Crown Ethers In Water Research Articles

Enhanced molecular binding affinity toward aromatic dications by anthracene-derived crown ethers in water.

The pursuit of high molecular binding affinity using conventional crown ethers in water remains a challenging task in the field of supramolecular chemistry and may hold great promise in the creation of advanced biocompatible nanoconstructs. In this work, the molecular binding strength toward a series of structurally relevant cationic guests has been greatly enhanced by tetrasulfonated 1,5-dianthracenyl-42-crown-10 and as investigated by means of 1H NMR, UV-vis, and fluorescence spectroscopy, the host-guest association constants can reach up to 108 M-1 order of magnitude in aqueous solution. X-ray crystal diffraction analysis further demonstrates that the aromatic dication can be tightly encapsulated in the ring of anthracene-derived crown ether via multiple π-stacking and electrostatic interactions. Meanwhile, the obtained association constants are remarkably higher than the ones in the cases of the known benzene- and naphthalene-derived sulfonated crown ethers, substantiating that the appropriate extension of π-conjugation in the molecular skeleton of crown ether is a feasible method in attaining a highly affiliative host-guest complex. Taken together, our results indicate that the anthracene-based sulfonated crown ether can be developed as a new family of water-soluble macrocyclic receptors in the fabrication of functional nanoarchitectures.

Insights in the determination of saxitoxin with fluorogenic crown ethers in water

In this contribution, we present new insights and a critical discussion in the optical detection of saxitoxin using fluorophores with crown ethers. Fluorescence enhancement is caused by the reduction of photoinduced electron transfer upon complexation with the analyte. Our attempts to improve this detection method neither did yield a functioning sensor nor were the attempts to reproduce published data in this area successful. Due to the fact that only low concentrations of saxitoxin are available, multiple surrogates were investigated at high concentrations. However, no turn on response was observed. Moreover, a fluorescent decomposition product of saxitoxin that forms under UV light was discovered which was in our opinion misinterpreted as a sensor response by previous publications.Graphical abstract

Partition coefficients of macrocyclic crown ethers in water–organic biphasic system: DFT/COSMO-RS approach

The partition coefficients for a large number of macrocyclic crown ethers in different water–organic bi-phasic systems at BP-SVP-AM1 and BP-TZVP level of theory using novel conductor like screening model for real solvents (COSMO-RS) approach are presented here for the first time. The predicted values of partition coefficient obtained from the present calculation are compared with the available reported experimental results. The calculated values of partition coefficient obtained from the first principle based COSMO-RS theory are in reasonably good agreement with the available experimental results. The present study reveals that the solvents with strong hydrogen bond donating, weak hydrogen bond accepting and high dipolarity/polarizability are the good solvents for partitioning of a neutral organic solute. The partitioning of a neutral solute in a particular solvent is enhanced due to increased hydrophobicity.

Water soluble crown ethers: selective masking agents for improving extraction-separation of zinc and lead cations

The presence of crown ethers 12C4, 15C5 and 18C6 (CE) in aqueous phase influences extraction-separation of zinc and lead ions (M2+) by acidic extractant bis(2-ethylhexyl)phosphoric acid (DEHPA) in cyclohexane. In fact, higher complexing ability of the crown ethers towards lead ions causes a greater shift toward higher pH region of the extraction curves versus aqueous phase pH, and consequently an enhancement in the extraction selectivity. The order of extraction selectivity in the presence of the crown ethers varies as 18C6 > 15C5 > 12C4. The analysis of extraction data allows evaluating the stability constants of [M•CE]2+ complexes in the aqueous phase. It is demonstrated that the influence of aqueous crown ethers on the extraction process is deeply affected by the organic diluent used. The influence of temperature on the extraction process was studied in the range 286–302 K. This study lets estimating the thermodynamic parameters, i.e., free-energy (ΔGo), enthalpy (ΔΗo), and entropy (ΔSo) changes associated with the extraction process as well as the complexation of cations by the crown ethers in water.

Stabilities in nitromethane of alkali metal ion complexes with dibenzo-18-crown-6 and dibenzo-24-crown-8 and their transfer from nitromethane to other polar solvents

Stability constants for the 1:1 complexes of Na +, K +, Rb +, and Cs + with dibenzo-18-crown-6 (DB18C6) and dibenzo-24-crown-8 (DB24C8) have been determined by conductometry at 25 °C in a poorly solvating solvent, nitromethane. For both the crown ethers, the stability constant decreases with increasing metal ion size, Na + > K + > Rb + > Cs +, regardless of the size compatibility between the metal ions and the ligand cavities. A comparison of the results with those in several other solvents (S: acetonitrile, propylene carbonate, water, methanol, and N, N-dimethylformamide) leads to the conclusion that the selectivity sequence of these crown ethers in nitromethane agrees with the intrinsic one in the absence of a solvent. Transfer activity coefficients of the crown ethers and their complexes from nitromethane to S have been determined to evaluate the solute–solvent interactions. It is shown that DB24C8 shields the alkali metal ions more effectively from the solvents than DB18C6 because of the larger number of oxygen atoms and the more flexible structure of DB24C8. Regarding the complexation in nitromethane as a reference, the complex stability and selectivity in S are discussed. The selectivities of these crown ethers in water, methanol, and N, N-dimethylformamide, which apparently obey the size-fit concept, are largely due to the solvation of the free alkali metal ions.

Calorimetric study of the interactions of disaccharides with crown ethers in water

In aqueous solutions, D-maltose and especially sucrose can form specific intermolecular interactions with 18-crown-6; this is in contrast to their behaviour with 15-crown-5.

Complex Formation of Metal Ions with Sulfonated Crown Ethers in Water as Ion Size Selective Masking Reagents.

A new type of water-soluble sulfonated crown ether has been prepared and utilized as an ion size selective masking reagent with a view to establishing a highly selective extraction-separation system. In the synergistic extraction of alkaline earths with 4-benzoyl-3-methyl-1-phenyl-5-pyrazolone and trioctylphosphine oxide in cyclohexane, the extraction of these with larger ionic radii shifted to a higher pH region on adding the sulfonated crown ether to the aqueous phase, giving improved separations. A similar result was achieved in the extraction of lanthanides into cyclohexane with bis(2-ethylhexyl)phosphoric acid. The complex formation of alkaline earth and lanthanide ions with the sulfonated crown ethers in the aqueous solution were evaluated via the solvent extraction method.

Enthalpic and volume effects in the interaction of d-glucose with crown ethers in water

The enthalpies of solution of 12-crown-4, 15-crown-5, 18-crown-6 and 1,10-diaza-18-crown-6 in aqueous d-glucose, were determined experimentally. The cross coefficients of the virial expansion of the excess enthalpies were calculated. On the basis of experimental density data, the limiting partial molar volumes of transfer of crown ethers from water to 1 m aqueous d-glucose solution were also evaluated. It is shown that the interactions between crown ethers and d-glucose are weak, but that the endothermic effect of these interactions decreases with an increase in the size of the crown ether macrocycle.

Enthalpies of interaction of some amino acids and peptides with crown ethers in water at 25°C

Enthalpies of dilution of ternary aqueous solutions containing glycine, diglycine, triglycine, l-α-alanine, l-α-alanyl- l-α-alanine and 12-crown-4, 15-crown-5, 18-crown-6, 1,10-diaza-18-crown-6 at 298.15 K have been determined. The results have been analysed in terms of the McMillan-Mayer formalism to obtain the enthalpic virial coefficients for heterotactic interactions. It is concluded that the solvation state and the macrocycle size of the crown ethers do not determine the entire change of the cross enthalpic coefficients h xy for the peptide-crown interaction. On the contrary, the influence of specific contributions to the host-guest interaction leads to linearity of the dependence of h xy values for 18-crown-6/peptide interaction versus the heat capacity of solution Δ sol C p of glycyl peptides. The effect of the solvent on the selectivity of the peptide-crown interaction is also discussed.

Cation-crown ether complex formation in water. II. Alkali and alkaline earth cations and 12-crown-4, 15-crown-5, and 18-crown-6

The stability constants and the partial molal volume and isentropic partial molal compressibility changes of complex formation between cations and crown ethers in water at 25°C are presented. The cations involved are Na+, K+, Rb+, Cs+, Ca2+, and Ba2+, and the crown ethers are 12-crown-4, 15-crown-5, and 18-crown-6. Values of ΔV of complex formation have been discussed in terms of two simple models, one based on the scaled particle theory, and the others on the Drude-Nernst continuum model. The results indicate that the charge of the potassium cation in 18-crown-6 is especially well screened from the water. On this basis hydration numbers of complexed cations have been calculated. This shows that the size of the cation compared to the crown ether hole is important for the contacts between complexed cations and water.