Pillar[5]arene-based supramolecular pseudorotaxane polymer material for ultra-sensitive detection of Fe3+ and F. RSC Adv 2023;13:12270-12275. [PMID: 37091614 PMCID: PMC10113919 DOI: 10.1039/d3ra00997a] [Citation(s) in RCA: 0] [Impact Index Per Article: 0]

Recent advancements in ultra-sensitive detection, particularly the Aggregation Induced Emission (AIE) materials, have demonstrated a promising detection method due to their low cost, real-time detection, and simplicity of operation. Here, coumarin functionalized pillar[5]arene (P5C) and bis-bromohexyl pillar[5]arene (DP5) were successfully combined to create a linear AIE supramolecular pseudorotaxane polymer (PCDP-G). The use of PCDP-G as a supramolecular AIE polymer material for recyclable ultra-sensitive Fe³⁺ and F^- detection is an interesting application of the materials. According to measurements, the low detection limits of PCDP-G for Fe³⁺ and F^- are 4.16 × 10^-10 M and 6.8 × 10^-10 M, respectively. The PCDP-G is also a very effective logic gate and a material for luminous displays.

The Detection of Food Additives Using a Fluorescence Indicator Based on 6– p–Toluidinylnaphthalence-2-sulfonate and Cationic Pillar[6]arene

The current study investigated host-guest complexation in 6-p-toluidinylnaphthalene-2-sulfonate (TNS), a fluorescence probe used to investigate hydrophobic regions that contain the water-soluble cationic pillar[6]arene (CP6). After complexation with CP6, the fluorescence intensity of TNS was significantly increased. The decreases in the fluorescence intensity of the TNS•CP6 complex when phenolic food-additives are added have been used in indicator displacement assays to detect food additives in the water.

Noncovalently bound and mechanically interlocked systems using pillar[n]arenes

Pillar[n]arenes are pillar-shaped macrocyclic compounds owing to the methylene bridges linking the para-positions of the units. Owing to their unique pillar-shaped structures, these compounds exhibit various excellent properties compared with other cyclic host molecules, such as versatile functionality using various organic synthesis techniques, substituent-dependent solubility, cavity-size-dependent host-guest properties in organic media, and unit rotation along with planar chiral inversion. These advantages have enabled the high-yield synthesis and rational design of pillar[n]arene-based mechanically interlocked molecules (MIMs). In particular, new types of pillar[n]arene-based MIMs that can dynamically convert between interlocked and unlocked states through unit rotation have been produced. The highly symmetrical pillar-shaped structures of pillar[n]arenes result in simple NMR spectra, which are useful for studying the motion of pillar[n]arene wheels in MIMs and creating sophisticated MIMs with higher-order structures. The creation and application of polymeric MIMs based on pillar[n]arenes is also discussed.

Carboxylato-Pillar[6]arene-Based Fluorescent Indicator Displacement Assays for Caffeine Sensing

In the present work, we have developed a new indicator displacement system based on pillararene for anionic water-soluble carboxylato pillar [6] arene (WP6) and aromatic fluorescent dye safranine T (ST). A large fluorescence enhancement and colour change of ST were observed after complexation with electron-rich cavity in WP6 because of host-guest twisted intramolecular charge-transfer interactions. The constructed pillararene-indicator displacement system can be applied for caffeine selective detection in water.

Pillar[6]arene-based supramolecular polymeric materials constructed via electrostatic interactions for rapid and efficient organic dye removal from water

The first pillar[6]arene-based supramolecular polymeric material constructed from electrostatic interactions was designed and prepared successfully. Importantly, it can adsorb and remove organic dye from water efficiently.

Pillar[5]arene-based ion-pair recognition for constructing a [2]pseudorotaxane with supramolecular interaction induced LCST behavior

Here, we report a novel [2]pseudorotaxane based on perbromoethylated pillar[5]arene/imidazolium iodide ionic liquid ion-pair recognition and this pseudorotaxane shows supramolecular interaction induced LCST behavior in solution.

A pillar[5]arene-based 3D polymer network for efficient iodine capture in aqueous solution

A pillar[5]arene-based 3D polymer network is constructed. It possesses good stability, recyclability and high efficiency in iodine capture in aqueous solution.

Pillar[n]arene-Based Supramolecular Switches in Solution and on Surfaces

The design and synthesis of new synthetic macrocycles has driven the rapid development of supramolecular chemistry and materials. Pillar[n]arenes, as a new type of macrocyclic compounds, are used as a promising type of building blocks for switchable supramolecular systems due to their versatile functionalization and the ability of binding toward various guest molecules. A number of guests can form inclusion complexes with pillar[n]arenes and their derivatives in solution, which are sensitive to different external triggers. Interestingly, the pursuit of complex stimuli-responsive functional materials and devices has largely motivated the shift of pillar[n]arene-based switches from solution media to surfaces for controllable macroscopic motions on solid platforms. Facilitated by the facile modification of pillar[n]arenes on various solid supports and the dynamic binding of host-guest complexes, numerous functional hybrid materials with adjustable physical or chemical properties and integrated functionalities have been reported in the last decade. Here, the advance of supramolecular switches in solution and on surfaces based on pillar[n]arenes and derivatives with an emphasis on the efforts and the latest contributions from the field is discussed.

Functional supramolecular gels based on pillar[n]arene macrocycles

Supramolecular gels constructed from low-molecular-weight gelators via noncovalent interactions have received increasing attention. The rapid development of stimuli-responsive supramolecular gels with attractive properties is highly desirable to meet the ever-growing demand of materials science and chemistry. The inherent reversible and dynamic nature of noncovalent interactions in supramolecular gels endows the materials with sensing, processing, and actuating functions in response to specific environmental changes and offers them great potential in flexible biomaterials and intelligent devices. In particular, pillar[n]arenes with symmetrical pillar-shaped architectures have been recognized as an emerging class of synthetic macrocycles after crown ethers, cyclodextrins, calixarenes, and cucurbiturils, and proven to be excellent candidates for the fabrication of functional supramolecular gels due to their many advantages including facile synthesis, diverse functionalization, and appealing host-guest properties. This review provides a comprehensive overview of recent progress in supramolecular gels involving pillar[n]arenes and their derivatives as synthetic macrocyclic arenes, from the viewpoints of the synthetic approach, controllable assembly, stimuli-responsiveness, and functions. Perspectives of this burgeoning field of research are also given at the end.

Synthesis and characterisation of rylene diimide dimers using molecular handcuffs

Mechanically interlocked handcuffs provide a strategy to study rylene diimide dimers and to investigate their electronic and magnetic properties.

A strategy for positioning, and loosely connecting, molecules in close proximity using mechanically interlocked handcuffs is described. The strategy is demonstrated using rylene diimides, creating dimeric structures in which two components are linked through pillar[5]arene/imidazolium rotaxanes. Investigation of the resulting molecules demonstrates intriguing and new properties that arise from placing these redox active dye molecules together, allowing interactions, whilst allowing the molecules to separate as required. In particular we observe excimer emission from a perylene diimide dimer handcuff and the formation of an unusual radical anion π-dimer upon double reduction of the same molecule. The latter exhibits a unique visible absorption profile for a PDI-based molecule. We demonstrate the flexibility of our approach by making an unprecedented mixed perylene diimide/naphthalene diimide dimer which also reveals interactions between the two components. Our synthetic strategy facilitates the creation of unusual dimeric structures and allows the investigation of intermolecular interactions and the effects they have on electronic and magnetic properties.

Enantioselective Dynamic Self-Assembly of Histidine Droplets on Pillar[5]arene-Modified Interfaces

The self-assembly of macroscopic droplets on interfaces has attracted much attention and shown promising potential in the field of materials as a sensing or delivery system. Herein, we reported a new strategy to construct a d-tartaric acid-functionalized pillar[5]arene (d-TP5) interface for macroscopic differentiation of histidine enantiomers. At the molecular level, it has been proved that d-TP5 has the ability to distinguish between l-Histidine and d-Histidine ( K_L/ K_D = 4.6). Furthermore, a functional d-TP5 surface was constructed by a click reaction and characterized by contact angle measurements and attenuated total reflection-Fourier-transform infrared spectroscopy and X-ray photoelectron spectroscopy analyses. The d-TP5 surface exhibited the selective dynamic adhesion of l-His droplets on the tilted interface. It means that a d-TP5 surface can distinguish histidine enantiomers at a macrolevel. The amount of d/l-His absorbed by a d-TP5 surface and the morphology of His particles formed by removing the solvent have been investigated to prove that the self-assembly of His occurs on the d-TP5 surface. The possible mechanism has been discussed from host-guest interaction and chiral recognition. The proposed chiral material displays rapidly remarkable selectivity and is convenient to be utilized, which should be suitable for comprehending chiral recognition processing and applied to chiral recognition detection of histidine in a living body.

Construction of a [2]pseudorotaxane and a [3]pseudorotaxane based on perbromoethylated pillar[5]arene/pyridinium iodide ion-pair recognition

Herein we report the preparation of a [2]pseudorotaxane and a [3]pseudorotaxane based on perbromoethylated pillar[5]arene/pyridinium iodide ion-pair recognition.

LCST behavior controlled by size-matching selectivity from low molecular weight monomer systems

LCST behavior was controlled by crown ether–cation recognition motifs via size-matching selectivity.

A [2]pseudorotaxane based on a pillar[6]arene and its application in the construction of a metallosupramolecular polymer

A novel metallosupramolecular polypseudorotaxane was constructed by pillar[6]arene-based host–guest recognition and metal coordination.

Restricting shuttling in bis(imidazolium)…pillar[5]arene rotaxanes using metal coordination

Metal coordination to a series of bis (imidazolium)…pillar[5]arene [2]rotaxanes through the formation of metal-carbene bonds facilitates a new strategy to restrict the shuttling motion in [2]rotaxanes. Whereas the pillar[5]arene macrocycle rapidly shuttles along the full length of the bis (imidazolium) rod for the parent [2]rotaxane, Ag(i) coordination to the imidazolium groups through the formation of N-heterocyclic carbenes leads to restricted motion, effectively confining the shuttling motion of the [2]rotaxane. The Ag(i) coordinated [2]rotaxanes can be reacted further, either removing the Ag-carbene species to recreate the parent [2]rotaxane, or reaction with more bulky Pd(ii) species to further restrict the shuttling motion through steric inhibition.

Synthesis of a water-soluble 2,2'-biphen[4]arene and its efficient complexation and sensitive fluorescence enhancement towards palmatine and berberine

A water-soluble 2,2′-biphen[4]arene (2,2’-CBP4) containing eight carboxylato moieties was synthesized and characterized. Its complexation behavior towards two alkaloids, palmatine (P) and berberine (B), was investigated by means of fluorescence and ¹H NMR spectroscopy in aqueous phosphate buffer solution (pH 7.4). In the presence of 2,2’-CBP4, ¹H NMR signals of P and B displayed very large upfield shifts, indicating the formation of inclusion complexes with strong binding affinities. Fluorescence titration experiments showed that P and B exhibited dramatic fluorescence enhancement of more than 600 times upon complexation with 2,2’-CBP4. Particularly, the fluorescence intensity is strong enough to be readily distinguished by the naked eye. Although the two guests have similar structures, the association constant of B with 2,2’-CBP4 (K_a = (2.29 ± 0.27) × 10⁶ M⁻¹) is 3.9 times larger than that of P (K_a = (5.87 ± 0.24) × 10⁵ M⁻¹).

Hybrid Molecular Container Based on Glycoluril and Triptycene: Synthesis, Binding Properties, and Triggered Release

We designed and synthesized a "hybrid" molecular container 1, which is structurally related to both cucurbit[n]uril (CB[n]) and pillar[n]arene type receptors. Receptor 1 was fully characterized by ¹ H NMR, ¹³ C NMR, IR, MS and X-ray single crystal diffraction. The self-association behavior, host-guest recognition properties of 1, and the [salt] dependence of K_a were investigated in detail by ¹ H NMR and isothermal titration calorimetry (ITC). Optical transmittance and TEM measurements provide strong evidence that receptor 1 undergoes co-assemble with amphiphilic guest C10 in water to form supramolecular bilayer vesicles (diameter 25.6±2.7 nm, wall thickness ≈3.5 nm) that can encapsulate the hydrophilic anticancer drug doxorubicin (DOX) and the hydrophobic dye Nile red (NR). The release of encapsulated DOX or NR from the vesicles can be triggered by hexamethonium (8 c) or spermine (10) which leads to the disruption of the supramolecular vesicles.

Stimuli-Responsive Supramolecular Assemblies Constructed from Pillar[ n]arenes

Supramolecular assemblies are constructed from at least two molecules through various noncovalent bonding modes such as hydrogen bonding, cationic-anionic electrostatic interactions, aromatic interactions, metal-ligand bonding, hydrophobic-hydrophilic interactions, and charge-transfer interactions. Owing to the dynamic and reversible nature of these noncovalent bonds, the assembly and disassembly of these molecules are dynamic and reversible. Molecules self-assemble to form the most conformationally and thermally stable structures through these noncovalent interactions. The formation of these noncovalent interactions is affected by the properties of the environment such as its polarity, temperature, and pressure; thus, the structure of the assembled compounds is determined by the environment. The sizes and shapes of the supramolecular assemblies play an important role in determining their functions. Therefore, controlling their size and shape is important. Introducing stimuli-responsive groups into supramolecular assemblies is a useful way to control their size and shape. Controlling supramolecular structures and motions with external stimuli, i.e., periodic and rotational motions on the molecular scale, structures, and molecular weights at the nano- and micrometer scales, visible shrinking/expansion, and adhesive behavior at a macroscopic scale, is very useful. Macrocyclic host molecules are useful building blocks for the construction of stimuli-responsive supramolecular assemblies because their host ability can be tuned by changing the shape and electron density of the cavity. The size-dependent hosting ability of the cavity is similar to the lock-and-key model in biological systems. Stimuli-responsive supramolecular assemblies have been developed by using macrocyclic compounds such as cyclodextrins, cucurbit[ n]urils, calix[ n]arenes, crown ethers, and related macrocycles. We successfully developed new pillar-shaped macrocyclic hosts in 2008, which were coined pillar[ n]arenes. The unique structural features of pillar[ n]arenes allowed new properties. This year, 2018, marks one decade of research into pillar[ n]arene chemistry, and in that time the properties of pillar[ n]arenes have been widely investigated by various scientists. Thanks to their efforts, the characteristic properties of pillar[ n]arenes that result from their pillar-shaped structures have been elucidated. Their host ability, the chirality of their pillar-shaped structure, and their versatile functionality are unique features of pillar[ n]arenes not seen in other well-known hosts, and these properties are very useful for the creation of new stimuli-responsive supramolecular assemblies. In this Account, we describe photo-, pH- and redox-responsive supramolecular assemblies based on pillar[ n]arenes. First, we discuss molecular-scale stimuli-responsive supramolecular assemblies, i.e., pseudorotaxanes, pseudocatenanes, and supramolecular polymers. We also highlight subnanometer- and micrometer-scale stimuli-responsive supramolecular assembles such as particles and vesicles. Finally, we discuss the macroscopic stimuli-responsive structural changes of surfaces and gels. This Account will provide useful information for researchers working on not only pillar[ n]arene chemistry but also the chemistry of other macrocyclic hosts, and it will inspire new discoveries in the field of supramolecular assemblies and systems containing macrocyclic hosts.

A novel pillar[5]arene-based supramolecular organic framework gel to achieve an ultrasensitive response by introducing the competition of cationπ and ππ interactions

Ultrasensitive response properties are an intriguing concern for stimuli-responsive materials. Herein, we report a novel method to achieve an ultrasensitive response by introducing the competition of cationπ and ππ interactions into a pillar[5]arene-based supramolecular organic framework (SOF-AMP). SOF-AMP was constructed with a novel bis-naphthalimide functionalized pillar[5]arene, which was able to form a stable supramolecular gel (SOF-AMP-G) in cyclohexanol. Interestingly, SOF-AMP-G shows an ultrasensitive response to Fe3+ through the competition of cationπ and ππ interactions. Meanwhile, the Fe3+ coordinated SOF (MSOF-Fe) shows an ultrasensitive response to H2PO4-. SOF-AMP-G displayed yellow fluorescence whereas, after the addition of 0.5 equiv. of Fe3+ to SOF-AMP-G, the yellow fluorescence was quenched. The detection limit of SOF-AMP-G for Fe3+ is 7.54 × 10-9 M. More interestingly, the Fe3+ coordinated SOF gel (MSOF-Fe-G) could sense H2PO4- with a fluorescence "turn-on". The detection limit of MSOF-Fe-G for H2PO4- is 4.21 × 10-9 M. Simultaneously, the Fe3+ and H2PO4- responsive thin films based on these SOF gels were prepared. Moreover, these SOF gels could be used as ultrasensitive ion sensors, fluorescent display materials and sensitive logic gates.

Photo/pH-controlled host-guest interaction between an azobenzene-containing block copolymer and water-soluble pillar[6]arene as a strategy to construct the "compound vesicles" for controlled drug delivery

Herein, dual stimuli-responsive compound vesicles were constructed based on host-guest interaction between a water-soluble pillar[6]arene (WP6) and an amphiphilic azobenzene-containing block copolymers (BCP). Reversible morphological transformation between compound vesicles and solid aggregates was achieved by repeated pH- and photo-stimuli. These compound vesicles were then applied in the controlled release of water-soluble anticancer drug, doxorubicin hydrochloride (DOX · HCl). Upon external stimuli, the DOX · HCl displayed a faster release rate than that without stimuli. Moreover, the compound vesicles showed an excellent cytocompatibility toward the human breast cancer cells (Michigan Cancer Foundation-7, MCF-7), and the drug-loaded compound vesicles exhibited lower cytotoxicity than free drug. The drug-loaded compound vesicles could be taken up by MCF-7 cells and can release the DOX · HCl in cancer cells due to the acid environment, which was important for applications in the therapy of cancers as a controlled-release drug carrier.

Biological and related applications of pillar[n]arenes

Pillar[n]arenes are a new class of synthetic supramolecular macrocycles streamlined by their particular pillar-shaped architecture which consists of an electron-rich cavity and two fine-tuneable rims. The ease and diversity of the functionalization of the two rims open possibilities for the design of new architectures, topological isomers, and scaffolds. Significantly, this emerging class of macrocyclic receptors offers a unique platform for biological purposes. This review article covers the most recent contributions from the pillar[n]arene field in terms of artificial membrane transport systems, controlled drug delivery systems, biomedical imaging, biosensors, cell adhesion, fluorescent sensing, and pesticide detection based on host-guest interactions. The review also uniquely describes the properties of sub-units that make pillar[n]arenes suitable for biological applications and it provides a detailed outline for the design of new innovative pillar-like structures with specific properties to open up a new avenue for pillar[n]arene chemistry.

Laterally functionalized pillar[5]arene: a new building block for covalent self-assembly

Laterally functionalized pillar[5]arenes were synthesized for the first time by bromination at the methylene bridge of dimethoxypillar[5]arene. The synthesized molecule was then used as a novel building block by being covalently self-assembled into polymer nanocapsules and 2D polymer films.

Recent advances in pillar[n]arenes: synthesis and applications based on host-guest interactions

Pillar[n]arenes (n = 5-15) are a novel class of macrocyclic molecules with hydroquinone as the repeating unit linked by methylene bridges at para-positions. Introduced by T. Ogoshi for the first time in 2008, pillararenes have attracted increasing interest and have been widely studied during the last eight years, due to their unique structural advantages as host molecules, such as symmetrical rigid architecture, electron-rich cavities and facile functional modification. In this review, we first describe the syntheses of pillar[n]arenes including cyclooligomerization of pillar[n]arenes and modification of pillar[n]arenes after cyclooligomerization, summarising almost twenty different kinds of guest motifs and dividing them into three types: cationic, neutral and anionic motifs. The main section of this review examines the applications of pillar[n]arenes based on the host-guest interactions in different research fields, including biology, materials science and environmental science. Finally, future research directions and potential for novel applications are discussed.

Construction of [2]rotaxane-based supramolecular polymers driven by wheel-stopper π⋯π interactions

A new strategy for supramolecular polymerization is designed and presented, which is based on the wheel-stopper charge-transfer interactions of [2]rotaxanes.

Supramolecular control over pillararene-based LCST phase behaviour

Based on the supramolecular interactions between pillar[5]arenes and ionic liquids, supramolecular control was successfully introduced into thermo-responsive systems to adjust LCST phase behaviour in water.

Self-locked dipillar[5]arene-based pseudo[1]rotaxanes and bispseudo[1]rotaxanes with different lengths of bridging chains

The relationships between lengths of bridging chains and self-locked behaviors of dipillar[5]arene-based pseudo[1]rotaxanes and bispseudo[1]rotaxanes were studied in detail.

Three-dimensional supramolecular polymerization based on pillar[n]arenes (n = 5, 6) and halogen bonding interactions

Three dimensional supramolecular polymerization networks based on pillar[5,6]arenes were constructed both in solution and in the solid state.

An AIEE fluorescent supramolecular cross-linked polymer network based on pillar[5]arene host–guest recognition: construction and application in explosive detection

A novel fluorescent supramolecular cross-linked polymer network with aggregation induced enhanced emission properties was constructed and further used for explosive detection.

Supramolecular motifs for the self-assembly of monosubstituted pillar[5]arenes with an amide fragment: from nanoparticles to supramolecular polymers

The effects of solvents on the aggregation properties of novel monosubstituted pillar[5]arenes containing an N-alkylamide fragment have been investigated.

A bis-naphthalimide functionalized pillar[5]arene-based supramolecular π-gel acts as a multi-stimuli-responsive material

A novel approach for the design of multi-stimuli-responsive supramolecular functional materials was successfully developed by introducing the competition of π–π stacking and cation–π interactions into a pillar[5]arene-based supramolecular π-gel (MP5-G).

Supramolecular chemotherapeutic drug constructed from pillararene-based supramolecular amphiphile

A therapeutic supramolecular amphiphile, P5⊃CPT-ss-Py, with GSH-responsiveness was constructed using pillar[5]arene-based host–guest molecular recognition. Cellular internalization and anticancer efficacy were greatly increased through this supramolecular strategy.

A thermoresponsive supramolecular polymer gel from a heteroditopic calix[4]pyrrole

Anion recognition was utilized on heteroditopic calix[4]pyrrole host–guest systems to obtain a thermoresponsive supramolecular polymer gel.

Pillar[5]arene-Based Supramolecular Organic Framework with Multi-Guest Detection and Recyclable Separation Properties

The selective detection and separation of target ions or molecules is an intriguing issue. Herein, a novel supramolecular organic framework (SOF-THBP) was constructed by bis-thioacetylhydrazine functionalized pillar[5]arenes. The SOF-THBP shows a fluorescent response for Fe³⁺ , Cr³⁺ , Hg²⁺ and Cu²⁺ ions. The xerogel of SOF-THBP shows excellent recyclable separation properties for these metal ions and the absorption rates were up to 99.29 %. More interestingly, by rationally introducing these metal ions into the SOF-THBP, a series of metal-ion-coordinated SOFs (MSOFs) such as MSOF-Fe, MSOF-Hg and MSOF-Cu were constructed. These metal ions coordinated MSOFs could selectively sense F^- , Br^- , and l-Cys, respectively. The detection limits of these MSOFs for F^- , Br^- and l-Cys were about 10^-8  m.