Non-covalent interactions for directing self-assembly of supramolecular architectures towards nanocontainers
(2021)
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- Self-assembly and folding with primary oligomers rely on various non-covalent interactions are important for generating higher-order secondary or tertiary structures of large biological molecules, from which emerge their sophisticated functions. Mimicking this approach for the self-assembly of complex artificial supramolecular structures is still challenging. Building blocks with characteristics like low symmetry and flexibility, while common in biological systems, pose numerous problems for synthetic self-assembly. In this thesis, the research aims to advance knowledge of how non-covalent interactions designed into aromatic amide based building blocks for self-assembly can be used to control conformation and generate complementary shapes for directing self-assembly of larger structures and through this to develop an approach that could allow the formation of more complex structures with interesting properties and reactivities. This work is divided into two different but complementary approaches: 1) Metal-based self-assembly of aromatic amide units and 2) The use of multiple helix formation in aromatic oligoamides as a driving force for self-assembly of larger systems. In chapter 3, a series of heteroaromatic amide-based ligands (L1-L5) were synthesized and used for coordination-driven self-assembly of MnL2n polyhedral cages. Despite the flexibility around the amide bonds, non-covalent interactions in the ligands lead to preferential curved conformational states that orient the coordination sites and allow sufficient control over the bend angles of the ligands giving access to M2(L1)4, M6(L2)12, and M12(L2)24 cages. Additionally, the multiple endohedral hydrogen bonding sites on the ligand were found to play a role in the binding and discrimination of neutral guests. The subsequent work in chapter 4 studied the more complex novel dual curvature ligands (L6-L18). These were obtained using a Diels-Alder reaction to break the symmetry of the ligands and incorporate additional steric constraints and complementary shapes for self-assembly. Mixing the dual curvature ligands with Pd2+ ions demonstrates that these constraints could help direct self-assembly towards a single M2L4 cage or M4L8 double-walled metallomacrocycle out of hundreds of possible isomers. Moreover, this gives access to endohedrally functionalized M4L8 cages for different applications. Next, using the idea of the Diels-Alder reaction, we studied covalent post-modification in chapter 5 as a shorter alternative pathway to achieve similar complex structural and functional diversity. Two dienophiles, 4-Phenyl-1,2,4-triazoline-3,5-dione and 1-Methyl-1H-pyrrole-2,5-dione used for the synthesis of ligands (L19 and L20) and their self-assembly studied. Importantly, the ligand L19, due to the high dynamic exchange between its enantiomers, simplified the self-assembled mixtures, allowing easy NMR characterization and crystallization. Using this as a reference, we were able to covalently post-modify the metal-organic architectures at room temperature using 4-phenyl-1,2,4-triazoline-3,5-dione 5.01 and found that a new cage species could be formed. Although the nature of this cage species still requires further study, it demonstrates a rapid and facile approach to tune structures and functionalities of metal-organic architectures through covalent post-modification. Finally, in chapter 6, we describe another important advance in this thesis, a proof of concept work on the use of multiple helix formation with aromatic oligoamide foldamers as a driving force for the self-assembly of higher-ordered architectures. Based on the results and experience from coordination-driven self-assembly, two kinds of ligands were designed with central linkers differing in bend angles and rigidity. An optimized synthetic method was established and allowed us to obtain two foldamer-based ligands, L22 and L23. Importantly, NMR and MS studies for ligand L22 showed promising results suggesting it can assemble into larger structures, providing a proof of concept for our idea.
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Liu, C. (2021). Non-covalent interactions for directing self-assembly of supramolecular architectures towards nanocontainers. https://hdl.handle.net/2078.5/234753