"Click" cucurbit[7]uril hosts on self-assembled monolayers: Quantitative supramolecular complexation with ferrocene guests

Cucurbit[7]uril (CB[7]), 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 cucurbit[7]uril molecule host and ferrocene derivatives molecule guests (Fc@CB[7]) 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[7] 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[7] 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[7]-tethered SAMs enabled the determination of complexation properties of CB[7] 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[7]. Moreover, the as-strong binding affinity of surface-bound CB[7] toward an anionic ferrocene derivative confirms the feasibility of employing Fc@CB[7] as the conjugation motif for immobilizing biological macromolecules (that are often negatively charged) to biochip surfaces.