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Abstract: 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. [Copyright &y& Elsevier]

Ubiquinone (UQ) is one of the mainelectron and proton shuttlemolecules in biological systems, and dipalmitoylphosphatidylcholine(DPPC) is one of the most used model lipids. Supported planar bilayers(SPBs) are extensively accepted as biological model membranes. Inthis study, SPBs have been deposited on ITO, which is a semiconductorwith good electrical and optical features. Specifically, topographicatomic force microscopy (AFM) images and force curves have been performedon SPBs with several DPPC:UQ ratios to study the location and theinteraction of UQ in the SPB. Additionally, cyclic voltammetry hasbeen used to understand the electrochemical behavior of DPPC:UQ SPBs.Obtained results show that, in our case, UQ is placed in two maindifferent positions in SPBs. First, between the DPPC hydrophobic chains,fact that originates a decrease in the breakthrough force of the bilayer,and the second between the two leaflets that form the SPBs. This secondposition occurs when increasing the UQ content, fact that eventuallyforms UQ aggregates at high concentrations. The formation of aggregatesproduces an expansion of the SPB average height and a bimodal distributionof the breakthrough force. The voltammetric response of UQ dependson its position on the bilayer. [ABSTRACT FROM AUTHOR]