Arene Units Research Articles

Discrete Macrocyclic Polymer Hosts-Induced Cascade Luminescence Enhancement and Application in Bioimaging.

The integration of polymers, supramolecular macrocycles and aggregation-induced emission (AIE) molecules provides numerous possibilities for constructing various functional supramolecular systems. Herein, we constructed supramolecular assembled systems based on discrete macrocyclic polymer hosts via the cooperation of hydra-headed macrocycles containing two or three pillar[5]arene units (defined as P2, P3), the block polymer F127 and AIE molecules (alkyl-cyano modified tetraphenylethene, alkyl-triazole-cyano modified 9,10-distyrylanthracene, defined as TPE-(CN)4 and DSA-(TACN)2). Compared with the binary assembly between hydra-headed hosts or F127 and AIE molecules, cascaded supramolecular assembly-induced emission enhancement (SAIEE) in aqueous solution was achieved in discrete macrocyclic polymer-based supramolecular assembled systems. Considering the cascaded SAIEE performance, we have successfully applied discrete macrocyclic polymer-based supramolecular assembled systems to bioimaging and constructed an artificial light-harvesting system (LHs) to explore more potential applications. The supramolecular assembly form of discrete macrocyclic polymers hosts and AIE molecules proposed in this work provides new inspiration for the construction and application of high-performance supramolecular luminescent systems.

Potential MRSA inhibitory activity of some new benzofuran-pyrazolo[1,5-a]pyrimidine hybrids attached to arene units via methylene or azo linkage

MRSA, a resistant bacteria causing severe infections, is targeted by researchers developing new anti-resistance compounds. The study aimed to investigate the MRSA inhibitory activity of two series of benzofuran-pyrazolo[1,5-a]pyrimidines 1 and 2, attached to arene units via methylene or azo linkage, respectively. The desired products were prepared, in 82–92% yields, by reacting benzofuran-based enaminone 4 with the appropriate 1H-pyrazole-3,5-diamines 5 in pyridine at reflux for 5–6 h. The new hybrids showed a wide spectrum of antibacterial activity against different ATCC strains. Products with azo linkage and para-substituted arene units with electron-releasing groups demonstrated higher antibacterial activity. 3-((4-Methoxyphenyl)diazenyl)-linked pyrazolo[1,5-a]pyrimidine 2e demonstrates activity that exceeded the reference ciprofloxacin with MIC/MBC values of 1.8/3.6 µM against S. aureus and E. coli strains. Also, it demonstrated more effective MRSA inhibitory activity than the reference linezolid, with MIC/MBC values of 3.6/14.4 and 1.8/7.2 µM against MRSA ATCC:33591 and ATCC:43300 strains, respectively.

A Pillar[5]arene-Containing Metal-Organic Framework for Rapid and Highly Capable Adsorption of a Mustard Gas Simulant.

Mustard gas causes irreversible damage upon inhalation or contact with the human body. Consequently, the development of adsorbents for effective interception of mustard gas at low concentrations and high flow rates is an urgent necessity. Here we report a stable porous pillar[5]arene-containing metal-organic framework (MOF) based on zirconium (EtP5-Zr-scu), demonstrating that embedding pillar[5]arene units in MOFs can provide specific binding sites for efficient adsorption of a mustard gas simulant, 2-chloroethyl ethyl sulfide (CEES). EtP5-Zr-scu achieves a higher capacity and more rapid adsorption compared to its counterpart without embedded pillar[5]arene units (H4tcpt-Zr-scu) and perethylated pillar[5]arene (EtP5) alone. Single crystal X-ray diffraction and solid-state nuclear magnetic resonance reveal that the enhanced performance of EtP5-Zr-scu is derived from the host-guest complexation between CEES and pillar[5]arene moieties. Moreover, breakthrough experiments confirmed that the interception performance of EtP5-Zr-scu against CEES (800 ppm, 120 mL/min) was significantly improved (566 min/g) compared with H4tcpt-Zr-scu (353 min/g) and EtP5 (0.873 min/g), attributed to the integration of open channels with specific recognition sites. This work marks a significant advancement in the development of macrocycle-incorporated crystalline framework materials with recognition sites for the efficient capture of guest molecules.

A highly selective and sensitive oligomers-based fluorescent sensor for Cu2+ detection in aqueous solution incorporating pillar[5]arene and imidazo[4,5-f][1,10]phenanthroline moieties

A conjugated oligomers (Co-P[5]ImPhen) containing pillar[5]arene (P[5]) unit as fluorophore and 1H imidazo[4,5-f][1,10]phenanthroline (ImPhen) unit as recognition group was designed and synthesized by Suzuki coupling. The Co-P[5]ImPhen has good fluorescent performance in DMSO aqueous solutions. The Co-P[5]ImPhen has an excellent selectivity and sensitivity for Cu2+ detection in DMSO/H2O (1:3, v:v) solution while showing fluorescence quenching response to Cu2+ (1 − I/I0= 94.2%) and excellent anti-interference ability against paraquat analogs and metal ions. Additionally, the Stern-Volmer quenching constant (Ksv) was calculated to be 2.544 × 106 M-1 by fluorescence titration, indicating that the oligomer has strong binding capacity to Cu2+. The detection limit for Cu2+ was remarkably low (1.17 × 10-10 M). The binding mechanism of Co-P[5]ImPhen with Cu2+ was verified utilizing 1H NMR spectra and quantum chemical calculations. The study indicated that the Co-P[5]ImPhen interacts with Cu2+ primarily through two nitrogen atoms on phenanthroline. Furthermore, the oligomers Co-P[5]ImPhen showed potential application in the detection of Cu2+ in practical samples.

Host–guest complexation‐induced chirality switching of pillararenes by perylene diimide‐based hexagonal metallacages

AbstractChirality in confined nanospaces has brought some new insights into chirality transfer, amplification, and chiroptical properties. However, chirality switching, which is a common phenomenon in biological systems, has never been realized in confined environments. Herein, we report a type of hexagonal metallacages that shows good host–guest interactions with ethoxy pillar[5]arene and pillar[6]arene, as confirmed by single‐crystal X‐ray analysis. Importantly, when a chiral pillar[5]arene‐based molecular universal joint (MUJ) is used as the guest, the host–guest complexation would drive the alkyl ring of the MUJ flip from outside to inside the cavity of its pillar[5]arene unit, which enables the configuration change along with the chirality inversion of the MUJ. Moreover, the host–guest complexation facilitates the chirality transfer from guests to hosts, giving circularly polarized luminescence to the system. This study provides a unique metallacage‐pillararene recognition motif for the chirality switching of planar chiral pillararenes, which will promote the construction of host–guest systems with tunable chirality for advanced applications.

The (o-p-o)-Terphenyl Embedded Calix[2]phyrin(2.2.1.1.1) and Its Cu(II) Complex.

The introduction of a higher arene unit as a structural motif is unprecedented in calixphyrin chemistry. Herein, the syntheses, spectral and structural characterization of heretofore anonymous terphenylene unit (o-p-o) incorporated calixphyrin with fused sp2 meso carbons is reported. The explicitly tailored macrocyclic core is utilized to stabilize the Cu(II) metal ion. The molecular structures of the calixbenziphyrin and Cu(II) complex are unambiguously confirmed by single-crystal X-ray analysis. Moreover, theoretical supports uphold experimental conclusions.

Synthesis, Structure, Spectral, Electrochemical, and Theoretical Studies of Ru(II) Complexes of 3-Pyrrolyl BODIPY-Based Ligands.

3-Pyrrolyl BODIPY having an appended pyrrolyl group at the 3-position of BODIPY (4,4-difluoro-4-bora-3a,4a-diaza-s-indacene) and its functionalized derivatives have been used as ligands to prepare one example of Ru(II) complex of pyrrolyl dipyrrin and three unique examples of bichromophoric BODIPY-Ru(II) complexes in good yields. The complexes were characterized by HR-MS, 1D and 2D NMR, X-ray analysis for two complexes, absorption, cyclic voltammetry, and DFT/TD-DFT techniques. The X-ray structure of the Ru(II) complex of pyrrolyl dipyrrin revealed that the geometry around the Ru(II) ion was pseudo-octahedral with an arene unit occupying three coordination sites in η6-fashion and two nitrogen atoms of the dipyrrin ring and one chloro group adopting the "three legs piano-stool" structure. The X-ray structure of the bichromophoric BODIPY-Ru(II) complex revealed that the BODIPY core was planar and the central B(III) was coordinated with two pyrrole nitrogens of the dipyrrin unit and two axial fluoride ions in a tetrahedral geometry, and Ru(II) was bonded to appended pyrrole "N" and "N" of benzimidazole substituent present at the α-position of appended pyrrole, one chloro group, and one arene ring in a pseudo-octahedral geometry. The spectral studies revealed that the electronic properties of the BODIPY unit in BODIPY-Ru(II) complexes were significantly altered, and electrochemical studies indicated that the BODIPY-Ru(II) complexes exhibit one oxidation corresponding to Ru(II) to Ru(III) and one reduction corresponding to the BODIPY unit. The DFT/TD-DFT studies corroborated the experimental observations.

Pillararene incorporated metal-organic frameworks for supramolecular recognition and selective separation.

Crystalline frameworks containing incorporated flexible macrocycle units can afford new opportunities in molecular recognition and selective separation. However, such functionalized frameworks are difficult to prepare and challenging to characterize due to the flexible nature of macrocycles, which limits the development of macrocycle-based crystalline frameworks. Herein, we report the design and synthesis of a set of metal-organic frameworks (MOFs) containing pillar[5]arene units. The pillar[5]arene units were uniformly embedded in the periodic frameworks. Single crystal X-ray diffraction analysis revealed an interpenetrated network that appears to hinder the rotation of the pillar[5]arene repeating units in the frameworks, and it therefore resulted in the successful determination of the precise pillar[5]arene host structure in a MOF crystal. These MOFs can recognize paraquat and 1,2,4,5-tetracyanobenzene in solution and selectively remove trace pyridine from toluene with relative ease. The work presented here represents a critical step towards the synthesis of macrocycle-incorporated crystalline frameworks with well-defined structures and functional utility.

Novel AIEE pillar[5]arene-fluorene fluorescent copolymer for selective recognition of paraquat by forming polypseudorotaxane

A novel conjugated polymer (Co-P[5]Flu) was synthesized by copolymerizing a difunctionalized pillar[5]arene and a fluorene derivative monomer. Co-P[5]Flu displayed an aggregation-induced emission enhancement (AIEE) effect because of the restricted intramolecular rotations of the pillar[5]arene unit. Co-P[5]Flu exhibited high selectivity and sensitivity towards the pesticide paraquat (PQ) with excellent anti-interference properties. It presented fluorescence quenching response (1–I/I0=96.6%) only towards paraquat and not towards other competitive guests. The fluorescence titration experiments revealed that the detection limit (LOD) for paraquat was as low as 1.69×10−8 M, and the Stern-Volmer constant (KSV) was determined to be 2.11×104 M−1. The recognition mechanism was studied using both 1H NMR titration and theoretical calculations. The Co-P[5]Flu showed fluorescence quenching for PQ due to the synergistic effect of polypseudorotaxane formation and photoinduced electron transfer (PET). Additionally, the polymer chemosensor demonstrated potential for the detection of paraquat in practical samples.

Supramolecular nanoassemblies of rim-differentiated pillar[5]arene-rod-coil macromolecules via host-guest interactions for the sensing of cis-trans isomers of 1,4-diol-2-butene

Over the past few years, pillar[n]arene molecules have gained attention as novel functional materials due to their unique properties, including their pore size structure and exceptional host-guest capabilities. Among them, rim-differentiated pillar[5]arene is particularly favored for its unique asymmetric structure. In this study, we present a self-assembled macrocyclic host molecule (H1) based on a rim-differentiated pillar[5]arene unit and five rod-coil side chains containing a hepta (ethylene glycol) mono-methyl ether modified biphenyl and phenyl groups, which was self-assemble into 2D columnar nanostructures in the bulk state. It self-organizes into a double-layer vesicular aggregate when in a CHCl3 solution. The host-guest interactions between the nanoobjects and the guest molecule (G) composed of tetraphenylethene and hexanenitrile groups resulted in the construction of ordered nanostructures with good luminescent properties, such as lamellar nanostructure in the bulk state and a single-layer nanosheet in CHCl3 solution. This demonstrated that the morphology of the H1 can be manipulated by forming host-guest complexes, and by adjusting the intermolecular interactions between the molecules. Moreover, in the presence of cis-trans isomers of 1,4-diol 2-butene, we successfully separated and visually detected the trans isomers through competitive host guest interactions. This result not only provides a general approach for separating the cis-trans isomers of 1,4-diol 2-butene through supramolecular chemistry, but also sets a precedent for future research in this field.

Shape‐ and Size‐Tunable Synthesis of Covalent Organic Cages through Rh‐Catalyzed Regioselective [2+2+2] Cycloaddition

AbstractCovalent organic cages have potential applications in molecular inclusion/recognition and porous organic crystals. Bridging arene units with sp3 atoms enables facile construction of rigid isolated internal vacancies, and various prismatic arene cages have been synthesized by kinetically controlled covalent bond formation. However, the synthesis of a tetrahedral one, which requires twice as much bond formation as prismatic ones, has been limited to a thermodynamically controlled dynamic SNAr reaction, and this reversible covalent bond formation made the resulting cage product chemically unstable. Here we report the Rh‐catalyzed high‐yielding and highly 1,3,5‐selective room temperature [2+2+2] cycloaddition of push‐pull alkynes and its application to the synthesis of chemically stable aryl ether cages of various shapes and sizes, including prismatic and tetrahedral forms. These aryl ether cages are highly crystalline and intertwine with each other to form regular packing structures. Some aryl ether cages encapsulated isolated water molecules in their hydrophobic cavity by hydrogen bonding with the multiple ester moieties.

Shape- and Size-Tunable Synthesis of Covalent Organic Cages through Rh-Catalyzed Regioselective [2+2+2] Cycloaddition.

Covalent organic cages have potential applications in molecular inclusion/recognition and porous organic crystals. Bridging arene units with sp3 atoms enables facile construction of rigid isolated internal vacancies, and various prismatic arene cages have been synthesized by kinetically controlled covalent bond formation. However, the synthesis of a tetrahedral one, which requires twice as much bond formation as prismatic ones, has been limited to a thermodynamically controlled dynamic SN Ar reaction, and this reversible covalent bond formation made the resulting cage product chemically unstable. Here we report the Rh-catalyzed high-yielding and highly 1,3,5-selective room temperature [2+2+2] cycloaddition of push-pull alkynes and its application to the synthesis of chemically stable aryl ether cages of various shapes and sizes, including prismatic and tetrahedral forms. These aryl ether cages are highly crystalline and intertwine with each other to form regular packing structures. Some aryl ether cages encapsulated isolated water molecules in their hydrophobic cavity by hydrogen bonding with the multiple ester moieties.

3+2] Cycloaddition Synthesis of New Piperazine‐Linked Bis(chromene) Hybrids Possessing Pyrazole Units as Potential Acetylcholinesterase Inhibitors

Two series of piperazine-linked bis(chromene) hybrids that are attached to pyrazole units were synthesized in the current study. Both series are attached to an acyl unit at pyrazole-C3, with one series attached to an acetyl unit and the other to an ethoxycarbonyl unit. A [3+2] cycloaddition protocol was conducted to produce the target hybrids with good yields by reacting the appropriate hydrazonoyl chlorides with chromene-based bis(enaminone) in dioxane containing triethylamine at reflux for 4 h. New hybrids were tested for acetylcholinesterase inhibitory activity at concentrations of 15 and 25 μM, as well as their ability to quench 2,2-diphenylpicrylhydrazyl (DPPH) free radicals at a concentration of 25 μg/mL. In general, the inhibitory activity is related to the electronic properties of the para-substituent that is attached to the arene unit at pyrazole-N1. Furthermore, the acyl unit attached to pyrazole-C3 has a significant effect on the new hybrids' inhibitory activity. At the previous concentrations, the (3-acetylpyrazole)-linked hybrid attached to p-NO2 units demonstrated the best acetylcholinesterase inhibitory activity, with inhibition percentages of 79.7 and 90.2. Furthermore, the previous hybrid demonstrated the most effective DPPH inhibitory activity, with an inhibition percentage of 87.5.

New Arylazo-Based (Chromene-Thiazole) Hybrids as Potential MRSA Inhibitors.

A three-component protocol was established to efficiently synthesize (chromene-thiazole) and related arylazo analogs in good to excellent yields. The desired products were prepared by reacting the appropriate salicylaldehydes, 2-cyanothioacetamide, and chloroacetone or hydrazonyl chlorides. Using piperidine as a mediator in ethanol at 80 °C for 4-6 h, the three-component protocol produce the target hybrids in 87-96 % yields. The newly synthesized products showed a broad range of antibacterial activity. The addition of an arylazo unit at the chromene-C6 position significantly improved the antibacterial activity, while the impact of adding an arylazo group at the thiazole-C5 position varied based on the electronic characteristics of the para-substituted arene unit. Generally, series that is linked to two arylazo units, one at chromene-C6 and the other at thiazole-C5, showed the best activity. Some new hybrids showed effective antibacterial activity than ciprofloxacin with MIC/MBC values up to 1.9/3.9 μM against S. aureus and E. coli. Additionally, they demonstrated better effectiveness against MRSA ATCC:33591 and ATCC:43300 compared to linezolid, with MIC/MBC values up to 4.0/16.1 and 3.9/15.6 μM, respectively. The data predicted for the physicochemical properties, lipophilicity, pharmacokinetics, and drug-likeness of new arylazo-based chromene-thiazole hybrids evaluated by SwissADME. As a result of the above, products that are linked to two arylazo units can be considered drug-like scaffolds.

Three-component regioselective synthesis and antibacterial evaluation of new arene-linked bis(pyrazolo[1,5-a]pyrimidine) hybrids

In the current study, a three-component protocol was adopted to efficiently synthesize butane-linked bis(pyrazolo[1,5-a]pyrimidines) 1 attached to arene units in 74–81% yields. The one-pot reaction involved reacting bis(aldehyde) with the respective 1H-pyrazole-3,5-diamines and acetophenones in ethanol at 80 °C in the presence of potassium hydroxide for 6 h. Using a similar protocol, another series of regioisomeric bis(pyrazolo[1,5-a]pyrimidines) 2 was prepared, in 77–87% yields, utilizing the appropriate synthons bis(acetyl) and benzaldehydes. The new products showed a wide spectrum of antibacterial activity against six different ATCC strains. In general, products attached to 3-(4-methoxybenzyl) units exceeded their analogues attached to 3-(4-chlorobenzyl) units in antibacterial activity. Moreover, hybrids which are linked to arene units with para-electron releasing substituents demonstrated improved antibacterial activity. The hybrid 2h, 3-(4-methoxybenzyl) and 7-(4-methoxyphenyl) units, had the best antibacterial activity against all strains tested. It demonstrated more effective activity than ciprofloxacin with MIC/MBC values up to 2.0/4.0 µM.

Hinged Bipodal Furoylthiourea-Based Ru(II)-Arene Complexes: Effect of (ortho, meta, or para)-Substitution on Coordination and Anticancer Activity.

We set out to design and synthesize bipodal ligands with the phenyl group as the spacer and varied the substitution on the spacer between ortho (L1), meta (L2), and para (L3). The respective ligands and complexes containing either p-cymene (PL1-PL3) or benzene (BL1-BL3) as the arene unit were synthesized and characterized successfully. The influence of the ligands due to substitution change on their coordination behavior was quite minimal; however, the differences were seen in the anticancer activity of the complexes. DFT studies revealed the structural variations between the three different substitutions, which was further confirmed by single-crystal X-ray diffraction studies. The anticancer activity of the complexes could be correlated with their rate of hydrolysis and their lipophilicity index as determined by UV-visible spectroscopy. The cell death mechanism of the active complexes was deduced to be apoptotic via staining assays, flow cytometry, and Western blot analysis.

Calix[4]arene-Decorated Covalent Organic Framework Conjugates for Lithium Isotope Separation.

Lithium isotope separation has attracted extensive interest due to its important role in fusion and fission reactions. Up to now, it is still a great challenge to separate lithium isotopes (6Li and 7Li) in an efficient manner due to the low capture ability for lithium ions of related materials and highly similar physicochemical properties between lithium isotopes. In this work, three calix[4]arene-decorated crystalline covalent organic frameworks (COFs) with wave-like extension and AA-stacking configuration were designed and utilized for lithium adsorption and its isotope separation. Experimental studies show that these COFs exhibit an outstanding lithium adsorption capacity up to 94.66 mg·g-1, which is about 2 times beyond that of adsorbents reported in the literature. The high adsorption capacity of COFs could be attributed to the abundant adsorption sites from calix[4]arene unit. More importantly, this study demonstrates for the first time that calixarene groups can separate lithium isotopes with an excellent separation factor up to 1.053 ± 0.002, comparable to the most successful solid-phase lithium separation adsorbent. The calculation based on density functional theory showed that calixarene played an important role in the lithium adsorption. Interestingly, the lithium isotope separation performance is mainly affected by the amine bridging units. This work demonstrated that calixarene COFs are promising adsorbents for lithium isotope separation.

Efficient manipulation of Förster resonance energy transfer through host-guest interaction enables tunable white-light emission and devices in heterotopic bisnanohoops.

In this study, we synthesized and reported the heterotopic bisnanohoops P5-[8,10]CPPs containing cycloparaphenylenes (CPPs) and a pillar[5]arene unit, which act not only as energy donors but also as a host for binding energy acceptors. We demonstrated that a series of elegant FRET systems could be constructed successfully through self-assembly between donors P5-[8,10]CPPs and acceptors with different emissions via host-guest interaction. These FRET systems further allow us to finely adjust the donors P5-[8,10]CPPs and acceptors (BODIPY-Br and Rh-Br) for achieving multiple color-tunable emissions, particularly white-light emission. More importantly, these host-guest complexes were successfully utilized in the fabrication of white-light fluorescent films and further integrated with a 365 nm LED lamp to create white LED devices. The findings highlight a new application of carbon nanorings in white-light emission materials, beyond the common recognition of π-conjugated molecules.

A low dielectric constant material synergized by calix[4]arene and benzocyclobutene units

A novel low-kmaterial (Dkis as low as 2.23) was prepared from functionalized 4-tert-butylcalix[4]arene with different numbers of benzocyclobutene (BCB) units (2 or 4) and spacers (–(CH2)3– or –(CH2)6–).

Nanocapsules of unprecedented internal volume seamed by calcium ions.

The inception of an unprecedented class of voluminous Platonic solids displaying hierarchical geometry based on pyrogallol[4]arene moieties seamed by divalent calcium ion is described. Single-crystal X-ray structural determination has established the highly conserved geometry of two original Ca2+-seamed nanocapsules to be essentially cubic in shape with C-ethylpyrogallol[4]arene units located along the twelve edges of the cube which are then bridged by metallic polyatomic cations ([Ca4Cl]7+ or [Ca(HCO2)Na4]5+) at the six cube faces. The accessible volume of the nanocapsules is ca. 3500 Å3 and 2500 Å3 and is completely isolated from the exterior of the capsules. These remarkable nanocapsule discoveries cast a spotlight on a marginalized area of synthetic materials chemistry and encourage future exploration of diversiform supramolecular assemblies, networks, and capsules built on calcium, with clear benefits deriving from the intrinsic biocompatibility of calcium. Finally, a proof-of-concept is demonstrated for fluorescent reporter encapsulation and sustained release from the calcium-seamed nanocapsules, suggesting their potential as delivery vehicles for drugs, nutrients, preservatives, or antioxidants.