pH-Responsive Supramolecular Control of Polymer Thermoresponsive Behavior by Pillararene-Based Host–Guest Interactions

We demonstrate precise control of the lower critical solution temperature (LCST) behavior of a thermoresponsive polymer in water by pillararene-based host–guest interactions. The LCST value of the polymer increases upon the stepwise addition of either of the two pillararene hosts. On account of the pH-responsiveness of the pillararene-based host–guest interactions, the recovery of the LCST is achieved by treatment with acid, reflecting the pH-responsive supramolecular control of the LCST

A Dual-Responsive Supra-Amphiphilic Polypseudorotaxane Constructed from a Water-Soluble Pillar[7]arene and an Azobenzene-Containing Random Copolymer

Macromolecular supra-amphiphiles refer to a kind of macromolecular amphiphiles whose hydrophlic and hydrophobic parts are connected by noncovalent forces. They have applications in various fields, such as drug delivery, sensor systems, and biomedical materials. Here we report a novel molecular recognition motif between a new thermoresponsive water-soluble pillar[7]­arene (<b>WP7</b>) and an azobenzene derivative. Furthermore, we utilized this recognition motif to construct the first pillararene-based supra-amphiphilic polypseudorotaxane which can self-assemble to form vesicles in water. Due to the dual-responsiveness of the molecular recognition motif (the thermoresponsiveness of <b>WP7</b> and photoresponsiveness of azobenzene), the reversible transformations between solid nanospheres based on the self-assembly of the polymer backbone and vesicles based on the self-assembly of the supra-amphiphilic polypseudorotaxane were achieved by adjusting the solution temperature or UV–visible light irradiation. These dual-responsive aggregation behaviors were further used in the controlled release of water-soluble dye calcein molecules

A Supramolecular Cross-Linked Conjugated Polymer Network for Multiple Fluorescent Sensing

A supramolecular cross-linked network was fabricated and demonstrated to act as a multiple fluorescent sensor. It was constructed from a fluorescent conjugated polymer and a bisammonium salt cross-linker driven by dibenzo[24]­crown-8/secondary ammonium salt host–guest interactions. Compared with the conjugated polymer, the network has weak fluorescence due to the aggregation of polymer chains. Thanks to the multiple stimuli-responsiveness of host–guest interactions, the fluorescence intensity of the system can be enhanced by four types of signals, including potassium cation, chloride anion, pH increase, and heating. Hence, the network can serve as a cation sensor, an anion sensor, a pH sensor, and a temperature sensor. It can be used in both solution and thin film. Interestingly, exposure of a film made from this supramolecular cross-linked network to ammonia leads to an increase of fluorescence, making it a good candidate for gas detection

Redox-Responsive Amphiphilic Macromolecular [2]Pseudorotaxane Constructed from a Water-Soluble Pillar[5]arene and a Paraquat-Containing Homopolymer

Here we report a redox-responsive host–guest complex between a new water-soluble pillar[5]­arene (<b>WP5</b>) and a paraquat derivative. Compared with the neutral form of the paraquat derivative that binds <b>WP5</b> weakly, its dication form binds <b>WP5</b> much more strongly. Furthermore, we utilize this new water-soluble redox-responsive molecular recognition motif to construct the first pillararene-based amphiphilic macromolecular [2]­pseudorotaxane, which self-assembles into redox-responsive polymeric vesicles in water. Such pillararene-based supramolecular vesicles were further used to construct a drug delivery system to encapsulate and controlled release DOX·HCl, an anticancer drug. The uptake of these DOX·HCl-loaded supramolecular vesicles by cancer cells was studied with confocal laser scanning microscopy. Meanwhile, DOX·HCl-loaded supramolecular vesicles showed anticancer activity in vitro comparable to free DOX·HCl under the examined conditions

Supramolecular Copolymer Constructed by Hierarchical Self-Assembly of Orthogonal Host–Guest, H‑Bonding, and Coordination Interactions

Supramolecular copolymers with complex architectures and emergent functions constitute a class of challenging but enticing synthetic targets in polymer science. Individual building blocks can be tailored to endow a resulting supramolecular copolymer with increased structural and functional complexity. Herein, we describe the construction of a linear supramolecular copolymer comprising mechanically interlocked segments with hydrogen-bonding metallorhomboidal units. Specifically, a hierarchical supramolecular polymerization of a crown ether-based [2]­rotaxane and a discrete organoplatinum­(II) metallacycle driven by 2-ureido-4-pyrimidinone (UPy) quadruple hydrogen bonding provides the impetus for its formation. This system demonstrates enhanced structural complexity accessed by the unification of orthogonal noncovalent interactions: metal coordination, host–guest chemistry, and multiple hydrogen bonding interfaces

Physical Removal of Anions from Aqueous Media by Means of a Macrocycle-Containing Polymeric Network

Reported here is a hydrogel-forming polymer network that contains a water-soluble tetracationic macrocycle. Upon immersion of this polymer network in aqueous solutions containing various inorganic and organic salts, changes in the physical properties are observed that are consistent with absorption of the constituent anions into the polymer network. This absorption is ascribed to host–guest interactions involving the tetracationic macrocyclic receptor. Removal of the anions may then be achieved by lifting the resulting hydrogels out of the aqueous phase. Treating the anion-containing hydrogels with dilute HCl leads to the protonation-induced release of the bound anions. This allows the hydrogels to be recycled for reuse. The present polymer network thus provides a potentially attractive approach to removing undesired anions from aqueous environments

Supramolecular Micelles Constructed by Crown Ether-Based Molecular Recognition

A novel supramolecular amphiphilic polymer constructed by crown ether-based molecular recognition has been fabricated and demonstrated to self-assemble into core–shell supramolecular micelles in water. The reversible transition between assembled and disassembled structures can be achieved by changing the pH. This transition was used to realize the controlled release of small molecules. The supramolecular micelle was characterized by various techniques including conductivity, transmission electron microscopy (TEM), dynamic laser light scattering (DLS), and fluorescence titration. TEM images showed dark gray spherical aggregates, and the mean size of the micelles was 50 nm in diameter and of uniformly dispersed size, in good agreement with the DLS results. The release of hydrophobic molecules from the micelles was realized by adding acid (aqueous HCl), weakening the host–guest interactions and leading to disassembly of the supramolecular micelles

Hierarchical Self-Assembly: Well-Defined Supramolecular Nanostructures and Metallohydrogels via Amphiphilic Discrete Organoplatinum(II) Metallacycles

Metallacyclic cores provide a scaffold upon which pendant functionalities can be organized to direct the formation of dimensionally controllable nanostructures. Because of the modularity of coordination-driven self-assembly, the properties of a given supramolecular core can be readily tuned, which has a significant effect on the resulting nanostructured material. Herein we report the efficient preparation of two amphiphilic rhomboids that can subsequently order into 0D micelles, 1D nanofibers, or 2D nanoribbons. This structural diversity is enforced by three parameters: the nature of the hydrophilic moieties decorating the parent rhomboids, the concentration of precursors during self-assembly, and the reaction duration. These nanoscopic constructs further interact to generate metallohydrogels at high concentrations, driven by intermolecular hydrophobic and π–π interactions, demonstrating the utility of coordination-driven self-assembly as a first-order structural element for the hierarchical design of functional soft materials