A combined experimental-molecular modeling study of crown ether europium complexes: Effects of the coordinated anion on structural and luminescence properties

It is reported the synthesis, characterization by elemental analysis, thermogravimetry; electronic absorption, infrared, excitation, and emission spectroscopies of the [Eu(12C4)(phen)2(X)n]X2 complexes, where 12C4 = 12-crown-4, phen = 1,10-phenanthroline, and X  = F-, Cl-, Br-, SCN-, ClO4-, and NO3-. It is verified that the polarizability of the anion X- exerts remarkable effects on the emission process. As a general trend, lower wavenumbers for the 7F0→5L6, 7F0→5D2 and 7F0→5D1 transitions are associated with the anions with higher volumes and, consequently, higher polarizability. The molecular modeling results performed with quantum methods (RHF and DFT) suggest some relationships between the calculated structures, electronic, and luminescence properties with the presence of the LMCT (ligand-to-metal charge transfer) states, which explains the differences in the emission spectra of these complexes due to the coordinated anion.

An isotope generator of Po-210 based on SR resin

The work describes an isotope generator of polonium-210 based on an extraction chromatographic resin SR Resin. It was shown that a high selectivity of 4,4'(5')-di-t-butylcyclohexano-18-crown-6, an active component of SR Resin, for lead allows a clear separation of Pb-210 from impurities, easy elution of Po-210 with 5-7 mL of 0.05 M nitric acid solution as well as good retention of Pb-210 in the generator. The content of alpha emitting impurities in the Po-210 eluate did not exceed 0.65%. The experience of 3-years exploitation of the generator is described. It was shown that the SR Resin was stable against irradiation and complete drying, and Pb-210 loss from the SR Resin column for 3 years (seven elutions) was near to loss due to its radioactive decay within the error limits (less than 7%).

Molecular recognition effect enabled by novel crown ether as macrocyclic host towards highly reversible Zn anode

Aqueous Zn2+ ion batteries present notable advantages, including high abundance, low toxicity, and intrinsic nonflammability. However, they exhibit severe irreversibility due to uncontrolled dendrite growth and corrosion reactions, which limit their practical applications. Inspired by their distinct molecular recognition characteristics, supramolecular crown ethers featuring interior cavity sizes identical to the diameter of Zn2+ ions were screened as macrocyclic hosts to optimize the Zn2+ coordination environment, facilitating the suppression of the reactivity of H2O molecules and inducing the in-situ formation of organic-inorganic hybrid dual-protective interphase. The in-situ assembled interphase confers the system with an "ion-sieving" effect to repel H2O molecules and facilitate rapid Zn2+ transport, enabling the suppression of side reactions and uniform deposition of Zn2+ ions. Consequently, we were able to achieve dendrite-free Zn2+ plating/stripping at 98.4% Coulombic efficiency for approximately 300 cycles in Zn||Cu cell, steady charge-discharge for 1360 h in Zn||Zn symmetric cell, and improved cyclability of 70% retention for 200 cycles in Zn||LMO full cell, outlining a promising strategy to challenge lithium-ion batteries in low-cost, and large-scale applications.

Macrocyclic chemosensors with anthraquinone signaling unit built into ionophore. Experimental and computational studies (part I) - synthesis and effect of proton binding on spectrophotometric and electrochemical properties

Two macrocyclic chemosensors with anthraquinone signaling unit incorporated into ionophore system (via positions 1 and 8) have been synthesized and subsequently their physicochemical properties became the subject of our extensive research. First ligand, labeled in the paper as AQ-Ncrown is characterized by a cyclic structure of a crown ether, while second one AQ-Ncrypt includes an additional ethoxy bridge, which ensures the bicyclic character of a cryptand. The studied macrocycles possess both oxygen and nitrogen heteroatoms in the ionophore cavity. Dualistic (chromophore and electrophore) signaling nature of described compounds, makes them potentially attractive molecular recognition systems. The aim of our research was to synthesize and analyze the spectroscopic, acid-base and redox properties of aforesaid macrocycles. Furthermore, we have combined experimental approach together with theoretical investigations. The equilibrium structures of AQ-Ncrown and AQ-Ncrypt were determined with the use of DFT calculations. The sensitivity of studied macrocycles towards interactions with protons was scrutinized. The complete pH-spectrophotometric characteristic of studied ligands together with their protolytic forms and corresponding pK_a values were determined. The influence of medium (aprotic and protic solvent) on spectral effects was described. Furthermore, the molecular electrostatic potential maps for ligands and differential electron densities for their mono and dianions were calculated. The redox reactions was investigated at different pHs by cyclic voltammetry. Electrochemical results have presented intriguing phenomenon: the specific stabilization of the reduced form of the protonated molecules. The calculations have revealed that this is a consequence of barrierless intramolecular proton transfer (from the macrocycle cavity onto the anthraquinone moiety) that might occur during the reduction process in acidic medium.

A Bioinspired Free-Standing 2D Crown-Ether-Based Polyimine Membrane for Selective Proton Transport

Biological proton channels play important roles in the delicate metabolism process, arousing great interest in mimicking selective proton transport. Herein, we designed a bioinspired proton transport membrane by bringing flexible 14-crown-4 (14C4) units into rigid frameworks of polyimine films by an interfacial Schiff base reaction. The Young's modulus of the membrane reaches ~8.2 GPa. The 14C4 units could grab water forming hydrogen bond-water networks and acting as jumping sites to lower the energy barrier of proton transport. The molecular chains present a vertical orientation to the membrane, and the ions travel between the quasi-planar molecular sheets. Also, the 14C4 moieties could bond alkali ions via host-guest interaction. Thus, the ion conductance follows H+ ≫ K+ > Na+> Li+, and an ultrahigh selectivity of H+/Li+ (~215) is resulted. This study provides an effective avenue for developing ion-selective membranes by embedding macrocycles motif with inherent cavities.

Synthesis of crown ether-based microporous organic networks: A new type of efficient adsorbents for chlorophenols

Microporous organic networks (MONs) are a booming class of functional materials in elimination of environmental pollutants. However, the limit varieties of MONs still restrict their broad applications. Here we report the synthesis of a novel type of crown ether (CE)-based MONs via the coupling between brominated 18-crown-6 ether and different aromatic alkynyls. The constructed CE-based MONs integrates the good conjugation property of MONs and the inherent host-guest binding sites of CE, allowing the ultrafast and efficient adsorption and removal of a typical environmental priority pollutant 2,4,6-trichlorophenol (2,4,6-TCP). The hydrophobic CE-based MONs can also address the recovery challenge of unstable discrete CE in most organic and inorganic solvents. All CE-based MONs displayed fast adsorption kinetics (< 3 min) and large adsorption capacities (229.1-341.7 mg g^-1) for 2,4,6-TCP. The CE-based MONs also gave stable adsorption capacities for 2,4,6-TCP in pH range of 4.0-6.0, NaCl concentration of 0-40 mg L^-1, HA concentration of 0-30 mg L^-1, or H₂O₂ ratio of < 5 %. Density functional theory calculation, Fourier transform infrared and X-ray photoelectron spectra evaluation revealed adsorption process involved hydrophobic, π-π and hydrogen bonding interactions. The CE-based MONs also showed favorable reusability and good adsorption for other toxic chlorophenols. This work highlights the potential of CE-based MONs in contaminants elimination.

Cell-inspired selective potassium removal towards hyperkalemia therapy by microphase-isolated core-shell microspheres

Hyperkalemia is a common metabolic problem in patients with chronic kidney disease. Although oral medications and hemodialysis are clinically applied for lowering serum potassium, the intrinsic limitations encourage alternative therapy in the trend of adsorbent-based miniaturized blood purification devices. Cells serve as the biological K⁺ storage units that accumulate K⁺ through multiple mechanisms. Inspired by cells, our strategy aims at favorable permeation and enrichment of K⁺ in the microsphere. We incorporate cation-affinitive groups into core-shell structures with submicron-sized phase separation. These nano-spaced side-groups cooperate to form interlinked clusters, where crown ethers with Angstrom-scale ring for size-matched complexation, while ionic sulfonic acid groups for hydrophilicity and charge-buffering. The unique structure with such non-covalent interactions facilitates K⁺ for permeation across the shell and binding to the core while also ensuring mechanical strength and anti-swelling durability in biofluids. The microspheres exhibit high selectivity ratios of K⁺ (S_K/Na, S_K/Ca, S_K/Mg up to 9.8, 21.6, and 17.7). As column adsorbents for hemoperfusion simulation, they effectively lower elevated K⁺ levels to the normal range (clearance rates up to 44.4%/45.3% for hyperkalemic human serum/blood). Blood compatibility tests show low protein adsorption, preferable hemocyte compatibility, and anticoagulation property in vitro. This promising strategy has clinical potential for hyperkalemia in high-risk patients. STATEMENT OF SIGNIFICANCE: Hyperkalemia (serum potassium >5 mmol/L) is a common complication in chronic renal failure patients. The limitations of existing treatments prompt a shift to wearable artificial kidney technology for clinical convenience and efficacy. Existing treatments have limitations, and we turn to adsorbent-based miniaturized blood purification devices in the prospect of wearable artificial kidney technology. There exists a lack of ion-specific adsorbents applied in extracorporeal circuits to redress electrolyte imbalances like hyperkalemia. Inspired by cells, we aim at the favorable permeation and enrichment of K⁺ by microspheres. The microspheres have a microphase-isolated core-shell structure, whose nano-spaced groups form cation-affinitive clusters. Selective K⁺ removal and blood compatibility are achieved. We expect this strategy to enlighten alternative hyperkalemia therapy for these high-risk patients.

Synthesis of multifunctional crown ether covalent organic nanospheres as stationary phase for capillary electrochromatography

Crown ethers are macrocyclic polyether compounds containing multiple -oxo-methylene-structural units, which are often used for recognition of metal ions and ammonium ions. Inspired by the molecular design of rotaxanes, a novel covalent organic nanospheres material (CON ADBC-Tp) constructed by 4,4'-diaminodibenzo-18-crown-6 (ADBC) and 2,4,6-triformylphloroglucinol (Tp) was rationally designed as stationary phase for the separation of compounds containing imidazole structure. Scanning electron microscopy (SEM) and Fourier transform infrared spectroscopy (FT-IR) were carried out to confirm the morphology and composition of ADBC-Tp and ADBC-Tp modified capillary column. Thanks to the introduction of crown ether building ligands, the prepared capillary column exhibited excellent separation selectivity towards protonated imidazole structure, with benzimidazole and its 2-substituted derivatives as modal analytes. Moreover, separation of fungicides, nucleobases, short peptides and sulfanilamides were achieved on ADBC-Tp@capillary. The multifunctional ADBC-Tp@capillary with satisfactory reproducibility and stability gives great promise for separation science.

A Review on Recent Progress in Organic Fluorimetric and Colorimetric Chemosensors for the Detection of Cr3+/6+Ions

Chromium occurs in the environment primarily in two valence states, trivalent Cr3+ and hexavalent Cr6+, which have different physicochemical and biochemical properties. However, the higher concentration of Cr3+/6+ can cause various adverse effects on human health. Therefore, detecting Cr3+/6+ ions is important in various samples. Colorimetric and fluorescent chemosensors are the most powerful tools for the detection of Cr3+/6+ ions. These chemosensors have excellent bioimaging capability and significant sensitivity and selectivity. In this article, different colorimetric and fluorescent chemosensors based on organic compounds, including Schiff base, antipyrine, diarylethene, pyrene, crown ether, dansyl, pyridine, thiazole, coumarin, boradiazaindacene, rhodamine, imidazole, hydrazone, and other functional groups for detection of Cr3+/6+ ions have been reviewed, classified them according to different fluorophore and recognition mode. I hope this article will help the readers for the future design of highly effective, sensitive, and selective chemosensors for the detection and determination of Cr3+/6+ ions.

A fundamental study on selective extraction of Li+ with dibenzo-14-crown-4 ether: Toward new technology development for lithium recovery from brines

The present study has proposed a selective Li⁺ extraction process using a novel extractant of dibenzo-14-crown-4 ether functionalized with an alkyl C16 chain (DB14C4-C16) synthesized based on the ion imprinting technology (IIT). Theoretical analysis of the possible complexes formed by DB14C4-C16 with Li⁺ and the competing ions of Na⁺, K⁺, Ca²⁺ and Mg²⁺ was performed through density functional theory (DFT) modeling. The Gibbs free energy change of the complexes of metal ions with DB14C4-C16 and water molecules were calculated to be -125.81 and -166.01 kJ/mol for lithium, -55.73 and -117.77 kJ/mol for sodium, and -196.02 and -291.52 kJ/mol for magnesium, respectively. Furthermore, the solvent extraction experiments were carried out in both single Li⁺ and multi-ions containing solutions, and the results delivered a good selectivity of DB14C4-C16 towards Li⁺ over the competing ions, showing separation coefficients of 68.09 for Ca²⁺-Li⁺, 24.53 for K⁺-Li⁺, 16.32 for Na⁺-Li⁺, and 3.99 for Mg²⁺-Li⁺ under the optimal conditions. The experimental results are generally in agreement with the theoretical calculations.

Acetyl Cellulose Film with 18-crown-6 Ether for Colorimetric Phosgene Detection

The use of a cellulose detection film as a carrier for a colorimetric sensor to detect phosgene and allied compounds to be evaluated primarily visually is studied. For the case study, a benzimidazole-rhodamine dye and an acetyl cellulose film were selected. The detection complex was modified using cyclic ether 18-crown-6 to achieve more desirable analytic properties. The chromatic properties of detection film was verified using reflectance colorimetry in the visible light spectrum. The employed detection agent demonstrated high sensibility to phosgene vapours, but acid gases, acyl chlorides, base organic solvents, and in higher concentrations, even some organophosphorus substances interfered. The detection film application was adjusted to the in-situ preparation of simple detection devices (a spray or a marker) as well as to manufacture detection strips with beforehand excluded polymer film.

Crown ether-based anion exchange membranes with highly efficient dual ion conducting pathways

Anion exchange membranes (AEMs) are a crucial constituent for alkaline fuel cells. As the core component of fuel cells, the low performance AEMs restrict the development and application of the fuel cells. Herein, the trade-off between the OH^- conductivity and dimensional stability was solved by constructing AEMs with adequate OH^- conductivity and satisfactory alkali resistance using Tröger's base (TB) poly (crown ether)s (PCEs) as the main chain, the embedded quaternary ammonium (QA) and Na⁺-functionalized crown ether units as the cationic group. Crown ether is an electron donator, and can capture Na⁺ to form Na⁺-functionalized crown ether units to conveniently transfer OH^- and significantly promote the alkaline stability of the AEMs. The influence of the Na⁺-functionalized crown ether units on the performance of AEMs was studied in detail. The PCEs based AEMs show an obvious hydrophobic-hydrophilic microphase separation. These features make them ideal platforms for the OH^- conduction applications. As expected, the as-prepared PCEs-QA-100% (100% is the degree of cross-linking) AEM with an ionic exchange capacity (IEC) of 2.07 meq g^-1 has a high OH^- conductivity of 159 mS cm^-1 at 80 °C. Furthermore, the membrane electrode assemblies fabricated using the PCEs-QA-100% AEM possess a maximum power density of 291 mW cm^-2 under the current density of 500 mA cm^-2.

An asymmetric pulsed current-assisted electrochemical method for Sr(Ⅱ) extraction using supramolecular composites

The development of effective, economical, and sustainable seawater extraction strontium techniques is of great significance to the environment and industrial needs. In this paper, an asymmetric pulsed current-assisted electrochemical (AP-CE) method was used to extract Sr(Ⅱ) from seawater using a carbon electrode modified by dibenzo-18-crown-6-ether and cellulose acetate. An asymmetric pulsed current was used to prevent unwanted cations from blocking adsorption sites to prevent water splitting. It also prevented the cellulose acetate membrane from sealing the crown ether. Compared with traditional physicochemical adsorption of Sr(Ⅱ), the AP-CE method achieved a higher removal efficiency and adsorption capacity. When the concentrations of Sr(Ⅱ) were 10, 20, 50, and 100 mg L^-1, the removal efficiencies of Sr(Ⅱ) were 99.3%, 97.6%, 97.3%, and 96.1%, and the adsorption capacities of Sr(Ⅱ) were 14.9, 29.3, 73.0, and 144.2 mg g^-1, respectively. This method exhibited excellent selectivity for Sr(Ⅱ) adsorption from simulated seawater, suggesting that the asymmetric pulse electrochemical method is promising for extracting strontium ions from seawater.

Fast enantiomeric separation of amino acids using liquid chromatography/mass spectrometry on a chiral crown ether stationary phase

Fast enantiomeric separation of amino acids was studied by liquid chromatography/mass spectrometry (LC/MS) on a chiral crown ether stationary phase. A chiral crown ether bonded silica column (3 mm internal diameter (i.d.), 5 cm long) packed with 3 μm particles was employed instead of a 15 cm column packed with 5 μm particles used in our previous study. In addition, the extra-column variance, becoming more serious for smaller columns, was reduced by replacing 0.127 mm i.d. post-column tubes with shorter, smaller-diameter (0.0635 mm i.d.) tubes. The results demonstrated the benefits of using shorter columns packed with smaller particles and the reduction of the extra-column band broadening for fast enantiomeric separation. Finally, the enantiomeric separation of 18 pairs of proteinogenic amino acids was achieved within 2 min with a resolution (Rs) > 1.5 for each pair using an isocratic mobile phase of acetonitrile/water/trifluoroacetic acid (ACN/W/TFA) = 96/4/0.5, and a flow rate 1.2 mL/min at 30°C. This is the highest throughput method for simultaneous chiral separation of all proteinogenic amino acids except proline to date.

Simultaneous determination of nine atmospheric amines and six inorganic ions by non-suppressed ion chromatography using acetonitrile and 18-crown-6 as eluent additive

Atmospheric amines contribute to the nucleation and initial growth of new particles as well as secondary organic aerosol formation, influencing the radiative balance of the Earth's atmosphere. In this study, we develop an ion chromatography (IC) method for separating and quantifying the nine most abundant amines (methylaminium (MMAH⁺), dimethylaminium (DMAH⁺), trimethylaminium (TMAH⁺), ethylaminium (MEAH⁺), diethylaminium (DEAH⁺), propylaminium (MPAH⁺), butylaminium (MBAH⁺), ethanolaminium (MEOH⁺), and triethanolaminium (TEOH⁺)) from six common inorganic species in atmospheric aerosols. The retention times of the amines were altered by the addition of acetonitrile to the eluent because acetonitrile can reduce the adsorption of hydrophobic amines on the stationary phase. The developed method achieved the successful separation of DEAH⁺ and TMAH⁺ from inorganic cations, which often coelute with each other in established IC methods. The interference of K⁺ on the determination of MEAH⁺ was eliminated by the complexation of K⁺ with 18-crown-6, which prolonged the retention time of K⁺. Finally, 9 target amines and 6 common inorganic cations were separated, with a resolution Rs ≥ 1.2 for DEAH⁺ and MPAH⁺ and Rs > 1.5 for other species. The detection limits varied in the range of 0.34-1.48 ng for the 9 amines and 0.19-0.56 ng for the inorganic cations. The developed method was successfully applied for the determination of low molecular weight amines and inorganic cations in PM_2.5 collected from an urban site in Shanghai and an isolated coast of Chongming Island. Eight amines were detected in the urban samples, in which MMAH⁺ and DMAH⁺ dominated. The average amine concentration in the urban aerosols was 76.3 ± 38.4 ng m^-3, which is approximately 4-fold higher than those in the marine samples collected from the coast.

Interaction and selectivity of 14-crown-4 derivatives with Li+, Na+, and Mg2+ metal ions

The interactions between crown ether ligands (14-crown-4, 14C4; 4,4,5,5-tetramethylbenzo-14-crown-4, BC₄H₁₂-14C4; 4,4,5,5,9,9,10,10-octamethyl-14-crown-4, C₈H₂₄-14C4; dibenzo-14-crown ether-4, DB14C4) and alkaline and alkaline earth metal ions (Li⁺, Na⁺, Mg²⁺) were investigated using density functional theory modeling at the M062X/def2SVP and def2TZVP level. The condensed softness analysis of crown ethers, a condensed Fukui function, a condensed dual descriptor, and frontier molecular orbital theory were used to analyze the reactivities of the complexes. The complex stability was analyzed in terms of the binding energies, standard Gibbs free energy of formation, and energy decomposition of the interaction in aqueous solution. The results show that the active sites were mainly located at the carbon atoms of the benzene ring and oxygen atoms. The reactivities of DB14C4 and BC₄H₁₂-14C4 are higher than those of 14C4 and C₈H₂₄-14C4. The electrostatic interaction is the principal factor determining the stability of the complexes. The complexes containing Li⁺ has the greatest stability in aqueous solution among the complexes containing Li⁺, Na⁺, and Mg²⁺. BC₄H₁₂-14C4 shows selective adsorption toward Li⁺ in a mixed solution of Li⁺, Na⁺, and Mg²⁺. To evaluate the stability of complexes containing Mg²⁺, the solvent effect must be accurately described. An energy decomposition analysis was used to evaluate the stability of complexes containing Li⁺, Na⁺, and Mg²⁺, and the solvent effects were considered.

Structural basis of polyethylene glycol recognition by antibody

Background

Polyethylene glycol (PEG) is widely used in industry and medicine. Anti-PEG antibodies have been developed for characterizing PEGylated drugs and other applications. However, the underlying mechanism for specific PEG binding has not been elucidated.

Methods

The Fab of two cognate anti-PEG antibodies 3.3 and 2B5 were each crystallized in complex with PEG, and their structures were determined by X-ray diffraction. The PEG-Fab interactions in these two crystals were analyzed and compared with those in a PEG-containing crystal of an unrelated anti-hemagglutinin 32D6-Fab. The PEG-binding stoichiometry was examined by using analytical ultracentrifuge (AUC).

Results

A common PEG-binding mode to 3.3 and 2B5 is seen with an S-shaped core PEG fragment bound to two dyad-related Fab molecules. A nearby satellite binding site may accommodate parts of a longer PEG molecule. The core PEG fragment mainly interacts with the heavy-chain residues D31, W33, L102, Y103 and Y104, making extensive contacts with the aromatic side chains. At the center of each half-circle of the S-shaped PEG, a water molecule makes alternating hydrogen bonds to the ether oxygen atoms, in a similar configuration to that of a crown ether-bound lysine. Each satellite fragment is clamped between two arginine residues, R52 from the heavy chain and R29 from the light chain, and also interacts with several aromatic side chains. In contrast, the non-specifically bound PEG fragments in the 32D6-Fab crystal are located in the elbow region or at lattice contacts. The AUC data suggest that 3.3-Fab exists as a monomer in PEG-free solution but forms a dimer in the presence of PEG-550-MME, which is about the size of the S-shaped core PEG fragment.

Conclusions

The differing amino acids in 3.3 and 2B5 are not involved in PEG binding but engaged in dimer formation. In particular, the light-chain residue K53 of 2B5-Fab makes significant contacts with the other Fab in a dimer, whereas the corresponding N53 of 3.3-Fab does not. This difference in the protein-protein interaction between two Fab molecules in a dimer may explain the temperature dependence of 2B5 in PEG binding, as well as its inhibition by crown ether.

Integrating Stimuli-Responsive Properties in Host-Guest Supramolecular Drug Delivery Systems

Host-guest motifs are likely the most recognizable manifestation of supramolecular chemistry. These complexes are characterized by the organization of small molecules on the basis of preferential association of a guest within the portal of a host. In the context of their therapeutic use, the primary application of these complexes has been as excipients which enhance the solubility or improve the stability of drug formulations, primarily in a vial. However, there may be opportunities to go significantly beyond such a role and leverage key features of the affinity, specificity, and dynamics of the interaction itself toward "smarter" therapeutic designs. One approach in this regard would seek stimuli-responsive host-guest recognition, wherein a complex forms in a manner that is sensitive to, or can be governed by, externally applied triggers, disease-specific proteins and analytes, or the presence of a competing guest. This review will highlight the general and phenomenological design considerations governing host-guest recognition and the specific types of chemistry which have been used and are available for different applications. Finally, a discussion of the molecular engineering and design approaches which enable sensitivity to a variety of different stimuli are highlighted. Ultimately, these molecular-scale approaches offer an assortment of new chemistry and material design tools toward improving precision in drug delivery.

Modification of gold surface by electrosynthesized mono aza crown ether substituted catechol-terminated alkane dithiol and its application as a new electrochemical sensor for trace detection of cadmium ions

Among the toxic metals, cadmium is a very dangerous pollutant because it can extremely damage organs in humans and animals. This toxic metal is introduced into water from different industries such as metal plating, batteries, and alloys. Cadmium bioaccumulates in vital organs and unlike organic pollutants does not show any biological degradation. In this study, an electroactive self-assembled monolayer (SAM) was developed by covalent attachment of a novel mono aza-crown ether substituted catechol-terminated hexane dithiol onto the gold surface. The electrochemical behavior of the fabricated SAM electrode was investigated using voltammetry techniques and electrochemical impedance spectroscopy (EIS). The obtained results from voltammetric experiments revealed that the crown ether moiety of SAM forms a selective complex with cadmium ion. Under optimal conditions, Cd²⁺ could be detected in the range of 15 μM to 65 μM with a detection limit of 4.5 μM. Selectivity measurements reveal that the sensor is specific for Cd²⁺ even in the presence of high concentrations of other metal ions. The proposed sensor was applied to the determination of cadmium ion in water samples with high sensitivity and good selectivity.

Quantitative Collision Cross-Sections from FTICR Linewidth Measurements: Improvements in Theory and Experiment

Two corrections to the equation used in the cross-sectional areas by Fourier transform ion cyclotron resonance ("CRAFTI") technique are identified. In CRAFTI, ion collision cross-sections are obtained from the pressure-dependent ion linewidths in Fourier transform mass spectra. The effects of these corrections on the accuracy of the cross-sections obtained using the CRAFTI technique are evaluated experimentally using the 20 biogenic amino acids and several crown ether complexes with protonated alkyl monoamines. Good absolute agreement is obtained between the CRAFTI cross-sections and the corresponding cross-sections obtained using both static drift ion mobility spectrometry and computational simulations. These results indicate that the CRAFTI cross-sections obtained using the updated equation presented here are quantitatively descriptive of the size and shape of the gas-phase ions. Cross-sections that differ by less than 3% are measured for the isobaric isomers n-butylamine and tert-butylamine complexed with the crown ethers. This level of precision is similar to what has been achieved previously using traveling wave ion mobility devices. These results indicate that CRAFTI can be used to probe subtle structural differences between ions with approximately the same precision as that achieved in traveling wave ion mobility devices. Graphical Abstract ᅟ.

12-Crown-4 Ether Disrupts the Patient Brain-Derived Amyloid-β-Fibril Trimer: Insight from All-Atom Molecular Dynamics Simulations

Recent experimental data elucidated that 12-crown-4 ether molecule can disrupt Aβ40 fibrils but the mechanism of disruption remains elusive. We have performed a series of all-atom molecular dynamics simulations to study the molecular mechanism of Aβ40 fibril disruption by 12-crown-4. In the present study we have used the Aβ40 fibril trimer as it is the smallest unit that maintains a stable U-shaped structure, and serves as the nucleus to form larger fibrils. Our study reveals that 12-crown-4 ether can enter into the hydrophobic core region and form competitive, hydrophobic interactions with key hydrophobic residues; these interactions break the intersheet hydrophobic interactions and lead to the opening of the U-shaped topology and a loss of β-sheet structure. Furthermore, we observed periods of time when 12-crown-4 was in the hydrophobic core and periods of time when it interacted with Lys28 (chain C), a "tug of war"; the 12-crown-4 binding with Lys28 destabilizes the salt-bridge between Asp23 and Lys28. In addition to the two aforementioned binding modes, the 12-crown-4 binds with Lys16, which is known to form a salt-bridge with Glu22 in antiparallel arranged Aβ fibrils. Our results are in good agreement with experimental results and suggest that molecules that have the ability to interact with both the hydrophobic core region and positively charged residues could serve as potential inhibitors of Aβ fibrils.

Synthesis and biological evaluation of crown ether acyl derivatives

A set of crown ethyl acyl derivatives based on 18-crown-6 moiety was synthesized and evaluated for biological activity. In vitro antiproliferative profiling demonstrated significant activities against HBL-100, HeLa, SW1573 and WiDr human cell lines. The most active compound exhibited GI₅₀ values in the range of 3.7-5.6μM. Antimicrobial evaluation showed that three polyaromatic compounds were active against Staphylococcus aureus (MIC₉₀ values from 8.3μM to 50μM), whereas a (decyloxy)benzene substitution exhibited moderate activity against Candida albicans (MIC₉₀ values 36μM). According to SAR evaluation, the size of the crown ether and the acyl side chain had a significant effect on the bioactivity. Aromatic moieties close to the acyl group led to improved bioactivity as exemplified by some of the tested compounds. These results provide further evidence on the potential of crown ethyl structure as a scaffold for developing new biological probes and lead candidates for drug development.

Radiostrontium monitoring of bivalves from the Pacific coast of eastern Japan

In early April 2011, radiostrontium was accidentally released from the Fukushima Daiichi Nuclear Power Plant to the Pacific coast of eastern Japan. We developed a simple procedure to analyze radiostrontium levels in marine mussels (Septifer virgatus) and seawater using crown ether (Sr Resin; Eichrom). Then, we used our method to describe the spatial and temporal distribution of radiostrontium in mussels and seawater on the Pacific coast of eastern Japan from 2011 to 2013 and for 2015. Activity of (90)Sr in mussels and seawater decreased with distance from the Fukushima Daiichi Nuclear Power Plant and between 2011 and 2013 tended to be higher in areas south of the Fukushima Daiichi Nuclear Power Plant than to the north of it. Activity in mussels and seawater also tended to decrease from 2011 to 2013 and by 2015 had reached levels experienced prior to the Fukushima accident. Our results suggest that radiostrontium discharged from the Fukushima Daiichi Nuclear Power Plant was dispersed by coastal currents in a southerly direction along the Pacific coast of eastern Japan from 2011 to 2013, following which its activity decreased to background levels by 2015.

Studies of a pyridino-crown ether-based chiral stationary phase on the enantioseparation of biogenic chiral aralkylamines and α-amino acid esters by high-performance liquid chromatography

This paper reports the enantioseparation ability of a pyridino-18-crown-6 ether-based chiral stationary phase [(S,S)-CSP-1]. The enantiomeric discrimination of chiral stationary phase (S,S)-CSP-1 was evaluated by HPLC using the mixtures of enantiomers of various protonated primary aralkylamines [1-phenylethylamine hydrogen perchlorate (PEA), 2,3-dihydro-1H-inden-1-amine (1-aminoindan), 2,2'-(1,2-diaminoethane-1,2-diyl) diphenol (HPEN)] and perchlorate salts of α-amino acid esters [alanine benzyl ester (Ala-OBn), phenylalanine benzyl ester (Phe-OBn), phenylalanine methyl ester (Phe-OMe), phenylglycine methyl ester (PhGly-OMe), glutamic acid dibenzyl ester (Glu-diOBn), and valine benzyl ester (Val-OBn)]. The best enantioseparation was achieved in the case of PEA. The high enantioselectivity was rationalized by the strong π-π interaction of the extended π system of the aryl-substituted pyridine unit.

MRI sensing of neurotransmitters with a crown ether appended Gd(3+) complex

Molecular magnetic resonance imaging (MRI) approaches that detect biomarkers associated with neural activity would allow more direct observation of brain function than current functional MRI based on blood-oxygen-level-dependent contrast. Our objective was to create a synthetic molecular platform with appropriate recognition moieties for zwitterionic neurotransmitters that generate an MR signal change upon neurotransmitter binding. The gadolinium complex (GdL) we report offers ditopic binding for zwitterionic amino acid neurotransmitters, via interactions (i) between the positively charged and coordinatively unsaturated metal center and the carboxylate function and (ii) between a triazacrown ether and the amine group of the neurotransmitters. GdL discriminates zwitterionic neurotransmitters from monoamines. Neurotransmitter binding leads to a remarkable relaxivity change, related to a decrease in hydration number. GdL was successfully used to monitor neural activity in ex vivo mouse brain slices by MRI.