• Journal of the Korean Applied Science and Technology
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• v.22 no.1
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• pp.50-55
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• 2005

A comparison of alkali metal cation and alkaline earth cation solvent extraction was made for three additional monoionizable crown ethers and one diionizable crown ether. sym-(n-Octyldibenzo)-16-crown-5-oxyacetic acid $\underline{1}$ exhibited high efficiency and selecvity in solvent extraction of alkali metal cations with respect to that observed with alkaline earth cations. Sizes of $Na^+$ and $Ca^{2+}$ appropriately match with the cavity size of monoethyl sym-bis[4(5)-tert-butylbenzo]-16-crown-5-oxymethylphosphonic acid $\underline{3}$. As the result, $Na^+$ and $Ca^{2+}$ are the best extracted. sym-(n-Octyldibenzo)-16-crown-5-oxymethyldiphosphonic acid $\underline{4}$was found to be somewhat selective for $Na^+$ over $Li^+$ and other alkaline earth metal cations. In the complexation of alklaine earth cations by crown ether diphosphonic acid $\underline{4}$, $Ca^{2+}$ and $Sr^{2+}$ are the appropriate sizes, but lager $Ba^{2+}$ may be due to favorable formation of a sandwich type complex between the crown ether cavity and the dianion of the deprotonated crown ether phoaphonic acid moiety.

• Bulletin of the Korean Chemical Society
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• v.12 no.5
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• pp.487-490
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• 1991

Electrochemical studies of alkali metal cations $(Na^+, K^+, Rb^+, Cs^+)$ were performed in methanolic solutions of 18-crown-6 and tetrabutylammonium salts at dropping mercury electrodes (DME) and thin mercury film electrodes (TMFE). All the cations investigated were reduced reversibly at DME in the absence and presence of 18-crown-6, and in the latter the limiting currents were decreased and the reduction potentials shifted to the negative direction. The reduction potentials of the metal ions (0.2 mM) in the presence of the crown (10 mM) were - 2.14 $(Na^+)$, - 2.26 $(K^+)$, - 2.20 $(Rb^+) and - 2.14 $(Cs^+)$ V vs. SCE, respectively. The measured potentials were rationalized with ion recognition of the cations by the crown. Electroreduction at TMFE were highly irreversible. A new representation method of ion recognition is presented. In aqueous solutions, electroreduction of the alkali metal ions were characterized by adsorption.

• Journal of Photoscience
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• v.11 no.32
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• pp.83-87
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• 2004

A porphyrin compound containing a crown ether moiety (Por-Crown) and its zinc complex (ZnPor-Crown) have been prepared and the effect of the addition of alkali metal on their fluorescence has been investigated. As alkali metal cations were added, the absorption and fluorescence maxima did not change. However, the absorbance and intensity of fluorescence increased dramatically. Among the alkali metal cations tested, addition of K$^{+}$ and Cs$^{+}$ showed strongest enhancement of absorbance and fluorescence intensity of Por-Crown and ZnPor-Crown.own.

• Bulletin of the Korean Chemical Society
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• v.20 no.10
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• pp.1129-1135
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• 1999

Free energy perturbation and molecular dynamics simulations were carried out to investigate the relative binding affinities of [17] ketonand (1) toward alkali metal cations in methanol. The binding affinities of 1 toward the alkali metal cations were calculated to be in the order Li+ > Na+ > K+ > Rb+ > Cs+, whereas our recent theoretically predicted and experimentally observed binding affinities for [18]starand (2) were in the order K+ > Rb+ > Cs+ > Na+ > Li+. The extremely different affinities of 1 and 2 toward smaller cations, Li + and Na+ , were explained in terms of the differences in their ability to change the conformation to accommodate cations of different sizes. The carbonyl groups constituting the central cavity of 1 can reorganize to form a cavity with the optimal M+ -O distance, even for the smallest Li+, without imposing serious strain on 1. The highest affinity of 1 for Li+ was predominantly due to the highest Coulombic attraction between the smallest Li+ and the carbonyl oxygens of 1.

• Bulletin of the Korean Chemical Society
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• v.26 no.3
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• pp.393-398
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• 2005

The stability constants for the diaza-18-crown-6 ethers 2-6 and alkali metal cations ($Na^+,\;K^+,\;Rb^+\;and\;Cs^+$) were determined using potentiometry in 95% methanol. For each metal ion the stability constants of the partiallyfluorinated ligands 3-6 were larger than that of the non-fluorinated ligand 2, which might reflect an interaction between fluorine atoms and alkali metal cations. The stability constant of the ligand 4 was larger than that of the ligand 5 for each metal cation tested. This finding was also supported by the results of cation-induced chemical shifts in $^1H-,\;^{19}F$-NMR and extraction experiment. The potentiometry and NMR results as well as the X-ray crystal structures revealed that the position and number of fluorine atoms in the benzyl side arms was crucial for the enhanced interaction between a ligand and an alkali metal.

• Analytical Science and Technology
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• v.10 no.1
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• pp.60-65
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• 1997

Solvent extraction of alkali metal and alkaline earth metal cations by mono-crown ether(benzo-15-crown-5) and bis-(crown ether)s(ethylenediamine bis(4'-formyl benzo-15-crown-5)) containing benzo-15-crown-5 moieties were investigated with water-chloroform system at $25^{\circ}C$. The order of the extraction equilibrium constants($K_e$) and the complexation constants($K_c$) for the alkali metal and alkaline earth metal cations with mono-crown ether and bis-(crown ether)s were Ca(II)>Na(I)>Sr(II)>K(I)>Mg(II)>Rb(I) and Sr(II)>Ca(II)>K(I)>Rb(I)>Mg(II)>Na(I) respectively. These results were explained in terms of the size effect of metal cation and electron density effect. Also, the bis-(crown ether)s was found to extract metal cations more effectively than the corresponding mono-crown ether.

• Bulletin of the Korean Chemical Society
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• v.31 no.2
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• pp.453-456
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• 2010

The structural and energetic preferences of thiacalix[4]biscrown-5 with and without alkali metal ions ($Na^+$, $K^+$, $Rb^+$, and $Cs^+$) have been theoretically investigated for the first time using molecular dynamic (MD) simulations and density functional theory (MPWB1K/6-31G(d)//B3LYP/6-31G(d)) methods. The formation of the metal ion complex by the host is mainly driven by the electrostatic attraction between crown-5 oxygens and a cation together with the minor contribution of the cation-$\pi$ interaction between two facing phenyl rings around the cation. The computed binding energies and the atomic charge distribution analysis for the metal binding complexes indicate the selectivity toward a potassium ion. The theoretical results herein explain the experimentally observed extractability order by this host towards various alkali metal ions. The physical nature and the driving forces for cation recognition by this host are discussed in detail.

• Bulletin of the Korean Chemical Society
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• v.18 no.2
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• pp.139-141
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• 1997

• Bulletin of the Korean Chemical Society
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• v.18 no.11
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• pp.1147-1148
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• 1997

• Bulletin of the Korean Chemical Society
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• v.17 no.6
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• pp.564-567
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• 1996