ATP synthase is a ubiquitous transmembrane protein that utilises the free energy available from ion gradients across lipid membranes to synthesise adenosine triphosphate (ATP). It may be separated into two parts - the membrane-embedded (i.e. hydrophobic) FO and the hydrophilic F₁. Each undergoes a rotary motion. Single-molecule studies on the rotation of the isolated hydrophilic F₁ have been performed for many years; attempts to construct an experiment in which to view the rotation of the membrane-embedded F₁F_O complex under high space- and time- resolution (such as by attachment of a rotational probe) have not yet seen a satisfactory method emerge in the literature. Most particularly, a clear ability to generate and control a proton-motive force across the membrane in which the F₁F_O is sited is needed to probe ATP synthesis. This thesis presents the development of a candidate method for such single-molecule studies. By the use of a water-in-oil emulsion, giant unilamellar lipid vesicles are formed which entrap arbitrary components - including functionalised gold nanospheres of 60-100 nm diameter, which move freely in the internal space. A charge-based lipid fusion is developed, using mixtures of natural lipid extracts with anionic and cationic lipids. It is demonstrated that anionic giant vesicles fuse with cationic small vesicles with full content mixing and transfer of bilayer leaflets. It is shown that F₁F_O is functional in the cationic lipid mixture. Methods are shown to bind such a cationic proteoliposome to a surface and for it to fuse with an anionic giant vesicle containing functionalised gold nanospheres. Backscatter laser darkfield is used to search for rotation of the gold nanospheres under ATP hydrolysis conditions of the F₁F_O; unidirectional rotation is seen in one instance and other suggestive traces are shown with speculative analysis. Further work is proposed.

Les nanomatériaux sont une classe de contaminants qui est de plus en plus présent dans l’environnement. Leur impact sur l’environnement dépendra de leur persistance, mobilité, toxicité et bioaccumulation. Chacun de ces paramètres dépendra de leur comportement physicochimique dans les eaux naturelles (i.e. dissolution et agglomération). L’objectif de cette étude est de comprendre l’agglomération et l’hétéroagglomération des nanoparticules d’argent dans l’environnement. Deux différentes sortes de nanoparticules d’argent (nAg; avec enrobage de citrate et avec enrobage d’acide polyacrylique) de 5 nm de diamètre ont été marquées de manière covalente à l’aide d’un marqueur fluorescent et ont été mélangées avec des colloïdes d’oxyde de silice (SiO2) ou d’argile (montmorillonite). L’homo- et hétéroagglomération des nAg ont été étudiés dans des conditions représentatives d’eaux douces naturelles (pH 7,0; force ionique 10 7 à 10-1 M de Ca2+). Les tailles ont été mesurées par spectroscopie de corrélation par fluorescence (FCS) et les résultats ont été confirmés à l’aide de la microscopie en champ sombre avec imagerie hyperspectrale (HSI). Les résultats ont démontrés que les nanoparticules d’argent à enrobage d’acide polyacrylique sont extrêmement stables sous toutes les conditions imposées, incluant la présence d’autres colloïdes et à des forces ioniques très élevées tandis que les nanoparticules d’argent avec enrobage de citrate ont formées des hétéroagrégats en présence des deux particules colloïdales. / Nanomaterials are a class of contaminants that are increasingly found in the natural environment. Their environmental risk will depend on their persistence, mobility, toxicity and bioaccumulation. Each of these parameters will depend strongly upon their physicochemical fate (dissolution, agglomeration) in natural waters. The goal of this paper is to understand the agglomeration and heteroagglomeration of silver nanoparticles in the environment. Two different silver nanoparticles (nAg; citrate coated and polyacrylic acid coated) with a diameter of 5 nm were covalently labelled with a fluorescent dye and then mixed with colloidal silicon oxides (SiO2) and clays (montmorillonite). The homo- and heteroagglomeration of the silver nanoparticles were then studied in waters that were representative of natural freshwaters (pH 7.0; ionic strength 10-7 to 10-1 M of Ca2+). Sizes were followed by fluorescence correlation spectroscopy (FCS) and results were validated using enhanced darkfield microscopy with hyperspectral imaging (HSI). Results have demonstrated that the polyacrylic acid coated nAg was extremely stable under all conditions, including in the presence of other colloids and at high ionic strength, whereas the citrate coated nAg formed heteroagregates in the presence of both natural colloidal particles.

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