Novel studies on the electrochemical oxidation of 2-[4-(N,N-dimethylamino)phenyl]-6-methyl benzothiazole (DPMB) in acetonitrile at platinum electrodes

The electrochemical oxidation mechanism of 2-[4-(N,N-dimethylamino)phenyl]-6-methyl benzothiazole (DPMB) is studied in a 0.1 M N(C₄H₉)₄ClO₄ + acetonitrile (ACN) reaction medium by cyclic (CV) and square wave voltammetries (SWV) as well as by controlled potential bulk electrolysis at platinum electrodes. The primary radical cation formed by the one electron oxidation of DPMB undergoes a deprotonation process, which is the rate-determining step, followed by a radical–radical coupling. On the other hand, an initial quasi-reversible monoelectronic charge transfer mechanism is inferred from cyclic and square wave voltammograms recorded at scan rates and frequencies higher than 0.4 V s^?1 and 40 Hz, respectively. Diffusion coefficients of DPMB at different temperatures were calculated from the quasi-reversible convoluted cyclic voltammograms. DigiSim® and COOL software were used to fit the quasi-reversible cyclic and square wave voltammetric responses, respectively. Formal potentials, formal rate constants and positive transfer coefficients at different temperatures were evaluated from the fitting of cyclic voltammograms. The experimental activation parameters were also determined. The effects of the analytical concentration of the reagent and the temperature, as well as the addition of trifluoracetic acid and a strong base such as lutidine on the electrochemical responses are discussed. A general reaction mechanism as well as probable structures for dimeric products are proposed.Besides, the presence of an acid–base equilibrium in DPMB solutions is also studied by employing UV–Vis spectroscopic measurements at different trifluoracetic acid concentrations. An apparent value of (1.5 ± 0.2) × 10³ M^?1 was estimated for the DPMB basic constant at 20.0 °C     

A stannum/bismuth/poly(p-aminobenzene sulfonic acid) film electrode for measurement of Cd(II) using square wave anodic stripping voltammetry

In the present work, a new method for a trace analysis of metal cadmium ion has been developed on the stannum/bismuth/poly(p-aminobenzene sulfonic acid) film electrode in combination with square wave anodic stripping voltammetry. This new electrode was prepared by in situ depositing stannum, bismuth and target metal on the poly(p-aminobenzene sulfonic acid)(p-ABSA) coated glassy carbon electrode. Some key factors including the pH of measure solution, the proper proportion between Bi(III) and Sn(II), the preconcentration time and the preconcentration potential have been studied and optimized. Compared with the traditional bismuth-film electrode, the stannum/bismuth/poly(p-ABSA) film electrode displayed higher stripping current response. In addition, it has the advantages of better stability and less toxicity. Under the optimum conditions, the linear calibration graph for Cd(II) in the concentration range of 0.5–55 μg L⁻¹ was obtained and the detection limit was 0.32 μg L⁻¹. The method was applied to the analysis of cadmium ion in tap water sample with satisfactory results.     

Electrochemical behaviour of oxocarbons on single crystal platinum electrodes Part 3. Croconic acid oxidation on Pt(111) surfaces in acid medium

The electrochemical behaviour of croconic acid (CRA) on Pt(111) electrodes has been studied in acid medium by cyclic voltammetry. Its oxidation proceeds via a dual path mechanism. The direct oxidation path takes place at potentials higher than 0.9 V, probably involving incipient surface oxide formation.The formation of strongly adsorbed species upon CRA adsorption is influenced by the concentration of CRA and the adsorption potential. At open circuit, only CO_ads is formed, while at controlled potentials lower than 0.40 V, other adsorbates, probably with more than one carbon atom, exist. These are oxidized to CO in the range 0.4–0.6 V. The activity for poison formation at open circuit is much lower for concentrations higher than 1 mM. FTIR experiments clearly indicate that carbon monoxide is not formed at potentials lower than 0.40 V. Linearly- and bridge-bonded CO adspecies appear at potentials higher than 0.40 V, which are oxidized to CO₂ before the direct oxidation of CRA begins. A band at 1780 cm^?1 indicates the presence of leuconic acid at potentials between 0.95 and 1.22 V as a product of the latter process. At higher potentials, CRA is completely oxidized to CO₂.     

Monomolecular films of a nickel(II) pentaazamacrocyclic complex for the electrocatalytic oxidation of hydrogen peroxide at gold electrodes

Self-assembled monolayers (SAMs) of a redox active nickel(II) pentaazamacrocyclic complex 1 and mixed monolayers of 1 with ethyl disulfide have been fabricated on a gold electrode, and their electrochemical behavior has been studied by cyclic voltammetry in aqueous solutions of Na₂SO₄ and NaNO₃. The results demonstrate that the redox behavior as well as the electrocatalytic activity towards the oxidation of H₂O₂ of the SAM and mixed monolayers of 1 largely depend on the electrolyte anions, i.e. SO₄^2? and NO₃^?: the formal potential in the SO₄^2? electrolyte is about 220 mV less positive than that in the NO₃^? electrolyte, and the SAM and mixed monolayers of 1 possess an efficient electrocatalysis for the oxidation of H₂O₂ in the NO₃^? electrolyte, but not in the SO₄^2? electrolyte. In addition, a unique cyclic voltammogram with a sharp peak of inverted ‘V’ shape has been observed in the cathodic scan for the electrocatalytic oxidation of H₂O₂, largely depending on the concentration of the NO₃^? electrolyte anion and the solution pH. These electrolyte anion-dependent redox behaviors have been discussed on the basis of different coordinating tendencies of SO₄^2? and NO₃^? to the nickel(III) centre of the complex and a possible reaction mechanism for the observed electrocatalytic reaction.     

Note on the oxidation of methanol at Pt(1 1 1) and Pt(3 3 2) electrodes in alkaline solutions

The cyclic voltammetric behavior of different concentrations of CH₃OH has been studied in alkaline solutions on Pt(1 1 1) and Pt(3 3 2). The oxidation of CH₃OH gives well-defined current density–potential curves at around the potential where the adsorption of OH occurs on Pt.The current–potential behavior of the hydrogen adsorption–desorption shows that CH₃OH or related species adsorbs on the step sites of (3 3 2) surface, but less on the (1 1 1) surface.The analysis of the voltammograms with less concentrated methanol solutions is suggested in order to understand the mechanism of CH₃OH oxidation reaction in alkaline media.     

A comparative evaluation on the voltammetric behavior of boron-doped diamond (BDD) and glassy carbon (GC) electrodes in different electrolyte media

Voltammetric responses of boron-doped diamond (BDD) and glassy carbon (GC) electrodes on the anodic oxidation of two dissimilar compounds namely 2,6-dimethoxyphenol and 1,3,5-trimethylbenzene in acidic, neutral and basic media have been explored. Cyclic voltammetric (CV) analysis reveals that the BDD electrode shows wider cathodic potential window and lower background current in all the media than the GC. However, in the anodic side, the window is wide only in aqueous acidic medium and the background limit for both the electrodes is similar in both neutral and alkaline media containing solvents other than water. Further, the anodic oxidation of 2,6-dimethoxyphenol takes place at less potential on the GC when compared to the BDD and the oxidation peak current is also higher on the former electrode. CV results show that no anodic peak appears for the oxidation of 1,3,5-trimethylbenzene on the GC electrode in any of the above media, whereas in the acidic medium, a broad anodic wave appears on the BDD.     

Electro-oxidation of phenol and its derivatives on poly-Ni(OH)TPhPyPc modified vitreous carbon electrodes

The electrochemical oxidation of phenol and its derivatives using poly-nickel hydroxy tetraphenoxypyrrolephthalocyanine (poly-Ni(OH)TPhPyPc) modified vitreous carbon electrodes are described. The films were formed by the electro-transformation of the electropolymerized pyrrole-substituted phenoxyphthalocyanine poly-NiTPhPyPc modified electrode in aqueous 0.1 M NaOH solution. The poly-Ni(OH)TPhPyPc films showed better stability and resistance to electrode fouling compared to poly-NiTPhPyPc and unmodified electrodes. The resistance to surface fouling and stability can be attributed to the structure of the ring substituent on the phthalocyanine macrocycle and to the particular O–Ni–O bridged architecture of the nickel phthalocyanine film.     

Thermodynamic studies of anion adsorption at the Pt(111) electrode surface in sulfuric acid solutions

The thermodynamics of the so-called perfectly polarized electrode were employed to analyze the total charge densities for a Pt(111) electrode in solutions of H₂SO₄ with an excess of an inert electrolyte (0.1 M HClO₄). A high quality Pt(111) single crystal electrode with a low defect density was employed in this study. The total charge densities were calculated by integration of cyclic voltammetry curves. A complete thermodynamic analysis using the electrode potential and the charge as independent variables has been performed. The best results were obtained when the charge was the independent variable. These results show that the maximum Gibbs excess of (bi)sulfate attains a value of ～3×10¹⁴ ions cm^?2, which corresponds to the packing density of ～0.2 monolayer. This number agrees well with the results of a radioactive labeling method (Kolics and Wieckowski, J. Phys. Chem. Sect. B 105 (2001) 2588) and with recent STM studies (Itaya, Prog. Surf. Sci. 58 (1998) 121; Funtikov, Linke, Stimming and Vogel, Surf. Sci. 324 (1995) L343). The calculated Esin–Markov coefficient and electrosorption valencies exhibit an important dependence on the electrode potential (or charge).     

Conducting films obtained by electro-oxidation of p-aminodiphenylamine (ADPA) in the presence of aniline in buffer aqueous solution at pH 5

The electrochemical oxidation of aniline and p-aminodiphenylamine (ADPA) was carried out in a phosphate buffer solution at pH 5. Cyclic voltammetry and “in situ” FTIR spectroscopy were combined to study the redox behavior of the oxidation products. When ADPA is oxidized in the presence of aniline, two redox processes are observed. One of these redox processes is related to a soluble species, while the other pertains to a species attached to the electrode surface. Only those films synthesized from ADPA oxidation in the presence of aniline are electroactive in this buffered medium. No evidence pointing to the occurrence of autocatalytic polymerization exists under the experimental conditions employed.     

A strategy for immobilisation of carbon nanotubes homogenised in room temperature ionic liquids on carbon electrodes

Functionalised multi-walled carbon nanotubes (MWCNT) were homogenised in the room temperature ionic liquids (RTILs) 1-butyl-3-methylimidazolium bis(trifluoromethane)sulfonimide (BmimNTF₂), 1-butyl-1-methylpyrrolidinium bis(trifluoromethane)sulfonimide (BmpyNTF₂) and 1-butyl-3-methylimidazolium nitrate, and the composite obtained was applied on the top of glassy carbon or carbon film electrode substrates. The modified electrodes were characterised electrochemically in aqueous electrolytes and ionic liquids using cyclic voltammetry and electrochemical impedance spectroscopy and the model redox couples potassium hexacyanoferrate and ferrocene were used for electrode characterisation in aqueous and RTIL media, respectively. It was found that the combination of MWCNT with BmimNTF₂ gave the best composite which augurs well for application in sensors and biosensors.     

Electrochemical quartz crystal microbalance study of mass transport during electrochemical oxidation of [Os(bpy)3]2+ in clay-modified electrodes

Mass transport in clay films containing [Os(bpy)₃]²⁺ cations was investigated by EQCM and crystal impedance spectroscopy. Admittance measurements on 10 μg clay films exchanged with [Os(bpy)₃]²⁺ show no change in the width or height of the conductance peaks before and after potential scans or potential steps. The [Os(bpy)₃]²⁺ exchanged films could be considered to be rigid with no change in their viscoelastic properties, and the shifts in resonant frequency in the EQCM measurements interpreted as mass changes. In an electrode coated with a 8.5 μg clay film, oxidation of the adsorbed cations resulted in a large increase in frequency, corresponding to a decrease in mass. The mass per mole of electron transferred (MPE) was ?205 g/mol, or about one third of the weight of one [Os(bpy)₃]²⁺ ion. This was consistent with the ejection of one [Os(bpy)₃]³⁺ from the film for each three [Os(bpy)₃]²⁺ cations oxidized. The ratio of cathodic charge to anodic charge of 0.7 was also consistent with the loss of one third of the oxidized [Os(bpy)₃]³⁺ ions. The mechanism of charge neutralization was dependent of the weight of the clay films. Oxidation of [Os(bpy)₃]²⁺ in a 33 μg clay film resulted in a small decrease in frequency, corresponding to an increase in mass. The MPE, +50 g/mol, was consistent with charge neutralization by adsorption of sulfate anions from the electrolyte.     

Electrooxidation of pyridoxal (PL) on a polycrystalline gold electrode in alkaline solutions

The electrooxidation of pyridoxal (PL) on a polycrystalline gold electrode is studied by cyclic voltammetry in alkaline media. Two oxidation peaks, A and B, are obtained in the positive scan within the potential range of the double-layer region. The behavior observed allows to propose an oxidation mechanism where the anion hemiacetal (ha^?) and hemiacetal (ha) are the electroactive species for peaks A and B, respectively. The oxidation product for both peaks is pyridoxic acid, in agreement with the analysis of the products obtained after controlled potential electrolysis.     

Voltammetric study of the interfacial electron transfer between bis(butylcyclopentadienyl)iron in 1,2-dichloroethane and hexacyanoferrate in water

The electron transfer (ET) reaction between bis(butylcyclopentadienyl)iron(II) ([Fe^II(C₅H₄Bu)₂]) in 1,2-dichloroethane (1,2-DCE) and the hexacyanoferrate redox couple ([Fe^II/III(CN)₆]^4?/3?) in water (W) at the 1,2-DCE∣W interface has been studied by use of normal pulse voltammetry and cyclic voltammetry. In normal pulse voltammetry, S-shaped current vs. potential curves with well-defined limiting currents attributable to the interfacial ET reaction were observed. The voltammetric results can be explained well by the theoretical equations [M. Senda, Rev. Polarogr. (Jpn), 49 (2003) 219; 50 (2004) 60] according to a so-called IT-mechanism, that is, the [Fe^II(C₅H₄Bu)₂] molecule is transferred from the 1,2-DCE to the W phase across the interface, then the ET reaction takes place homogeneously in the W phase between [Fe^III(CN)₆]^3?(W) and [Fe^II(C₅H₄Bu)₂](W) to produce [Fe^II(CN)₆]^4?(W) and [Fe^III(C₅H₄Bu)₂]⁺(W), which is followed by the transfer of the [Fe^III(C₅H₄Bu)₂]⁺ ion from the W to the 1,2-DCE phase across the interface to give the voltammetric current. Experimental results from cyclic voltammetry are also explained well by the IT-mechanism.     

Electrochemical quartz crystal microbalance study of copper adatoms on Au(111) electrodes in solutions of perchloric and sulfuric acid

The adsorption of anions on highly ordered (111)-type gold electrodes with and without Cu adatoms in perchloric and sulfuric acid electrolyte solutions was investigated on an electrochemical quartz crystal microbalance. A distinct increase in mass due to the specific adsorption of hydrated bisulfate and perchlorate anions was observed in Cu²⁺-free solutions and their amounts were determined as a function of the potential. The composition of the Cu-adlayer (θ_Cu and θ_anion, coverages of Cu adatoms and co-adsorbed anions) during formation or removal in the potential sweep was also determined in both electrolyte solutions. A pair of reversible anodic and cathodic peaks in the voltammogram for the first Cu-upd region in H₂SO₄ was found to correspond well to the reversible changes in θ_Cu and θ_anion. In contrast, asymmetric features of the voltammograms for the second Cu-upd region in H₂SO₄ and for whole processes in HClO₄ corresponded to the large hysteresis in changes of θ_Cu and θ_anion, probably originating from a slow rearrangement of both species.     

磷酸钙/聚乳酸羟基乙酸复合骨水泥对破骨前体细胞炎症因子表达的影响

目的观察磷酸钙/聚乳酸羟基乙酸复合骨水泥(CPC/PLGA)对破骨前体细胞炎症因子TNF-α、IL-1、IL-6表达的影响,了解PLGA促进CPC降解的机理。方法 1根据高效液相色谱法检测出的乳酸、羟基乙酸浓度配置CPC/PLGA替代液。2将RAW264.7细胞分别培养在DMEM培养基(对照组),第6小时CPC初凝块浸提液(A组)及CPC/PLGA替代液(B组)。通过CCK-8法检测各组细胞的增殖变化,并通过RT-PCR法检测各组中TNF-α、IL-1、IL-6 mRNA的表达情况。结果增殖实验结果示,A组细胞的增殖率在5 d时达到最高值(1.01±0.02),而B组细胞的增殖率在5 d时达到最高值(1.07±0.02),均与对照组相比有统计学意义(P<0.05)。RT-PCR法示A组和B组细胞TNF-αmRNA、IL-1 mRNA在6 h时表达最高,IL-6mRNA在12 h时表达最高,与对照组比较均有统计学差异(P<0.05)。结论磷酸钙/聚乳酸羟基乙酸复合骨水泥调控破骨前体细胞炎症因子增高。     

Oxygen reduction in alkaline medium at thin MnxCo3−xO4 (0≤x≤1) spinel films prepared by spray pyrolysis. Effect of oxide cation composition on the reaction kinetics

We have studied the relationships between the cation distributions in bulk and on the surface and the electrocatalytical reactivity towards the oxygen reduction reaction (orr) on thin film electrodes of cobalt and manganese spinel type oxides Mn_xCo_3?xO₄ (0≤x≤1). The cationic distributions were computed from XRD, XPS, magnetism and oxidation power measurements showing the presence of the Co³⁺/Co²⁺ and Mn⁴⁺/Mn³⁺ solid state redox couples and also vacancies in octahedral sites. The electrocatalytic activity and kinetic parameters for the orr were determined using the RRDE technique in 1 M KOH solution at 25 °C. Two Tafel zones of slopes b_c1 and b_c2 around ?60 and ?120 mV dec^?1 were observed. The disk current/ring current ratio, (I_D/I_R), increases with x and decreases with the applied overpotential. At constant overpotential η the real electrocatalytical current densities j increase when x increases. The orr can be characterized by an intrinsic kinetic parameter J′ obtained from this current ratio at various electrode rotational frequencies. This J′ increases with the redox couple Co²⁺/Co³⁺ ratio, increasing more in the bulk than at the surface of the electrode.     

The influence of poly(acrylic) acid number average molecular weight and concentration in solution on the compressive fracture strength and modulus of a glass-ionomer restorative

Objectives

The aim was to investigate the influence of number average molecular weight and concentration of the poly(acrylic) acid (PAA) liquid constituent of a GI restorative on the compressive fracture strength (σ) and modulus (E).

Methods

Series of PAA solutions for eight experimental PAAs with molecular weights ranging from 5000 to 200,000 were prepared at concentrations ranging from 10 to 60%. The PAA number average molecular weights were determined using gel permeation chromatography and the viscosity at each concentration was determined using a digital viscometer. The PAA solutions were hand-mixed with a commercial GI restorative powder (Ionofil Molar; Voco, Cuxhaven, Germany). σ and E were determined at 24 h using cylindrical (6 mm height, 4 mm diameter) specimens (n = 20). Data was analyzed using regression analyses and two-way analyses of variance at p < 0.05.

Results

Regression analyses showed a significant reduction in PAA solution viscosity with reducing PAA number average molecular weight. Two-way ANOVAs for σ and E indicated a significant interaction of number average molecular weight × concentration (p < 0.001 and p < 0.001, respectively). Quadratic regression analyses showed significant curvature (n-shaped curves) within σ and E data for individual PAA number average molecular weights with increasing concentration. As a result, the optimum PAA concentration for each PAA number average molecular weight was determined from the curve vertexes.

Significance

The choice of PAA molecular weight and concentration and the subsequent viscosity of the PAA solution have a significant influence on the σ and E of a GI restorative, however, the relationship is not a simple one.     

Influence of the nature of the supporting electrolyte on the formation of poly[4,4′-bis(butylsulphanyl)-2,2′-bithiophene] films. A role for both counter-ion and co-ion in the polymer growth and p-doping processes

Electrode deposits of a polythiophene with particularly interesting characteristics, i.e., poly[4,4^′-bis(butylsulphanyl)-2,2^′-bithiophene], have been generated in the presence of different supporting electrolytes. The formation of the coatings has been studied by coupling conventional electrochemical techniques with quartz crystal microbalance measurements. The results of simultaneous voltammetric or chronoamperometric and microgravimetric experiments allow us to show the influence exerted by the nature of the supporting electrolyte on the polymerisation and concomitant charging–discharging processes of the conducting polymer.