G. Sato

Diffusion current at microdisk electrodes—application to accurate measurement of diffusion coefficients

Abstract Stationary electrodes (platinum and glassy carbon) were used for accurate measurement of diffusion coefficients. The theoretical diffusion current-time profile was calculated by digital simulation, by means of which the diffusion coefficient and the product of the charge number of electrode reaction n and the reactant concentration co were determined simultaneously from a single chronoamperogram. The feasibility of the method was demonstrated by measuring the diffusion coefficients of Tl(I) ions. When the nco value agreed with the corresponding known value, the diffusion coefficients were in good agreement with the standard values determined by the thin-walled hanging mercury drop electrode method. The diffusion coefficient of hexacyanoferrate(III) ions in 1 mol dm−3 KCl at, 25°C was also determined.

Real-Time Monitoring of the Secretory Function of Cultured Adrenal Chromaffin Cells

A system to discriminate the real‐time dynamics of the secretory function in cultured adrenal chromaffin cells, using a cell bed perfusion technique and an amperometric detector, was established. Examination of basal conditions revealed that the electrode potential and flow rate are crucial factors for monitoring precise dynamics of the secretory process. Stimulation of the cells either with acetylcholine (ACh) or with high K* concentration caused a transient current response. The current responses showed concentration dependence for both stimuli, and also showed a high correlation with the amount of catecholamines (CA) in the respective peak fraction of perfusate. Either prolonged cholinergic stimulation or maintained depolarization produced a transient response, which is not attributable to a depletion of releasable storage of CA as indicated by double‐stimulation experiments. Stimulation with high K* concentration evoked an additional release of CA even after the cellular response to prolonged ACh was inactivated, whereas maintained depolarization with high K* produced both facilitatory and inhibitory effects on the cell responsiveness to ACh. Most probably the transient natures of the secretory responses to ACh and to high K* are mediated by different mechanisms. All the results suggest that the direct monitoring is profitable for studies on the regulatory mechanisms of the secretory function.

Preparation, characterization and electrochemical properties of mixed-ligand ruthenium(III) and ruthenium(II) complexes with two kinds of β-diketones

Abstract The mixed-ligand ruthenium(III) complexes with the following compositions were synthesized and isolated chromatographically: [Ru(acac)2(tfpb)], [Ru(acac)(tfpb)2], [Ru(acac)2(hfac)] and [Ru(dpm)2(hfac)] (acac−, 2, 4-pentanedionate ion; tfpb−, 4,4,4-trifluoro-1-phenyl-1,3-butanedionate ion; hfac−, 1,1,1,5,5,5-hexafluoro-2,4-pentanedionate ion; dpm−, 2,2,6,6-tetramethyl-3,5-heptanedionate ion). Attempts to isolate [Ru(acac)(hfac)2] failed; but a mixture of K[Ru(acac)(hfac)2] and K[Ru(hfac)3] was obtained. The structure of one of the three geometrical isomers of [Ru(acac)(tfpb)2] was determined by means of single-crystal X-ray structure analysis. The 1H NMR and UVVis spectral data of the isolated complexes are presented. Each of these complexes gave a Nernstian one-electron reduction step and a Nernstian or quasi-Nernstian one-electron oxidation step in 0.1 mol dm−3 (C2H5)4NClO4— acetonitrile solution at 25 °C. The linear dependence of their reversible half-wave potentials on the ligand composition is discussed in detail.

Effects of substituents and chalcogen atoms on the reduction half-wave potentials of (substituted η-cyclopentadienyl)-1,2-substituted 1,2-ethylenedichalcogenolato)cobalt(III) complexes in acetonitrile solutions

Abstract Twenty-six (substituted η-cyclopentadienyl)(substituted 1,2-ethylenedithiolato)cobalt(III) complexes underwent Nernstian one-electron reduction at a platinum electrode in 0.1 mol dm−3 tetraethylammonium perchlorate + acetonitrile solutions at 25 °C. Their reversible half-wave potentials were linearly dependent on the sum of the field parameters of the substituents. A substituent at the cyclopentadienyl ligand affects the half-wave potential to a larger extent than one at the dithiolato ligand does. The chemical shifts of cyclopentadienyl carbon and hydrogen atoms varied linearly with the half-wave potential when the substituents at the dithiolato ligand were changed. A linear relationship was found also between the half-wave potential and the chemical shift of dithiolene carbon atoms of the complexes having substituted cyclopentadienyl ligands. A substituent at one ligand affects the electron density at the other ligand through the central atom. The effects of substituents were almost additive. Six complexes in which the sulphur atoms were replaced by selenium were also reduced through a Nernstian one-electron reduction step, and the half-wave potential changed linearly with the number of selenium atoms. The effect of replacement of the chalcogen atoms was independent of the substituents at the two ligands.

Anodic behavior of mercury electrode in aqueous ethylenediaminetetraacetic acid solutions

Summary It was found by conventional and phase-selective a.c. polarography that the dissolution of mercury in the solution of EDTA consists of at least two steps. The first step is probably the formation of ethylenediaminetetracetatomercurate (HgY 2− ) followed by its adsorption on the electrode surface. The second step corresponds to the dissolution of mercury into the solution as mercury-EDTA complexes. The adsorption of HgY 2− on the electrode makes the dissolution of mercury (the second step) irreversible, and also leads to the complicated behavior of the phase angle in the a.c. measurements. The adsorption kinetics of the product were studied by using a complex plane analysis. At lower pH values, the adsorption is controlled by both diffusion and adsorption kinetics. With increasing pH the adsorption becomes a kinetic-controlled process.

Electrochemical polymerization of tetraphenylporphyrinatoruthenium(II) complexes with diaza compounds as axial ligands

The tetraphenylporphyrinatoruthenium(II) polymers bridged by the diaza compound (so called ‘shish kebab’-type polymers) were formed on the electrode by the two-electron oxidation of [Ru(tpp)L2] (H2tpp=5,10,15,20-tetraphenylporphyrin; L=4,4′-bipyridine, trans-1,2-bis(4-pyridyl)ethene, 1,2-bis(4-pyridyl)ethine, 4,4′-azopyridine, 1,2-bis(4-pyridyl)disulfide)) in 0.1 mol dm−3 (C4H9)4N(ClO4)CH2Cl2. This is the first example of electrochemical formation of shish kebab-type polymers, which until now have only been synthesized chemically. The polymer formed electrochemically was different from the polymer synthesized chemically. The former has the positively charged bridging ligands. The polymers showed reversible oxidation waves corresponding to the oxidation of RuII to RuIII, and a reduction wave corresponding to the reduction of a positively charged bridging ligand.

Notes. Ligand additivity in the oxidation potentials of bidentate mixed-ligand ruthenium(II) complexes

Reversible oxidation half-wave potentials E½r have been found to be additive according to the number of ligands x by analysing the potential map of [Ru(bipy)3–xLx]n+ complexes (bipy = 2,2′-bipyridine; L = polypyridine or β-diketone). The slope of plots of E½rvs. x depends on the kind of ligand L and affords a measure of the π-donor/π-acceptor ability of the bidentate ligands. Ligand parameters, PL, for various bidentate ligands, are proposed.

Beryllium-9 quadrupole coupling constants and rotational correlation times of bis(acetylacetonato)beryllium(II) in acetonitrile at different temperatures

The 9Be quadrupole coupling constants, eQq/h, in 2.15 mol kg−1 [Be(acac)2]–CD3CN (acac− = pentane-2,4-dionate ion) at eight temperatures between 240 and 309 K were determined by the dual spin probe technique. The value of eQq/h was 348 kHz independent of temperature. By using the eQq/h value, the rotational correlation time of the complex in CH3CN at infinite dilution, τr∞, was evaluated from the 9Be relaxation rate measured in 12.7 mmol kg−1 [Be(acac)2]–CH3CN. The τr∞ thus obtained was proportional to η0/T, where η0 is the viscosity of the solvent at temperature T. The proportional constant was compared with that of [Co(acac)3] in CH3CN, which was determined elsewhere. We deduce that [Be(acac)2] interacts with acetonitrile molecules more weakly than [Co(acac)3].

A precise Cottrell cell

Abstract A precise Cottrell cell with glassy carbon electrode for chronoamperometric determination of diffusion coefficients is described. The validity of the measurement was demonstrated by comparing the observed diffusion coefficient of thallium(I) ions in 0.5 mol dm −3 KNO 3 solution at 25°C with the standard value previously determined by the thin-walled hanging mercury drop electrode method. The essential points for successful measurement are a right choice of the material and a precise finish of that part of the cell where the diffusion is made to occur.

Polarographic study of disproportionation kinetics of fluorescein radical anions in aqueous alkaline solutions

Abstract Fluorescein radical anions were generated in situ by controlled potential electrolysis with a mercury pool electrode. Analysis of the time dependence of the polarographic currents of a partially electrolyzed solution revealed that two radical anions disproportionated into one original fluorescein anion and one electroinactive entity. The reaction rate was proportional to the square of the radical concentration. The second-order rate constant was a linear function of hydrogen ion concentration in the pH range of 11.1–14 (ionic strength=1 mol dm−3). The kinetic results were interpreted on the basis of a reaction scheme consisting of two parallel paths, direct disproportionation and hydrogen-ion catalyzed disproportionation. An activation energy of 63.6 kJ mol−1 was obtained for the first path. Existence of other path(s), e.g., disproportionation between two protonated radical anions, at lower pH values was suggested.