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 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.

Bioinspired Self-Resettable Hydrogel Actuators Powered by a Chemical Fuel

“…Inspired by the autonomous mechanical actuation of muscle powered by ATP, here, we show our access to soft hydrogel actuators with autonomous self-resetting behaviors powered by a chemical fuel. As shown in Figure b, the actuators have a typical double-layer structure with a responsive layer composed of a simple poly­(acrylic acid) (PAA) hydrogel and an irresponsive layer made of soft poly­(dimethylsiloxane) (PDMS); 1-ethyl-3-(3-dimethylaminopropyl)­carbodiimide (EDC) is used as a chemical fuel, which has been widely used to fuel the formation of carboxylic anhydride. − The addition of EDC drives the conversion of carboxylic acid groups in the PAA hydrogel into hydrophobic anhydrides, leading to dehydration and thereby bending of the actuator; meanwhile, the anhydrides undergo spontaneous hydrolysis over time, enabling autonomous recovery of the actuator to the original state once EDC is depleted. The concentration of EDC determines the actuation extent and duration.…”

Transient and Dissipative Host–Guest Hydrogels Regulated by Consumption of a Reactive Chemical Fuel

“…Indeed, CB [7] binding was previously shown to dramatically reduce the hydrolysis rate for ester-containing guest species. [44] This effect is likely to also underlie the prolonged kinetics of dissipation observed in the hydrogel state, as CB [7] binding serves to drive accumulation of the methyl ester species by slowing its hydrolysis and thereby promote hydrogel formation and stability.…”

Switchable aqueous catalytic systems for organic transformations

“…However, the system works in organic solvent (CH 2 Cl 2 or toluene). Recently, van der Helm et al 165 reported cucurbit[7]uril (CB[7]) as a supramolecular host to encapsulate aniline (catalyst molecule) in an aqueous environment, which can be released via addition of hydrolytically unstable esters as chemical fuel (Fig. 8d ).…”

“… 33 Zn(II)-based catalyst, Pseudo-aqueous solution 140 Presence of CO & Cl − ON, 100% Absence of CO and Cl − OFF, No reaction 34 Cu(II)-based catalyst, HEPES buffer (pH 7.0) 170 Oxidative potential ON, - N.R. Reductive potential OFF, - N.R 35 Hydrolysis of acetal Acid catalysis in ‘nanoflask’, Water-saturated toluene 127 UV light ( λ = 365 nm) ON, ~85% Visible light OFF, ~55% 36 Oxidation Cu(I)-bpy & TEMPO, Aqueous borate buffer (pH 9.5)/acetonitrile (1/1) 143 ssDNA antitrigger sequence ON, - N.R ssDNA trigger sequence OFF, No reaction 37 Aneli system, Water/organic substance 177 No CO 2 ON, >94% CO 2 & magnetic field OFF, No reaction 38 Hydrazone formation Aniline, PBS buffer (pH 7.5) 165 Glycine betaine methyl ester ON, - N.R Ester hydrolysis OFF, - N.R 39 Oxidation of furoic acid PBT, Water 173 CO 2 & light ON, >99% N 2 OFF, No reaction 40 Arylation PBT, Water 173 CO 2 & light, ON, 85% N 2 OFF, No reaction …”