Electrochemical properties of a ruthenium complex immobilized as thin films and in carbon paste electrodes

The electrochemical properties of mer-[RuCl₃(dppb)(4-pic)] (dppb = Ph₂P(CH₂)₄PPh₂, 4-pic = CH₃C₅H₄N), Rupic, in CHCl₃ are governed by the formation of species such as [Ru₂Cl₅(dppb)₂], [Ru₂(dppb)₂Cl₄(4-pic)] and trans-[RuCl₂(dppb)(4-pic)₂] upon the reduction of “[RuCl₂(dppb)]”. The overall behavior depends on whether Rupic is immobilized in cast or Langmuir–Blodgett (LB) films, or incorporated into a carbon paste electrode (CPE). In cyclic voltammograms, one redox process appears for LB/Rupic films and CPE/Rupic, at E_pa = 0.35 V, E_pc = 0.25 V vs SCE, and E_pa = 0.32 V, E_pc = 0.24 V vs Ag/AgCl, respectively. This redox process was ascribed to the Ru^III/Ru^II charge transfer. For cast films the redox pair was poorly defined, with E_pa = 0.27 V and E_pc = 0.20 V. The reason for the difference lies in the phase separation and formation of aggregates onto ITO for the cast film, in contrast to the LB film. With aggregation, the formation of species occurring in solution is impaired for Rupic in cast films. The electrochemical properties for Rupic in LB films and incorporated into CPE allowed the electrocatalytic activity of Rupic to be exploited in sensors for dopamine and ascorbic acid.     

苝红化合物氧化还原反应的研究

苝红化合物作为一种新型功能性染料,由于吸收光能在可见范围,且性能稳定,在光导液晶及太阳能电池等方面已得到了应用^[1].     

Evaluation of an amperometric glucose biosensor based on a ruthenium complex mediator of low redox potential

An amperometric glucose ring-disk biosensor based on a ruthenium complex mediator of low redox potential was fabricated and evaluated. This thin-layer radial flow microsensor (10 μl) with ring-disk working electrode displayed remarkable amperometric sensitivity. For Ru₃(μ₃-O)(AcO)₆(Py)₃(ClO₄) (Ru-Py), a trinuclear oxo-acetate bridged cluster, a reversible redox curve of low redox potential and narrow potential window (redox potentials were −0.190 and −0.106 V versus Ag/AgCl wire, respectively) was observed, which is comparable to many reported mediators such as ferrocene derivatives and other ruthenium complexes. The glucose and hydrogen peroxide assays were carried out with this complex-modified electrode Ru-Py-HRP-GOx/Nafion. The sensitivity was obtained 24 nA (15.4 mA M⁻¹ cm⁻²) for 10 μM glucose and 126 nA (160 mA M⁻¹ cm⁻²) for 5 μM H₂O₂, respectively with a working potential at 0 V versus Ag/AgCl. Ascorbic acid was studied as interference to the glucose assay. The application of 0 V potential versus Ag/AgCl did not avoid the occurrence of the oxidation of ascorbic acid, however, the pre-coating of ascorbate oxidase on the disk part of the ring-disk working electrode efficiently pre-oxidized the ascorbic acid and hence eliminated its interference on the glucose response. The practical reliability was also evaluated by assaying the dialysate from the prefrontal cortex of Wistar rats.     

铋(Ⅲ)-8-羟基喹啉-5-磺酸的吸附伏安法研究

探讨了8-羟基喹啉-5-磺酸(HQSA)和络合物Bi(Ⅲ)-HQSA的电化学性质,特别是它们在汞电极上的吸附性。在pH=7.0的磷酸盐底液中,Bi(Ⅲ)-HQSA有一灵敏还原峰,为反应物弱吸附,E_pc=-0.44V(vs.饱和Ag/AgCl)。据此建立了吸附伏安法测定铋的新方法,检测限为2.0×10^-9mol/L,线性范围5.0×10^-9～1.0×10^-6mol/L。     

Redox characteristics of Schiff base manganese and cobalt complexes related to water-oxidizing complex of photosynthesis

In an effort to obtain synthetic analogues of water-oxidizing complex (WOC) of photosystem II (PS II) of plant photosynthesis, a Schiff base manganese and a cobalt complex, employing Niten, a SALEN type ligand, have been prepared. Cyclic and square wave voltammetric measurements have been performed to assess their redox characteristics. Both complexes undergo several reduction processes in cathodic negative potential region at more or less similar potentials. In view of these reductions being independent of the nature of the metal, they are thought to be ligand-localized. Although similar in negative region, a marked difference in the behavior of the complexes is observed in anodic region. While the cobalt complex is electrochemically inactive in the positive potentials up to +1.0 V vs. Ag/AgCl, the manganese complex displays two oxidation waves at +0.25 and +0.5 V vs. Ag/AgCl. The presence of oxidation wave in manganese complex at +0.5 V vs. Ag/AgCl or +0.7 V vs. NHE suggests that this complex can catalyze the oxidation of water and can, thus, simulate the WOC of PS II.     

Determination of Amino Acids by Ru(bpy)_3~(2+) Cathodic Electrochemiluminescence with High Sensitivity

The unique cathodic electrochemiluminescence(ECL) emission of Ru(bpy)32+(bpy=2,2′-bipyridine) was observed via Nafion film at Au electrode[Au/Nafion/Ru(bpy)32+] at about 0.20 V(vs. Ag/AgCl) and applied to the determination of several amino acids without prior derivatization with high sensitivity. The cathodic electrochemilumi-nescence(ECL) exhibits the detection limits and linear ranges of several amino acids comparable to or better than those of capillary electrophoresis with conventional ECL detection method(at 1.10—1.20 V vs. Ag/AgCl) based on precolumn derivatization. The results suggest that the cathodic ECL is promising for the detection of amino acids in bioanalysis.     

盘状多酸P_5W_(30)/阳离子聚电解质/氧化石墨烯杂化多层膜的电致变色性能

为了提高薄膜[PEI/P_5W_(30)]_(30)的电致变色性能,将具有大的二维尺寸和良好导电性的氧化石墨烯引入该薄膜中。通过层层自组装(LBL)技术构筑了基于盘状多酸K12.5Nal.5[Na P_5W_(30)O_(110)]·15H_2O(P_5W_(30))、氧化石墨烯(GO)的复合薄膜[PEI/P_5W_(30)/PEI/GO]_(30)(PEI:聚乙烯亚胺),并利用UV-Vis光谱对薄膜的组成及增长进行监测;通过原子力显微镜对薄膜的表面形貌进行考察,利用循环伏安法对薄膜电化学氧化还原性质进行研究;薄膜在外加氧化还原电位下呈现出无色/蓝色的可逆变化,电致变色响应时间在10 s以内;此外,薄膜在阶跃电位0.75 V/-0.75 V下循环150次,电致变色性能没有明显减弱,体现了薄膜良好的电致变色可逆性。氧化石墨烯的引入使薄膜[PEI/P_5W_(30)/PEI/GO]_(30)呈现出响应速度快、抗电疲劳强的电致变色性能,将在电致变色器件领域有广阔的应用前景。     

三种食用色素的电化学行为的理论计算与验证

用量子理论计算柠檬黄、日落黄、胭脂红的相对焓（Hm）、相对熵（Sm）,计算柠檬黄、日落黄、胭脂红的还原电位分别为-0．969,-0．901,-0．854V（vs．Ag／AgCl／Cl）。探讨了琼脂对色素的电催化机理,采用循环伏安法在玻碳琼脂电极上研究了食用色素柠檬黄、日落黄、胭脂红的电化学行为,分别于-1．064,-0．910,-0．882V（vs．Ag／AgCl／Cl）产生还原峰,理论预测与试验结果基本一致。     

Preparation,Characterization, Luminescent and Electrochemical Properties of Ru(bpy)2-functionalized Silica Nanoparticles

Ru(II)-complex functionalized silica nanoparticles(nano-SiO₂) were prepared via a coordination reaction of cis-dichlorobis(2,2'-bipyridine)ruthenium[Ru(bpy)₂Cl₂] complex with poly(4-vinylpyridine)(P4VP)-modified nano-SiO₂ particles. Both the Ru-complex and the functionalized nano-SiO₂P4VP-Ru(bpy) hybrids were doped in poly(methyl methacrylate)(PMMA) to form optically transparent thin films. The composition and spectroscopic properties of the nano-SiO₂P4VP-Ru(bpy) hybrids were evaluated with the help of thermogravimetric and elemental analysis, and UV-Vis absorption spectroscopy, infrared spectroscopy, X-ray photoelectron spectroscopy, and fluorescence spectroscopy. Microscopy images revealed that the nanohybrids were approximately 12 nm in diameter and readily formed aggregates following the functionalization with P4VP and Ru(bpy)₂Cl₂. The as-prepared nano-SiO₂P4VP-Ru(bpy) hybrids produced emissions at approximately 604 and 654 nm under radiation both in solution and in doped thin films. Finally, cyclic voltammetry studies on the nanohybrid-modified electrode revealed a redox couple with the cathodic and anodic potentials at approximately 0.28 and 0.73 V(vs. Ag/AgCl), attributed to the one electron transfer of Ru(bpy)₂^2+/3+ immobilized on the nano-SiO₂ particles.     

Physicochemical and photophysical studies on porphyrin-based donor-acceptor systems: effect of redox potentials on ultrafast electron-transfer dynamics

We report new polychromophoric complexes, where different porphyrin (P) derivatives are covalently coupled to a redox active Mo center, MoL*(NO)Cl(X) (L* is the face-capping tridentate ligand tris(3,5-dimethylpyrazolyl) hydroborate and X is a phenoxide/pyridyl/amido derivative of porphyrin). The luminescence quantum yields of the bichromophoric systems (1, 2, and 5) were found to be an order of magnitude less than those of their respective porphyrin precursors. Transient absorption measurements revealed the formation of the porphyrin radical cation species (P(.)(+)) and photoinduced electron transfer from the porphyrin moiety to the respective Mo center in 1, 2, and 5. Electrochemical studies showed that the reduction potentials of the acceptor Mo centers in a newly synthesized pyridyl derivative (2; E(1/2)[Mo(I/0)] = approximately -1.4 V vs Ag/AgCl) and previously reported phenoxy- (1; E(1/2)[Mo(II/I)] = approximately -0.3 V vs Ag/AgCl) and amido- (3; E(1/2)[Mo(II/I)] = approximately -0.82 V vs Ag/AgCl) derivatives were varied over a wide range. Thus, studies with these complexes permitted us to correlate the probable effect of this potential gradient on the electron-transfer dynamics. Time-resolved absorption studies, following excitation at the Soret band of the porphyrin fragment in complexes 1, 2, and 5, established that forward electron transfer took place biexponentially from both S2 and S1 states of the porphyrin center to the Mo moiety with time constants 150-250 fs and 8-20 ps, respectively. In the case of MoL*(NO)ClX (where X is pyridine derivative 2), the high reduction potential for the MoI/0 couple allowed electron transfer solely from the S2 state of the porphyrin center. Time constants for the charge recombination process for all complexes were found to be 150-300 ps. Further, electrochemical and EPR studies with the trichromophoric complexes (3 and 4) revealed that the orthogonal orientation of the peripheral phenoxy/pyridyl rings negated the possibility of any electronic interaction between two paramagnetic Mo centers in the ground state and thereby the spin exchange, which otherwise was observed for related Mo complexes when two Mo centers are separated by a polyene system with comparable or larger separation distances.     

阿魏酸聚合修饰玻碳电极的制备及其对NADH的催化氧化

研究了阿魏酸修饰电极的制备、性质及对NADH的电催化作用.该电极在0.1mol/L磷酸缓冲溶液(pH=6.60)中,于-0.1～+0.50V(vs.Ag/AgCl)电位范围内呈现一对氧化还原峰,其式量电位E₀为+0.188V(vs.Ag/AgCl),且E₀随pH增加而负向移动.电子转移系数为0.496,表观电极反应速率常数(ks)为6.6s^-1.电极反应的电子数为1且有1个质子参与.该修饰电极对NADH氧化具有很好的催化作用.在NADH存在下,电极过程由扩散控制,扩散系数为1.76×10^-6cm²/s.NADH浓度在0.01～5.0mmol/L范围内与峰电流呈现良好的线性关系.通过计时安培法测得催化速率常数为6.82×10³mol^-1·L·s^-1.     

The voltammetric behaviour of solid 2,2-diphenyl-1-picrylhydrazyl (DPPH) microparticles

The electrochemical behaviour of 2,2-diphenyl-1-picrylhydrazyl (DPPH) microparticles, attached to a graphite electrode and adjacent to an aqueous electrolyte solution, has been studied by cyclic voltammetry. DPPH exhibits one reversible redox couple with a formal potential of 0.340 V versus Ag|AgCl (pH=7.0). At more positive potentials, a redox couple appears with a formal potential E_f=0.733 V versus Ag|AgCl. The oxidation at this potential is followed by an irreversible chemical reaction generating a product which gives a redox couple with a formal potential at 0.177 V versus Ag|AgCl. The reduction process of this couple is followed by a slow chemical reaction in the course of which DPPH is reformed.     

Direct Electrochemistry of Cytochrome c on a Silica Sol‐Gel Film Modified Electrode

Dilute silica sol‐gel was simply dropped on the surface of a basal plane graphite electrode (BPGE) to form a silica sol‐gel film modified electrode. Direct electrochemical response of cytochrome c (Cyt c) on the modified electrode was observed by cyclic voltammetry (CV). The results suggested that Cyt c could be tightly adsorbed on the surface of the silica sol‐gel film modified electrode. A couple of well‐defined and nearly reversible redox peaks can be observed in a phosphate buffer solution (pH 7.0), which anodic and cathodic peak potentials were at ?0.243 and ?0.306 V (vs. Ag/AgCl), respectively. Cyt c adsorbed on the surface of silica sol‐gel film shows a remarkable electrocatalytic activity for the reduction of oxygen. Based on these, a third‐generation biosensor could be constructed to detect the concentration of oxygen in aqueous solution.     

A spectroelectrochemical study on single-oscillator model and optical constants of sulfonated polyaniline film

The optical properties of sulfonated polyaniline (SPAN) thin film prepared by electrochemical method have been investigated. Polychromic behavior of SPAN thin film (transparent yellow-green-dark blue) was observed when the cyclic voltammograms were taken between -0.25 V and +1.90 V (vs. Ag/AgCl, sat.) during the growth of polyaniline film. In situ UV-vis spectra of the polymers-indium tin oxide (ITO) glass electrode were taken during the oxidation of the polymers at different applied potentials. The direct band gap values of SPAN thin film changed from 3.771 eV to 3.874 eV with the applied potentials. From in situ UV-vis spectra, the optical constants such as refractive index and dielectric constant of the SPAN thin film were determined. The important changes in absorption edge, refractive index and the dielectric constant were observed due to the applied potentials. The refractive index dispersion curves of the film obey the single-oscillator model and oscillator parameters changed with the applied potentials. The most significant result of the present work is in situ spectroelectrochemical method, which can be used to modify the optical band gaps and constants.     

碳酸钾催化的铁基氧载体煤催化化学链燃烧

研究了K₂CO₃催化剂及惰性担体对铁基氧载体煤化学链燃烧的影响.实验结果表明,K₂CO₃的添加可明显促进铁基氧载体与煤之间的反应速率,其原因可归结为从氧载体上迁移到煤颗粒上的K₂CO₃对煤-CO₂气化步骤的催化作用(该步骤为整个还原过程的速率控制步骤);由于K₂CO₃本身的促熔效果及加入K₂CO₃后导致的剧烈氧化还原反应,可以发现,K₂CO₃会增大铁基氧载体的烧结;不同惰性担体对铁基氧载体与煤的反应性影响不大,这是由于惰性担体对还原速控步没有影响;K₂CO₃在多循环化学链燃烧过程中依然可以保持一定的催化活性,另外由于催化剂的流失与失活,使得氧载体的反应活性有所下降.     

Spring open two-plus-two electron storage in a disulfide-strapped methyl viologen derivative

The synthesis of a disulfide-strapped viologen derivative is described starting from 4,4'-bipyridinyl-3,3'-diol. The first two one-electron reduction potentials, as determined by cyclic voltammetry, occur at E(1/2) = -0.03 V and E(1/2) = -0.16 V vs Ag/AgCl. This is accompanied by two more well separated one-electron reductions at E(1/2) = -1.26 V and E(1/2) = -1.54 V vs Ag/AgCl and the breaking of the disulfide bridge. To alleviate electrostatic repulsion between the two thiolate ions the molecular system must twist or "spring open" to accommodate the final two electrons.     

The fabrication and performance of an Ag/AgCl reference electrode in human serum

A simple set of electric circuits was used to assemble a pulse generator. With pulse potentials and under galvanostatical control, a clean silver wire was anodized electrochemically for 0.2–0.5 min in 1.0 mol l⁻¹ HCl with a pulse current density of 20 mA cm⁻², and the pulse wave parameters of t_a/t_c = 1 and a cycle of 4 s forming an Ag/AgCl reference electrode. Even though the AgCl layer was consumed during the working period when the Ag/AgCl electrode was used as a cathode, the AgCl layer could be in situ recovered electrochemically in serum used when a reversed potential was applied to the electrode system immediately after the measuring program was finished. The current response curve of the anode indicated that an AgCl layer in high density was basically accomplished during the first 6 pulse cycles in human serum. In order to keep a stable and uniform AgCl layer on the reference electrode after each measuring cycle, the ratio of the recovery time (t_r) to the working time (t_w) was measured and the smallest value was obtained at 0.03. The open-circuit potential of the Ag/AgCl electrode with respect to a SCE in 0.1 mol l⁻¹ KCl was monitored over a period of 14 days and the mean value was 40.09 mV vs SCE with a standard deviation of 2.55 mV. The potential of the Ag/AgCl reference electrode did remain constant when the measurements were repeated more than 600 times in undiluted human serum with a standard deviation of 1.89 mV. This study indicated that the Ag/AgCl reference electrode could been rapidly fabricated with a pulse potential and could be used as a reference electrode with long-term stable properties in human serum samples.     

Electrochemical Preparation of Brilliant‐Blue‐Modified Poly(diallyldimethylammonium Chloride) and Nafion‐Coated Glassy Carbon Electrodes and Their Electrocatalytic Behavior Towards Oxygen and L‐Cysteine

Brilliant blue FCF‐modified glassy carbon electrodes have been prepared by cycling the Nafion (or poly(diallyldimethylammonium chloride) (PDDAC)) coated electrodes repeatedly 15 cycles in brilliant blue FCF (BB FCF) dye solution. The BB FCF molecules are incorporated into Nafion coating by cycling the film‐covered electrode between +0.3 to 1.2 V (vs. Ag/AgCl) in pH 1.5 BB FCF solution while PDDAC‐coated electrode cycled between 0 to ?1.0 V (vs. Ag/AgCl) in pH 6.5 BB FCF solution to immobilize the dye. Electrostatic interaction between dye molecule and PDDAC was predominant in PDDAC coating whereas immobilization of dye in Nafion film attributed to the combined effect of electrostatic and hydrophobic interactions. The voltammetric features of BB FCF‐modified electrodes resemble that of surface‐confined redox couples. The peak potentials of BB FCF‐incorporated PDDAC‐coated electrode were shifted to more positive potential region with decreasing pH of contacting solution. BB FCF‐modified electrodes showed electrocatalytic activity towards reduction of oxygen and oxidation of L ‐cysteine with significant decease of overvoltage compared to unmodified electrode. The BB FCF‐modified Nafion‐coated electrode was tested for its analytical applications toward determination of L ‐cysteine. The linear range of calibration plot at BB FCF‐modified Nafion‐coated electrode is 10 to 100 μM, which coincides with L ‐cysteine levels in biological fluids. Sensitivity and detection limit of the electrode are 111 nA μM^?1 and 0.5 μM, respectively.     

Electrochemical impedance spectroscopy analysis of chalcopyrite CuFeS2 electrodes

A chalcopyrite CuFeS₂ electrode obtained from the “El Teniente” mine has been studied by Electrochemical Impedance Spectroscopy (EIS) in an alkaline solution for different oxidation potentials. The experimental results can be interpreted from a Randles equivalent circuit, V_dc<0.4 V vs. saturated calomel electrode (SCE), and a surface layer model for V_dc>0.4 V vs. SCE. From these results, the variation with the d.c. applied potentials of charge transfer electrical resistance of the redox reaction, the double layer capacitance and other characteristic parameters are considered.     

Electropreparation of Poly(benzophenone‐4) Film Modified Electrode and Its Electrocatalytic Behavior Towards Dopamine,Ascorbic Acid and Nitrite

The oxidation of benzophenone‐4 (2‐hydroxy‐4‐methoxybenzophenone‐5‐sulfonic acid) at glassy carbon electrode gives rise to stable redox active electropolymerized film during repetitive potential cycling between 0 to 1.3 V (Ag/AgCl). Cyclic voltammogram of poly(benzophenone‐4) film shows a redox couple with well‐defined peaks. The redox response of the modified electrode was found to be depending on the pH of the contacting solution. The peak potentials were shifted to a less positive region with increasing pH and the dependence of the peak potential was found to be 51 mV/pH. The electrocatalytic behavior of poly(benzophenone‐4) film modified electrode towards oxidation of dopamine, ascorbic acid and reduction of nitrite was investigated. The oxidation of dopamine and ascorbic acid occurred at less positive potential on poly(benzophenone‐4) film compared to bare glassy carbon electrode. For dopamine, the overpotential was reduced about 180 mV. Feasibility of utilizing poly(benzophenone‐4) film coated electrode in analytical estimation of dopamine, ascorbic acid and nitrite was also demonstrated.