Controlled Noncovalent Synthesis of Secondary Supramolecular Polymers.

Dynamic supramolecular polymers, with their functional similarities to classical covalent polymers and their adaptive and self-repairing nature reminiscent of biological assemblies, have emerged as highly promising systems for the design of smart soft materials. Recent advancements in mechanistic investigations and novel synthetic strategies, such as living supramolecular polymerization, have significantly enhanced our ability to control the primary structure of these supramolecular polymers. However, realizing their full functional potential requires expanding their topological diversity in a manner akin to classical polymers as well as achieving precise molecular organization at higher hierarchical levels of self-assembly. In this paper, we present a remarkable advancement in this field, introducing an unprecedented and controlled synthesis of secondary supramolecular polymers. Our innovative strategy combines chirality-controlled surface-catalyzed secondary nucleation and a bioinspired peptide design, effectively stabilizing higher-order assembly. Furthermore, by harnessing this stereoselective nucleation process, we demonstrate the successful synthesis of racemic supramolecular polymers featuring parallelly stacked conglomerate microstructures─a previously unreported topology in synthetic self-assembled systems. Additionally, we elucidate that the extent of secondary supramolecular polymers can be regulated by modulating the enantiomeric excess of the chiral monomers. Consequently, our study unveils new topologies that exhibit enhanced higher-order structural complexity in the realm of supramolecular polymers.

Secondary Nucleation-Triggered Physical Cross-Links and Tunable Stiffness in Seeded Supramolecular Hydrogels.

Mechanistic understanding and the control of molecular self-assembly at all hierarchical levels remain grand challenges in supramolecular chemistry. Functional realization of dynamic supramolecular materials especially requires programmed assembly at higher levels of molecular organization. Herein, we report an unprecedented molecular control on the fibrous network topology of supramolecular hydrogels and their resulting macroscopic properties by biasing assembly pathways of higher-order structures. The surface-catalyzed secondary nucleation process, a well-known mechanism in amyloid fibrilization and chiral crystallization of small molecules, is introduced as a non-covalent strategy to induce physical cross-links and bundling of supramolecular fibers, which influences the microstructure of gel networks and subsequent mechanical properties of hydrogels. In addition, seed-induced instantaneous gelation is realized in the kinetically controlled self-assembled system under this study, and more importantly, the extent of secondary nucleation events and network topology is manipulated by the concentration of seeds.

Energy transfer in FRET pairs in a supramolecular hydrogel template.

Fluorescence resonance energy transfer (FRET) in pairs of chromophores has mostly been achieved using covalently bound chromophores. In this study, we have demonstrated energy transfer in FRET pairs by taking advantage of the self-assembly of the chromophores on metal cholate hydrogel fibers.

Supramolecular Gelation of Europium and Calcium Cholates through the Nucleation-Elongation Growth Mechanism.

A detailed understanding of gelation mechanism can enable the properties of gels to be tuned for various applications, and may possibly help in understanding the aggregation of different biomolecules. We report a detailed study of the morphological and physio-chemical changes, dynamics (of a probe), and kinetics during the gelation of europium and calcium cholate hydrogels, leading to the development of a growth model. AFM images showed the transition of aggregated particles (100-150 nm) in the sol phase growing to a fibrous network in the gel through the entanglement of fibres, and not by dendritic growth (height analysis). The dynamic changes during this phase transformation were studied using a fluorescence probe (change in intensity and lifetime). We have been able to delineate the growth mechanism by using a combination of Eu(III) luminescence and a polarity sensitive fluorescence probe. The growth was found to follow the nucleation-elongation model, and these two phases responded in distinctly different fashions in rheological and luminescence measurements.

A Stimuli-Responsive Metallohydrogel Exhibiting Cyclohexane-Like Hydrophobicity.

Silver(I) forms a hydrogel in the presence of cholate with unusual properties, which are not observed with other cations. Polarity-sensitive probes have shown that the spherical aggregates observed in the gel have 'pockets' with hydrophobicity comparable to that of degassed cyclohexane. The gel exhibited thermo- and mechanoresponsive properties. Color tunability from blue to cyan and green was observed with prodan. The two sol phases of the gel formed by applying stress and temperature showed very different properties.