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Electrochemical Behaviour (electrochemical + behaviour)
Selected AbstractsMixed-Metal Dawson Sandwich Complexes: Synthesis, Spectroscopic Characterization and Electrochemical Behaviour of Na16[MIICo3(H2O)2(P2W15O56)2] (M = Mn, Co, Ni, Zn and Cd)EUROPEAN JOURNAL OF INORGANIC CHEMISTRY, Issue 11 2007Laurent Ruhlmann Abstract Mixed-metal Dawson sandwich complexes [MCo3(H2O)2(P2W15O56)2]16, (represented as {MCo3P4W30}) have been synthesized by the reaction of M2+ (where M = Mn, Co, Ni, Zn and Cd) with the "lacunary" sandwich complex ,,-[NaCo3(H2O)2(P2W15O56)2]17, (represented as {NaCo3P4W30}): [NaCo3(H2O)2(P2W15O56)2]17, + M2+,,,[MCo3(H2O)2(P2W15O56)2]16, + Na+. The {MCo3P4W30} species were characterized by IR spectroscopy, elemental analysis and 31P solution NMR spectroscopy. The electrochemical behaviour of these mixed-metal sandwich complexes was investigated in aqueous solution and compared with that of ,,-[Co4(H2O)2(P2W15O56)2]16, (represented as ,,-{Co4P4W30}) and {NaCo3P4W30}. (© Wiley-VCH Verlag GmbH & Co. KGaA, 69451 Weinheim, Germany, 2007) [source] Chemical and Electrochemical Behaviours of a New Phenolato-Bridged Complex [(L)MnIIMnII(L)]2+.EUROPEAN JOURNAL OF INORGANIC CHEMISTRY, Issue 21 2006Dinuclear Mono-µ-Oxido [(L)MnIII(µ-O)MnIII/IV(L)]2+/3+ Species, Pathways to Mononuclear Chlorido [(L)MnII/III/IVCl]0/1/2+ Abstract The X-ray structure of a new dinuclear phenolato-bridged Mn2II complex abbreviated as [(L)MnMn(L)]2+ (1), where LH is the [N4O] phenol containing ligand N,N -bis(2-pyridylmethyl)- N, -salicylidene-ethane-1,2-diamine ligand, is reported. A J value of ,3.3 cm,1 (H = ,J,1·,2) was determined from the magnetic measurements and the 9.4 GHz EPR spectra of both powder and frozen acetonitrile solution samples were analyzed with temperature. The cyclic voltammetry of 1 displays a reversible anodic wave at E1/2 = 0.46 V vs. SCE associated with the two-electron oxidation of 1 yielding the dinuclear Mn2III complex [(L)MnMn(L)]4+ (2). The easy air oxidation of 1 gives the mono-,-oxido Mn2III complex [(L)Mn(, - O)Mn(L)]2+ (3). A rational route to the formation of the mixed-valence Mn2III,IV complex [(L)Mn(, - O)Mn(L)]3+ (4) starting from 1 by bulk electrolysis at EP = 0.75 V vs. SCE in the presence of one equiv. of base per manganese ion is also briefly reported. Addition of chloride ions to 1 led to the cleavage of the phenolato bridges to give the mononuclear MnII complex [(L)MnCl] (5). Cyclic voltammetry of 5 displays two reversible anodic waves at E1/2 = 0.21 and E1/2 = 1.15 V vs. SCE, assigned to the two successive one-electron abstractions giving the MnIII and MnIV species [(L)MnCl]+ (6) and [(L)MnCl]2+ (7), respectively. The electronic signatures from UV/Visible and EPR spectroscopy of the electrochemically prepared samples of 6 and 7 confirmed the respective oxidation states. For instance, 7 displays a broad and intense absorption band characteristic of a phenolato to MnIV charge-transfer transition at 690 nm (2000 M,1,cm,1) and its 9.4 GHz EPR spectrum shows a strong transition at g = 5.2 consistent with a rhombically distorted S = 3/2 system with a zero-field splitting dominating the Zeeman effect. (© Wiley-VCH Verlag GmbH & Co. KGaA, 69451 Weinheim, Germany, 2006) [source] Electrochemical behaviour and electrochemical polymerization of fluoro-substituted anilinesPOLYMER INTERNATIONAL, Issue 8 2002Atilla Cihaner Abstract The electrochemical behaviour of three fluoro-substituted aniline monomers, 2-fluoroaniline (2FAN), 3-fluoroaniline (3FAN) and 4-fluoroaniline (4FAN), was investigated in aqueous acidic and organic media by means of cyclic voltammetry (CV) studies. Constant potential electrolysis (CPE) of the monomers in acetonitrile,water mixture (1:1 by volume) using NaClO4 as supporting electrolyte yielded soluble polymers. The mechanism of electrochemical polymerization was investigated using in situ electron spin resonance (ESR) and in situ UV,VIS spectroscopic techniques for one of the monomers (4FAN). Both CV and in situ UV,VIS measurements indicated that the polymers obtained are in the emeraldine base form. In situ ESR studies indicated that electrochemical polymerization involves a radical-cation as an intermediate. Characterization of polymer products have been carried out using FTIR and NMR spectroscopic techniques, and thermal behaviour was studied using differential scanning calorimetry (DSC). It was found that conductivity can be imparted to as-synthesized polyfluoroanilines via iodine doping. © 2002 Society of Chemical Industry [source] Directly Heated Bismuth Film Electrodes Based on Gold MicrowiresELECTROANALYSIS, Issue 13 2010Martin Jacobsen Abstract As a nontoxic substitute for mercury electrodes, bismuth electrodes attained a lot of attention during the last years. In this report we describe for the first time the preparation of two different directly heatable bismuth-modified microwire electrodes. We characterized the electrochemical behaviour using cyclic voltammetry in acetate buffer and alkaline tartrate solution. The bismuth electrodes show a significantly wider potential window compared with bare gold wires. In the presence of picric acid as one example for the detection of explosives, the bismuth electrodes deliver higher signals. By applying heat during the measurements, the signals can be enhanced further. We used the temperature pulse amperometry (TPA) technique to improve the electrochemical response at the different types of electrodes. In this preliminary study, we were able to detect 3,ppm traces of picric acid. [source] Ferrocene Conjugates Containing Diarginine and Aspartic Acid: Salt Bridge Interactions in WaterEUROPEAN JOURNAL OF INORGANIC CHEMISTRY, Issue 29-30 2009Anas Lataifeh Abstract The ferrocene peptide conjugates of diarginine (MeO-Fc-Arg-Arg-NH2) (1) and aspartic acid [Boc-Fca-Asp(OH)-OH] (2) were found to form a stable 1:1 associate in aqueous solution. The molecular recognition was achieved through a combination of multipoint hydrogen bonding (H-bonding) sites and a guanidinium-carboxylate ion pair. The associate stoichiometry was confirmed by using ESI-MS and NMR experiments; the NMR titration curve shows multiple equilibria with stepwise interconversion from 1:2,,,1:1 binding ratios, and the electrochemical behaviour of the ferrocenyl groups (Fc, Fca) confirm the formation of an ion pair. The CD spectra in the peptide region exhibit a characteristic absorption of a more ordered structure, while the ferrocene helical chirality remains intact. The solid-state IR measurements exclude the involvement of the amide backbone in the interaction.(© Wiley-VCH Verlag GmbH & Co. KGaA, 69451 Weinheim, Germany, 2009) [source] Off the Back or on the Side: Comparison of meso and 2-Substituted Donor-Acceptor Difluoroborondipyrromethene (Bodipy) DyadsEUROPEAN JOURNAL OF ORGANIC CHEMISTRY, Issue 15 2010Andrew C. Benniston Abstract The preparation of several difluoroborondipyrromethene (Bodipy) dyads is described incorporating covalently attached hydroquinone/quinone groups at the 2-position (BD-SHQ, BD-SQ, BD-SPHQ, BD-SPQ). The compounds, currently under investigation as chemical sensors for reactive oxygen species, show various levels of fluorescence depending on the oxidation state of the appended group. The 19F NMR spectrum for BD-SHQ in CDCl3 at room temperature reveals the two fluorines are inequivalent on the NMR timescale. In contrast, the 19F NMR spectrum for the counterpart quinone compound, BD-SQ, is consistent with two equivalent fluorine atoms. The two results are interpreted as the quinone is free to rotate around the connector bond, whereas this motion is restricted for the hydroquinone group and makes the fluorines chemically inequivalent. Cyclic voltammograms recorded for all derivatives in CH2Cl2 electrolyte solution are consistent with typical Bodipy-based redox chemistry; the potentials of which depend on factors such as presence of the phenylene spacer and oxidation state of the appended group. A comparison of the electrochemical behaviour with the counterpart meso derivatives reveals some interesting trends which are associated with the location of the HOMO/LUMOs. The absorption profiles for the compounds in CH3CN are again consistent with Bodipy-based derivatives, though there are some subtle differences in the band-shapes of the closely-coupled systems. In particular, the absorption spectra for the dyad, BD-SQ, in a wide range of solvents are appreciably broader than for BD-SHQ. Femtosecond transient absorption spectroscopy performed on the hydroquinone derivatives, BD-SHQ and its meso analogue is interpreted as electron transfer occurs from the hydroquinone unit to the first-excited singlet (S1) state of the Bodipy center, followed by ultrafast charge recombination to reinstate the ground state. The coupling of OH vibrations to the return electron transfer process is invoked to explain the lack of clear identification of the charge-separated state in the transient records. [source] A block-on-ring tribocorrosion setup for combined electrochemical and friction testingLUBRICATION SCIENCE, Issue 3 2007M.S. Jellesen Abstract The combined action of corrosion and wear can cause degradation of equipment, and thereby financial losses related to the renewal or repair of damaged equipment. In the food industry, metal degradation is a major concern since metal release eventually can cause health risks for consumers. This study describes a block-on-ring testing facility used to determine sliding wear, and additionally allowing for electrochemical measurements, such as potentiodynamic polarization curves and potentiostatic monitoring of current and potential. To verify the reliability and reproducibility of this block-on-ring tribocorrosion setup, the tribological and electrochemical behaviour of stainless steel sliding against a ceramic ring in sulphuric acid has been determined. Furthermore, a case taken from the food industry has been examined. The study shows that results made on the described block-on-ring testing facility are reliable and can provide improved information about material properties when the material is exposed to combined chemical and mechanical degradation. Copyright © 2007 John Wiley & Sons, Ltd. [source] A comparative electrochemical study of commercial and model aluminium alloy (AA5050)MATERIALS AND CORROSION/WERKSTOFFE UND KORROSION, Issue 6 2009P. Premendra Abstract A comparative electrochemical study of commercially recycled AA5050 and model AA5050, in their as-cast state, is carried out to investigate the effect of recycling and furthermore the effect of trace elements like Pb, Cu, etc on electrochemical activation and filiform corrosion (FFC) susceptibility. A systematic combination of surface analytical techniques like scanning Kelvin probe force microscopy (SKPFM), scanning electron microscopy (SEM) and energy dispersive X-ray (EDX) is used to study the composition and electrochemical behaviour of second phase particles. These results, together with localized breakdown measurements using the electrochemical micro-cell, elucidate the effect of recycling and the role played by trace elements in influencing the electrochemical behaviour of the alloy. [source] Mechanical and corrosion behaviour of a Ti-Al-Nb alloy after deformation at elevated temperaturesMATERIALS AND CORROSION/WERKSTOFFE UND KORROSION, Issue 12 2008M. V. Popa Abstract The mechanical properties of Ti6Al7Nb alloy deformed and heat treated at elevated temperatures were correlated with its microstructure and corrosion behaviour in Ringer (of different pH values: 2.49, 6.9 and 8.9) and Ringer,Brown solutions. Microstructural analysis revealed a Widmanstatten structure for the alloys deformed at 1100,°C (, field) and structure with , grains at 930,°C (,,+,, field). The thermo-mechanical processing improved the electrochemical behaviour of Ti6Al7Nb alloys, especially their passive state. Open circuit potential variations in time reflected more compact, stable, resistant passive films on the surface of the treated alloys. Open circuit potential gradients simulating the non-uniformities of pH along the implant surface have very low values that cannot generate galvanic corrosion. Corrosion rates and ion release are very much reduced. Impedance spectra were fitted with a two time-constants equivalent circuit for some alloys and with three time-constants equivalent circuit for other alloys. [source] | |||||||||||||