Per-Arylation of Pillar[n]arenes: An Effective Tool to Modify the Properties of Macrocycles

Introducing Prism[4]arene: A Macrocycle with Enantiomerically Resolvable Inherent Chirality and Intriguing Chiroptical Properties

This study presents the first report of an inherently chiral prismarene with resolved enantiomers. Prism[4]arenes, synthesized via a thermodynamic template approach using a tailor-made selective cation, effectively maintain their chirality due to their strained macrorings and narrow annuli, which prevent the flipping of naphthalene rings. The solid-state structure of the synthesized PrS[4]iPe revealed a racemic crystal composed of all-pR and all-pS enantiomeric pairs, forming supramolecular polymeric chains of homochiral molecules interlinked by intermolecular host-guest interactions. Both enantiomers were resolved by using chiral high-performance liquid chromatography (HPLC), and their chiroptical properties were thoroughly investigated. Configurational assignment was achieved through time-dependent density functional theory (TDDFT) computations alongside electronic circular dichroism/ultraviolet-visible (ECD/UV-vis) spectral analysis. Notably, the circularly polarized luminescence (CPL) properties exhibited a significant dissymmetry ratio of 0.008 for these prism[4]arenes, due to electric and magnetic dipole transition moments both directed along the cylinder axis. Furthermore, the ability of PrS[4]iPe to achieve enantioselective recognition with chiral ammonium guests was demonstrated.

Benzo[1,3]oxathiol-2-one Motif-Based a New Chromogenic Copillar[5]arene: Synthesis, Solid-State Assembly, Photophysical Studies, and Colorimetric Recognition of S2

Herein, for the first time, we have reported a route to the introduction of benzo[1,3]oxathiol-2-one group onto pillar[5]arene to synthesize a new copillar[5]arene, which gives a new pillar[5]arene derivative 1 upon further functionalization. The well-defined cavity of this new copillar[5]arene exhibits solvent inclusion properties as characterized by single-crystal X-ray structures. The present study explores the inclusion of ethyl acetate (EtOAc) and acetonitrile (CH3CN) and the supramolecular assemblies with different features in the solid state. Copillar[5]arene 1 shows inclination to form dimers in both EtOAc and CH3CN. While ethyl acetate-occupied macrocycles give 2D arrangement involving π-π interaction, acetonitrile-occupied macrocycles follow π-π, C-H⋅⋅⋅π, and H-bond interactions in 2D arrangement and create a rhombus-shaped molecular channel with a diameter of ~5.5 Å in 3D packing. Compound 1 shows good photophysical behavior and aggregation. It acts as a chromogenic sensor for the selective recognition of sulfide (S2-) over a series of other anions in both organic and aqueous-organic solvents. The detection limit for S2- is determined to be 3.81×10-7 M.

Enantioselective Synthesis of Inherently Chiral Pillar[5]Arenes Through Copper-Catalyzed Azide-Alkyne Cycloaddition

Pillar[n]arenes have been extensively investigated as carrier materials for applications in host-guest chemistry, nanoscience, information science, materials science, and other domains. Despite its success, the enantioselective synthesis of pillar[n]arenes is challenging and has not yet been achieved. Herein, a novel asymmetric extended side-arm strategy is presented for synthesizing chiral pillar[5]arenes through an iterative copper-catalyzed azide-alkyne cycloaddition reaction. An increase in the steric hindrance on both sides of the macrocyclic molecule efficiently produced a wide range of pillar[5]arenes in high yields with excellent enantioselectivities. Moreover, this principle enables iterative copper-catalyzed azide-alkyne cycloaddition to enantioselectively functionalized pillar[5]arenes with different triazoles using a one-pot process.

A water-soluble cationic [2]biphenyl-extended pillar[6]arene: synthesis, host-guest interaction with hemin and application in chemodynamic/photodynamic cancer therapy

A water-soluble cationic [2]biphenyl-extended pillar[6]arene (CBpExP6) was designed and synthesized successfully. It could form a stable 1 : 1 complex with hemin, thereby enhancing the stability of hemin in water, and can be further applied in cancer CDT and PDT.

Supramolecular Double-Helical Polymers: Supramolecular Chiral Induction and Asymmetric Catalysis

Seeking a supramolecular chiral system induced by trace chiral molecules instead of traditional complex and expensive chiral ligands to achieve high yield or ee value conversion of the products is of great significance in asymmetric synthesis but still remains a challenge. Herein, two types of double helical supramolecular chiral systems, (M)-Helix and (P)-Helix, with opposite chiral optics were constructed in situ using tyrosine-functionalized pillar[5]arene as inducers. These systems exhibit chiroptical stability and enable remarkable chirality amplification from 7 mol% chiral seeds. When applied to intermolecular olefin cyano-trifluoromethylation, (M)-Helix exhibits remarkable catalytic efficiency (yield up to 89%), whereas (P)-Helix achieves higher enantioselectivity (ee up to 84%). This research will provide new ideas for supramolecular chiral catalysts in organic asymmetric catalysis applications.

Step Cyclization to Give Part Belt Oxygen-Functionalized Pillar[6,10]arenes

Part belt oxygen-functionalized pillar[6,10]arenes are synthesized by step cyclization. An oxygen-substituted tetramer and hexamer have been prepared to construct the O3 pillar[6]arene 4 via a hexamer cyclization reaction and the O6 pillar[10]arene 7 through a [4 + 1+4 + 1] cyclization reaction. X-ray crystallographic studies reveal that both macrocycles have a large cavity and indicate that the part belt oxygen-functionalized pillar[6,10]arenes have both similar cyclic structures and certain differences in configuration compared to pillararene. A variable-temperature 1H NMR experiment also demonstrated the structure differences between O3 pillar[6]arene 4 and traditional pillararene.

Boosting the circularly polarized luminescence of pyrene-tiaraed pillararenes through mechanically locking

Attributed to their unique dynamic planar chirality, pillar[n]arenes, particularly pillar[5]arenes, have evolved as promising platforms for diverse applications such as circularly polarized luminescence (CPL) emitters. However, due to the unit flipping and swing, the achievement of excellent CPL performances of pillar[5]arenes in solution state remains a formidable challenge. To deal with this key issue, a mechanically locking approach has been successfully developed, leading to boosted dissymmetry factor (glum) values of pyrene-tiaraed pillar[5]arenes up to 0.015 through the formation of corresponding [2]rotaxanes. More importantly, taking advantage of the stably locked co-conformers, these resultant [2]rotaxanes maintain excellent CPL performances in diverse solvents and wide range of concentrations, making them promising candidates for practical applications. According to this proof-of-concept study, we have not only successfully developed a powerful strategy for the rational design of chiral luminescent materials with desired CPL performances but also contributed a promising platform for the construction of smart chiral materials.

Supramolecular control over the variability of color and fluorescence in low-molecular-weight glass

Colorful and fluorescent transparent materials have been extensively used in industrial and scientific activities, with inorganic and polymeric glasses being the most typical representatives. Recently, artificial glass originating from low-molecular-weight monomers has attracted considerable attention. Compared with the deep understanding of the building blocks and driving forces of supramolecular glass, related studies on its optical properties are insufficient in terms of systematicness and pertinence. In this study, a supramolecular strategy was applied to introduce versatile colors and fluorescence emissions into a low-molecular-weight glass. Pillar[5]arene and cucurbit[8]uril were selected to recognize the functional components and yield the desired optical performances. Macrocycle-based host-guest chemistry endows artificial glass with controllable and programmable colors and fluorescence emissions.

Configurationally Stepping Confinement Achieved Tunable Chiral Near-Infrared Luminescence Supramolecular Phenothiazine Organic Framework

Herein, thermally responsive reversible chiral supramolecules are reported, constructed by the chirality transfer from tripeptides to achiral network supramolecular organic frameworks (SOF) based on configurationally stepping confinement, which displayed not only highly selective reversible chirality transfer but also efficient enhanced near-infrared (NIR) luminescence. Taking advantage of macrocyclic confinement, CB[8] separately encapsulated two kinds of tetracationic bis(phenothiazines) derivatives (G1, G2) at 2:1 stoichiometric to form organic 2D SOFs, efficiently enhancing 12.6 fold NIR luminescence and blueshifted from 705 to 680 nm for G1, and redshifted from 695 to 710 nm for G2, respectively. Uncommonly, the tripeptide coassembled with two kinds of achiral noncovalent frameworks (G1/CB[8] or G2/CB[8]) displayed different opposite circular dichroism signals based on different binding modes and affinity, achieving chirality transfer from tripeptide to organic supramolecular assemblies with further enhanced NIR fluorescence up to 46.2 times and the quantum yield (QY) increased from 0.71% to 10.29% for G2/CB[8], showing reversible chirality transfer and tunable NIR fluorescence under thermal stimulus. Therefore, the current research has achieved controllable chirality transfer from tripeptide to the SOFs and the enhancement of tunable NIR fluorescence, which is successfully applied in thermal responsive chiral logic gates, information encryption, and cell imaging.

Six-Cyclic Crown Ether-Type Pillar[5]Arene: Enhanced Binding Ability to Bispyridinium Derivatives

A six-cyclic crown ether-type pillar[5]arene was synthesized, and the five ethylene oxide loops were located outside the cavity and not affected by temperature changes which was confirmed by variable-temperature NMR experiment in DMSO-d6 and CDCl3 and 2D 1H-1H NOESY experiment in CDCl3. The six-cyclic pillar[5]-crown also showed greater binding ability of host-guest with bis(pyridinium) derivatives than conventional alkoxy pillar[5]arenes that illustrated through 1H NMR titration spectroscopic experiment in acetone-d6/CDCl3 (1 : 1) and UV-vis titration experiments in CHCl3 at room temperature. The five benzocrown ethers at the periphery were able to bind metal cations by 1H NMR titration spectroscopic experiment in CD2Cl2/methanol-d4(9 : 1).

Hollow spherical nano-traps using pillararene-based polymer for efficient uranium extraction from seawater

Herein, a hollow spherical pillar[5]arene-based polymer (P5-AO) adsorbent was synthesized. The P5-AO adsorbent was capable of effectively capturing uranium from simulated seawater (139.5 mg g-1) and real seawater (8.1 mg g-1). We also elucidated the uranium adsorption mechanism of P5-AOvia extended X-ray absorption fine structure (EXAFS). This study provides a novel direction for the development of uranium capture adsorbents.

Propanediamine modified pillar[5]arene: A novel stationary phase for the high selectivity separation of versatile analytes

The unique properties of pillar[5]arene, including hydrophobic cavities, π-π conjugated and easy modification, make it a promising candidate as stationary phase for HPLC. Herein, we fabricated a novel propanediamine modified pillar[5]arene bonded silica as the stationary phase (PDA-BP5S) for reversed-phase liquid chromatography (RPLC). Benefiting from the significant hydrophobicity, π-π conjugative, p-π effect, and hydrogen bonding, the PDA-BP5S packed column showed high separation performance of versatile analytes involving polycyclic aromatic hydrocarbons, alkyl benzenes, phenols, arylamine, phenylethane/styrene/ phenylacetylene, toluene/m-xylene/mesitylene, halobenzenes, benzenediol and nitrophenol isomers. Especially, the separation of halobenzenes appeared to be controlled by both the size of the halogen substituents and the strength of the noncovalent bonding interactions, which was further confirmed by molecular dynamics simulation. The satisfactory separation and repeatability revealed the promising prospects of amine-pillar[5]arene-based stationary phase for RPLC.

Pillar[5]arenes decorated with six-membered-ring aromatics at all the substitution positions

Macrocyclic molecules have characteristic properties different from linear ones, such as high symmetry and guest-inclusion ability. To bring drastic changes to these properties, direct introduction of many substituents is a challenging but effective tool. Herein, we attain direct installation of ten six-membered-ring aromatic π-units into both rims of a pillar[5]arene. In contrast to previous pillar[n]arenes with less hindered five-membered-ring units, which showed conformational complexity and crushed crystal structures, the per-phenyl-substituted pillar[5]arene has a cylinder-shaped crystal structure with a dichloromethane inside the cavity and is obtained as a single pair of D 5-symmetric enantiomers. The average dihedral angles between the core and peripheral benzene rings sharply increase from 38° to 66°. These differences indicate the importance of local steric repulsion on both rims for determining the structures and properties of macrocycles.

Directed evolution of Escherichia coli surface-displayed Vitreoscilla hemoglobin as an artificial metalloenzyme for the synthesis of 5-imino-1,2,4-thiadiazoles

Artificial metalloenzymes (ArMs) are constructed by anchoring organometallic catalysts to an evolvable protein scaffold. They present the advantages of both components and exhibit considerable potential for the in vivo catalysis of new-to-nature reactions. Herein, Escherichia coli surface-displayed Vitreoscilla hemoglobin (VHbSD-Co) that anchored the cobalt porphyrin cofactor instead of the original heme cofactor was used as an artificial thiourea oxidase (ATOase) to synthesize 5-imino-1,2,4-thiadiazoles. After two rounds of directed evolution using combinatorial active-site saturation test/iterative saturation mutagenesis (CAST/ISM) strategy, the evolved six-site mutation VHbSD-Co (6SM-VHbSD-Co) exhibited significant improvement in catalytic activity, with a broad substrate scope (31 examples) and high yields with whole cells. This study shows the potential of using VHb ArMs in new-to-nature reactions and demonstrates the applicability of E. coli surface-displayed methods to enhance catalytic properties through the substitution of porphyrin cofactors in hemoproteins in vivo.

Silapillar[n]arenes: Their Enhanced Electronic Conjugation and Conformational Versatility

During recent decades, methylene-bridged macrocyclic arenes have been widely used in supramolecular chemistry. However, their π-conjugations are very weak, as the methylene bridges disrupt the electronic communication between π orbitals of the aromatic units. Herein, we successfully synthesized a series of silapillar[n]arenes (n = 4, 6, and 8) using silylene bridging. These showed enhanced electronic conjugation compared with the parent pillar[n]arenes because of σ*-π* conjugation between σ* (Si-C) orbitals and π* orbitals of the benzenes. Owing to the longer Si-C bond compared with the C-C bond, silylene-bridging provides additional structural flexibility into the pillar[n]arene scaffolds; a strained silapillar[4]arene was formed, which is unavailable in the parent pillar[n]arenes because of the steric requirements. Furthermore, silapillar[n]arenes displayed interesting size-dependent structural and optical properties.

Stereoselective Single Step Cyclization to Give Belt-Functionalized Pillar[6]arenes

Two macrocycles were synthesized through cyclization reactions of secondary benzylic alcohols, giving pillar[6]arenes with a methyl substituent at each belt position. These macrocycles form stereoselectively with only the rtctct isomer with alternating up and down orientations of the belt methyl groups definitively identified. Isolated yields were modest (7 and 9%), but the macrocycles are prepared in a single step from either a commercially available alcohol or a very readily prepared precursor. X-ray crystal structures of the macrocycles indicate they have a capsule-like structure, which is far from the conventional pillar shape. Density functional theory calculations reveal that the energy barrier required to obtain the pillar conformation is significantly higher for these belt-functionalized macrocycles than for conventional belt-unfunctionalized pillar[6]arenes.

Alignment and Dynamic Inversion of Planar Chirality in Pillar[n]arenes

Pillar[n]arenes are symmetrical macrocyclic compounds composed of benzene panels with para-methylene linkages. Each panel usually exhibits planar chirality and prefers chirality-aligned states. Because of this feature, pillar[n]arenes are attractive scaffolds for chiroptical materials that are easy to prepare and optically resolve and show intense circular dichroism (CD) signals. In addition, rotation of the panels endows the chirality of pillar[n]arenes with a dynamic nature. The chirality in tubular oligomers and supramolecular assemblies sometimes show time- and procedure-dependent alignment phenomena. Furthermore, the CD signals of some pillar[n]arenes respond to the addition of chiral guests when their dynamic chirality is coupled with host-guest properties. By using diastereomeric pillar[n]arenes with additional chiral structures, the response can also be caused by achiral guests and changes of the environment, providing molecular sensors.