Nature uses catalysis as an indispensable tool to control assembly and reaction cycles in vital non-equilibrium supramolecular processes. For instance, enzymatic methionine oxidation regulates actin (dis)assembly, and catalytic guanosine triphosphate hydrolysis is found in tubulin (dis)assembly. Here we present a completely artificial reaction cycle which is driven by a chemical fuel that is catalytically obtained from a 'pre-fuel'. The reaction cycle controls the disassembly and re-assembly of a hydrogel, where the rate of pre-fuel turnover dictates the morphology as well as the mechanical properties. By adding additional fresh aliquots of fuel and removing waste, the hydrogels can be reprogrammed time after time. Overall, we show how catalysis can control fuel generation to control reaction / assembly kinetics and materials properties in lifelike non-equilibrium systems. File list (4) download file view on ChemRxiv REV_SachCHO_20191221_Chemrxiv.pdf (1.38 MiB) download file view on ChemRxiv REV_SI_SachCHO_20191221_GF_v2.pdf (1.37 MiB) download file view on ChemRxiv Video1_gel-sol-gel_vial.mp4 (109.69 MiB) download file view on ChemRxiv Video2_microscopy.mp4 (62.71 MiB)

Fuel‐driven reaction cycles are found in biological systems to control the assembly and disassembly of supramolecular materials such as the cytoskeleton. Fuel molecules can bind noncovalently to a self‐assembling building block or they can react with it, resulting in covalent modifications. Overall the fuel can either switch the self‐assembly process on or off. Here, a closer look is taken at artificial systems that mimic biological systems by making and breaking covalent bonds in a self‐assembling motif. The different chemistries used so far are highlighted in chronological order and the pros and cons of each system are discussed. Moreover, the desired traits of future reaction cycles, their fuels, and waste management are outlined, and two chemistries that have not been explored up to now in chemically fueled dissipative self‐assembly are suggested.

Controlling supramolecular growth at solid surfaces is of great importance to expand the scope of supramolecular materials. A dendritic benzene-1,3,5-tricarboxamide peptide conjugate is described in which assembly can be triggered by a pH jump. Stopped-flow kinetics and mathematical modeling provide a quantitative understanding of the nucleation, elongation, and fragmentation behavior in solution. To assemble the molecule at a solid-liquid interface, we use proton diffusion from the bulk. The latter needs to be slower than the lag phase of nucleation to progressively grow a hydrogel outwards from the surface. Our method of surface-assisted self-assembly is generally applicable to other gelators, and can be used to create structured supramolecular materials.

Narcissistic self-sorting in supramolecular assemblies can help to construct materials with more complex hierarchies. Whereas controlled changes in pH or temperature have been used to this extent for two-component self-sorted gels, here we show that a chemically fueled approach can provide three-component materials with high precision. The latter materials have interesting mechanical properties, such as enhanced or suppressed stiffness, and intricate multistep gelation kinetics. In addition, we show that we can achieve supramolecular templating, where pre-existing supramolecular fibers first act as a templates for growth of a second gelator, after which they can selectively be removed.

The method of neutron imaging was adopted to map the concentration evolution of aqueous paramagnetic Gd(NO3)3 solutions. Magnetic manipulation of the paramagnetic liquid within a miscible nonmagnetic liquid is possible by countering density-difference driven convection. The formation of salt fingers caused by double-diffusive convection in a liquid-liquid system of Gd(NO3)3 and Y(NO3)3 solutions can be prevented by the magnetic field gradient force.

Nature uses catalysis as an indispensable tool to control assembly and reaction cycles in vital non-equilibrium supramolecular processes. For instance, enzymatic methionine oxidation regulates actin (dis)assembly, and catalytic guanosine triphosphate hydrolysis is found in tubulin (dis)assembly. Here we present a completely artificial reaction cycle which is driven by a chemical fuel that is catalytically obtained from a ‘pre-fuel’. The reaction cycle controls the disassembly and re-assembly of a hydrogel, where the rate of pre-fuel turnover dictates the morphology as well as the mechanical properties. By adding additional fresh aliquots of fuel and removing waste, the hydrogels can be re-programmed time after time. Overall, we show how catalysis can control fuel generation to control reaction / assembly kinetics and materials properties in life-like non-equilibrium systems.

Controlling the flow properties of aqueous formulations is essential in fields as diverse as biotechnology, cosmetics, paints, or chemically enhanced oil recovery, to cite a few. This work presents a study of the association, in aqueous solutions, of complementary polyacrylamides carrying amino and aryl aldehyde side-groups. Through free radical polymerization, copolymers with tunable molar masses (M n ranging from 60 to 370 kg·mol–1), functionality (2 to 17 mol %), and permanent charge degrees (0 to 98 mol %) were obtained. Imine formation was studied on model systems consisting of amino polyacrylamides and a benzaldehyde derivative. It was found that the presence of permanent charges on the amino polyacrylamide does not prevent imine formation but influences the association degree. In addition, imines were efficiently formed in the presence of NaCl and the dynamic cross-links proved to be thermoresponsive, with a reversible displacement of the equilibrium toward amine and aldehyde with increasing temperature. The associative formulations were subsequently studied by rheology. It was shown that the functionality, charge degree, and molar mass of the copolymers can be used to rationally manipulate interchain association, which proved to be a powerful tool to control the viscosity and rheological profile of the different formulations. Dynamic light scattering was utilized to further study the microstructural dynamics of one of the formulations, showing good agreement with rheology. Finally, taking advantage of the influence of temperature on the imine cross-links, a thermoresponsive hydrogel was prepared that undergoes reversible sol–gel transition over multiple heating–cooling cycles between 30 and 80 °C.

Controlling supramolecular growth at solid surfaces is of great importance to expand the scope of supramolecular materials. A dendritic benzene‐1,3,5‐tricarboxamide peptide conjugate is described in which assembly can be triggered by a pH jump. Stopped‐flow kinetics and mathematical modeling provide a quantitative understanding of the nucleation, elongation, and fragmentation behavior in solution. To assemble the molecule at a solid–liquid interface, we use proton diffusion from the bulk. The latter needs to be slower than the lag phase of nucleation to progressively grow a hydrogel outwards from the surface. Our method of surface‐assisted self‐assembly is generally applicable to other gelators, and can be used to create structured supramolecular materials.