Redox properties of [Fe2(SC6H5)2(NO)4]: an experimental study and quantum chemical modeling

Reduction of the complex [Fe₂(SC₆H₅)₂(NO)₄] in an aprotic solvent was studied by cyclic voltammetry in a wide range of potential scan rates. It was established that transfer of the first electron is reversible and the redox potential of this reaction was determined. Further reduction of the complex is irreversible because the product of attachment of the second electron is unstable and partially decomposes during the characteristic time of potential scan. The molecular and electronic structures of mono- and dianion of the complex as well as its theoretical redox potential value were calculated using the density functional theory methods with the local (BP86) and hybrid (B3LYP) functionals. The former functional better describes the geometry of the complex while the latter gives a better insight into its electronic structure. The extra negative charge is delocalized over NO groups, phenyl ligands, and iron atoms. The calculated redox potentials of one-electron reduction of the complexes are close to the experimental values obtained by analyzing cyclic voltammograms. Attachment of the second electron opens the decomposition channel of the complex, which is also consistent with experimental data.     

Electron transfer of horse spleen ferritin at gold electrodes modified by self-assembled monolayers

Electron transfer is known to be an important step in the sequestering of iron by cellular ferritin. In this work, direct electron transfer between ferritin and a gold electrode was performed in order to probe its electron transfer kinetics. Gold electrodes were modified by the formation of self-assembled monolayers of 3-mercapto-propionic acid on the gold surface. Cyclic voltammetry using these electrodes shows that ferritin exhibits slow electron transfer kinetics at low potentials, yet fairly well-defined current—potential curves. In addition, the voltammetry indicates that adsorption of ferritin precedes the electron transfer step. Controlled potential electrolysis measurements yielded an n-value of 1910 electrons transferred per mole of ferritin. Cyclic voltammetry of a solution containing ferritin as well as nitrilotriacetate yields no electrolytic currents at potentials where the iron—nitrilotriacetate complex undergoes redox reactions, indicating that the currents observed in the voltammetry of ferritin were not due to free iron in the ferritin sample. In addition, the voltammetry of iron-free ferritin (apoferritin) did not yield appreciable currents, providing additional support to the suggestion that the observed voltammetric currents were due to the redox reactions of ferritin iron. Self-assembled monolayers containing carboxylate end groups effectively promoted the direct electron transfer of ferritin at a gold electrode, thus demonstrating that the electron transfer mechanisms of ferritin can now be probed electrochemically.     

Electrochemical Characterization of Polymerized Cresol Red Film Modified Glassy Carbon Electrode and Separation of Electrocatalytic Responses for Ascorbic Acid and Dopamine Oxidation

A cresol red modified glassy carbon electrode was prepared using an electrochemical method. The cyclic voltammograms of the modified electrode indicate the presence of a couple of well-defined redox peaks, and the formal potential shifts in the negative direction with increasing solution pH. The modified electrode exhibits high electrocatalytic activity toward ascorbic acid oxidation, with an overpotential of 300 mV less than that of bare glassy carbon electrodes, and drastic enhancement of the anodic currents. The calibration graph obtained by linear sweep voltammetry for ascorbic acid is linear in the range of 50∼500 µM. The electrode markedly enhances the current response of dopamine and can separate the electrochemical responses of ascorbic acid and dopamine. The separation between the anodic peak potentials of ascorbic acid and dopamine is 190 mV by cyclic voltammetry. The linear sweep voltammetric peak currents for dopamine in the presence of 2 mM ascorbic acid vary linearly with a concentration of between 10 and 100 µM.     

硫化亚铁阴极的电极过程机理

应用循环伏安法研究了硫化亚铁阴极的电极过程机理 ,电极反应过程伴随着难溶硫化亚铁的形成与溶解 ,该电极过程受欧姆电阻控制 .根据循环伏安曲线峰电流和峰电位与扫描速度平方根成线性关系 ,提出了电极过程的欧姆电阻控制模型 ,导出峰电位和峰电流与扫描速度之间的关系式 ,理论分析与实验结果一致 .     

聚邻甲苯胺的合成及物理化学性质

聚苯胺的导电性和电化学特性已被广泛地研究。最近,对苯胺衍生物的聚合物也开始了研究,如聚邻甲氧基苯胺、聚邻苯二胺和聚邻氨基酚,其中聚邻甲氧基苯胺是一种可溶性的导电高分子材料。为了探讨苯胺聚合的机理和苯胺上不同基团对聚苯胺性质的影响,我们使用了十六种苯     

Cyclic voltammetry at microstructured electrodes

We present the theoretical treatment of cyclic voltammograms at microstructured electrodes. Calculations of voltammograms permit the determination of electrochemical parameters of redox systems in a single cell in parallel with the determinations of the spectroscopic parameters. The structural parameters of the electrode can be determined using the theoretical treatment presented if the electrochemical parameters of the redox system are known. Furthermore, lithographic-galvanic (LIGA) structures can be used as a model for microporous electrodes. Regression analysis was used to compare experimental and calculated cyclic voltammograms as well as to determine the electrochemical and spectroscopic parameters. A modified Randles-Sevčik equation has been derived to described the peak current dependence of cyclic voltammograms at micro-structured electrodes for both reversible and quasi-reversible charge transfer.     

Electrochemical properties of composite materials based on platinum modified with molybdenum compounds

The composite coating Pt-MoOx is produced by an electrochemical technique under potentiodynamic conditions on the surface of a preliminarily prepared electrode of glassy carbon. The inclusion of molybdenum into the composition of the obtained electrode deposit is confirmed by the data of cyclic voltammetry and the secondary-electron emission spectra. In the cyclic voltammograms that are obtained in a 2 M solution of sulfuric acid one can distinguish a pair of peaks at potentials equal to 0.46 V (anodic run) and 0.3 V (cathodic run), which are connected with the redox transitions experienced by molybdenum compounds. It is discovered that the obtained deposit possesses catalytic properties with respect to the oxygen reduction reaction. The number of electrons that are corresponding to the redox transitions experienced by molybdenum compounds is calculated. It amounts to 0.27 electrons per molybdenum atom.     

Voltammetric studies of the activity of an electrode made of a graphite-epoxy composite in redox reactions of ascorbic acid and hydroquinone

The potentials of the anodic peak of ascorbic acid oxidation and the potential differences of anodic and cathodic peaks (ΔE _p) of the hydroquinone/benzoquinone redox system at an electrode made of a graphite-epoxy composite are determined in weakly acidic and neutral supporting electrolytes by direct and cyclic voltammetry. The results obtained are compared with thermodynamic values and with the available values of these parameters at different solid electrodes for the above-mentioned redox systems. The effect of aging of the surface of electrodes made of graphite-epoxy composites on the potentials and peak currents of the anodic oxidation of ascorbic acid are studied. It is demonstrated that the regeneration of the electrode surface by mechanically cutting thin layers is important for reducing the δE _p value of the hydroquinone/benzoquinone redox system down to 28–30 mV in supporting electrolytes with pH 2.0 and 7.0. This value is typical of thermodynamically reversible electrode reactions involving two-electron transfer at 20–25°C.     

Two-electron-transfer redox systems,part 7: two-step electrochemical oxidation of the boron subhalide cluster dianions B6X 2- 6 (X = Cl,Br, I)

Boron subhalide cluster dianions B6X 2- 6 (X = Cl, Br, I) are electrochemically oxidized in two steps. According to cyclic voltammograms, the first step is chemically reversible and yields the corresponding radical anions B6X .- 6. The electron transfer is nearly diffusion controlled. The second, slower electron-transfer step leads to a species which we assume to be the hitherto not yet described neutral compounds B6X 2- 6. The voltammograms indicate a coupled fast catalytic reaction, producing the radical anions in a reduction by an electrolyte component. Computer simulations of the cyclic voltammograms reveal mechanistic details of the redox reactions, as well as quantitative values for formal potentials, rate constants, and diffusion coefficients. The results are compared to other BnXn redox systems.     

旋转铂盘电极上Cu(phen)22+与6-巯基嘌呤的相互作用

在 Tris-NaCl(pH=7.2)缓冲溶液中,应用循环伏安法、微分脉冲伏安法、 旋转圆盘电极实验、交流阻抗法及其数据模拟等技术研究了Cu(phen)22+（phen=1,10-邻菲咯啉）与6-巯基嘌呤（6-MP）的相互作用.结果显示, Cu(phen)22+与6-MP无论在扩散控制过程或电化学控制过程都发生了相互作用. Cu(phen)22+及其与6-MP的作用产物于铂电极上均呈现一对氧化还原峰,但后者呈现的氧化还原峰负移,峰电流减小，交流阻抗结果显示,无论6-MP存在与否, Cu(phen)22+在交流阻抗谱上均呈现两个清晰的电容弧,但当6-MP存在时,电化学反应电阻和电化学吸脱附电阻均增大. Cu(phen)22+在不同转速下的阻抗拟合结果显示,随转速增大,电化学反应电阻和电化学吸脱附电阻均减小,双电层电容呈增大趋势,而吸脱附电容呈减小趋势;当6-MP存在时,仍然呈现此变化规律.     

Electrochemistry of Tris(1,10-phenanthroline)iron(II) inside a polymeric hydrogel. Coupled chemical reactions and migration effects

The retention, release, and detection of metallic complexes in polymeric hydrogels are of interest in drug delivery, analytical chemistry, and water remediation. The electrochemistry of the redox complexes inside the hydrogel could be affected by the viscoelastic properties of the gel, local ionic force and pH, and interactions (e.g., hydrophobic) between the complex and the polymer chains. In this work, it is shown that a simple setup, consisting of a disk electrode pressed on the hydrogel, allows to perform electrochemistry of a redox couple: Tris(1,10-phenanthroline)iron(II) (Fe(phen)₃ ²⁺) inside a hydrogel matrix. The behavior is compared with the same couple in solution, and it is found that the electrochemical properties of the redox couple are strongly affected by the presence of the hydrogel matrix. The cyclic voltammogram of the hydrogel loaded with complex shows a response, which suggests electrochemical-chemical mechanism. The chemical step is likely linked to a catalytic oxidation of free hydrated Fe²⁺ ions present inside the hydrogel together with the redox complex. Since Fe²⁺ ions have small charge transfer constants on the glassy carbon electrodes, only the catalytic current is observed. Indeed, when excess ligand (phenanthroline) is absorbed inside the hydrogel, the measured cyclic voltammograms show a single reversible oxidation/reduction step. It seems that the complexation equilibrium shifts toward the complex, making the free iron concentration negligible. Accordingly, the cyclic voltammetry shape and peak potential difference agree with a reversible oxidation/reduction. Additionally, the peak currents of the cyclic voltammograms show a linear dependence with the square root of time, as predicted by a Randles-Sevcik equation. However, the measured currents are smaller than the simulated ones. The differences are in agreement with simulations of the cyclic voltammograms where the migration of the redox species is considered. Chronoamperometry is used to measure the mass transport of redox species inside the hydrogel. It is found that the current transients still obey Cottrell’s equation, but the diffusion coefficients obtained from the slopes of Cottrell’s plots have to be corrected for migration effects. The effective diffusion coefficient of Fe(phen)₃ ²⁺ measured inside the hydrogel (D _Red-hydrogel = 5.5 (±0.5) × 10^?8 cm² s^?1) is ca. 80 times smaller than the one measured in solution (D _Red-solution = 4.4 (±0.5) × 10^?6 cm² s^?1). The simple setup has a true semi-infinite boundary condition, which allows characterizing the hydrogel in the same condition as the bulk material and easily changing both the redox species and the hydrogel structure.     

血红素修饰电极及其催化氧还原性质

金属大环络合物（卟啉、酞箐、维生素Ｂ_(１２)等）修饰电极对氧、一氧化氮和其它生物物质的催化作用［１－３］引起了化学工作者的极大兴趣,血红素是一种重要的铁卟啉化合物,是血液中血红蛋白的重要组成部分,承担携氧的任务,由于其特殊的生理功能,研究血红素修饰电极的性质和作用对进一步研究开发燃料电池具有很重大的意义．卟啉在电极上的修饰有多种方法,当卟啉或金属卟啉环侧链上具有苯氨基、苯酚基、乙烯基或吡咯等取代基时［３］,可采用电氧化聚合法制备聚卟啉膜．本文采用循环伏安法在水溶液中制备了聚血红素膜电极,研究了聚…     

旋转铂盘电极上Cu(phen)_2~(2 )与6-巯基嘌呤的相互作用

在Tris-NaC1*(pH=7.2)缓冲溶液中,应用循环伏安法,微分脉冲伏安法、旋转圆盘电极实验、交流阻抗法及其数据模拟等技术研究了Cu(phen)2 25(phcn=1.10-邻菲咯啉)与6-巯基嘌呤(6-MP)的相互作用.结果显示.Cu(phen)2 2MP与6-MP无论在扩散控制过程或电化学控制过程都发生了相互作用.Cu(phen)2 2及其与6-MP的作用产物于铂电极上均呈现一对氧化还原峰,但后者呈现的氧化还原峰负移.峰电流减小.交流阻抗结果显示,无论6-MP存在与否,Cu(phen)2 2在交流阻抗谱上均呈现两个清晰的电容弧,但当6-MP存在时,电化学反应电阻和电化学吸脱附电阻均增大.Cu(phen)2 2在不同转速下的阻抗拟合结果显示.随转速增大.电化学反应电阻和电化学吸脱附电阻均减小.双电层电容呈增大趋势,而吸脱附电容呈减小趋势:当6-MP存在时.仍然呈现此变化规律.     

Electroactive self-assembled biferrocenyl alkanethiol monolayers on Au(111) surface and on gold nanoclusters

The spectroscopic and electrochemical characterizations of electrochemically stable biferrocene-modified Au clusters and chemisorbed biferrocenylalkanethiols on Au(111) surface were studied. The characterizations of biferrocene-modified Au cluster using TEM, UV-vis, and NMR techniques are also reported. Two successive reversible one-electron redox waves were observed for the biferrocenylalkanethiol Au nanoclusters and biferrocenylalkanethiol monolayers on Au(111) surface in the cyclic voltammetry. Furthermore, the positive and negative current peaks for each redox wave occur at almost the same potential, and the peak current increases almost linearly with the sweep rate. Repeat scanning does not change the voltammograms, demonstrating that these monolayers are stable to electrochemical cycling. The coverages of electroactive biferrocene in the monolayers were calculated from the cyclic voltammograms. The standard electron-transfer rate constant was calculated from the splitting between the oxidation and reduction peaks.     

Electrochemical behaviour of poly(3,4-ethylenedioxythiophene) in a room-temperature ionic liquid

The cyclic voltammetry responses and the redox switching dynamics of poly(3,4-ethylenedioxythiophene) (PEDOT) in a room-temperature ionic liquid, 1-ethyl-3-methylimidazolium bis((trifluoromethyl)sulfonyl)amide (EMImTf₂N), were investigated. The shape of the cyclic voltammograms showed two anodic and two cathodic peaks. These peak currents varied linearly with the scan rate indicating a thin-layer behaviour. No memory effects were observed during the cyclic voltammetry experiments in this ionic liquid. On the other hand, the redox switching dynamics of PEDOT were studied by means of potential step experiments. The analysis of chronocoulograms in term of RC-circuits indicated that the time dependence of the charge transferred during the potential step showed two time constants. These results were consistent with the postulated structure or morphology of the PEDOT film which contained two types of coexisting zones: a compact and an open structures.     

Synthesis of crowded triarylphosphines carrying functional sites

4,4′-Diphosphinobiaryls and 1,3- and 1,4-borylphosphinobenzenes carrying crowded triarylphosphine moieties were synthesized by reaction of the corresponding diarylchlorophosphine with an arylcopper(I) reagent. Intramolecular interaction of the phosphorus redox center with the other phosphorus or the boron redox center was investigated by cyclic voltammetry. 4,4′-Diphosphinobiaryls displayed two-step reversible redox waves with slight differences of the oxidation potentials due to weak interaction between two phosphorus redox centers across 4,4′-biarylene linkage. Borylphosphinobenzenes showed two step redox waves corresponding to oxidation at the phosphorus and reduction at the boron. Although significant interaction between the phosphorus and boron redox centers was not observed in the cyclic voltammograms due to large difference of the redox potentials between phosphorus and boron redox centers, an absorption due to weakly interacting phosphorus and boron was observed in the UV-Vis spectrum of the 1,4-borylphosphinobenzene.     

甲醛在脯氨酸膜修饰电极上的电催化氧化

应用电化学法和光谱电化学法研究了脯氨酸膜修饰电极的制备 ,用循环伏安法探讨了该膜的电化学性质及其对甲醛的催化氧化 .该电极催化稳定性良好 ,在NaOH溶液中 ,掺杂Ni (Ⅱ )后的脯氨酸膜修饰电极对甲醛和乙醇的氧化均有一定的催化活性 ,但对甲醛的催化活性更佳     

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.     

Electrochemical investigations of oligomers and polymers containing ruthenium- and iron-arene complexes

Cyclic voltammetry was employed to investigate the electrochemical behavior of numerous cyclopentadienyliron (CpFe⁺) and pentamethyl-cyclopentadienylruthenium (Cp*Ru⁺) coordinated oligomers and polymers. The electrochemical behavior of the iron systems indicated the cyclopentadienyliron complexes had isolated redox centers and that changes in the reversibility of the redox couple occurred with changes in solvent and temperature. In contrast, the monometallic ruthenium systems showed large peak separations that suggested slow kinetics on the CV timescale. The cyclic voltammograms of the larger ruthenium-containing oligomers and polymers showed multiple redox steps indicating complex electrochemical behavior.