Portugaliae
Electrochimica Acta

The aim of this work is to check that the poly 2,5-di-(2-thienyl)pyrrole, poly(SNS), is a linear polymer which behaves, from an electrochemical point of view as an organic metal. Like inorganic metals poly(SNS) oxidizes, reduces, dissolves and deposits electrochemically. The polymeric films can be electrodissolved by flow of a cathodic current and are able to be electrodeposited again by flow of an anodic current through a solution containing soluble reduced polymer.

A study of many physical and electrochemical properties such as refractive index and specific conductance of the ternary system water-dimethylsulfoxide-copper sulphate as a function of temperature (in the interval 20 °C-50 °C) is reported, as well as the variations for the peak potentials in the cyclic voltammograms, at several temperatures (between 20 °C and 80 °C) of copper sulphate 1 mM in many water-dimethylsulfoxide mixtures and the galvanic potentials at 20 °C of some metallic electrodes in water-dimethylsulfoxide mixtures.

BaSn0.9Sb0.1O3 /Ti electrodes were prepared by painting a slurry containing the oxide, synthesised by high-temperature solid state reaction, and Triton X-100 on titanium supports. The electrochemical behaviour of the electrodes was studied by cyclic voltammetry. From the voltammetric data the electrodes surface roughness was estimated and it was possible to conclude that an insulating film of TiC>2 is formed at the support/oxide layer interface.

In this study, conducting polymer films were synthesised by electrochemical polymerisation of aniline on the stainless steel substrates, and such films were employed for the process of electroless precipitation of silver. The electropolymerisation mode and conditions were carefully selected to provide films displaying structure and electroactivity appropriate to the process. The influence on the metal recovery efficiency of the both PANI surface area and electrolyte composition was also analysed.

Complexation of copper with bromazepam is investigated using Differential Pulse Polarography in KNO3 0.10 mol.dm"3 and pH ~ 7. It is apparent from the experimental data that copper in the +1 oxidation state is stabilised by complex formation with bromazepam and so thermodynamic information regarding complexation with Cu(II) and Cu(I) is obtained from the voltammetric results.

A technique has been developed to measure the overall diffusion coefficients of KC1 and LiCl in acrylamide hydrogels immersed in electrolyte solutions. Once a majority of these kind of polymers are used in connection with electrolyte aqueous solutions, this technique allows the determination of diffusion coefficients representative of systems of aqueous electrolyte solutions normally surrounding polymeric materials. The capillary cell is based on the open-ended capillary conductimetric cell earlier designed to measure diffusion coefficients of electrolytes in aqueous solutions. Polymeric matrices of different hydrophilic character have been studied showing the complex interactions between the different species (water with different structures, polymer and electrolyte). The different thermodynamic effects of cations on the water structure enhance this behaviour. The water structure breaking effect due to potassium ions, when compared with lithium ions, results in the diffusion flux decrease, mainly due to the decrease of water content available as diffusional media inside the matrix.

The electrochemical oxidation of perphenazine was studied using a glassy-carbon electrode in different buffer solutions having verified that the peak potential is practically independent of pH. It was shown that using a pH 1.9 buffer solution at which the perphenazine peak is maximal there was no interference from the other active substance, amitriptyline, which is also present in current pharmaceutical preparations available in the Portuguese market. The results obtained for the electrochemical quantification of perphenazine in four pharmaceutical preparations are in good agreement with the results from the reference method (HPLC).

Short chain ferrocenyalkylthiols, (C5H5)Fe(C5FLi)CO(CH2)„SH (n= 3, 5 and 7), were self-assembled on gold (111). The influence of the chain length and adsorption time on stability, surface coverage and order of the monolayers were assessed electrochemically and by the use of optical ellipsometry. The redox behaviour and structure of the SAMs were strongly dependent on the chain length. Long adsorption times were required to obtain ordered monolayers with high surface coverage. Ellipsometry indicated that the thicknesses of the layers were dependent on the surface concentration of the ferrocene derivatives. The thickness of the monolayer with the longer alkyl chain was estimated to be 2.9 nm with a complex refractive index fi= 1.472-0.076i. Imaging Ellipsometry allowed the visualisation of the lateral thickness distribution of a monolayer deposited on gold.

Mean activity coefficients of sodium chloride in water-ethanol mixtures were determined from Potentiometrie data, at 25 °C, using the classic Pitzer model, based on molalities, and the Pitzer-Simonson model, based on molar fractions. The molalities of NaCl varied from 0.1 mol kg"1 to near saturation, in mixed solvents with compositions of 5, 10, 15 and 20% (w/w) ethanol. The results obtained from the two models were compared.

Radical cyclisation is rapidly becoming an irnporlanl method for the formation of cyclic systems. Hence, some electrochemical results obtained in the study of electroreductive intramolecular cyclisation of different types of unsaturated halides using nickel(II) complexes as mediators, are presented.

The electrochemical behaviour, as studied by cyclic voltammetry and controlled potential electrolysis, of the dinitrogen-organocyanamide complexes /ra7M-[Mo(N2)(NCNR2)(dppe)2] (1, R = Me; 2, R = Et, dppe = Ph2PCH2CH2PPh2) is reported, and the electrochemical Ph ligand parameter for the cyanamides is estimated showing that they behave as effective net electron-donors with a remarkable stabilizing influence on the coordination of dinitrogen.

Ionic conductivity measurements, X-ray diffraction analysis and thermal studies have been carried out on polymer electrolyte films prepared by the addition of zinc trifluoromethanesulphonate (triflate) to polyethylene oxide), PEO. In general this electrolyte system was found to behave in a manner similar to other divalent salt-based electrolytes with an increase in crystalline morphology as the concentration of the salt component in the electrolyte was decreased. The conductivity isotherms calculated for this system show an almost constant level of ionic conductivity over the entire range of composition studied.

Guaiacol is an undesired compound in some natural products, mainly because of its aroma. In this work, the voltammetric determination of guaiacol by oxidation at a carbon paste electrode following a cathodic accumulation was first tried, with no sucess, because there was no accumulation of the compound. On the contrary, it was found that there is accumulation of a product formed after oxidation of guaiacol, probably a dimeric product, that can be determined by reduction. Using an accumulation time of 5 minutes and a potential at which guaiacol is being oxidized, a determination limit of 2 ug/L was obtained by cathodic stripping voltammetry, a value about ten times lower than that obtained in the anodic determination. The method was applied to the determination of guaiacol in cork stoppers.

The inhibitive effect of thiourea, 2-amino [4-p-chlorophenyl] thiazole and different derivatives of their condensation products, N-2[4-p-chlorophenyl] 2-thiazolyl] thiocarbamide on the corrosion of mild steel in 20% formic acid solution has been studied using weight loss and electrochemical polarisation techniques. Different concentrations of inhibitors and temperatures have been tested. The inhibition efficiencies calculated by both the techniques are in fairly good agreement except at higher concentrations of some inhibitors. The results observed have been discussed in the light of the molecular structures of the compounds and their adsorption on the surface of the corroding metal. All the inhibitors have been found to be good inhibitors. The polarisation measurements indicate that these inhibitors influence both anodic and cathodic reactions and thereby they contribute to reduce the corrosion rate.

Voltammetric studies on copper, nickel and cupronickel alloys of various compositions in neutral chloride solutions revealed that the passivation is due to the formation of duplex film consisting of inner compact Cu2O layer with outer chloro hydroxy layer. Under transient cyclic polarisation conditions, the presence of nickel hindered the passive film formation decreasing its thickness and ohmic conductivity. The reduction of these passive films to copper was markedly favoured by chloride ions. The presence of nickel in the alloy hindered the reduction of these passive films.

In this paper we discuss the advantages of using interactive simulation programmes for electrochemical dynamical experiments to help both researchers and students in understanding the phenomena underlying these experiments, as well as in obtaining meaningful chemical and electrochemical parameters associated with the redox transformation mechanisms. A PC computer programme developed for this purpose, and which is available to anyone interested, is also presented and applied to the demonstration of virtual cyclic voltammetry.

Porous unsupported Pt-Ru single phase alloy electrodes with different compositions viz., 9:1, 7:3 and 5:5 are prepared by NaBFL reduction method at room temperature. The reactivity of these alloy electrodes towards the methanol oxidation reaction (MOR) is systematically investigated in different electrolytes of high and low pH with various quantities of methanol at room temperature by using cyclic voltammetric (CV) and steady-state galvanostatic polarisation techniques. Various electrochemical processes occurring in different potential regions are discussed. The highest activity of the MOR is obtained for a 7:3 electrode in 2.5 M H2S04 / 2.5 M CH3OH and in 6 M KOH / 6 M CH3OH mixtures, respectively. It is concluded that by choosing the proper ratio of OH ions and CH3OH in solution, it is possible to remove completely the intermediate organic species and/or poisonous species that retard the MOR.

Four complexes of 2,2'-bi-4,5-dihydrothiazine (btz) with Co(II), Ni(II), Mn(II) and Cu(II), and two complexes of 2,2'-bi-thiazoline (bt) with Co(II) were synthesized and characterized, three of them, the Mn(II) complex and the two bt complexes, for the first time. These six complexes were studied using cyclic voltammetry in acetonitrile solution.All displayed reversible or quasi-reversible behaviour, and two waves were observed in the case of [Co(btz)3] [C104]2- All the results are described and discussed.

The oxide films formed by potential cycling on commercial Ti6A14V alloy, that has been surface implanted with iridium, are studied by capacitance measurements and Auger analysis. It is observed that these films become enriched in iridium when etched in sulphuric acid solution prior to their formation, simultaneously with a change in the type of semiconductivity (n-type to p-type).