Dibenzo-18-crown-6 Research Articles

Surface Molecular Tailoring Using pH-Switchable Supramolecular Dendron-Ligand Assemblies

The rational design of materials with tailored properties is of paramount importance for a wide variety of biological, medical, electronic and optical applications. Here we report molecular level control over the spatial distribution of functional groups on surfaces utilizing self-assembled monolayers (SAMs) of pH-switchable surface-appended pseudorotaxanes. The supramolecular systems were constructed from a poly(aryl ether) dendron-containing a dibenzo[24]crown-8 (DB24C8) macrocycle and a thiol ligand-containing a dibenzylammonium recognition site and a fluorine end group. The dendron establishes the space (dendritic effect) that each pseudorotaxane occupies on the SAM. Following SAM formation, the dendron is released from the surface by switching off the noncovalent interactions upon pH stimulation, generating surface materials with tailored physical and chemical properties.

Polymeric Pseudo-Liquid Membranes from Poly(N-oleylacrylamide).

A polymeric pseudo-liquid membrane (PPLM) was constructed from poly(N-oleylacrylamide) (PC18AAm), which exhibited a rubbery state under membrane transport conditions and used as the membrane matrix. In the present study, dibenzo-18-crown-6 (DB18C6) and dibenzo-21-crown-7 (DB21C7) were adopted as transporters for alkali metal ions. KCl was adopted as a model substrate for DB18C6 and CsCl the latter. Chiral transporter, O-allyl-N-(9-anthracenylmethyl)cinchonidinium bromide (AAMC) was used as a transporter for chiral separation of a racemic mixture of phenylglycine (Phegly). The l-somer was transported in preference to the antipode. The present study revealed that PPLMs are applicable to membrane transport, such as metal ion transport and chiral separation.

Voltammetric study of the transfer of ε-poly-L-lysine at nitrobenzene | water interface

The transfer of a biopolymer, ε-poly-L-lysine (εPL), at a polarized nitrobenzene (NB) | water (W) interface was studied voltammetrically. Despite the polydispersity of sample (n=25–35, n being the degree of polymerization), an S-shaped current-potential curve with a well-defined limiting current was observed in normal pulse voltammogram for the transfer of εPL at the NB | W (pH 3.0) interface. In the W-phase, εPL would exist in the fully protonated form, and the limiting current can be explained by the diffusion of the polycationic εPL species. Also a pair of anodic and cathodic peak currents was observed by cyclic voltammetry. The midpoint potential was in agreement with the half-wave potential in the normal pulse voltammogram. The influence of pH and the supporting electrolyte anions in both phases on the voltammograms has been also studied. By the addition of dibenzo-18-crown-6 (DB18C6) to NB, the half-wave potential shifted to negative potentials. This can be interpreted as being due to the εPL-transfer facilitated by the formation of εPL-DB18C6 complex in NB. The concentration dependence of the half-wave potential can be explained by the formation of 1:n εPL-DB18C6 complex. The results suggest the applicability of the voltammetric technique to compare the phase-transfer characteristics of εPL and the derivatives.

Microhydration Effects on the Encapsulation of Potassium Ion by Dibenzo-18-Crown-6

We have measured electronic and conformer-specific vibrational spectra of hydrated dibenzo-18-crown-6 (DB18C6) complexes with potassium ion, K(+)•DB18C6•(H2O)n (n = 1-5), in a cold, 22-pole ion trap. We also present for comparison spectra of Rb(+)•DB18C6•(H2O)3 and Cs(+)•DB18C6•(H2O)3 complexes. We determine the number and the structure of conformers by analyzing the spectra with the aid of quantum chemical calculations. The K(+)•DB18C6•(H2O)1 complex has only one conformer under the conditions of our experiment. For K(+)•DB18C6•(H2O)n with n = 2 and 3, there are at least two conformers even under the cold conditions, whereas Rb(+)•DB18C6•(H2O)3 and Cs(+)•DB18C6•(H2O)3 each exhibit only one isomer. The difference can be explained by the optimum matching in size between the K(+) ion and the crown cavity; because the K(+) ion can be deeply encapsulated by DB18C6 and the interaction between the K(+) ion and the H2O molecules becomes weak, different kinds of hydration geometries can occur for the K(+)•DB18C6 complex, giving multiple conformations in the experiment. For K(+)•DB18C6•(H2O)n (n = 4 and 5) complexes, only a single isomer is found. This is attributed to a cooperative effect of the H2O molecules on the hydration of K(+)•DB18C6; the H2O molecules form a ring, which is bound on top of the K(+)•DB18C6 complex. According to the stable structure determined in this study, the K(+) ion in the K(+)•DB18C6•(H2O)n complexes tends to be pulled largely out from the crown cavity by the H2O molecules with increasing n. Multiple conformations observed for the K(+) complexes will have an advantage for the effective capture of the K(+) ion over the other alkali metal ions by DB18C6 because of entropic effects on the formation of hydrated complexes.

The new threading system 2-benzyl-5,6-dimethyl-1H-benzo[d]imidazolium – dibenzo-24-crown-8: a model for Monte Carlo calculations incorporating an anion for the first time in threaded structures

A new [2]pseudorotaxane containing a benzimidazolium hydrogen-bonding station for a dibenzo-24-crown-8 (DB24C8) macrocycle is described. The structure of the [2]pseudorotaxane formed is established by 1H NMR spectroscopy, 2D NOESY and a Monte Carlo protocol (including an anion for the first time).

Quantum Chemical Calculations on Binding Energy of Alkyl Substituted Crown Ethers with Sr<sup>2+</sup>

Structures of Dibenzo-18-crown-6(DB18C6), Di-methyl-dibenzo-18-crown-6(DMB18C6), Di-tert-butyl-dibenzo-18-crown-6(DTBB18C6), Di-tert-amyl-dibenzo-18-crown-6(DTAB1C6) and their complexes with strontium ion were optimized based upon DFT at B3LYP using 3-21G basis. The binding energy of crown ethers with Sr2+ was calculated according to the energy of optimal structures. The complex strength increased gradually from DB18C6 to DTAB18C6, which could be related to the changes of cavity size of crown ethers and electron density on the crown rings. Addition and extension of alkyl groups on DB18C6 could enhance the combination between crown and Sr2+.

Analytical solution for the facilitated ion transfer at the interface between two immiscible electrolyte solutions via successive complexation reactions in any voltammetric technique: Application to square wave voltammetry and cyclic voltammetry

Simple, analytical and explicit expressions are presented for the I/E response, interfacial concentrations and concentration profiles for the reversible ion transfer at ITIES of an ion undergoing several equilibrium complexation reactions in both the aqueous and the organic phase. Semi-infinite planar diffusion and excess of ligand in the organic phase have been assumed. These equations are valid for any multipotential step technique, and for any value of the diffusion coefficient for all the species involved. The I/E expressions of cyclic voltammetry and cyclic square wave voltammetry are deduced as particular cases of these equations. An in-depth study of the evolution of the concentration profiles of the free and complexed ion with different parameters of interest has been made, and some interesting conclusions are drawn about the magnitude of their Nernst and δ99 diffusion layer thicknesses. The morphology and behavior of the cyclic and square wave voltammograms in response to changes in the equilibrium complexation constants and in the diffusion coefficients ratio are also studied. Based on these studies, simple methods for the quantitative determination of the equilibrium constants and/or de diffusion coefficients are proposed. The application of these equations to the experimental study of the transfer of decylammonium facilitated by the presence of dibenzo-18-crown-6 (DB18C6) in the membrane has been carried out.

Polymeric pseudo-liquid membranes from poly(octadecyl methacrylate)

The novel liquid membrane system, which is named polymeric pseudo-liquid membrane, was constructed from poly(octadecyl methacrylate) (PC18MA), which showed a rubbery state under operating conditions, as a membrane matrix, and dibenzo-18-crown-6 (DB18C6) for the transport of KCl or O-allyl-N-(9-anthracenylmethyl)cinchonidinium bromide (AAMC) for that of racemic mixture of phenylglycine (Phegly) as a carrier. The results of KCl transport revealed that KCl transport was attained by carrier-diffusion mechanism even though membrane matrix was composed of polymeric material. The polymeric pseudo-liquid membrane containing chiral carrier AAMC showed optical resolution ability, in other words, the membrane selectively transported l-Phegly and its permselectivity toward l-Phegly reached 1.48 at the operating temperature of 40°C. Chiral separation ability was greatly dependent on the operating temperature and a wide range of permselectivity from l-isomer to d-isomer permselectivity was attained by adjusting the operating temperature. The present study revealed that the polymeric pseudo-liquid membrane is a promising membrane system in membrane separation.

Sophisticated Design of PVC Membrane Ion-Selective Electrodes Based on the Mixed Potential Theory

The mixed potential (MP) theory was successfully utilized to design an ionophore-based polyvinyl chloride (PVC) membrane K(+) ion-selective electrode (ISE). Prior to the application of the MP theory, the transfer of K(+) and interfering ions (Na(+), Li(+), and H(+)) facilitated by bis(benzo-15-crown-5) (BB15C5) or dibenzo-18-crown-6 (DB18C6) at a micro PVC membrane/water interface was studied by ion-transfer voltammetry (ITV). The reversible half-wave potentials were then obtained for the facilitated transfer of the ions. Using such voltammetric data and the literature data about diffusion coefficients of ions, we could well-predict the potential responses of the BB15C5- or DB18C6-based K(+) ISE, as the function of the concentrations of primary and interfering ions, and also of the counterion for K(+) [e.g., tetrakis(4-chlorophenyl)borate] added to the membrane. Thus, the MP theory has been proven to be useful to optimize the membrane composition for a higher ion selectivity and a lower detection limit. It has also been found that the leaching of ions from an inner solution is too small to affect the detection limit, at least for the designed PVC membrane ISE.

Preparation of silica gel bound crown ether and its extraction performance towards zirconium and hafnium

A new silica gel bound Dibenzo-18-crown-6(DB-18-C-6) solid extractant (SGN18) was synthesized, and its structure was characterized by FT-IR, TGA, BET and Element analysis. The adsorption and separation behaviors of SGN18 on Zr(IV) and Hf(IV) were investigated in terms of acidity, shaking time and initial concentrations. The complexes of [Zr(DB-18-C-6)] and [Hf(DB-18-C-6)] were investigated by DFT theory to predict the extraction ability of DB-18-C-6 for Zr(IV) and Hf(IV). The results showed that DB-18-C-6 was successfully grafted on the silica gel with a satisfactory grafting degree (17.16wt.%). Analysis on kinetic data indicated that the rate decisive adsorption step was interparticle diffusion for Zr(IV), and film diffusion for Hf(IV), as well as Langmuir isotherm mode was only applicable for Zr(IV). The separation factor of SGN18 for Zr(IV) was greater than for Hf(IV), which was highly consistent with DFT calculation results that the binding energy of DB-18-C-6 with Zr(IV) was greater than Hf(IV). All the experiment outcome proved that the adsorption capacity of SGN18 for Zr(IV) was stronger than the Hf(IV).

Synthesis of a Novel Secondary Dialkylammonium Salt with Three Stations and its Threading Through the Cavity of Two Crown Ethers

In this paper, a novel secondary dialkylammonium salt with three stations (G1) was synthesized in 5 steps. 1H NMR was used to study the threading of G1 through the cavity of dibenzo-24-crown-8 (DB24C8) and benzo-21-crown-7 (B21C7). The complexation of G1 and two crown ethers was proved to be slow-exchange systems. This result lays the foundation on the integrative self-sorting organization of G1, DB24C8 and B21C7.

Polymeric pseudo-liquid membranes from poly(dodecyl methacrylate): KCl transport and optical resolution

A polymeric pseudo-liquid membrane (PPLM) was constructed from poly(dodecyl methacrylate) (PC12MA), which exhibited a rubbery state under membrane transport conditions and was used as the membrane matrix, and from dibenzo-18-crown-6 (DB18C6) or O-allyl-N-(9-anthracenylmethyl)cinchonidinium bromide (AAMC), which was used as a model transporter. Membrane performance was studied using KCl or a racemic mixture of phenylglycine (Phegly) as a model substrate. The PPLM with DB18C6 transported KCl. The membrane transport ability depended on the DB18C6 concentration, implying that DB18C6 worked as a transporter within the PC12MA membrane matrix. L-Phegly was preferentially transported over D-Phegly through the membrane with AAMC from the racemic mixture of Phegly, and the permselectivity was determined to be 1.55. The present results suggest that PPLMs are applicable not only in metal ion transport but also in optical resolution. Polymeric pseudo-liquid membrane (PPLM) was constructed from poly(dodecyl methacrylate), which showed rubbery state under membrane transport conditions, as a membrane matrix and dibenzo-18-crown-6 or O-allyl-N-(9-anthracenylmethyl)cinchonidinium bromide as a model transporter. Membrane performance was studied adopting KCl or racemic mixture of phenylglycine as a model substrate. The present results suggest that PPLMs were applicable to not only metal ion transport but also optical resolution.

PH-Controlled Reversible Formation of a Supramolecular Hyperbranched Polymer Showing Fluorescence Switching

A π-conjugated AB2 monomer 1 with a dibenzo[24]crown-8 (DB24C8) ring and two secondary amine centres has been synthesised. Treatment of a solution of 1 in dichloromethane with trifluoroacetic acid (TFA) leads to protonation of the amine groups, and then the DB24C8 rings are threaded by the dialkylammonium ion centres of other monomer molecules, leading to the formation of a supramolecular hyperbranched polymer, TFA-1. Rather strong π-π stacking interactions between the conjugated cores are evident in this polymer. The supramolecular hyperbranched polymer (SHP) can be completely depolymerised by adding a slight excess of N-tert-butyl-N',N',N'',N'',N''',N'''-hexamethylphosphorimidic triamide, tetrabutylammonium fluoride, or tetrabutylammonium acetate. The acid-base-controlled process induces a reversible change in the fluorescence intensities of the solutions due to the controllable presence of the π-π stacking interactions between the conjugated cores. This dynamic behaviour is significant with respect to "smart" supramolecular polymer materials.

Comparative metal ion extraction of Ag(I), Cu(II), Ni(II), Zn(II), Mn(II), Cd(II) and Co(II) cations using dibenzo 18C6 as a carrier

The competitive metal ion extraction of Ag(I), Cu(II), Ni(II), Zn(II), Mn(II), Cd(II) and Co(II) cations were examined and compared each with other. The experiments were buffered (acetic acid/sodium acetate and formic acid/sodiumformate) at pH 4–6. The extraction of Cu(II) and Ag(I) and Co(II) with Dibenzo 18 crown 6 (DB18C6) ligand is possible, but the extraction efficiency for Ag(I) is much better than Cu(II) and Co(II) ion. The concentrations in the all experiments for the cations and ligand were 0.01M and 1.0×10−3M respectively. Organic phase employed chloroform, dichloromethane and 1,2dichloroethane in individual experiments. The effect of picric acid in aqueous phase to the efficiency of extraction was investigated. The effect of extraction time, rate of shaking, concentration of ligand and presence of picric acid were investigated and optimized.

Separation of Cobalt From Europium with Mesoporous Hybrid Silica-Poly(Styrene) Impregnated Chelating Resin

This article describes resins for extraction chromatography capable of separating cobalt from europium. Radionuclides Eu-152 and Co-57 were used to represent the REEs and heavy metals. Resins were prepared by immobilizing poly(styrene) on porous silica particles and impregnating the particles with an organic extractant: Octyl(phenyl)-N,N-disiobutylcarbamoylmethylphosphineoxide (CMPO), bis(2,4,4-trimethylphentyl)dithiophosphinic acid (Cyanex-301), 2-thenoyl trifluoroacetone (HTTA), tributylphosphate (TBP) or dibenzo-21-crown-7 (DB21C7). The specific adsorption of Eu(III) and Co(II) was studied by measuring distribution coefficients and uptake percentages as a function of contact time, solution pH and metal ion concentration. The new resins, especially Cyanex 301/SiO2-P, provide rapid kinetics and high adsorption selectivity for Co(II). The efficient and selective adsorption of Eu(III) on SiO2-P impregnated with CMPO, a bifunctional organophosphorus compound and HTTA, a β-diketone compound, is attributed to strong complex formation between the soft donor atom of each chelating ligand and trivalent ion.

SELECTIVE RECOGNITION IN POTENTIOMETRIC SENSING BASED ON TWO COMPETITIVE RECOGNITION SITES FOR STATIC AND HYDRODYNAMIC DETERMINATION OF CAMYLOFIN AS A SMOOTH MUSCLE RELAXANT

A poly (vinyl chloride) matrix membrane sensors for selective determination of camylofin (CY) in pharmaceutical formulations were developed based on the use of dibenzo-18crown-6 (DB18C6) as a neutral carrier and ion-association complex ([CY]2[PM])of (CY) cation with phosphomolybdate anion (PM). Subsequently, these electroactive materials were dispersed in dioctyl sebacate (DOS) as solvent mediator designed and can be easily used in flow injection system. Under static mode of operation, the sensors revealed a near Nernstain response over a wide CY + concentration range 8.5x 10 -6 and 5 x 10 -6 to 1.0 x 10 -2 mol L -1 with a detection limit of 6.0x10 -6 and 2.5x10 -6 mol L -1 , respectively. In flow injection potentiometry, excellent reproducibility (RSD %±0.7%), fast response, high sensitivity with a near-Nernstian 53.9±1.1 and 40.2±0.8 mV decade -1 , linear range 1.0x10 -4 -1.0x10 -2 mol L -1 , detection limit 16.4±0.3 and 5.9±0.3 μg mL -1 , high sampling rate (20-22 and 40-45 sample h -1 ) and stable baseline was observed in the presence of 0.05 mol L -1 citrate buffer, pH 4.5 as a carrier for ([CY]2[PM] and (DB18C6) membrane based sensors, respectively. The utility of the sensors was tested for field monitoring of CY + in different pharmaceutical formulations collected from the local market.

Thermally-Induced Phase Transition of Pseudorotaxane Crystals: Changes in Conformation and Interaction of the Molecules and Optical Properties of the Crystals

This paper presents a pseudorotaxane that acts as a thermally driven molecular switch in the single-crystal state. Crystals of the cationic pseudorotaxane consisting of dibenzo[24]crown-8 (DB24C8) and N-(xylylammonium)-methylferrocene as the cyclic and axle component molecules, respectively, undergo crystalline-phase transition at 128 °C with heating and 116 °C with cooling, according to differential-scanning-calorimetry measurements. X-ray crystallographic analyses revealed that the phase transition was accompanied by rotation of the 4-methylphenyl group of the axle component molecule and a simultaneous shift in the position of the PF(6)(-) counteranion. Crystalline phase transition changes the conformation and position of the DB24C8 molecule relative to the ammonium cation partially; the interaction between the cyclic component and the PF(6)(-) anion in the crystal changes to a greater extent. Moreover, there are changes in the vibration angle (θ) and birefringence (Δn) on the (001) face of the crystal transitionally; θ is rotated by +12°, and Δn is decreased from 0.070 to 0.059 upon heating across the phase transition temperature. The phase transition and accompanying change in the optical properties of the crystal occur reversibly and repeatedly upon heating and cooling processes. The switching rotation of the aromatic plane of the molecule induces a change in the optical anisotropy of the crystal, which is regarded as a demonstration of a new type of optical crystal. Partial replacement of the PF(6)(-) anion with the bulkier AsF(6)(-) anion forms crystals with similar crystallographic parameters. An increase in the AsF(6)(-) content decreases the reversible-phase-transition temperature gradually down to 99 °C (T(end)) and 68 °C (T(exo)) ([AsF(6)(-)]:[PF(6)(-)] = 0.4:0.6).

Stereoselective reduction of dibenzo-18-crown-6 ether to dicyclohexano-18-crown-6 ether catalyzed by ruthenium catalysts

Abstract With different kinds of ruthenium catalysts, dibenzo-18-crown-6 (DB18C6) was hydrogenated to dicyclohexano-18-crown-6 (DCH18C6) in n-butyl alcohol solvent at 408 K and 10.0 MPa. The catalysts' activity and stereoselectivity are found to be influenced dramatically by the particle size and valence state of ruthenium, respectively. Especially, high selectivity for cis - syn - cis -DCH18C6 prefers to occur on Ru(0) catalysts. With ruthenium nanoparticles as catalyst, the syn / anti ratio of DCH18C6 product reaches up to 6:1, at a high conversion of DB18C6 (99.4%).

Energy Transfer and Concentration-Dependent Conformational Modulation: A Porphyrin-Containing [3]Rotaxane

A zinc porphyrin-containing [3]rotaxane A was synthesized through a copper(I)-catalyzed azide-alkyne cycloaddition (CuAAC) reaction. Energy donors and acceptor porphyrin were introduced to dibenzo[24]crown-8 (DB24C8) and dibenzyl ammonium (DBA) units of [3]rotaxane A to understand the intramolecular energy transfer process. Investigations of the photophysical properties of [3]rotaxane A demonstrated that the intramolecular efficient energy transfer readily occurred from the donors on the wheels to the porphyrin center on the axis. The fluorescence of energy donors in the region of 400 to 450 nm was efficiently absorbed by the porphyrin acceptor under irradiation at 345 nm, and finally a red light emission at about 600 nm was achieved. Further investigation indicated that the conformation of [3]rotaxane A was self-modulated by changing its concentration in CH(2)Cl(2). The triazole groups on the wheel coordinated or uncoordinated to Zn(2+) through intramolecular self-coordination with the change in the concentration of [3]rotaxane A in CH(2)Cl(2). Therefore, this conformational change was reversible in a non-coordinating solvent such as CH(2)Cl(2) but inhibited in a coordinating solvent such as THF. Such interesting behaviors were rarely observed in porphyrin derivatives. This self-modulation feature opens up the possibility of controlling molecular conformation by varying concentration.

Main-chain hyperbranched polyrotaxane: Synthesis, photophysical properties, and energy funnel

A main-chain hyperbranched polyrotaxane (HBP) assembled by the interaction between dibenzo[24]crown-8 (DB24C8) and dibenzyl ammonium (DBA) was synthesized through Cu(I)-catalyzed azide-alkyne cycloaddition. Energy donors and acceptors were attached to DB24C8 and DBA units, respectively, to investigate the effect of such polyrotaxane structure on the intramolecular and intermolecular energy transfer channel. Our investigations indicated that HBP with higher molecular weight was obtained in relatively lower concentration. AFM, DLS, and SLS analyses revealed that our HBP molecule was described as a ball-shaped nanoparticle with the radius of about 4–8 nm. Benefitting from such unique topology, the aggregation of the chromophores through π-π stacking was effectively suppressed both in solution and in solid state. Meanwhile, the steady-state and time-resolved fluorescence characterization demonstrated that HBP exhibited the excellent energy funneling ability from A3 to B2 unit with high energy transfer efficiency and fast rate, which was attributed to the large spectral overlap between the emission features of the donors and the absorption of the acceptors, and the unique highly branched mechanically interlocked architecture. The energy transfer quantum yield of HBP was calculated to be as high as 99%, and this energy transfer process was estimated to occur with a rate of 7.58 × 109 s−1 with single exponential.