“Click” Cucurbit[7]uril Hosts on Self-Assembled Monolayers: Quantitative Supramolecular Complexation with Ferrocene Guests

The ultrahigh stability of the ferrocene@cucurbit[7]uril (Fc@CB[7]) host–guest inclusion complex enables its promising application as a novel immobilization/conjugation motif for constructing biosensors and molecular devices. However, its supramolecular complexation on surface has been rarely studied, which is partially due to the limited success of current CB[7] immobilization strategies (suffering from either poor stability or inconvenient and time-consuming procedures). In this work, we have successfully tethered alkyne-functionalized CB[7] (≡-O-CB[7]) on azide-terminated self-assembled monolayers (SAMs) on gold via the copper(I)-catalyzed azide–alkyne cycloaddition reaction with high efficiency. With this new approach, highly stable and uniform CB[7]-functionalized SAMs were obtained, which enabled us to gain insights into the recognition properties of CB[7] toward various Fc derivatives on the surface. In particular, the derived complexation thermodynamic (e.g., for FcMeOH, Kf = (1.6 ± 0.3) × 107 M–1) and kinetic (ka = (2.6 ± 0.4) × 103 M–1 s–1, kd = (5.1 ± 0.3) × 10–5 s–1) data indicate the strong interfacial host–guest binding of surface-bound CB[7] toward both cationic and neutral ferrocene derivatives. Remarkably, a comparable binding stability was observed for the anionic ferrocene derivative with an increased distance between the ferrocene core and negatively charged substituent, which is significant for immobilizing/conjugating negatively charged biological macromolecules (e.g., DNA probes).