Transient host-guest complexation to control catalytic activity

Abstract

Signal transduction mechanisms are key to living systems. Cells respond to signals by changing catalytic activity of enzymes. This signal responsive catalysis is crucial in the regulation of (bio)chemical reaction networks (CRNs). Inspired by these networks, we report an artificial signal responsive system that shows signal-induced temporary catalyst activation. We use an unstable signal to temporarily activate an out of equilibrium CRN, generating transient host guest complexes to control catalytic activity. Esters with favourable binding towards the cucurbit[7]uril (CB[7]) supramolecular host are used as fleeting signals to form a transient complex with CB[7], replacing a CB[7]-bound guest. The esters are hydrolytically unstable, generating acids and alcohols, which do not bind to CB[7], leading to guest re-uptake. We demonstrate the feasibility of the concept using signal-controlled temporary dye release and re-uptake. The same fleeting signal controlled system was then used to tune the reaction rate of aniline catalysed hydrazone formation. Varying the ester structure and concentration gave access to different catalyst liberation times and free catalyst concentration, regulating the overall reaction rate. With fleeting signal controlled transient complex formation we can tune the kinetics of a second chemical reaction, in which the signal does not participate. This system shows promise for building more complex non biological networks, to ultimately arrive at signal transduction in organic materials.