Supramolecular copolymerization through self-correction of non-polymerizable transient intermediates

Kinetic control over structures and functions of complex assembly systems has aroused widespread interest. Understanding the complex pathway and transient intermediates is helpful to decipher how multiple components evolve into complex assemblies. However, for supramolecular polymerizations, thorough and quantitative kinetic analysis is often overlooked. Challenges remain in collecting the information of structure and content of transient intermediates in situ with high temporal and spatial resolution. Here, the unsolved evolution mechanism of a classical self-sorting supramolecular copolymerization system was addressed by employing multidimensional NMR techniques coupled with a microfluidic technique. Unexpected complex pathways were revealed and quantitatively analyzed. A counterintuitive pathway involving polymerization through the 'error-correction' of non-polymerizable transient intermediates was identified. Moreover, a 'non-classical' step-growth polymerization process controlled by the self-sorting mechanism was unraveled based on the kinetic study. Realizing the existence of transient intermediates during self-sorting can encourage the exploitation of this strategy to construct kinetic steady state assembly systems. Moreover, the strategy of coupling a microfluidic technique with various characterization techniques can provide a kinetic analysis toolkit for versatile assembly systems. The combined approach of coupling thermodynamic and kinetic analyses is indispensable for understanding the assembly mechanisms, the rules of emergence, and the engineering of complex assembly systems.

Formation of sandwich, macrocyclic and box supramolecular assemblies that were controlled by the distance of two oxygen atoms in hydrogen bonding donors

Sandwich, macrocyclic and box supramolecular assemblies were synthesized. They can further self assemble to form a double-layer supramolecular polymer, nanotubes and one-dimensional “iron chain type” supramolecular polymer.

Tunable Adhesion from Stoichiometry-Controlled and Sequence-Defined Supramolecular Polymers Emerges Hierarchically from Cyanostar-Stabilized Anion-Anion Linkages

Sequence-controlled supramolecular polymers offer new design paradigms for generating stimuli-responsive macromolecules with enhanced functionalities. The dynamic character of supramolecular links present challenges to sequence definition in extended supramolecular macromolecules, and design principles remain nascent. Here, we demonstrate the first example of using stoichiometry-control to specify the monomer sequence in a linear supramolecular polymer by synthesizing both a homopolymer and an alternating copolymer from the same glycol-substituted cyanostar macrocycle and phenylene-linked diphosphate monomers. A 2:1 stoichiometry between macrocycle and diphosphate produces a supramolecular homopolymer of general formula (A)_n comprised of repeating units of cyanostar-stabilized phosphate-phosphate dimers. Using a 1:1 stoichiometry, an alternating (AB)_n structure is produced with half the phosphate dimers now stabilized by the additional counter cations that emerge hierarchically after forming the stronger cyanostar-stabilized phosphate dimers. These new polymer materials and binding motifs are sufficient to bear normal and shear stress to promote significant and tunable adhesive properties. The homopolymer (A)_n, consisting of cyanostar-stabilized anti-electrostatic linkages, shows adhesion strength comparable to commercial superglue formulations based on polycyanoacrylate but is thermally reversible. Unexpectedly, and despite including traditional ionic linkages, the alternating copolymer (AB)_n shows weaker adhesion strength more similar to commercial white glue based on poly(vinyl acetate). Thus, the adhesion properties can be tuned over a wide range by simply controlling the stoichiometric ratio of monomers. This study offers new insight into supramolecular polymers composed of custom-designed anion and receptor monomers and demonstrates the utility of emerging functional materials based on anion-anion linkages.

Integrative Self-Sorting: One-Pot Synthesis of a Hetero[4]rotaxane from a Daisy-Chain-Containing Hetero[4]pseudorotaxane

The structural complexity of mechanically interlocked molecules are very attractive to chemists owing to the challenges they present. In this article, novel mechanically interlocked molecules with a daisy-chain-containing hetero[4]rotaxane motif were efficiently synthesized. In addition, a novel integrative self-sorting strategy is demonstrated, involving an ABB-type (A for host, dibenzo-24-crown-8 (DB24C8), and B for guest, ammonium salt sites) monomer and a macrocycle host, benzo-21-crown-7 (B21C7), in which the assembled species in hydrogen-bonding-supported solvent only includes a novel daisy-chain-containing hetero[4]pseudorotaxane. The found self-sorting process involves the integrative recognition between B21C7 macrocycles and carefully designed components simultaneously containing two types of secondary ammonium ions and a host molecule, DB24C8 crown ether. The self-sorting strategy is integrative to undertake self-recognition behavior to form one single species of pseudorotaxane compared with the previous report. This self-sorting system can be used for the efficient one-pot synthesis of a daisy-chain-containing hetero[4]rotaxane in a good yield. The structure of hetero[4]rotaxane was confirmed by ¹ H NMR spectroscopy and high-resolution electrospray ionization (HR-ESI) mass spectrometry.

4-Methylcoumarin-bridged fluorescent responsive cryptand: from [2+2] photodimerization to supramolecular polymer

A fluorescent responsive BMP32C10-based cryptand host was successfully synthesized by introducing a 4-methylcoumarin group to the third arm of the cryptand. The cryptand was able to undergo [2+2] photodimerization on UV irradiation (λ = 365 nm) and, based on the photodimerization and host-guest interaction, a new supramolecular polymer was constructed in a convenient manner.

Complexation of Racemic 2,6-Helic[6]arene and Its Hexamethyl-Substituted Derivative with Quaternary Ammonium Salts, N-Heterocyclic Salts, and Tetracyanoquinodimethane

Complexation of racemic 2,6-helic[6]arene 1 and its hexamethyl-substituted derivative 2 with quaternary ammonium salts, N-heterocyclic salts, and tetracyanoquinodimethane have been described in detail. It was found that host 2 could form stable complexes with acetyl choline, thiaacetyl choline, N,N,N-trimethylbenzenammonium salt, pyridinium, and 4,4'-bipyridinium salts in solution and/or in the solid state. The unsubstituted macrocycle 1 showed more significant complexation with the widely tested quaternary ammonium salts and N-heterocyclic salts, and exhibited stronger complexation towards the guests than its derivative 2. Moreover, it was found that macrocycle 1 and its derivative 2 could also complex with neutral electron-deficient tetracyanoquinodimethane (TCNQ), and the association constants were determined to be 2840±94 and 1358±46 m^-1 , respectively. These results could make this new macrocycle and its derivatives find wide applications in the design and construction of functional supramolecular assemblies.

Supramolecular polymers based on a pillar[5]arene-fused cryptand: design, fabrication and degradation accompanied by a fluorescence change

Novel supramolecular polymers based on a pillar[5]arene-fused cryptand have been constructed easily and conveniently, in which three orthogonal interactions were combined together.

A Kinetic Self-Sorting Approach to Heterocircuit [3]Rotaxanes

In this proof-of-concept study, an active-template coupling is used to demonstrate a novel kinetic self-sorting process. This process iteratively increases the yield of the target heterocircuit [3]rotaxane product at the expense of other threaded species.

Nitrogen-Rich Triptycene-Based Porous Polymer for Gas Storage and Iodine Enrichment

A new kind of nitrogen-rich triptycene-based porous polymer (NTP) with high surface area of up to 1067 m² g^-1 was synthesized by a modified Yamamoto-type Ullmann cross-coupling reaction. Having structure features of expanded conjugated area and nitrogen atoms doping in polymer networks, the NTP displays extraordinary gas storage ability and excellent iodine adsorption capability.

Supramolecular Guest-Host Interactions for the Preparation of Biomedical Materials

Supramolecular chemistry has emerged as an important technique for the formation of biomaterials, including nano- and microparticles and hydrogels. One specific class of supramolecular chemistry is the direct association of guest-host pairs, which involves host macrocycles such as cyclodextrins and cucurbit[n]urils and a wide range of guest molecules, where association is typically driven by molecule size and hydrophobicity. These systems are of particular interest in the biomedical field due to their dynamic nature, chemical diversity, relative ease of synthesis, and ability to interact with biological or synthetic molecules. In this review, we discuss aspects of polymeric material assembly mediated by guest-host interactions, including the fundamentals of assembly into functional biomedical materials. Additionally, applications of biomaterials that utilize guest-host interactions are discussed with a focus on injectable material formulations, the sequestration and delivery of encapsulated cargo (i.e., drugs, biomolecules), and the investigation of cell-material interactions (i.e., adhesion, differentiation, and delivery). While methodologies for guest-host mediated assembly and biological interaction have rapidly evolved in recent years, they remain far from realizing their full potential in the biomaterials field.

A Cu2+ specific metallohydrogel: preparation, multi-responsiveness and pillar[5]arene-induced morphology transformation

A Cu²⁺ specific metallohydrogel was constructed from a terpyridine-based low molecular weight ligand. The metallohydrogel showed multi-responsiveness and its morphology could be transformed by pillararene-based host–guest interaction.

From self-sorted coordination libraries to networking nanoswitches for catalysis

This feature article sketches our long way from the development of dynamic heteroleptic coordination motifs to the self-sorting of multi-component libraries and finally the design of a new family of triangular nanomechanical switches, which are useful for ON–OFF control of catalysis and in bidirectional communication.

Cross-linked supramolecular polymer metallogels constructed via a self-sorting strategy and their multiple stimulus-response behaviors

Novel cross-linked supramolecular polymer metallogels were successfully constructed from four components via a self-sorting strategy, and feature interesting multiple stimulus-response behaviors under various external stimuli, including halide, base, and competitive guests.