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Title: Multivalent supramolecular systems
Author: Motloch, Petr
ISNI:       0000 0004 9354 0419
Awarding Body: University of Cambridge
Current Institution: University of Cambridge
Date of Award: 2019
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Nature uses multivalency as one of the most important governing principles to control selective molecular recognition and assembly. By combining a large number of weak interactions, it is possible to obtain high affinity, selective and reversible non-covalent binding processes. Multivalency has also become an important tool in the design of synthetic molecular systems. The result of multiple binding events is not just a simple sum of individual contributions due to cooperative interactions between binding sites. The main part of this thesis deals with the study of chelate cooperativity in multivalent supramolecular systems. Firstly, a well-known H-bonded rosette system was revisited and the effective molarity was determined experimentally by 1H NMR titrations to be around 2 M, which is a high chelate cooperativity compared to other supramolecular systems. Moreover, the concept of peripheral crowding in solution was revisited, since rosettes based on less bulky pyrimidines showed higher stabilities and effective molarities than the rosettes based on bulky pyrimidines. The following two chapters deal with efforts towards a supramolecular system inside a porphyrin nanoring. The porphyrin nanoring shows the highest value of effective molarity reported in the literature and is, therefore, a great system to study the cooperative behaviour when a covalent ligand is replaced with a supramolecular system. The first studied system was based on small molecules containing simple hydrogen-bond acceptors and donors. Unfortunately, solubility issues led to the termination of the project. The second system used the hydrogen-bonded rosette motif. A number of different pyridine-pyrimidine and pyridinebarbiturate ligands were synthesised and their assembly inside the porphyrin nanoring was studied in detail by UV-vis-NIR experiments. The effective molarities for the sequential binding of the rosette systems to 6-ring were determined to range from 0.23 to 3.7 M, which is significantly lower compared to the system that utilised a covalent hexadentate ligand (126 M). The final part of the thesis introduces a new class of hybrid hydrogen-bonded/metalcoordinated cages based on the rosette motif. These complexes are a rare example of architectures where both hydrogen-bonding and metal-coordination form the crucial part of the topology of the complex since if either is removed, the architecture changes drastically.
Supervisor: Hunter, Christopher A. Sponsor: European Union's Horizon 2020 Programme ; Cambridge Philosophical Society
Qualification Name: Thesis (Ph.D.) Qualification Level: Doctoral
Keywords: multivalency ; cooperativity ; supramolecular chemistry ; effective molarity