Hiroko Yamaguchi

722—The effect of pH on the temperature dependence of the redox potential of horse heart cytochrome c at a bis(4-pyridyl)disulfide-modified gold electrode

Abstract The thermodynamic parameters of the cytochrome c electron-transfer reaction have been estimated electrochemically using a bis(4-pyridyl)disulfide-modified gold electrode in phosphate buffer solutions (pHs 6–8) containing 0.1 M NaC104. The temperature dependence of the formal redox potential, U°′, obtained in the temperature range of 0–55°C showed biphasic behavior in an alkaline solution with an intersection point at ca. 40°C, which would be attributable to a structural change in the protein moiety of cytochrome c, while in acidic and neutral solutions a monotonous relationship between U°′ and temperature was observed. For the electron-transfer reaction entropies (ΔS°rc = S°red - S°ox) of −12.7 ± 1.6, −11.8 ± 1.1, and −10.3 ± 1.5 (below 40°C) and −41.1 ± 7.5 (above 40°C) were obtained at pHs 6, 7, and 8, respectively.

Reversible electrochemical reduction and oxidation of cytochrome c at a bis(4-pyridyl) disulphide-modified gold electrode

At a gold electrode on which bis(4-pyridyl) disulphide had been pre-adsorbed, horse heart ferricytochrome c exhibited a well developed quasi-reversible redox wave by cyclic voltammetry in the absence of any promoter in the solution.

Anodic oxidation of acridine in acetonitrile

Abstract To clarify the product and the reaction pathway, anodic oxidation of acridine was investigated in acetonitrile. The voltammogram of acridine exhibited two anodic waves at 1.35 (Ia) and 2.0 (IIa) V vs. Ag/AgClO4 (0.01 M). Waves Ia and IIa were due to oxidation of acridine and protonated acridine respectively. The oxidation product was obtained by preparativescale electrolysis at 1.45 V. The results of precise analysis and electrochemical behavior of the oxidation product were somewhat complicated. The puzzling results are, finally, interpreted clearly in terms of a dication of the tetramer (on the basis of acridine) which is in equilibrium with acridyl acridinium cation radical (eqn. 1). The oxidation pathway for producing the tetramer by an ECEC mechanism (eqns. 2–5) was proposed.

Anodic bromination of anisole in acetonitrile

Anodic bromination of anisole at a platinum electrode gave p-bromoanisole in high regio-selectivity; p-/o-ratios were about 12 or more. The current efficiency for the bromination was ca. 80% at anode potentials of 1.3–1.8 V vs. Ag/Ag+. The ratio of the concentration of anisole to that of bromide ion, [Anisole]/[Br−] ratio, showed a pronounced effect on the current efficiency and p-/o-isomer selectivity. and [Anisole]/[Br−] ratios 10 were preferable. The effective potentials for the bromination were more positive than those of a new wave (IIIa) which developed by adding anisole to the solution containing bromide ion, while no appreciable bromination occurred when electrolyses were undertaken at the plateaux of the first and the second waves for oxidation of bromide ion. The bromination also occurred in the anisole/Br2 system by passing electricity further. The limiting current of wave IIIa showed kinetic-controlled characteristics. Thus, the formation of an oxidizable intermediate which was formed by a reaction of anisole with Br2 was proposed to be important, the bromination occurring efficiently via the electrochemical oxidation of the intermediate. No significant influence of the light on the bromination was observed. Neither dibromo derivatives nor side-chain brominated products were detected under the present experimental conditions.

Effect of Moisture on Polarographic Reduction of Anthraquinone Derivatives in Dimethylformamide

非水溶媒中でのアントラキノン (以下 AQ と略記する) 系化合物のポーラログラムは可逆的な2段波を示し, 電子付加のみの還元であることが認められている。しかし絶対無水の溶媒で実験をすることには無理があるので, 実際には電子付加反応だけではなくプロトン付加反応もともなう場合があると考えられる。そこで, 本報ではジメチルホルムアミド (以下 DMF と略記する) 中でのアントラキノン系化合物のカルボニル基の還元機構におよぼす水分の影響について含水率0-20vol% の範囲で検討した。