Deprotonation usually occurs as an unwanted side reaction in the Lewis pair polymerization of Michael acceptors, for which the conjugated addition of the Lewis base to the acid-activated monomer is the commonly accepted initiation mechanism. This has also been reported for B-P-based bridged Lewis pairs (BLPs) that form macrocyclic addition products. We now show that the formerly unwanted deprotonation is the likely initiation pathway in the case of Al-P-based BLPs. In a detailed study of a series of Al-P-based BLPs, using a combination of single-crystal diffraction experiments (X-ray and neutron) and mechanistic investigations (experimental and computational), an active role of the methylene bridge was revealed, acting as a base towards the α-acidic monomers. Additionally, the polymerization studies proved a living behavior combined with significantly high activities, narrow molecular mass distributions, and the possibility of copolymerization.

AbstractDie Deprotonierung tritt in der Regel als unerwünschte Nebenreaktion bei der Lewis‐Paar‐Polymerisation von Michael‐Akzeptoren auf, bei der die konjugierte Addition der Lewis‐Base an das säureaktivierte Monomer der gängige Initiationsmechanismus ist. Dies wurde auch für B‐P‐basierte verbrückte Lewis‐Paare (Bridged Lewis Pairs, BLPs) berichtet, die makrozyklische Additionsprodukte bilden. Wir konnten zeigen, dass bei Al‐P‐basierten BLPs die bisher unerwünschte Deprotonierung der wahrscheinliche Initiationsweg ist. In einer detaillierten Studie mit einer Reihe von Al‐P‐basierten BLPs unter Verwendung von Einkristalldiffraktometrie (Röntgen und Neutronen) und mechanistischen Untersuchungen (experimentell und rechnerisch) wurde eine aktive Rolle der Methylenbrücke aufgedeckt, die als Base für die α‐aziden Monomere agiert. Darüber hinaus bewiesen Polymerisationsstudien ein lebendes Verhalten in Kombination mit signifikant hohen Aktivitäten, engen Molmassenverteilungen und der Möglichkeit zur Copolymerisation.

The field of supramolecular chemistry and molecular self-assembly has entered a new phase in which the use of chemical reactions to create out-of-equilibrium molecular assemblies is becoming more common. These dynamic assemblies have vastly different properties than their in-equilibrium counterparts, which include the ability to be controlled over space and time or the ability to self-replicate. Such behaviors would set significant steps toward the synthesis of artificial life. However, a limiting factor toward the revolution of the field is the lack of clear definitions and design rules for such systems. In this review, we explain the core principles that help to design energy-dissipating chemical reaction cycles that can drive molecular assemblies. We discuss strategies for coupling these reaction cycles to building blocks for the materials. We conclude with an outlook for the field of dissipative self-assembly and its potential role as a material or model for life.

We describe the self-assembly of gold and iron oxide nanoparticles regulated by a chemical reaction cycle that hydrolyzes a carbodiimide-based fuel. In a reaction with the chemical fuel, the nanoparticles are chemically activated to a state that favors assembling into clusters. The activated state is metastable and decays to the original precursor reversing the assembly. The dynamic interplay of activation and deactivation results in a material of which the behavior is regulated by the amount of fuel added to the system; they either did not assemble, assembled transiently, or assembled permanently in kinetically trapped clusters. Because of the irreversibility of the kinetically trapped clusters, we found that the behavior of the self-assembly was prone to hysteresis effects. The final state of the system in the energy landscape depended on the pathway of preparation. For example, when a large amount of fuel was added at once, the material would end up kinetically trapped in a local minimum. When the same amount of fuel was added in small batches with sufficient time for the system to re-equilibrate, the final state would be the global minimum. A better understanding of pathway complexity in the energy landscape is crucial for the development of fuel-driven supramolecular materials.

Solutions of silicon nanocrystals (SiNCs) are used in a diverse range of applications because of their tunable photoluminescence, biocompatibility, and the abundance of Si. In dissipative supramolecular materials, self-assembly of molecules or nanoparticles is driven by a chemical reaction network that irreversible consumes fuel. The properties of the emerging structures are controlled by the kinetics of the underlying chemical reaction network. Herein, we demonstrate the dissipative self-assembly of photoluminescent SiNCs driven by a chemical fuel. A chemical reaction induces self-assembly of the water-soluble SiNCs. However, the assemblies are transient, and when the chemical reaction network runs out of fuel, the SiNCs disassemble. The lifetime of the assemblies is controlled by the amount of fuel added. As an application of the transient supramolecular material, we demonstrate that the platform can be used to control the delayed uptake of the nanocrystals by mammalian cells.

In this chapter, we focus on nonequilibrium self-assembly of molecules into supramolecular assemblies. Structures formed via nonequilibrium assembly are exchanging energy and matter with their environment and are thus, by definition, not in equilibrium. We will further subdivide these assemblies in kinetically trapped assemblies, metastable assemblies, and dissipative nonequilibrium assemblies. In the first section, we will explain the subdivision in these classes and their relation with their free-energy landscapes. We will then detail each example with state-of-the-art man-made assemblies and highlight the unique material properties for each class of nonequilibrium assemblies, followed by examples of supramolecular biomaterials for each class. We will close this chapter with a perspective on where the field could benefit from a better understanding and especially better design rules for nonequilibrium assemblies.

Dissipative self-assembly is a process in which energy-consuming chemical reaction networks drive the assembly of molecules. Prominent examples from biology include the GTP-fueled microtubule and ATP-driven actin assembly. Pattern formation and oscillatory behavior are some of the unique properties of the emerging assemblies. While artificial counterparts exist, researchers have not observed such complex responses. One reason for the missing complexity is the lack of feedback mechanisms of the assemblies on their chemical reaction network. In this work, we describe the dissipative self-assembly of colloids that protect the hydrolysis of their building blocks. The mechanism of inhibition is generalized and explored for other building blocks. We show that we can tune the level of inhibition by the assemblies. Finally, we show that the robustness of the assemblies towards starvation is affected by the degree of inhibition.

Many biological materials exist in non-equilibrium states driven by the irreversible consumption of high-energy molecules like ATP or GTP. These energy-dissipating structures are governed by kinetics and are thus endowed with unique properties including spatiotemporal control over their presence. Here we show man-made equivalents of materials driven by the consumption of high-energy molecules and explore their unique properties. A chemical reaction network converts dicarboxylates into metastable anhydrides driven by the irreversible consumption of carbodiimide fuels. The anhydrides hydrolyse rapidly to the original dicarboxylates and are designed to assemble into hydrophobic colloids, hydrogels or inks. The spatiotemporal control over the formation and degradation of materials allows for the development of colloids that release hydrophobic contents in a predictable fashion, temporary self-erasing inks and transient hydrogels. Moreover, we show that each material can be re-used for several cycles.

AbstractLösungen von Siliciumnanokristallen (SiNCs) werden z. B. wegen ihrer einstellbaren Photolumineszenz, Biokompatibilität und der Verfügbarkeit von Si in zahlreichen Anwendungen eingesetzt. In dissipativen supramolekularen Materialien wird die Selbstassemblierung von Molekülen oder Nanopartikeln durch ein chemisches Reaktionsnetzwerk angetrieben, das irreversibel Brennstoff verbraucht. Die Eigenschaften der entstehenden Strukturen werden durch die Kinetik des zugrunde liegenden chemischen Reaktionsnetzwerkes gesteuert. Hier wird die dissipative Selbstassemblierung von photolumineszierenden SiNCs demonstriert, die von einem chemischen Brennstoff angetrieben werden. Eine chemische Reaktion setzt die Selbstassemblierung der wasserlöslichen SiNCs in Gang. Allerdings sind die Strukturen transient, und wenn dem chemischen Reaktionsnetzwerk der Brennstoff ausgeht, deassemblieren sich die SiNCs. Die Lebensdauer der Strukturen ist durch die zugegebene Brennstoffmenge steuerbar. Die Plattform kann für die gesteuerte, verzögerte Aufnahme der Nanokristalle durch Säugetierzellen genutzt werden.