Study on the electrochemical behavior of epinephrine at a poly(3-methylthiophene)-modified glassy carbon electrode

A poly(3-methylthiophene) (P3MT)-modified glassy carbon electrode (GCE) has been prepared in undeaerated acetonitrile solution under ambient conditions. The electrochemical behavior of epinephrine was studied systematically at the P3MT-modified GCE using cyclic voltammetry. The results indicate that the number and height of redox peaks of epinephrine are strongly dependent on the pH value of the phosphate buffer solution (PBS). Three peaks, one irreversible oxidation peak and one pair of reversible redox peaks, can be observed in neutral PBS while only one pair of redox peaks appear in 0.5 M sulfuric acid solution. In pH 4.0 PBS, the oxidation of epinephrine gives one more cathodic peak than that reported in the literature; in other words, six peaks or three pairs of redox peaks can be obtained due to the oxidation of epinephrine and the following chemical reaction. The effects of other conditions on the oxidative behavior of epinephrine were examined and the oxidative mechanism of epinephrine at the P3MT-modified GCE was discussed.     

Electrochemical impedimetry of electrodeposited poly(propylene imine) dendrimer monolayer

Voltammetric and electrochemical impedance spectroscopic (EIS) studies of generation one poly(propylene imine) (G1 PPI) dendrimer as an electroactive and catalytic nanomaterials both in solution and as an electrode modifier based on a simple one step electrodeposition method is presented. The G1 PPI exhibited a reversible one electron redox behaviour at E^0′ ca 210 mV in phosphate buffer pH 7.2 with diffusion coefficient and Warburg coefficient of 7.5 × 10⁻¹⁰ cm² s⁻¹ and 8.87 × 10⁻⁴ Ω s^−1/2 respectively. Cyclic voltammetric electrodeposition of a monolayer of G1 PPI on glassy carbon electrode was carried out between −100 mV and 1100 mV for 10 cycles. The nanoelectrode was electroactive in PBS at E^0′ ca 220 mV. Kinetic profiles such as time constant (4.64 × 10⁻⁵ s rad⁻¹), exchange current (1.55 × 10⁻⁴ A) and heterogeneous rate constant (4.52 × 10⁻³ cm s⁻¹) obtained from EIS showed that the dendrimer layer catalysed the redox reaction of Fe^2+/3+ in [Fe(CN)₆]^3−/4− redox probe.     

Nucleation and growth of poly(3,4-ethylenedioxythiophene) in acetonitrile on platinum under potentiostatic conditions

The electrodeposition mechanisms of 3,4,-ethylenedioxythiophene (EDOT) were studied according to electrocrystallization theory. The analyis of the chronoamperograms indicated that the initial stage of the electrodeposition was a combination of instantaneous 2-D and instantaneous 3-D mechanisms since the electrodeposition was carried out under charge transfer control rather than diffusion. In the later stages, layer-by-layer growth mode in accordance with the Stranski–Krastanov model was observed. Our results shown a variation of the anodic transfer coefficient as a function of monomer concentration. Under our experimental conditions, the growth rate constant of the 2D nucleus and the growth perpendicular to the surface rate constant did not depend upon potential beyond a monomer concentration of 0.15 mol l^?1. The quasi-metallic behaviour of oxidized poly(3,4-ethylenedioxythiophene) (PEDOT) was analyzed according to Feldberg’s model. A Feldberg parameter of 0.61 V^?1 was obtained. The stability of PEDOT was studied during successive polarization between ?0.6 and 0.5 V at a scan rate of 0.2 V s^?1 in acetonitrile and in aqueous solutions containing tetrabutylammonium perchlorate and lithium perchlorate as electrolyte. About 86 and 66% of the electrochemical activity were retained after polarization for 1200 cycles in acetonitrile and aqueous solutions, respectively. These results indicated the good stability of the thin film of PEDOT on the electrode surface.     

Electrochemical doping of poly(vinyl chloride) obtained by photodehydrochlorination from laminated poly(vinyl chloride) + polypyrrole films

The poly(vinyl chloride) (PVC) in laminated PVC + polypyrrol (PPy) films has been converted to an electrically conducting structure by photodehydrochlorination and subsequent electrochemical doping. The maximum conductivity (6 × 10^?1 S cm^?1) of the PVC film was obtained by potentiostatic oxidation at 0.3 V vs. SCE in HCl solution. The reflection spectra of the PVC film showed a new band around 600 to 800 nm after the electrochemical doping, indicating the formation of a charge-transfer complex. The maximum conductivity of the PVC film was reached with the highest concentration of the charge transfer complex, polyene⁺ … X^?, formed between the photogenerated polyenes and dopant anions.     

Electrocatalytic properties of nickel(II) hydrotalcite-type anionic clay: application to methanol and ethanol oxidation

Glassy carbon electrodes modified with a [Ni/Al–Cl] hydrotalcite-type anionic clay have been studied with respect to the electrochemical oxidation of the Ni(II) centres. The oxidation of Ni(II) is quasi-reversible and the presence in the hydrotalcite lattice of nickel with mixed oxidation states increases the conductivity of the coverage strongly. It has been verified that these nickel redox systems may act as redox mediators for the oxidation of alcohol substrates (methanol and ethanol have been tested) which are not oxidised at the bare electrode in the potential window available. For both alcohols the height of the current responses in linear sweep voltammetry is roughly linear with varying concentration in solution up to a limit of ca. 3000 ppm, with a detection limit of 3–4 ppm.     

Electrochemical oxidation of poly[(hexamethyltrisilanylene)oligo(2,5-thienylene)] films

Electrochemistry of σ–π-conjugated polymers, poly[(hexamethyltrisilanylene)oligo(2,5-thienylene)] has been investigated in acetonitrile by using cyclic voltammetric and spectroelectrochemical techniques. Cyclic voltammograms of these polymers films display generally two pairs of main redox peaks, indicating the doping and dedoping processes of the polymers. The electrochemical oxidation of the polymer films results in their partial decomposition, besides the doping, which is shown by electrochemical quartz crystal microbalance and spectroelectrochemical measurements. The decomposition products are characterized by UV-visible absorption spectroscopy, fluorescence spectroscopy, FT-IR, and GPC measurements. It is concluded that the decomposition originates mainly from electrochemical cleavage of silicon–silicon bonds in the polymer chains, and the electrochemical stability of the σ–π-conjugated polymers may be improved by decreasing the oligosilanylene block size in the polymer chains.     

Electrocatalytic behavior of Pt-modified polyaniline electrode for methanol oxidation: Effect of Pt deposition modes

Platinum dispersed in polyaniline film is a better catalyst than bulk platinum for methanol electrooxidation in sulfuric acid solution. The effect of deposition modes of platinum particles on their electrocatalytic activity has been studied. Several electrodeposition methods, including constant potential, cyclic potential and double potential step, have been applied to characterize the performance of different electrodeposition modes. Besides the variation of the electrodeposition methods, rotating disk electrode technique is applied to disperse Pt particles under the control of convection–diffusion condition. The results show that the enhanced electrocatalytic activity may be due to the dispersion of Pt particles in the polyaniline film matrix and the synergistic effects between the dispersed Pt particles and the polyaniline film. Variables related to reaction kinetics, such as mass transport of species, concentration of methanol and acidity of solution, are investigated and reaction mechanism for methanol oxidation is discussed.     

Mixed ion transfer in redox processes of poly(3,4-ethylenedioxythiophene)

A model considering the transfer of counter ions and solvent molecules has been presented to explain the complicated ion transfer in polymer films during electrochemical redox processes. The developed mixed ion transfer model is used to analyze the ion transfer behavior of poly(3,4-ethylenedioxythiophene) during doping and dedoping processes. The results indicate that both anions and cations are involved in n-doping as well as in p-doping processes. The behavior of different electrolyte ions is also studied. The developed model shows that solvent molecules are also transferred in conjunction with the ion transfer.     

EIS study of the redox reaction of Fe(CN)63−/4− at poly(3,4-ethylenedioxythiophene) electrodes: influence of dc potential and cOx:cRed ratio

The electron transfer between the ferri/ferrocyanide redox couple and poly(3,4-ethylenedioxythiophene) (PEDOT) electrodes has been investigated by electrochemical impedance spectroscopy (EIS). Different thicknesses of the conducting polymer films were investigated (i) at a constant concentration of ferrocyanide in the solution at different applied dc potentials and (ii) at the open circuit potential with different ratios of Fe(CN)₆^3?:Fe(CN)₆^4? in the solution. PEDOT was prepared by galvanostatic electropolymerization on platinum electrodes from aqueous solutions containing 0.01 M 3,4-ethylenedioxythiophene (EDOT) and 0.1 M poly(sodium 4-styrenesulfonate) (NaPSS) as the supporting electrolyte. All impedance spectra were obtained in aqueous solutions with 0.1 M KCl as the supporting electrolyte at dc potentials, where the polymer is in the oxidized state. The EIS data were fitted to an equivalent electrical circuit resembling the Randles' circuit, where the double layer capacitance is replaced by the bulk redox capacitance and the associated transport impedance of the conducting polymer. The same potential and thickness dependence of the charge transfer resistance (R_ct) were obtained both (i) by varying the concentration ratio of the redox species in the solution and (ii) by applying different potentials at a constant concentration of ferrocyanide. The potential dependence of k₀ calculated from R_ct indicates that the conducting polymer influences the rate of electron transfer for the ferri/ferrocyanide redox couple.     

Electrochemical deposition of iridium (IV) oxide from alkaline solutions of iridium(III) oxide

Cyclic voltammetry is used to deposit films of hydrous iridium oxide onto glassy carbon electrodes from a basic solution of saturated iridium(III) oxide. An acidic solution of Ir(OH₂)₂Cl₄^? is first prepared from either IrCl₆³ or IrCl₆^2?. When this solution is made basic, iridium (IV) oxide is deposited by oxygen generated from oxidation of hydroxide. A strongly adherent, bright blue deposit of iridium oxide is formed after 10 to 20 scans between ?0.3 and +1.0 V vs. Ag|AgCl. The modified electrodes exhibit a super-Nernstian response to pH similar to that observed for iridium oxide grown electrochemically on iridium substrates. The ph response is reproducible and remains stable over a period of several days.     

计算机辅助颅颌面畸形的三维诊断

利用侧位Ｘ线头影测量对颅颌面畸形进行诊断分析，已有相当长的时间．但因该方法取自颅颌面结构左右两侧的均值，用其测量分析不对称颅颌面畸形，有很大局限性．本文报告一种将正位和侧位两张Ｘ线头影片结合起来的三维Ｘ线头影测量分析方法，以及标准化与个体化相结合的诊断方法在复杂、不对称颅颌面畸形诊断中的应用．     

Accuracy of adaptation of thermoformed poly(methyl methacrylate)

Thermoformed poly(methyl methacrylate) (PMMA) sheet is used to produce a number of different dental appliances such as stents, occlusal splints and baseplates for occlusal rims. The purpose of the present study was to measure the accuracy of adaptation of Perspex PMMA sheet and to determine the effect of annealing on the accuracy of the thermoformed specimens. The results of the study showed that PMMA can produce specimens that are accurately adapted to the cast. Immersion in water resulted in an increase in the space between the cast and the specimen for both thermoformed and thermoformed and annealed acrylic resin. Annealing of the thermoformed specimens had significantly less increase in space between the cast and the specimens when immersed in water over a period of 3 months.     

Electrocatalytic oxidations of biological molecules (ascorbic acid and uric acids) at highly oxidized electrodes

Highly oxidized glassy carbon and other metal (gold and platinum) electrode surfaces were generated by applying 2.0 V vs. SCE for 600 s in pH 7 solution. The effects of oxidation on the functional, physical, and chemical characteristics of the electrodes went beyond the usual conditioning of such electrode surfaces through cycling to slightly beyond the medium decomposition potentials. The oxidized electrodes showed enhanced electrochemical activities and lower background currents. Besides cleaning the surface of contaminants introduced in the polishing stage of electrode preparation, application of such high potentials for an extended time interval changed the chemical nature of the glassy carbon surface itself. The chemical changes influenced the electro-oxidation reaction of bio-molecules such as ascorbic acid and uric acid but did not influence the reaction of the ferri- and ferrocyanide system. As a result the biological molecules (uric acid and ascorbic acid) were detected using an electrochemical method individually and simultaneously without the necessity for any electron relay complex.     

Preparation of clay-modified electrodes by electrophoretic deposition of clay films

The application of an electric potential across aqueous suspensions of montmorillonite resulted in the electrophoretic deposition of very thin, uniform and continuous clay films. Scanning electron microscopy shows that the electrodeposited films were much more uniform than films prepared by spin-coating. The thickness of the films increased with the deposition time, reaching ca. 20 nm after 3000 s. From then on, the films grew much more slowly. The thickness of the electrophoretically deposited film never exceeded about 30 nm even after several hours of deposition. The voltammetric waves for [Ru(bpy)₃]²⁺ adsorbed in the electrodeposited films were much smaller than those obtained even with very thin spin-coated films. This was due to a very low effective diffusion coefficient for [Ru(bpy)₃]²⁺ in the electrodeposited films, 5×10^?15 cm² s^?1, four orders of magnitude smaller than in a 400 nm thick spin-coated film. The electroactive concentration of [Ru(bpy)₃]²⁺ in the electrodeposited CMEs was actually ten times larger than in the 400 nm thick spin-coated film. However, the electroactive concentration of [Ru(bpy)₃]²⁺ in the spin-coated CMEs was found to increase with decrease of the film thickness. The electroactive concentration of [Ru(bpy)₃]²⁺ in a very thin 40 nm thick spin-coated film was comparable with that in the electrodeposited films. The high electroactive concentrations and extremely low diffusion coefficients obtained in the very thin CMEs suggests the participation of some of the electrostatically bounded [Ru(bpy)₃]²⁺ in the electrochemical reaction.     

Liquid membrane system for extraction and electrodeposition of silver(I)

The process of Ag⁺ ions extraction from nitric solutions by bulk liquid membranes containing di(2-ethylhexyl)phosphoric acid and tri-n-octylamine accompanied with silver(I) electrodeposition from perchloric acid solutions is studied at galvanostatic electrodialysis. The effects of the current density as well as of composition of the liquid membrane and aqueous solutions on the rate of the silver(I) transport are determined. More than 90% of silver ions was extracted from the feed solution containing 0.01 mol l⁻¹ AgNO₃ and about 40% of metal was electrodeposited during 1 h of electrodialysis. Sound adherent silver coatings have been deposited on platinum and copper cathodes.     

丙二醇/反丁烯二酰氯缩聚物复合材料力学性能研究

目的 :研究丙二醇 /反丁烯二酰氯缩聚物复合材料中无机组分对材料力学性能的影响。方法 :以前期合成丙二醇 /反丁烯二酰氯缩聚物为基础 ,复合氯化钠、β -磷酸三钙。交联固化后 ,做成压缩试件 ,测定材料力学性能 ,并对结果进行统计学分析处理。结果 :复合材料最大压缩强度为 (4 0 .37± 3.0 7)MPa ,最大压缩模量为 (5 4 3.6 7±7.0 2 )MPa。β -磷酸三钙对材料的压缩强度及压缩模量均有影响 ;氯化钠对压缩强度有明显影响 ,对压缩模量的影响无统计学意义 ;β -磷酸三钙与氯化钠对材料的压缩强度和压缩模量的影响存在交互作用。 结论 :通过改变复合材料中无机组分的剂量 ,可以优化材料的力学性能 ,使之接近人体正常骨组织的生物力学性能要求 ,以用于不同部位骨缺损     

Electrochemical anion doping of poly[(tetraethyldisilanylene) oligot 2,5-thienylene)] derivatives and their p-type semiconducting properties

Chemically synthesized poly[(tetraethyldisilanylene)oligo(2,5-thienylene)] derivatives (DS/mT; m = 3 to 5) have been successfully anion-doped by electrochemical oxidation. Band-gap energies of 2.52, 2.65, 2.82 and 3.27 eV were evaluated for DS5T, DS4T, DS3T and DS2T respectively. The DS5T, DS4T and DS3T films exhibited electrical conductivities of the order of 10^?3 to 10^?4 S cm^?1 when doped with BF₄^?. The work functions of the films changed from 5.1 to ca. 5.5 eV with electrochemical anion doping. In cyclic voltammograms of the polymer films for anion doping and dedoping, an anodic peak potential and a cathodic one (E_pc.) shifted to the positive direction as the number m of thienylene units decreased. E_pcs at a sweep rate of 100 mV s^?1 were about 0.8, 0.9 and 1.0V for DS5T, DS4T and DS3T respectively. Reversible electrochemical doping and dedoping of the DS5T film were feasible when the potential was cycled between 0 and 1.2 V. At potentials more positive than 1.2 V, however, both overoxidation of the oligo(thienylene) unit and Si-Si bond cleavage took place, leading to decreases in conductivity and work function of the film.     

Electrochemical synthesis and in situ spectroelectrochemical characterization of poly(3,4-ethylenedioxythiophene) (PEDOT) in room temperature ionic liquids

The electrochemical synthesis and the charging–discharging reactions of poly(3,4-ethylenedioxythiophene) (PEDOT) in two room-temperature ionic liquids, 1-butyl-3-methyl-imidazolium tetrafluoroborate (BMIMBF₄) and 1-butyl-3-methyl-imidazolium hexafluorophosphate (BMIMPF₆) were studied with cyclic voltammetry, in situ attenuated total reflection Fourier transform infrared (ATR–FTIR) spectroscopy and by in situ UV–Vis spectroelectrochemistry. The structures of the films prepared in ionic liquids was compared to PEDOT films prepared in common organic media. The doping induced changes in absorption of the material both in the mid infrared and in the UV–Vis region were studied and interpreted according to spectra reported for PEDOT films prepared from common organic media.     

Electrocatalytic dehalogenation of organohalides on a nickel(II) tetraazamacrocyclic complex-modified graphite felt electrode

Electrocatalytic dehalogenation of organohalides was studied using a nickel(II) tetraazamacrocyclic complex-modified graphite felt electrode. The nickel(II) tetraazamacrocyclic complex-modified graphite felt electrode was prepared by attaching nickel(II) (6-(2′-hydroxyethyl)-1,4,8,11-tetraazacyclotetradecane)perchlorate chemically to the carboxyl groups of a thin poly(acrylic acid) layer coated on the graphite felt. The modified electrode gave a reversible electron transfer for the nickel(II)/nickel(I) redox couple in cyclic voltammetry at ?0.95 V versus Ag/AgCl. A preparative electrocatalytic dehalogenation of organohalides was successfully achieved on the modified electrode with an adequate current efficiency (55.6–94.8%), conversion (34.2–100%) and turnover number of the Ni catalyst (667–3333).