Calixarenes - the third generation of supramolecules

Synthesis of cyclodextrin-based polyrotaxanes and polycatenanes for supramolecular pharmaceutical sciences

Cyclodextrins (CDs) are essential in the pharmaceutical industry and have long been used as food and pharmaceutical additives. CD-based interlocked molecules, such as rotaxanes, polyrotaxanes, catenanes, and polycatenanes, have been synthesized and have attracted considerable attention in supramolecular chemistry. Among them, CD polyrotaxanes have been employed as slide-ring materials and biomaterials. CD polycatenanes are new materials; therefore, to date, no examples of applied research on CD polycatenanes have been reported. Consequently, we expect that applied research on CD polycatenanes will accelerate in the future. This review article summarizes the syntheses and structural analyses of CD polyrotaxanes and polycatenanes to facilitate their applications in the pharmaceutical industry. We believe that this review will promote further research on CD-based interlocked molecules.

Molecular vessels from preorganised natural building blocks

Supramolecular vessels emerged as tools to mimic and better understand compartmentalisation, a central aspect of living matter. However, many more applications that go beyond those initial goals have been documented in recent years, including new sensory systems, artificial transmembrane transporters, catalysis, and targeted drug or gene delivery. Peptides, carbohydrates, nucleobases, and steroids bear great potential as building blocks for the construction of supramolecular vessels, possessing complexity that is still difficult to attain with synthetic methods - they are rich in functional groups and well-defined stereogenic centers, ready for noncovalent interactions and further functions. One of the options to tame the functional and dynamic complexity of natural building blocks is to place them at spatially designed positions using synthetic scaffolds. In this review, we summarise the historical and recent advances in the construction of molecular-sized vessels by the strategy that couples synthetic predictability and durability of various scaffolds (cyclodextrins, porphyrins, crown ethers, calix[n]arenes, resorcin[n]arenes, pillar[n]arenes, cyclotriveratrylenes, coordination frameworks and multivalent high-symmetry molecules) with functionality originating from natural building blocks to obtain nanocontainers, cages, capsules, cavitands, carcerands or coordination cages by covalent chemistry, self-assembly, or dynamic covalent chemistry with the ultimate goal to apply them in sensing, transport, or catalysis.

Least Absolute Shrinkage and Selection Operator-Based Prediction of the Binding Constant of p-Sulfonatocalix[6]/[8]arenes with Alkaloids

p-Sulfonatocalix[n]arenes (SCnA) have demonstrated great potential for drug encapsulation through host-guest complexation to improve solubility, stability, and bioavailability. In this study, the solubilization effect of SCnA (n = 4, 6, 8) on 95 active compounds derived from traditional Chinese medicine (TCM) was investigated. Based on the significant solubilization effect on alkaloids, SC6A/SC8A and 76 alkaloids were selected as the host and guest, respectively, to determine the binding constant by competitive fluorescence titration. LASSO regression was adopted to investigate the mechanism of the complex of SCnA with alkaloids. The binding constant of alkaloids-SC6A and alkaloids-SC8A was related to the alkaloid alkalinity. Also, the electronegativity, polarization, first ionization potential, hydrogen bond potential, the molecular size, and shape of alkaloids are critical properties to determine alkaloids-SC6A binding constant as well as electronegativity, polarization, hydrophobicity, and the molecular size and shape of alkaloids play an important role for the alkaloids-SC8A binding constant.

Novel mitochondrial and DNA damaging fluorescent Calix[4]arenes bearing isatin groups as aromatase inhibitors: Design, synthesis and anticancer activity

Breast cancer causes a high rate of mortality all over the world. Therefore, the present study focuses on the anticancer activity of new lower rim-functionalized calix[4]arenes integrated with isatin and the p-position of calixarenes with 1,4-dimethylpyridinium iodine against various human cancer cells such as MCF-7 and MDA-MB-231 breast cancer cell lines, as well as the PNT1A healthy epithelial cell line. It was observed that compound 6c had the lowest values in MCF-7 (8.83 µM) and MDA-MB-231 (3.32 µM). Cell imaging and apoptotic activity studies were performed using confocal microscopy and flow cytometry, respectively. The confocal imaging studies with 6c showed that the compound easily entered the cell, and it was observed that 6c accumulated in the mitochondria. The Comet assay test was used to detect DNA damage of compounds in cells. It was found that treated cells had abnormal tail nuclei and damaged DNA structures compared with untreated cells. In vitro human aromatase enzyme inhibition profiles showed that compound 6c had a remarkable inhibitory effect on aromatase. Compound 6c displayed a significant inhibition capacity on aromatase enzyme with the IC50 value of 0.104 ± 0.004 µM. Thus, not only the anticancer activity of the new fluorescent derivatives, which are the subject of this study, but the aromatase inhibitory profiles have also been proven.

The unusual (syn-/anti-)2 conformation of a di-meth-oxy-pyrimidyl-based tennimide

The tennimide macrocycle, (I) (C52H40N16O16.0.167H2O), was synthesized from 2-amino-4,6-di-meth-oxy-pyrimidine and pyridine-2,6-dicarbonyl dichloride. Compound (I) represents the first tennimide incorporating pyridine rings in the macrocycle scaffold. In the macrocycle ring, the carbonyl groups at each successive dicarbon-yl(pyridine) moiety adopt the (syn/anti)2 conformation. This contrasts with all previously reported tetra-imide macrocycles, which exhibit the (syn)4 conformation. The effect is to close any potential cavity or niche by having two of the central pyridine C5N rings aligned close to each other [with closest pyridine Cg⋯Cg ring centroid separations of 3.5775 (19) Å; closest C⋯C = 3.467 (5) Å]. A partial occupancy water mol-ecule (with s.o.f. = 0.167), resides with its oxygen atom on a twofold axis at hydrogen-bonding distances to the carbonyl O atom, in a mol-ecular niche between two pyridine rings. Macrocyles of (I) have all six C=O groups and all eight meth-oxy O atoms present on the macrocycle surface. However, all twelve N atoms are effectively shielded on steric grounds from any potential inter-molecular inter-actions. The remaining two C=O O atoms inter-act with the partial occupancy water mol-ecule via two O-H⋯O=C hydrogen bonds. Macrocycles of (I) stack as one-dimensional chains along the b-axis direction with primary inter-molecular inter-actions involving weak C-H⋯O=C/OCH3/H2O contacts. Chains inter-lock weakly via meth-oxy-meth-oxy C-H⋯O inter-actions into two-dimensional sheets.

Sulfonamides with Heterocyclic Periphery as Antiviral Agents

Sulfonamides are the basic motifs for a whole generation of drugs from a large group of antibiotics. Currently, research in the field of the new sulfonamide synthesis has received a "second wind", due to the increase in the synthetic capabilities of organic chemistry and the study of their medical and biological properties of a wide spectrum of biological activity. New reagents and new reactions make it possible to significantly increase the number of compounds with a sulfonamide fragment in combination with other important pharmacophore groups, such as, for example, a wide class of N-containing heterocycles. The result of these synthetic possibilities is the extension of the activity spectrum-along with antibacterial activity, many of them exhibit other types of biological activity. Antiviral activity is also observed in a wide range of sulfonamide derivatives. This review provides examples of the synthesis of sulfonamide compounds with antiviral properties that can be used to develop drugs against coxsackievirus B, enteroviruses, encephalomyocarditis viruses, adenoviruses, human parainfluenza viruses, Ebola virus, Marburg virus, SARS-CoV-2, HIV and others. Since over the past three years, viral infections have become a special problem for public health throughout the world, the development of new broad-spectrum antiviral drugs is an extremely important task for synthetic organic and medicinal chemistry. Sulfonamides can be both sources of nitrogen for building a nitrogen-containing heterocyclic core and the side chain substituents of a biologically active substance. The formation of the sulfonamide group is often achieved by the reaction of the N-nucleophilic center in the substrate molecule with the corresponding sulfonylchloride. Another approach involves the use of sulfonamides as the reagents for building a nitrogen-containing framework.

Photophysical Properties of Naphthalene-oxacalix[m]arene and Recognition of Fullerene C60

Three different pore sizes of oxacalix[m]arene[n]pyrimidines modified with a naphthalene substituent were synthesized and characterized by HRMS, ¹H NMR, and single-crystal analysis (8OA and 8OA-N). Steady-state spectroscopy indicates these naphthalene-oxacalix[m]arenes exhibit good fluorescence properties, which isattributed to the locally excited (LE) state emission, and electrochemical results show that the photoinduced electron transfer (PET) process occurs from the naphthalene substituent to the linked pyrimidine. Nanosecond transient absorption spectra, singlet oxygen quantum yields (Φ_Δ4OA-N = 45.1%, Φ_Δ6OA-N = 56.6%, and Φ_Δ8OA-N = 65.7%) and theoretical calculations demonstrate that the torsion angle between the donor (naphthalene) and the acceptor (pyrimidine) promotes intersystem crossing (ISC), and the lifetime of the triplet state reaches ca. 8 ms. Interestingly, all three host molecules (4OA-N, 6OA-N, and 8OA-N) showed a high affinity for fullerene C₆₀, and significant binding constants in the range of 4.10-6.68 × 10⁴ M^-1 were obtained by fluorescence titration; in contrast, previous reports indicated that the similar oxacalix[m]arene[n]pyrimidine scaffold could not efficiently complex with C₆₀. In the frontier molecular orbital theory calculations of the supramolecular system of 4OA-N@C ₆₀ , the HOMO is distributed on 4OA-N and the LUMO is localized on fullerene. The calculation results further demonstrated that there are strong interactions between the host and the fullerene guest, which is consistent with the result of the experiments. The characteristic photophysical properties of these novel naphthyl-decorated oxacalix[m]arene[n]pyrimidines broaden their application field, and the stable host-guest system with fullerene can be applied to supramolecular chemistry.

Synthesis of New Quinoline-Conjugated Calixarene as a Fluorescent Sensor for Selective Determination of Cu2+ Ion

A novel quinoline-functionalized calix [4] arene derivative (Quin-Calix) has been successfully synthesized at partial cone conformation and duly characterized by using FTIR, ¹H-NMR, ¹³C-NMR, ESI-MS and elemental analysis techniques. Moreover, the cation-binding property of the calix [4] arene derivative (Quin-Calix) has been investigated towards Cu²⁺, Ba²⁺, Cd²⁺, Co²⁺, Ni²⁺, Zn²⁺ and Fe³⁺ ions, and the recognition event monitored by UV-Vis absorption and fluorescence studies. The results indicated that Quin-Calix displays a remarkable affinity and selectivity only for Cu²⁺ ion. The binding constant and stoichiometry of the complex formed between Quin-Calix and Cu²⁺ ion have been also calculated from the fluorescence data. In addition, Stern-Vohmer equation has been used to elucidate the mechanism of quenching.

A fluorescent calix[4]arene with naphthalene units at the upper rim exhibits long fluorescence emission lifetime without fluorescence quenching

We synthesised a new compound with four naphthyl groups in the upper rims of calix[4]arene (1). Compared to the monomer unit, compound 1 has redshifted absorption and fluorescence, together with high fluorescence quantum yield and long fluorescence lifetime, which is extremely rare because long fluorescence lifetime emission tends to reduce the quantum yield. Single-crystal X-ray analysis and quantum calculations in the S1 state revealed π-π through-space interactions between naphthalene rings.

Theoretical assessment of calix[4]arene-N-β-ketoimine (n=1-4) derivatives: Conformational studies, optoelectronic, and sensing of Cu2+cation

Herein, we have investigated the key functions of the calix[4]arene, abbreviated as CX [1], and designed its several derivatives by substitution of the functional groups. Molecular geometry provides an intuitive understanding of the effect of functional groups on various physical properties. The addition of the N-β-ketoimine (n = 1-4) ligands has a direct effect on the stretching vibration of the H-bonding interaction. The results showed that all molecules possess absorption bands at 190 nm and in the range between 200 and 300 nm assigned to π-π* and n-π* transitions. HOMO-LUMO energy gap of the CX[4]-N-β-ketoimine, one with chemical hardness of 1.62 eV, has been found to be 3.24 eV calculated at B3LYP/6-31 + G(d) level of theory. This finding explains the good kinetic stability of this compound. The large values of electrophilicity make the current molecules as a good electrophilic species. The atom in molecule (AIM) and the reduced density gradient (RDG) analyses showed the type and the strength of the interactions taking place between Cu²⁺ and the β-ketoimine ligands.

Oxaphosphacyclophanes Constructed from a Bis(triphenylphosphine oxide) Moiety Linked by Dioxyalkyl Chains: Synthesis and Crystal Structures

Oxaphosphacyclophanes, a bis(triphenylphosphine oxide) moiety linked by dioxypropane, dioxybutane, dioxypentane, and dioxyhexane, were synthesized from the reaction of bis(4-hydroxyphenyl)phenylphosphine oxide and dibromoalkanes. Single-crystal X-ray diffraction analysis and exploring intermolecular interactions by using the Hirshfeld surface revealed that the butylene-linked oxaphosphacyclophane (2) had a one-dimensional (1D) supramolecular structure via CH/π interactions between the terminal phenyl group of 2 and a phenylene group of the cavities. In the packing diagram of pentylene-linked oxaphosphacyclophane (3) with antiform, one macrocycle recognized two terminal phenyl groups to form a 1D supramolecular chain via π/π interactions. The syn-form of 3 was obtained by the recrystallization from toluene and CHCl₃. In this crystal, a toluene molecule avoid construction of a 1D chain. The antiform of hexylene-linked oxaphosphacyclophane 4 was obtained by the recrystallization from cyclohexane and CHCl₃. Cyclohexane was captured in the cavity via CH/π interactions. Two molecules of 4 with the syn-form recognized each other to construct a dimeric structure via CH/π interactions.

Supramolecular-Macrocycle-Based Crystalline Organic Materials

Supramolecular macrocycles are well known as guest receptors in supramolecular chemistry, especially host-guest chemistry. In addition to their wide applications in host-guest chemistry and related areas, macrocycles have also been employed to construct crystalline organic materials (COMs) owing to their particular structures that combine both rigidity and adaptivity. There are two main types of supramolecular-macrocycle-based COMs: those constructed from macrocycles themselves and those prepared from macrocycles with other organic linkers. This review summarizes recent developments in supramolecular-macrocycle-based COMs, which are categorized by various types of macrocycles, including cyclodextrins, calixarenes, resorcinarenes, pyrogalloarenes, cucurbiturils, pillararenes, and others. Effort is made to focus on the structures of supramolecular-macrocycle-based COMs and their structure-function relationships. In addition, the application of supramolecular-macrocycle-based COMs in gas storage or separation, molecular separation, solid-state electrolytes, proton conduction, iodine capture, water or environmental treatment, etc., are also presented. Finally, perspectives and future challenges in the field of supramolecular-macrocycle-based COMs are discussed.

Conformational Mobility Study in Mono Quinone Derivative of Calix[4]arene by Low Temperature NMR Spectroscopy

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Calix[4]monoquinone (3) has been synthesized by oxidation of rigid cone conformation of tripropoxy calix[4]arene (2), and conformational characteristics of this molecule have been studied by means of dynamic nuclear magnetic resonance (DNMR) and HH- correlated nuclear magnetic resonance spectroscopy (HH-COSY NMR). On the basis of the data that have been obtained, free Gibbs energy of activation (ΔG#) for quinone ring interconversion process of 3 was determined 12.3±0.05 Kcal/mol by coalescence approximation method.

Controlled binding of organic guests by stimuli-responsive macrocycles

Synthetic supramolecular chemistry pursues not only the construction of new matter, but also control over its inherently dynamic behaviour.

Amphiphilic calix[4]arenes as a highly selective gas chromatographic stationary phase for aromatic amine isomers

Efficient separation of aromatic amine isomers is a challenging issue in chemical industry and environmental analysis. Here we report the use of p-amino-tetradecyloxy-calix[4]arene (C4A-NH₂) as a novel stationary phase for gas chromatographic (GC) separations. The statically coated C4A-NH₂ capillary column showed a high column efficiency of 4332 plates/m for a 0.25 mm ID column and medium polarity. The C4A-NH₂ stationary phase exhibited an excellent separation performance both for aromatic amine isomers and a complex mixture of aliphatic analytes with a wide ranging polarity, showing distinct advantages over the commercial polysiloxane stationary phases via diversified molecular interactions covering H-bonding, π-π, van der Waals interactions and shape-fitting selectivity. The retention mechanisms of aromatic amine isomers on C4A-NH₂ column were further investigated by quantum chemistry calculations. In addition, the C4A-NH₂ column showed good column repeatability with relative standard deviation (RSD) values of 0.03%-0.07% for run-to-run, 0.10%-0.27% for day-to-day and 2.6%-5.7% for column-to-column, respectively, and thermal stability up to 240℃.

Stable suprachannels via a columnar cyclodimeric ensemble: exchange and matrix of various liquid guests in SCSC fashion

Self-assembly of ZnI₂ with di(isoquinolin-5-yl)isophthalate (L) as a new bidentate N-donor gives rise to discrete crown-shaped M₂L₂ cyclodimers, 3.5CH₃CN·0.7THF@[Zn₂I₄L₂]. These metallacyclodimers are composed of a characteristically eclipsed molecular array, resulting in the formation of unusual 10.0 × 15.1 Ų diameter suprachannels. The suprachannels adsorb/desorb various liquid molecules in a rigid manner, which enables scientists to solve the structures of various liquids. This columnar molecular ensemble is an efficient, tolerant, and reproducible suprachannel matrix for structural determination of general liquid compounds via easy single-crystal-to-single-crystal (SCSC) guest exchange without any desolvation process.

Assessment of the in vitro toxicity of calixarenes and a metal-seamed calixarene: a chemical pathway for clinical application

Calixarenes are known to form host-guest complexes and supramolecular nanoassemblies with well-defined architectures. However, the use of these materials in conjunction with drug moieties is still under explored. One reason is the insuffcient biocompatibility studies. Our present study represents a systematic in vitro investigation of the cytotoxicity associated with C-methylresorcin[4]arene, C-methylpyrogallol[4]arene, p-phosphonated calix[8]arene and a metal-seamed calixarene-copper(II) complex, using human HEK293 and rat C6G cell lines and two different cell viability assays (MTT and CellTiter-Glo) to avoid species-biased results. All compounds showed low to moderate toxicity. The trend in the CC₅₀ values indicated that the suppression of the coordination ability and the presence of phosphonate groups decrease the overall cytotoxicity of the compounds. The results of this study not only establish calixarenes and their immediate families as potential drug carriers and drug modifiers, but also reveal a pathway for fine-tuning their toxicological behaviour by appropriate chemical modification.

[Supramolecular Pharmaceutical Sciences: A Novel Concept for Future Pharmaceutical Sciences]

Supramolecular chemistry is a useful and important domain for understanding pharmaceutical sciences, since various physiological reactions (e.g., protein association) and drug activities (e.g., the substrate/receptor reaction) are based on supramolecular chemistry. Biological components, such as DNA and cells, are also supermolecules. However, supramolecular chemistry to date has not been a major domain in the field of pharmaceutical study. In this article, we propose a new concept in pharmaceutical sciences termed "supramolecular pharmaceutical sciences" which combines pharmaceutical sciences and supramolecular chemistry. "Supramolecular pharmaceutical sciences" could encompass strictly controlled molecular arrangement, stimulus responsible molecular motion, new functions beyond those of existing molecules, more accurate drug design, new active pharmaceutical ingredients, new perspectives for the investigation of the drug mechanisms, and novel pharmaceutical technologies. Moreover, pharmaceutical sciences are useful for supramolecular chemistry, because biological reactions are very accurate reactions, making this a win-win relationship. Thus, supramolecular pharmaceutical sciences could be useful for developing new methods, hypotheses, ideas, materials, mechanisms, and strategies in the realm of pharmaceutical science.

Separation performance of p-tert-butyl(tetradecyloxy)calix[6]arene as a stationary phase for capillary gas chromatography

This work presents the first example of the utilization of p-tert-butyl(tetradecyloxy)calix[6]arene (C6A-C10) as a stationary phase for capillary gas chromatographic (GC) separation.

Conformation of alkali metal ion-calix[4]arene complexes investigated by IR spectroscopy in the gas phase

The OH bands of M⁺·C4A shift to the red from K⁺ to Cs⁺, indicating reduction of conformer distortion.

Performance and selectivity of lower-rim substituted calix[4]arene as a stationary phase for capillary gas chromatography

This work presents the investigation of p-tert-butyl(tetradecyloxy)calix[4]arene (C4A-C10) as stationary phase for capillary gas chromatographic (GC) separations. The statically-coated C4A-C10 capillary column showed weak polarity and column efficiency of 2566 plates per m determined by n-dodecane at 120 °C. Impressively, the C4A-C10 column exhibited extremely high resolving capability for a wide range of analytes from nonpolar to polar, including n-alkanes, esters, ketones, aldehydes, alcohols and bromoalkanes. Most importantly, the C4A-C10 column exhibited an excellent separation performance for positional, structural and cis-/trans-isomers. Among them, the column displayed advantageous resolving capability over the commercial polysiloxane stationary phase for aromatic amine isomers. Moreover, the C4A-C10 column showed good column repeatability with RSD values below 0.06% for run-to-run, 0.12–0.27% for day-to-day and 2.8–5.3% for column-to-column.

This work presents the investigation of p-tert-butyl(tetradecyloxy)calix[4]arene (C4A-C10) as stationary phase for capillary gas chromatographic (GC) separations.

p-Nitro-tetradecyloxy-calix[4]arene as a highly selective stationary phase for gas chromatographic separations

Here, we report the first example of the utilization of p-nitro-tetradecyloxy-calix[4]arene (C4A-NO₂) as a stationary phase for capillary gas chromatographic (GC) separations.

Columnar self-assembly, gelation and electrochemical behavior of cone-shaped luminescent supramolecular calix[4]arene LCs based on oxadiazole and thiadiazole derivatives

A new class of blue light-emitting supramolecular liquid crystalline cone or bowl-shaped compounds were synthesized from substituted 1,3,4-oxadiazoles and 1,3,4-thiadiazoles with calix[4]arene derivatives.

Synthesis, in-Vitro and in Silico Studies of Azo-Based Calix[4]arenes as Antibacterial Agent and Neuraminidase Inhibitor: A New Look Into an Old Scaffold

Calixarene derivatives are reported as potential therapeutic agents. Azo derivatives of calixarenes have not been given much consideration to explore their biomedical applications. In the present study, some azo-based derivatives of calix[4]arene were synthesized and characterized and their antibacterial and antiviral potentials were studied. The mono azo products of sulphanilamide, sulfaguanidine and 2-methyl-4-aminobenzoic acid showed good activity against bacterial strains with minimum inhibition concentration values ranging from 0.97 to 62.5 μg/mL. For mono azo products, the diazotized salt was applied as a limiting reagent. The use of calix[4]arene and sodium acetate trihydrate in 1:3 (molar ratio) helped in partial substitution. Molecular docking was performed to see the interaction of the designed compounds with two bacterial and one viral (neuraminidase) receptor. Some of the derivatives showed good interaction with the active site of bacterial and neuraminidase enzymes through hydrogen, hydrophobic and pi-pi interactions, and could inhibit the activity of the selected enzymes.

Supramolecular Pharmaceutical Sciences: A Novel Concept Combining Pharmaceutical Sciences and Supramolecular Chemistry with a Focus on Cyclodextrin-Based Supermolecules

Supramolecular chemistry is an extremely useful and important domain for understanding pharmaceutical sciences because various physiological reactions and drug activities are based on supramolecular chemistry. However, it is not a major domain in the pharmaceutical field. In this review, we propose a new concept in pharmaceutical sciences termed "supramolecular pharmaceutical sciences," which combines pharmaceutical sciences and supramolecular chemistry. This concept could be useful for developing new ideas, methods, hypotheses, strategies, materials, and mechanisms in pharmaceutical sciences. Herein, we focus on cyclodextrin (CyD)-based supermolecules, because CyDs have been used not only as pharmaceutical excipients or active pharmaceutical ingredients but also as components of supermolecules.