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The structure and the electrochemical behaviour of Langmuir and Langmuir-Blodgett (LB) films of the biological ubiquinone-10 (UQ) and a mixture of dipalmytoilphosphatidylcholine (DPPC) and UQ at the molar ratios DPPC:UQ 5:1 and 10:1 have been investigated. The surface pressure-area isotherms of the Langmuir films and the AFM images of the LB films show the formation of a monolayer in the DPPC:UQ mixture till a certain surface pressure is attained, and then at higher surface pressures the UQ is progressively expelled. The cyclic voltammograms of DPPC:UQ LB films formed on indium tin oxide, ITO, at different surface pressures show one reduction and one oxidation peak at low surface pressures, but two or even more reduction and oxidations peaks at medium and high surface pressures. The electrochemical behaviour is correlated with the film structure.

Ubiquinone and plastoquinone are two of the main electron and proton shuttle molecules in biological systems, and monogalactosyldiacylglycerol (MGDG) is the most abundant lipid in the thylakoid membrane of chloroplasts. Saturated MGDG, ubiquinone-10 (UQ) and MGDG:UQ mixed monolayers at the air/water interface have been studied using Surface Pressure-Area isotherms and Brewster Angle Microscopy. Moreover, the transferred Langmuir-Blodgett films have been observed by Atomic Force Microscopy. The results show that MGDG:UQ mixtures present more fluid phase than pure MGDG indicating a higher order degree for the later. It is also observed an important influence of UQ on the MGDG matrix before UQ collapse pressure and a low influence after this event, due to UQ expulsion from the MGDG matrix. This expulsion leads to a similar remaining UQ content for all the tested mixtures, indicating a limiting content of this molecule in the MGDG matrix at high surface pressures. The thermodynamic studies confirm the stability of the MGDG:UQ mixtures at low surface pressures, although presenting a non-ideal behaviour. Results point to consider UQ as a good candidate for studies of artificial photosynthesis.

The electrodeposition of zinc from sulphate-tartrate baths on a vitreous carbon electrode has been studied. The influence of the tartrate ion on the reduction kinetics of Zn(II) metal ion, and on the mechanism of the electrodeposition process, has been investigated using potentiodynamic and potentiostatic electrochemical techniques and scanning electron microscopy. The voltammetric analysis has shown that the presence of tartrate species in the sulphate bath shifts the reduction potential of Zn(II) to more positive values. A set of equilibria have been proposed to represent the electrochemical process and the influence of pH. From the analysis of the chronoamperometric transients and the SEM images, an instantaneous nucleation with 2D growth at the initial stages has been proposed, and a nucleus density of the order of 10 9 cm -2 has been calculated from both techniques. In order to elucidate the correct mechanism of the electrodeposition process the results obtained from chronoamperometric transients must be corroborated by those of direct observation using microscopic techniques.2

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