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.     

Complexation of di-benzyloxy ether derivatives of calix[4]arene with alkali earth metal cations

The synthesis and complexing abilities of 26,28-bis-benzyloxy-25,27-dihydroxy-5,11,17,23-tetra-tertbutyl-calix[4]arene towards alkali earth metal ions Mg²⁺, Ca²⁺, Sr²⁺, and Ba²⁺ in a methanol-chloroform mixture have been evaluated at 25°C, using UV-Vis spectrophotometric techniques. The results showed that the ligand is capable to complex all alkali earth cations by 1:1 metal to ligand ratios. The selectivity presented considering the calculated stability constants are in the order Mg²⁺ > Ca²⁺ > Sr²⁺ > Ba²⁺ towards the ligand.     

Synthesis of hexahomotrioxacalix[3]naphtalenes and a study of their alkali-metal cation binding properties

The first syntheses of the C3-symmetrical and unsymmetrical hexahomotrioxacalix[3]naphthalenes 3 and 4, respectively, and the corresponding tert-butyl hexahomotrioxacalix[3]naphthalene 3a are reported. A convergent synthesis of the linear hexahomotrimer precursors 19 and 19a is described, but the direct synthesis of 3 and 3a can also be achieved from the monomers 20 and 20a, respectively. A limited study of the binding properties of alkali-metal cations by 3 or 3a using a picrate-CHCl3 extraction showed only weak abilities to bind with the cations examined.     

Novel ion-pair receptors based on hexahomotrioxacalix[3]arene derivatives

A series of novel heteroditopic hexahomotrioxacalix[3]arene triamide receptors capable of binding an anion and cation simultaneously in a cooperative fashion has been prepared. The lower rim functionalized cone-hexahomotrioxacalix[3]arene derivatives cone-5a-5d bearing three amide groups were synthesized from cone-3 by a stepwise reaction. The crystal structures of 5c and 5d and (1)H NMR studies in nonpolar solvents strongly indicate that a number of interesting intramolecular hydrogen bonding interactions exist in these receptors. The binding abilities of these compounds towards n-butylammonium chloride and bromide salts have been investigated using (1)H NMR titration experiments in CDCl(3) solvent. Owing to the 'flattened cone' conformations and intramolecular hydrogen bonding involving the amide NH and neighbouring O atoms in cone-5a-5d, the affinities toward n-Bu(4)NX (X = Cl(-) and Br(-)) were weakened. However, it should be noted that triamides cone-5a-5d show a single selectivity for halide anions in the presence of n-BuNH(3)(+) through intermolecular hydrogen bonding with the amide NH hydrogen atoms in the receptors in CDCl(3) solution. Association constants were calculated from the chemical shift changes of the amide protons.     

Interaction between p-tetraphenyl tetrahomodioxacalix[4]arene amide derivatives and alkali and alkaline-earth metal cations

The binding properties of four amido derivatives of p-tetraphenyl tetrahomodioxacalix[4]arene towards alkali and alkaline-earth metal cations using UV-absorption spectrophotometry, ¹H NMR and ESI-mass spectrometry techniques are reported.     

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.     

Determination of binding constants of various alkali metal cations with p-sulfonatocalix[8]arene by using inclusion equilibrium with thionine dye

The binding constants of various alkali metal cations with water-soluble p-sulfonatocalix[8]arene (Calix-S8) were determined spectrophotometrically by using the inclusion equilibrium of thionine (Th) dye as a chemical indicator. Depending on the kind of alkali metal cations, the inclusion constants of Calix-S8 for Th decrease steeply with an increase in salt concentrations. Alkali metal cations compete with the organic guest Th in the Calix-S8 inclusion. Based on a competitive binding experiment, the binding constants of alkali metal cations with Calix-S8 were evaluated to be 17, 60, and 11 dm⁶ mol^?2 for Na⁺, K⁺, and Cs⁺, respectively. We have demonstrated an absorption-based method of evaluating the binding constants of spectroscopically inert metal cations with Calix-S8 and shown the effects of salts on the molecular recognition of Calix-S8.     

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 effects of O-substituents of hexahomotrioxacalix[3]arene on potentiometric discrimination between dopamine and biological organic/inorganic cations

As an interesting type of molecular recognition at a membrane surface, the tri-O-acetic acid ester (host 2) of hexahomotrioxacalix[3]arene, when incorporated into poly(vinyl chloride) (PVC) liquid membranes, displays a high potentiometric selectivity for dopamine over, not only other catecholamines (noradrenaline, adrenaline), but also quaternary ammonium guests (tetramethylammonium, choline, and acetylcholine) and inorganic cations (Na+, K+, NH4+). Interestingly, changes in membrane potential based on the host-guest complexation of host 2 that were observed dopamine/inorganic cation selectivity were not displayed by the related hosts 3 and 4, which contain amide substituents. This paper describes our efforts to separately estimate the two factors contributing to the dopamine selectivities, i.e., the guest lipophilicity factor and the host-guest complexation factor, in an attempt to understand the effects of the O-substituents of these hosts. The potentiometric experiments showed that, although the guests had roughly equal lipophilicity, the electromotive force (EMF) response for dopamine by host 2 was excellent. Furthermore, host 2 displayed ca. a 20-fold stronger complexation for dopamine, compared to noradrenaline, adrenaline, K+, and NH4+ cations. These results indicate that the high potentiometric selectivity of the ion-selective electrode for dopamine mainly reflect, not the guest lipophilicity factor but the host-guest complexation factor. On the other hand, host 3 displayed ca. a 3000-fold stronger binding to Na+ than dopamine, thus explaining the reasons for the lower dopamine-selectivities of host 3 compared to host 2. It is interesting to note that the high potentiometric selectivities for dopamine were displayed by not only host 2 but also host 5, regardless of the simple structure of the O-substituents.     

Conformational properties of the calix[4]naphthalenes

The base-catalyzed condensation of 1-naphthol and formaldehyde in refluxing dimethylformamide affords three isomeric cyclic tetramers which are conformationally flexible over a wide temperature range. Their tetrabenzoate esters however show restricted flexibility. Variable-temperature NMR and low-temperature COSY is used to analyze the conformational preferences of these calix[4]naphthalenes.This paper is dedicated to the commemorative issue on the 50th anniversary of calixarenes.     

Conformational features of calix[4]arenes with alkali metal cations: A quantum chemical investigation with density functional theory

A variety of conformations for three model calix[4]arenes with 8 or 12 OH groups have been investigated by calculations at density functional (RI-BP86) and RI-MP2 level of approximation. The calixarenes form stable complexes with the alkali metal cations of lithium up to caesium. For the investigations all-valence electron basis sets as well as various effective core potentials were probed. The stabilities of complexes were analysed in comparison with the corresponding benzene complexes, M⁺·C₆H₆. The formation of the calixarene metal complexes is considered in two steps, (a) in a distortion from the equilibrium conformation of the free calixarenes and (b) subsequent complexation. The distortion energies are small for the ‘crown’ and larger for the ‘boat’ conformations. On the other hand the latter are more stabilized by significant interaction energy of the cation with two adjacent π-systems of the aromatic rings. As a result, these two conformations are of similar stabilities for K⁺ to Cs⁺ complexes with resorc[4]arenes, with a slight advantage for the ‘boat’ structure. The most stable conformation for the coordination products of these cations with the calix[4]arene with 12 OH groups is a slightly flattened ‘crown’ that is derived by maximum hydrogen bonding of the OH-groups and the most effective cation-π interactions. Special cases are complexes of Li⁺ and Na⁺ which in most instances prefer the coordination on the oxygen atoms of the upper rim of the calixarene cavities and thus form ‘boat’-like structures.     

Heteroditopic receptors tris(2-pyridylamide) derivatives derived from hexahomotrioxacalix[3]arene triacetic acid

The lower rim functionalized cone-hexahomotrioxacalix[3]arene tris(2-pyridylamide) derivatives cone- 3 and cone-7 having the hydrogen bonding groups and 2-pyridyl groups were synthesized from triol 1 by a stepwise reaction. Extraction data for alkali metal ions, transition metal ions, and alkyl ammonium ions from water into dichloromethane are discussed. Due to the strong intramolecular hydrogen bonding between the neighboring NH and CO groups, their affinities to metal cations were weakened. The complexation modes of cone-3 and cone -7 with n-BuNH₃Cl and AgSO₃CF₃ were also demonstrated by ¹H NMR titration in CDCl₃. Tris(2-pyridylamide) derivatives cone-3 and cone-7 can complex with n-butyl ammonium ion and silver cation at the same time to form the heteroditopic complexation.     

Ionic recognition by thiacalixarenes: binding of alkali and heavy metal ions by thiacalix[4]arene-bis-crown[n] ethers

The binding properties of two thiacalix[4]arene-bis-crown[n] derivatives (n = 5 and 6) were examined through extraction experiments. The stability constants of the resulting complexes in methanol were determined. The replacement of the bridging CH2 groups by sulfur atoms leads to a strong decrease in both extraction and complexation levels of alkali metal ions but does not affect the selectivity within the series of crown ethers. The stability of complexes with heavy metal ions does not change markedly on passing from thiacalix[4]arene-bis-crown[n] ethers to their calix[4]arene-bis-crown[n] counterparts; therefore no clear-cut conclusions about the possible interactions between these cations and the sulfur atoms can be drawn.     

Synthesis, binding properties and theoretical studies of p-tert-butylhexahomotrioxacalix[3]arene tri(adamantyl)ketone with alkali, alkaline earth, transition, heavy metal and lanthanide cations

p-tert-Butylhexahomotrioxacalix[3]arene tri(adamantyl)ketone (1b) was synthesized for the first time. Compound 1b was obtained in a cone conformation in solution at room temperature, as established by NMR spectroscopy (¹H and ¹³C). The binding properties of ligand 1b for alkali, alkaline earth, transition, heavy metal and lanthanide cations have been assessed by phase transfer and proton NMR titration experiments. Molecular mechanics and ab initio techniques were also employed to complement the NMR data. The results are compared to those obtained with other closely related homooxacalixarene derivatives. Although triketone 1b is a weak extractant, it shows a strong peak selectivity for Na⁺ and also some preference for Ag⁺. Proton NMR titrations indicate the formation of 1:1 complexes between 1b and the cations studied, and also that they should be located inside the cavity defined by the phenoxy and carbonyl oxygen atoms. Although the molecular mechanics results show little correlation with the NMR data, a good agreement was obtained with the ab initio models.     

Complex-forming and selectivity properties of substituted tetraphenylethylenediphosphine dioxides with respect to alkali metal cations

The complex-forming reactivity of mono- and disubstituted ethylenediphosphine dioxides of the general formula Ph₂P(O)CH₂C(R¹R²)P(O)Ph₂, and of a tetraphosphorylated monopodand, ortho-bis[4,5-bis(diphenylphosphinyl)-pentoxy]benzene, relative to alkali metal cations have been determined conductometrically in THF-CHCl₃ medium (4:1). Introduction of alkyl substituants in the ethylene bridge of tetraphenylethylenediphosphine dioxide increases its Li/Na selectivity; maximum Li/Na selectivity equal to 40 is observed for the dimethyl-substituted tetraphenylethylenediphosphine dioxide derivative. Among the ligands examined herein the hexadentate tetraphosphoryl-containing monopodand ortho-bis[4,5-bis(diphenylphosphinyl)pentoxy]benzene was found to be the most effective complex-forming agent with respect to lithium (log=6.0), with a high Li/Na selectivity value equal to 40. The syntheses of 1,1-dimethyltetraphenylethylenediphosphine dioxide and of ortho-bis[4,5-bis(diphenylphosphinyl)pentoxy]benzene are described.Translated from Izvestiya Akademii Nauk SSSR, Seriya Khimicheskaya, No. 4, pp. 873–877, April, 1990.The authors wish to thank Z. N. Vostroknutovii for carrying out the stability constant measurements in anhydrous acetonitrile.     

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.     

Ultraviolet-ultraviolet hole burning spectroscopy in a quadrupole ion trap: dibenzo[18]crown-6 complexes with alkali metal cations

Conformation selective: A new technique of ultraviolet-ultraviolet hole burning spectroscopy that can be applied to ions stored in a quadrupole ion trap (QIT) is developed and used to obtain the conformation-selective electronic spectra of dibenzo[18]crown-6 complexes with alkali metal cations (M(+), see picture; F(+) = fragment).     

p-t-Butylcalix[4]arene tetra-acetamide: a new strong receptor for alkali cations [1]

From the reaction ofp-t-butylcalix[4]arene with -chloro-N,N-diethyl acetamide a new lipophilic ether-amide ligand (2) has been obtained in high yield. Solution studies show (2) to be a very strong cation receptor for alkali cations, especially sodium and potassium. The X-ray crystal structure determination of the free ligand (2) and two potassium complexes (KI and KSCN) shows the calix[4]arene in a fixed cone structure and the cation completely encapsulated in a polar cavity of eight oxygen atoms. Supplementary Data relating to this article are deposited with the British Library as supplementary publication No. SUP 82059 (57 pages).Presented at the Fourth International Symposium on Inclusion Phenomena and the Third International Symposium on Cyclodextrins, Lancaster, U.K., 20–25 July 1986.     

Complexation of decamethylcucurbit[5]uril with alkali metal ions

Four coordination compounds, namely [Na(H₂O)(H₂O)₂⊂C₄₀H₅₀N₂₀O₁₀](C₆H₆O₂)₂Cl·8H₂O (1), [K₂(H₂O)₂(H₂O)⊂C₄₀H₅₀N₂₀O₁₀](C₆H₆O₂)₂Cl₂·7H₂O (2), [Rb₂(H₂O)₂(H₂O)⊂C₄₀H₅₀N₂₀O₁₀](C₆H₆O₂)₂Cl₂·7H₂O (3) and [Cs(H₂O)₂(H₂O⊂C₄₀H₅₀N₂₀O₁₀)](C₆H₆O₂)₂Cl·6H₂O (4), were obtained by the reactions of the corresponding alkali metal salts with decamethylcucurbit[5]uril (Me₁₀Q[5]) in the presence of hydroquinone, and their structures were determined by single-crystal X-ray diffraction. The results revealed that in compounds 1 and 4 each Me₁₀Q[5] ligand coordinates one Na⁺ or Cs⁺ ion to form a molecular bowl structure, while in compounds 2 and 3 each Me₁₀Q[5] ligand coordinates two K⁺ or Rb⁺ ions to form a closed molecular capsule structure, and adjacent molecular capsules bridge each other through water molecules to form 1D coordination polymers. In addition, we found that the coordination distances for the metal ions and the height of the metal ions out-of-portal-plane for the four compounds are in the same order, 1 < 2 < 3 < 4, which is attributed to the fact that the radius of alkali cations is in the order Na⁺ < K⁺ < Rb⁺ < Cs⁺. Although each portal of Q[6] binds with two alkali cations (not including Cs⁺), the Q[6]-based alkali cations complexes display similar structural trends.