Arene Macrocycle Research Articles

Iridium-Catalyzed C-H Borylations: Regioselective Functionalizations of Calix[4]arene Macrocycles.

We report iridium-catalyzed C-H borylations for the regioselective synthesis of distally disubstituted calix[4]arene macrocycles. The atom- and step-economical method led to a broad family of calix[4]arenes in good yields and functional group tolerance. The synthetic utility of the C-H borylation protocol was finally illustrated with several late-stage modifications for the synthesis of elaborate calix[4]arenes frameworks, otherwise challenging to achieve with commonly employed procedures.

Probing noncovalent binding, spectroscopic characteristics and antiproliferative behavior of inclusion complex between quinoline and para-sulfonatothiacalix[4]arene

The inclusion complex between bowl-shaped para-sulfonatothiacalix[4]arene (TSCX4) macrocycle and quinoline has been studied with a unison of UV–visible, infra-red, flourescence emission and 1H nuclear magnetic resonance (NMR) and 2D nuclear overhauser effect spectroscopy (NOESY), high resolution mass spectrometry (HRMS) experiments. Both 1H NMR titration and HRMS experiments point to 1:1 stoichiometry for the water soluble Q⊂TSCX4 complex. The electronic structure of the inclusion complex obtained from density functional theory (DFT) showed a partial encapsulation of quinoline guest, which is held within the host cavity by C–H---π, π---π and hydrogen bonding interactions. The fluorescence emission spectra upon complexation display marginal blue shift of the 411 nm band in TSCX4. Moreover, the binding constant (7.1 × 103 M−1) determined from fluoresence emission experiments underline the effective host–guest binding in the complex, which was corroborated through frequency up-shift (‘blue shift’) of characteristic Ar-OH (3433 cm−1) and SO3- vibrations (1141 cm−1 and 1037 cm−1) in the measured infrared spectra of TSCX4. The antiproliferative activitities of the Q⊂TSCX4 complex against HeLA, MDA-MB-231and N2a cells are presented. The Q⊂TSCX4 complex has been shown to be efficient against N2a (neuroblastoma) cell line.

Host-Guest Cocrystallization of Phenanthrene[2]arene Macrocycles Facilitating Structure Determination of Liquid Organic Molecules.

Single-crystal X-ray diffraction analysis has emerged as the most reliable method for determining the structures of organic molecules. However, numerous analytes, such as liquid organic molecules, pose challenges in crystallization, making their structures directly elusive via X-ray crystallography methods. Herein, we introduced the rapid cocrystallization of a macrocycle named phenanthrene[2]arene (PTA, host) with 15 liquid organic molecules (guests). The guest liquid organic molecules were successively cocrystallized with the aid of the PTA host. Moreover, the chemical structures of the liquid organic molecules could be determined through single-crystal X-ray diffraction analysis. PTA exhibited high adaptivity and was capable of encapsulating liquid organic molecules without forming covalent bonds or strong directional interactions. The results revealed that the adaptive crystals of PTA exhibited excellent cocrystallization capacity. Weak noncovalent interactions between the host and guest molecules were crucial for organizing the guests in an ordered pattern.

Host-Guest Chemosensor Ensembles based on Water-Soluble Sulfonated Calix[n]arenes and a Pyranoflavylium Dye for the Optical Detection of Biogenic Amines.

Biogenic amines (BAs) are biologically active nitrogen-containing compounds formed during the food spoilage process and are often related as key markers of food quality, safety, and freshness. Because their presence in foods at high levels can cause significant health problems, researchers have been focused on developing novel strategies and methods for early detection and capture of these analytes. Herein, water-soluble sulfonated calix[n]arene macrocycles (SC4, SC6, and SC8) and a pH-sensitive dye (4'-hydroxy-10-methylpyranoflavylium) were investigated as host-guest systems for BA sensing. The hosts were able to bind the flavylium cation of the dye with association constants of 103 to 104 M-1. The dye complexation also allowed tuning its pKa from 6.72 (free) toward high values: 7.68 (SC4), 7.79 (SC6), and 8.45 (SC8). These data were crucial to optimize the host-guest complexes as optical sensing systems for putrescine/tyramine (pH 7.2-7.6), yielding a colorimetric redshift from yellow to red. The BA sensing was also demonstrated by fluorescence quenching for the calix[n]arene/dye complexes and fluorescence recovery after the addition of BAs. 1H NMR spectroscopy was used to demonstrate the interaction mode, confirming an encapsulation-driven mechanism. Overall, these host-guest systems demonstrated great potential for the detection of BAs, one of the main key markers of food spoilage.

Molecularly Mixed Composite Membranes for Gas Separation Based on Macrocycles Embedded in a Polyimide.

Polyimides are a polymer class that has been extensively investigated as a membrane material for gas separation owing to its interesting permselective properties in a wide range of operation temperatures and pressures. In order to improve their properties, the addition of different filler types is currently studied. p-tert-Butylcalix[n]arene macrocycles (PTBCs) with different cavity sizes (PTBC4, PTBC6, PTBC8) were used as fillers in a commercial thermoplastic polyimide, with a concentration in the range 1-9 wt%, to develop nanocomposite membranes for gas separation. The selected macrocycles are attractive organic compounds owing to their porous structure and affinity with organic polymers. The nanocomposite membranes were prepared in the form of films in which the polymeric matrix is a continuous phase incorporating the dispersed additives. The preparation was carried out according to a pre-mixing approach in a mutual solvent, and the solution casting was followed by a controlled solvent evaporation. The films were characterized by investigating their miscibility, morphology, thermal and spectral properties. The gas transport through these films was examined as a function of the temperature and also time. The results evidenced that the incorporation of the chosen nanoporous fillers can be exploited to enhance molecular transport, offering additional pathways and promoting rearrangements of the polymeric chains.

Linking electron-rich Pillar[5]arene into hyper-cross-linked polymers for highly effective adsorption of iodine vapor

Four hyper-cross-linked polymers were synthesized by linking electron-rich monomers with an electron-rich cross-linker via the Friedel–Crafts reaction. Among these polymers, P4, which was constructed with decaalkyne pillar[5]arene and bibenzyl chloride, adsorbed iodine vapor with a capacity of 3.930 g g−1, outperforming most supramolecular macrocycle-based porous polymers. The pillar[5]arene macrocycle contributed various types of adsorption sites, including aromatic rings, diynes, and oxygen atoms. The abundance of effective adsorption sites and the high specific surface area (1615.5 m2 g−1) were responsible for the excellent adsorption capacity of P4. Because these polymers are easy to synthesize and regenerate and can be mass produced, they are promising candidates for large-scale applications.

Tuning vibration-induced emission through macrocyclization and catenation.

In order to investigate the effect of macrocyclization and catenation on the regulation of vibration-induced emission (VIE), the typical VIE luminogen 9,14-diphenyl-9,14-dihydrodibenzo[a, c]phenazine (DPAC) was introduced into the skeleton of a macrocycle and corresponding [2]catenane to evaluate their dynamic relaxation processes. As investigated in detail by femtosecond transient absorption (TA) spectra, the resultant VIE systems revealed precisely tunable emissions upon changing the solvent viscosity, highlighting the key effect of the formation of [2]catenane. Notably, the introduction of an additional pillar[5]arene macrocycle featuring unique planar chirality endows the resultant chiral VIE-active [2]catenane with attractive circularly polarized luminescence in different states. This work not only develops a new strategy for the design of new luminescent systems with tunable vibration induced emission, but also provides a promising platform for the construction of smart chiral luminescent materials for practical applications.

Highly selective Cu2+ detection with a naphthalimide-functionalised pillar[5]arene fluorescent chemosensor.

Ligand 1, a rim-differentiated pillar[5]arene macrocycle modified with five naphthalimide groups through click chemistry, serves as an effective ratiometric fluorescent chemosensor for Cu2+. In contrast to the monomeric naphthalimide control compound 2, which shows only monomer emission, ligand 1 demonstrates dual emission characteristics encompassing both the monomer and excimer of the naphthalimide moieties. The binding properties of ligand 1 toward 15 different metal ions were systematically investigated in CH2Cl2/CH3CN (v/v, 1 : 1) by UV-vis and fluorescence spectroscopy. Remarkably, ligand 1 exhibits exceptional selectivity for Cu2+ ions. Upon complexation with Cu2+, the excimer emission of ligand 1 diminishes, concomitant with an enhancement of its monomer emission. The binding ratio for 1·Cu2+ was determined to be 1 : 1, with an association constant of (3.39 ± 0.40) × 105 M-1 calculated using a nonlinear least-squares curve-fitting method. Furthermore, the limit of detection (LOD) was found to be 185 ± 7 nM. Our results from 1H NMR titration, high-resolution mass spectrometry analysis and density functional theory calculations of 1·Cu2+ suggest synergistic coordination between Cu2+ and the triazole groups on ligand 1.

Multipodal Au-C grafting of calix[4]arene molecules on gold nanorods.

The interface robustness and spatial arrangement of functional molecules on metallic nanomaterials play a key part in the potential applications of functional nano-objects. The design of mechanically stable and electronically coupled attachments with the underlying metal is essential to bring specific desirable properties to the resulting hybrid materials. In this context, rigid multipodal platforms constitute a unique opportunity for the controllable grafting of functionality. Herein, we provide for the first time an in-depth description of the interface between gold nanorods and a chemically-grafted multipodal platform based on diazonium salts. Thanks to Raman and X-ray photoelectron spectroscopies and theoretical modeling, we deliver insights on the structural and electronic properties of the hybrid material. More importantly, it allows for the accurate assignment of Raman bands. The combination of experimental and theoretical results establishes the formation of four carbon-gold anchors for the calix[4]arene macrocycle leading to the exceptional stability of the functionalized nano-objects. Our results lay the foundations for the future design of robust and versatile platforms.

HOMO- AND HETERONUCLEAR Yb(III) AND Lu(III) COMPLEXES WITH CALIX[4]ARENE MODIFIED WITH PORPHYRIN SUBSTITUENTS.

In this work we describe the approaches for the synthesis of lanthanide-containing homo- and heteronuclear complexes using 5,11,17,23-tetra-tert-butyl-25,27-dihydroxy-26,28-bis[(N-meso-­(p-aminophenyl)-meso-triphenylporphyrincarbonyl)methoxy]-calix[4]arene (1). Such spatially preorganizedcalix[4]arene macrocycle facilitates lanthanide cation coordination, impacting the structure and analytical signal of porphyrin substituents. The study employs two synthesis stra­tegies resulting in mononuclear and homobinuclear complexes, influenced by steric effects and changes in hydrogen bonding. The complexes exhibit changes in fluorescence spectra due to intramolecular dimerization and hydrogen bonding during complex formation. Mononuclear complexes (Ln-1) are synthesized under mild conditions, while homobinuclear complexes (Ln2-1) require high-boiling solvents and specific reaction conditions, detailed synthesis procedures are described. The structural changes during complex formation were analyzed with the use of NMR analysis. The absorption spectra of lanthanide complexes demonstrate shifts in maxima, reflecting coordination changes, with notable variations between mononuclear and homobinuclear complexes. Additionally, heteronuclear compounds with copper(II), zinc(II), and palladium(II) exhibit distinctive absorption patterns, emphasizing the role of d-metal ions. Luminescence stu­dies reveal the sensitization of 4f-luminescence by both calix[4]arene and porphyrin fragments. The use of deuterated solvents enhances 4f-luminescence intensity, highlighting solvent effects. Furthermore, 4f-luminescence characteristics were investigated in both solid and solution states for heterometallic compounds, emphasizing differences between copper-containing and zinc/palladium-containing complexes. The results offer valuable insights into the design, synthesis, and spectral properties of these complexes, showcasing their potential applications in various fields, and the findings contribute to the understanding of lanthanide-porphyrin systems and their coordination behavior.

Crystal structure and supramolecular features of a bis-urea-functionalized pillar[5]arene

The crystal structure of a bis-urea derivative based on A1/A2-functionalized pillar[5]arene (DUP) that encapsulates dimethyl formamide (DMF) inside the macrocyclic cavity is reported. The crystal structure of DUP·DMF, C63H70N4O12·C3H7NO, reveals that out of two urea functionalized spacers, one arm is oriented above the macrocyclic cavity with strong hydrogen-bonding interactions between the urea H atoms and DMF guest, whereas, the other arm is positioned away from the macrocycle, leading to intermolecular hydrogen-bonding interactions between the urea H atoms of two adjacent pillar[5]arene macrocycles, resulting in the formation of a supramolecular dimer.

Selective turn-on sensing of adenosine diphosphate and phosphate anions by ruthenium (II) polypyridine anchored p-tert-butylcalix[4]arene platform

BackgroundNucleoside polyphosphate (NPP) anions are important for enzymatic activity and should be monitored by scientists in industry and medicine. By elucidating enzyme kinetics and processes, it aids in the discovery of effective inhibitors and activators. Nucleoside polyphosphate (NPP) anions are used by kinases, GTPases, and glycosyltransferases (GTs). Phosphorylation of certain amino acid residues (Ser, Thr, and Tyr) on proteins requires the breakdown of ATP by protein kinases, which produces ADP. Protein kinases, breakdown of ATP, and NPP are the focus of oncology drug development because the aberrant control of kinase activity is a common cause of cancer. ResultsHowever, a discriminative turn-on fluorescent property is exhibited by non-fluorescent p-tertbutylcalix[4]arene modified 1,2,3-triazole containing bis-ruthenium polypyridyl complex (RL) upon the addition of phosphate anions such as (dihydrogen pyrophosphate (H2P2O72−) and dihydrogen phosphate (H2PO4−)) in CH3CN solvent and Adenosine Diphosphate (ADP) in CH3CN/HEPES (pH = 7.4) buffer (9/1, v/v). The probe RL shows a better-recognizing ability with pyrophosphate anion (H2P2O72−) than dihydrogen phosphate anion (H2PO4−). With H2P2O72− and H2PO4− anions, the RL detection limit was calculated to be as low as 83 nM and 198 nM, respectively. SignificanceThe calix[4]arene macrocycle's excellent size and binding cone conformation make it a good host–guest interface for the pyrophosphate anion and ADP. The bis-ruthenium polypyridyl complex's connection to the p-tertbutyl calix[4]arene moiety creates the ADP selectivity turn-on sensor. When moving from mono-nuclear to bi-nuclear ruthenium complex anchored on p-tertbutyl calix[4]arene, the probe can differentiate ADP, ATP, and AMP. Furthermore, this platform is a great resource for creating devices to simultaneously assess phosphate anions in environmental samples.

Insights into the Self‐Filling Effects of Branched Isopropyl Groups on the Conformational and Supramolecular Properties of Isopropoxyprism[6]arene

AbstractIn this work, the direct macrocyclization of a prism[6]arene macrocycle bearing branched alkyl chains on the rims is reported. Isopropoxyprism[6]arene adopts in solution and in the solid state a cuboid D2‐conformation in which four isopropyl groups are folded inside the cavity, to give C−H⋅⋅⋅π interactions and filling the internal void. The conformational features of isopropoxyprism[6]arene have been studied by dynamic 1H NMR experiments. The presence of branched isopropyl chains on the prism[6]arene rims, stabilizes the cuboid D2‐conformation to a greater extent than ethyl or propyl groups in PrS[6]Et and PrS[6]nPr. The higher resistance of PrS[6]iPr to open its cuboid D2 conformation, with respect to PrS[6]Et and PrS[6]nPr, also affected its binding abilities. In fact, alkylammonium‐based endo‐cavity complexes of PrS[6]iPr show lower binding constant values than the analogous propoxy/ethoxy‐prism[6]arene complexes.

Azo‐bridged hydroxyl‐rich porous pillar[5]arene polymers for efficient carbon dioxide conversion

AbstractTwo new azo‐bridged hydroxyl‐rich porous organic polymers (POPs), named PPDA‐P5 and TB‐P5, were designed and successfully fabricated via azo‐coupling reaction with per‐hydroxylated pillar[5]arene macrocycle as the core and p‐phenylenediamine and Troger's base (TB) diamine as the linker, respectively. Owing to the abundant nitrogen and hydroxyl groups, both polymers exhibited excellent interaction affinity toward carbon dioxide (CO2) and then were applied as efficient heterogeneous catalysts for the transformation of CO2 to cyclic carbonates with high yield, even under mild conditions. Interestingly, TB‐P5 exhibited superior catalytic performance toward PPDA‐P5, indicating TB's positive role as an organic base. This design strategy and results provided new insight into the development of macrocycle‐based POPs in the field of heterogeneous catalysis.

Insertion of pillar[5]arene into Tröger's base-derived porous organic polymer for promoted heterogeneous catalytic performance in Knoevenagel condensation and CO2 fixation

Development of new metal-free heterogeneous catalysts has long been the focus of intense research interest. The integration of multifunctional monomers into the skeletons of porous organic polymers (POPs) provides an efficient pathway to achieve this goal. Herein, we rationally designed and successfully prepared a new Tröger's base (TB)-derived POPs by insertion of pillar[5]arene macrocycle as a positively auxiliary group. Combined the both merits of pillar[5]arene macrocycle and TB moiety, the as-prepared polymer was further explored as an effective metal-free heterogeneous catalyst and exhibited promoted catalytic performance in Knoevenagel condensation and CO2 conversion. This work provides a new strategy to fabricate metal-free heterogeneous catalysts based on macrocyclic POPs.

Gold(I)-catalysed hydroarylations of alkynes for the synthesis of inherently chiral calix[4]arenes.

We describe the first gold(I)-catalysed intramolecular hydroarylation of alkynes for the straightforward synthesis of inherently chiral calix[4]arenes. This step- and atom-economical approach, which exploits a formal meta-functionalisation of the calix[4]arene macrocycle, is able to deliver an ample family of N-heterocyclic, chiral compounds in high yields and functional group tolerance.

Catalysis enabled synthesis, structures, and reactivities of fluorinated S8-corona[n]arenes (n = 8-12).

Previously inaccessible large S8-corona[n]arene macrocycles (n = 8-12) with alternating aryl and 1,4-C6F4 subunits are easily prepared on up to gram scales, without the need for chromatography (up to 45% yield, 10 different examples) through new high acceleration SNAr substitution protocols (catalytic NR4F in pyridine, R = H, Me, Bu). Macrocycle size and functionality are tunable by precursor and catalyst selection. Equivalent simple NR4F catalysis allows facile late-stage SNAr difunctionalisation of the ring C6F4 units with thiols (8 derivatives, typically 95+% yields) providing two-step access to highly functionalised fluoromacrocycle libraries. Macrocycle host binding supports fluoroaryl catalytic activation through contact ion pair binding of NR4F and solvent inclusion. In the solid-state, solvent inclusion also intimately controls macrocycle conformation and fluorine-fluorine interactions leading to spontaneous self-assembly into infinite columns with honeycomb-like lattices.

A 4-state acid-base controlled molecular switch based on a host-guest system.

A novel ZnII funnel complex that presents three phenol functions within a calix[6]arene macrocycle is described. Host-guest studies, monitored by 1H NMR spectroscopy, evaluate the impact of the replacement of three anisole moieties present in a previously described system with phenols. It is now shown that the dicationic complex is responsive to anions, whereas deprotonation of one phenol unit completely inhibits any hosting response. These properties, combined with those of the corresponding protonated ligand, allow us to obtain different molecular switches, and one of them shows guest embedment changes between four different host states, thus giving rise to a rare case of a triple molecular switch.

Hydrogen adsorption and sensing properties of p-tert-butylcalix[4]arene and its transition metal complexes: A DFT study

The safety storage of hydrogen molecule is an important issue for researchers. Today, hydrogen adsorption and detection is one of these issues. In this study, the interactions of calix[4]arene macrocycle and its metal complexes with hydrogen molecule were investigated by Density Functional Theory (DFT) method. WB97XD hybrid method was used in DFT calculations. The most stable complexes of calix[4]arenes with metal atoms were determined. All interactions were determined to be weak van der Waals interactions. It has been revealed that metal atoms in the complexes have positive effect on adsorption and the best adsorbent is the Fe-calix[4]arene complex. It has been determined that pristine calix[4]arene compound can be used as an electronic sensor against hydrogen molecule at room temperature.

Confused-Prism[5]arene: a Conformationally Adaptive Host by Stereoselective Opening of the 1,4-Bridged Naphthalene Flap.

The confused-prism[5]arene macrocycle (c-PrS[5]Me ) shows conformational adaptive behavior in the presence of ammonium guests. Upon guest inclusion, the 1,4-bridged naphthalene flap reverses its planar chirality from pS to pR (with reference to the pS(pR)4 enantiomer). Stereoselective directional threading is also observed in the presence of directional axles, in which up/down stereoisomers of homochiral (pR)5 -c-PrS[5]Me pseudorotaxanes are formed.