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.     

Ester derivatives of hexahomotrioxacalix[3]naphthalenes: conformational and binding properties with alkali metal cations

The syntheses of the triesters formed between ethyl bromoacetate and hexahomotrioxacalix[3]naphthalene 8, and its tert-butyl analogue 11, are described. Depending on the conditions employed, cone or partial cone conformers are produced. The conformations appear to have some influence on their complexation in neutral medium, with alkali metal cations. The X-ray structure of the partial cone triester 10 is presented.     

Binding of inorganic cations by p-sulfonatocalix[4]arene monitored through competitive fluorophore displacement in aqueous solution

A new working principle for detecting inorganic cation binding by water-soluble calix[4]arenes involves the displacement of a fluorescent azoalkane as guest. Fluorescence regeneration is observed for various metal ions, and binding of monovalent cations (alkali and ammonium) to p-sulfonatocalix[4]arene is detected and quantified for the first time.     

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.     

Selectivity of solid-contact Ag potentiometric sensors based on thiacalix[4]arene derivatives

Potentiometric sensors based on glassy carbon electrode covered with polyaniline and thiacalix[4]arenes containing amidopyridine, morpholide, pyrrolidide and hydrazide functional groups in cone, partial cone and 1,3-alternate conformations have been developed and applied for determination of Ag(+) ions in the range from 1.0 x 10(-2) to 4.0 x 10(-7)M and limits of detection from 1 x 10(-7) to 3.5 x 10(-8)M. The sensitivity of Ag(+) detection decreases in the following range of thiacalix[4]arene substituents: morpholide>pyrrolidide>amidopyridine>hydrazide. Potentiometric selectivity coefficients predominantly showed binding of Ag(+), Hg(II) and Fe(III) ions over other transient and alkali metals. The influence of functional groups and conformation of receptor on the selectivity of the sensor response was investigated. As shown, selectivity and sensitivity of Ag(+) determination depends on the steric accessibility of the binding site and flexibility of the receptor structure. For Fe(III) ions, changes of the sensor potential are also determined by their implementation in redox reactions of polyaniline.     

Suzuki-Miyaura coupling on the three upper rims of hexahomotrioxacalix[3]arenes

The efficient functionalization of three upper rims based on Suzuki-Miyaura coupling to temporarily lower rim-protected hexahomotrioxacalix[3]arenes was developed. After deprotection of the three protecting groups, the three upper rim-functionalized and lower rim-free hexahomotrioxacalix[3]arenes 5a-5m were synthesized.     

Self-assembly of [2]pseudorotaxanes based on pillar[5]arene and bis(imidazolium) cations

A simple bis(imidazolium) dication, 1,4-bis[N-(N'-hydroimidazolium)]butane, can act as a new template for formation of [2]pseudorotaxane with pillar[5]arene, in which the dethreading/rethreading process can be controlled by addition of base and acid. The effect on the association constant of both the solvent and counterion is also described.     

Complexation of some univalent organic cations with hexaethyl p-tert-butylcalix[6]arene hexaacetate in nitrobenzene saturated water

From extraction experiments and γ-activity measurements, the exchange extraction constants corresponding to the general equilibrium C⁺(aq) + 1·Cs⁺(nb) ?1·C⁺ (nb) + Cs⁺(aq) taking place in the two–phase water–nitrobenzene system (C⁺ = methylammonium, ethylammonium, propylammonium, ethanolammonium, diethanolammonium, triethanolammonium, protonated tyramine, protonated dopamine, protonated DL–noradrenaline; 1 = hexaethyl p-tert-butylcalix[6]arene hexaacetate; aq = aqueous phase, nb = nitrobenzene phase) were evaluated. Furthermore, the stability constants of the 1·C⁺ complex species in nitrobenzene saturated with water were calculated; they were found to increase in the following cation order: protonated tyramine < protonated dopamine < triethanolammonium < diethanolammonium < protonated DL-noradrenaline < propylammonium < ethanolammonium < ethylammonium < methylammonium.     

New fluorescent sensor for antimony and transition metal cations based on rhodamine amide-arm homotrioxacalix[3]arene

A new fluorescent sensor 1 based on the rhodamine amide-armed homotrioxacalix[3]arene was synthesized, and its sensing behavior toward metal ions was investigated by UV–vis and fluorescence spectroscopies. Upon the addition of metal cations (Sb³⁺, Fe³⁺, Ni²⁺), a significant fluorescent enhancement in the range of 500–600 nm and colorimetric change was observed.     

Colourimetric and spectroscopic discrimination between nucleotides and nucleosides using para-sulfonato-calix[4]arene capped silver nanoparticles

The complexation of nucleosides and nucleotides by hybrid nanoparticles capped by para-sulfonato-calix[4]arene shows clear discrimination between purine and pyrimidine based molecules. For the pyrimidine nucleotides there is appearance of a new absorption band around 550 nm, and a colour change from yellow to orange red and pink.     

Synthesis, Structures and Ion Selectivity of Homocalix[3]arene Thioketals derived from Homocalix[3]arene Ketones

The hetero-functionalized host bearing pyrene andtosyl moieties substituted at the lower and upper rims of cyclodextrin, namely,mono-3^A-deoxy-3^A-pyrenebutylamido-6^X-O-mono-(p-toluenesulfonyl)mono-altro--cyclodextrin(mixture :gamma; -1; X = A, B, C, D, E, F, G,or H), has been synthesized in order to investigate itsfluorescent sensing system for organic guests such as steroidsand terpenoids. This host showed pure monomer fluorescence, in which the host fluorescence increasedin intensity on accommodation of bile acids and terpenoids or decreased in fluorescence intensityupon addition of ketosteroids. The extent of fluorescence variation with a guest was employed to evaluatethe sensing ability of the host. The sensing parameter I/I°, where I and I°are the fluorescence intensities in the presence and absence of a guest and I is I - I°, was used to describe the sensing ability. The host detected ketosteroids with negative parameters, on theother hand, bile acids and terpenoids were recognized by the host with positive parameters. Thebehaviors of the appended moieties of the host during host–guest complexation were studied by induced circulardichroism (ICD) and fluorescence spectra. The host compound showed different patterns depending on theguest. The guest-induced variations in the ICD and fluorescent spectra suggest that the pyrene moietyacts to elevate the binding ability and the tosyl moiety plays a roll as a spacer to regulate thecyclodextrin cavity size.     

Hexahomotrioxacalix[3]arene derivatives as ionophores for molecular recognition of dopamine, serotonin and phenylethylamine

The lower rim functionalized hexahomotrioxacalix[3]arene derivatives cone-3 and cone-5 bearing three benzyl and three N,N-diethyl-2-aminoethoxy groups, respectively, were synthesized from triol 1. Their complexation with 2-(3,4-dihydroxyphenyl)ethylamine (dopamine), 5-hydroxytryptamine (serotonin), and 2-phenylethylamine (phenethylamine), which have biologically important activities, has been studied by (1)H-NMR spectroscopy. The chemical shifts of the aromatic protons of the host and guest molecules and the up-field shifts of the ethyl protons of the guest molecules strongly suggest the formation of inclusion complexes in solution. The formation of the host-guest complexes is assisted by a hydrogen bond and/or an electrostatic interaction between the host and ammonium ion (RNH(3)(+)) of the guest. The structures of receptors cone-3 and cone-5 have been determined by X-ray crystallography.     

Study on thermal decomposition of calix[6]arene and calix[8]arene

Thermal decomposition kinetics of calix[6]arene (C6) and calix[8]arene (C8) were studied by Thermogravimetry analysis (TG) and Differential thermal analysis (DTA). TG was done under static air atmosphere with dynamic heating rates of 1.0, 2.5, 5.0, and 10.0 K min⁻¹. Model-free methods such as Friedman and Ozawa–Flynn–Wall were used to evaluate the kinetic parameters such as activation energy (E _a) and pre-exponential factors (ln A). Model-fitting method such as linear regression was used for the evaluation of optimum kinetic triplets. The kinetic parameters obtained are comparable with both the model-free and model-fitting methods. Within the tested models, the thermal decomposition of C6 and C8 are best described by a three dimensional Jander’s type diffusion. The antioxidant efficiency of C6 and C8 was tested for the decomposition of polypropylene (PP).     

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.     

Hydrogen bonding nature between calix[6]arene and piperidine/triethylamine

We investigated the binding nature of the 1,2,3-alternate calix[6]arene with one piperidine, two piperidines, and two triethyl amines with a special emphasis on the hydrogen bonding networks by density functional theory calculations. The 1,2,3-alternate calix[6]arene strongly binds with piperidines and triethylamines at two different binding sites, exo and endo sites. In the two binding sites, the hydrogen bonding nature shows a characteristic difference. In the exo site, there formed only one hydrogen bond, while in the endo site, two hydrogen bonds except for the triethylamine. The proton transfer within the hydrogen bonding and the hydrogen bonding types, normal hydrogen bonding (NHB), short strong hydrogen bond (SSHB), and low barrier hydrogen bonding (LBHB), will be discussed in detail.     

Modification of the upper rim of homooxacalix[3]arenes and complexation between a nitrohomooxacalix[3]arene derivative and n-hexylamine

Several functional groups were introduced on the upper rim of (lower rim free) homooxacalix[3]arene for the first time. The swinging nitrohomooxacalix[3]arene host 1 was fixed in the cone conformation by complexation with n-hexylamine.     

Recognition of quaternary ammonium cations by calix[4]arene derivatives supported on gold nanoparticles

Calix[4]arene derivatives supported on monolayer protected gold clusters show a remarkable enhanced binding efficiency towards quaternary ammonium salts in homogeneous solution of apolar solvents with respect to the corresponding unsupported hosts.     

Comparative study of the response of membrane electrodes based on calix[6]arene and calix[8]arene derivatives to organic ammonium ions.

p-tert-Butylcalix[8]arene-octaacetic acid octaethyl ester and calix[8]arene-octaacetic acid octaethyl ester well recognized 2-phenylethylamine and phenylalanine methyl ester compared with the corresponding calix[6]arene derivatives. Moreover, the calix[8]arene derivatives, especially one having tert-butyl groups, gave better selectivity against biologically active amines having a complicated structure, such as norephedrine. We considered the interaction between calixarenes and organic ammonium ions from the viewpoint of molecular symmetries.     

Supramolecular interaction between water-soluble calix[4]arene and ATP--the catalysis of calix[4]arene for hydrolysis of ATP

The catalysis effect of water-soluble calix[4]arene C[4] (calix[4]arene-5,11,17,23-tetrasulfonate) on hydrolysis of ATP in aqueous solution was studied by HPLC. Using laser photolysis and pulse radiolysis, the supramolecular interaction between water-soluble calix[4]arene and ATP was investigated.