Reductive bond cleavage of chloro-substituted 10-methyl- tribenzotriquinacenes: Transition between concerted and stepwise mechanisms

The electrochemical reduction of 1-chloro-, 1,4-dichloro- and 1,4,7-trichloro-10-methyl-tribenzotriquinacenes in ACN and DMF was found to occur by concerted electron transfer and bond breaking process, showing irreversible cyclic voltammetric peaks. However, the transition of the process to the stepwise mechanism upon increasing the driving force by raising the scan rate was established. Both CCl bonds are reduced successively in the dichloro compound, but only two bonds overall were reduced in the trichloro compound. The reduction mechanism is discussed. The homolytic dissociation energy of CCl bond in monochloro compound was estimated to be equal to 2.9 eV.     

Electrochemical reductive cleavage of carbon-chlorine bond in 1-chloro-2,4-dinitrobenzene

The electrochemical reductive cleavage of carbon-chlorine bond in 1-chloro-2,4-dinitrobenzene at gold electrodes is analyzed from a mechanistic point of view. The initial electron transfer forms the radical anion of 1-chloro-2,4-dinitrobenzene which subsequently undergoes bond cleavage following an EC mechanism. At low scan rates, the reduction is under the kinetic control by the chemical step, while the voltammetric wave becomes reversible at high scan rates and a mixed chemical-diffusion control is observed at intermediate scan rates. The cleavage rate constant of the carbon-chlorine bond has been deduced using the voltammetric data in conjunction with convolution analysis and the results have been verified by simulating the experimental voltammogram under the frame work of EC mechanism.     

Solvent effect on kinetics of the C-Cl bond cleavage in radical anions of chloroanthracenes

Rate constants of CCl bond cleavage, k_cl, in radical anions of 2-chloro- and 9,10-dichloroanthracenes were determined in a number of aprotic solvents by means of the voltammetric method. They were discussed in terms of the Savéant concerted mechanism and the recent formulation including the impact of the electronic coupling on the activation barrier height. The very low slope, equal to −0.09, of the relationship between RT ln k_cl and the thermodynamic driving force was observed.     

The mechanism and kinetics of the electrochemical cleavage of azo bond of 2-hydroxy-5-sulfophenyl-azo-benzoic acids

The electrochemical reduction of 2-hydroxy-5-[(4-sulfophenyl)azo]benzoic acid, 2-hydroxy-5-[(3-sulfophenyl)azo]benzoic acid, 2-hydroxy-5-[(2-sulfophenyl)azo]benzoic acid and 2-hydroxy-5-azo-benzoic acid has been carried out in aqueous solutions at glassy carbon electrode using cyclic voltammetry and chronoamperometry. The position of sulfo substituent relative to azo bridge as well as pH of the solution have significant impact on the electrochemical behavior of these compounds. It has been proposed that these compounds are reduced predominantly as hydrazone tautomers resulting in corresponding hydrazo compounds. The overall electrochemical reduction follows DISP2 mechanism, ultimately leading to the 5-amino salicylic acid and sulfanilic acid. The rate determining step is the homogenous redox reaction between intermediate hydrazo compound and 5-amino salicylic acid quinoneimine. The mechanism is proposed in which activated complex of 5-amino salicylic acid quinoneimine and intermediate hydrazo compound is formed with the simultaneous loss of one proton.     

Cyclic voltammograms obtained from the optical signals: Study of the successive electro-oxidations of rutin

This paper describes a novel method of obtaining cyclic voltammograms (CVs) from optical signals. The obtained CVs correspond to the various specific species involved in the electrode process, which give more detailed information on the system under investigation than the common CV. For this purpose cyclic voltabsorptometry was used to investigate the successive oxidation processes of rutin on a graphite-wax electrode by using a long optical-path thin-layer electrochemical cell. The dynamic UV spectra of rutin showed the information on the structures of the oxidation products at different potentials. Cyclic voltabsorptiograms (CVAs) were measured in three potential ranges at the characteristic absorption wavelengths of rutin, 346, 254 and 296 nm, respectively. The CVs of three species in solution (rutin and its two products) were obtained from the derivative cyclic voltabsorptiograms (DCVAs). Based on this the redox mechanisms of rutin in different CV peaks were discussed.     

Electrochemical reduction of 2-nitroimidazole in aprotic medium: Influence of its dissociation equilibrium on the reduction mechanism

The electrochemical reduction of 2-nitroimidazole in a non-aqueous medium using cyclic voltammetry (CV) at a mercury electrode was carried out.The 2-nitroimidazole derivative in DMF + 0.1 M tetra(n-butyl)ammonium hexafluorophosphate (TBAHFP6) resulted in the following dissociation equilibrium:

HNRNO₂ ? ⁻NRNO₂ + H⁺     

Electrochemical chlorination of azulene derivatives: Insight into the mechanism of anodic oxidative chlorination

The cyclic voltammetry behavior of a series of five 1-substituted azulenes has been investigated as well as the electrochemical chlorination of these compounds. In the case of azulene compounds containing electron withdrawing groups which have higher oxidation potentials than that of the chloride ion, the electrochemical chlorination led usually to 3-chloro derivatives. The electrochemical chlorination fails for azulenes with lower oxidation potentials. Additionally some polyhalogenated compounds were obtained by controlled potential electrolyses. The paper also discusses the reaction mechanism of the electrochemical halogenation of 1-substituted azulenes.     

Effect of metals on silver electrodeposition: Application to the detection of cisplatin

In the present work, the influence of several metals (Co, Ru, Pd, Os, Pt, Cu, Pb), deposited on a carbon paste electrode, towards silver electrodeposition was tested. First, adequate conditions for the electrodeposition of metals on the electrode were found. Then, the cyclic voltammograms registered (silver deposition curves and analytical signals) showed that Co, Cu, Pt and Pd were able to accelerate silver electrodeposition. Finally, a valid methodology for the detection of cisplatin was established. It is based on the deposition of silver on a Pt (from cisplatin) modified electrode and the analytical signal corresponds to the anodic stripping of the deposited silver. A limit of detection of 3.2 × 10⁻⁹ mol dm⁻³ (1 ng cm⁻³) cisplatin was obtained.     

Electropolymerization of o‐phenylenediamine on Pt‐electrode from aqueous acidic solution: Kinetic,mechanism, electrochemical studies and characterization of the polymer obtained

Electropolymerization of O‐phenylenediamine (o‐PD) on Pt‐electrode from a deoxygenated aqueous acid medium was carried out using cyclic voltammetry technique. The kinetic parameters were calculated by means of electrochemical data. The experimentally obtained kinetic equation was R_P,_E = k_E [monomer]^1.19 [acid]^1.23 [electrolyte]^0.87 from the value of the anodic current density using cyclic voltammetry technique. The apparent activation energy (E_a) is found to be 28.34 kJ mol^?1. The polymer films obtained have been characterized by X‐ray diffraction, elemental analysis, scanning electron microscopy, ¹H‐NMR, ¹³C‐NMR, UV‐visible, and IR spectroscopy. The mechanism of the electrochemical polymerization reaction has been discussed. TGA is used to confirm the proposed structure and determination of the number of water molecules in the polymeric chain unit. © 2009 Wiley Periodicals, Inc. J Appl Polym Sci, 2009     

Electropolymerization of p‐phenylenediamine on Pt‐electrode from aqueous acidic solution: Kinetics,mechanism, electrochemical studies,and characterization of the polymer obtained

Ar plasma‐induced graft polymerization of poly(ethylene glycol) (PEG) on Ar plasma pretreated poly(methyl methacrylate) (PMMA) surfaces was carried out to improve the antistatic properties. The surface composition and microstructure of the PEG‐grafted PMMA surfaces from plasma induction were characterized by attenuated total reflectance Fourier transfer infrared (ATR‐FTIR) spectroscopy, water contact angles (CA), and atomic force microscopy (AFM) measurements. The measurements revealed that the antistatic properties can be remarkably improved with the surface resistivity of PEG‐grafted PMMA surface decreasing significantly by 3–6 orders of magnitude, with the optimum condition for polymerization grafted onto the Ar plasma pretreated PMMA surface being 40 W for RF power and 3 min for glow discharge time. © 2010 Wiley Periodicals, Inc. J Appl Polym Sci, 2010     

Immobilization of Nafion-ordered mesoporous carbon on a glassy carbon electrode: Application to the detection of epinephrine

A stable suspension of ordered mesoporous carbon (OMC) was obtained by dispersing OMC in a solution of Nafion. By coating the suspension onto glassy carbon (GC) electrode, cyclic voltammetry was used to evaluate the electrochemical behaviors of Nafion-OMC-modified GC (Nafion-OMC/GC) electrode in 0.1 mmol L⁻¹ hexaammineruthenium(III) chloride (Ru(NH₃)₆Cl₃)/0.1 mol L⁻¹ KCl solution, where Nafion-OMC/GC electrode shows a faster electron transfer rate as compared with OMC/GC, Nafion/GC and GC electrodes. Due to the unique properties of Nafion-OMC, an obvious decrease in the overvoltage of the epinephrine (EP) oxidation (ca. 100 mV at pH 4.1 and 115 mV at pH 7.0) as well as a dramatic increase in the peak current (12 times at pH 4.1 and 6 times at pH 7.0) was observed at Nafion-OMC/GC electrode compared to that seen at GC electrode. By combining the advantages of OMC with those of Nafion, the anodic peak of EP and that of ascorbic acid (AA) were separated successfully (by ca. 144-270 mV) in the pH range of 2.0-10.0, which may make Nafion-OMC/GC electrode potential for selective determination of EP in the presence of AA at a broad pH range. As an EP sensor, the EP amperometric response at Nafion-OMC/GC electrode in pH 7.0 PBS is extremely stable, with 99% of the initial activity remaining (compared to 32% at GC surface) after 120 min stirring of 0.20 mmol L⁻¹ EP. And Nafion-OMC/GC electrode can be used to readily detect the physiological concentration of EP at pH 7.0. These make Nafion-OMC/GC electrode potential candidates for stable and efficient electrochemical sensor for the detection of EP. The solubilization of OMC by Nafion may provide a route to more precise manipulation, and functionalization for the construction of OMC-based sensors, as well as allowing OMC to be introduced to biologically relevant systems.     

The effect of intracanal placement of various medicaments on the bond strength of three calcium silicate-based cements to root canal dentin

This study aimed to evaluate the effect of intracanal placement of various medicaments on the bond strength of ProRooT MTA, Biodentine, and Endosequence root repair material (ERRM) putty. Ninety extracted human mandibular premolar teeth were decoronated and instrumented using Protaper Next rotary system and #1 to #6 Peeso reamers. The prepared teeth were randomly divided into six groups according to the intracanal medicaments: Group 1: double antibiotic paste (DAP) consisting of metronidazole and ciprofloxacin; Group 2: Triple antibiotic paste (TAP) with cefaclor; Group 3: TAPwith clindamycin; Group 4: amoxicillin and clavulanic acid (Augmentin®); Group 5: calcium hydroxide (CH); Group 6: control (no medicament) (n = 15). Parallel transverse sections were obtained in the coronal to the apical direction (4 slices/ tooth) and were divided into three subgroups according to the cements: Group A: ProRoot MTA; Group B: Biodentine; Group C: ERRM (n = 20 slices/subgroup). A push-out test was used to measure bond strength. Data were analyzed using two-way analysis of variance and Tukey’s post hoc test. The bond strength was significantly lower for DAP and TAPs than for Augmentin®, CH, or the control (p < 0.05). Biodentine and ERRM had significantly higher bond strength values than ProRooT MTA (p < 0.05) regardless of the intracanal medicaments tested, while no significant difference existed between Biodentine and ERRM (p > 0.05). While the application of DAP or TAPs decreased the bond strength, application of CH or Augmentin® did not. ERRM and Biodentine had higher bond strength values than ProRoot MTA.     

Mechanistic study of electrochemical oxidation of catechols in the presence of 4-hydroxy-1-methyl-2(1H)-quinolone: Application to the electrochemical synthesis

Electrochemical oxidation of catechols (1a-1c) has been studied in the presence of 4-hydroxy-1-methyl-2(1H)-quinolone (3) as a nucleophile in aqueous solution using cyclic voltammetry and controlled-potential coulometry. The results indicate that the quinones derived from catechols (1a-1c) participate in Michael addition reactions with 3 to form the corresponding benzofuran (or isochromeno[4,3-c]quinoline) derivatives (6a-6c). The electrochemical synthesis of (6a-6c) has been successfully performed in an undivided cell in good yield and purity. The oxidation mechanism was deduced from voltammetric data and by coulometry at controlled-potential. The products have been characterized after purification by IR, ¹H NMR, ¹³C NMR and MS.     

Application of the electrochemical quartz crystal microbalance technique to copper sonoelectrochemistry: Part 1. Sulfate-based electrolytes

The applicability of the electrochemical quartz crystal microbalance technique in an ultrasonic field created by an ultrasound probe is demonstrated for the electrodeposition of copper. Cyclic voltammetry and potentiostatic depositions in acidic sulfate-based copper electrolytes were performed at different ultrasonic intensities. The electrochemical quartz crystal microbalance was operated in ultrasonic fields with intensities up to 30 W cm⁻². For cyclic voltammetry, potential resolved and averaged (apparent) current efficiencies were calculated from mass and charge data in function of the amplitude of the ultrasonic horn. Ultrasound slightly affected the current efficiencies during copper deposition in cyclic voltammetry, but did not change the efficiencies during dissolution. During potentiostatic depositions the current efficiency increased from 84% to almost 100% upon application of ultrasound. Morphology of deposits prepared by potentiostatic depositions was analyzed by scanning electron microscopy, and found to be different at high ultrasonic intensities.     

Electrodes covered with random arrays of microdroplets: heterogeneous electron transfer coupled to catalytic reaction at the liquid/liquid interface in the prism film geometry approximation

A model for the catalytic (EC’) mechanism on the three-phase electrode arrangement is developed. It is assumed that a solid electrode surface is partly covered by an insulating solution of substance A in an organic liquid which is immiscible with water and immersed into an aqueous solution of a depolarizer and a supporting electrolyte. At the liquid/liquid interface the substance A reacts with the aqueous phase product of the electrode reaction occurring at the uncovered parts of the electrode with regeneration of the depolarizer. An average cyclic voltammetry response, a distribution of the current density and a pure kinetic current are calculated using a finite difference method.     

Influence of anode material on the electrochemical oxidation of 2-naphthol: Part 1. Cyclic voltammetry and potential step experiments

The anodic oxidation of 2-naphthol has been studied by cyclic voltammetry and chronoamperometry, using a range of electrode materials such as Ti-Ru-Sn ternary oxide, lead dioxide and boron-doped diamond (BDD) anodes. The results show that polymeric films, which cause electrode fouling, are formed during oxidation in the potential region of supporting electrolyte stability. IR spectroscopy verified the formation of this organic film. While the Ti-Ru-Sn ternary oxide surface cannot be reactivated, PbO₂ and BDD can be restored to their initial activity by simple anodic treatment in the potential region of electrolyte decomposition. In fact, during the polarization in this region, complex oxidation reactions leading to the complete incineration of polymeric materials can take place on these electrodes due to electrogenerated hydroxyl radicals. Moreover, it was found that BDD deactivation was less pronounced and its reactivation was faster than that of the other electrodes.     

PEB/St-AN悬浮接枝共聚反应机理的研究

研究了乙烯-1-丁烯共聚物（PEB）与苯乙烯-丙烯腈（St-AN）悬浮接枝共聚体系的反应行为随反应时间的延长而变化的规律。核磁共振氢谱（1 H-NMR）分析表明反应产物由未接枝PEB、接枝共聚物PEB-g-SAN和非接枝共聚物SAN构成,无交联产物存在。体系在反应的最初阶段接枝共聚反应速率高于非接枝共聚反应速率。凝胶渗透色谱（GPC）分析表明,在整个反应过程中发生了未接枝PEB和PEB-g-SAN主链的降解反应。共聚反应在反应时间为240min时结束,此后发生少量未接枝PEB和PEB-g-SAN结合的反应,导致产物的橡胶接枝率逐渐提高、产物与SAN树脂共混物的缺口冲击强度逐渐上升、以及用SEM分析证实的共混物增韧机理由空穴化的脆性断裂向高度剪切屈服的韧性断裂转变。     

The instantaneous image effect: A novel contribution to the mechanism of heterogeneous catalysis

A novel contribution to the mechanism of heterogeneous catalysis is discussed for a model H₂-on-nickel (100) system. The effect, which corresponds in a first approximation to the dispersion energy between adsorbate molecule and metal, is calculated through (1) admixture of an ionic component in the wave function of the adsorbate; (2) interaction between this ionic component and the image dipole which it creates in the polarizable metal. A single VB model, using an Anderson-type evaluation of the delocalization energy between adsorbate and metal, shows the image contribution to be 10 to 15% of the total adsorbate metal interaction energy.Presented in part at the 3rd International Symposium on the Mechanisum of Heterogeneous Catalysis Berkeley, Cal., 12–14 November, 1990.     

Use of DTA with infrared analysis of evolved gas to investigate the effect of flame retardants on gas evolution from pyrolysed cellulose (cotton)

DTA combined with infrared analysis of the evolved gas (EGA) has been used to study the temperature behaviour, both in air and nitrogen, of commercial phosphorus- and nitrogen- and/or bromine-containing flame retardants applied to cotton. By reference to the DTA traces and also the maxima occurring in the CO, CO₂ and H₂O evolution rates, seven significant peak temperatures were assigned. Two new relatively low temperature peaks have been observed: the higher of these is DTA-sensitive and occurs in all unretarded and retarded samples and is ascribed to the formation of an ‘activated cellulose’ state previously proposed by Bradbury, Sakai and Shafizadeh;¹⁷ the lower peak is an exotherm (188-220°C) associated with H₂O and CO₂ evolution from flame-retarded samples only. These observations are interpreted in terms of the mechanism of the cellulose pyrolysis/combustion and the influence of the flame retardants.