Quantitative electroanalysis of host-guest binding at organized supramolecular interfaces

As a young and important class of supramolecular host-guest chemistry, the macrocyclic cucurbit[n]uril (CB[n]) hosts consisting of one hydrophobic inner cavity and multiple carbonyl portals have shown dramatically increased research interests since 1980s, with tens of thousand publications focusing on their synthesis, distinct structural features, exceptional physical and chemical properties. More importantly, their excellent host-guest recognition behavior leads to their great application potentials in many fields, such as nanofabrication, biomedical/pharmaceutical science, analytical chemistry, catalytic chemistry, and adaptive chemistry, which have been explored extensively in the past two decades. Particularly, CB[7], an attractive member of CB[n] family, shows ultra-strong host guest binding ability towards small aromatic or ring-structured organic compounds, which is mainly attributed to its proper-sized inner cavity. As a representative, the host-guest complexes formed between CB[7] and various redox-active ferrocene (Fc) derivatives have extremely high binding affinities (109 to 1012 M-1), which have been employed as an alternative of natural binding pairs (e.g., antigen-antibody, biotin-avidin) for fabricating versatile functional molecular and biomolecular interfaces. In order to gain further understanding of this particular host-guest binding pair formed at molecular interfaces, in this thesis, based on both conventional cyclic voltammetry and advanced structural characterizations, the binding thermodynamics and kinetics were investigated on mixed ferrocenylundecanethiolate/octanethiolate self-assembled monolayers on gold as a highly-organized model system. The results show that the inclusion binding behavior of this host-guest pair, while significantly affected by the surface, still has satisfactory stability for practical application. In addition, the broad potential of this new interfacial Fc@CB[7] host-guest binding system is manifested as nanoscale probes for the distribution of Fc terminal groups on SAMs (as an indicative of their structural heterogeneity), as an environmental regulator of long-range electron transfer process, and as an electrochemical sensor for pharmaceutical drugs via competitive host-guest assay strategy. It is expected that this new interfacial host-guest binding system can be further explored for fabricating well-controlled, ratiometric electrochemical biosensors.