Portugaliae
Electrochimica Acta

Oxygen electroreduction is a slow reaction and, therefore, to obtain electric currents high enough for practical applications, a catalyst is needed. For this purpose many materials have been scrutinized, and surface modification of some of them to achieve higher catalytic efficiencies have been attempted. A comprehensive reference is first made to the several classes of materials tested so far. Then the techniques that have been applied to the study of oxygen electroreduction are reviewed, with some emphasis being given to the analysis of the electrochemical data. The application of these techniques are finally illustrated with a detailed discussion of the electroreduction of oxygen on pure and modified surfaces of carbon and gold.

Compounds containing the group [Mo(NO)]3+ are redox-active. Incorporation into tris(3,5-dimethylpyrazolyl)borato L*) systems, eg. [MoL*(NO)XY] where X, Y = halide, alkoxide, aryloxide, amide anilide, thiolate, etc. affords a variety of species which undergo one-electron reduction. The factors influencing this behaviour are described. Attachment of the molybdenum redox centre to macrocyclic polyethers and the effect of added cation is discussed. The group {MoL*(NO)X} can be attached to the periphery of tetra-aryl porphyrins, and the electrochemistry and photochemistry of the extra-ring metallated species is reported. A series of ferrocenyl compounds, [(i75-C5H5Fe(i75C5H4C6H4E{ML*(NO)X}]; trans-[(T?5-C5H5Fe(Tj5C5H4C6H4Z=ZC6H4E{ML*(NO)X}], where Z = CH or H, E = O or NH, M = Mo or W; X = CI or I) have been prepared, their electrochemistry investigated and several compounds identified as having non-linear optical (Secondary Harmonic Generation) properties.

Metallothioneins (MT) are sulphydryl-rich, small molecular weight proteins which form complexes with heavy metals such as cadmium, copper, mercury and zinc. Functions attributed to MT include detoxification, storage and regulation of metals. Their induction may signify exposure to excessive concentrations of metal ions in cells. Consequently, the potential value of these relatively specific biochemical indicators of metal contamination would seem to be obvious. To date however, the full value of MT as a monitoring tool has rarely been demonstrated, partly due to difficulties in determining protein concentrations. In this study differential pulse polarography has been used, together with the Brdicka electrolyte, to measure directly the levels of MT in marine organisms. The quantitative sulphydryl-specific Polarographie procedure described, is.based on the linear relationship between the height of the second of two Polarographie waves (following cobalt reduction) and the protein concentration. At room temperature, using the operating conditions described, the linear detection range was 5 - 300 ^g MT 1 , based on rabbit liver MT standard. Levels of MT-like proteins are reported for a variety of marine molluscs, collected at sites in Portugal and the United Kingdom, and range from 1.69 - 21.3 mg/g (dry weight), depending on the species and tissue analysed. The technique is clearly sensitive enough to be of value in future environmental effects assessments.

Parmi les substances neuroleptiques possédant en commun un hétéracycle central à 7 atmos avec un groupaient amidine semi-cyclique nous avons choisi le Lo:-:apine. Loxapine a été étudié pour le tecnique de polarography impuIsionel1e, extrêmement sensible, a diferent valeurs de pH et à une concentration constant. Le potential de pic dans le marge de pH étudié oscille entre 906 mV et 1240 mV.

Pulse amplitude, frequency, drop time, concentration, buffer strength, ionic strength, pH and temperature effects oh the morphology of chlorhexidine waves have been studied. It has been proved that the irreversibility of the waves decreases the height of polarograms with respect to the theoretical polarograms which should correspond in a reversible process. The cathodic and anodic values of the transfer coefficients are explained by means of an electrodlc model in which the protonation steps are alternated with electronic transfer steps in the reduction and reoxidatlon of four azomethinic groups of the adsorbed protonated chlorhexidine.