Metal-ligated pillararene materials: From chemosensors to multidimensional self-assembled architectures

Supramolecular palladium complexes based on guanidinium pillar[5]arene for cancer therapy

The supramolecular palladium complex G-Pd, formed via self-assembly of the Pd-complex of guanidinium pillar[5]arene with Pd2+, was used to encapsulate doxorubicin to form G-Pd@DOX. The nanoparticles exhibit responsiveness to glutathione, controlled drug release, the ability to damage mitochondria, and potent anticancer activity while maintaining low toxicity towards normal cells. This work provides a good example for the application of pillararene-based palladium complexes in cancer therapy and is significant for the discovery of new medicines from supramolecular coordination complexes.

Optical detection strategies for Ni(II) ion using metal-organic chemosensors: from molecular design to environmental applications

Nickel is an important element utilized in various industrial/metallurgical processes, such as surgical and dental prostheses, Ni-Cd batteries, paint pigments, electroplating, ceramics, computer magnetic tapes, catalysis, and alloy manufacturing. However, its extensive use and associated waste production have led to increased nickel pollution in soils and water bodies, which adversely affects human health, animals and plants. This issue has prompted researchers to develop various optical probes, hereafter luminescent/colorimetric sensors, for the facile, sensitive and selective detection of nickel, particularly in biological and environmental contexts. In recent years, numerous functionalized chemosensors have been reported for imaging Ni2+, both in vivo and in vitro. In this context, metal-based receptors offer clear advantages over conventional organic sensors (viz., organic ligands, polymers, and membranes) in terms of cost, durability, stability, water solubility, recyclability, chemical flexibility and scope. This review highlights recent advancements in the design and fabrication of hybrid receptors (i.e., metal complexes and MOFs) for the specific detection of Ni2+ ions in complex environmental and biological mixtures.

Self-Assembled Nanohelixes Driven by Host-Guest Interactions and Metal Coordination

Helical nanostructures fabricated via the self-assembly of artificial motifs have been a captivating subject because of their structural aesthetics and multiple functionalities. Herein, we report the facile construction of a self-assembled nanohelix (NH) by leveraging an achiral aggregation-induced emission (AIE) luminogen (G) and pillar[5]arene (H), driven by host-guest interactions and metal coordination. Inspired by the "sergeants and soldiers" effect and "majority rule" principle, the host-guest complexation between G and H is employed to fixate the twisted conformation of G for the generation of "contortion sites", which further induced the emergence of helicity as the 1D assemblies are formed via Ag(I) coordination and hexagonally packed into nano-sized fibers. The strategy has proved feasible in both homogeneous and heterogeneous syntheses. Along with the formation of NH, boosted luminescence and enhanced productivity of reactive oxygen species (ROS) are afforded because of the efficient restriction on G, indicating the concurrent regulation of NH's morphology and photophysical properties by supramolecular assembly. In addition, NH also exhibits the capacity for bacteria imaging and photodynamic antibacterial activities against Staphylococcus aureus (S. aureus) and Escherichia coli (E. coli).

Pillararenes: a new frontier in antimicrobial therapy

Pillararenes have gained great interest among researchers in many fields due to their symmetric structure and facile functionalization. In this review, we summarize recent progress for pillararenes as antimicrobial agents, ranging from cationic pillararenes and peptide-modified pillararenes to sugar-functionalized pillararenes. Moreover, their structure-activity relationships are presented, and their mechanisms of action are discussed. As a state-of-the-art technology, their opportunities and outlook are also outlined in this emerging field. Overall, their potent inhibitory activity and high biocompatibility give them potential for the development of novel antimicrobial agents.

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.

Continuous symmetry and chirality measures: approximate algorithms for large molecular structures

Quantifying imperfect symmetry of molecules can help explore the sources, roles and extent of structural distortion. Based on the established methodology of continuous symmetry and chirality measures, we develop a set of three-dimensional molecular descriptors to estimate distortion of large structures. These three-dimensional geometrical descriptors quantify the gap between the desirable symmetry (or chirality) and the actual one. They are global parameters of the molecular geometry, intuitively defined, and have the ability to detect even minute structural changes of a given molecule across chemistry, including organic, inorganic, and biochemical systems. Application of these methods to large structures is challenging due to countless permutations that are involved in the symmetry operations and have to be accounted for. Our approach focuses on iteratively finding the approximate direction of the symmetry element in the three-dimensional space, and the relevant permutation. Major algorithmic improvements over previous versions are described, showing increased accuracy, reliability and structure preservation. The new algorithms are tested for three sets of molecular structures including pillar[5]arene complexes with Li+, C100 fullerenes, and large unit cells of metal organic frameworks. These developments complement our recent algorithms for calculating continuous symmetry and chirality measures for small molecules as well as protein homomers, and simplify the usage of the full set of measures for various research goals, in molecular modeling, QSAR and cheminformatics.

Fluorescent and chromogenic organic probes to detect group 10 metal ions: design strategies and sensing applications

Group 10 metals including Ni, Pd and Pt have been extensively applied in various essential aspects of human social life, material science, industrial manufactures, medicines and biology. The ionic forms of these metals are involved in several biologically important processes due to their strong binding capability towards different biomolecules. However, the mishandling or overuse of such metals has been linked to serious contamination of our ecological system, more specifically in soil and water bodies with acute consequences. Therefore, the detection of group 10 metal ions in biological as well as environmental samples is of huge significance from the human health point of view. Related to this, considerable efforts are underway to develop adequately efficient and facile methods to achieve their selective detection. Optical sensing of metal ions has gained increasing attention of researchers, particularly in the environmental and biological settings. Innovatively designed optical probes (fluorescent or colorimetric) are usually comprised of three basic components: an explicitly tailored receptor unit, a signalling unit and a clearly defined reporter unit. This review deals with the recent progress in the design and fabrication of fluorescent or colorimetric organic sensors for the detection of group 10 metal ions (Ni(II), Pd(II) and Pt(II)), with attention to the general aspects for design of such sensors.

Toward Pathogenic Biofilm Suppressors: Synthesis of Amino Derivatives of Pillar[5]arene and Supramolecular Assembly with DNA

New amino derivatives of pillar[5]arene were obtained in three stages with good yields. It was shown that pillar[5]arene containing thiaether and tertiary amino groups formed supramolecular complexes with low molecular weight model DNA. Pillar[5]arene formed complexes with a DNA nucleotide pair at a ratio of 1:2 (macrocycle/DNA base pairs), as demonstrated by UV-visible and fluorescence spectroscopy. The association constants of pillar[5]arene with DNA were lgKass1:1 = 2.38 and lgKass1:2 = 5.07, accordingly. By using dynamic light scattering and transmission electron microscopy, it was established that the interaction of pillar[5]arene containing thiaether and tertiary amino groups (concentration of 10-5 M) with a model nucleic acid led to the formation of stable nanosized macrocycle/DNA associates with an average particle size of 220 nm. It was shown that the obtained compounds did not exhibit a pronounced toxicity toward human adenocarcinoma cells (A549) and bovine lung epithelial cells (LECs). The hypothesis about a possible usage of the synthesized macrocycle for the aggregation of extracellular bacterial DNA in a biofilm matrix was confirmed by the example of St. Aureus. It was found that pillar[5]arene at a concentration of 10^-5 M was able to reduce the thickness of the St. Aureus biofilm by 15%.

Pillar[n]arene-calix[m]arene hybrid macrocyclic structures

To reserve planar chirality, enhance molecular recognition, and build advanced self-assemblies, hybrid macrocyclic hosts containing rigid pillar[n]arene and flexible calix[m]arene were designed, prepared and investigated for interesting applications. This review summarizes and discusses different synthetic strategies for constructing hybrid macrocyclic structures. Pillar[n]arene dimer with rigid aromatic double bridges provided the possibility of introducing calix[m]arene cavities, where the planar chirality was reserved in the structure of pillararene. The capacity for molecular recognition was enhanced by hybrid macrocyclic cavities. Interestingly, the obtained pillar[n]arene-calix[m]arene could self-assemble into "channels" and "honeycomb" in both the solid state and solution phase as well as donate the molecular architecture as the wheel for the formation of mechanically interlocked molecules, such as rotaxane. In addition, the pillar[n]arene and calix[m]arene could also be coupled together to produce pillar[n]arene embeded 1,3-alternate and cone conformational calix[m]arene derivatives, which could catalyze the oxidative polymerization of aniline in aqueous solutions. Except for building hybrid cyclophanes by covalent bonds, weak supramolecular interactions were used to prepare pillar[n]arene-calix[m]arene analogous composites with other pillar-like pillar[n]pyridiniums and calix-like calix[m]pyrroles, exhibiting reasonable performances in enhancing molecular recognition and trapping solvent molecules.

Cyclodextrin-pillar[n]arene hybridized macrocyclic systems

Cyclodextrin (CD) and pillar[n]arene are significant macrocyclic host molecules in supramolecular chemistry, and have either similar or contrasting physicochemical properties, for example, both can provide capable cavities available for recognizing various favorite guest molecules, while they usually possess different solubility in aqueous solutions, and exhibit diverse chiral characteristics. To balance their similarity and differences inherited from each chemical structure and incorporate both advantages, the CD-pillar[n]arene hybrid macrocyclic system was recently developed. In this review, we will focus on the preparation and application of CD-pillar[n]arene hybrid macrocyclic systems. Both noncovalent interactions and covalent bonds were employed in the synthesis strategies of building the hybrid macrocyclic system, which was in the form of host-guest inclusion, self-assembly, conjugated molecules, and polymeric structures. Furthermore, the CD-pillar[n]arene hybrid macrocyclic system has been primarily applied for the removal of organic pollutants from water, induced chirality, as well as photocatalysis due to the integration of both cavities from CD and pillar[n]arene as hybrid hosts and chiral characteristics inherited from their chemical structures.

Hybrid Macrocyclic Polymers: Self-Assembly Containing Cucurbit[m]uril-pillar[n]arene

Supramolecular self-assembly by hybrid macrocycles containing both cucurbit[m]uril (CB[m]) and pillar[n]arene was discussed and summarized in this review. Due to different solubility, diverse-sized cavities, and various driving forces in recognizing guests, the role of CB[m] and pillar[n]arene in such hybrid macrocyclic systems could switch between competitor in capturing specialized guests, and cooperator for building advanced hybridized macrocycles, by controlling their characteristics in host-guest inclusions. Furthermore, both CB[m] and pillar[n]arene were employed for fabricating advanced supramolecular self-assemblies such as mechanically interlocked molecules and supramolecular polymers. In those self-assemblies, CB[m] and pillar[n]arene played significant roles in, e.g., microreactor for catalyzing particular reactions to bridge different small pieces together, molecular "joint" to connect different monomers into larger assemblies, and "stabilizer" in accommodating the guest molecules to adopt a favorite structure geometry ready for assembling.

Fullerene-containing pillar[n]arene hybrid composites

The construction and application of fullerene-containing pillar[n]arene organic–inorganic hybrid composites/systems has been discussed and summarized.

Supramolecular systems prepared using terpyridine-containing pillararene

Recent progresses about the preparation of terpyridine-containing pillararene, as well as the utilization of those building blocks for making external stimulud-responsive supramolecular systems were summarized in this review.

Cross-Linked Supramolecular Polymer Networks Constructed by Pillar[5]arene-Based Host–Guest Recognition and Coordination/Oxidation of Catechol

In this work, two cross-linked supramolecular polymers are prepared by pillar[5]arene-based molecular recognition and coordination/oxidation of catechol. In addition, two supramolecular glues are obtained at high concentrations of the cross-linked...

Construction of a pillararene-based supramolecular polymer network and its application in efficient removal of dyes from water

An AB-type monomer based on a pillar[5]arene host and an imidazolium salt guest was successfully synthesized through a facile way. This monomer can self-assemble into linear supramolecular polymers in chloroform. After the addition of silver ions, the imidazolium salt group coordinated with silver ions to crosslink the linear supramolecular polymers at their ends, resulting in the formation of supramolecular polymer networks. Meanwhile, after further adding iodide ions, the supramolecular polymer network changed back to the linear supramolecular polymer. As a result, the topological structure of the system can be reversibly tuned. Furthermore, this supramolecular polymer network can be applied to remove organic dyes in water, suggesting its great potential in the treatment of waste water.

Catechol-Containing Schiff Bases on Thiacalixarene: Synthesis, Copper (II) Recognition, and Formation of Organic-Inorganic Copper-Based Materials

For the first time, a series of catechol-containing Schiff bases, tetrasubstituted at the lower rim thiacalix[4]arene derivatives in three stereoisomeric forms, cone, partial cone, and 1,3-alternate, were synthesized. The structure of the obtained compounds was proved by modern physical methods, such as NMR, IR spectroscopy, and HRMS. Selective recognition (K_b difference by three orders of magnitude) of copper (II) cation in the series of d-metal cations (Cu²⁺, Ni²⁺, Co²⁺, Zn²⁺) was shown by UV-vis spectroscopy. Copper (II) ions are coordinated at the nitrogen atom of the imine group and the nearest oxygen atom of the catechol fragment in the thiacalixarene derivatives. High thermal stable organic-inorganic copper-based materials were obtained on the base of 1,3-alternate + Cu (II) complexes.

Coordination array for accurate colorimetric sensing of multiple heavy metal ions

Heavy metals detection is of great significance to the environment and human health, and most of the detection methods require expensive instruments and laborious operation. Herein, we present a coordination array for accurate and rapid colorimetric heavy metal ions sensing. The array was composed of six chelates and has cross response to Hg²⁺, Cd²⁺, Pb²⁺ and Cu²⁺. The results could be observed by naked eyes or detected by plate reader combined with pattern analysis. Linear discrimination analysis was applied for the pattern analysis and the four heavy metal ions (Pb²⁺, Cd²⁺, Hg²⁺ and Cu²⁺) generated a clustering map at 1 μM. The coordination array demonstrates a great potential for sensing heavy metal ions simultaneously.

Pillararene-based self-assemblies for electrochemical biosensors

The ingenious design and synthesis of novel macrocycles bring out renewed vigor of supramolecular chemistry in the past decade. As an intriguing class of macrocycles, pillararene and pillararene-based functional materials that are constructed through the noncovalent bond self-assembly approach have been undergoing a rapid growth, benefiting from their unique structures and physiochemical properties. This review elaborates recent significant advances of electrochemical studies based on pillararene systems. Fundamental electrochemical behavior of pillar[n]arene[m]quinone and pillararene-based self-assemblies as well as their applications in electrochemical biosensors are highlighted. In addition, the advantages and functions of pillararene self-assembly systems resulted from the unique molecular architectures are analyzed. Finally, current challenges and future development tendency in this burgeoning field are discussed from the viewpoint of both fundamental research and applications. Overall, this review not only manifests the main development vein of pillararene-based electrochemical systems, but also conquers a solid foundation for their further bioelectrochemical applications.

Supramolecular Fluorescent Sensors: An Historical Overview and Update

Since as early as 1867, molecular sensors have been recognized as being intelligent "devices" capable of addressing a variety of issues related to our environment and health (e.g., the detection of toxic pollutants or disease-related biomarkers). In this review, we focus on fluorescence-based sensors that incorporate supramolecular chemistry to achieve a desired sensing outcome. The goal is to provide an illustrative overview, rather than a comprehensive listing of all that has been done in the field. We will thus summarize early work devoted to the development of supramolecular fluorescent sensors and provide an update on recent advances in the area (mostly from 2018 onward). A particular emphasis will be placed on design strategies that may be exploited for analyte sensing and corresponding molecular platforms. Supramolecular approaches considered include, inter alia, binding-based sensing (BBS) and indicator displacement assays (IDAs). Because it has traditionally received less treatment, many of the illustrative examples chosen will involve anion sensing. Finally, this review will also include our perspectives on the future directions of the field.

Crown ether-pillararene hybrid macrocyclic systems

A combination of Nobel macrocycle-crown ether and star macrocycle-pillararenes together in organic synthesis and material science is significant in obtaining hybrid systems, with rigid/flexible structural architecture, induced planar chirality, a negative cooperative effect and multiple fused cyclic hosts. In this review, we will discuss the synthesis/preparation of crown ether-pillararene hybrid macrocyclic systems by covalent bonds, supramolecular interactions and mechanical bonds, leading to hybrid compounds, supramolecular assemblies and mechanically interlocked molecules. The practical applications of crown ether-containing pillararenes will also be discussed in diverse areas, such as molecular recognition via fused multiple macrocycles and ion channels as well as external stimuli-responsive smart materials. We also call the attention of related researchers towards academic and technical issues about topological structures and applied functions in this fresh new fused macrocyclic field.

Unveiling the structural features of the host–guest complexes of carboxylated pillar[5]arene with viologen derivatives

Here we describe inclusion and self-assembly behavior of carboxylated pillar[5]arene with four viologen derivatives.

Pillararene-based conjugated porous polymers

The synthesis and application of promising polymeric materials–pillararene-based conjugated porous polymers–are discussed and summarized in this review.

Incorporation of carboxylated pillar[5]arene and strontium(ii) into supramolecular coordination complexes of different nuclearities

The nuclearity of the coordination complexes of carboxylated pillar[5]arene and strontium(ii) can be varied with the aid of phenanthroline as a coligand.