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The Lewis acidic uranyl center and the amide units of receptor 1 bind the anion of the hydrophilic, biologically relevant salt KH2PO4 specifically, and simultaneously the crown ether units bind the cation. The complexation properties of 1 were studied with NMR spectroscopy, mass spectrometry, and cyclic voltammetry. The recognition demonstrated for this simple salt could be of great importance for membrane transport, extraction, and sensor technology.

A simulation scheme for the calculation of theoretical chronopotentiograms at microelectrodes in solutions containing low amounts of supporting electrolyte is presented. The scheme allows computation of the changes in the concentration profiles of the substrates, products and the supporting electrolyte ions with time. The electrode potentials that are established after reaching the steady-state, together with the appropriate current intensities, can be used for constructing the steady-state voltammograms. The simulation of the mixed diffusional and migrational transport is based on the Crank-Nicolson method with an exponentially expanding time and space grids. The scheme does not impose any limitations on diffusion coefficients and it can be applied both to simple electrode reactions (one reactant-one product) and more complicated reactions under the assumption that the double-layer thickness is small in comparison to the diffusion layer. Five simple types of electrode reactions and an example of a more complicated scheme were considered. The results obtained demonstrate that the dependence of the steady-state limiting current on the support ratio (Csupp.el./Csubst) depends not only on the charge of the reactant and the product, but also on the diffusion coefficient ratio of the substrate and product. If the difference between diffusion coefficients is large, the predictions based on simpler theories available in literature can become invalid.

A method for extracting single peaks from complex linear sweep and cyclic voltamperograms is presented. Voltamperograms are transformed by means of semidifferentiation, then all undesired peaks are removed from the semiderivative curve and replaced by calculated baselines. The resulting curve is ~~nte~ated back, giving a vol~m~~gram with one peak only. Baselines in the semiderivative domain are determined by the least-squares curve-fitting of datapoints from peak border regions, using the equation that describes the semiderivative peak of a reversible electrode process. With this procedure peaks can be removed without assumptions about the mechanism of the underlying electrode reaction. Due to its design, the algorithm presented is suitable for the fully automatic processing of cyclic and linear sweep voltamperograms. Performance of the procedure was checked with generated reversible voltamperograms as well as in real experiments with both reversible and irreversible systems. The smallest distance between two peaks of equaI height, for which the described method can yield correct results, has been found to be 110 mV for a reversible one-electron process at 298 K. This procedure can also be applied to the elimination of the cathodic current from the cyclic voltamperogram of a single component in order to get a pure anodic current value, free from cathodic contribution, or vice versa.

The use of microelectrodes for voltammetric investigations of the complexation equilibria at very low concentrations of supporting electrolyte allows the risk of competitive complexation or contamination to be avoided, makes the activities of the species involved closer to their concentrations (which facilitates comparisons with the spectroscopic results) and finally. allows the concentrations of the species to be varied over a broader range. This paper presents the calculations of the steadystate currents for a wide range of complexes that are inert on the experimental time scale, and reports the influence of the concentration of the electroinactive ionic species on the limiting currents. Also, for a number of cases the variation of halfwave potential with the ligand concentration, resulting from changes in the ohmic drop, is given. It is assumed that only one species (the complex or the uncomplexed form) is electroactive; if this is the complex, it may or may not change the number of ligands. The theoretical results were obtained either employing the Myland-Oldham theory extended in this paper or by digital simulation. The results of calculations show that the magnitude of the changes in the steady-state limiting current on complexation depends on the type of complexation equilibrium, the type of the change in the reactant charge number in the electrode process, and the complex formation constant. In a number of situations migrational effects are negligibly small and no special treatment is necessary, despite the lack of supporting electrolyte. In other cases, where migration is significant, the relations between the measured steady-state limiting current and the complex formation constant :? are given in the form of fitted equations that can be used to obtain p from appropriate experimental data.

Three newly synthesized polyanthraquinone derivatives: 7,13-bis(9,10-dioxo-1-anthryl)-1,4,10-trioxa-7,13-diazacyclopentadecane, (AQ)A 2 15C5, 7,16-bis(9,10-dioxo-1-anthryl)-1,4,10,13-tetraoxa-7,16-diazacyclooctadecane, (AQ)A 2 18C6, and tris[(9,10-diokso-1-antryl)-aminoethyl]amine, (AQNet) 3 N, were examined by cyclic and normal pulse voltammetry. All anthraquinone groups in these compounds were electroactive and formed the radicals and dianions similarly to simple anthraquinone. The differences between the voltammograms obtained in the absence and presence of supporting electrolyte are discussed, and the diffusion coefficients of the compounds and the rates of the chemical reactions following the first reduction step were evaluated. (AQNet) 3 N appears to be a good model compound for multi electron transfers in aprotic solvents. It offers two consecutive nearly reversible 3-electron redox systems: 0/À 3 and À 3/À 6. The interactions of the radicals and dianions of the above compounds with alkali metal cations were examined.

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