Spectroelectrochemical investigation of Azotobacter vinelandii bacterial ferritin

Bacterial ferritin of Azotobacter vinelandii (AvBF) contains a function in accepting electrons from platinum electrode directly for complete iron release in the absence of a mediator. The reduction potentials of electron tunnels of −125, −310, and −370 mV for iron release are determined by direct spectroelectrochemical technique, which suggests which should be defined as midpoint potentials of electron–tunnel–heme on the surface of protein shell. A kinetic study for complete iron release by the electrode reduction at −600 mV fits the zero-order reaction law.     

Electrochemical Behavior from Pig Spleen Ferritin and Bacterial Ferritin of Azotobacter vinelandii

Being electrochemical studies, a rate of the core potential shifting to negative as a form of -205mV+(-115mV/pH) from horse spleen ferritin (HSF) has been measured by microcoulometry in the presence of mediator such as methyl viologen^[1]. It was well indicated that the mediator played an important role in transferring the electrons between the ferritin and the electrode. However, using cyclic voltammetry of pulse polarography, HSF appeared appreciable currentless at the mercury electrode at scan rate 5 mV.s^-1, moreover, and its mineral core isolated from protein shell showed the reductive current^[2]. Evidently, these results was known that the ferritin shell be no a redox protein due to it no exhibited the current at the electrode at low potential.     

Studies on the heme and H2-uptake reaction from Azotobacter vinelandii bacterial ferritin

Bacterial ferritin of Azotobacter vinelandii (AvBF) is directly able to pick electrons up for iron release from or transfer them for storage to a platinum electrode in the absence of mediator or other reducer. The ferritin containing the structure of heme-Co2+ in part shows weakened activity to electrode and decreases the rate of iron release greatly. A reversible reduction process of the ferritin is observed by the spectral change regularly ranging from 310 to 260 nm under mixed gases containing 98% H2 and 2% to O2. The activity of nitrogen fixation from the whole cell of A. vinelandii increases greatly by H2 reduction with potentials ranging from -397 to -425 mV vs. NHE, indicating two important roles of H2-uptake reaction of the ferritin in increasing activity of nitrogen fixation and in supplying iron to synthesize nitrogenase.     

Mass spectrometric characteristics and kinetics of iron release in visceral mass of Saccostrea cucullata

Ferritins with electrophoretic homogeneity were prepared from the visceral mass of Saccostrea cucullata in batch. The native PAGE approach showed similar electrophoretic mobility among pig pancreatic ferritin, liver ferritin of Dasyatis akajei, and visceral mass ferritin of Saccostrea cucullata. SDS-PAGE indicated that the Saccostrea cucullata visceral ferritin (SCVF) consisted of a single subunit type and had a molecular weight (MW) of approximately 20 kDa, suggesting that the protein shell in SCVF was composed of a single subunit. In addition, peptide mass fingerprinting and transmission electron microscopy were used to identify SCVF further, and to observe its molecular structure. We found that the molecular structure in SCVF was similar to that of most mammalian ferritins, which are composed of a protein shell and an iron core. The results of matrix-assisted laser desorption/ionization time-of-flight mass spectrometry under the assistance of an acidic matrix, sinapic acid, also showed that SCVF was composed of a single subunit type and its subunit MW was calculated to be 19871.042 Da in the absence of heme. Kinetics analysis revealed that the complete process of iron release fitted the law of a first-order reaction, which is similar to that of most ferritins in mammals. Similar to bacterial ferritin, studies indicated that the shell consisted of a single subunit type and showed similar kinetics of iron release, suggesting that this subunit plays two important roles in iron release and storage, and that it shows different stability and intensity of interaction in carrying out its physiological functions in SCVF.     

MALDI-TOF质谱、电泳和透射电子显微镜技术研究魟鱼肝铁蛋白H和L亚基特性

小批量制备质谱纯魟鱼肝铁蛋白(liver ferritin of Dasyatis akajei, DALF),以透射电子显微镜术(TEM)测定DALF、蛋白壳和铁核的分子尺寸.SDS-PAGE技术指出,DALF由H 和L两种不同类型的亚基组成.采用肽质量指纹图谱(PMF)技术进一步佐证H和L亚基类型和同源性.氧化还原剂中性红、劳氏紫、甲基紫精和 pH 1.5酸度均无法削弱DALF的H-L和L-L亚基之间的相互作用强度、并解吸出L亚基离子,供MALDI-TOF质谱仪分析.通过增加激光强度和降低基质pH途径,可直接分析DALF的H和L亚基的分子量,指出DALF中H-L和L-L亚基之间的相互作用强度明显高于H-H亚基类型.     

Effect of pH and phosphate on trapping capacity of various heavy metal ions with ferritin reactor in flowing seawater

We describe a protein reactor consisting of native liver ferritin of Dasyatis akajei (DALF) and a dialysis bag. Our goal was to study a ferritin reactor for its capacity to trap various heavy metal ions (M²⁺) in flowing seawater. The reactor is sensitive and inexpensive and can be operated by nonprofessional technicians. A positive relationship between the number of trapped M²⁺ with the DALF reactor and its concentration in the flowing seawater was observed. Both the pH in the medium and the phosphate content within the ferritin cavity strongly affected trapping capacity. It was found that the ferritin released its phosphate compound directly with a shift in pH without the need for releasing reagent, which differs from the phosphate release characteristics of horse spleen ferritin, as previously described. This behavior evidently makes the trapping capacity with the ferritin reactor weaken, indicating that this trapping capacity is tightly connected to its phosphate compound. Our study shows that a self-regulation ability of the ferritin shell rather than its phosphate compound plays an important role in controlling the rate and capacity of trapping M²⁺. The ferritin reactor was constructed to monitor the contamination level of M²⁺ in flowing seawater. Our preliminary data along with fieldwork indicate that the DALF reactor is an analytical means for effectively monitoring the contamination level of M²⁺ in flowing seawater.     

A Ferritin Reactor for Entrapping Various Heavy Metal Ions in Flowing Seawater

Recent studies showed that the ferritins had three tunnels across the protein shell with 0.7~0.9 nm diameter for iron metabolism^[1-2]. However, very little was known the mechanism(s) that the ferritin reactor entrapped various heavy metal ions (M²⁺) and other small organic molecules in the flowing seawater directly.     

Electrochemical polymerization of toluidine blue o and its electrocatalytic activity toward NADH oxidation

A stable electroactive thin film of poly(toluidine blue o) (PTOB) has been deposited on the surface of a glassy carbon electrode by cyclic voltammetry from an aqueous solution containing toluidine blue o (TOB). Cyclic voltammograms of PTOB indicate the presence of two redox couples and the formal potential shifts linearly in the negative direction with increasing solution pH with a slope of 58 and 54 mV per pH unit for couple I and couple II, respectively. The PTOB modified glassy carbon electrode shows electrocatalytic activity toward NADH oxidation in phosphate buffer solution (pH 7.0), with an overpotential ca. 470 mV lower than that of the bare electrode. The catalytic rate constant of the modified glassy carbon electrode for the oxidation of NADH is determined by cyclic voltammetry and rotating disk electrode measurements. The experimental results indicate that the electrode can be used as a detector for NADH determination with a linear range of 5.0×10⁻⁶ to 2.0×10⁻³ mol l⁻¹ and the detection limits of (5.0±0.3)×10⁻⁷ mol l⁻¹ at optimal conditions.     

Electrochemical Study and Application on Shikonin at Poly(diallyldimethylammonium chloride) Functionalized Graphene Sheets Modified Glass Carbon Electrode

The electrochemical behaviors of shikonin at a poly(diallyldimethylammonium chloride) functionalized graphene sheets modified glass carbon electrode(PDDA-GS/GCE) have been investigated. Shikonin could exhibit a pair of well-defined redox peaks at the PDDA-GS/GCE located at 0.681 V(E_pa) and 0.662 V(E_pc)[vs. saturated calomel electrode(SCE)] in 0.1 mol/L phosphate buffer solution(pH=2.0) with a peak-to-peak separation of about 20 mV, revealing a fast electron-transfer process. Moreover, the current response was remarkably increased at PDDA-GS/GCE compared with that at the bare GCE. The electrochemical behaviors of shikonin at the modified electrode were investigated. And the results indicate that the reaction involves the transfer of two electrons, accompanied by two protons and the electrochemical process is a diffusional-controlled electrode process. The electrochemical parameters of shikonin at the modified electrode, the electron-transfer coefficient(α), the electron-transfer number(n) and the electrode reaction rate constant(k_s) were calculated to be as 0.53, 2.18 and 3.6 s^-1, respectively. Under the optimal conditions, the peak current of differential pulse voltammetry(DPV) increased linearly with the shikonin concentration in a range from 9.472×10^-8 mol/L to 3.789×10^-6 mol/L with a detection limit of 3.157×10^-8 mol/L. The linear regression equation was I_p=0.7366c+0.7855(R=0.9978; I_p: 10^-7 A, c: 10^-8 mol/L). In addition, the modified glass carbon electrode also exhibited good stability, selectivity and acceptable reproducibility that could be used for the sensitive, simple and rapid determination of shikonin in real samples. Therefore, the present work offers a new way to broaden the analytical application of graphene in pharmaceutical analysis.     

铜物理显影动力学和机理——电化学探讨

本文采用镀铜铂电极和暂态恒电流阶跃的方法测得了铜物显(铜物理显影)体系的极化曲线。结果表明,单电极Cu²⁺还原的阴极极化曲线与NaBH₄氧化的阳极极化曲线交点的混合电位E_mp=-715mV,对应的i_R为8.9×10^-4Acm^-2。这与直接测得的铜物显体系的E_mp=-720mV,和i_R=8.7×10^-4Acm^-2很相近。这意味着应用混合电位理论来分析铜物显过程是合理的。在铜物显的混合电极系统中,Cu²⁺还原的阴极反应与BH₄^-氧化的阳极反应相互影响很小。当镀铜电极表面涂有明胶时,反应速率降低(6.09μgcm^-2min^-1),与动力学测得的结果(4.82μg cm^-2 min^-1)比较接近,而在不涂明胶的电极上反应速率则大得多(17.12 μg cm^-2 min^-1),这表明了明胶对物显过程的显著影响。根据Tafel方程,从极化曲线斜率可求碍转移系数α=0.48,并推测铜沉积过程是两步单电子转移反应,且第一个电子的转移是控制步骤。     

N~1,N~2-Bis[1-(2-hydroxyphenyl)methylidene]ethanedihydrazide as a neutral ionophore for preparation of a new Ho~(3+) PVC-membrane sensor

N¹,N²-Bis[1-（2-hydroxyphenyl）methylidene]ethanedihydrazide（MEH） was used as new compound which plays the role of an excellent ion carrier in the fabrication of a Ho（Ⅲ） membrane electrode.The electrode shows a good selectivity for Ho（Ⅲ） ion with respect to most common cations including alkali,alkaline earth,transition and heavy metal ions.This electrode has a wide linear dynamic range from 1.0×10^-6 to 1.0×10^-2 mol/L with a Nernstian slope of 19.8±0.3 mV per decade and a low detection limit of 5.8×10^-7 mol/L in the pH range of 2.5-9.8,while the response time was rapid（<10 s）.The suggested sensor was applied to the determination of Ho（Ⅲ） ions in tap water and river water samples.     

玻碳电极表面复合配位银电结晶机理研究

以具有实际应用价值的复合配位体系无氰镀银电解液为研究对象, 运用循环伏安和电位阶跃等实验方法, 结合 Scharifker-Hill 经典理论模型分析, 成功获得了Ag在玻碳电极（GCE）表面电沉积的成核机理及成核动力学参数, 并分析了温度对成核方式及成核动力学参数的影响. 结果表明, 该体系下Ag在GCE表面的电沉积是由扩散控制的不可逆过程, 遵循三维瞬时成核生长机理. 随着阶跃电位从-750 mV 负移至-825 mV, 峰值还原电流Im逐渐增大, 达到峰值还原电流所需时间tm逐渐缩短; 扩散系数D变化不大, 基本稳定在（7.61±0.34）×10^-5 cm²·s^-1; 成核密度数N₀则从3.26 ×10⁵ cm^-2提高至10.2×10⁵ cm^-2. 银沉积初期的形貌观察, 验证了其三维瞬时成核生长机理. 提高温度可以显著改善电解液中具备活性的银配位离子的扩散能力, 缩短成核时间, 提升成核密度数N0.     

PVC膜四氯络铁(Ⅲ)阴离子电极的研制

Cattrall等_[1]曾报导用Allqat 336S的四氯络铁(Ⅲ)酸盐为电活性物质制成铂基PVC膜涂层电极,并用于测定铁矿石中的铁含量_[2]。惜所用季铵盐碳链较短,检测下限欠佳。本文报导用长键季铵盐作活性物质,以制备其内导体系为溶液接触型的PVC膜四氯络铁(Ⅲ)阴离子选择电极的研究结果。     

Synthesis of 5-[(2-hydroxynaphthalen-1-yl)diazenyl]isophthalic acid and its application to electrocatalytic oxidation and determination of adrenaline,paracetamol, and tryptophan

In this study,Au nanoparticles/poly 5-[(2-hydroxynaphthalen-l-yl)diazenyl]isophthalic acid film modified glassy carbon electrode(AuNPs/poly(NDI)/GCE) has shown excellent electrocatalytic activity toward the oxidation of adrenaline(ADR),paracetamol(PAC),and tryptophan(Trp).The bare glassy carbon electrode(GCE) fails to separate the oxidation peak potentials of these molecules,while the poly(NDI) film modified electrode can resolve them.Electrochemical impedance spectroscopy(EIS)indicates that the charge transfer resistance of the bare electrode decreases as 5-[(2-hydroxynaphthalen-l-yl)diazenyl]isophthalic acid is electropolymerized on the bare electrode.Furthermore,EIS exhibits enhancement of electron transfer kinetics between analytes and the electrode after electrodeposition of Au nanoparticles.Differential pulse voltammetry results show that the electrocatalytic current increases linearly in the ranges of 0.01-680.0 μmol L~1 for ADR,0.05-498.0 μmol L~1 for PAC,and 3.0-632.0 μmol L~1 for Trp;with detection limits(S/N = 3) of 0.009 μmol L~1,0.005 μmol L~1,and 0.09 μmol L~1 for ADR,PAC,and Trp,respectively.The proposed method has been successfully applied for simultaneous determination of ADR,PAC,and Trp in biological samples.     

Direct evaluation of meat spoilage and the progress of aging using biosensors

A direct sensing method for monitoring meat quality was developed. The sensor is composed of an Ag/AgCl electrode and a platinum electrode on which putrescine oxidase or xanthine oxidase were immobilized to estimate bacterial spoilage or the progress of aging, respectively. A potential-step chronoamperometric method was applied in which the potential was stepped from 300 mV to 600 mV. A linear relationship was obtained between 5 and 60 nmol g⁻¹ for putrescine (Put) and 0.05 and 1.0 μmol g⁻¹ for hypoxanthine (Hx). The coefficient of variation was 0.75% for 20 nmol ml⁻¹ Put solution and 2.2 for a meat sample using the putrescine sensor, and 1.09% for 0.25 μmol ml⁻¹ Hx solution and 2.6% for a meat sample using the xanthine sensor. The pH requirements and substrate selectivity were suitable for the direct measurement of substrates on the surface of meat. From the results of practical experiments, the direct sensing method was indicated to be useful with some modifications for the estimation of meat quality during aging.     

硫堇衍生化自组装膜修饰金电极的电化学性质及其对抗坏血酸的电催化氧化

将硫堇共价键合到自组装在金电极表面的半胱胺单分子层上,制成了衍生化自组装单分子膜修饰电极,并用电化学方法研究了它的电化学性质.循环伏安图显示其在pH＝7.7的磷酸盐缓冲液中,于－0.45～＋0.50V(vs.SCE)范围内有2对氧化还原峰.峰电位分别为E_pa¹＝214mV。E_pc¹＝82mV,E_pa2＝－75mV,E_pc2＝－160mV(vs.SCE).pH在5.0～9.0范围内,峰1有2个质子参与反应,峰2有1个质子参与反应.它的表面电子转移速率常数k_s＝0.02S^－1.此膜对抗坏血酸的氧化有催化作用,其氧化过电位较在裸金电极上降低了约250mV.催化电流与抗坏血酸的浓度在1.0×10^-6～4.0×10^-3mol/L范围内呈良好的线性关系.抗坏血酸催化氧化的异相速率常数为2.68×10^-3cm/s.     

Electrochemical determination of quercetin by self-assembled platinum nanoparticles/poly(hydroxymethylated-3,4-ethylenedioxylthiophene) nanocomposite modified glassy carbon electrode

A simple and sensitive platinum nanoparticles/poly(hydroxymethylated-3,4-ethylenedioxylthiophene)nanocomposite(PtNPs/PEDOT-MeOH) modified glassy carbon electrode(GCE) was successfully developed for the electrochemical determination of quercetin.Scanning electron microscopy and energy dispersive X-ray spectroscopy results indicated that the PtNPs were inserted into the PEDOTMeOH layer.Compared with the bare GCE and poly(3,4-ethylenedioxythiophene)(PEDOT) electrodes,the PtNPs/PEDOT-MeOH/GCE modified electrode exhibited a higher electrocatalytic ability toward the oxidation of quercetin due to the synergic effects of the electrocatalytic activity and strong adsorption ability of PtNPs together with the good water solubility and high conductivity of PEDOT-MeOH.The electrochemical sensor can be applied to the quantification of quercetin with a linear range covering0.04-91 μmol L~(-1) and a low detection limit of 5.2 nmol L~(-1).Furthermore,the modified electrode also exhibited good reproducibility and long-term stability,as well as high selectivity.     

The role of n–p junction electrodes in minimizing the charge recombination and enhancement of photocurrent and photovoltage in dye sensitized solar cells

The composite electrode comprising n-type TiO₂ and p-type NiO oxides when sensitized with Ru-dye showed short-circuit photocurrent (I_sc) of 17 mA/cm² and open-circuit photovoltage (V_oc) of 730 mV compared to I_sc of 12 mA/cm² and 700 mV for TiO₂ electrodes. Formation of a n–p junction between TiO₂ and NiO oxide layers contributes to the enhanced photocurrent, photovoltage, fill factor and efficiency. In addition to the junction effect, NiO acts as a barrier for charge recombination leading to higher cell performance. The efficiency of the NiO coated TiO₂ solar cell is 30% more than that of bare TiO₂. The negative shift of the flat-band potential of the NiO coated TiO₂ electrode compared to TiO₂ also could be one of the reasons for higher photovoltage observed for TiO₂/NiO electrode. The highest cell efficiencies were obtained immersing TiO₂ thin films in Ni²⁺ solution and converting them to NiO by firing and the optimum NiO coating thickness was found to be only a few angstroms. The energy levels of the excited dye and the band positions of TiO₂ and NiO suggest that the electron transfer from the excited dye to the underlying n-type oxide layer occurs by tunneling through the p-type NiO layer.     

Long-lived photoinduced charge separation in carbazole–pyrene–viologen system incorporated in Langmuir–Blodgett films of substituted diazacrown ethers

Diaza-18-crown-6 ethers appending two pyrenyl (Py) or two carbazolyl (Cz) groups were synthesized. These macrocyclic compounds form 1:1 host–guest complexes with methyl viologen chloride (MV²⁺), and these complexes were assembled into monolayers by Langmuir–Blodgett technique. The generated assembly involves the general structure of donor–sensitizer–acceptor (Cz–Py–MV²⁺) in space, although any of the photo- and redox-active components are not covalently bonded. Photoirradiation of the pyrenyl group resulted in the charge-separated pair Cz√⁺–Py–MV√⁺ which survived up to hours in a well anaerobic atmosphere. An electrode was fabricated by transferring the L–B film on an ITO glass. The photoinduced voltage of this electrode was measured with a saturated calomel reference electrode in hydroquinone (H₂Q) solution to be ca. 168 mV when the light intensity was 218 mW/cm². This electrode was also used as the light electrode to construct a photogalvanic cell with a platinum electrode as the dark electrode. Irradiation of the light electrode with visible light results in anodic photocurrent, and there is no net chemical change associated with the function of the cell which converts light to electricity.     

Electrochemical behavior of methyl viologen at graphite electrodes modified with Nafion sol–gel composite

Electrodes were prepared by spin-coating spectroscopic graphite rods with a Nafion doped sol. Coating solutions consisting of Nafion:TEOS (tetraethoxysilane) ratios of 3:1 and 4:1 gave smooth films on the electrode surface. These modified electrodes were evaluated and compared with Nafion modified and bare spectroscopic graphite electrodes using methyl viologen (MV²⁺) as a representative cationic electroactive probe. Substantial partitioning of MV²⁺ into the Nafion:sol–gel matrix to the electrode surface was observed by cyclic voltammetry and square wave voltammetry. Cyclic voltammograms of MV²⁺ in 0.1 M NaCl at Nafion:sol–gel 4:1 modified electrodes showed a reversible reduction to MV⁺ with E^0′=−0.695 V vs. Ag/AgCl. Results of scan rate variation showed the wave to be characterized by semi-infinite diffusion for scan rates in the range 50–500 mV/s. Slowing the scan rate below 50 mV/s resulted in a transition to thin-layer behavior. MV²⁺ partitioned much more quickly into the sol–gel-Nafion modified electrodes compared to pure Nafion modified electrodes. Reversibility of the MV²⁺-loaded modified Nafion-doped sol–gel coatings on electrodes was obtained by soaking in 1 M NaCl solution. Concentration calibration plots for MV²⁺ at the sol–gel-Nafion modified electrodes were nonlinear. Substantial enhancement of current signal at low concentrations was observed by square wave voltammetry.