Pseudo-crown Ether Research Articles

Chitosan grafted with crown ether with high selectivity and adsorption on lithium-ion

Currently, Lithium is the lightest metal known in nature, which is widely applied in most walks of life. However, the present storage of lithium resources in the world is far from meeting the consumption market surge demand for lithium resources. Liquid lithium resources such as Salt Lake brine and seawater brine will become the primary source and inevitable choice for lithium extraction in the future due to a large amount of lithium, and its recovery requires a simple and effective process. This study synthesized TEG4MEC, a pseudo-crown ether monomer with a ring unit, to achieve effective Lithium-ion (Li+) recognition through specific interaction with Li+. Then, the TEG4MEC monomer was grafted onto the surface of cross-linked chitosan microspheres (CCS) by surface initiation polymerization. A series of static and dynamic adsorption studies showed that the pH value of the solution had a significant effect on Li+ adsorption. For CCS-TEG4MEC microspheres, the best adsorption effect was observed at pH = 7.0. The maximum adsorption capacity of Li+ on CCS-TEG4MEC microspheres obtained by Langmuir isotherm fitting is 156.16 mg g−1. In addition, CCS-TEG4MEC microspheres also showed effective regeneration performance and highly stable adsorption capacity, which could be reused.

Fast room‐temperature self‐healing vitrimers enabled by accelerated associative exchange kinetics

Enhanced dynamicity remains a matter of concern in vitrimer design for fast self-healing materials. In this study, we fabricated pseudo-cyclic vinylogous urethane (VU) vitrimers with accelerated associative exchange kinetics and enhanced mechanical properties based on a bottom-up strategy. Unique cation-templated pseudo-crown ether building blocks were prepared via coordination of alkali metal ions. The resultant pseudo-cyclic VU vitrimers possess higher crosslinking densities and more orderly arranged network topologies than their counterpart vitrimer based on linear building blocks, which were confirmed by swelling experiments and free volume parameters determination. Tensile strength and toughness were significantly improved, which are positively correlated with complexation strength. Furthermore, both stress relaxation and creep recovery experiments demonstrate that pseudo-cyclic vitrimers can undergo more rapidly topological rearrangement due to the synergetic effect of unique pseudo-cyclic structure and alkaline metal salts-promoted catalytic dynamic exchange. Given that the resultant vitrimers exhibit a high-efficient self-healable capability at room temperature. This work contributes to tailor-make fast room‐temperature self‐healing vitrimers via a building block design and expands the potential of vitrimers.

Pseudo-crown ether III: Naphthalimide-Pd(II) based fluorogenic ensemble for solution, vapour and intracellular detection of amine and anti-counterfeiting applications

A bis-naphthalimide based pseudo-crown ether as metal complex-based ensemble (DN-1 + Pd2+) is reported for the sensing of tris(2-aminoethylamine) (TAEA). The DN-1 moiety exhibited cyan blue fluorescence in solution and solid state (CIE plot) with high quantum yield (φ = 0.92). The DN-1 showed selective fluorescence quenching at 450 nm upon addition of Pd2+ ions, whereas ensemble showed revival of the fluorescence upon addition of TAEA owing to displacement of Pd2+ ions from the binding cavity due to higher binding affinity of TAEA for Pd2+ ions. The detection limit of DN-1 for Pd2+ is 0.1 µM and the ensemble for TAEA is 0.8 µM. The complexation–decomplexation mechanisms were supported by optical, NMR, DLS, CV and AFM studies. The DN-1 and ensemble were successfully utilized for the intracellular imaging of Pd2+ ions and TAEA, respectively, in MG-63 live cells. The ensemble was successfully utilized for fabrication of solution and SiNPs based test kits for the detection of TAEA in solution and vapour phase. The DN-1 was further employed as information security ink for the anti-counterfeiting applications and for fabrication of IMPLICATION logic gate.

Pseudo-Crown ether II: Intracellular and solution-, SiNPs based test-kits for ppm level detection of H2S gas

Perylene diimide based pseudo-Crown ether derivatives have been synthesized and characterized and their photophysical properties towards Fe3+ and H2S in 50% HEPES buffer–CH3CN and CH3CN solutions have been studied. PDI 1 showed formation of supramolecular aggregates with nanorods (dimer) morphology. Upon addition of Fe3+ ions, nanorods of PDI 1 transformed to spheres and PDI 1/2 showed a decrease in absorbance at (542 nm) and emission (578 nm) intensities supported by Job's plot, DLS, CV, WXRD and NMR techniques. The detection limits for Fe3+ are as low as 0.6 μM. We utilized PDI 1+Fe3+ complex as an ensemble for detection and discrimination of bio thiol derivatives. Upon addition of H2S (7.5 μM) and Cys (19 μM), the ensemble showed an increase at 542/578 nm (‘OFF-ON’) and further addition of H2S/Cys caused a decrease at same wavelength (‘ON-OFF’) with formation of new absorbance band at 630 nm (‘OFF-ON’). The mechanism of interaction of H2S involves reduction of Fe3+ to Fe2+ ions, followed by binding of HS− to form (PDI 1+Fe2++HS) complex. PDI 1 and PDI 1+Fe3+ complex has been successfully utilized for bioimaging of Fe3+ ions and H2S, respectively in live MG-63 cells. The solution and silica NPs based colorimetric test-kits were fabricated and detection of 30–60 ppm H2S gas has been achieved. These ‘OFF-ON-OFF’ and ‘ON-OFF-ON’ molecular switches mimic functioning of IMPLICATION, AND logic gates.

Cation Template‐Assisted RAFT Cyclopolymerization of Hexa(Ethylene Glycol) Di(meth)acrylates to Thermoresponsive Pseudo‐Crown Ether Polymers

Front Cover: In article number 2000670 by Yoshihiko Kimura and Takaya Terashima, hexa(ethylene glycol) di(meth)acrylates efficiently interact with a potassium cation to dynamically form pseudo cyclic monomers. Combined with such a supramolecular technique, RAFT cyclopolymerization of hexa(ethylene glycol) di(meth)acrylates with a potassium cation template is developed to successfully synthesize cyclopolymers comprising 24-membered hexa(ethylene glycol) rings. The cyclopolymers serve as thermoresponsive pseudo-crown ether polymers.

Pseudo-crown ether having AIE and PET effects from a TPE-CD conjugate for highly selective detection of mercury ions

A new tetraphenylethylene-cyclodextrin (TPE-CD) conjugate with a linkage composed of long triethylene glycol chain and triazole ring on the CD rim has been designed and synthesized. The TPE-CD conjugate exists in a stretched form in DMSO and enhances its fluorescence after addition of a small amount of water due to aggregation-induced emission (AIE) effect. However, in the presence of a large amount of water, the TPE unit will enter the cyclodextrin cavity to form a folded self-inclusion compound. In the self-inclusion compound, not only nitrogen-containing pseudo-crown ether is formed but also arouses photo-induced electron transfer (PET) process from nitrogen atoms of triazole ring to TPE unit and quenches the fluorescence although more aggregation occurs in more water. This is the first finding that TPE-macrocycle conjugate can form pseudo-crown ether and has both the AIE phenomenon and the PET effect. Interestingly, only mercury ion arouses the fluorescence recover of the self-inclusion compound by entering the pseudo-crown ether cavity and blocking the PET process by binding to the nitrogen atoms, while other tested metal ions almost have no effect on the fluorescence. Therefore, the TPE-CD conjugate can be used for the highly selective fluorescence "Turn-On" detection of Hg2+.

A novel magnetic layered double hydroxide as potent mesoporous recyclable heterogeneous nanocatalyst for the synthesis of 1H‐chromeno[2,3‐b]pyridine‐3‐carbonitrile derivatives

A magnetically separable cobalt complex of macrocyclic pseudo‐crown ether (PCE) immobilized on magnetic Cu/Al‐layered double hydroxide (γ‐Fe2O3@Cu3Al‐layered double hydroxide (LDH)/PCE‐Co) was readily fabricated using a simple four‐step postsynthetic modification strategy. This newly prepared nanocomposite was characterized by different chemo‐physical approaches, including Fourier transform infrared (FT‐IR), scanning electron microscopy (SEM), transmission electron microscopy (TEM), inductively coupled plasma optical emission spectroscopy (ICP‐OES), vibrating sample magnetometer (VSM), X‐ray diffraction (XRD), nitrogen adsorption–desorption isotherms, energy‐dispersive X‐ray spectroscopy (EDX), and elemental mapping. The catalytic performance of these nanoparticles (NPs) was explored in the synthesis of diverse 1H‐chromeno[2,3‐b]pyridine‐3‐carbonitrile derivatives via one‐pot three‐component reactions under green reaction conditions. Environmentally benign reaction conditions, simple separation, high yields of the reactions, versatility, easy magnetic separation, and reusability for several runs without significant loss of catalytic performance are the key advantages that make this protocol an ideal alternative method for the synthesis of chromene derivatives.

Cation Template-Assisted RAFT Cyclopolymerization of Hexa(Ethylene Glycol) Di(meth)acrylates to Thermoresponsive Pseudo-Crown Ether Polymers.

Cation template-assisted reversible addition fragmentation/chain transfer (RAFT) cyclopolymerization of hexa(ethylene glycol) diacrylate (PEG6DA) or hexa(ethylene glycol) dimethacrylate (PEG6DMA) is developed as a versatile system to produce large in-chain ring cyclopolymers, thermoresponsive pseudo-crown ether polymers. For an efficient synthesis, potassium hexafluorophosphate (KPF6 ) is employed as a cation template; PEG6DA as well as PEG6DMA recognizes the potassium cation with the hexa(ethylene glycol) spacer to dynamically form a pseudo-cyclic divinyl monomer. Those monomers interacting with the potassium cations are efficiently polymerized with RAFT agents and radical initiators into cyclopolymers comprising 24-membered hexa(ethylene glycol) rings. The cation template-assisted RAFT cyclopolymerization is also effective for the synthesis of amphiphilic random cyclocopolymers bearing hydrophilic hexa(ethylene glycol) rings and hydrophobic butyl groups. Cyclopolymers of PEG6DA and PEG6DMA further show thermoresponsive solubility in water. The cloud point temperature of cyclopoly(PEG6DA)s is higher than that of a cyclopoly(PEG6DMA).

Controllable polymeric pseudo-crown ether fluorescent sensors: responsiveness and selective detection of metal ions

A series of responsive polymeric fluorescent sensors were fabricated by post-grafting pyrene and poly(ethylene glycol) onto the backbone of a pseudo-crown ether containing cyclopolymers, and showed good selective recognition toward metal ions.

Multiple Stimuli-Responsiveness Fluorescent Probe Derived from Cyclopolymers and Pyrene-Ended Ammonium Salts

A multiple stimuli-responsiveness fluorescent probe was fabricated by host-guest recognition between cyclopolymers with larger pseudo crown ether cavities in backbones and pyrene-ended ammonium sal...

PEO-based electrolytes blended with star polymers with precisely imprinted polymeric pseudo-crown ether cavities for alkali metal ion batteries

Tailor-made star polymers comprised of cross-linked cores containing polymeric pseudo-crown ether cavities and linear poly(ethylene oxide) (PEO) arms are designed via cation template-assisted cyclopolymerization. The pseudo-crown ether cavities in cross-linked cores can coordinate with alkali metal cations and offer more cation diffusion channels. Moreover, the functional linear PEO arms are beneficial to the conductivity of cations and increase the compatibility with the PEO matrix. By selecting monomers with different chain lengths and cation templates, the tailor-made star polymers can be employed as efficient conductors for lithium-ion, sodium-ion, and potassium-ion batteries. The lithium-ion conductivity of the solid-state polymer electrolytes obtained from a potassium cation template and poly(ethylene glycol) dimethacrylate (PEGDMA750) monomer (K-SPE750-Li) is 2.82 × 10-5 S cm-1 at 20 °C. Furthermore, the cell of Li|K-SPE750-Li|LiFePO4 shows stable cycling performance and a good rate property.

A novel fluorescence sensor for K + based on bis-Bodipy: The ACQ effect controlled by cation complexation of pseudo crown ether ring

Three novel bis-Bodipy 3a-3c bridged with crown ether chain were prepared in yields of 70∼78%. Their complexation absorption and fluorescent spectra for fourteen metal ions suggested that compound 3b exhibited the selective response for K+ with obvious ACQ effect. The association constant of compound 3b with K+ was 4.3×105 M-1 and 1:1 complex mode was deduced. The complexation mechanism of ACQ effect controlled by cation complexation of pseudo crown ether ring was confirmed by the fluorescent titrations, complexation FT-IR spectra, complexation 1H NMR spectra, complexation ESI-MS spectra and contrast experiment of similar mono-Bodipy derivative. The K+ was binded in the cavity of a pseudo crown ether ring, leading to the closed distance for two Bodipy units and then enhancing the ACQ effect obviously. Both the structure of the crown ether chain and two Bodipy units were decisive factors for the selective fluorescence sensor for K+.

Aqueous self-assembly and cation selectivity of cobaltabisdicarbollide dianionic dumbbells.

The anion [3,3'-Co(C2B9H11)2](-) ([COSAN](-)) produces aggregates in water. These aggregates are interpreted to be the result of C-H⋅⋅⋅H-B interactions. It is possible to generate aggregates even after the incorporation of additional functional groups into the [COSAN](-) units. The approach is to join two [COSAN](-) anions by a linker that can adapt itself to act as a crown ether. The linker has been chosen to have six oxygen atoms, which is the ideal number for K(+) selectivity in crown ethers. The linker binds the alkaline metal ions with different affinities; thus showing a distinct degree of selectivity. The highest affinity is shown towards K(+) from a mixture containing Li(+), Na(+), K(+), Rb(+) and Cs(+); this can be indicative of pseudo-crown ether performance of the dumbbell. One interesting possibility is that the [COSAN](-) anions at the two ends of the linker can act as a hook-and-loop fastener to close the ring. This facet is intriguing and deserves further consideration for possible applications. The distinct affinity towards alkaline metal ions is corroborated by solubility studies and isothermal calorimetry thermograms. Furthermore, cryoTEM micrographs, along with light scattering results, reveal the existence of small self-assemblies and compact nanostructures ranging from spheres to single-/multi-layer vesicles in aqueous solutions. The studies reported herein show that these dumbbells can have different appearances, either as molecules or aggregates, in water or lipophilic phases; this offers a distinct model as drug carriers.

Polymeric pseudo-crown ether for cation recognition via cation template-assisted cyclopolymerization

Cyclopolymerization is a chain polymerization of bifunctional monomers via alternating processes of intramolecular cyclization and intermolecular addition, to give soluble linear polymers consisting of in-chain cyclic structures. Though cyclopolymers comprising in-chain multiple large rings potentially show unique functionality, they generally require the elaborate design of bifunctional monomers. Here we report cation template-assisted cyclopolymerization of poly(ethylene glycol) dimethacrylates as an efficient strategy directly yielding polymeric pseudo-crown ethers with large in-chain cavities (up to 30-membered rings) for selective molecular recognition. The key is to select a size-fit metal cation for the spacer unit of the divinyl monomers to form a pseudo-cyclic conformation, where the two vinyl groups are suitably positioned for intramolecular cyclization. The marriage of supramolecular chemistry and polymer chemistry affords efficient, one-pot chemical transformation from common chemical reagents with simple templates to functional cyclopolymers.

Reactions of a Cyclodimethylsiloxane (Me2SiO)6with Silver Salts of Weakly Coordinating Anions; Crystal Structures of [Ag(Me2SiO)6][Al] ([Al] = [FAl{OC(CF3)3}3], [Al{OC(CF3)3}4]) and Their Comparison with [Ag(18-Crown-6)]2[SbF6]2

Two silver-cyclodimethylsiloxane cation salts [AgD6][Al] ([Al] = [Al(ORF)4](1) or [FAl(OR(F))3](2), R(F) = C(CF3)3, D = Me2SiO) were prepared by the reactions of Ag[Al] with D6 in SO2(l). For a comparison the [Ag(18-crown-6)]2[SbF6]2(3) salt was prepared by the reaction of Ag[SbF6] and 18-crown-6 in SO2(l). The compounds were characterized by IR, multinuclear NMR, and single crystal X-ray crystallography. The structures of 1 and 2 show that D6 acts as a pseudo crown ether toward Ag(+). The stabilities and bonding of [MDn](+) and [M(18-crown-6)](+) (M = Ag, Li, n = 4-8) complexes were studied with theoretical calculations. The calculations predicted that D6 adopts a puckered C(i) symmetric structure in the gas phase in contrast to previous reports. 18-Crown-6 was calculated to bind more strongly to Li(+) and Ag(+) than D6. (29)Si[(1)H] NMR results in solution, and calculations in the gas phase established that a hard Lewis acid Li(+) binds more strongly to D6 than Ag(+). A comparison of the [MD(n)](+) complex stabilities showed D7 to form the most stable metal complexes in the gas phase and the solid state and explained why [AgD7][SbF6] was isolated in a previous reaction where ring transformations resulted in an equilibrium of [AgD(n)](+) complexes. In contrast, the isolations of 1 and 2 were possible because the corresponding equilibrium of [AgD(n)](+) complexes was not observed with [Al](-) anions. The formation of the dinuclear complex salt 3 instead of the corresponding mononuclear complex salt was shown to be driven by the gain in lattice enthalpy in the solid state. The bonding to Li(+) in D6 and 18-crown-6 metal complexes was described by a quantum theory of atoms in molecules (QTAIM) analysis to be mostly electrostatic while the bonding to Ag(+) also had a significant charge transfer component. The charge transfer from both D6 and 18-crown-6 to Ag(+) and Li(+) metal ions was depicted by the QTAIM analysis to be of similar strength, and the difference in the stabilities of the complexes was attributed mostly to more attractive electrostatic interactions between 18-crown-6 and the metal ions despite the more negative oxygen atomic charges calculated for D6.

Selective BODIPY® based fluorescent chemosensor for imaging Pb2+ ion in living cells

A new fluorescent probe has been designed and synthesized by linking dicarboxylate pseudocrown ether to the BODIPY® (4,4-difluoro-4-bora-3a,4a-diaza-s-indacene) fluorophore. The probe allows determination of free lead ions in living cells.

Ion recognition properties of poly[Cu(3-MeOsalpd)] films

Poly[Cu(3-MeOsalpd)] films with good physical, chemical and electrochemical stability may be potentiodynamically electrodeposited with high deposition efficiency from acetonitrile solutions of the monomer. Comparative coulometric assays with the Ni-based analogue show that the metal in the salen motif does play a role in the electronic structure of the polymer, but that the electroactive response is ligand (not metal) based. The dynamics of redox switching are ultimately limited by coupled electron/counter ion diffusion, but this process is sufficiently rapid that it influences the voltammetric response only for thick films (Γ >420 nmol cm−2) at high scan rates. Redox cycling in monomer-free electrolyte shows a voltammetric signature that responds, via interaction with the pseudo-crown ether receptor sites, to the presence of Li+, K+, Mg2+ and Ba2+ ions in solution. The most prominent change is associated with the first anodic peak in the i-E signature. For each of the metal ions considered, this peak potential responds logarithmically to concentration in a manner that varies with individual complexed cation and film thickness and to an extent greater than predicted by the Nernst equation. The film characteristics offer some analytical promise, including a trade-off between sensitivity and dynamic range and signal amplification, possibly due to supramolecular effects.

Construction of Cooperative and Responsive Supramolecular Systems for Molecular Functional Modulation

Abstract The transfer and modulation of the molecular information are necessary processes for cooperative and responsive molecular functions. When functional molecules are responsive to external (intermolecular) as well as internal (intramolecular) stimuli, the molecules exhibit cooperative functions in principle. We have developed a variety of cooperative and responsive supramolecular systems created on the basis of new concepts for the molecular design of sophisticated functional systems. The first uses pseudomacrocycles including pseudocrown ether, pseudocryptands, and pseudocyclophanes as novel frameworks for response functions by utilizing a metal ion as an effector. The second utilizes a molecular gate responding to an external signal. The gate is opened and closed by a signal achieving perfect on–off switching for guest recognition. The next exploits metal-accumulated molecular systems bearing oligo C=N moieties as a binding site for metal ions. This strategy is remarkably useful for producing new binding sites by structural fixation of multi-metal complexes and to modulate properties of metal ions. Other cooperative molecular assembling systems for host generation are also demonstrated in this account. Metallo-frameworks and self-assembled metallo-systems recently developed in our laboratories, which have high potential for synergistic molecular functions, are discussed. Future cooperative functional systems will be widely applicable as multi-responsive multi-functional supramolecules, molecular functional cascades for successive molecular functions and function amplification. Study of cooperative and responsive molecular systems may lead to more general fields such as complex systems science, which is at the interface of chemistry, physics, biology, and mathematics.

Real-Time Monitoring of Copolymer Stabilized Growing Gold Nanoparticles

A great challenge in the production of nanoparticles with defined sizes and properties is to control their growth in situ. We developed a dedicated combined small-angle X-ray scattering (SAXS) and X-ray absorption spectroscopy (XAS) setup to monitor nanoparticle formation in solution. The capabilities of simultaneously deriving particle sizes and oxidation states of atoms/ions are illustrated for the formation of spherical gold nanoparticles by the reduction of hydrogen tetrachloroaureate (HAuCl(4)). Particles with initial radii of 4.60 +/- 0.10 nm and final radii of 5.67 +/- 0.10 nm were produced in a levitated droplet with a volume of 4 microL. An ethylene oxide/propylene oxide triblock copolymer PEO-PPO-PEO (Pluronic F-127) functions as reducing agent and colloidal stabilizer. XANES shows in situ how the gold was reduced in the droplet from Au(III) to Au(0), and simultaneously SAXS recorded the size distribution of the formed nanoparticles. It is shown that the final particle number is reached quickly. Thereafter, only the particles' sizes increase. Comparison of XANES and SAXS shows that the quantity of Au(0) is higher than the quantity of gold located in the nanoparticles while the particles are growing. Finally, all the Au(0) is found in the nanoparticles. We tentatively attribute this finding to the pseudo crown ether effect of the polymer surfactant that kinetically stabilizes gold atoms when formed from gold ions within their protecting cavity. A simple "burst" mechanism for the gold nanoparticle formation is the consequence. The possibility of an inhomogeneous particles structure with an enhanced density near the particle surface is discussed.

Preparation and use of Leadfluor-1, a synthetic fluorophore for live-cell lead imaging

Leadfluor-1 (LF1) is a small-molecule fluorescent sensor for detecting lead in biological and environmental samples, including live cells. This dye uses a xanthenone fluorescent scaffold coupled to a dicarboxylate pseudocrown ether receptor to achieve selective detection of Pb(2+) in the presence of biologically relevant metal ions, including divalent calcium, magnesium and zinc. LF1 fluorescence increases by up to 18-fold on binding Pb(2+). In this protocol, we describe the synthesis and application of LF1 to imaging lead accumulation within live cells. The preparation of LF1 is anticipated to take 14-21 d, and the imaging assays can be performed in 1-2 d with cultured cells.