No / The relationship between molecular self-assembly processes and nucleation during crystallization from solution is an important issue, both in terms of fundamental physical chemistry and for the control and application of crystallization processes in crystal engineering and materials chemistry. This contribution examines the extent to which the occurrence of crystal polymorphism can be used as an indicator of the nature of molecular aggregation processes in supersaturated solutions. For the specific case of 2,6-dihydroxybenzoic acid a combination of solubility, spectroscopic, crystallization, and molecular modeling techniques are used to demonstrate that there is a direct link between the solvent-induced self-assembly of this molecule and the relative occurrence of its two polymorphic forms from toluene and chloroform solutions.

Supercapacitors have emerged as a promising energy storage technology with unique characteristics that set them apart from conventional batteries and capacitors. Supercapacitors bridge the gap between these two technologies by combining the high power density of capacitors with the high energy storage capacity of batteries, offering a compelling solution for various applications. In the pursuit of enhancing supercapacitor performance, magnetite (Fe3O4) has been researched as a potential anode material. Fe3O4 offers several desirable properties, including high theoretical capacitance, low cost, and environmental friendliness. Compositing Fe3O4 with conductive additives has served to address the issue of limited conductivity in Fe3O4 anodes for practical uses, however, a focus must be shifted to enhancing the capacitive performance of such anodes to unlock their full potential. Achieving the full potential of Fe3O4 for supercapacitor applications requires addressing challenges in the colloidal fabrication of high-active mass electrodes. This is done by exploring the exceptional adsorption properties of two dispersing and capping agents: 3,4-dihydroxybenzoic acid and murexide. Exceptional adsorption properties of catecholate-type 3,4-dihydroxybenzoic acid molecules were explored for surface modification of Fe3O4 nanoparticles to enhance their colloidal dispersion as verified by sedimentation test results and Fourier-transform infrared spectroscopy measurements. Electrodes prepared in the presence of 3,4-dihydroxybenzoic acid exhibited nearly double the capacitance at slow charging rates as compared to the control samples without the dispersant or with benzoic acid as a non-catecholate dispersant. Density functional theory analysis of adsorption behavior of 3,4-dihydroxybenzoic acid and benzoic acid at the (001) surface of Fe3O4 corroborated these experimental results by providing an understanding of the basic mechanism of 3,4-dihydroxybenzoic acid adsorption on the surface of nanoparticles. Furthermore, murexide for surface modification of Fe3O4 nanoparticles effectively enhanced the performance of multi-walled carbon nanotube-Fe3O4 supercapacitor anodes. Our experimental results demonstrate significant improvements in electrode performance when murexide is used as a capping or dispersing agent compared to the case with no additives. From impedance measurements, we revealed a substantial decrease in the real part of impedance for samples prepared with murexide, indicating easier charge transfer at more negative electrode potentials, and reinforcing the role of murexide as a capping agent and charge transfer mediator. The theoretical investigation allowed us to identify the nature of chemical bonds between murexide and the surface, with significant charge transfer taking place between the Fe3O4 surface and murexide adsorbate. / Thesis / Master of Applied Science (MASc)

Les travaux présentés concernent dans une première partie la synthèse biomimétique d’un alcaloïde indolomonoterpénique : la bipléiophylline. La bipléiophylline est le résultat de l’assemblage complexe de deux unités indoliques identiques ancrées sur une plateforme aromatique. Une stratégie générale de synthèse biomimétique de la bipléiophylline consistant i) à la synthèse de l’unité indolique pléiocarpamine et ii) à l’oxydation de l’acide 2,3-dihydroxybenzoïque a été envisagée. L’accès au squelette complexe de la pléiocarpamine a été étudié selon plusieurs stratégies de synthèse totale mais également par hémisynthèse. Parallèlement une étude des conditions d’oxydation notamment par électrochimie de l’acide 2,3-dihydroxybenzoïque ont permis de déterminer et caractériser son potentiel d’oxydation et de mettre au point les conditions de formation de sa forme oxydée. La seconde partie est consacrée à la synthèse biomimétique d’un modèle du cœur central de l’haliclonine A, un alcaloïde de la famille des manzamines. La synthèse de plusieurs précurseurs a été réalisée ainsi que l’étude de l’étape clé de double addition nucléophile sur un 5,6-dihydropyridinium. / Our work deals in the first part with a biomimetic synthesis of bipleiophyllin, an indolomonoterpenic alkaloid. The bipleiophyllin is the result of a complex anchorage of two identical indolic subunits on an aromatic platform. A general strategy for the biomimetic synthesis of bipleiophyllin consisting of i) the synthesis of the indolic unit pleiocarpamin and ii) the oxidation of 2,3-dihydroxybenzoic acid; was considered. Access to the complex skeleton of pleiocarpamin has been studied by different total synthesis strategies but also by hemisynthesis. Meanwhile this work, a study of the oxidation conditions of 2,3-dihydroxybenzoic acid including by electrochemistry, helped identify and characterize its oxidation potential and develop the required conditions to obtain its oxidized form. The second part is devoted to the biomimetic synthesis of a model compound, mimic of the central core of haliclonin A, an alkaloid of the family of manzamins. The synthesis of several precursors and the study of the key step consisting in a double nucleophilic addition to a 5,6-dihydropyridinium were done.