Kazuo Yasukouchi

Electrocatalytic reduction of nitrate and nitrite to hydroxylamine and ammonia using metal cyclams

Abstract Co(III)-cyclam (cyclam = 1,4,8,11-tetra-azacyclotetradecane) has been demonstrated to act as a new and excellent catalyst for NO − 3 and NO − 2 reduction by cyclic voltammetry and controlled-potential electrolysis (CPE). CPE of a KNO 3 solution at an Hg electrode gave hydroxylamine selectively with high current yields (ca. 90%); the current densities were > 5 mA/cm 2 in 0.1 M KNO 3 solution at −1.5 V (vs. SCE) in the presence of only 20 μ M or less of the catalyst. The turnover frequency was > 500 h −1 (using an 8 cm 2 Hg pool electrode), and no deactivation of the catalyst was observed after CPE for several hours. At Ag, Cu and Pb electrodes, hydroxylamine was reduced further to give ammonia preferentially. Ni(II)-cyclam also acted as a catalyst, but the effective potential region was ca. 0.2 V more negative than that of Co(III)-cyclam. Some mechanistic investigations suggested that the formation of Co(I)- and Ni(I)-cyclam, which adsorbed onto the electrode surface, would be effective, and also that the role of cyclam as a ligand would be to provide sufficient nucleophilicity of the catalysts and/or a suitable structure for interaction with nitrogen oxyanions.

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.

Enzyme immunosensors based on electropolymerized polytyramine modified electrodes.

Highly sensitive amperometric enzyme immunosensors for human immunoglobulin G (IgG) were prepared on the basis of electrogenerated polytyramine (PTy, tyramine = p-(2-aminoethyl)-phenol) modified electrodes. Properties of PTy films changed depending on electrolysis conditions. On the basis of the found properties of the films, an effective IgG sensor was prepared: a PTy film was formed first from an acid solution on a Pt electrode, and the surface was further covered with a PTy film from an alkaline methanol solution to give a PTy doubly coated electrode on which anti-IgG was then immobilized. This electrode provided a large surface area with little non-specific adsorption of proteins. By means of the competitive enzyme immunoassay technique using glucose oxidase (GOD) labeled IgG conjugates, IgG was determined in the concentration range of c. 10 pg/ml-1 mg/ml from the oxidation current of H2O2 generated by the enzyme (GOD) reaction using the above IgG sensor. Also, an anti-IgG immobilized electrode, prepared by using a Pt electrode singly covered with a PTy film from an alkaline methanol solution, acted as an effective IgG sensor with a detection limit for IgG of c. 100 pg/ml.

Reduction of nitrate to give hydroxylamine at a mercury electrode using cobalt(III)–and nickel(II)–cyclams as catalysts

Electrocatalytic reduction of NO3– takes place efficiently in the presence of a small amount of CoIII– or NiII–cyclam (cyclam = 1,4,8,11-tetra-azacyclotetradecane) in aqueous solutions to give NH2OH selectively at an Hg electrode.

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.

Electrochemical analysis of enzyme reactions for sarcosine oxidases.

同一の基質及び反応に対する特異性を持つ,由来の異なる2種類のサルコシンオキシダーゼ(SOD:from Arthrobacter sp. 及びSOX: from Bacillus sp.)について,メディエーターを用いた電気化学的手法によって酵素反応の解析を行った.SOD,SOXいずれに対しても,Mo(CN)84-がメディエーターとして最も有効であったが,他のメディエーターの選択性については2種の酵素で若干違いが見られた.基質及びメディエーター{Mo(CN)84-}存在下で,酵素反応に基づく触媒電流から酵素反応速度式を評価した.その結果,SODの酵素反応はV=Vmax/(1+Kml/[S]+Km2/[M])で表される通常のミカエリス型の反応機構であることが明らかとなった.一方,SOXは,活性中心が1個であるにもかかわらず,その酵素反応速度式は基質,メディエーターに対してほぼ二次の依存性を示し,SODとSOXは,その酵素反応の細部については,互いに異なる挙動を示すことが明らかとなった.

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。