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A new 15‐membered‐macrocyclic molecular entity, oxa‐TriQuinoline (o‐TQ), was designed and synthesized. In o‐TQ, three oxygen atoms were joined onto three quinoline units at the 2‐ and 8‐positions in a head‐to‐tail fashion by three‐fold SNAr reactions, giving rise to the characteristic N3O3 aza‐oxa‐crown architecture. o‐TQ can serve as a new tridentate nitrogen ligand to capture a CuI cation and adopt a bowl shape, before supramolecular complexation with corannulene and [12]cycloparaphenylene (CPP) occurs through π–π and CH–π interactions. In the presence of the CuI cation, the non‐emissive o‐TQ becomes a highly emissive material in the solid state, whereby the emission wavelengths depend on the ancillary ligand on the CuI cation. The o‐TQ/CuI complex is able to promote carbene catalysis to provide a range of enamines with a gem‐difluorinated terminus. [ABSTRACT FROM AUTHOR]

Modified crown ethers are fundamental building blocks in supramolecular chemistry, with applications in phase transfer catalysis, metal extraction, smart materials, and molecular machines. Here we report on a one‐pot highly chemo‐ and regioselective photocatalytic fluoroalkylation protocol for the mono‐functionalization of benzo substituted crown ethers. For this important class of macrocycles, the method described here represents one of the few late‐stage functionalization procedures that is both high yielding and scalable. Because of its breadth of scope and substrate tolerance, the devised approach can be applied to a wide range of aromatic crown ethers (18 examples, up to 99 % yield), including those engaged in mechanically interlocked molecules. [ABSTRACT FROM AUTHOR]

Multicomponent reactions (MCR) are power tools in modern organic synthesis. These reactions have many advantages over single component reactions, including saving time and chemicals. Moreover, compounds with complicated structures can be synthesized based on simple substrates and one‐step reactions, without the tedious work of separating intermediate compounds. Taking full advantage of this tool, over the past 10 years we have synthesized novel crown compounds with the successful introduction of different bioactive moieties into molecules. As part of our ongoing research, this study reports on the synthesis of a new type of crown ether based on a three component reaction of an aldehyde, a ketone, and ammonium acetate in dry solvent, at specific temperature. The structure of the new compounds was identified using physical‐chemical methods of analysis including IR, 1H & 13C NMR, HRMS and single‐X ray diffraction. The effects of the newly synthesized azacrown ethers on the enzyme α‐glucosidase were then explored and they were shown to be potential candidates in the search for new antidiabetic drugs. Among five tested compounds, two compounds are active again the enzyme α‐glucosidase and expressed IC50 values of 407.17±9.01 μM and 345.90±6.75 μM. Molecular docking studies were also performed to investigate the binding mode of the synthetic compounds to α‐glucosidase. Finally, ADMET parameters were assessed to investigate the relationship between structure and biological activities. [ABSTRACT FROM AUTHOR]

Under atmospheric pressure and solvent-free conditions, β-hydroxyethyl alkyl sulfides (RSCH2CH2OH) were synthesized using crown ether as phase transfer agent, inorganic acid potassium salts (KA) as catalyst, ethylene carbonate (EC) and mercaptan (RSH) as raw materials. The solid/liquid phase transfer effect of 18-crown-6 on the β-hydroxyethylation of RSH catalyzed by KA and the effect of EC/RSH molar ratio on the selectivity of RSCH2CH2OH were systematically investigated. The results showed that 18-crown-6 itself had no catalytic activity. Compared with KA alone, the synergistic catalysis of KA with 18-crown-6 could significantly accelerate the reaction rate and the conversion of RSH was greatly increased. In the case of 0.3 mol% K2CO3 in combination with 0.6 mol% 18-crown-6 catalyzed β-hydroxyethylation of n-octyl mercaptan, the conversion of n-C8H17SH reached 100%, whereas the selectivity of n-C8H17SCH2CH2OH gradually decreased from 97.6 to 90.3% with increasing the molar ratio of EC/n-C8H17SH from 1.02 to 1.50, and the by-products were vinyl n-octyl sulfide and ethylene glycol. Under solvent-free conditions, the phase interface restriction between the KA catalyst and the liquid-phase reactants can be effectively broken after the addition of 18-crown-6, thereby enhancing the β-hydroxyethylation of RSH reaction efficiently. [ABSTRACT FROM AUTHOR]

The use of "fuel" compounds to drive chemical systems out of equilibrium is currently of interest because of the potential for temporally controlled, responsive behavior. We have recently shown that transiently formed crown ethers exhibit counterintuitive templation effects when generated in the presence of alkali metal cations: "matched" cations, such as K+ with an 18‐crown‐6 analogue, suppress the formation of the macrocycles (negative templation). In this work, we describe two macrocyclic diacids that, on treatment with carbodiimides, give transient macrobicyclic cages analogous to polyether cages. Negative templation effects are observed for the smaller cage when generated in the presence of K+ and Na+, but there is a weak, but reproducible, positive templation effect in the presence of Li+. The larger cage behaves similarly in the presence of Li+, K+, Rb+, and Cs+, but differently with Na+, which appears to bind to both the cage and the initial macrocycle. [ABSTRACT FROM AUTHOR]

Enantioenriched, highly functionalized cyclopropane derivatives were prepared by a simple and green approach using monosaccharide‐based chiral crown ethers as phase transfer catalysts. The Michael‐initiated ring closure (MIRC) reactions of diethyl bromomalonate with 2‐cyano‐3‐phenylacrylate took place with complete diastereoselectivity in the presence of chiral lariat ethers derived from carbohydrates and enantioselectivity up to 87 % ee was achieved. Among the catalysts tested, the monoaza‐15‐crown‐5 lariat ether having a methyl β‐d‐glucopyranoside unit and a 2‐(3,4‐dimethoxyphenyl)ethyl group on the nitrogen generated the highest asymmetric induction (87 % ee). In the reactions of analogous 2‐cyano‐3‐arylacrylates, enantioselectivity was in the range of 8–91 % ee. [ABSTRACT FROM AUTHOR]

Among various directions in the science of photoactive organic compounds, the design, creation, and study of multichromophore supramolecular devices and machines attract special attention, since this way can open up new approaches to the construction of complex hierarchical "smart" materials. [ABSTRACT FROM AUTHOR]

A series of subporphyrin‐based fluorescent probes bearing 1‐aza‐15‐crown‐5 or 1‐aza‐18‐crown‐6 moieties at the meso or axial positions were prepared by Pd‐catalyzed Buchwald‐Hartwig amination reaction of the corresponding bromosubporphyrins. Both types of aza‐crown‐ether‐incorporated subporphyrins were fluorescent in solution and exhibited cation‐dependent absorption and fluorescence changes. In fluorescence titration experiments, opposite responses were observed for the two types of subporphyrins. Namely, fluorescence quenching occurred for the meso‐substituted subporphyrins while fluorescence enhancement was observed for the axially‐substituted subporphyrins. These results demonstrate the advantage of subporphyrins being viable to serve as turn‐off‐type or turn‐on‐type fluorescence probes, depending upon substitution pattern. [ABSTRACT FROM AUTHOR]

We describe here a controlled approach to C1‐symmetrical cyclotriveratrylenes (CTVs). In this approach dimers are synthesized through Barluenga boronic coupling (BBC) and after borylation, the last aromatic ring is introduced by a second BBC. After functional transformations of the trimers, the CTVs are formed using intramolecular SEAr. [ABSTRACT FROM AUTHOR]

Mild methods to cleave the carbon-oxygen (C−O) bond in alkyl ethers could simplify chemical syntheses through the elaboration of these robust, readily available precursors. Here we report that dibromoboranes react with alkyl ethers in the presence of a nickel catalyst and zinc reductant to insert boron into the C−O bond. Subsequent reactivity can effect oxygen-to-nitrogen substitution or one-carbon homologation of cyclic ethers and more broadly streamline preparation of bioactive compounds. Mechanistic studies reveal a cleavage-then-rebound pathway via zinc/nickel tandem catalysis. [ABSTRACT FROM AUTHOR]

We present the synthesis and characterization of (15‐crown‐5)BiI3 (1) and (15‐crown‐5)BiI3 ⋅ 0.5TIE (2), a halogen bonded adduct with tetraiodoethylene (TIE), a typical halogen bond donor. Single crystal structure analysis of 2 suggests a halogen bonding interaction between crown ether complex and TIE. The two compounds' thermal, optical and vibrational properties are investigated in comparison, with differences pointing towards a notable interaction between the two building blocks in 2. Our results show that crown ether complexes of main group metal halides can be employed as halogen bond acceptors for the synthesis of new supramolecular aggregates. [ABSTRACT FROM AUTHOR]

Novel flat crown ether molecules have been characterized in silico using density functional theory. Monomer units of Si2C3 with a planar tetracoordinate carbon (ptC) atom have been used as building blocks. Alkali (Li+, Na+, K+, Rb+, and Cs+) and alkaline‐earth (Be2+, Mg2+, Ca2+, Sr2+, and Ba2+) metal ions, and uranyl (UO22+) ion selective complexes have also been theoretically identified. The high symmetry and higher structural rigidity of the host molecules may likely impart higher selectivity in chelation. The potential energy surface of the parent elemental composition, Si2C3H2, has been investigated using coupled‐cluster (CC) approximation. The molecule with a ptC atom within the latter is a low‐lying isomer lying 12.41 kcal mol−1 above the global minimum at the CCSD(T)/cc‐pVTZ level. The crown ether molecules identified here could theoretically be considered the derivatives of the ptC atom isomer. Theoretical binding energies (ΔE; 0 K) and thermally corrected Gibbs free energies (ΔG; 298.15 K) for crown ether molecules have been computed to gauge their binding affinities. [ABSTRACT FROM AUTHOR]

Among the various directions of the science of photoactive organic compounds, the design, creation, and study of photoactive supramolecular devices and machines are attracting special attention, since in this way it is possible to discover new approaches to construct complex hierarchical "smart" materials. [ABSTRACT FROM AUTHOR]

The uranyl cation, (U(VI)O2)2+, has previously demonstrated photocatalytic reactivity in organic solutions, which results in the formation of uranyl peroxide species. Past studies indicated that the phototransformation process typically ends with the formation of uranyl peroxide solid phases. In the current study, we explore the transformation of uranyl nitrate crown ether complexes, (18‐crown‐6)[UO2(NO3)2(H2O)2] ⋅ 2 H2O (1 a), (18‐crown‐6)[UO2(NO3)2(H2O)2] (1 b), and (18‐crown‐6) [K(18‐crown‐6)] [(UO2)2(OH)2(NO3)4(H2O)4] (2) in the presence of ethanol to create a uranyl peroxide intermediate phase, (18‐crown‐6)[(UO2)2(O2)(NO3)2(H2O)4] (3), followed by a second alteration to a black solid (4). These compounds were structurally evaluated using both single‐crystal and powder X‐ray diffraction and then further characterized using Raman, NMR, and XPS spectroscopy. The initial transformation from the yellow uranyl nitrate phase (1 a, 1 b, and 2) to the uranyl peroxide (3) follow previously reported mechanisms. The second transformation to the black phase (4) is likely due to additional degradation of the 18‐crown‐6 molecule as a result of hydrogen abstraction and ring‐opening. In addition, we discuss the nature of confinement effects to impact the hydrogen abstraction process and the possibility that nitrate anions in the system may synergistically enhance the degradation process and lead to the formation of 4. [ABSTRACT FROM AUTHOR]

A series of catenanes have been synthesized through olefin metathesis from a BMP32C10-based cryptand and paraquat guests attached with two terminal alkenes. Distribution of the catenane products can be significantly affected by the linkage length on the paraquat guests. In the presence of BMP32C10-based cryptand, the paraquat salt with a long linkage facilitates intramolecular olefin metathesis to release a [2]catenane as the sole catenation product, while the use of a paraquat salt with a shorter linkage leads to the simultaneous generation of [2]-, [3]-, and [4]-catenanes. [ABSTRACT FROM AUTHOR]

Herein we report that an imine‐based iron complex decorated with crown‐ether moieties self‐assembles in CH3CN solution from three building blocks (namely Fe(CH3CN)2(OTf)2, 2‐picolylamine and aldehyde 6a) added in the proper molar ratio (1:2:2, respectively). Aldehyde 6a, endowed with a benzocrown‐ether receptor, can be prepared in two steps from commercial materials with high yields (79 %) and no need of chromatographic separations. The self‐assembled complex is highly stable in CH3CN solution. The complex has been tested as catalyst for the oxidation of aromatic compounds endowed with primary ammonium anchoring group with H2O2. An unexpected yet moderate selectivity for remote meta over ortho hydroxylation was obtained, which is mainly due to the steric hindrance of the catalyst. [ABSTRACT FROM AUTHOR]

Crown ethers have been known since the middle of the 20th century as metal chelating agents with numerous applications. For example, amino acids functionalized with crown ethers have been used to create artificial ion channels. However, only a few of those crown amino acids are known, all of which contain exclusively oxygen as heteroatoms in the crown ether moiety. Alternative structures may be desirable to explore new biological or pharmaceutical applications. Hence, we aim to expand the scope of available crown ether amino acids ‐ in particular those with heteroatoms other than oxygen. Herein we describe the synthesis of three previously unknown amino acids bearing a crown ether moiety. We use two distinct synthetic routes to avoid the use of hazardous reagents. Two of these three amino acids bear sulfur atoms in the crown ether, while the third contains a nitrogen atom. [ABSTRACT FROM AUTHOR]

This work presents the synthesis of six new phase-transfer organocatalysts in which the squaramide unit is directly linked to the nitrogen atom of an aza-crown ether. Four chiral skeletons, namely hydroquinine, quinine, cinchonine (cinchonas), and α-d-glucopyranoside were responsible for the asymmetric construction of an all-carbon quaternary stereogenic center in α-alkylation and Michael addition reactions of malonic esters. We investigated the effects of these different chiral units and that of crown ethers with different sizes on catalytic activity and enantioselectivity. During extensive parameter investigations, both conventional and emerging green solvents were screened, providing valuable α,α-disubstituted malonic ester derivatives with excellent yields (up to 98%).

A stepwise self‐assembly protocol has been used to synthesize [2]‐ and [3]catenanes. Firstly, binuclear Cp*Rh/Ir‐directed (Cp*=pentamethylcyclopentadienyl) pseudorotaxanes were prepared through self‐assembly, driven by donor–acceptor interactions between electron‐deficient naphthalenediimide (NDI) units and an electron‐rich crown ether. Subsequently, the pre‐organized pseudorotaxanes were applied as tectons for self‐assembly of [2]‐ and [3]catenanes by combination with very simple linkers. The structures of the catenanes were confirmed by NMR spectroscopy, ESI mass spectrometry, single‐crystal X‐ray diffraction analysis, and elemental analysis. [ABSTRACT FROM AUTHOR]

Cyanide is extremely hazardous to living organisms and the environment. Owing to its wide range of applications and high toxicity, the development of functional materials for cyanide detection and sensing is highly desirable. Host–guest complexation between bis(p‐phenylene)‐34‐crown‐10 H and N‐methylacridinium salt G remarkably decreases the detection limit for cyanide anions compared with that of the guest itself. The [2]pseudorotaxane selectively recognizes the cyanide anion with high optical sensitivity as a result of the nucleophilic addition of the cyanide anion at the 9‐position of G. The host–guest complexation is further incorporated into supramolecular materials for the visual detection of cyanide anions, especially the detection of cellular cyanide excretion with a detection limit of 0.6 μm. This supramolecular method provides an extremely distinct strategy for the visual detection of cyanide anions. [ABSTRACT FROM AUTHOR]

Over the years, we developed highly selective fluorescent probes for K+ in water, which show K+‐induced fluorescence intensity enhancements, lifetime changes, or a ratiometric behavior at two emission wavelengths (cf. Scheme 1, K1–K4). In this paper, we introduce selective fluorescent probes for Na+ in water, which also show Na+ induced signal changes, which are analyzed by diverse fluorescence techniques. Initially, we synthesized the fluorescent probes 2, 4, 5, 6 and 10 for a fluorescence analysis by intensity enhancements at one wavelength by varying the Na+ responsive ionophore unit and the fluorophore moiety to adjust different Kd values for an intra‐ or extracellular Na+ analysis. Thus, we found that 2, 4 and 5 are Na+ selective fluorescent tools, which are able to measure physiologically important Na+ levels at wavelengths higher than 500 nm. Secondly, we developed the fluorescent probes 7 and 8 to analyze precise Na+ levels by fluorescence lifetime changes. Herein, only 8 (Kd=106 mm) is a capable fluorescent tool to measure Na+ levels in blood samples by lifetime changes. Finally, the fluorescent probe 9 was designed to show a Na+ induced ratiometric fluorescence behavior at two emission wavelengths. As desired, 9 (Kd=78 mm) showed a ratiometric fluorescence response towards Na+ ions and is a suitable tool to measure physiologically relevant Na+ levels by the intensity change of two emission wavelengths at 404 nm and 492 nm. [ABSTRACT FROM AUTHOR]

As demand grows for lithium, its recovery from geothermal brines provides an attractive alternative to slow mining. One promising extraction method uses crown ethers as extractants in supercritical carbon dioxide with cation exchangers to facilitate extraction from brine. Molecular dynamics modeling is used to understand the mechanism of binding between lithium (or sodium) and combinations of 14‐crown‐4 ethers and cation exchangers, and the predictive capability of computational modeling to test lithium selectivity is established for four combinations of crown ethers [methylene‐14‐crown‐4 (M14C4) and a fluorinated 14‐crown‐4 (F14C4)] and cation exchangers [di(2‐ethyl‐hexyl)phosphoric acid (HDEHP) and tetraethylammonium perfluoro‐1‐octanesulfonate (TPFOS)]. Binding free energies (given in kcal mol−1) of lithium and sodium, respectively, to crown ether–cation exchangers are 85 and 71 for M14C4–HDEHP, 90 and 71 for F14C4–HDEHP, 93 and 80 for M14C4–TPFOS, and 104 and 93 for F14C4–TPFOS. Good agreement is found between computational predictions and supercritical carbon dioxide extraction experiments at 60 °C and 250 bar. Binding free energy gives a suitable metric to describe extraction efficiency. Differences in the binding free energies of sodium and lithium to crown ethers determine the extraction selectivity. Fluorine groups are found to exert a positive influence to optimize extraction efficiency. Of the systems studied, F14C4 with TPFOS offers the most selective and efficient extraction system. [ABSTRACT FROM AUTHOR]

Herein, we report the systematic evaluation of the BODIPY series functionalized with pseudo‐crown ethers against metal cations and assessment of their potential as novel off‐on fluorescent probes selective for aluminum(III) cations. [ABSTRACT FROM AUTHOR]

A new family of 2D coordination polymers based on 3d‐4f 15‐metallacrown‐5 (MC) units were designed and characterized. The connection of the 15‐metallacrown‐5 subunits by the coordination of CuII and ligand led to the formation of 2D network of metallacrowns. Analysis of the magnetic properties of these coordination polymers reveals that the GdIII (1), TbIII (2), and DyIII (3) complexes exhibit slow magnetic relaxation and under 1000 Oe dc field, and the DyIII (3) complex exhibits single‐molecule magnet behavior. [ABSTRACT FROM AUTHOR]

Here is reported the synthesis of a new molecular shuttle: it consists of a dibenzo‐24‐crown‐8 (DB24C8) that surrounds a molecular axle containing an ammonium group and a newly considered Weinreb amide as stations. At the protonated state the DB24C8 is localized around the best ammonium station, while deprotonation‐carbamoylation of the ammonium triggers the shuttling of the macrocycle around the Weinreb amide site. Further post‐interlocking modification of the [2]rotaxane was attempted through the cleavage of the Weinreb amide bond using a Grignard reagent. While the non‐interlocked molecular axle was cleaved after a short time in mild conditions, the Weinreb amide bond remained unaltered in the [2]rotaxane species over time, even in the presence of a larger amount of Grignard and at a higher temperature, highlighting the protection shield of the macrocycle around the encircled axle. [ABSTRACT FROM AUTHOR]

The first highly enantioselective arylogous Michael reaction (AMR) of 3‐unsubstituted phthalides has been described. This phase‐transfer methodology, which uses catalytic amounts of KOH/18‐crown‐6 catalyst in mesitylene in the presence of N,O‐bis(trimethylsilyl)acetamide (BSA), gives access to a broad range of 3‐monosubstituted phthalides with high levels of syn diastereoselectivity and good yields, starting from 3‐unsubstituted derivatives and diverse α,β‐unsaturated carbonyl compounds. The reaction also applies to unactivated 3‐alkyl phthalides to afford 3,3‐dialkyl derivatives. A plausible mechanism has been suggested. DFT analysis of possible transition states gives a rationale of the high syn diastereoselectivity observed and its correlation with the solvent's dielectric constant. [ABSTRACT FROM AUTHOR]

The molecular structure of the complex of ammonia borane (AB) with acyclic ether tetraglyme Me(OCH2CH2)4OMe (1), 1·(AB)2 was determined by single‐crystal X‐ray structure analysis for the first time. The crystal structure features two AB molecules, bonded by dihydrogen bonds, per one tetraglyme unit. The intermolecular BH···HN distances of 1.94 Å are shorter than those in the solid ammonia borane (2.02–2.32 Å). A comparison of the hydrogen and dihydrogen bonds in 1·(AB)2 and in the complexes of AB with crown‐ethers (CE) was carried out. The complex formation with both the CE and the acyclic polyether 1 activates the B–H bond in AB via N–H···O hydrogen bonds and therefore increases the reducing activity of AB. Supposedly, the structure of 1·(AB)2 is related to the initial steps of the AB activation in a polyether solution. The effect of the substituents on the complexation of the substituted derivatives of 1 comes down to a structural adjustment minimizing steric repulsion. Computations reveal that the complexation of diastereomeric disubstituted glymes with AB leads to the formation of diastereomeric complexes that differ noticeably in stability. This is a prerequisite for inducing stereoselectivity, which makes such complexes attractive for potential synthetic applications. [ABSTRACT FROM AUTHOR]

Linear Fisher classification functions, canonical linear discriminant functions, and trees (rules) for classification and prediction of the stability of sodium (18-crown-6Na+) and potassium coronates (18-crown-6K+) from the properties of aqueous-organic solvents (water—methanol, water—propan-2-ol, and water—acetonitrile) have been obtained basing on multivariate exploratory analysis. The proposed approach to prediction of the coronates stability has been verified using independent experimental data on the stability constants of sodium and potassium coronates in water—dioxane and water—acetone mixtures. The constructed classification functions and rules have possessed high predictive potential. [ABSTRACT FROM AUTHOR]

The introduction and development of neutral macrocyclic hosts capable of complexing ions within their pre-organized cavity, has been of utmost importance in supramolecular chemistry. Their ability to form stable organic-soluble metal-macrocycle complexes opened up the way to their application in phase-transfer catalysis (PTC) as a viable alternative to quaternary onium salts. In particular, their conformationally rigid preorganized backbone, accommodating organic substrates in defined orientations, promotes highly efficient stereoselective reactions. This short review summarizes the applications of neutral macrocyclic hosts in stereoselective PTC, highlighting the difference and possible complementarity with quaternary ammonium salts. 1 Introduction 2 Crown Ethers and Related Coronands 2.1 Enantioselective PTC with Chiral Macrocyclic Coronands 2.2 Enantioselective PTC Reactions Catalyzed by Chiral Quaternary Ammonium Salts with Achiral Crown Ether Co-catalysts 3 Cyclic Peptoids 4 Miscellaneous Chiral Macrocyclic Hosts 5 Summary and Outlook. [ABSTRACT FROM AUTHOR]

Benzo-15-crown-5 ether derivatives of 1-hydroxy-9,10-anthraquinone-9-imine bearing a substituted benzoylamino group, NHCO(p-C6H4NO2) or NHCOC6F5, in position 2 were synthesized by a photochemical method. The structure of the fluorine-containing compound was determined by single-crystal X-ray diffraction. Both synthesized dyes, as well as their analogue without substituents on the benzoyl ring, are capable of binding Sr2+ and Ba2+ to form sandwich-type 2:1 (ligand:metal) complexes. In MeCN, these complexes exhibit higher stability constants (K2:1) than the corresponding 1:1 complexes (K1:1). The para-substitution of the benzoyl ring with a nitro group leads to a significant increase in both the K2:1 constant and the K2:1/K1:1 ratio. The fluorination of the benzoyl ring insignificantly affects the stability of sandwich complexes. Density functional theory calculations showed that this is related to steric interactions in the benzoylamino group. The calculated structures of the dyes and their sandwich complexes with Ba2+ are consistent with the 2D NOESY data. [ABSTRACT FROM AUTHOR]

A new strategy for the construction of crystalline supermolecular rotors is presented. We obtained the hybrid crystal [(18‐Crown‐6)K]3[NH2(CH3)2]2(Bi2Cl11)·2DMF (1) by introducing the flexible 18‐crown‐6 into the inorganic [Bi2Cl11]5– binuclear anion cluster lattice through the KCl (screw) to connect the organic molecule with inorganic component, in which the coordinated DMF (N,N‐Dimethylformamide) molecule functions as an polar rotator with monocycle shape, revealed by its significant dielectric relaxation above 358 K. The hybrid solid also exhibits dielectric phase transformation and conductivity switch around 413 K, the response mechanism was investigated by variable‐temperature X‐ray single crystal and powder diffraction as well as DSC, TG techniques. The analysis results reveal that the dielectric anomaly and conductivity switch are triggered by the losing of DMF molecules which is fixed with the [(18‐Crown‐6)K]+. And the ionic conductivity reach to 1.10 × 10–3 S cm–1 at 473 K. The interesting molecular structure and molecular thermal motion feature are promising application in the field of artificial molecular machine and dielectric switch. [ABSTRACT FROM AUTHOR]

Abstract: This work presents two molecular fluorescent probes 1 and 2 for the selective determination of physiologically relevant K+ levels in water based on a highly K+/Na+ selective building block, the o‐(2‐methoxyethoxy)phenylaza‐18‐crown‐6 lariat ether unit. Fluorescent probe 1 showed a high K+‐induced fluorescence enhancement (FE) by a factor of 7.7 of the anthracenic emission and a dissociation constant (Kd) value of 38 m m in water. Further, for 2+K+, we observed a dual emission behavior at 405 and 505 nm. K+ increases the fluorescence intensity of 2 at 405 nm by a factor of approximately 4.6 and K+ decreases the fluorescence intensity at 505 nm by a factor of about 4.8. Fluorescent probe 2+K+ exhibited a Kd value of approximately 8 m m in Na+‐free solutions and in combined K+/Na+ solution a similar Kd value of about 9 m m was found, reflecting the high K+/Na+ selectivity of 2 in water. Therefore, 2 is a promising fluorescent tool to measure ratiometrically and selectively physiologically relevant K+ levels. [ABSTRACT FROM AUTHOR]

Abstract: We developed novel size‐complementary molecular and macromolecular rotaxanes using a 2,6‐dimethylphenyl terminal group as the axle‐end‐cap group in dibenzo‐24‐crown‐8‐ether (DB24C8)‐based rotaxanes, where the 2,6‐dimethylphenyl group was found to be less bulky than the 3,5‐dimethylphenyl group. A series of molecular and macromolecular [2]rotaxanes that bear a 2,6‐dimethylphenyl group as the axle‐end‐cap were synthesized using unsubstituted and fluorine‐substituted DB24C8. Base‐induced decomposition into their constituent components confirmed the occurrence of deslipping, which supports the size‐complementarity of these rotaxanes. The deslipping rate was independent of the axle length but dependent on the DB24C8 substituents. A kinetic study indicated the rate‐determining step was that in which the wheel is getting over the end‐cap group, and deslipping proceeded via a hopping‐over mechanism. Finally, the present deslipping behavior was applied to a stimulus‐degradable polymer as an example for the versatile utility of this concept in the context of stimulus‐responsive materials. [ABSTRACT FROM AUTHOR]

Abstract: The chemistry of aqueous salt solutions is rich with ambiguities, especially in stimuli‐responsive supramolecular systems. Rational use of ion specificity to design supramolecular responsive materials, however, remains a challenging task. In this work, a low‐molecular‐weight supramolecular system was developed that was used to reveal the underlying systematic relationship between ions, water, and solutes. By utilizing these water‐attenuated supramolecular forces (with Ka only ca. 30  m−1), an alternative concept for fabricating an aqueous responsive system in ionic medium was demonstrated. This work not only provides mechanistic insight into the underdeveloped role of topology in ion specificity upon noncharged polar surfaces, but also demonstrates the feasibility of utilizing weak supramolecular approaches to control the thermoresponsiveness. [ABSTRACT FROM AUTHOR]

Abstract: In this contribution, we present new insights and a critical discussion in the optical detection of saxitoxin using fluorophores with crown ethers. Fluorescence enhancement is caused by the reduction of photoinduced electron transfer upon complexation with the analyte. Our attempts to improve this detection method neither did yield a functioning sensor nor were the attempts to reproduce published data in this area successful. Due to the fact that only low concentrations of saxitoxin are available, multiple surrogates were investigated at high concentrations. However, no turn on response was observed. Moreover, a fluorescent decomposition product of saxitoxin that forms under UV light was discovered which was in our opinion misinterpreted as a sensor response by previous publications.Graphical abstract: [ABSTRACT FROM AUTHOR]

Reactions of mixtures between Ag(NO3) and alkaline earth nitrates with the bifunctional ligand 2,2'-{1,2-phenylenebis[ oxyacetyl(N,N-diethylthiourea)]}, H2Lcat, give {2}-metallacoronates of the composition {M ⊂ [Ag2(Lcat)2]} (M = Ca2+, Sr2+, or Ba2+). The trinuclear assemblies show further aggregation in the solid state, where they establish dimeric or polymeric entities stabilized by weak Ag···N(amide) interactions. Discrete {2}- metallacryptate species {M ⊂ [Hg2(Lcat)3]} (M = Sr2+ or Ba2+) result from similar reactions between H2Lcat, Hg(NO3)2, and strontium nitrate or barium nitrate. The complexes contain HgII ions in an uncommon distorted trigonal-bipyramidal environment with a S3O2 coordination sphere. The central alkaline earth ions are mainly bonded by the six carbonyl oxygen atoms of the three organic ligands. [ABSTRACT FROM AUTHOR]

The syntheses and structures of four new bis(pyrazol-1-yl)acetate- or bis(3,5-dimethylpyrazol-1-yl)acetate-based bisligand nickel(II) complexes [Ni(bdmpzmp)2] (1), [Ni-(bdmpzpen)2] (2), [Ni(bdmpza)2] (3), and [Ni(bpza)2] (4) are described. The results of single crystal structure determinations reveal for all four complexes κ³-coordination of the scorpionate ligands. The sterically hindered bis(3,5-di-tert-butyl-pyrazol-1-yl)acetateto (bdtbpza) ligand allows the synthesis of the nickel(II) chlorido complex [Ni(bdtbpza)Cl] (5). Furthermore, controlled formation of a novel trinuclear linear complex [Ni(bdmpza)2{Ni(acac)(bdmpza)}2] (6) [bdmpza = bis(3,5-dimethylpyrazol-1-yl)acetate] by a self-assembling reaction and alkali metal-mediated template syntheses of [Na{Ni(acac)-(bdmpza)}3]NO3 (7), [Na{Ni(acac)(bdmpza)}3]I (8) and [Li{Ni-(acac)(bdmpza)}3]NO3 (9) are reported. ESI MS allowed a detailed characterization in solution and is supported by X-ray structure analysis. Compounds 7, 8 and 9 exhibit [12-MC-3] metallacrown structures with a sixfold coordinated alkali metal ion in the center. The magnetic properties are studied by SQUID. Crystallographic data reveal broken symmetry in the solid state for all three [12-MC-3] metallacoronates 7, 8 and 9. The linear structure of [Ni(bdmpza)2{Ni(acac)(bdmpza)}2] (6) (length ≈ 2 nm) obtained through synthesis without template, as well as the molecular structure of the [12-MC-3] metallacoronates 7, 8 and 9 (Ø ≈ 1.3 nm) are at the nanoscale. [ABSTRACT FROM AUTHOR]

Abstract: A family of dimeric LnIII[12‐MCGa(III)N(shi)‐4] metallacrowns (MCs) (LnIII=Pr, Nd, Sm, Eu, Gd, Tb, Dy, Ho, Er, Tm, and Yb) was synthesized using the isophthalate group (ip2−) as a linker. The [LnGa4]2 complexes exhibit remarkable photophysical properties, with large molar absorptivities of ≈4×104  m−1 cm−1, high quantum yields and long luminescence lifetimes with values of (i) 31.2(2)% and 1.410(1) ms, respectively for the visible‐emitting [TbGa4]2 complex and (ii) 2.43(6)% and 30.5(1) μs for the near‐infrared (NIR) emitting [YbGa4]2 in the solid state. The NIR emission was obtained not only from Yb, Nd, and Er complexes but also from the less frequently observed emitters such as Pr and Ho. In addition, emission in both visible and NIR domains could be detected for Dy and Sm MCs. ESI‐MS and UV/Vis data revealed that the complexes are highly stable in dimethylsulfoxide (DMSO) solution with the 1H‐ and COSY‐NMR spectra of the diamagnetic [YGa4]2 analogue providing evidence for long‐term solution stability. This new approach allows one to construct a basis for highly luminescent MCs that may be further modified to be adapted for applications such as optical imaging. [ABSTRACT FROM AUTHOR]

The appropriate choice of the host molecules with well-defined optical activity (S-H/R-H) helps in the differentiation between two secondary ammonium ion-derivative guest molecules with different optical activities (R-G/S-G) based on the fluorescence resonance energy transfer (FRET)-based luminescence responses. Crown ether-based host molecules with opposite chiral configurations (R-H, S-H) have been derived from 1,1′-bi-2-naphthol (BINOL) derivatives that have axially chiral biaryl centers. These chiral crown ethers form host–guest complexes (i.e., [2]pseudorotaxanes) with chiral secondary ammonium ion derivatives (R-G, S-G). NMR spectroscopic studies show that the complexes are in a dynamic equilibrium in solution. Results of the 1H NMR and fluorescence spectroscopic studies indicate a head-on orientation of the host and guest in the [2]pseudorotaxanes. The difference in the efficiency in the FRET-based responses between anthracene and the BINOL derivatives allow efficient chiral discrimination of the guests. Isothermal titration calorimetry and NMR investigations reveal that inclusion complexes between hosts and guests of the same chirality (R-H⋅R-G, S-H⋅S-G) are more stable relative to those of opposite chirality (R-H⋅S-G, S-H⋅R-G). However, FRET-based energy-transfer efficiency is higher for R-H⋅S-G and S-H⋅R-G complexes. NMR spectroscopic studies show that the relative orientation of the guest in the host cavity is significantly different when the host binds a guest of the same or opposite chirality; furthermore, the latter is more favorable for FRET, thus enabling discrimination between enantiomers. Interestingly, chiral discrimination of guest ions could also be achieved by using silica surfaces modified with chiral host molecules. [ABSTRACT FROM AUTHOR]

A series of crown ether-based dinuclear bis(alkynyl)-bridged gold(I) isocyanide complexes has been designed, synthesized, and characterized. The intramolecular Au ···Au interactions of these complexes are used to bind potassium ions. Most of the bis(crown ether)-containing gold(I) complexes are found to obey the 1:1 binding mode towards K+. Upon addition of K+ ions, the sandwich complex of crown ether can be formed, which brings the two gold(I) centers into close proximity, resulting in the switching on of the Au ···Au interaction. The influence of the length of the bridging ligands between the two AuI centers has also been studied. Apart from the potassium ion-induced intramolecular assembly, intermolecular Au ···Au interactions of the crown ether-containing dinuclear gold(I) complexes have also been demonstrated by varying the solvent composition. [ABSTRACT FROM AUTHOR]

A new p-azacrown[N,S,O]-styryl modified boron-phenylpyrrin compound, synchronously possessing a diethylamino receptor (C-BPP-A), has been designed and synthesized. Systematic optical studies show that C-BPP-A displays a distinct two-step fluorescence response to an increasing quantity of Cu2+, commensurate with the sequential transition from free ligand (L) to 1:1 (ML) and 2:1 (M2L) complexes: added Cu2+ ions (0-1 equiv.) are first coordinated with the p-azacrown[N,S,O] moiety of C-BPP-A, forming the 1:1 Cu2+-C-BPP-A complex and leading to significant enhancement of the fluorescence at 621 nm. Subsequently, the N atom of the diethylamino group from the Cu2+-C-BPP-A complex coordinates with the additional Cu2+ (1-2 equiv.), forming an M2L type of complex, which induces the fluorescence quenching of the 1:1 Cu2+-C-BPP-A complex at 621 nm. Meanwhile, successively increasing the added Cu2+, from 0 to 1 equiv. and from 1 to 2 equiv., also induces a gradual/fast increase, respectively, in the two-absorption-band ratio I530/ I603, accompanied by an obvious change in the solution color from blue to violet to purple. These results show C-BPP-A to be the first highly sensitive colorimetric, OFF-ON-OFF fluorescence, and absorption-ratiometric sensor for quantitative Cu2+ detection. [ABSTRACT FROM AUTHOR]

A new p-azacrown[N,S,O]-styryl modified boron-phenylpyrrin compound, synchronously possessing a diethylamino receptor (C-BPP-A), has been designed and synthesized. Systematic optical studies show that C-BPP-A displays a distinct two-step fluorescence response to an increasing quantity of Cu2+, commensurate with the sequential transition from free ligand (L) to 1:1 (ML) and 2:1 (M2L) complexes: added Cu2+ ions (0-1 equiv.) are first coordinated with the p-azacrown[N,S,O] moiety of C-BPP-A, forming the 1:1 Cu2+-C-BPP-A complex and leading to significant enhancement of the fluorescence at 621 nm. Subsequently, the N atom of the diethylamino group from the Cu2+-C-BPP-A complex coordinates with the additional Cu2+ (1-2 equiv.), forming an M2L type of complex, which induces the fluorescence quenching of the 1:1 Cu2+-C-BPP-A complex at 621 nm. Meanwhile, successively increasing the added Cu2+, from 0 to 1 equiv. and from 1 to 2 equiv., also induces a gradual/fast increase, respectively, in the two-absorption-band ratio I530/ I603, accompanied by an obvious change in the solution color from blue to violet to purple. These results show C-BPP-A to be the first highly sensitive colorimetric, OFF-ON-OFF fluorescence, and absorption-ratiometric sensor for quantitative Cu2+ detection. [ABSTRACT FROM AUTHOR]

Herein, we report the synthesis, X-ray crystal structure and photophysical studies of six new 8-amino-BODIPY derivatives containing crown or azo-crown ether moieties. The influence of steric hindrance, caused by the crown ether, on the planarity of the BODIPY core and its relationship with the fluorescent properties has been established. 1H NMR spectroscopic studies were undertaken to clarify the changes in fluorescence observed in the presence of ZnII. [ABSTRACT FROM AUTHOR]