Individual Supramolecular Host-Guest Interactions Probed by Dynamic Single Molecule Force Spectroscopy

摘要

Until now single molecule force spectroscopy experiments have been performed almost exclusively on biologically relevant systems consisting of receptors with high molar masses and very slow unbinding kinetics. In this paper we report on force spectroscopy results of the complexation behavior of ferrocene moieties, self-assembled on an AFM tip, in β-cyclodextrin (β-CD) receptors, immobilized in highly ordered self-assembled monolayers on Au(111). For this system the unbinding kinetics are on a shorter time scale than the AFM time scale. Multiple pull-off events could be observed, while the addition of an external guest was shown to reversibly block the β-CD cavities. The adhesion between β-CD and ferrocene was found to be quantized. The force of 56 +- 10 pN could be identified as single host-guest complex rupture force. This rupture force was found to be independent of the (un-)loading rate which is indicative for a thermodynamically controlled experiment. Our report is the first example where single Supramolecular host-guest interactions could be monitored for complexation reactions with fast unbinding kinetics.