Abiotic Chemical Fuels for the Operation of Molecular Machines

Abstract

Natural molecular machines require a continuous fuel supply to perform motions and/or remain in a functional state. Consequently, the aim of developing artificial devices and materials with life‐type properties has motivated a growing interest in abiotic chemical fuels and in their supply modalities. Many artificial molecular machines have been developed in which the sequential addition of several chemical reagents allows the machine to perform complete cycles of motion. Only recently, examples of molecular machines whose cycles of motion are triggered by a single pulse of fuel have been reported. The latter systems are the object of this Minireview where the abiotic chemical fuels used so far to trigger the complete cycles of motion of molecular machines are described, with particular emphasis on the operation mechanism of the machine/fuel systems.

Improving Fatigue Resistance and Autonomous Switching of pH Responsive Hydrazones by Pulses of a Chemical Fuel

“…Over the years, several abiotic chemical fuels were synthesized to rival the efficiency of biotic fuels (e. g., ATP and GTP). [39][40][41] Trichloroacetic acid (TCA) undergoes base-catalysed decarboxylation, leading to the formation of only by-products: CO 2 (a gas), and CHCl 3 , a volatile solvent. Thus, it can switch the global pH of the reaction medium for a particular period.…”

“…Chemical fuel delivers an influx of energy to perform useful task, for example, to form transient self‐assembled supramolecular materials, [33,34] temporally control host‐guest systems, [35] modulate dissipative signalling, [36] generate off‐equilibrium switches or machines, [37,38] etc. Over the years, several abiotic chemical fuels were synthesized to rival the efficiency of biotic fuels (e. g., ATP and GTP) [39–41] . Trichloroacetic acid (TCA) undergoes base‐catalysed decarboxylation, leading to the formation of only by‐products: CO 2 (a gas), and CHCl 3 , a volatile solvent.…”

Control over Dethreading Kinetics Allows Evaluating the Entropy Stored in an Interlocked Molecular Machine Out‐of‐Equilibrium**

“…Here, this implies observing the formation of state iv from state iii , and then following dethreading relaxation from high‐energy state iv to state i . This observable dynamic is considered a dissipative process, of high current interest in relation to transient supramolecular assemblies [29–37] . Engineering dethreading kinetics in crown ether rotaxanes is challenging, because subtle changes in stopper structure often lead to a sharp transition from pseudorotaxane to rotaxane‐like character of the complex, an effect termed “all‐or‐nothing” substituent effect [38,39] .…”

Dissipative Cyclic Reaction Networks: Mechanistic Insights into a Minor Enantiomer Recycling Process

“…Nucleoside triphosphates [27] and carbodiimides [28] have commonly been used as chemical fuels, but a variety of other activating species have also been found to be efficient [2,29,30] . In networks driven by the consumption of a fuel producing CO 2 as waste, the dissipated energy is associated with an overall entropy gain resulting from the liberation of CO 2 to the atmosphere; reversible gelation has, for example, been shown to be powered by the transformation of sucrose to CO 2 [31] .…”