Coupled Electron‐Proton Transport in Electropolymerized Methylene Blue and the Influences of Its Protonation Level on the Rate of Electron Exchange with β‐Nicotinamide Adenine Dinucleotide

This paper describes electrochemical characteristics of poly(methylene blue) electrolytically deposited on glassy carbon and examines the electrocatalytic activity of the polymer toward oxidation of the coenzyme NADH. Redox‐active properties of the cationic polyelectrolyte arose from both electron self‐exchange between electroactive sites and a high ionic film‐conductivity. The diffusion coefficient of charge carriers in the film increased with decreasing solution pH, indicating the pH dependence of the electron diffusion coefficient. The electrocatalytic oxidation of NADH at the polymer‐modified electrode proceeded via an intermediate charge‐transfer complex of the reduced polymer with the oxidized coenzyme. The complex dissociated more rapidly into the oxidation products as the reduced polymer protonated. Thus, the rate constant for the cross‐exchange reaction rose with a decrease in pH. For NADH oxidation, the polyelectrolyte exhibited an electrocatalytic activity higher than the monomeric dye because of a stronger oxidizing power of the second oxidized form of the polymer.     

Preparation and sensor evaluation of a Pacman phthalocyanine

We report both the preparation and sensor evaluation of a new metal-free calixarene bridged binuclear phthalocyanine.     

Bismuth Film Electrode for Analysis of Tetracycline in Flow Injection System

A bismuth film was prepared on glassy carbon electrode (GCE) and used in a flow injection amperometric system to analyze tetracycline. Bismuth film electrode (BiFE) preparation and flow injection amperometric parameters were optimized. System performances of BiFE were compared to GCE. BiFE was validated with three different lots of real sample, 250 mg tetracycline capsules, the results showed good agreement, i.e., between 240 and 260 mg per capsule. Good relative recoveries were also obtained in the range of 86–106%.     

胆绿素还原酶电极及电位法测定胆红素的研究

本文研制了胆绿素还原酶电极,采用电位法测定胆红素。胆绿素还原酶以牛血清白蛋白和戊二醛固定化制成酶膜,覆盖在石墨电极上在辅酶Ⅰ存在下进行测定,铁氰离子作为电子传递介质。胆红素在空气存在下氧化为胆绿素,再以胆绿素还原酶电极进行检测。线性响应范围为1×10~(-6)-1×10~(-4)mol/L胆绿素(胆红素),酶膜寿命约60h。本法可在水溶液中测定胆红素。     

Electrochemical studies of single-wall carbon nanotubes as nanometer-sized activators in enzyme-catalyzed reaction

Chronoamperometry based on the “controlling-diffusion layer” concept of the convective system was used to assay the activity of lactate dehydrogenase (LDH) on a bare glassy carbon (GC) electrode and a GC electrode modified by a single-wall carbon nanotube (SWNT) film. The effects of lanthanum ion, oxalic acid, and nicotine on the LDH activity were monitored. Analysis of the experimental results revealed that the single-wall carbon nanotubes could markedly increase the activity of LDH. The activation and inhibition were characterized by three quantities: the real initial reaction rate (V₀) and the maximum reaction rate (V_max) of the enzyme-catalyzed reaction and the Michaelis-Menten constant (K_m). Tapping mode atomic force microscopy (AFM) images and the Raman spectra unambiguously demonstrated that the single-wall carbon nanotubes could interact with the enzyme LDH while the SWNT-modified electrode was under the potential control. In this case, the activation of SWNT was attributed to the interaction of SWNTs with the enzyme.     

Effect of Rotation Rate on the Formation of Platinum-modified Polyaniline Film and Electrocatalytic Oxidation of Methanol

The oxidation of methanol was investigated on platinum-modified polyaniline electrode.Changes in the electrode rotation rates (Ω) during platinum electrodeposition remarkably affect the formation and distribution of platinum in the polymer matrix and consequently lead to different currents of methanol oxidation. The results show that platinum loading is proportional to rotation rates Ω^1/2.     

奥美拉唑在碳糊电极上的吸附伏安测定法研究

研究了奥美拉唑在碳糊电极上的电化学行为及检测方法 ;在1.2mol·L -1H2SO4 底液中 ,通过富集用碳糊电极吸附伏安法测定奥美拉唑 ;阴极峰电位为0.403V(vsSCE) ,峰电流与奥美拉唑的浓度在7.8×10-8～3.7×10-5 mol·L-1 范围内呈良好的线性关系 ;该法的检出限为1.43×10-8 mol·L-1;用标准加入法测得回收率范围为94 %～102 % ;对奥美拉唑胶囊用该法进行了测定 ,获得了满意的结果 ;该法的优点是成本低 ,操作方便 ,重复性好及检出限较低 ;对电极响应机理进行了探讨 ,奥美拉唑的电极过程是一个两电子两质子的准可逆过程     

Adsorption of methylamine at a polycrystalline gold/solution interface

Adsorptive behaviour of the methylamine molecules has been investigated by measuring changes in the differential capacitance of the double layer at the gold/solution interface by the tensammetric method. The differences in adsorption parameters at Θ < 0.8 and >0.8 have been explained by changes in arrangement of the adsorbate.     

Voltammetric Determination of Leucoindigo Adsorbed on Pretreated Carbon Paste Electrodes: Its Application in a Flow System

The determination of leucoindigo adsorbed on the surface of pretreated carbon paste electrodes has been performed by cyclic (CV) and alternating current voltammetry (ACV). The water‐soluble compound called leucoindigo is obtained through the reduction of water insoluble indigo in an alkaline media and in presence of a dithionite salt (Na₂S₂O₄) as a reducing agent. Cyclic voltammograms of leucoindigo show two reversible electrodic processes, in the aqueous 0.1 M Tris‐HCl pH 7.2, at the formal potential of ?0.4 V and +0.3 V (vs. Ag/AgCl/sat. KCl). In a batch protocol, leucoindigo was quantified by CV with a change of medium between accumulation and detection steps. Reversible voltammetric processes of leucoindigo were greatly enhanced by other voltammetric technique like alternating current voltammetry. Limit of detection in the nanomolar range was achieved for a 2 min accumulation time by ACV in a batch procedure. A flow system was also employed, with adsorptive voltammetric detection of leucoindigo, since this automates the methodology and decreases analysis time. Parameters related to the electrochemical technique are optimized and calibration plots obtained are reported. These data provide useful information about the suitability of using leucoindigo in the detection system of alkaline phosphatase (AP) and horseradish peroxidase (HRP) based affinity devices, in which indigo is generated by the enzymatic hydrolysis of the 3‐indoxyl phosphate substrate.