Yasuhiko Ohsawa

A correlation between the half-wave potential and the micelle-solubilization equilibrium of ferrocene in cationic micellar solutions

Abstract The reversible half-wave potential of the ferricinium/ferrocene redox couple in aqueous 0.2 M Li 2 SO 4 , (0.165±0.005) V vs. SCE, is determined directly by cyclic voltammetry of ferrocene, in spite of its poor solubility. The reversible half-wave potentials of this couple in cationic micellar solutions of alkyltrimethylammonium bromide are independent of the ferrocene concentration, showing that the pseudo-phase model or the Poisson distribution is applicable to these micellar solutions. The relation between the half-wave potentials in the water and the micellar solution is formulated on the basis of the micelle-solubilization equilibrium. The solubility data and the above half-wave potential data of ferrocene together offer corroborating evidence for the validity of this relation. This fact means that the voltammetric technique can be applied to a complicated micellar system to yield a clear-cut conclusion, and can be used in conjunction with the solubility measurement to determine the formal standard potential of a substance which is insoluble in water but can be solubilized in micellar solution.

Electrochemical detection of C60 6? at low temperature

Low temperature cyclic voltammetry (CV) in water-free N,N-dimethylformamide (DMF)–toluene (2:3) mixture containing 0.1 mol dm–3 tetraethylammonium hexafluorophosphate (TEAH) showed a complete set of six one-electron reversible waves for C60, providing evidence for the existence of C606–.

The mechanism of the electrode oxidation of 5,10-dimethyl-5,10-dihydrophenazine in cationic micellar solution

Abstract The electrode oxidation mechanism of a neutral substance, 5,10-dimethyl-5,10-dihydrophenazine (DMPZ), in cationic micellar solutions of alkyltrimethylammonium bromide was studied. Cyclic voltammetry and the spectrophotometric determination of the solubility of DMPZ in micellar solution led to the conclusion that the micelle solubilization equilibrium of DMPZ obeyed the Poisson distribution. A formal oxidation potential which water-insoluble DMPZ would have in water, (−0.041±0.010) V vs. SCE, was determined on this basis. The result of potential-step chronoamperometry could be interpreted on the basis of the proposed reaction scheme, in which the charge-transfer process was preceded by the exit process of DMPZ from the micelle into the water. The exit rate constants ranged from 10 3 to 10 4 s −1 , depending on the surfactants alkyl chain lengths which ranged from C 16 to C 12 .

An electrochemical study of quenching reactions of polypyridine complexes of Ru(II) and Os(II) in excited states

The quenching of the excited states of the complexes, Ru(bpy)32+, Ru (4-dmbpy)32+, Ru(5-dmbpy)32+, Ru(bpy)2(CN)2, Os(bpy)32+, Os(5-dmby)32+, Os(phen)32+ and Os(5-Clphen)32+ (bpy=2,2-bipyridine; 4-dmbpy=4,4′-dimethyl-2,2′-bipyridine; 5-dmbpy=5,5′-dimethyl-2,2′-bipyridine; phen=1,10-phenanthroline; 5-Clphen=5-chloro-1,10-phenanthroline), by Fe3+ aquaions in aqueous solution is studied by an electrochemical transient method. An electrolyte containing one of the complexes, M(II), and iron aquaions, Fe3+ and Fe2+, in sulphuric acid is irradiated by a flash of 3 μs width from a xenon lamp. A cathodic current flows at a platinum grid electrode which is placed in the solution and kept at the formal, standard potential of the Fe3+/Fe2+ redox couple. The current vs. time curve is recorded after the irradiation is complete. A theoretical expression for this curve is derived by taking both the electron-and energy-transfer quenching paths into consideration and solving Ficks diffusion equation. Analysis of the experimental results is conducted, on this theoretical basis and yields the Stern-Volmer constant Ksv and the second-order rate constant kt for the electron-transfer reaction between M(III) and Fe2+. Agreement in kt and Ksv between this and previous works is satisfactory. No cathodic photocurrent is observed for the iron complexes studied, Fe(bpy)32+, Fe(bpy)2(CN)2 and Fe(phen)32+.

Preparation of polyimide Langmuir-Blodgett films containing [Ru(bpy)3]2+ complex

Abstract The preparation of polyimide Langmuir-Blodgett (LB) films containing [Ru(bpy)3]2+ (bpy ≡ 2,2-bipyridine) is described. Newly synthesized [Ru(5,5-diamino-bpy)(bpy)2]2+ was found to undergo a direct polymerization reaction with acid dianhydrides, which affords the corresponding polyamic acids (potential precursors of polyimide LB films). For LB film deposition, the copolymerization approach using flexible 4,4-diaminodiphenyl ether was adopted, because of the insufficient stability of a monolayer of the polyamic acid long alkyl amine salt from only [Ru(5,5-diamino ≡ bpy) (byp)2]2+. Thus obtained polyamic acid LB films using 1,2,3,4,-cyclobutanetetrarboxylic dianhydride were finally converted into the polyimide LB films containing [Ru(bpy)3]2+. The photoelectrochemical characteristics of the polyimide LB films on indium tin oxide electrodes were also studied.