Liu, Jia; (2023) Supramolecular electrochemistry using cucurbituril-based complexes for analytical and sensing applications. Doctoral thesis (Ph.D), UCL (University College London).

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Abstract

Supramolecular electrochemistry, especially the cucurbit[n]uril-based (CBn, n = 5-8, 10) electrochemistry, has sparked extensive research interests for the combining advantages of complexation-induced unique properties of guest molecules, outstanding features of rigid macrocyclic CBn host as well as rich thermodynamic and kinetic information provided by electrochemical techniques. CBn perform pronounced binding ability towards a wide range of molecules, giving rise to substantial application potentials, such as reactivity modulation and sensing. Quantitative analysis of binding behaviours between CBn and guest molecules can effectively offer instructive guidance to design the host-guest systems better catering for the ending applications, thus being of great interests and importance in supramolecular chemistry area. Herein, this research started from the investigation of the complexation events between CB7/CB8 host and redox active resazurin (RZ). Interestingly, it has been discovered that the electrochemical activity of RZ can be oppositely modulated upon the complexation with CB7 and CB8, manifesting the effect of the host-guest encapsulation tightness on the reaction activity. In addition to the research regarding reactivity modulation caused by CBn complexation, we also explored quantitative analysis for binding behaviours by proposing a rapid and simple electrochemical approach for rapidly estimating binding constants of CB8-methyl viologen (CB8-MV²⁺)-based ternary complexes by uncovering the correlation between their electrochemical characteristics and binding constants. This electrochemical scheme has overcome the shortcomings, such as long experimental period, complicated data analysis, expensive instrument, limited applicability to sparsely soluble guests, etc, presented by conventional supramolecular titration methodologies. Furthermore, it is notable that we extended the binding constant estimation applicability boundary from simple buffer solution to complex bio-media, ranging from synthetic urine (SU), human serum (HS), fetal bovine serum (FBS) to animal blood of sheep blood (SB) and horse blood (HB), with the aid of simple CB8-MV²⁺ assay via electrochemical titration measurements. Other than quantitative analysis, the application potentials for supramolecular-based electrochemical sensing have also been explored. A dual-functional assay that can work as either associative binding assay (ABA) or the indicator displacement assay (IDA) was established by employing CB8-MV²⁺ molecular platform, in which the redox active MV²⁺ worked as a sensitive electrochemical reporter. Moreover, included but not limited to simple biologically relevant buffer solution, CB8-MV²⁺ also presented sensing ability for biomolecules, which are of diverse binding affinities and structural conformation in complex bio-media (e.g. SU, HS, FBS, SB and HB), with decent sensing properties, i.e. down to 10¯⁸ M of minimum detectable concentration (MDC) and linear detection range located within physiologically relevant micromolar range. In a nutshell, this research has explored the analytical and sensing applications of CBn-based electrochemistry, which is readily to be extended for other applications based on different supramolecular systems.

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