Catalysis of Supramolecular Hydrogelation

Abstract

CONSPECTUSOne often thinks of catalysts as chemical tools to speed up a reaction, or to have a reaction run under more benign conditions. As such, catalysis has a role to play in the chemical industry and in lab scale synthesis that is not to be underestimated. Still, the role of catalysis in living systems (cells, organisms) is much more extensive, ranging from the formation and breakdown of small molecules and biopolymers, to controlling signal transduction cascades and feedback processes, motility and mechanical action. Such phenomena are only recently starting to receive attention in synthetic materials and chemical systems. 'Smart' soft materials could find many important applications ranging from personalized therapeutics to soft robotics, to name but a few. Until recently, approaches to controlling the properties of such materials were largely dominated by thermodynamics, for instance looking at phase behavior and interaction strength. However, kinetics play a large role in determining the behavior of such soft materials, for instance in the formation of kinetically trapped (metastable) states, or the dynamics of component exchange. As catalysts can change the rate of a chemical reaction, catalysis could be used to control the formation, dynamics and fate of supramolecular structures, when the molecules making up these structures contain chemical bonds whose formation or exchange are susceptible to catalysis. In this Account, we describe our efforts to use synthetic catalysts to control the properties of supramolecular hydrogels. Building on the concept of synthesizing the assembling molecule in the self-assembly medium from non-assembling precursors, we will introduce the use of catalysis to change the kinetics of assembler formation, and thereby the properties of the resulting material. In particular, we will focus on the synthesis of supramolecular hydrogels where the use of a catalyst provides access to gel materials with vastly different appearance and mechanical properties, or controls localized gel formation and the growth of gel objects. As such, catalysis will be applied to create molecular materials that exist outside of chemical equilibrium. In all, using catalysts to control the properties of soft materials constitutes a new avenue for catalysis, far beyond the traditional use in industrial and lab scale synthesis.

Free-standing supramolecular hydrogel objects by reaction-diffusion

“…RD-SA requires a multicomponent reaction inducing a SA process, to allow independent diffusion of reactants and SA of products at the crossing of the diffusional fronts. We have recently reported a supramolecular hydrogelator that is formed in the gelation medium by a multicomponent chemical reaction26. In this work, the acid-catalysed reaction of hydrazide H and aldehyde A leads to the formation of the trishydrazone gelator HA 3 (Fig.…”

Low-Molecular-Weight Gels: The State of the Art

“…This can be achieved by heating to improve solubility, initially dissolving in a good solvent before adding an anti-solvent, choosing a pH at which the molecule is soluble and then adjusting the pH in one of a number of different ways to render the molecule less soluble, 62 adding a salt to charge screen, 63 using a pro-gelator with a cleavable, solubilizing group, 64 or using a chemical or enzymatic reaction to generate the gelator in situ from suitable precursors. 65,66 To the best of our knowledge, there are no examples where a molecule is simply added to a solvent and gelation results (although there are many examples where ''instant'' gelation can be induced by mixing two components that react or interact to form a gelator on contact). 67 Because of this, how the gelation is carried out matters.…”

Dynamic Proteoids Generated From Dipeptide‐Based Monomers

“…Aromatic interactions and hydrogen bonds have been found to play important roles during the formation of nanomaterials . In addition, supramolecular hydrogels composed of low‐molecular‐weight gelators, which can be applied as smart materials, have been prepared through acylhydrazone formation betweenhydrazides and aldehydes . Herein, we prepared dialdehyde 1 and dipeptide hydrazides ( 2 – 7 ) as reported previously .…”