Portugaliae
Electrochimica Acta

Computer simulation methods are now well established and powerful tools for studying very many problems of chemical interest. Phase transitions, electrical and thermal conductivity, surfaces and adsorption, liquid crystals, structure and dynamics of polymers, electrochemical interfaces, metal oxides, chemical reactivity, catalysis and drug design are examples of problems that can be approached by computer simulation. In this paper we shall focus on computer simulation in Statistical Thermodynamics, namely the Molecular Dynamics and Monte Carlo methods. The present achievements, future challenges and some applications with interest for Electrochemistry will be reviewed.

The influence of the synthesis potential on the kinetics of electropolymerization and the properties of a hybrid material polypyrrole doped with heteropolytungstate was studied in organic solutions by potential steps and cyclic voltammetry techniques. It was found the presence of side reactions at low potentials when thin films were electrogenerated. The productivity of the hybrid material kept always a high constant value whatever the studied potentials.

The influences of the polymerisation condition on both, production and properties of electrochemically synthesised polypyrrole film in presence of poly(maleic acid-co-olefin) were studied. Polymerisation variables as polymerisation potentials, polarisation times, concentration of pyrrole and concentration of poly(maleic acid-co-olefin) were followed by their influence on both, productivity of the polymerisation charge and the ability to store charge in every electrogenerated film.

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.