A conductance study of the binding of benzo-15-crown-5 with alkali cations in acetonitrile

The decrease in the molar electrolytic conductance of Na⁺, K⁺, Rb⁺, and Cs⁺ tetraphenylborates, caused by the addition of benzo-15-crown-5 in acetonitrile at constant ionic strength, is analyzed according to a model involving 1:1 stoichiometry. The stability constant,K, and the limiting molar conductivity, _c , for each 1:1 complex are determined from the conductance measurements by using a nonlinear least squares curve fitting procedure. The stability sequence of the 1:1 complexes, as deduced from data at 288, 293, 298, 303, and 308 K, has the order Na⁺>K⁺>Rb⁺>Cs⁺. Values of H ⁰, S ⁰, and _c at 298 K are reported and their significance is discussed.     

ESR studies of the alkali metal complexes of verdazyl-labeled benzo-15-crown-5

A verdazyl derivative of benzo-15-crown-5 ($\text{1}$) has been prepared, and the complex formation between the spin labeled crown ether ($\text{1}$) and the alkali metal salts has been studied by ESR spectroscopy.     

Effect of competing alkali metal cations on neutral Host's anion binding ability

Anion binding by neutral hosts in organic solvents can be inhibited by the presence of alkali metal cations. The binding inhibition is due to salt ion-pairing which increases in the order Cs(+) < K(+) < Na(+). The binding inhibition can be reversed by using heteroditopic hosts that simultaneously bind both the metal cation and the anion. The largest cation-induced enhancements are observed with the less basic anions.     

Relative binding affinities of alkali metal cations to

The binding affinity and selectivity of a new ionophore, [1(8)]starand (1), toward alkali metal cations in methanol were examined through NMR titration experiments and free energy perturbation (FEP) and molecular dynamics simulations. The preference was determined to be K(+) > Rb(+) > Cs(+) > Na(+) > Li(+) in both FEP simulations and NMR experiments. The FEP simulation results were able to predict the relative binding free energies with errors less than 0.13 kcal/mol, except for the case between Li(+) and Na(+). The cation selectivity was rationalized by analyzing the radial distribution functions of the M-O and M-C distances of free metal cations in methanol and those of metal-ionophore complexes in methanol.     

Structural aspects of crown complexes with alkali and alkaline earth cations. Benzo-15-crown-5 as a discriminating macrocycle

X-ray structural results have been reviewed for the related M^z+ L _z ^– -B15C5 complexes where M^z+=Li⁺ to Cs⁺ and Mg²⁺ to Ba²⁺, L^–=2,4,6-trinitrophenolate (Picrate or Pic) and 3,5-dinitrobenzoate (Dnb), and B15C5=benzo-15-crown-5. These results combined with those for come MX_z-B15C5 (X=NCS^–, I^–, NO ₃ ^– , ClO ₄ ^– , BPh ₄ ^– ) complexes have revealed that B15C5 is a useful macrocycle with regard to the within-the-group and between-the-groups discriminations of M^z+ in the solid state.     

A thermodynamic study of the association of alkali metal cations with dicyclohexano-18-crown-6

A thermodynamic study of the association of Na⁺, K⁺, Rb⁺, and Cs⁺ with dicyclohexano-18-crown-6 in acetonitrile has been carried out at 308, 303, 298, 293, and 288 K using a conductometric technique. The observed molar conductivities, A, were found to decrease significantly for mole ratios less than unity. A model involving 11 stoichiometry has been used to analyze the conductivity data. The stability constant,K, and the limiting molar conductivity, A _c , for each 11 complex were determined from the conductivity data by using a nonlinear least squares curve fitting procedure. The binding sequence, based on the value of logK at 298 K, as derived from this study is K⁺>Na⁺>Rb⁺>Cs⁺. Values of H ^o and S ^o are reported and their significance is discussed.     

Synthesis of alkynylbenzo-15-crown-5 ethers

Reactions of 4"-iodobenzo-15-crown-5 ether with ethynylarenes or 4"-ethynylbenzo-15-crown-5 ether with haloarenes in the presence of catalytic amounts of Pd^IIcomplex salts, CuI, and Et₃N gave 4"-(arylethynyl)benzo-15-crown-5 ethers in 55—80% yields.     

A DFT study of the complexation behavior of hemispherands toward alkali metal cations

A density functional theory study of the behavior of hemispherands toward alkali metal ions (Li⁺, Na⁺, and K⁺) is performed. The effect of the replacement of the rigid anisyl group(s) by the mobile ether group(s) on the binding energy of hemispherands with alkali metal ions is investigated. The results indicated that the binding energies are inversely proportional to the ionic radius of the cations. Moreover, increasing the flexibility of the ligand results in decreasing the binding toward small ions. The structures of the hosts and the guests are correlated to the binding energies, and the correlations are interpreted in terms of the principle of preorganization. © 2010 Wiley Periodicals, Inc. Int J Quantum Chem, 2010     

Effect of solvent upon competitive liquid-liquid extraction of alkali metal cations by isomeric dibenzo-16-crown-5-oxyacetic acids

The selectivity and efficiency of competitive liquid-liquid extraction of alkali metal cations into organic solvents containingsym-(octyl)dibenzo-16-crown-5-oxyacetic acid (2) andsym-bis[4(5)-tert-butylbenzo]-16-crown-5-oxyacetic acid (3) have been determined. Solvents examined include: dichloromethane, chloroform, carbon tetrachloride, 1,2-dichloroethane, 1,1,1-trichloroethane, benzene, toluene,p-xylene, chlorobenzene, 1,2-dichlorobenzene, and 1,2,3,4-tetrahydronaphthalene. The Na⁺/K⁺ and Na⁺/Li⁺ extraction ratios are highest in chloroform. The extraction selectivity is found to correlate with the diluent parameter (DP) of the organic solvent.This paper is dedicated to the memory of the late Dr C. J. Pedersen.     

Synthesis of bis-benzo-15-crown-5 and bis-benzo-18-crown-6-ethers

Bis-crown ethers with benzo-15-crown-5 and benzo-18-crown-6 moieties bridged by different length of polyethylene ethers have been successfully synthesized.     

Synthesis of novel chromogenic azocalix[4]arenemonoquinones and their binding with alkali metal cations

Five new chromogenic azocalix[4]arenemonoquinones have been synthesized, characterized and examined for their interaction with alkali metal cations (Li⁺, Na⁺, K⁺, Rb⁺ and Cs⁺) by UV-visible spectroscopic and cyclic voltammetric techniques. It has been determined that 4a selectively exhibits a significant bathochromic shift in its UV-visible spectrum on interaction with potassium ion in comparison to its treatment with other alkali metal cations. The binding stoichiometry of 4a and potassium ion was established to be 1:1 with an association constant of 3.27 × 10⁴ M^?1. Cyclic voltammetric experiments in 4:1 dichloromethane-acetonitrile also revealed a significant anodic shift (ΔE _(1/1′) = 115 mV) of the original redox waves of 4a on interaction with potassium ion.     

Raman study of 12-crown-4, 15-crown-5, 18-crown-6 and their complexation with metal cations using Fourier deconvolution of CH stretching spectra

The Raman CH stretching spectra of 12-crown-4, 15-crown-5 and 18-crown-6 and their complexes with some metal cations— Li⁺, Na⁺, K⁺ and Cu⁺ in water solutions are studied. For the first time Fourier deconvolution is applied to resolve the overlapped components in the corresponding isotropic and anisotropic spectra. A model is introduced which explains the variety of components in the spectra by means of splitting of the unperturbed CH stretching frequency owing to intramolecular interactions and Fermi resonance. The coupling constants of these interactions, as well as all parameters according to the model, are calculated for studied crowns and their complexes. The differences in the number and intensity of the resolved components in the spectra of the various crowns are explained with the corresponding differences in the coupling constants and model parameters. It is established that complexation leads to some increase in the unperturbed stretching frequency, probably owing to the increase in strain of the crown molecule. It is concluded that 15-crown-5 forms 2:1 and 1:1 complexes with K⁺ and Na⁺ cations respectively and 12-crown-4 forms a 2:1 complex with the Na⁺ cation.     

Complexation of acyclic ligands having two terminal quinoline units with alkali metal cations

Abstract

Acyclic multidentate ligands consisting of an oligooxyethylene chain (di-, tri-, tetra-, and penta-) and two terminal rigid quinaldate end groups were newly prepared and their complexation properties with alkali metal cations were estimated by the solvent extraction method to indicate a better affinity for K⁺. Among them, the tetraethylene glycol derivative showed the highest K⁺ binding on about the same level as 18-crown-6. Their conformations in solution and in the solid state were examined by using ¹H- and ¹³C-NMR spectroscopy and X-ray crystal analyses, respectively. The better binding of K⁺ in comparison with the corresponding glymes or analogues having the same donor sites was reasonably explained by considering the effective co-ordination of the carbonyl oxygen of the ester groups and the parallel π-stacking interaction between two quinaldate surfaces.     

Study of alkali metal cations binding selectivity of beta-cyclodextrin by ESI-MS

Cyclodextrins (CDs), cyclic oligosaccharides commonly composed of six, seven or eight (alpha, beta, and gamma respectively) D-glucopyranosyl units connected by alpha-(1,4)- glycosidic linkages, have the ability to form inclusion complexes with a wide range of substrates in aqueous solution. This property has led to their applications in different areas such as enzyme mimics, catalysis and the encapsulation. of drugs. ESI-MS has begun to be viewed as a useful tool for investigating the general area of molecular recognition thus providing a powerful mean for the analysis of a wide array of host-guest complexes and other non covalent complexes present in solution. The evaluation of the binding selectivity of beta-cyclodextrin towards the first group alkali cations is reported. The estimation of the affinity degrees has been achieved by competition ESI-MS experiments. In these experiments beta-CD was incubated at the presence of two different cations at the same time, and the ratio of the mass peaks corresponding to the two complexes was calculated. In general, it appears a much larger affinity of the beta-cyclodextrin molecule with sodium with respect to all the other alkaline cations, thus giving evidence that it is the size of the beta-cyclodextrin ring in relation with the cationic radius, which drives the formation of what, at this point, could be defined as an inclusion complex.     

The Synthesis of Perfluorocyclohexano-15-crown-5 Ether

Perfluorocyclohexano-15-crown-5 ether, trans- (1) and cis-(2) isomers have been prepared by direct fluorination using the LaMar fluorination technique¹. They have several potential applications and are of special interest in a variety of fields².     

氧化偶氮双苯并-15-冠-5的合成及其性质

合成了一种新的双冠醚,氧化偶氮双苯并15-冠-5。初步探讨了它的光异构现象及其对稀土和碱金属离子的萃取能力。     

单苯并15-冠-5的超声作用合成

以邻苯二酚、一缩二乙二醇双氯乙醚为原料,氢氧化钠为模板剂,DMF为溶剂及适量抗氧化剂2,6-二-叔丁基对甲苯酚存在下,在超声辐射作用下60~70 ℃反应合成了B-15-C-5。 反应时间缩短为2 h,产率最高可达30.7%。     

Synthesis and design of tetrapyrrole molecular receptors for alkali metal cations

meso-Phenylporphyrins containing at the benzene ring a conformationally labile polyether fragment with a terminal pyridine ring were synthesized, and their spectral and physicochemical properties were studied. The relations found between the spectral parameters of the tetrapyrrole chromophore, on the one hand, and acid-base equilibria and complex formation with alkali metal cations, on the other, showed the possibility for design of porphyrin-based molecular ensembles possessing useful properties.     

Coordination chemistry of alkali and alkaline earth cations: Synthesis and crystal structure of potassium(benzo-15-crown-5)2 [3,5-dinitrobenzoate(3,5-dinitrobenzoic acid)2]

The interaction of K(35-Dnb) (35-Dnb=3,5-dinitrobenzoate) with benzo-15-crown-5 (B15C5) in ethanol yields a charge-separated sandwich structured complex [K(B15C5)₂]⁺[35-Dnb(35-DnbH)₂]^– even when equimolar amounts of reactants were used and no external 35-DnbH was added to the reaction mixture. The complex (KC₄₉H₅₁O₂₈N₆, FW=1211.1), is monoclinic,P2₁/c,a=11.063(2),b=10.680(1),c=46.548(8) Å, =91.629(2)⁰,Z=4,D ₀=1.485 g/cm³,D _c=1.468 g/cm³, CuK =1.5418 Å, =17.01 cm^–1, 2<130⁰,F(000)=2520,T=298 K. FinalR for the 6618 observed reflections was 0.071. In the sandwich moiety, the K⁺ is 10-coordinated through all the oxygens of the crown molecules (K⁺–O, 2.76–3.11 Å). The 35-Dnb anion lies 5.3 Å below the lower crown mean plane and is charge separated with respect to K⁺ (K⁺–O^–>7 Å) but undergoes strong hydrogen bonding (2.59 and 2.49 Å) through each carboxylate oxygen with the carboxylic protons of two separate 35-DnbH molecules. Supplementary Data relating to this article are deposited with the British Library as Supplementary Publication No. SUP 82014 (52 pages).