Chemically Fueled Supramolecular Materials

Abstract

Metrics & MoreArticle Recommendations CONSPECTUS:In biology, the function of many molecules is regulated through nonequilibrium chemical reaction cycles. The prototypical example is the phosphorylation of an amino acid in an enzyme which induces a functional change, e.g., it folds or unfolds, assembles or disassembles, or binds a substrate. Such phosphorylation does not occur spontaneously but requires a phosphorylating agent with high chemical potential (for example, adenosine triphosphate (ATP)) to be converted into a molecule with lower chemical potential (adenosine diphosphate (ADP)). When this energy is used to regulate an assembly, we speak of chemically fueled assemblies; i.e., the molecule with high potential, the fuel, is used to regulate a self-assembly process. For example, the binding of guanosine triphosphate (GTP) to tubulin induces self-assembly. The bound GTP is hydrolyzed to guanosine diphosphate (GDP) upon assembly, which induces tubulin disassembly.The result is a dynamic assembly endowed with unique characteristics, such as time-dependent behavior and the ability to self-heal. These intriguing, unique properties have inspired supramolecular chemists to create similar chemically fueled molecular assemblies from the bottom up. While examples have been designed, they remain scarce partly because chemically fueled reaction cycles are rare and often complex. Thus, we recently developed a carbodiimide-driven reaction cycle that is versatile and easy to use, quantitatively understood, and does not suffer from side reactions. In the reaction cycle, a carboxylate precursor reacts with a carbodiimide to form an activated species like an anhydride or ester. The activated state reacts with water and thereby reverts to its precursor state; i.e., the activated state is deactivated. Effectively, the precursor catalyzes carbodiimides' conversion into waste and forms a transient activated state.We designed building blocks to regulate a range of assemblies and supramolecular materials at the expense of carbodiimide fuel. The simplicity and versatility of the reaction cycles have democratized and popularized the field of chemically fueled assemblies. In this Account, we describe what we have "learned" on our way. We introduce the field exemplified by biological nonequilibrium selfassembly. We describe the design of the carbodiimide-driven reaction cycle. Using examples from our group and others, we offer design rules for the building block's structure and strategies to create the desired morphology or supramolecular materials. The discussed morphologies include fibers, colloids, crystals, and oil-and coacervate-based droplets. We then demonstrate how these assemblies form supramolecular materials with unique material properties like the ability to self-heal. Besides, we discuss the concept of reciprocal coupling in which the assembly exerts feedback on its reaction cycle and we also offer examples of such feedback mechanisms. Finally, we close the Account with a discussion and an outlook on this field. This Acco...

Carbodiimide‐Driven Toughening of Interpenetrated Polymer Networks

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Switched “On” Transient Fluorescence Output from a Pulsed-Fuel Molecular Ratchet

“…Biology uses chemically fueled ratcheting − in numerous metabolic processes, including molecular-level information processing − and transportation . Chemically powered ratcheting also forms the basis of a number of artificial molecular motors, − pumps, ,− and dissipative materials. ,,− A molecular energy ratchet ,,− was recently reported in which a crown ether (a “reading head” that responds to particular “symbols” encoded on a molecular tape) is pumped from solution onto a molecular strand by a pulse ,,− of a chemical fuel . Further fuel pulses transported the macrocycle along the tape before releasing it back to the bulk solution off the other end of the strand.…”

Dynamic supramolecular hydrogels mediated by chemical reactions

“…1(c)), the non-assembling precursors are converted into self-assembling hydrogelators by their reaction with the chemical fuels immediately or by incorporating a signal, for example pH, released by the chemical fuel governed reactions. 53–56 As a consequence, the activated hydrogelators are allowed to self-assemble into hydrogels with the consumption of chemical energy. However, the hydrogelators are unstable and will transform backwards to the non-assembling state when the chemical fuels are depleted.…”