Pillar[5]arenes bearing phosphine oxide pendents as Hg2+ selective receptors

Self-Associated 1,8-Naphthalimide as a Selective Fluorescent Chemosensor for Detection of High pH in Aqueous Solutions and Their Hg2+ Contamination

A novel diamino triazine based 1,8-naphthalimide (NI-DAT) has been designed and synthesized. Its photophysical properties have been investigated in different solvents and its sensory capability evaluated. The fluorescence emission of NI-DAT is significantly impacted by the solvent polarity due to its inherent intramolecular charge transfer character. Moreover, the fluorescence emission quenched at higher pH as a result of photo-induced electron transfer (PET) from triazine moiety to 1,8-naphthalimide after cleaving hydrogen bonds in the self-associated dimers. Furthermore, the new chemosensor exhibited a good selectivity and sensitivity towards Hg²⁺ among all the used various cations and anions in the aqueous solution of ethanol (5:1, v/v, pH = 7.2, Tampon buffer). NI-DAT emission at 540 nm was quenched remarkably only by Hg²⁺, even in the presence of other cations or anions as interfering analytes. Job's plot revealed a 2:1 stoichiometric ratio for NI-DAT/Hg²⁺ complex, respectively.

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.

Green, Efficient Detection and Removal of Hg2+ by Water-Soluble Fluorescent Pillar[5]arene Supramolecular Self-Assembly

Developing a water-soluble supramolecular system for the detection and removal of Hg²⁺ is extremely needed but remains challenging. Herein, we reported the facile construction of a fluorescent supramolecular system (H⊃G) in 100% water through the self-assembly of carboxylatopillar[5]arene sodium salts (H) and diketopyrrolopyrrole-bridged bis(quaternary ammonium) guest (G) by host–guest interaction. With the addition of Hg²⁺, the fluorescence of H⊃G could be efficiently quenched. Since Hg²⁺ showed synergistic interactions (coordination and Hg²⁺- cavity interactions with G and H, respectively), crosslinked networks of H⊃G@Hg²⁺ were formed. A sensitive response to Hg²⁺ with excellent selectivity and a low limit of detection (LOD) of 7.17 × 10⁻⁷ M was obtained. Significantly, the quenching fluorescence of H⊃G@Hg²⁺ can be recovered after a simple treatment with Na₂S. The reusability of H⊃G for the detection of Hg²⁺ ions was retained for four cycles, indicating the H⊃G could be efficiently used in a reversible manner. In addition, the H⊃G could efficiently detect Hg²⁺ concentration in real samples (tap water and lake water). The developed supramolecular system in 100% water provides great potential in the treatment of Hg²⁺ detection and removal for environmental sustainability.

Highly efficient actinide(III)/lanthanide(III) separation by novel pillar[5]arene-based picolinamide ligands: A study on synthesis, solvent extraction and complexation

Selective extraction of highly radiotoxic actinides(III) is an important and challenging task in nuclear wastewater treatment. Many proposed ligands containing S or P atoms have drawbacks including high reagent consumption and possible secondary pollution after incineration. The present work reports five novel pillar[5]arene-based extractants that are anchored with picolinamide substituents of different electronic nature by varying spacer. These ligands reveal highly efficient separation of actinides(III) over lanthanides(III). Specifically, almost all of these ligands could extract Am(III) over Eu(III) selectively at around pH 3.0 (SF_Am/Eu>11) with fast extraction kinetics. Variation of the pyridine nitrogen basicity via changing para-substitution leads to an increase in the distribution ratios by a factor of over 300 times for Am(III) with an electron-withdrawing group compared to those with an electron donating group. Investigation of complexation mechanism by slope analysis, NMR, IR, EXAFS, and DFT techniques indicates that each ligand binds two metal ions by pyridine nitrogen and amide oxygen. Finally, these ligands do not show obvious decrease in both extraction and separation ability after being exposed to 250 kGy absorbed gamma radiation. These results demonstrate the potential application of pillar[5]arene-picolinamides for actinide(III) separation.

Radiation stability of phosphine oxide functionalized pillar[5]arenes

The radiation stability of three phosphine oxide functionalized pillar[5]arenes (POP5A) was studied by an electron accelerator with dose up to 5 MGy in air at room temperature. The structures of both irradiated and unirradiated pillar[5]arenes samples were comparatively characterized by Micro-FTIR, NMR, UV-vis, ESI-HRMS and HPLC techniques. The results revealed different degrees of radiation damage at different doses for POP5A, and the degradation products are mainly composed of organic species containing hydroxyl groups and carbonyl groups. The possible radiolytic degradation pathway was proposed. In addition, extraction of uranyl ion with irradiated POP5A samples was examined. The distribution ratio of uranyl ion was found to increase at low radiation dose and decrease until 3000 kGy. This is the first time that the irradiation stability of pillar[5]arenes derivative extractants has been studied in detail and it provides reliable data support for further application of pillar[5]arenes extractants in practical applications.

Insights into the synthesis of pillar[5]arene and its conversion into pillar[6]arene

The synthesis of pillar[5]arenes from p-dialkoxybenzene and formaldehyde in the presence of iron(iii) chloride and tetramethylammonium chloride under mild reaction conditions was investigated in detail.

Pillararenes as macrocyclic hosts: a rising star in metal ion separation

Pillararenes are macrocyclic oligomers of alkoxybenzene akin to calixarenes but tethered at the 2,5-positions via methylene bridges. Benefiting from their unique pillar-shaped architecture favorable for diverse functionalization and versatile host-guest properties, pillararenes decorated with chelating groups worked excellently as supporting platforms to construct extractants or adsorbents for metal ion separation. This feature article provides a detailed summary of pillararenes in Ln/An separation by liquid-liquid extraction and heavy metal separation by solid-liquid extraction. The preorganization effect of the rigid pillararene framework has a profound impact on the extraction of metal ions, and a unique extraction mechanism is observed when employing ionic liquids as solvents. The rich host-guest chemistry of pillararenes enables construction of a wide variety of supramolecular materials as metal ion adsorbents. We also discuss the differences between pillararenes and several well-known macrocycles, with a focus on the metal-ligand coordination and its influencing factors. We hope this review will provide useful information and unleash new opportunities in this field.

Monosubstituted pillar[5]arene functionalized with (amino)phosphonate fragments are “smart” building blocks for constructing nanosized structures with some s- and p-metal cations in the organic phase

Pillar[5]arenes with phosphonate- and 1-aminophosphonate-substituents form complexes with Na⁺, K⁺, Cs⁺ and Pb²⁺ with a 1 : 1 stoichiometry and lg K_a values between 2.0 and 4.8, and that Pb²⁺ is the most effectively bound cation.

The synthesis of water-soluble phosphate pillar[5]arenes functionalized graphene as a fluorescent probe for sensitive detection of paraquat

We describe a selective and sensitive fluorescence platform for the detection of paraquat (PQ) based on competitive host-guest recognition between phosphate pillar[5]arenes (PWP5) and probe (Safranine T, ST) with using PWP5 functionalized reduced graphene (PWP5-rGO) as the receptor. PQ is a positive charge molecule that is captured by PWP5 via electrostatic interactions. The host-guest interaction between PWP5 and PQ is studied by ¹H NMR. Therefore, a selective and sensitive fluorescence sensing of detection PQ is developed. It has a linear response ranges of 0.01-2.0 and 2.0-50.0 μM and a low detection limit of 0.0035 μM (S/N = 3) for PQ. The sensing platform is also used to test PQ in two water samples with satisfying results. It suggests that this approach has potential applications for the determination of PQ.

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.

Pillararene-based fluorescent chemosensors: recent advances and perspectives

This feature article summarizes recent research in the pillararene-based fluorescent chemosensor field in terms of ion sensing, small molecule recognition, biomolecule detection, fluorescent supramolecular aggregates, and biomedical imaging.

Pillar-Shaped Macrocyclic Hosts Pillar[n]arenes: New Key Players for Supramolecular Chemistry

In 2008, we reported a new class of pillar-shaped macrocyclic hosts, known as "pillar[n]arenes". Today, pillar[n]arenes are recognized as key players in supramolecular chemistry because of their facile synthesis, unique pillar shape, versatile functionality, interesting host-guest properties, and original supramolecular assembly characteristics, which have resulted in numerous electrochemical and biomedical material applications. In this Review, we have provided historical background to macrocyclic chemistry, followed by a detailed discussion of the fundamental properties of pillar[n]arenes, including their synthesis, structure, and host-guest properties. Furthermore, we have discussed the applications of pillar[n]arenes to materials science, as well as their applications in supramolecular chemistry, in terms of their fundamental properties. Finally, we have described the future perspectives of pillar[n]arene chemistry. We hope that this Review will provide a useful reference for researchers working in the field and inspire discoveries concerning pillar[n]arene chemistry.

Highly efficient extraction of actinides with pillar[5]arene-derived diglycolamides in ionic liquids via a unique mechanism involving competitive host–guest interactions

A novel extraction mechanism is described.

A non-symmetric pillar[5]arene based on triazole-linked 8-oxyquinolines as a sequential sensor for thorium(iv) followed by fluoride ions

A novel non-symmetric pillar[5]arene bearing triazole-linked 8-oxyquinolines at one rim was synthesized and demonstrated as a sequential fluorescence sensor for thorium(iv) followed by fluoride ions with high sensitivity and selectivity.

Role of polar solvents for the synthesis of pillar[6]arenes

An efficient procedure for the synthesis of pillar[6]arenes has been developed.

Ditopic CMPO-pillar[5]arenes as unique receptors for efficient separation of americium(iii) and europium(iii)

A unique host–guest recognition process involving a new class of homoditopic CMPO-pillar[5]arenes and lanthanides was revealed to proceed in a stepwise manner, and correlated to the efficient and selective separation of americium(iii) from europium(iii) under acidic feed conditions.