Dibenzo-18-crown-6 Research Articles

Synthesis of a pH-Sensitive Hetero[4]Rotaxane Molecular Machine that Combines [c2]Daisy and [2]Rotaxane Arrangements.

The synthesis of a novel pH-sensitive hetero[4]rotaxane molecular machine through a self-sorting strategy is reported. The original tetra-interlocked molecular architecture combines a [c2]daisy chain scaffold linked to two [2]rotaxane units. Actuation of the system through pH variation is possible thanks to the specific interactions of the dibenzo-24-crown-8 (DB24C8) macrocycles for ammonium, anilinium, and triazolium molecular stations. Selective deprotonation of the anilinium moieties triggers shuttling of the unsubstituted DB24C8 along the [2]rotaxane units.

Spectroscopic Study of Charge-Transfer Complexation of Iodine with DB18C6 in Chloroform, Dichloromethane and Their 1:1 Mixture

The charge-transfer complexes of dibenzo-18-crown-6(DB18C6) (L) with iodine, as a typical σ-acceptor, were studied spectrophotometrically in chloroform, dichloromethane and their 1:1 (v/v) mixture at 25.0 ± 0.1 °C. Spectral data, formation constants and the effect of the solvent have been determined. Spectral characteristics and formation constants are discussed in the terms of donor molecular structure and solvent polarity. The stoichiometry of the complexes was established to be 1:1. The formation constants (K CT) of the complexes were determined. The complexes were isolated and characterized by FTIR and 1H-NMR spectroscopy. The observed time dependence of the charge-transfer band and subsequent formation of $$ {\text{I}}_{3}^{ - } $$ in solution were related to the slow transformation of the initial 1:1 L:I2 outer complex to an inner electron donor–acceptor complex, followed by fast reaction of the inner complex with iodine to form a triiodide ion. The pseudo-first-order rate constants for the transformation process were evaluated in different solvent systems.

Assembly of Tetraphenylethene Containing Amine and Crown Ether Units and Aggregation-Induced Emission Properties

Dibenzo-24-crown-8 (DB24C8) and dibenzylammonium (DBA) are always utilized for the construction of supramolecular assemblies. We reported a new kind supramolecular assembly polymer constructed by M1 which was synthesized from tetraphenylethene (TPE) linked with DB24C8 and DBA through click reaction. The chemical structures of all the compounds were fully characterized by H NMR, C NMR, and MS. The H NMR titration showed that the supramolecular assembly was successfully constructed in acidic condition. The fluorescent results showed that the assemblies displayed ratio-metric properties with the changes of aggregation-induced emission and monomer-emission, and fluorescence quenching with addition of Pd.

Cocrystals of ammonium perchlorate with a series of crown ethers: preparation, structures, and properties

Three cocrystals of ammonium perchlorate (AP) with a series of crown ethers have been prepared successfully through the solvent/antisolvent method, including 18-crown-6 (18C6), benzo-18-crown-6 (B18C6), and dibenzo-18-crown-6 (DB18C6). Crystal structures of the three cocrystals characterized by single crystal X-ray diffraction (SXD) reveal that all the cocrystals belong to the monoclinic system, in which the space group of the 1 : 1 cocrystal of AP/18C6 and AP/B18C6 is P21/n, P21/c for the 1 : 1.5 cocrystal of AP/DB18C6. The main intermolecular interactions in the three cocrystals are hydrogen bonds and π–π stacking. Powder X-ray diffraction (PXRD) analyses have been performed to scrutinize the purity of all the crystals. The water contact angles of the three cocrystals were measured to be 23.3° (AP/18C6), 25.4° (AP/B18C6), and 75.4° (AP/DB18C6), increasing with the number of phenyl groups connected to the crown ether, and the surface energy of the three cocrystals are greatly decreased compared to AP. The thermal properties of the cocrystals were investigated by thermogravimetry-differential scanning calorimetry (TG-DSC) and hot-stage optical microscopy (HSOM). The results indicate that the decomposition peak temperatures of the three cocrystals are greatly decreased compared to that of pure AP. In particular, the heat release increases from 475.5 J g−1 of AP to 1304.2 J g−1 for AP/B18C6 and 1488.4 J g−1 for AP/DB18C6. So, through carefully choosing the co-former of AP, cocrystallization can comprehensively tune the hygroscopicity and the thermal decomposition property of AP.

One-pot synthesis of a [c2]daisy-chain-containing hetero[4]rotaxane via a self-sorting strategy.

The construction and efficient synthesis of hetero[n]rotaxanes with high structural complexity are always attractive challenges. Herein, we demonstrate a facile one-pot preparation of a hetero[4]rotaxane, by employing a self-sorting strategy, which contains an interpenetrated dibenzo-24-crown-8 (DB24C8) based [c2]daisy chain structure and is ended with a benzo-21-crown-7 (B21C7) based rotaxane at each side. The key to the design involved encoding the selective threading using a steric hindrance-related "language", where highly selective self-assemblies occurred in a three-component self-sorting process, which included the threading of a benzylalkylammonium into a B21C7 and interpenetrated dimerized formation of a DB24C8 based [c2]daisy chain simultaneously; the precise pre-assembled system resulted in the efficient synthesis of hetero[4]rotaxane with a high-level of structural complexity under the "CuAAC" reaction.

Electrochemical Detection of Dopamine via Assisted Ion Transfer at Nanopipet Electrode Using Cyclic Voltammetry

We present here the detection of dopamine (DA) at nanopipet electrodes with radii of hundreds of nanometers ranging from 160 nm to 480 nm. Dibenzo-18-crown-6 (DB18C6) was employed as an ionophore to facilitate DA transfer, resulting in a half-wave transfer potential, E1/2, DA, of −0.322 (±0.020) V vs. E1/2, TBA. Well-defined steady-state sigmoidal cyclic voltammograms were observed for the transfer of DA. High resolution scanning electron microscopy was used to measure the size and taper angle of the nanopipet electrodes. The detection is linear with concentration of DA ranging from 0.25 mM to 2 mM; calculated diffusion coefficient at nanopipet electrodes with above mentioned sizes is 4.87 (±0.28) × 10−10 m2/s. The effect of the common interferent ascorbic acid on DA detection with nanopipet electrodes was evaluated, where DA detection still shows linear behavior with well-defined sigmoidal CVs with E1/2, DA being −0.328 (±0.029) V vs. E1/2, TBA. The diffusion coefficient for DA transfer in MgCl2 with the presence of 2 mM AA was measured to be 1.93 (±0.59) × 10−10 m2/s on nanoelectrodes with radii from 161 nm to 263 nm, but the physiological concentration of 0.1 mM AA had no effect on DA's diffusion coefficient.

Sensing and characterization of neurotransmitter 2-phenylethylamine based on facilitated ion transfer at solvent polymeric membranes using different electrochemical techniques

Square wave voltammetry (SWV), chronoamperometry and chronocoulometry are exploited to take advantage of their different performance characteristics in the determination, characterization and sensing of the neurotransmitter 2-phenylethylamine (PEA), based on the ion transfer of its protonated form at a solvent polymeric membrane facilitated by dibenzo-18-crown-6 (DB18C6). The general voltammetric features characterizing the PEA+ transfer are established by SWV and the standard ion transfer potential, diffusion coefficient and complexation constant value between PEA+ and DB18C6 are calculated from the SWV recordings. Next, the performance of double pulse chronoamperometry and double pulse chronocoulometry for the determination of PEA based on its facilitated ion transfer is studied. Limits of detection between 3.6 and 9.2μM for chronoamperometry and 1.7 and 2.7 for chronocoulometry are obtained. The influence of common ions on both chronoamperometric and chronocoulometric determination is also considered. The sensitivity ratio values found between foreign cations and PEA+ are 0.05, 0.3 and 0.2 for Na+, K+ and H+, respectively, whereas no interference was observed for Li+. In addition, the electrode is tested as a sensor for monitoring PEA+ concentration using a pulsed-amperometric mode. Interestingly, a simple procedure to extend significantly the range of linear response of quantitative electrochemical techniques based on a previous analysis of chronoamperometric recordings is proposed and successfully tested.

Conductometric study of complexation process between dibenzo-18-crown-6 and K+, Na+, and La3+ cations in some binary mixed non-aqueous solvents

The complexation reactions between K+, Na+, and La3+ cations and the macrocyclic ligand dibenzo-18-crown-6 (DB18C6) were studied in acetionitrile (AN)-dimethylformamide (DMF) binary mixtures. Also, the complexation of K+ and Na+ in 50% ethanol (EtOH)-50% DMF and 50% EtOH-50% AN binary mixtures was studied. The conductivity data show that the stochiometry of all the complexes is 1: 1. A non-linear behavior was observed for the log K f variation vs. composition of binary solvent, which was discussed in terms of heteroselective solvation and solvent-solvent interactions in binary solutions. It was found that the stability order of the complexes changes with composition of the mixed solvents. The stability sequence for AN-DMF (25 and 50 mol % DMF) solutions and pure AN at 25°C is [K(DB18C6)]+ > [Na(DB18C6)]+ > [La(DB18C6)]3+. However, at 75 mol % DMF it changes to [Na(DB18C6)]+ > [K(DB18C6)]+ > [La(DB18C6)]3+. The thermodynamical values (ΔH po , ΔS po ) for these complexation reactions were determined from the temperature dependence of the stability constants. The thermodynamics of the complexation reactions is affected by the nature and composition of the mixed solvents.

One-step synthesis of dimethyl carbonate from carbon dioxide, propylene oxide and methanol over alkali halides promoted by crown ethers

Crown ethers (i.e. [2,4]-dibenzo-18-crown-6 (DBC), 18-crown-6, 15-crown-5 and 12-crown-4) show obvious co-catalytic effect for alkali halides catalyzing one-step synthesis of dimethyl carbonate (DMC) from CO2, propylene oxide and methanol. Especially, the DMC yield of KCl catalyst promoted by DBC can increase by more than five times and reach about 40% under mild reaction conditions (i.e., low mole ratio of methanol and epoxieds: 7:3, low initial pressure of CO2: 1.5 MPa, reaction temperature: 140 °C, time: 10 h). The optimized molar ratio of KCl to DBC is 2: 1. Due to the good complexing ability between DBC and K+, KCl and DBC formed an organometallic complex. Actually, DBC can not only promote the reaction rate and equilibrium of cycloaddition and transesterification reactions, but also prevent side reaction. Importantly, DBC can conveniently achieve high recovery ratio and show excellent reusability.

Sorption of americium(III) from multicomponent solutions with sorbents based on dibenzo-18-crown-6 and its derivatives

A sorption of metals from multicomponent nitric acid solutions that simulate process solutions resulting from reprocessing of spent nuclear fuel was studied. The sorbent used was a highly porous polymeric sorbent impregnated with crown ethers. Chemicals used in the work were dibenzo-18-crown-6 (DB18C6) and its alkyl-substituted derivatives: di-tert-butyldibenzo-18-crown-6 (DTBDB18C6) and diisooctyldibenzo-18-crown-6 (DIODB18C6). Sorption coefficients were determined for all elements. With the aim to study the possibility of isolation of 241Am from multicomponent solutions, separation factors for Am and ballast elements were determined. The possibility of application of sorbents impregnated with crown ethers for recovery of 241Am from multicomponent process solutions was shown.

The idiosyncrasies of (BBIM-alkane)DB30C10 MIMs

In this present study we explore the mechanically interlocked molecules (MIMs) resulting from the combination of the BBIM(bis-benzimidazolium)-alkane systems with DB30C10 (Dibenzo-30-crown-10) in solvent acetonitrile. The (BBIM-alkane)DB30C10 systems chosen for the study are (BBIM)DB30C10, (BBIM-methane)DB30C10, (BBIM-ethane)DB30C10, (BBIM-propane)DB30C10 and (BBIM-butane)DB30C10. 1H NMR, 2D-NMR (COSY and NOESY), Monte Carlo calculations and HRMS have been done on the studied assemblies. Even though (BBIM)DB30C10 and (BBIM-methane)DB30C10 form normal threaded structures, in (BBIM-ethane)DB30C10, (BBIM-propane)DB30C10 and (BBIM-butane)DB30C10 systems the respective axles are cradled inside the crown ether. That is, the axles BBIM-ethane, BBIM-propane and BBIM-butane are cradled inside the boat-like cavity of DB30C10.

Revisiting the formation and tunable dissociation of a [2]pseudorotaxane formed by slippage approach.

A new [2]pseudorotaxane DB24C8⊃1-H·PF6 with dibenzo[24]crown-8 (DB24C8) crown ether-dibenzylammonium (1-H·PF6) binding which was formed by slippage approach at different solvents and temperature, had been isolated and characterized by NMR spectroscopy and mass spectrometry. The [2]pseudorotaxane DB24C8⊃1-H·PF6 was stable at room temperature. The dissociation rate of [2]pseudorotaxane DB24C8⊃1-H·PF6 could be tuned by using different stimuli such as triethylamine (TEA)/diisopropylethylamine (DIPEA) and dimethyl sulfoxide (DMSO). In particular, the dissociation of [2]pseudorotaxane DB24C8⊃1-H·PF6 by an excess of TEA/DIPEA base mixture possessed a long and sustained, complete dissociation over 60 days. Other stimuli by DMSO possessed a relatively fast dissociation over 24 h.

Ion Conduction in a Semicrystalline Polyviologen and Its Polyether Mixtures

Polyviologen (PV) with C6 spacers and bis(trifluoromethylsulfonyl)imide (Tf2N−) anions is a semicrystalline polymer. Its semicrystalline mixtures with 18‐crown‐6 (18C6), 30‐crown‐10 (30C10), dibenzo‐30‐crown‐10 (DB30C10), and poly(ethylene glycol) dimethyl ether 1000 (PEGDME) are prepared by evaporation of solutions. The ionic conductivities, measured by dielectric relaxation spectroscopy, of all of the mixtures are 10–100× higher than that of PV itself in spite of the fact that the ionic contents are reduced by ≈25%. The room temperature (RT) ionic conductivity of PV is 1.1 × 10−9 S cm−1, and that of its mixture with DB30C10 is over 100‐fold higher even though its Tg is slightly above that of PV. The mixtures with 30C10 and PEGDME have similar RT conductivities. However, the 18C6 mixture, in spite of a 9 °C drop in Tg, displays a room temperature (RT) conductivity 10× lower than the other mixtures. Although plasticization probably plays a role, complexation of the polyethers with the viologen units plays a role in the higher conductivities, it is believed, because it increases the fraction of non‐ion‐paired mobile anions. With 30C10 and DB30C10, polypseudorotaxane formation is envisioned to play a significant role in conductivity enhancement. image

Interaction between adrenaline and dibenzo-18-crown-6: Electrochemical, nuclear magnetic resonance, and theoretical study

The interaction between adrenaline (Ad) and dibenzo-18-crown-6 (DB18C6) was studied by cyclic voltammetry, nuclear magnetic resonance spectroscopy, and the theoretical calculations, respectively. The results show that DB18C6 will affect the electron transfer properties of Ad. DB18C6 can form stable supramolecular complexes with Ad through ion-dipole and hydrogen bond interactions.

Anomalous behaviour of the bis(benzimidazolium)butane [2]pseudorotaxanes of dibenzo-24-crown-8: a comparative study of methane, ethane, propane and butane bis(benzimidazolium)alkane]dibenzo-24-crown-8 systems with variable spacers

Bis(benzimidazolium)butane (BBIM-butane) system acts as a new guest molecule for dibenzo-24-crown-8 (DB24C8). This is the only [BBIM]DB24C8 pseudorotaxanes where two conformers coexist (detected by 1H NMR and structure established by DFT studies); major conformer and minor conformer. Low temperature 1H NMR (240, 253 K) was done for a representative [BBIM-butane]DB24C8 pseudorotaxane that could not be detected at room-temperature. DFT calculations for this [BBIM-butane]DB24C8 pseudorotaxane were done both with B3LYP and MPW1PW91 functionals. The MPW1PW91 optimized structures identified possible stable major and minor conformer with the strongest H-bonding. We have compared the characteristics of [BBIM]DB24C8 [2]pseudorotaxanes comprising the [BBIM-methane]DB24C8, [BBIM-ethane]DB24C8, [BBIM-propane]DB24C8 and [BBIM-butane]DB24C8 systems. The feasibility of formation of these pseudorotaxanes decreases considerably from [BBIM-methane]DB24C8 to the [BBIM-butane]DB24C8 system. The presence of these threaded complexes was initially screened based on 1H NMR and substantiated further by 2D NMR spectroscopy (NOESY and COSY), X-ray crystallography, HR-ESI-MS and DFT calculations.

Adsorptivity of various metal ions onto benzo-18-crown-6 and dibenzo-18-crown-6 resins

Adsorptivity of metal ions onto silica-supported benzo-18-crown-6 (B18C6) and dibenzo-18-crown-6 (DB18C6) resins was investigated in nitric acid and hydrochloric acid media to evaluate the applicability of these resins for selective separation of nuclides from radioactive waste solutions. Both resins adsorbed Pd(II) and Ag(I) from HNO3, and Fe(III) and Ba(II) from HCl. It was also found that the B18C6 and DB18C6 resins adsorbed Sr(II) from HCl and Ca(II) from HNO3, respectively. This indicates that the two resins adsorb metal ions with smaller cationic diameters with different selectivity. This behavior is different from other impregnated adsorbents and extractants containing the 18-crown-6 moiety.

Polyhalides as scaffolds for supramolecular, ion-conducting crown ether stacks

"Crown ethers, such as dibenzo-18-crown-6 (DB18C6) are in principle perfect building blocks to be stacked on top of each other for one-dimensional (1D) channel formation. However, in the more than 1000 publications on crown ethers in the solid state, only one case was of channel formation described, but not as main focus of research.[1] We now present a way to systematically induce the stacking of DB18C6 with the help of polyhalides, which play the roles of scaffolds via halogen bonding.[2] These compounds can be considered as ""supramolecular straws"". Using for example potassium as couter ion for triiodide for example, we obtained a solid which contains three differently filled, parallel channels in the solid state, which are arranged between the polyhalide anions. Exchanging potassium with sodium by immersion of a single crystal into NaOH solution leads to a single-crystal-to-single-crystal transformation into a compound with two channel types. This transition from a system crystallizing initially in the P2-space group to yield a compound in Pccn is only possible under these very special conditions. We will further present how the ion transport through these channels can be quantified and which process is involved in ion exchange. The role of the polyhalide anions, which cannot be replaced by other linear anions, will be emphasized as well. "

A musclelike [2](2)rotaxane: synthesis, performance, and molecular dynamics simulations.

A novel bistable symmetric [2](2)rotaxane was prepared by a threading-followed-by-stoppering strategy and characterized with (1)H, (13)C, and 2D ROESY NMR spectroscopy and HR-ESI spectrometry. The symmetric [2](2)rotaxane system consists of an anthracene-based bis(crown ether) as macrocycles, and each of the two dibenzo[24]crown-8 (DB24C8) rings is threaded by the pendant substituents of a symmetrically substituted central rotatable ferrocene subunit that possesses two distinguishable recognition sites for the DB24C8 ring: namely, a dibenzylammonium site and an N-methyltriazolium site. The uniform shuttling motion of the thread relative to the two DB24C8 rings in [2](2)rotaxane can be driven by external acid-base stimuli, which was evidenced by (1)H and 2D ROESY NMR spectroscopy. Furthermore, molecular dynamics simulations of the [2](2)rotaxane were carried out both in protonated (stretched) and in neutral (contracted) forms. The calculated percentage change in molecular length of the [2](2)rotaxane between the two end-capping bis(methoxyl)phenyl groups is about 48% in the two different states (in acetone), which is much larger than the percentage change (∼27%) in human muscle. Moreover, in the two states, the C*-Cp-Cp-C* dihedral angles are computed as -177° in the stretched state and -112° in the contracted state, indicating a correlation between the translational and rotational motions of the [2](2)rotaxane.

A multiple-responsive self-healing supramolecular polymer gel network based on multiple orthogonal interactions.

Supramolecular polymer networks have attracted considerable attention not only due to their topological importance but also because they can show some fantastic properties such as stimuli-responsiveness and self-healing. Although various supramolecular networks are constructed by supramolecular chemists based on different non-covalent interactions, supramolecular polymer networks based on multiple orthogonal interactions are still rare. Here, a supramolecular polymer network is presented on the basis of the host-guest interactions between dibenzo-24-crown-8 (DB24C8) and dibenzylammonium salts (DBAS), the metal-ligand coordination interactions between terpyridine and Zn(OTf)2 , and between 1,2,3-triazole and PdCl2 (PhCN)2 . The topology of the networks can be easily tuned from monomer to main-chain supramolecular polymer and then to the supramolecular networks. This process is well studied by various characterization methods such as (1) H NMR, UV-vis, DOSY, viscosity, and rheological measurements. More importantly, a supramolecular gel is obtained at high concentrations of the supramolecular networks, which demonstrates both stimuli-responsiveness and self-healing properties.

Electrodriven Ion Transport through Crown Ether–Nafion Composite Membrane: Enhanced Selectivity of Cs+ over Na+ by Ion Gating at the Surface

Two types of Cs+ ion-selective crown ether–Nafion composite membranes have been prepared. In one case, the dibenzo-21-crown-7 (DB21C7) has been incorporated uniformly in the Cs+ form of Nafion-117 membrane in varying molar ratio with respect to Cs+, and in the other case, Cs+ driven loading of DB21C7 has been confined (ion gating) to a very small thickness (25 μm) from one of the surfaces of the Nafion-117 membrane. The surface confinement of Cs+ in the ion-gated membrane has been studied by energy dispersive X-ray spectroscopy and secondary ion mass spectrometry. The cation (Cs+/Na+) transport properties of the membranes have been studied under application of electric field. In the uniformly crown-ether-loaded membranes (Cs-Naf-CR), the decrease in crown ether molar ratio has been found to increase the mobility of Cs+ through the membrane at the cost of mutual cationic selectivity (Cs+ over Na+). On the other hand, enhanced selectivity of Cs+ over Na+ with significant cationic transport at room temperatu...