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The challenge of efficiently extracting Li+ from brines with high Na+ or Mg2+ concentrations has led to extensive research on developing highly selective separation membranes for electrodialysis. Various studies have demonstrated that nanofiltration membranes or adsorbents modified with crown ethers (CEs) such as 2-OH-12-crown-4-ether (12CE), 2-OH-18-crown-6-ether (18CE), and 2-OH-15-crown-5-ether (15CE) show selectivity for Li+ in brines. This study aims to develop high-performance cation exchange membranes (CEMs) using CEs to enhance Li+ selectivity and to compare the performance of various CE-modified membranes for selective electrodialysis. The novel CEM (CR671) was modified with 12CE, 18CE, and 15CE to identify the optimal CE for efficient Li+ recovery during brine electrodialysis. The modification process included polydopamine (PDA) treatment and the deposition of polyethyleneimine (PEI) complexes with the different CEs via hydrogen bonding. Interfacial polymerization with 1,3,5-benzenetricarbonyl trichloride-crosslinked PEI was used to create specific channels for Li+ transport within the modified membranes (12CE/CR671, 15CE/CR671, and 18CE/CR671). The successful application of CE coatings and Li+ selectivity of the modified membranes were verified through Fourier-transform infrared spectroscopy, zeta-potential measurements, and electrochemical impedance spectroscopy. Bench-scale electrodialysis tests showed significant improvements in permselectivity and Li+ flux for all three modified membranes. In brines with high Na+ and Mg2+ concentrations, the 15CE/CR671 membrane demonstrated more significant improvements in permselectivity compared to the 12CE/CR671 (3.3-fold and 1.7-fold) and the 18CE/CR671 (2.4-fold and 2.6-fold) membranes at current densities of 2.3 mA/cm2 and 2.2 mA/cm2, respectively. At higher current densities of 14.7 mA/cm2 in Mg2+-rich brine and 15.9 mA/cm2 in Na+-rich brine, the 15CE/CR671 membrane showed greater improvements in Li+ flux, approximately 2.1-fold and 2.3-fold, and 3.2-fold and 3.4-fold compared to the 12CE/CR671 and 18CE/CR671 membranes. This study underscores the superior performance of 15CE-modified membranes for efficient Li+ recovery with low energy demand and offers valuable insights for advancing electrodialysis processes in challenging brine environments. [ABSTRACT FROM AUTHOR]

Efficient delivery of therapeutic agents to the lesion site or specific cells is an important way to achieve "toxicity reduction and efficacy enhancement". Macrocycles have always provided many novel ideas for drug or gene loading and delivery processes. Specifically, macrocycles represented by crown ethers, cyclodextrins, cucurbit[n]urils, calix[n]arenes, and pillar[n]arenes have unique properties, which are different cavity structures, good biocompatibility, and good stability. Benefited from these diverse properties, a variety of supramolecular drug delivery systems can be designed and constructed to effectively improve the physical and chemical properties of guest molecules as needed. This review provides an outlook on the current application status and main limitations of macrocycles in supramolecular drug delivery systems. [ABSTRACT FROM AUTHOR]

Crown ethers are famous for the highly selectively grab Sr(II) from concentrated nitric acid solution due to the size match, but they suffer from the high leakage into the liquid phase caused by the presence of a large number of hydrophilic groups. To reduce their leakage, two novel porous silica-based adsorbents, (DtBuCH18C6 + Dodec)/SiAaC-g-ABSA and (DtBuCH18C6 + Dodec)/SiAaC-g-3-ABSA, were prepared by vacuum impregnation with organic contents of about 55.9 wt.% and 56.1 wt.%, respectively. The two adsorbents have good reusability and structural stability, and the total organic carbon leakage rates in 2 M HNO3 solution are lower than 0.56 wt.% and 0.29 wt.%, respectively. Batch adsorption experiments revealed that the two adsorbents possessed good adsorption selectivity towards Sr, with SFSr/M over 40, except that of SFSr/Ba in 2 M HNO3 solution. The adsorption equilibrium of Sr in 2 M HNO3 solution was reached within 1 h, with saturated adsorption capacities of 36.9 mg/g and 37.5 mg/g, respectively. Furthermore, the XPS results indicate that the adsorption mechanism is the coordination of the crown ether ring with Sr. This work not only develops two novel adsorbents for the separation of Sr in nitric acid environments; it also provides a method for effectively reducing the water solubility of crown ethers. [ABSTRACT FROM AUTHOR]

Polymer materials with a low dielectric constant and low dielectric loss have the potential to be applied to high-frequency signal transmissions, such as mobile phone antennas and millimeter wave radars. Two types of diamines, 4,4′-diamino-p-tetraphenyl (DPT) and crown ether diamine (CED), were prepared for ternary copolymerization with BPDA in this study. Cross-links with molecular chains were formed, increasing molecular chain distance by utilizing rings of CED. The MPI films exhibit a good thermal performance with the increase in CED addition, with Tg > 380 °C and CTE from −4 × 10−6 K−1 to 5 × 10−6 K−1. The Young's modulus can reach 8.6 GPa, and the tensile strength is above 200 MPa when 5% and 7% CED are introduced. These MPI films exhibit good mechanical performances. The dielectric constant of PI−10% film can go as low as 3.17. Meanwhile, the relationship between dielectric properties and molecular structure has been demonstrated by Molecular Simulation (MS). PI molecules are separated by low dielectric groups, resulting in a decrease in the dielectric constant. [ABSTRACT FROM AUTHOR]

Because of environmental impact, there is a great need for chemosensors, especially for toxic heavy metals such as lead. The conventional instrumental analytical techniques rarely provide an available real-time sensing platform, thus the development of highly selective and stable synthetic chemosensor molecules is of great importance. Acridono-18-crown-6 ethers have such properties, and much research has proven their outstanding applicability in various supramolecular devices. In this present work, we aimed to enable their covalent immobilization capability by synthesizing functionalized derivatives while preserving the favored molecular recognition ability. Several new macrocycle analogues were synthesized, while synthetization difficulties and design aspects were also dealt with. The selectivity of the macrocycle analogues was studied using UV–Vis spectroscopy and compared with that of the parent compounds. The ultimate crown ether derivative showed high Pb2+-selectivity, reversibility (decomplexation by extraction with water) and stability. [ABSTRACT FROM AUTHOR]

This article presents the synthesis and molecular dynamics investigation of three novel cyclic thioethers: 2,3-(4′-methylbenzo)-1,4,7,10-tetrathiacyclododeca-2-ene (compound 1), 2,3,14,15-bis(4′,4″(5″)-methylbenzo)-1,4,7,10,13,16,19,22,25-octathiacyclotetracosa-2,14-diene (compound 2), and 2,3,8,9-bis(4′,4″(5″)-methylbenzo)-1,4,7,10-tetrathiacyclododeca-2,8-diene (compound 3). The compounds exhibit relatively high glass transition temperatures (Tg), which range between 254 and 283 K. This characteristic positions them within the so-far limited category of crown-like glass-formers. We demonstrate that cyclic thioethers may span both the realms of ordinary and sizeable molecular glass-formers, each featuring distinct physical properties. Furthermore, we show that the Tg follows a sublinear power law as a function of the molar mass within this class of compounds. We also reveal multiple dielectric relaxation processes of the novel cyclic thioethers. Above the Tg, their dielectric loss spectra are dominated by a structural relaxation, which originates from the cooperative reorientation of entire molecules and exhibits an excess wing on its high-frequency slope. This feature has been attributed to the Johari–Goldstein (JG) process. Each investigated compound exhibits also at least one intramolecular secondary non-JG relaxation stemming from conformational changes. Their activation energies range from approximately 19 kJ/mol to roughly 40 kJ/mol. Finally, we analyze the high-pressure molecular dynamics of compound 1, revealing a pressure-induced increase in its Tg with a dTg/dp coefficient equal to 197 ± 8 K/GPa. [ABSTRACT FROM AUTHOR]

In the present work, potentiometric sensors with polymer membranes used for chlorhexidine (CHXD) determination were developed. The polymer membranes were plasticized with bis(2-ethylheksyl)sebacate (DOS) or 2-nitrophenyloctyl ether (o-NPOE). The active compounds used in the membrane were cyclodextrins, crown ethers, and ion exchangers. The best-constructed electrode was based on neutral heptakis(2,3,6-tri-O-benzoyl)-β-cyclodextrin with lipophilic salt (KTpClBP)—potassium tetrakis(4-chlorophenyl) borate—dissolved in plasticizer, DOS. The presented electrode is characterized by an average cationic slope of 30.9 ± 2.9 mV decade−1 within a linear range of 1 × 10−6 to 1 × 10−3 mol × L−1, while the value of the correlation coefficient is 0.9970 ± 0.0026. The response time was about 5 s when increasing the sample concentration and about 10 s when diluting the sample. The electrode potential is independent of the pH within a range of 4.0–9.5. The polymeric membrane sensor was successfully applied for assays of chlorhexidine digluconate in pure samples and pharmaceutical samples. The relative error from three replicate measurements was determined to be 1.1%. and the accuracy was RSD = 0.3–1.1%. [ABSTRACT FROM AUTHOR]

The recovery and reuse of the enantioselective catalysts produced by tedious work are important not only from the perspective of green chemistry, but also from the point of view of productivity. Some of the carbohydrate-based crown ethers prepared in our research group were able to generate significant asymmetric induction in certain cases. However, they were not recoverable after the synthesis. Therefore, we modified the most effective structure with a propargyl group so that it can be attached to a polymer with an azide–alkyne reaction. It was investigated whether the position of the bonding affects the activity of the crown ethers, hence, the propargyl group was introduced either to the side chain, to the anomeric center or to the benzylidene protecting group. To anchor the macrocycles, low molecular weight PVC was modified with azide groups in 4% and 10%, respectively. It was found that glucose-based crown ether bearing the propargyl group on the benzylidene unit and grafted to PVC in 4% has the highest activity regarding the enantioselectivity (77% ee). The catalyst was recoverable in the Michael addition of diethyl acetamidomalonate to nitrostyrene and it could be reused five times without the loss of enantioselectivity. [ABSTRACT FROM AUTHOR]

Supramolecular chemistry enables the manipulation of functional components on a molecular scale, facilitating a "bottom-up" approach to govern the sizes and structures of supramolecular materials. Using dynamic non-covalent interactions, supramolecular polymers can create materials with reversible and degradable characteristics and the abilities to self-heal and respond to external stimuli. Pillar[n]arene represents a novel class of macrocyclic hosts, emerging after cyclodextrins, crown ethers, calixarenes, and cucurbiturils. Its significance lies in its distinctive structure, comparing an electron-rich cavity and two finely adjustable rims, which has sparked considerable interest. Furthermore, the straightforward synthesis, uncomplicated functionalization, and remarkable properties of pillar[n]arene based on supramolecular interactions make it an excellent candidate for material construction, particularly in generating interpenetrating supramolecular polymers. Polymers resulting from supramolecular interactions involving pillar[n]arene find potential in various applications, including fluorescence sensors, substance adsorption and separation, catalysis, light-harvesting systems, artificial nanochannels, and drug delivery. In this context, we provide an overview of these recent frontier research fields in the use of pillar[n]arene-based supramolecular polymers, which serves as a source of inspiration for the creation of innovative functional polymer materials derived from pillar[n]arene derivatives. [ABSTRACT FROM AUTHOR]

A novel hydrogen-bonded supramolecular crown-ether-based inclusion compound, [(DL-α-Phenylglycine)(18-crown-6)]+[(CoCl4)0.5]−(1), was obtained via evaporation in a methanolic solution at room temperature using DL-α-phenylglycine, 18-crown-6, cobalt chloride (CoCl2), and hydrochloric acid. Its structure, thermal properties, and electrical properties were characterized via elemental analysis, single-crystal X-ray diffraction, variable-temperature infrared spectroscopy, thermogravimetric analysis, differential scanning calorimetry, and variable temperature–variable frequency dielectric constant testing. The compound was a monoclinic crystal system in the C2 space group at low temperature (100 K) and room temperature (293 K). Analysis of the single crystal structure showed that [(CoCl4)0.5]− presented an edge-sharing ditetrahedral structure in the disordered state, while the protonated DL-α-phenylglycine molecule in the disordered state and intramolecular hydroxyl group (-OH) underwent dynamic rocking, causing a significant stretching motion of the O-H···Cl-type one-dimensional hydrogen bond chain. This resulted in dielectric anomalies in the three axes of the crystal, thus showing significant dielectric anisotropy. [ABSTRACT FROM AUTHOR]

A crown ether-loaded hybrid adsorbent suitable for the separation and enrichment of strontium from high-level liquid waste was synthesized. 4′,4′(5″)-di(tert-butylcyclohexano)-18-crown-6 (DtBuCH18C6) and its modifiers dodecyl benzenesulfonic acid (DBS) and 1-dodecanol were impregnated into silica-based polymer support. The hybrid adsorbent exhibited excellent Sr(II) selectivity ability, and effective chromatographic separation and recovery of Sr(II) from simulated high-level liquid waste could be achieved with a (DtBuCH18C6 + DBS + dodec)/SiO2-P packed column. The recovery rate of Sr(II) calculated based on the mass balance was approximately 99% and over 80% for the other coexisting metal ions. An appropriate increase in the concentration of Na-DTPA eluent was favorable to improve the efficiency of the elution process because of the increased complexation capacity of [DTPA]5− to Sr(II). The developed theoretical model can simulate the dynamic breakthrough curves of the material on the basis of short column data, thereby predicting the scale-up column of the practical operation. Density functional theory calculation was used to explore the action mechanism of DBS modifiers on the Sr(II) complexation process of crown ether groups. Two Sr(II) complexation isomeric models of DtBuCH18C6 were established, and the calculation results revealed a similar complexation ability. DtBuCH18C6 could form a stable Sr(II) complexation structure with DBS coordination, which further indicated that DBS could be a ligand to promote the Sr(II) adsorption ability of crown ether materials. [ABSTRACT FROM AUTHOR]

Lariat ethers are macrocyclic polyethers—crown ethers—to which sidearms are appended. 4,13-Diaza-18-crown-6 having twin alkyl chains at the nitrogens show biological activity. They exhibit antibiotic activity, but when co-administered at with an FDA-approved antibiotic, the latter's potency is often strongly enhanced. Potency enhancements and resistance reversals have been documented in vitro for a range of Gram-negative and Gram-positive bacteria with a variety of antimicrobials. Strains of E. coli and Staphylococcus aureus having resistance to a range of drugs have been studied and the potency enhancements (checkerboards) are reported here. Drugs included in the present study are ampicillin, cefepime, chlortetracycline, ciprofloxacin, doxycycline, kanamycin, minocycline, norfloxacin, oxycycline, penicillin G, and tetracycline. Enhancements of norfloxacin potency against S. aureus 1199B of up to 128-fold were observed. The properties of these lariat ethers have been studied to determine solubility, their membrane penetration, cytotoxicity and mammalian cell survival, and their effect on bacterial efflux pumps. It is shown that in some cases, the lariat ethers have complex antimicrobials with considerable selectivity. Based on these observations, including 1:1 complexation between lariat ethers and antimicrobials and the cytotoxicity of the MeI salts showing a separation index of 32-fold, they hold significant potential for further development. [ABSTRACT FROM AUTHOR]

Carbohydrate-based macrocycles can be enantioselective catalysts in certain reactions. Previously, it was proven that the carbohydrate moiety could affect the catalytic activity of the monoaza-15-crown-5 type macrocycles derived from sugars. According to our experiments so far, the most effective enantioselective catalysts were the d-glucose- and the d-galactose-based crown ethers. To obtain more information about the effect of the carbohydrate unit, a rare monosaccharide, d-idose was incorporated into the monoaza-15-crown-5 structure. The key intermediates were methyl 4,6-O-benzylidene-α-d-idopyranoside and methyl 4,6-O-benzylidene-β-d-idopyranoside, which were synthesized from d-galactose. The efficiency of the idopyranoside-based crown compounds synthesized was investigated in asymmetric phase transfer reactions. In liquid-liquid biphasic reactions the highest enantioselectivity was 81% ee, while in solid-liquid phase systems the highest asymmetric induction was 67% ee. It was observed that the enantiodiscrimination was strongly dependent on the configuration of the anomeric center, on the side arm of the nitrogen, and on the structure of the substrate. [ABSTRACT FROM AUTHOR]

This review presents all currently known macroheterocyclic compounds that include a bispidine (3,7-diazabicyclo[3.3.1]nonane) fragment in their structure. A classification of bispidine-containing macroheterocycles, which is based on the ring size and the nature of bispidinic nitrogen atoms, is suggested. Synthetic approaches to the studied compounds are classified and considered. The features of the crystal structures and solution behavior of bispidine macroheterocycles are analyzed. Prospects for the development of these organic receptors are proposed. [ABSTRACT FROM AUTHOR]

Rotaxanes, known as supramolecular compounds, are expected to find applications in functional materials due to their high degree of freedom. However, their synthesis requires multistep reactions, and there is a demand for more convenient methods to synthesize rotaxane materials. In this study, we aimed to investigate a simpler method for synthesizing highly functional rotaxane materials and explore the diversity of molecular designs. To achieve this, we successfully synthesized a host–guest conjugated compound that incorporates both crown ether as the host unit and secondary ammonium salts as the guest unit within the same molecule. Subsequently, the metathesis reaction of these compounds, which construct [c2]daisy-chain rotaxanes, enabled the one-pot synthesis of a topological polymer called "poly([c2]daisy-chain rotaxane)" with a pseudo-stopper. This methodology achieves the stabilization and polymerization of rotaxanes simultaneously, contributing to the easy materialization of rotaxanes. Furthermore, the thiol-ene reaction achieved the extension of the distance between rotaxane units and provided a useful approach to diversify the design of functional materials with rotaxane structures. [ABSTRACT FROM AUTHOR]

Positively charged metal–ammonia complexes are known to host peripheral, diffuse electrons around their molecular skeleton. The resulting neutral species form materials known as expanded or liquid metals. Alkali, alkaline earth, and transition metals have been investigated previously in experimental and theoretical studies of both the gas and condensed phase. This work is the first ab initio exploration of an f-block metal–ammonia complex. The ground and excited states are calculated for Th0–3+ complexes with ammonia, crown ethers, and aza-crown ethers. For Th3+ complexes, the one valence electron Th populates the metal's 6d or 7f orbitals. For Th0–2+, the additional electrons prefer occupation of the outer s- and p-type orbitals of the complex, except Th(NH3)10, which uniquely places all four electrons in outer orbitals of the complex. Although thorium coordinates up to ten ammonia ligands, octa-coordinated complexes are more stable. Crown ether complexes have a similar electronic spectrum to ammonia complexes, but excitations of electrons in the outer orbitals of the complex are higher in energy. Aza-crown ethers disfavor the orbitals perpendicular to the crowns, attributed to the N-H bonds pointing along the plane of the crowns. [ABSTRACT FROM AUTHOR]

Regulation of the sodium cations level in the case of renal failure diseases is a very challenging task for clinicians, and new pollutant extractors based on nanomaterials are emerging as potential treatments. In this work, we report different strategies for the chemical functionalization of biocompatible large pore mesoporous silica, denoted stellate mesoporous silica (STMS), with chelating ligands able to selectively capture sodium. We address efficient methods to covalently graft highly chelating macrocycles onto STMS NPs such as crown ethers (CE) and cryptands (C221) through complementary carbodiimidation reactions. Regarding sodium capture in water, C221 cryptand-grafted STMS showed better capture efficiency than CE-STMS due to higher sodium atom chelation in the cryptand cage (Na+ coverage of 15.5% vs. 3.7%). The sodium selectivity was hence tested with C221 cryptand-grafted STMS in a multi-element aqueous solution (metallic cations with the same concentration) and in a solution mimicking peritoneal dialysis solution. Results obtained indicate that C221 cryptand-grafted STMS are relevant nanomaterials to extract sodium cations in such media and allow us to regulate their levels. [ABSTRACT FROM AUTHOR]

In terms of isotopic technologies, it is essential to be able to produce materials with an enriched isotopic abundance (i.e., a compound isotopic labelled with 2H, 13C, 6Li, 18O or 37Cl), which is one that differs from natural abundance. The isotopic-labelled compounds can be used to study different natural processes (like compounds labelled with 2H, 13C, or 18O), or they can be used to produce other isotopes as in the case of 6Li, which can be used to produce 3H, or to produce LiH that acts like a protection shield against fast neutrons. At the same time, 7Li isotope can be used as a pH controller in nuclear reactors. The COLEX process, which is currently the only technology available to produce 6Li at industrial scale, has environmental drawbacks due to generation of Hg waste and vapours. Therefore, there is a need for new eco-friendly technologies for separation of 6Li. The separation factor of 6Li/7Li with chemical extraction methods in two liquid phases using crown ethers is comparable to that of COLEX method, but has the disadvantages of low distribution coefficient of Li and the loss of crown ethers during the extraction. Electrochemical separation of lithium isotopes through the difference in migration rates between 6Li and 7Li is one of the green and promising alternatives for the separation of lithium isotopes, but this methodology requires complicated experimental setup and optimisation. Displacement chromatography methods like ion exchange in different experimental configurations have been also applied to enrich 6Li with promising results. Besides separation methods, there is also a need for development of new analysis methods (ICP-MS, MC-ICP-MS, TIMS) for reliable determination of Li isotope ratios upon enrichment. Considering all the above-mentioned facts, this paper will try to emphasize the current trends in separation techniques of lithium isotopes by exposing all the chemical separation and spectrometric analysis methods, and highlighting their advantages and disadvantages. [ABSTRACT FROM AUTHOR]

Here, we present a ditopic ion-pair sensor, B1, containing the BODIPY reporter unit in its structure, which is shown to be able—thanks to the presence of two heterogeneous binding domains—to interact with anions in an enhanced manner in the presence of cations. This enables it to interact with salts even in 99% aqueous solutions, making B1 a good candidate in terms of visual salt detection in the aquatic environment. Receptor B1's ability to extract and release salt was applied in the transport of potassium chloride through a bulk liquid membrane. Working with a concentration of B1 in the organic phase and with the presence of a specific salt in an aqueous solution, an inverted transport experiment was also demonstrated. By varying the type and the amount of the anions added to B1, we were able to develop diverse optical responses, including a unique four-step ON1-OFF-ON2-ON3 output. [ABSTRACT FROM AUTHOR]

trans-3,4-Dihydroxyselenolane (DHS), a water-soluble cyclic selenide, exhibits selenoenzyme-like unique redox activities through reversible oxidation to the corresponding selenoxide. Previously, we demonstrated that DHS can be applied as an antioxidant against lipid peroxidation and a radioprotector by means of adequate modifications of the two hydroxy (OH) groups. Herein, we synthesized new DHS derivatives with a crown-ether ring fused to the OH groups (DHS-crown-n (n = 4 to 7), 1–4) and investigated their behaviors of complex formation with various alkali metal salts. According to the X-ray structure analysis, it was found that the two oxygen atoms of DHS change the directions from diaxial to diequatorial by complexation. The similar conformational transition was also observed in solution NMR experiments. The 1H NMR titration in CD3OD further confirmed that DHS-crown-6 (3) forms stable 1:1 complexes with KI, RbCl and CsCl, while it forms a 2:1 complex with KBPh4. The results suggested that the 1:1 complex (3·MX) exchanges the metal ion with metal-free 3 through the formation of the 2:1 complex. The redox catalytic activity of 3 was evaluated using a selenoenzyme model reaction between H2O2 and dithiothreitol. The activity was significantly reduced in the presence of KCl due to the complex formation. Thus, the redox catalytic activity of DHS could be controlled by the conformational transition induced by coordination to an alkali metal ion. [ABSTRACT FROM AUTHOR]

Unnatural amino acids with enhanced properties, such as increased complexing ability and luminescence, are considered to be highly attractive building blocks for bioinspired frameworks, such as probes for biomolecule dynamics, sensitive fluorescent chemosensors, and peptides for molecular imaging, among others. Therefore, a novel series of highly emissive heterocyclic alanines bearing a benzo[d]oxazolyl unit functionalized with different heterocyclic π-spacers and (aza)crown ether moieties was synthesized. The new compounds were completely characterized using the usual spectroscopic techniques and evaluated as fluorimetric chemosensors in acetonitrile and aqueous mixtures in the presence of various alkaline, alkaline-earth, and transition metal ions. The different crown ether binding moieties as well as the electronic nature of the π-bridge allowed for fine tuning of the sensory properties of these unnatural amino acids towards Pd2+ and Fe3+, as seen by spectrofluorimetric titrations. [ABSTRACT FROM AUTHOR]

We review crown ether-facilitated nucleophilic reactions using metal salts, presenting the studies using kinetic measurements and quantum chemical methods. We focus on the mechanistic features, specifically on the contact ion-pair (CIP) mechanism of metal salts for nucleophilic processes promoted by crown ethers and derivatives. Experimental verification of the CIP form of the metal salt CsF complexed with [18-Crown-6] by H-NMR spectroscopy is described. The use of chiral crown ethers and derivatives for enantioselective nucleophilic processes is also discussed. [ABSTRACT FROM AUTHOR]

Estradiol (E2) plays an important role in the progression of diseases such as breast cancer and endometriosis. Inhibition of 17β-hydroxysteroid dehydrogenase type 1 (17β-HSD1), the enzyme that catalyzes the last step in the biosynthesis of the estrogenic hormone E2, therefore constitutes an interesting approach for the treatment of these two estrogen-dependent diseases. In order to obtain new inhibitors of 17β-HSD1, the impact of a m-carbamoylphenyloxy group at position three of an estrane nucleus was evaluated by preparing three derivatives of estrone (E1) and E2 using a microwave-assisted synthesis of diaryl ethers. Their inhibitory activity was addressed on two cell lines (T-47D and Z-12) representative of breast cancer and endometriosis, respectively, but unlike T-47D cells, Z-12 cells were not found suitable for testing potential 17β-HSD1 inhibitors. Thus, the addition of the m-carbamoylphenyl group at C3 of E1 (compound 5) did not increase the inhibition of E1 to E2 transformation by 17β-HSD1 present in T-47D cells (IC50 = 0.31 and 0.21 μM for 5 and E1, respectively), and this negative effect was more obvious for E2 derivatives 6 and 10 (IC50 = 1.2 and 1.3 μM, respectively). Molecular docking allowed us to identify key interactions with 17β-HSD1 and to highlight these new inhibitors' actions through an opposite orientation than natural enzyme substrate E1′s classical one. Furthermore, molecular modeling experiments explain the better inhibitory activity of E1-ether derivative 5, as opposed to the E2-ether derivatives 6 and 10. Finally, when tested on T-47D and Z-12 cells, compounds 5, 6 and 10 did not stimulate the proliferation of these two estrogen-dependent cell lines. In fact, they reduced it. [ABSTRACT FROM AUTHOR]

Luminescent probes have wide applications in biological system analysis and environmental science. Here, one novel luminescent dinuclear europium compound with a crown ether analogous ligand was synthesized through a solvent–thermal reaction. Through transformation, upon the addition of Al3+ ions to the N,N′-dimethyl formamide solution of the europium compound, the luminescent intensity of the characteristic emission of Eu3+ decreased, and a new emission peak appeared at 346 nm and increased rapidly. The luminescent investigation indicated that it could act as a highly sensitive and selective luminescent probe for Al3+ ions. Moreover, mass spectrometry and single-crystal X-ray diffraction confirmed the formation of a new more stable trinuclear aluminium compound during the sensing process. [ABSTRACT FROM AUTHOR]

Nitrobenzofurazan derivatives are well known for their fluorescence, whilst crown ethers are known for their complexing capacity toward cationic species. In this study, we present the synthesis and structural characterization of a new derivative containing both nitrobenzofurazan moieties and a crown ether core. The new compound was obtained from dibenzo-18-crown-6 ether, which was first nitrated, reduced to the corresponding amine, and subsequently derivatized with NBD. Structural analyses performed by IR, NMR, UV–Vis, and MS confirmed its structure and physico-chemical behavior toward the complexation of alkaline cations. [ABSTRACT FROM AUTHOR]

Fluorescent molecules absorb photons of specific wavelengths and emit a longer wavelength photon within nanoseconds. Recently, fluorescent materials have been widely used in the life and material sciences. Fluorescently labelled heterocyclic compounds are useful in bioanalytical applications, including in vivo imaging, high throughput screening, diagnostics, and light-emitting diodes. These compounds have various therapeutic properties, including antifungal, antitumor, antimalarial, anti-inflammatory, and analgesic activities. Different neutral fluorescent markers containing nitrogen heterocycles (quinolones, azafluoranthenes, pyrazoloquinolines, etc.) have several electrochemical, biological, and nonlinear optic applications. Photodynamic therapy (PDT), which destroys tumors and keeps normal tissues safe, works in the presence of molecular oxygen with light and a photosensitizing drugs (dye) to obtain a therapeutic effect. These compounds can potentially be effective templates for producing devices used in biological research. Blending crown compounds with fluorescent residues to create sensors has been frequently investigated. Florescent heterocyclic compounds (crown ether) increase metal solubility in non-aqueous fluids, broadening the application window. Fluorescent supramolecular polymers have widespread use in fluorescent materials, fluorescence probing, data storage, bio-imaging, drug administration, reproduction, biocatalysis, and cancer treatment. The employment of fluorophores, including organic chromophores and crown ethers, which have high selectivity, sensitivity, and stability constants, opens up new avenues for research. Fluorescent organic compounds are gaining importance in the biological world daily because of their diverse functionality with remarkable structural features and positive properties in the fields of medicine, photochemistry, and spectroscopy. [ABSTRACT FROM AUTHOR]

Antimicrobial resistance (AMR) is a major concern for the survival of mankind. COVID-19 accelerated another silent pandemic of AMR through the uncontrolled use of antibiotics and biocides. New generations of antimicrobial agents are needed to combat resistant pathogens. Crown ethers can be used as models for drug action because they are similar to antibiotics. Iodine is a well-known microbicide but is characterized by instability and short-term effectivity. Iodine can be stabilized in the form of polyiodides that have a rich topology but are dependent on their immediate surroundings. In addition, copper has been successfully used since the beginning of history as a biocidal agent. We, therefore, combined iodine and copper with the highly selective crown ether 1,4,7,10-tetraoxacyclododecane (12-crown-4). The morphology and composition of the new pentaiodide [Cu(12-crown-4)2]I5 was investigated. Its antimicrobial activities against a selection of 10 pathogens were studied. It was found that C. albicans WDCM 00054 is highly susceptible to [Cu(12-crown-4)2]I5. Additionally, the compound has good to intermediate antimicrobial activity against Gram-positive and Gram-negative bacilli. The chain-like pentaiodide structure is V-shaped and consists of iodine molecules with very short covalent bonds connected to triiodides by halogen bonding. The single crystal structure is arranged across the lattice fringes in the form of ribbons or honeycombs. The susceptibility of microorganisms towards polyiodides depends on polyiodide bonding patterns with halogen-, covalent-, and non-covalent bonding. [ABSTRACT FROM AUTHOR]

Two non-toxic potassium compounds, 1 and 2, with a commercial oximate ligand have been prepared and fully spectroscopically characterized. Their activity as catalysts for the ring-opening polymerization (ROP) process of LLA has been studied, showing that they are extremely active and able to polymerize the monomer in a few minutes. For derivative 2, the presence of a crown ether in the potassium coordination sphere affects the nuclearity of the compound and consequently its solubility, with both aspects having an influence in the polymerization process. Detailed studies of the polymerization mechanism have been performed, and an unusual anionic mechanism was observed in absence of a co-initiator. Indeed, the monomer deprotonation generates a lactide enolate, which initiates the polymerization propagation. On the contrary, when a 1:1 ratio of cat:BnOH is used, a mixture of mechanisms is observed, the anionic mechanism and the activated monomer one, while from a cat:BnOH ratio of 1:2 and over, only the activated monomer mechanism is observed. [ABSTRACT FROM AUTHOR]

In the present review, works on the classes of chelating extractants for metals, compounds with several amide and carboxyl groups, azomethines, oximes, macrocyclic compounds (crown ethers and calixarenes), phenanthroline derivatives, and others are systematized. This review focuses on the efficiency and selectivity of the extractants in the recovery of metals from industrial wastewater, soil, spent raw materials, and the separation of metal mixtures. As a result of this study, it was found that over the past seven years, the largest number of works has been devoted to the extraction of heavy metals with amino acids (16 articles), azomethines and oximes (12 articles), lanthanids with amide compounds (15 articles), lanthanides and actinides with phenanthroline derivatives (7 articles), and noble metals with calixarenes (4 articles). Analysis of the literature showed that amino acids are especially effective for extracting heavy metals from the soil; thiodiglycolamides and aminocalixarenes for extracting noble metals from industrial waste; amide compounds, azomethines, oximes, and phenanthroline derivatives for extracting actinides; amide compounds for extracting lanthanides; crown ethers for extracting radioactive strontium, rhenium and technetium. The most studied parameters of extraction processes in the reviewed articles were the distribution ratios and separation factors. Based on the reviewed articles, it follows that chelate polydentate compounds are more efficient compounds for the extraction of metals from secondary resources compared to monodentate compounds. [ABSTRACT FROM AUTHOR]

Due to the chemical and biological relevance of amino acids, efficient methods for the recognition and separation of their enantiomers are highly sought after. Chiral receptors based on extended molecular scaffolds are typically employed for this purpose. These receptors are often effective only in specific environments and towards a narrow scope of amino acid guests. Recently we reported a simple, glucose-based macrocycle capable of enantioselective binding of a broad range of amino acid methyl esters in water. Herein we demonstrate that the same receptor can be used for chiral recognition of amino acid esters in organic solvents. We show that the binding affinity and selectivity of the receptor are highly dependent on the coordinating strength of the solvent. An in-depth analysis of the receptor's conformation and its interactions with amino acid methyl esters allowed us to propose a binding mode of amino acids to the receptor in CDCl3. The binding modes in CDCl3 and D2O were then compared, highlighting the main interactions responsible for binding affinity and selectivity in each solvent. We envision that the insight provided by this study will facilitate the development of further amino acid receptors based on monosaccharides with improved binding affinities and both enantio- as well as chemoselectivities. [ABSTRACT FROM AUTHOR]

K[(18-crown-6)-bis(tetrahydrofuran)anthracenide] was independently prepared by three groups, and its structure described by two of them. The third structure description, though listed in the Cambridge Crystallographic Data Centre (CSD) collection, contains no space group or atomic coordinates, but the cell constants leave no doubt that it is the same species as the two others, which were reported in 2006 and 2016. The compound crystallizes in space group P21, with Z′ = 2.0 at T = 123 K and R = 4.91% (I), and at 100 K and R = 4.44% (II); both impressive results in their individual quality and agreement, despite differences in experimental methods and the temperature of data collection. A more detailed examination of the published data for (I) and (II) reveals that the correct description for this very unusual, and thus far unique substance, is that it contains a radical anion crystallizing as a kryptoracemate rather than as a simple example of a Sohncke space group with Z′ = 2.0. The anthracenide anions present in (I) and (II) are virtually identical; in contrast, the internal pair of cationic species differ from one another in the dissymmetry of the flexible tetrahydrofuran ligands, having significantly different internal and external torsional angles. The two THF molecules attached to the K(crown-ether) cations are not centrosymmetrically related, and this is what makes this portion of the asymmetric unit responsible for the crystal being a kryptoracemate. Our presentation will be based on the more fully documented sample (II), unless specifically stated. [ABSTRACT FROM AUTHOR]

Cyclic organic compounds with several ether linkages in their structure are of much concern in our daily life applications. Crown ethers (CEs) are generally heterocyclic and extremely versatile compounds exhibiting higher binding affinity. In recent years, due to their unique structure, crown ethers are widely used in drug delivery, solvent extraction, cosmetics manufacturing, material studies, catalysis, separation, and organic synthesis. Beyond their conventional place in chemistry, this review article summarizes the synthesis, biological, and potential pharmacological activities of CEs. We have emphasized the prospects of CEs as anticancer, anti-inflammatory, antibacterial, and antifungal agents and have explored their amyloid genesis inhibitory activity, electrochemical, and potential metric sensing properties. The central feature of these compounds is their ability to form selective and stable complexes with various organic and inorganic cations. Therefore, CEs can be used in gas chromatography as the stationary phase and are also valuable for cation chromatographic to determine and separate alkali and alkaline-earth cations. [ABSTRACT FROM AUTHOR]

Thallium (Tl) is released into the environment, where is present at very low levels, from both natural and anthropogenic sources. Tl is considered as one of the most toxic heavy metals; it is a non-essential metal, present in low concentrations in humans. Tl toxicity causes dermatological and gastrointestinal diseases and disorders of the nervous system, and may even result in death. Many isotopes of Tl exist, with different uses. One of the isotopes of this metal (201Tl) is used in cardiovascular scintigraphy and for the diagnosis of malignant tumors such as breast or lung cancer and osteosarcoma bone cancer. Many Tl compounds are tasteless, colorless, and odorless. Due to these characteristics and their high toxicity, they have been used as poisons in suicides and murders for criminal purposes, as well as instances of accidental poisoning. Impaired glutathione metabolism, oxidative stress, and disruption of potassium-regulated homeostasis may play a role in the mechanism of Tl toxicity. Solanum nigrum L. and Callitriche cophocarpa have been suggested as promising agents for the phytoremediation of Tl. In addition, macrocyclic compounds such as crown ethers (18-crown-6) are good candidates to absorb Tl from wastewater. Through this review, we present an update to general information about the uses and toxicity of Tl. Furthermore, the attention is focused on detoxification therapies. [ABSTRACT FROM AUTHOR]

Newsupramolecular structureswere designed in thiswork using large-sized polyoxometalates (POMs) and crown-ether-based supramolecular cations selected as building blocks. Two novel supramolecular inorganic-organic hybrids [(3-F-4-MeAnis)([18]crown-6)]2[SMo12O40]•CH3CN (1) and [(4-IAnis)([18]crown-6)]3[PMo12O40]•4CH3CN (2) (3-F-4-MeAnis = 3-fluoro-4-methylanilinium and 4-IAnis = 4-iodoanilinium) were synthesized. Crystals 1 and 2 have been characterized by infrared spectroscopy (IR) and elemental analysis (EA). Based on X-ray diffraction analysis, Crystals 1 and 2 were constructed through noncovalent bonding interactions and belong to different space groups due to the difference of the building blocks used. Supramolecular cations formed due to strong N-H···O hydrogen bonding interactions between the six oxygen atoms of [18]crown-6 molecules and nitrogen atoms of anilinium derivatives. Crystal 1 has two different supramolecular cations with an anti-paralleled arrangement that forms a dimer throughweak hydrogen bonding interactions between adjacent [18]crown-6 molecules. Crystal 2 has three independent supramolecular cations that fill large spaces between the [PMo12O40] polyoxoanions forming a rhombus-shape packing arrangement in the ac plane. Crystals 1 and 2 are unstable at room temperature. [ABSTRACT FROM AUTHOR]

Small-molecule fluorescent probes play a myriad of important roles in chemical sensing. Many such systems incorporating a receptor component designed to recognise and bind a specific analyte, and a reporter or transducer component which signals the binding event with a change in fluorescence output have been developed. Fluorescent probes use a variety of mechanisms to transmit the binding event to the reporter unit, including photoinduced electron transfer (PET), charge transfer (CT), Förster resonance energy transfer (FRET), excimer formation, and aggregation induced emission (AIE) or aggregation caused quenching (ACQ). These systems respond to a wide array of potential analytes including protons, metal cations, anions, carbohydrates, and other biomolecules. This review surveys important new fluorescence-based probes for these and other analytes that have been reported over the past five years, focusing on the most widely exploited macrocyclic recognition components, those based on cyclam, calixarenes, cyclodextrins and crown ethers; other macrocyclic and non-macrocyclic receptors are also discussed. [ABSTRACT FROM AUTHOR]

Mismatched complexes of the alkali metals cations Li+ and Na+ were synthesized from 1,2-disila[18]crown-6 (1 and 2) and of K+ from 1,2,4,5-tetrasila[18]crown-6 (4). In these alkali metal complexes, not all crown ether O atoms participate in the coordination, which depicts the coordination ability of the C-, Si/C-, and Si-bonded O atoms. Furthermore, the inverse case--the coordination of the large Ba2+ ion by the relatively small ligand 1,2-disila[15]crown-5--was investigated, yielding the dinuclear complex 5. This structure represents a first outlook on sandwich complexes based on hybrid crown ethers. [ABSTRACT FROM AUTHOR]

Catalysis fulfills the promise that high-yielding chemical transformations will require little energy and produce no toxic waste. This message is carried by the study of the evolution of molecular catalysis of some of the most important reactions in organic chemistry. After reviewing the conceptual underpinnings of catalysis, we discuss the applications of different catalysts according to the mechanism of the reactions that they catalyze, including acyl group transfers, nucleophilic additions and substitutions, and C-C bond forming reactions that employ umpolung by nucleophilic additions to C=O and C=C double bonds. We highlight the utility of a broad range of organocatalysts other than compounds based on proline, the cinchona alkaloids and binaphthyls, which have been abundantly reviewed elsewhere. The focus is on organocatalysts, although a few examples employing metal complexes and enzymes are also included due to their significance. Classical Bronsted acids have evolved into electrophilic hands, the fingers of which are hydrogen donors (like enzymes) or other electrophilic moieties. Classical Lewis base catalysts have evolved into tridimensional, chiral nucleophiles that are N- (e.g., tertiary amines), P- (e.g., tertiary phosphines) and C-nucleophiles (e.g., N-heterocyclic carbenes). Many efficient organocatalysts bear electrophilic and nucleophilic moieties that interact simultaneously or not with both the electrophilic and nucleophilic reactants. A detailed understanding of the reaction mechanisms permits the design of better catalysts. Their construction represents a molecular science in itself, suggesting that sooner or later chemists will not only imitate Nature but be able to catalyze a much wider range of reactions with high chemo-, regio-, stereo- and enantioselectivity. Man-made organocatalysts are much smaller, cheaper and more stable than enzymes. [ABSTRACT FROM AUTHOR]

An alternative method for generating arynes from ortho-silylaryl triflates using cesium carbonate and 18-crown-6 is reported. The method was efficiently applied to a variety of reactions between several arynes and arynophiles. We also demonstrated that the efficiency of aryne generation is significantly affected by the alkali metal countercation of the carbonate. [ABSTRACT FROM AUTHOR]

The lock-and-key concept is discussed with respect to necessary extensions. Formation of supramolecular complexes depends not only, and often not even primarily on an optimal geometric fit between host and guest. Induced fit and allosteric interactions have long been known as important modifications. Different binding mechanisms, the medium used and pH effects can exert a major influence on the affinity. Stereoelectronic effects due to lone pair orientation can lead to variation of binding constants by orders of magnitude. Hydrophobic interactions due to high-energy water inside cavities modify the mechanical lock-and-key picture. That optimal affinities are observed if the cavity is only partially filled by the ligand can be in conflict with the lock-and-key principle. In crystals other forces than those between host and guest often dominate, leading to differences between solid state and solution structures. This is exemplified in particular with calixarene complexes, which by X-ray analysis more often than other hosts show guest molecules outside their cavity. In view of this the particular problems with the identification of weak interactions in crystals is discussed. [ABSTRACT FROM AUTHOR]

The reactions of newly designed lithiated triamidoamines Li 3 L R ( R = iPr, Pen, and Cy 2 ) with VCl 3 (THF) 3 under N 2 yielded dinitrogen-divanadium complexes with a μ-N 2 between vanadium atoms [{V( L R )} 2 (μ-N 2 )] ( R = iPr ( 1 ) and Pen ( 2 )) for the former two, while not dinitrogen-divanadium complexes but a mononuclear vanadium complex with a vacant site, [V( L Cy2 )] ( R = Cy 2 ( 3 )), were obtained for the third ligand. The V-N N2 and N-N distances were 1.7655(18) and 1.219(4) Å for 1 and 1.7935(14) and 1.226(3) Å for 2 , respectively. The ν( 14 N- 14 N) stretching vibrations of 1 and 2 , as measured using resonance Raman spectroscopy, were detected at 1436 and 1412 cm -1 , respectively. Complex 3 reacted with potassium metal in the presence of 18-crown-6-ether under N 2 to give a hetero-dinuclear vanadium complex with μ-N 2 between vanadium and potassium, [VK( L Cy2 )(μ-N 2 )(18-crown-6)] ( 4 ). The N-N distance and ν( 14 N- 14 N) stretching for 4 were 1.152(3) Å and 1818 cm -1 , respectively, suggesting that 4 is more activated than complexes 1 and 2 . The complexes 1 , 2 , 3 , and 4 reacted with HOTf and K[C 10 H 8 ] to give NH 3 and N 2 H 4 . The yields of NH 3 and N 2 H 4 (per V atom) were 47 and 11% for 1 , 38 and 16% for 2 , 77 and 7% for 3 , and 80 and 5% for 4 , respectively, and 3 and 4 , which have a ligand L Cy2 , showed higher reactivity than 1 and 2 .

The 2,4-Diacetylphloroglucinol (2,4-DAPG) and phenazine (PCA)-producing Pseudomonas inhibit wheat pathogens' development, but the relationship between communities of pathogens and genotypes of these bacteria has been little studied. Relationships between wheat crown fungi associated with the presence of 2,4-DAPG and PCA-producing pseudomonads were evaluated in four commercial wheat crops located in the La Araucanía and Los Lagos Regions of Chile, during two crops seasons. Portions of the base of the first internode of the culm collected during the grain-filling stage were cultured in an artificial medium for fungal isolation, while roots of the same wheat plants and from plants collected previous harvest, and also used to assess yield and plant height, were used for the detection of 2,4-DAPG and PCA-producing Pseudomonas spp. using PCR with specific primers. Genera Phaeosphaeria, Fusarium, Rhizoctonia, and Microdochium were repeatedly isolated (52.6%, 22.1%, 7.8%, and 4.9%, respectively) and the genetic composition of 2,4-DAPG and PCA-producing Pseudomonas spp. varied between fields and sampling periods. Genetic groups A, B, D, K, L, and P associated with the phlD gene were detected. The presence of 2,4-DAPG-producing bacteria benefited crop health, relating their existence with increasing yield and plant height, and the reduction in the incidence and severity of disease caused by pathogenic microorganisms on the first internode of wheat culms. [ABSTRACT FROM AUTHOR]

It seems interesting to adopt the idea of dance in the context of the arrangement of molecular blocks in the building of molecular systems. Just as various dances can create various feelings, the nature and arrangement of molecular blocks in the generated molecular system can induce different properties. We consider obtaining such "dancing" systems in which the still little-known azulene moieties are involved. The dark blue nonbenzenoid aromatic azulene has one less axis of symmetry relative to the two axes of its isomer, i.e., the fully benzenoid naphthalene, acquiring valuable properties as a result that can be used successfully in technical applications. In a dancing system, the azulene moieties can be connected directly, or a more or less complex spacer can be inserted between them. Several azulene moieties can form a linear oligomer or a polymer and the involvement of azulene moieties in nonlinear molecules, such as crown ethers, calixarenes, azuliporphyrins, or azulenophane, is a relatively new and intensely studied topic. Some aspects are covered in this review, which are mainly related to obtaining the mentioned azulene compounds and less to their characterization or physico-chemical properties. [ABSTRACT FROM AUTHOR]

Due to unique chelating and macrocyclic effects, crown ether compounds exhibit wide application prospects. They could be introduced into amphiphilic copolymers to provide new trigger mode for drug delivery. In this work, new amphiphilic random polymers of poly(lipoic acid-methacrylate-co-poly(ethylene glycol) methyl ether methacrylate-co-N-isopropylacrylamide-co-benzo-18-crown-6-methacrylamide (abbrev. PLENB) containing a crown ether ring and disulphide bond were synthesized via RAFT polymerization. Using the solvent evaporation method, the PLENB micelles were formed and then used to load substances, such as doxorubicin hydrochloride (DOX) and gold nanoparticles. The results showed that PLENB exhibited a variety of lowest critical solution temperature (LCST) in response to the presence of different ions, such as K+, Na+ and Mg2+. In particular, the addition of 150 mM K+ increased the LCST of PLENB from 31 to 37 °C and induced the release of DOX from the PLENB@DOX assemblies with a release rate of 99.84% within 12 h under 37 °C. However, Na+ and Mg2+ ions could not initiate the same response. Furthermore, K+ ions drove the disassembly of gold aggregates from the PLENB-SH@Au assemblies to achieve the transport of Au NPs, which is helpful to construct a K+-triggered carrier system. [ABSTRACT FROM AUTHOR]

Heavy metal poisoning is a rare health condition caused by the accumulation of toxic metal ions in the soft tissues of the human body that can be life threatening if left untreated. In the case of severe intoxications, hemodialysis is the most effective method for a rapid clearance of the metal ions from the bloodstream, therefore, the development of hemodialysis membranes with superior metal ions retention ability is of great research interest. In the present study, synthetic polysulfone membranes were modified with reduced graphene oxide functionalized with crown ether, an organic compound with high metal ions complexation capacity. The physico-chemical characteristics of the composite membranes were determined by FT-IR, Raman, XPS and SEM analysis while their efficiency in retaining metal ions was evaluated via ICP-MS analysis. The obtained results showed that the thermal stability of reduced graphene oxide was improved after functionalization with crown ether and that the presence of the carbonaceous filler influenced the membranes morphology in terms of pore dimensions and membrane thickness. Moreover, the ability of Cu2+ ions retention from synthetic feed solution was up to three times higher in the case of the composite membranes compared to the neat ones. [ABSTRACT FROM AUTHOR]

The analysis of the ratios of entropy and enthalpy characteristics and their contributions to the change in the Gibbs energy of intermolecular interactions of crown ethers and cyclodextrins with amino acids is carried out. Two different types of macrocycles were chosen for examination: crown ethers with a hydrophilic interior and cyclodextrins with a hydrophobic inner cavity and a hydrophilic exterior. The thermodynamics of complex formation of crown ethers and cyclodextrins with amino acids in water and aqueous-organic solvents of variable composition was examined. The contributions of the entropy solvation of complexes of 18-crown-6 with glycine, alanine, phenylalanine to the change in the entropy of complexation in water-ethanol and water-dimethyl sulfoxide solvents was calculated and analyzed. It was found that the ratios of the entropy and enthalpy solvation of the reagents for these systems have similar trends when moving from water to aqueous-organic mixtures. The relationship between the thermodynamic characteristics and structural features of the complexation processes between cyclodextrins and amino acids has been established. The thermodynamic enthalpy–entropy compensation effect was revealed, and its features for complexation of cyclodextrins and 18-crown-6 were considered. It was concluded that, based on the thermodynamic parameters of molecular complexation, one could judge the mode of the formation of complexes, the main driving forces of the interactions, and the degree of desolvation. [ABSTRACT FROM AUTHOR]

A great number of biologically active compounds contain at least one amine function. Appropriate selectivity can only be accomplished in a few cases upon the substitution of these groups, thus functionalization of amines generally results in a mixture of them. The separation of these derivatives with very similar characteristics can only be performed on a preparative scale or by applying pre-optimized HPLC methods. A tris(pyridino)-crown ether was designed and synthetized for overcoming these limitations at a molecular level. It is demonstrated, that this selector molecule is able to distinguish protonated primary, secondary and tertiary amines by the formation of reversible complexes with different stabilities. This degree of substitution-specific molecular recognition of amines opens the door to develop separation processes primarily focusing on the purification of biologically active compounds in a nanomolar scale.

The number of synthetic methods enabling the preparation of ammonium-based rotaxanes has increased very rapidly in the past ten years. The challenge in the synthesis of rotaxanes results from the rather weak interactions between the ammonium-containing rod and the crown ether macrocycle in the pseudorotaxane structure that rely mostly on O·H hydrogen bonds. Indeed, no strong base or polar solvent that could break up H-bonding can be used during the formation of rotaxanes because the two components will separate as two distinct entities. Moreover, most of the reactions have to be performed at room temperature to favor the formation of pseudorotaxane in solution. These non-trivial prerequisites have been taken into account to develop efficient reaction conditions for the preparation of rotaxanes and those are described in detail along this review. [ABSTRACT FROM AUTHOR]