Pillararene-Based Supramolecular Polymers for Adsorption and Separation

Intercage Polymerization of Postfunctionalized Phosphine Organic Prisms into Cage-Based Assemblies with Tunable Morphologies

Great effort has been dedicated to the engineering of porous organic cages (POCs) in geometry and topology. Yet, harnessing these cage-like entities as premade building units to construct infinite cage-based superstructures remains elusive. In this study, we design a type of vertex-modified phosphine organic prism by a postfunctionalized approach and use it as a ditopic cage monomer to achieve an intercage supramolecular polymerization via the synergy of metal coordination and π-π dimerization. The resulting cage-by-cage polymers can further hierarchically organize into superstructures of diverse morphologies and dimensionalities, including 1D fibers, 2D lamellae, and 3D vesicles. Control over the cosolvents is capable of well regulating their structural hierarchies and self-assembled shapes. This would pave a way for the creation of cage-based supramolecular assemblies and nanomaterials.

A supramolecular electrochemical probe based on a tetrazole derivative pillar[5]arene/methylene blue system

For the first time, an original synthetic approach has been developed that enables the introduce ten tetrazole fragments into the pillar[5]arene structure. A supramolecular electrochemical probe was assembled for the first time from the obtained macrocycles and an electrochemically active signal converter: methylene blue (MB) dye. The ability of pillar[5]arene containing tetrazole fragments to selectively bind MB was confirmed by UV-vis and 2D 1H-1H NOESY spectroscopy. The stoichiometry of the resulting pillar[5]arene/MB complex = 1 : 2. This new supramolecular probe pillar[5]arene/MB allowed the detection of changes in the electrochemical signals of MB implemented in the supramolecular complex depending on the presence or absence of some metal ions (Zn2+ and Co2+) that do not exert their own redox activity. This will find further applications for the enhancement of the range of analytes detected by their influence on host-guest complexation and for the design of biosensors based on specific DNA-MB interactions.

Pillararene-Based Stimuli-Responsive Supramolecular Delivery Systems for Cancer Therapy

Cancer poses a significant challenge to global public health, seriously threatening human health and life. Although various therapeutic strategies, such as chemotherapy (CT), radiotherapy, phototherapy, and starvation therapy, are applied to cancer treatment, their limited therapeutic effect, severe side effects, and unsatisfactory drug release behavior need to be carefully considered. Thus, there is an urgent need to develop efficient drug delivery strategies for improving cancer treatment efficacy and realizing on-demand drug delivery. Notably, pillararenes, as an emerging class of supramolecular macrocycles, possess unique properties of highly tunable structures, superior host-guest chemistry, facile modification, and good biocompatibility, which are widely used in cancer therapy to achieve controllable drug release and reduce the toxic side effects on normal tissues under various internal/external stimuli conditions. This review summarizes the recent advance of stimuli-responsive supramolecular delivery systems (SDSs) based on pillararenes for tumor therapy from the perspectives of different assembly methods and hybrid materials, including molecular-scale SDSs, supramolecular nano self-assembly delivery systems, and nanohybrid SDSs. Moreover, the prospects and critical challenges of stimuli-responsive SDSs based on pillararenes for cancer therapy are also discussed.

Clamparene: Synthesis, Structure, and Its Application in Spontaneous Formation of 3D Porous Crystals

Macrocyclic arenes have emerged as pivotal scaffolds in supramolecular chemistry. Despite their significant contributions to molecular recognition and diverse applications, challenges persist in the development of macrocyclic arene-based crystalline materials, particularly in achieving porosity and addressing limitations in adsorption efficiency resulting from the small cavity sizes of existing macrocyclic arenes. In this study, we present the design and synthesis of a novel macrocyclic arene, clamparene (CLP), featuring a rigid backbone, easy synthesis, and a sizable cavity. CLP self-assembles into one-dimensional sub-nanotubes that further organize into a three-dimensional porous framework in the solid state. The crystalline solid of CLP exhibits potential as a porous crystalline adsorbent for various benzene-based contaminants with rapid adsorption kinetics, large uptake amounts, and good recyclability.

Pillar[5]arene-Based Fluorescent Supramolecular Polymers Without Conventional Chromophores

Fluorescent supramolecular polymers have garnered significant attention due to their successful integration of supramolecular polymers and fluorescence, offering vast potential for applications in sensing, imaging, optoelectronics, and photonics. In this study, we present a novel supramolecular polymer based on P5-OH, derived from mono-substituted pillararene macrocycles. Notably, these formed supramolecular polymeric aggregates exhibit a prominent blue emission, representing a rare instance of fluorescent polymers devoid of conventional chromophores. Furthermore, through the modification of alkyl chain ending groups attached to pillar[5]arenes, slight shifts in the emission peak could be observed. This research expands the scope of functional supramolecular polymeric systems utilizing pillararenes, providing valuable insights for the design of innovative luminescent materials and optical devices.

Applications of Supramolecular Polymers Generated from Pillar[n]arene-Based Molecules

Supramolecular chemistry enables the manipulation of functional components on a molecular scale, facilitating a "bottom-up" approach to govern the sizes and structures of supramolecular materials. Using dynamic non-covalent interactions, supramolecular polymers can create materials with reversible and degradable characteristics and the abilities to self-heal and respond to external stimuli. Pillar[n]arene represents a novel class of macrocyclic hosts, emerging after cyclodextrins, crown ethers, calixarenes, and cucurbiturils. Its significance lies in its distinctive structure, comparing an electron-rich cavity and two finely adjustable rims, which has sparked considerable interest. Furthermore, the straightforward synthesis, uncomplicated functionalization, and remarkable properties of pillar[n]arene based on supramolecular interactions make it an excellent candidate for material construction, particularly in generating interpenetrating supramolecular polymers. Polymers resulting from supramolecular interactions involving pillar[n]arene find potential in various applications, including fluorescence sensors, substance adsorption and separation, catalysis, light-harvesting systems, artificial nanochannels, and drug delivery. In this context, we provide an overview of these recent frontier research fields in the use of pillar[n]arene-based supramolecular polymers, which serves as a source of inspiration for the creation of innovative functional polymer materials derived from pillar[n]arene derivatives.

A fluorescent controllable supramolecular crosslinked polymer constructed by complementary metal coordination interaction

In this work, two different monomers M1 and M2 were designed and synthesized. M1 + M2 + Zn(OTf)2 could self-assemble to form a supramolecular crosslinked polymer (SCP) based on complementary terpyridine-based metal coordination interaction. The self-assembly of M1 + M2 + Zn(OTf)2 was studied by various techniques, such as 1H NMR, 2D COSY NMR, 2D NOESY NMR, UV-Vis analysis, fluorescence analysis, viscosity measurement, and TEM. The experimental result indicated that the molecular weight of the SCP depended on the initial monomer concentration. The SCP could further turn into supramolecular polymer gel at high concentrations, and the reversible gel-sol transformation could be realized by heating/cooling. Moreover, the fluorescence quenching/enhancement of the SCP could be adjusted by adding base/acid.

Advanced Development of Molecularly Imprinted Membranes for Selective Separation

Molecularly imprinted membranes (MIMs), the incorporation of a given target molecule into a membrane, are generally used for separating and purifying the effective constituents of various natural products. They have been in use since 1990. The application of MIMs has been studied in many fields, including separation, medicine analysis, solid-phase extraction, and so on, and selective separation is still an active area of research. In MIM separation, two important membrane performances, flux and permselectivities, show a trade-off relationship. The enhancement not only of permselectivity, but also of flux poses a challenging task for membranologists. The present review first describes the recent development of MIMs, as well as various preparation methods, showing the features and applications of MIMs prepared with these different methods. Next, the review focuses on the relationship between flux and permselectivities, providing a detailed analysis of the selective transport mechanisms. According to the majority of the studies in the field, the paramount factors for resolving the trade-off relationship between the permselectivity and the flux in MIMs are the presence of effective high-density recognition sites and a high degree of matching between these sites and the imprinted cavity. Beyond the recognition sites, the membrane structure and pore-size distribution in the final imprinted membrane collectively determine the selective transport mechanism of MIM. Furthermore, it also pointed out that the important parameters of regeneration and antifouling performance have an essential role in MIMs for practical applications. This review subsequently highlights the emerging forms of MIM, including molecularly imprinted nanofiber membranes, new phase-inversion MIMs, and metal-organic-framework-material-based MIMs, as well as the construction of high-density recognition sites for further enhancing the permselectivity/flux. Finally, a discussion of the future of MIMs regarding breakthroughs in solving the flux-permselectivity trade-off is offered. It is believed that there will be greater advancements regarding selective separation using MIMs in the future.