Cucurbituril (CB), a symmetrical pumpkin-shaped molecule with an internal volume that can encapsulate guest molecules of complementary shape and size at a 1:1 ratio, has attracted tremendous attention in diverse fields. Particularly, the outstanding in-solution binding affinity (Kf > 10^9 M^-1) of the host-guest inclusion complexation between cucurbituril molecule host and ferrocene derivatives molecule guests (Fc@CB) enables their potential applications as conjugation/immobilization motifs for constructing biosensors and other molecular devices. However, their interfacial host-guest complexation behaviour has been rarely studied, partially due to the limitation of current CB surface immobilization strategies (suffering from either poor stability or time-consuming and inconvenient procedure). In this thesis, it was shown that the well-known copper(I)-catalyzed azide-alkyne cycloaddition "click" reaction (CuAAC) can be used to chemically attach alkyne-functionalized CB onto an azide-terminated self-assembled monolayer (SAM) on gold. The reaction time has been reduced from several hours to 30 min compared to conventional methods (e.g., the olefin metathesis reaction or the thiol-ene "click" reaction). Thus prepared CB-tethered SAMs enabled the determination of complexation properties of CB towards various Fc derivatives (e.g., neutral, positively charged and negatively charged substituents) on the surface via conventional cyclic voltammetry measurements. Particularly, the derived complexation thermodynamics (Kf = (1.6 ± 0.3) * 10^7 M^-1) for ferrocenemethanol (FcMeOH), and kinetics data (ka = (2.6 ± 0.4) * 10^3 M^-1s^-1, kd = (5.1 ± 0.3) * 10^-5 s^-1) confirms its strong interfacial host-guest binding with the surface-immobilized CB. Moreover, the as-strong binding affinity of surface-bound CB toward an anionic ferrocene derivative confirms the feasibility of employing Fc@CB as the conjugation motif for immobilizing biological macromolecules (that are often negatively charged) to biochip surfaces.
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Thesis advisor: Yu, Hogan
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