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 favorable binding toward the cucurbit[7]uril (CB[7]) supramolecular host are used as temporary 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 reuptake. We demonstrate the feasibility of the concept using signal-controlled temporary dye release and reuptake. The same signal controlled system was then used to tune the reaction rate of aniline catalyzed 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 temporary 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 nonbiological networks, to ultimately arrive at signal transduction in organic materials.

Dynamic regulation of chemical reactivity is important in many complex chemical reaction networks, such as cascade reactions and signal transduction processes. Signal responsive catalysts could play a crucial role in regulating these reaction pathways. Recently, supramolecular encapsulation was reported to regulate the activities of artificial catalysts. We present a host-guest chemistry strategy to modulate the activity of commercially available synthetic organocatalysts. The molecular container cucurbit[7]uril was successfully applied to change the activity of four different organocatalysts and one initiator, enabling up- or down-regulation of the reaction rates of four different classes of chemical reactions. In most cases CB[7] encapsulation results in catalyst inhibition, however in one case catalyst activation by binding to CB[7] was observed. The mechanism behind this unexpected behavior was explored by NMR binding studies and pKa measurements. The catalytic activity can be instantaneously switched during operation, by addition of either supramolecular host or competitive binding molecules, and the reaction rate can be predicted with a kinetic model. Overall, this signal responsive system proves a promising tool to control catalytic activity.