Castillo Bonillo, Alvaro; (2025) Reactivity Modulation by Supramolecular Interaction with Molecular Containers. Doctoral thesis (Ph.D), UCL (University College London).

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Abstract

Molecular containers have been frequently reported to alter the reactivity of the molecules they capture, both through conformation changes suffered by the guest upon encapsulation, and due to the altered chemical environment within the host. However, most of the existing research on these supramolecular interactions was found to separately address each event as a nearly independent phenomenon only affecting an specific sub-set of reactions. In response, this PhD project proposes the reinterpretation of these properties as tools for the assembly of bespoke stabilizers and catalysts, here using the supramolecular chemistry of the cucurbituril molecule (CB) as a testing ground for the key phenomena listed below: • The selectivity towards specific reactions, here seen as a targeted modulation of certain active sites. An event exemplified by the deactivation of the phenyl diazonium SN1(Ar) reaction in water media once its a-carbon is encapsulated by CB7, and which shows no effect on the SEAr reaction of the diazonium center. • The cooperation between supramolecular reactivity modulators, here observed at the cascade modulation of certain multi-stage reactions. A phenomenon found to assist the photo-reduction of the [MV • 2 Z-N2H2]2+ charge-transfer complex once this species is allowed to interact with CB8. • The composition changes at the CB portal vicinity, here explored through a preliminary quantification of the acid-catalysis they can trigger. An approach that confirms that the hydrolysis of CB hosted e-caprolactone is accelerated by the H+ attraction towards CB, but that also reveals that the effective pH is ruled by the balance between the attractive pull of the CB portal and the diffusive forces opposing the H+ accumulation. As a result, and acknowledging the need for further research to better understand and apply each of the reported interactions, this project is considered to evidence not only the CB ability to inhibit and/or catalyze specific reactions, but to also unlock multiple mechanisms that allow a selective modulation of the guest reactivity.

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