Dibenzo-18-crown-6 Research Articles

Electronic Interaction between Aromatic Chromophores in Dibenzo-Crown Ether Complexes with Alkali Metal Ions Investigated via Cold Gas-Phase Spectroscopy

This study investigated the geometric and electronic structures of dibenzo-21-crown-7 (DB21C7) and dibenzo-24-crown-8 (DB24C8) complexes with alkali metal ions, identified as M+(DB21C7) and M+(DB24C8) (M = Na, K, Rb, and Cs), respectively. We observed the ultraviolet photodissociation (UVPD) spectra of these complexes under cold (∼10 K) gas-phase conditions. The conformations of the M+(DB21C7) and M+(DB24C8) complexes were determined by comparing the UVPD spectra with the calculated electronic transitions of the local-minimum forms. The interactions between the electronic excited states of the two benzene chromophores in the M+(DB21C7) and M+(DB24C8) complexes were examined and compared with those of previously studied complexes (dibenzo-15-crown-5 (DB15C5) and dibenzo-18-crown-6 (DB18C6)). The S1-S0 and S2-S0 electronic excitations of the M+(DB21C7) complexes were almost localized in one of the benzene rings. In contrast, the closed conformers of the M+(DB24C8) (M = K, Rb, and Cs) complexes were delocalized over the two chromophores for electronic excitations, exhibiting strong electronic interactions between the benzene rings. For the M+(DB24C8) complexes (M = K, Rb, and Cs), the short distance between the benzene rings (∼3.9 Å) led to a strong interaction between the benzene chromophores. We conclude that this strong interaction in the M+(DB24C8) complexes correlates strongly with the broad absorption in the UVPD spectra, suggesting the presence of an intramolecular excimer for the K+(DB24C8), Rb+(DB24C8), and Cs+(DB24C8) complexes.

Synthesis of Ferrocene−Cyclodextrin, Anthracene−Cyclodextrin, and Pyrene−Cyclodextrin [2]Rotaxane Conjugates and Their Intercomponent Behavior as Observed in NMR Spectroscopy

AbstractFerrocene, anthracene, and pyrene‐terminated alkynylated moieties were reacted with azidized beta‐cyclodextrin derivatives to form supramolecular structures under various conditions. While initial experiments concerning mono‐azidized beta‐cyclodextrin proved difficult to isolate and have limited solubility, their reaction with peracetylated mono‐azidized beta‐cyclodextrin was more facile. Introduction and threading of the macrocycle, dibenzo‐24‐crown‐8 (DB24C8), allowed for [2]rotaxane synthesis. These compounds were characterized by infrared spectroscopy (IR), nuclear magnetic resonance spectroscopy (NMR), and mass spectrometry (MS). Among the compounds formed, the ferrocene‐capped species showed promising host‐guest inclusion complexation with the cyclodextrin cavity.

A Review of the Thermodynamics of Complexation of Crown Ethers With Metal Ion

Recently, macrocyclic and supramolecular chemistry has reached a hopeful area of research in the mutual interaction between chemistry, physics and biology. Charles J. Pedersen, at du Pont figure out a compound in the early 1960s famous for dibenzo-18-crown-6 (DB18C6) later on. The detection of the complex formation in solution, the designation of the stability of the consequence complex or complexes and the determination of the thermodynamic or the kinetic parameters of the complex formation can be attained by a manifold of physicochemical measurements. Conformational rigidity or flexibility of macrocycles has a considerable penetration on their selective behavior. The number, type, and arrangement of donor atoms in the macrocyclic rings play a main role in macrocycle selectivity. Based on chemistry terminology, this is known as “host-guest” chemistry where the ether plays the role as the host and the ionic species as the guest. In organic solutions, crown ethers take the role of phase-transfer catalysts and agents in order to enhance the solubility of inorganic salts. Macrocycles need to compete with solvent molecules for the cations during the process of complexation. Consequently, variation of the solvent makes a considerable change in the manifest binding characteristics of these ligands.

Dibenzo‐18‐Crown‐6‐Assisted Inhibition of Cation Migration for Stable Perovskite Solar Cells

Formamidinium–cesium (FACs)‐based perovskites are potential light‐absorbing materials for stable perovskite solar cells (PSCs), while long‐term stability deterioration caused by photo‐ and moisture‐induced cation migration and phase separation restrict their further commercial application. Herein, crown ether molecules with both, an electronegative cavity and a negatively charged π bond, dibenzo‐18‐crown‐6 (DB18C6), are introduced to FACsPbI3 films aiming at gaining better capability of inhibiting cation migration benefiting from the crown ether–cation complexation. Meanwhile, 18‐crown‐6 (18C6) with an electronegative cavity‐only is also employed for comparison. By tracing the changes of UV–vis absorption spectra, steady‐state photoluminescence, and Kelvin probe force microscopy of perovskite films under 24 h continuous light soaking, it is observed that the DB18C6‐modified FACsPbI3 film shows remarkably negligible degradation, in comparison with the unmodified and 18C6‐modified FACsPbI3 films. As a result, DB18C6‐modified PSCs with the architecture of ITO/SnO2/FACsPbI3/Spiro‐OMeTAD/Ag achieve an enhanced power conversion efficiency (PCE) exceeding 20.84%, which is a competitive efficiency for methylammonium‐free pure‐iodine n–i–p PSCs. The resultant unencapsulated DB18C6‐modified devices retain up to 94.73% and 90.18% of their original PCEs even after 500 h continuous full sunlight light soaking and 85 °C heating, respectively. Such crown ether modification provides a pathway on long‐term operational stabilized photovoltaics.

Voltammetric studies of glutathione transfer across arrays of liquid-liquid microinterfaces for sensing applications.

The simple and facilitated transfer of tripeptide glutathione across the water/2-nitrophenyl octhyl ether interface was studied via cyclic voltammetry at interface between two immiscible electrolyte solutions (ITIES). The micro-perforated membrane prepared with a laser with a femtosecond pulse was used for mechanical stabilization of the interface. The method of cyclic voltammetry was used to study the passive and facilitated interfacial transfer of glutathione and its complex with the crown ether dibenzo-18-crown-6 (DB18C6).The glutathione mass transfer mechanism was established and substantiated, the diffusion coefficients, thermodynamic characteristics of interphase transfer and the constant of complexation of the glutathione by DB18C6 were determined. Square wave voltammetry based on facilitated transfer was used for more accurate and sensitive determination of glutathione low detection limit (0.8μM) with wide linear dynamic range (from 3.0 to 80μM) was reached. The influence of various potentially interfering ions on the voltammetric determination of glutathione has also been investigated. The method developed was applied to determine glutathione in aqueous solutions and malt extract.

Host-guest interaction induced ion channels for accelerated OH− transport in anion exchange membranes

Anion exchange membranes (AEMs) with fast ion transport capability are highly desired in numerous industries. Improving the ion conductivity of AEMs through rational molecular structure design is of great importance. Inspired by the biological ion channels formed by the supramolecular assembly of protein chains, we herein develop a strategy for preparing high-performance AEMs by constructing ion conduction channels via crown ether-based supramolecular host-guest interaction. In relatively apolar solvent media, one dibenzo[24]crown-8 (DB24C8) ring tethers one dibenzylammonium salt (DBAS) guest molecule to form stable supramolecular assembly. Hence, by grafting DB24C8 rings and DBAS moieties onto the cationic side chains, the resulting host-guest interaction actuates cationic groups to assembly into connected ion conducting channels in AEM, as proved by small angle X-ray scattering and transmission electron microscopy analyses. The host-guest interaction induced ion channels boost the OH− conduction in AEM, thus the conductivity of the resultant AEM is twice that of the control membrane (without host-guest interaction) in spite of the same ion exchange capacity. Besides, a demonstration of the H2/O2 AEMFC using the host-guest interacted AEM offers almost two times higher peak power density than the control membrane. This design of supramolecular host-guest interaction induced ion channels provides a roadmap for developing AEMs with satisfactory ion conductivity.

Poly(terphenyl piperidinium) containing hydrophilic crown ether units in main chains as anion exchange membranes for alkaline fuel cells and water electrolysers

Poly(arylene piperidinium) polymers are recognized as promising anion exchange membrane (AEM) materials for alkaline fuel cell and water electrolysis, due to the aryl-ether free polyaromatic backbones and stable piperidinium cations. Herein, hydrophilic crown ether units have been introduced into poly(terphenyl piperidinium) (PDTP) by readily superacid-catalyzed polycondensation of dibenzo-18-crown-6 (DE), p-terphenyl and N-methyl-4-piperidine followed via quaternization. The obtained PDTP membranes showed much higher hydroxide conductivity than the control poly(terphenyl piperidinium) (PTP) sample without DE units, due to their high water uptake. The highest hydroxide conductivity of 110 mS/cm was reached at 80 °C for PDTP-10 (where 10 denoted the molar content of crown ether units) membrane with an ion exchange capacity (IEC) of 2.57 meq./g. The introduction of DE units alleviated the chemical degradation of PDTP membrane in 1 M NaOH at 80 °C as compared to the PTP membranes. Furthermore, membrane electrode assemblies based on PDTP-10 membrane shown a peak power density of 621 mW/cm2 at 60 °C in AEM fuel cells and a current density of 2000 mA/cm2 at 2.1 V for water electrolysers circulated with 1 M NaOH at 80 °C. The in-situ stability tests in fuel cells and water electrolysers also manifested that the chemical structure of PDTP-10 membrane remained intact during short-term durability tests under galvanostatic mode. The above results manifested that AEMs containing hydrophilic crown ether units in the polymer mainchain showed potential in the application for AEM based electrochemical devices.

Crown ether-based hypercrosslinked porous polymers for gold adsorption

With the over-exploitation of global resources, the recycling of gold becomes an urgent task to be solved. In this regard, design of stable adsorbents with low cost and large capacity is meaningful for the secondary utilization of resources. Herein, to obtain the efficient adsorbents, dibenzo-18-crown-6 (DB18C6) and dibenzo-24-crown-8 (DB24C8) were cross-linked for the first time by Friedel–Crafts reaction to synthesize crown ether-based hypercrosslinked porous polymers, named DB18C6-HCP and DB24C8-HCP, respectively. These adsorbents exhibit high porosity, good stability, and outstanding gold adsorption selectivity. Notably, DB18C6-HCP exhibits a high gold uptake capacity with 1667 mg g−1. Furthermore, gold ions are in situ reduced into gold nanoparticles by DB18C6-HCP and DB24C8-HCP along with gold ion adsorption process. In short, we have confirmed the potential of porous organic polymers for the adsorption of gold, and provided a powerful reference for the recovery and reduction of gold.

Study of [2]‐ and [3]Rotaxanes Obtained by Post‐Synthetic Aminolysis of a Kinetically Stable Carbonate‐Containing Pseudorotaxane

AbstractHere is reported the synthesis and study of dibenzo‐24‐crown‐8 (DB24C8)‐based [2]‐ and [3]rotaxanes that contain an ammonium as the best molecular station and carbamate moieties as secondary molecular stations. The common post‐interlocking synthesis relies on the aminolysis of the N‐succinimidyl carbonate extremity of an activated though insulated pseudorotaxane. The N‐succinimidyl carbonate‐based thread's extremity proved to be small enough to allow the slow slippage of the DB24C8 around the thread and large enough to allow insulation of the kinetically stable pseudorotaxane. Due to its sensitivity towards amine compounds, the activated carbonate end of the encircled thread allowed post‐interlocking aminolysis‐based conversion into mechanically interlocked rotaxanes by providing the same way the carbamate secondary station for the DB24C8 in the thread backbone. Translation of the DB24C8 along the threaded axle between the two molecular stations was investigated.

Investigating the synthesis and structure of [2]pseudorotaxanes assembled by crown ether as wheel component and dual-cation axle with phosphonium and ammonium cations

Pseudorotaxanes have attracted attention as intriguing building blocks for the construction of stimuli-responsive supramolecular materials. One of the primary goals of our laboratory is the development of synthetic supramolecular compounds containing phosphorous atoms. Herein, we report the design and synthesis of simple [2]pseudorotaxanes containing phosphonium salts. Dual-cation axle molecules were synthesized from a dialkylammonium cation, as a recognition site for 24-crown-8 (24C8) or dibenzo-24-crown-8 (DB24C8), and an alkyltriphenylphosphonium cation; these were used to obtain [2]pseudorotaxanes in a 1:1 ratio with 24C8 and DB24C8. The formation of [2]pseudorotaxanes with crown ethers positioned at ammonium cations on the axle compounds was confirmed by nuclear magnetic resonance (NMR) and X-ray crystallography, revealing that the CH/π interaction between phenyl group of alkyltriphenylphosphonium and that of DB24C8 increases the stability of a [2]pseudorotaxane.

Dibenzo-18-crown-6-based carbon paste sensors for the nanomolar potentiometric determination of daclatasvir dihydrochloride: An anti-HCV drug and a potential candidate for treatment of SARS-CoV-2

Daclatasvir dihydrochloride (DAC) is an anti-hepatitis C virus (HCV) drug that has recently proven to be a promising candidate for the treatment of SARS-CoV-2. Still, there is a lack of sensitive potentiometric methods for its determination. In this work, carbon paste sensors based on dibenzo-18-crown-6 (DB18C6) were fabricated and optimized for the sensitive and selective potentiometric determination of DAC in Daclavirocyrl® tablets, serum, and urine samples. The best performance was obtained by two sensors referred to as sensor I and sensor II. Both sensors exhibited a wide linear response range of 5×10−9 − 1×10−3 mol/L, and Nernstian slopes of 29.8 ± 1.18 and 29.5 ± 1.00 mV/decade, with limits of detection, 4.8×10−9 and 3.2×10−9 mol/L, for the sensors I and II, respectively. Sensors I and II displayed fast response times of 5–8 and 5–6 s, respectively, with great reversibility and no memory effect. Moreover, the sensors exhibited a lifetime of 16 days. For the study of sensors morphology and elucidation of the interaction mechanism, the scanning electron microscope (SEM), Fourier-transform infrared spectroscopy (FTIR), and nuclear magnetic resonance (1H NMR) techniques were performed. A selectivity study was performed, and the proposed sensors exhibited good discrimination between DAC and potentially coexisting interferents with sensor II displaying better selectivity. Finally, sensor II was successfully applied for the determination of DAC in the above-mentioned samples, with recovery values ranging from 99.25 to 101.42%, and relative standard deviation (RSD) values ranging from 0.79 to 1.53% which reflected the high accuracy and precision.

Exploring the reaction pathway involved in the dibenzo‐18‐crown‐6 synthesis from catechol and bis(2‐chloroethyl) ether in presence of base

AbstractComputational investigations reported in this work have proposed the mechanism involved in the synthesis of dibenzo‐18‐crown‐6 (DB18C6) from catechol and bis(2‐chloroethyl) ether in presence of base. The transition states on the reaction path have been identified, and the corresponding barrier heights are estimated. Paths related to the side‐product formations, such as benzo‐9‐crown‐3 and 1,2‐bis[2‐(2‐chloroethoxy)ethoxy]‐benzene, have been also tracked. The cation‐assisted (Na+ and K+ ions) cyclization process (template effect) creates more structurally ordered reactant and transition state species. This facilitates the cyclization step that is an intramolecular SN2 process. Additionally, it eliminates possibilities of different side‐product formations giving better yield of the crown ether, as reported previously. This cyclization step has a comparatively lower barrier height for Na+ system (by 3 kcal/mol) in gas phase than K+ system; however, it becomes reverse in 1‐butanol where the barrier height is almost 2.5 kcal/mol lower during the K+DB18C6 formation. Consequently, a faster cyclization has been found in this solvent from the reaction rate studies for the potassium system. This is in‐line with the experimental observations reported on the alkali‐metal‐catalyzed benzo‐18‐crown‐6 ether formation reactions. The dipole moment value of the transition state involved in this step for the larger alkali metal ion system is found to be significantly higher (by 5–8 D) than the reactant species.

Whither Second-Sphere Coordination?

Whither Second-Sphere Coordination?

Discrepancy Regarding the Dethreading of a Dibenzo‐24‐crown‐8 Macrocycle through a Perfluorobutyl End in [2]Pseudorotaxanes

AbstractHere are reported the synthesis and characterization of four new dibenzo‐24‐crown‐8 (DB24C8)‐based ammonium‐containing pseudorotaxanes, for which one of the two encircled axle's extremities consists of a perfluorobutyl moiety. The subsequent dethreading of the DB24C8 over the perfluorobutyl extremity was studied. Although the perfluorobutyl extremity of an ammonium‐containing axle did not allow threading of DB24C8, dethreading of a perfluorobutyl extremity‐containing pseudorotaxane was possible and its rate depended on both the strength of the template‐to‐DB24C8 complex and the nature of the axle. In particular, dethreading process may be assisted by the presence, in the threaded axle, of a poor secondary site of interaction for the DB24C8 and this assistance proved to be higher when this site is close to the DB24C8.

A New Perspective on Adsorbent Materials Based Impregnated MgSiO3 with Crown Ethers for Palladium Recovery.

The study of new useful, efficient and selective structures for the palladium ions’ recovery has led to the development of a new series of macromolecules. Thus, this study presents a comparative behavior of two crown benzene ethers that modify the magnesium silicate surface used as adsorbent for palladium. These crown ethers are dibenzo18-crown-6 (DB18C6) and dibenzo 30-crown-10 (DB30C10). The obtained materials were characterized by scanning electron microscope (SEM), energy-dispersive X-ray spectroscopy (EDX) and Fourier-transform infrared spectroscopy (FT-IR). The specific surface area (BET) and point of zero charge (PZC) of the two materials were determined. The palladium ions’ recovery from synthetic aqueous solutions studies aimed to establish the adsorption mechanism. For this desideratum, the kinetic, equilibrium and thermodynamic studies show that MgSiO3-DB30C10 have a higher adsorption capacity (35.68 mg g−1) compared to MgSiO3-DB18C6 (21.65 mg g−1). Thermodynamic studies highlight that the adsorption of Pd(II) on the two studied materials are spontaneous and endothermic processes. The positive values of the entropy (ΔS0) suggest that the studied adsorption processes show a higher disorder at the liquid/solid interface. Desorption studies were also performed, and it was found that the degree of desorption was 98.3%.

A Kinetic Study of Removing Methylene Blue from Aqueous Solutions by Modified Electrospun Polyethelene Terephthalate Nanofibres

The present research study investigates the potential use of the novel polyethylene terephthalate (PET) nanofibers extracted from waste bottles. The electrospinning process creates nanofibers, which are then impregnated with dibenzo-18-crown-6 (DB18C6) (crown ether) to obtain a modified PET nanofiber. The use of modified PET nanofibers to remove methylene blue (MB) from aqueous solutions at different contact times, temperatures and initial dye concentrations is the prime concern of the present study. The amount of MB adsorbed at equilibrium (qe) is calculated at different temperatures (303, 313, and 323 K) and different concentrations (5, 10, 15 mg/g). The Kinetic and equilibrium studies of MB removal are carried out. The results indicate that the adsorption kinetics of MB can be described by the pseudo-second-order model. The activation energy value is below 40 kJ/mol and this gives an idea about the physisorption process.

Adsorption behavior of copper ions using crown ether-modified konjac glucomannan

A novel supramolecular polysaccharide composite [KGM + DB18C6] was prepared from konjac glucomannan (KGM) and dibenzo-18-crown-6 (DB18C6) using ceric ammonium nitrate as initiator. The products were characterized by FTIR, TG, DSC, UV–Vis, XRD, solid-state 13C NMR, and SEM. Due to the introduction of crown ether, [KGM + DB18C6] showed good adsorption performance for Cu2+ in aqueous, and the maximum adsorption capacity was 194 mg/g under the optimal adsorption condition. The adsorption kinetics of [KGM + DB18C6] on Cu2+ could be described by the pseudo-second-order kinetic model. The adsorption isotherms of [KGM + DB18C6] on Cu2+ followed the dual-site Langmuir-Freundlich model. In addition, high recoveries of Cu2+ (from 82.65 to 88.47%), and low relative standard deviation (below 5.00%) were obtained by applying the product in real samples, indicating that [KGM + DB18C6] was a good absorbent for removing Cu2+ in wastewater.

Acid-Activated Motion Switching of DB24C8 between Two Discrete Platinum(II) Metallacycles.

The precise operation of molecular motion for constructing complicated mechanically interlocked molecules has received considerable attention and is still an energetic field of supramolecular chemistry. Herein, we reported the construction of two tris[2]pseudorotaxanes metallacycles with acid–base controllable molecular motion through self-sorting strategy and host–guest interaction. Firstly, two hexagonal Pt(II) metallacycles M1 and M2 decorated with different host–guest recognition sites have been constructed via coordination-driven self-assembly strategy. The binding of metallacycles M1 and M2 with dibenzo-24-crown-8 (DB24C8) to form tris[2]pseudorotaxanes complexes TPRM1 and TPRM2 have been investigated. Furthermore, by taking advantage of the strong binding affinity between the protonated metallacycle M2 and DB24C8, the addition of trifluoroacetic acid (TFA) as a stimulus successfully induces an acid-activated motion switching of DB24C8 between the discrete metallacycles M1 and M2. This research not only affords a highly efficient way to construct stimuli-responsive smart supramolecular systems but also offers prospects for precisely control multicomponent cooperative motion.

Conformation of K+(Crown Ether) Complexes Revealed by Ion Mobility-Mass Spectrometry and Ultraviolet Spectroscopy.

The conformation and electronic structure of dibenzo-24-crown-8 (DB24C8) complexes with K+ ion were examined by ion mobility-mass spectrometry (IM-MS), ultraviolet (UV) photodissociation (UVPD) spectroscopy in the gas phase, and fluorescence spectroscopy in solution. Three structural isomers of DB24C8 (SymDB24C8, Asym1DB24C8, and Asym2DB24C8) in which the relative positions of the two benzene rings were different from each other were investigated. The IM-MS results at 86 K revealed a clear separation of two sets of conformers for the K+(SymDB24C8) and K+(Asym1DB24C8) complexes whereas the K+(Asym2DB24C8) complex revealed only one set. The two sets of conformers were attributed to the open and closed forms in which the benzene-benzene distances in the complexes were long (>6 Å) and short (<6 Å), respectively. IM-MS at 300 K could not separate the two conformer sets of the K+(SymDB24C8) complex because the interconversion between the open and closed conformations occurred at 300 K and not at 86 K. The crown cavity of DB24C8 was wrapped around the K+ ion in the complex, although the IM-MS results availed direct evidence of rapid cavity deformation and the reconstruction of stable conformers at 300 K. The UVPD spectra of the K+(SymDB24C8) and K+(Asym1DB24C8) complexes at ∼10 K displayed broad features that were accompanied by a few sharp vibronic bands, which were attributable to the coexistence of multiple conformers. The fluorescence spectra obtained in a methanol solution suggested that the intramolecular excimer was formed only in K+(SymDB24C8) among the three complexes because only SymDB24C8 could possibly assume a parallel configuration between the two benzene rings upon K+ encapsulation. The encapsulation methods for K+ ion (the "wraparound" arrangement) are similar in the three structural isomers of DB24C8, although the difference in the relative positions of the two benzene rings affected the overall cross-section. This study demonstrated that temperature-controlled IM-MS coupled with the introduction of appropriate bulky groups, such as aromatic rings to host molecules, could reveal the dynamic aspects of encapsulation in host-guest systems.

Lead ion selective electrodes from dibenzo-18-crown-6 derivatives: An exploratory study

Dibenzo-18-crown-6 (DB18C6) and three of its derivatives (-COCH3, -Br, -NO2), are investigated via Density Functional Theoretical (DFT) modelling, Fourier Transform Infrared (FT-IR) and absorption spectroscopies, Differential Pulse Anodic Stripping (DPASV), Cyclic (CV) and Square Wave (SWV) voltammetries, as possible materials for preparing plasticiser free lead(II) ion selective electrodes. The spontaneous, entropy driven, interactions between lead(II) ions and DB18C6 derivatives are such that they form 1:1 complexes via coordination with the high electron density open ether cavity, except for the brominated derivative where the metal: ligand stoichiometry is 2:1 due to exo-cavity coordination via the high electron density bromine atoms. Monolayers resulting from electropolymerization of some derivatives (-H, -COCH3, -Br) and chemisorption of the -NO2 derivative, allows quantification of lead(II) ions at concentrations below 10 mg L−1 with minimal interference from other metal ions except Hg2+ and Al3+.