Thèse de doctorat en Chimie supramoléculaire
Sous la direction de Jean-Marie Lehn.
Soutenue en 2005
Synthèse et propriétés dynamiques de brins moléculaires et supramoléculaires
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This work studies dynamic properties of molecular and supramolecular strands on both molecular and supramolecular levels. Self-organisation of molecules into single helical architectures is a pervasive phenomenon in biomolecular structures. Recently, interest has grown for artificial oligomers and polymers which mimic self-organisation observed in nature. It has come to light that oligopyridinedicarboxamide strands can exist in helical conformations both in solution and in the solid state. The longest oligopyridinedicarboxamide helical strand reported to date and new chiral foldamers which adopt a helical conformation due to the intramolecular hydrogen bonding and aromatic stacking, have been synthesized. Their reversible structural interconversion between helical and extended forms induced by protonation/deprotonation was revealed by NMR, mass spectrometry and X-ray diffraction studies. Such molecular motions play a very important role in biological phenomena, and may lead to the design of functional molecular machines. Induced circular dichroism phenomenon as well as amplification of the molecular chirality revealed by helical strands is discussed in this work. Another part of the work presents a new two component homoditopic supramolecular polymer system, which was found to form an organogel at thermodynamic equilibrium. The main result obtained in the rheological study is the observation of a shear banding type instability in the flow experiments. This instability, that has been predicted theoretically for both regular covalently bonded polymers and equilibrium polymers has been observed for wormlike micellar systems. In the last part of the work, a novel type of supramolecular polymers is presented. Implementing dynamic character simultaneously on the molecular and supramolecular levels in the same system results in the formation of double dynamers – polymers, where molecular components are connected through reversible covalent as well as non-covalent interactions. The formation of such supramolecular polymer systems was corroborated by electron microscopy studies, which showed extensive branched fibrous aggregates, a feature in agreement with the formation of polymer chains. Component exchange in these double dynamers allows for the generation of dynamic constitutional diversity on both molecular and supramolecular levels.