate the renormalization of heavy quark wave functions and currents. All large logarithms arising from the physical range of quark masses and momentum transferq ² can be absorbed into wave function and vertex renormalization. Our results are more general than those of the heavy quark effective theory and agree with the latter only at zero recoil. The proposed GOS scheme is very suitable for the /m _Q expansion. As an application we discuss the renormalization of the flavour changing currentsb-c, t-b andt-c.Supported by Bundesministerium für Forschung und Technologie (BMFT)