Direct electrochemistry of xanthine oxidase at a gold electrode modified with single-wall carbon nanotubes.

The direct electrochemistry of xanthine oxidase (XOD) was accomplished at a gold electrode modified with single-wall carbon nanotubes (SWNTs). A pair of well-defined redox peaks was obtained for XOD with the reduction peak potential at -0.478 V and a peak potential separation of 28 mV at pH 7.0. Both FT-IR spectra and the dependence of the reduction peak current on the scan rate revealed that XOD adsorbed onto the SWNT surfaces. The redox wave corresponds to the redox center of the flavin adenine dinucleotide (FAD) of the XOD adsorbate. Compared to other types of carbonaceous electrode materials, the electron transfer rate of XOD redox reaction was greatly enhanced at the SWNT-modified electrode. The peak potential was shown to be pH dependent. Spectral methods verified that the attachment of XOD onto SWNTs does not perturb the XOD conformations drastically.     

二茂铁基超支化聚氨酯的电化学性能

通过循环伏安法(CV)测定了二茂铁基超支化聚氨酯(HAPE-Fc)的电化学性能.结果表明:HPAE-Fc表现为单对氧化还原峰,在二茂铁接枝到超支化聚氨酯上以后,二茂铁基团依然保持着自身的氧化还原独立性,具有较强的电子转移速率,这是其具有电化学特性和催化作用的前提条件.通过分析扫描速率与HPAE-Fc电化学行为之间的关系,发现HPAE-Fc的电极过程既受扩散控制,同时也受电极反应的控制.     

圆盘微电极的卷积和交流伏安行为

研究了可逆氧化还原对(以二茂铁为例)在圆盘微铂电极上的卷积法,包括一阶导数卷积(e),二阶导数卷积(e′),三阶导数卷积(e″)的行为.结果表明,在微电极上的 e-E曲线类似于常规电极的循环伏安曲线。e、e′和e″曲线的峰高与扫速幂次的关系与悬汞电极上的规律相符,但其值分别为0.5、1.5、2.5.还研究了微电极的交流伏安行为,得到铁氰化钾的特征电位值。     

金电极上偶氮腺嘌呤的电化学行为研究

本文研究了光滑金电极上偶氮腺嘌呤的电化学特性,并确定了相关动力学参数. 在含偶氮腺嘌呤的0.2 mol·L^-1的磷酸盐缓冲液(PBS,pH = 4.0 ~ 10.0）中,发现其循环伏安图上出现一对氧化还原峰. 基于对扫速和伏安峰值电位的分析,结果表明这是一个由吸附控制的可逆偶氮腺嘌呤氧化还原电化学过程. 当pH值从低到高改变时,氧化还原峰值向负电位移动,证实H⁺参与了该反应. 通过进一步实验数据分析和电极表面吸附量计算,发现该反应为分步进行的两电子两质子反应. 最后,通过快速循环伏安扫描方法确定了电化学过程的表观传递系数α和表观速率常数ks.     

Direct Electrochemistry of Catalase at a Gold Electrode Modified with Single‐Wall Carbon Nanotubes

The direct electrochemistry of catalase (Ct) was accomplished at a gold electrode modified with single‐wall carbon nanotubes (SWNTs). A pair of well‐defined redox peaks was obtained for Ct with the reduction peak potential at ?0.414 V and a peak potential separation of 32 mV at pH 5.9. Both reflectance FT‐IR spectra and the dependence of the reduction peak current on the scan rate revealed that Ct adsorbed onto the SWNT surfaces. The redox wave corresponds to the Fe(III)/Fe(II) redox center of the heme group of the Ct adsorbate. Compared to other types of carbonaceous electrode materials (e.g., graphite and carbon soot), the electron transfer rate of Ct redox reaction was greatly enhanced at the SWNT‐modified electrode. The peak current was found to increase linearly with the Ct concentration in the range of 8×10^?6–8×10^?5 M used for the electrode preparation and the peak potential was shown to be pH dependent. The catalytic activity of Ct adsorbates at the SWNTs appears to be retained, as the addition of H₂O₂ produced a characteristic catalytic redox wave. This work demonstrates that direct electrochemistry of redox‐active biomacromolecules such as metalloenzymes can be improved through the use of carbon nanotubes.     

Electrochemical characterization of anodic biofilms enriched with glucose and acetate in single-chamber microbial fuel cells

This study used a simple and efficient electrochemical technique, cyclic voltammogram (CV), to quantitatively measure the electron transfer capability of anodic biofilms enriched with acetate and glucose in single-chamber microbial fuel cells (MFCs). Two pairs of distinct redox peaks were observed by CV measurements in both biofilms, identical to the CV features of a pure Geobacter strain. The CVs also revealed a higher density of electroactive species in the acetate-enriched biofilm than that in the glucose-enriched biofilm. Based on the scan rate analysis, the apparent electron transfer rate constants (k(app)) in the acetate-enriched biofilm and glucose-enriched biofilm were determined to be 0.82 and 0.15s(-1), respectively, which supported the higher power output of the MFC fed with acetate. Meanwhile, the pH dependence of the biofilms was studied by monitoring the changes of the biofilm redox peak currents and potentials. It is concluded that redox reaction of the electrochemical active species in biofilms is pH dependent, and both electrons and protons are involved in the redox reactions.     

纳米氧化亚铜的制备及其电化学性质

研究了纳米氧化亚铜的软模板制备法,并用XRD和TEM对所制备的纳米氧化亚铜进行了表征.试验表明,利用十六烷基三甲基溴化胺为软模板制备的纳米氧化亚铜呈直径为10 nm左右,长度为250 nm左右的纳米晶须.利用Nafion将新制备的纳米氧化亚铜固定在玻碳电极表面,研究了纳米氧化亚铜的电化学性质.结果表明,纳米氧化亚铜在电极表面表现出一对对称性良好的氧化还原峰,对应于纳米氧化亚铜中心的Cu(Ⅱ)/Cu(Ⅰ)的氧化还原,峰电流随扫描速度的增大呈现线性关系,根据峰电位与扫速对数的线性关系,计算出了电子转移系数.表明纳米氧化亚铜在电极表面的反应是受表面控制的部分不可逆过程.     

Electron transfer of heme proteins on the ITO electrode in polymer solvents

The redox reaction of poly(ethylene oxide) (PEO)-modified hemoglobin (PEO–Hb) was analyzed in PEO oligomers with cyclic voltammetry. The PEO–Hb was made soluble in PEO with molecular weight of 200 (PEO₂₀₀) containing 0.5 M KCI. Quasi-reversible redox signals of PEO–Hb were obtained by using an indium tin oxide (ITO) glass working electrode. PEO–Hb, cast on the ITO electrode, also showed the redox response in PEO with molecular weight of 400 (PEO₄₀₀). The peak current of PEO–Hb on the ITO electrode gradually increased during potential cycling. The effect of the scan rate on the quantity of electricity (Q) was analyzed after the peak current reached a constant value. The constant Q value was observed at the scan rate ranging from 30 to 500 mV/sec. The number of reactive PEO–Hb molecules was estimated from this constant Q-value. It was suggested that the electron transfer was carried out at the first layer of the PEO–Hb which was in direct contact with the ITO electrode. The quantity of electricity of PEO–Hb increased when the ITO electrode was first washed in an aqueous medium with ultrasonicator. This strongly suggested that the more effective surface area of the ITO electrode turned to be covered with PEO–Hb when the microporous region of the ITO particles was more hydrated.     

Electrochemical Response of Polyaniline (PANI)/Thiokol Rubber (TR) Films in Cysteine Solution

The electrochemical character of polyaniline/thiokol rubber (PANI/TR) composite film on a Pt electrode was investigated in a cysteine sulphuric acid solution by cyclic voltammetry (CV) and electrochemical impedance spectroscopy (EIS). The significant change of the peak current and peak potential in the cyclic voltammograms was observed. The irreversible peaks of cyclic voltammetry for cysteine/cystine redox couple at a platinum electrode have turned into one pair of nearly reversible peaks at the above electrode; the reversibility of the redox couple has been greatly improved. We found that thiokol rubber could improve the electrocatalysis of the PANI film to the electrochemical reaction with S‐S bonds, as well as the adhesion of the PANI film to the Pt substrate. Several effective factors, such as the concentration of thiokol rubber in the nonaqueous electrodeposition solution, different potential scan rate, immersing time of the film electrode in the studied electrolyte were all taken into account.     

Cyclic voltammetric studies of the redox behavior of iron(III)-vitamin B6 complex at carbon paste electrode

Electrochemical redox behavior of Fe-vit B₆ complex is investigated in HEPES buffer in the pH range 5.1–13.1 using cyclic voltammetry. Well-defined anodic and cathodic peaks are observed in the voltammograms at pH 13.1. At pH 8.0, only one cathodic peak and at pH 5.1, only one anodic peak are found. At all the pH values, the peak potential separation is much higher than that of a reversible electrochemical reaction. The peak current ratio (i _pa/i _pc) is less than unity and decreases with the scan rate. Published in Russian in Elektrokhimiya, 2006, Vol. 42, No. 6, pp. 691–697. The text was submitted by the authors in English.     

Electrochemical Study of Catechol in the Presence of Dibuthylamine and Diethylamine in Aqueous Media: Part 1. Electrochemical Investigation

Electrochemical oxidation of catechol has been studied in the presence of secondary amines as nucleophiles in aqueous solution with various pH values using cyclic voltammetry and differential pulse voltammetry. Cyclic voltammetry of catechol in pure buffered solution (2.00 pH<9.00) shows one anodic and corresponding cathodic peak which relates to the transformation of catechol to corresponding o‐benzoquinone and vice versa within a quasi‐reversible two electron transfer process. Also, a little amount of o‐benzoquinone undergoes polymerization reaction. Cyclic voltammogram of catechol in the presence of nucleophilic amines, show one anodic peak in the first scan of potential but on the reverse scan the corresponding cathodic peak disappear and new peak is observed at less positive potential. In the second scan of potential also a new anodic peak is observed. On the other hand at high concentration of amines the redox peak attributable to formed polymer disappear showing that in this condition the polymerization reaction occurs at non‐measurable extent. On the basis of these observations we propose an ECE mechanism for the electrochemical oxidation of catechol in the presence of secondary amines.     

Electrocatalytic Oxidation of Paracetamol on Ni and NiCu Alloy Modified Glassy Carbon Electrode

In this study we investigated the electrocatalytic oxidation of anti‐inflammatory drug (paracetamol) on Nickel and Nickel–copper alloy modified glassy carbon electrodes (GC/Ni and GC/NiCu) in alkaline solution. These electrodes prepared by galvanostatic method and different electrochemical techniques such as cyclic voltammetry and chronoamperometry were used to track the oxidation process and its kinetics. From Voltammetric studies we concluded that in the presence of drugs the anodic peak current of low valences Nickel species increased, followed by a decrease in the corresponding cathodic current peak. This indicates that drugs were oxidized on the redox mediator which was immobilized on the electrode surface via an electrocatalytic mechanism. Using Laviron's equation, the values of α and k_s for the immobilized redox species were determined. The anodic peak currents show linear dependency with the square root of scan rate. This behavior is the characteristic of a diffusion controlled process. Under the CA regime the reaction followed a Cottrellian behavior and the diffusion coefficient of paracetamol was found in agreement with the values obtained from CV measurements.     

Synthesis of new binuclear ferrocenyl compounds by hydrosilylation reactions

Ferrocenyl silanes are prepared by treatment of Grignard reagents produced from 4-chlorobutylferrocene derivatives and chlorodimethylsilane in THF. Butenylferrocenes are prepared by the elimination reaction of 4-chlorobutylalkylferrocenes by sodium tert-butoxide in DMSO. A hydrosilylation reaction between a butenyl compound and ferrocenylsilane occurred in dry toluene at room temperature in the presence of the Karstedt catalyst to produce the desired binuclear ferrocenyl compound in good to high yields. The electrochemical behavior of new ferrocenyl compounds were studied by cyclic voltammetry in CH₃CN/0.1 M LiClO₄, and the relation between the peak currents and the square root of the scan rate, showed that the redox process is diffusion-limited.     

铁氰化镧修饰电极的制备及表征

An electroactive polynuclear inorganic compound of rare earth metal hexacyanoferrate, lanthanum hexacyanoferrate (LaHCF), was prepared by electrochemical deposition on the surface of a glassy carbon electrode with a potential cycling procedure. The cyclic voltammogram of LaHCF exhibits a pair of well-defined redox peaks with the formal potential of 208 mV (vs. SCE) at a scan rate of 100 mV/s in 0.2 mol/L NaCl solution and the redox peak currents increase linearly with the square root of the scan rate up to 1000 mV/s. The effects of the concentration of supporting electrolyte on the electrochemical characteristics of LaHCF were studied by voltammetry. LaHCF was also characterizated by scanning electron microscope (SEM), FTIR and XPS techniques.     

The Solid State Electrochemistry of Dysprosium(III) Hexacyanoferrate(II)

A new electroactive polynuclear inorganic compound of rare earth metal hexacyanoferrate, dysprosium hexacyanoferrate (DyHCF), was prepared chemically and characterized using techniques of FTIR spectroscopy, thermogravimetric analysis (TGA), UV‐vis spectrometry and X‐ray photoelectron spectroscopy (XPS) etc. The cyclic voltammetric behavior of DyHCF mechanically attached to the surface of graphite electrode was well defined and exhibited a pair of redox peaks with the formal potential of 217 mV (vs. SCE) at a scan rate of 100 mV/s in 0.2 M NaCl solution and the redox peak currents increased linearly with the square root of the scan rates.     

Cylic Voltammetric Studies on the Electrode Reaction of Polyacetylene Secondary Cell

Cells of lithium / Polyacetylene containing 0.5 · 1.5 M LiClO₄ in propylene carbonate as supporting electrolyte are constructed. The mechanism for electrochemical redox process of polyacetylene is studied using cyclic voltammetry in the potential range from ?0.8 to 0.2 volt vs. S.C.E. The electrode reactions are identified to be diffusion controlled. The difference of the peak potentials between the oxidation and reduction, ΔEp, is found to be a function of the scan time per cycle (τ sec/cycle) and is influenced by concentration of supporting electrolyte and isomeric structures of polyacetylene. However, there is a better reversible redox process of polyacetylene when the ClO₄^? - ions diffuse successfully in and out of the Polymer film, which has the cis-form structure, in concentrated supporting electrolyte solution and having a long scan time per cycle (τ). When the scan potential is extended to a more positive region, another peak is found, which may correspond to the irreversible chemical reaction caused by over-doping. The over-doping process is found to be controlled by the electrical field strength, concentration of the supporting electrolyte and isomerism of polyacetylene.     

氯过氧化物酶修饰电极对一氯二甲酮的催化氯化

通过将氯过氧化物酶溶液(Chloroperoxidase, CPO)与Nafion分散的单壁碳纳米管分散液混合后直接滴涂到玻碳电极表面制得修饰电极. 这个固定了氯过氧化物酶的碳纳米管修饰玻碳电极, 在pH=5.0的磷酸缓冲溶液中测得的循环伏安曲线上有一对准可逆的氧化还原电流峰, 经过与裸电极和没有固定氯过氧化物酶的碳纳米管修饰电极上测得的循环伏安行为对比后确认, 碳纳米管对氯过氧化物酶与电极之间的电子传递反应具有很好的促进作用. 利用该修饰电极能催化一氯二甲酮氯化为二氯二甲酮, 无需添加过氧化氢作为反应启动剂, 紫外光谱的测试结果表明, 每摩尔氯过氧化物酶可催化氯化4.0×105 mol 的一氯二甲酮, 表现出很高的催化效率.     

AOT/Triton X-100混合反胶束体系的导电性能

采用聚乙二醇辛基苯基醚(TritonX-100)和二(2-乙基己基)琥珀酸磺酸钠(AOT)双表面活性剂,与正己烷、正己醇和水构成混合反胶束体系;研究了表面活性剂质量比、助表面活性剂含量、水油体积比和温度等因素对反胶束体系导电性能的影响,同时采用循环伏安法研究了K3Fe(CN)6/K4Fe(CN)6在该体系中的电化学行为.结果表明:由两种表面活性剂构成的反胶束体系电导率σ明显大于单一表面活性剂反胶束体系电导率;体系电导率随AOT与TritonX-100的质量比w(w=mAOT∶mTritonX-100)的变化而变化,w为0-0.4时,电导率随w增大而线性增大,之后增加趋势变缓;w=0.96时,σ达到稳定值576μS·cm-1.混合体系电导率随溶水量的增大及温度的上升而提高;而增加助表面活性剂可显著降低体系的电导率.在所研究体系中,Fe(CN)36-/Fe(CN)46-电化学反应对的氧化还原峰电位几乎不随扫描速率变化,峰电位差约为75mV,峰电流的比值约为1,氧化峰电流与扫描速率的平方根成正比,说明K3Fe(CN)6/K4Fe(CN)6在混合反胶束体系中显示出良好的氧化还原可逆性,反应由扩散步骤控制.     

聚苯胺颗粒电极的制备与其电化学行为

采用循环伏安法,以含苯胺(An)的硫酸溶液为电解质,采用循环伏安技术在Pt微盘电极上得到随机、不连续沉积的聚苯胺(PAn)微颗粒和PAn膜.实验结果表明:H2SO4浓度、苯胺浓度、电位扫描上限和扫速对电化学合成随机、不连续沉积的PAn微颗粒具有重要影响.不连续随机沉积的PAn微颗粒电极与PAn膜电极在锂离子(Li-ion)电池电解质溶液中的行为有明显差异,不连续随机沉积的PAn微颗粒电极可以清楚地得到氧化还原电流峰,而PAn膜电极无法形成清晰的氧化还原电流峰.采用较缓慢扫描速度更有利于形成良好"结晶"的不连续PAn颗粒电极,该种电极可以同时具有高比能量和可逆性能.     

Enhancement of electron transfer kinetics on a polyaniline-modified electrode in the presence of anionic dopants

The electrocatalytic redox behavior of 1,4-naphthoquinone (NQ) has been studied on a polyaniline-modified platinum electrode (PANI) using cyclic voltammetry and rotating disc electrode (RDE) as diagnostic techniques. The modified electrode was prepared by electropolymerization of aniline in different acidic solutions. The PANI showed electrocatalytic activity toward the redox behavior of NQ. This process includes the participation of PANI to the redox reaction of NQ via the surface catalysis phenomena. The cyclic voltammograms of NQ in HCl on the PANI-Cl-modified electrode showed an overlapped oxidation peak, the peak potential of which did not change with increasing scan rate. The influence of other anions including and as dopant was also studied and compared with Cl⁻. The use of HClO₄ as a supporting electrolyte resulted in well-separated redox peaks. The RDE voltammogram was used to obtain a quantitative assessment of reaction rate at the PANI-modified electrode. It was found that PANI acts as an electrocatalyst for NQ reduction with decreasing ΔE _p and increasing k°.