A modular approach to organic, coordination complex and polymer based podand hosts for anions

A range of novel host molecules with various degrees of preorganisation for the supramolecular complexation of anionic guest species are analysed within the context of other recent advances in the field. A modular approach to the design of cationic podands incorporating both organic and coordination compound cores is discussed. Special attention is given to ‘pinwheel’ hosts with functionalities including pyridyl, bipyridyl, aminopyridyl and ureas. The electrochemical and photochemical anion sensing by these functionalised podands is also reviewed. Much larger and more pre-organised calixarene units with consequent alteration of complexation properties, as well as the extension of this work to polystyrene-based and coordination polymer systems and metallogels are also covered.     

杯[4]芳烃硫脲衍生物的合成及其对阴离子的络合性能

杯[4]芳烃四丁醚经过对位硝化反应后在水合肼作用下被还原成氨基衍生物， 并进一步与异硫氰酸苯酯反应得到单取代与1，3－二取代的杯[4]芳烃硫脲衍生物 ，总收率为50％。它们对系列阴离子的络合实验表明氢键的形成在络合过程中有重 要作用，其中杯[4]双硫脲衍生物5b对H2PO4^-显现出良好的选择性络合能力。     

Solvent-dependent host–guest complexation of two homologous merocyanines by a water-soluble calix[8]arene: Spectroscopic analysis and structural calculations

The sulfonated calixarene I₈C₁₂ acts as a host for homologous merocyanines Mc1 and Mc2 in organic solvents, exhibiting neither selectivity towards the guest dyes nor solvent dependence of the complexation equilibria. In water, on the contrary, only the lower homologue, Mc1, is solubilized in the presence of the calixarene. A combination of UV–visible and fluorescence spectroscopic and photophysical analysis and MD structural simulation of the calixarene-dye complexes was employed to account for the observations, and suggests that a radical change in the complexation mode occurs upon moving from an organic to an aqueous environment.     

Counterion‐Controlled Self‐Sorting in an Amphiphilic Calixarene Micellar System

Molecular recognition of small molecules and ions by artificial receptors in microheterogeneous media such as micelles and vesicles can, in principle, provide better models of biological systems in comparison with bulk solutions. In this work we have investigated the complexation of an organic fluorescent probe with amphiphilic calixarene receptor below and above the critical micelle concentration (CMC). For concentrations below the CMC, the probe forms a host–guest complex with the calixarene behaving like a traditional host–guest system operating in bulk solution. Above the CMC, multiple equilibrium processes are established and the probe can exchange between the recognition site of the calixarene in the monomeric state, micellized state and/or the micellar hydrophobic core. Careful analysis of the results obtained from NMR spectroscopy and fluorescence experiments allowed us to propose a quantitative model to describe the system. The increment of the local concentration of Na⁺ counterions at the Stern layer displace the dye to the micelle core through competitive binding of Na⁺ in the cavity of the receptor and is decisive for the observed self‐sorting behavior.     

Surface enhanced vibrational (IR and Raman) spectroscopy in the design of chemosensors based on ester functionalized p-tert-butylcalix[4]arene hosts

Surface-enhanced IR (SEIR) and Raman scattering (SERS) have been employed to study the adsorption of ester functionalized tert-butyl calix[4]arenes on Ag and Au nanostructured surfaces as well as their complexes with pyrene. The influence of adsorption and complexation with pyrene on the host calixarene structure was tested for two different calixarene molecules bearing carboethoxy groups (CH(3)CH(2)COOCH(2)-) in the low rim at positions 1,3- and 1,2,3,4-. The results obtained with SEIR were compared to those obtained with SERS, to better understand the interaction mechanism of the studied calixarenes with the metallic surfaces and the ligand as well as to investigate the structure/selectivity relationship of these two surface techniques in the analysis of recognition problems in which these ester functionalized calixarene molecules are involved.     

Novel phosphorylated calixarenes for the recognition of f-elements

The binding properties of three series of phosphorylated calixarene derivatives bearing phosphine oxide or phosphonate groups either at the wide or the narrow rims have been investigated towards some representative lanthanide and actinide ions using several approaches: (i) liquid–liquid extraction of europium, americium, thorium and uranyl ions from nitric acid solutions into the two diluents m-nitrobenzotrifluoride (m-NBTF) or dichloromethane; (ii) complexation in single media (methanol and acetonitrile) followed by UV-spectrophotometric and isoperibolic (micro)calorimetric titrations (ITC). The latter technique was found to be very useful for the determination of the stoichiometries of the complexes formed, in particular when the complexation did not induce significant spectral changes. It also provided a full thermodynamic characterization of these new systems. The influence of some structural features of the ligands as the nature of the substituents and the condensation degree of the calixarene moiety, on the distribution coefficients and on the complexation thermodynamic parameters has been established.     

Synthesis and Cation Complexation of Lariat Calix[4 ] crowns

Calixcrowns carrying bridging polyethyleneoxy moieties on the lower rim, which combine calixarene and crown ether in a single molecule, are a novel class of host compounds which have attracted increasing attention because of their increased ability for selective complexation of cations and neutral molecules compared with crown ethers or cal ixarenes.     

Mini-review: calixarene liquid crystals

Calixarene liquid crystals were important part among calixarene derivatives. The synthesis and mesomorphic properties of all kinds of calixarene liquid crystala have been discussed and reviewed. There are two methods to prepare calixarene liquid crystals. One way is to introduce the corresponding functional groups with long alkyl chains, which usually afford columnar liquid crystal with a rigid bowlic core. The organization of liquid crystals possesses interesting changes after the complexation of guests. Another way is to introduce triphenylene unit to obtain calixarenes bowlic column with triphenylene units as ancillary lateral columns or triphenylene column with calixarene units on ancillary side. Moreover, they showed interesting conversion between two kinds of liquid crystals before and after complexation with ions.     

Fluorescent chemosensors based on a new type of lower rim-dansylated and bridge-substituted calix[4]arenes

The synthesis, structural and chemosensing properties of several lower rim-dansylated calix[4]arenes bearing different methylene bridge substituents are described. Compared to bridge-unsubstituted pendants neither the conformational nor the fluorescence characteristics of the calixarene core are perceptibly influenced by the bridge substituent. X-ray structure as well as NMR measurements indicates the lower rim-propoxylated and-dansylated calixarenes to adopt the cone conformation capable of the complexation of Cu²⁺ ions at micromolar level. Fluorescent measurements point to selective 1:2 calixarene: Cu²⁺ complex formation with sensing parameters being of a suitable level to make the use as a potentially immobilisable chemosensor for the detection of Cu²⁺ ions promising.     

Solubilizing effect of the p-phosphonate calix[n]arenes towards poorly soluble drug molecules such as nifedipine, niclosamide and furosemide

This article reports the solubilization of the practically water insoluble drug molecules such as nifedipine, niclosamide and furosemide by guest:host inclusion complexation with p-phosphonates calix[n]arenes as drug soluble agent. This complexation studies were carried out by using the phase solubility technique. From the obtained results, it was observed that the solubility of drug molecules was significantly increased in the presence of calix[n]arene host molecules. The increase in solubility of drugs by the calix[n]arene was most probably due to inclusion complexation between drug molecules and cavities of the calixarene skeleton similar to drug:cyclodextrin complexes.     

The complexation of ferrocene derivatives by a water-soluble calix[6]arene

The complexation of several ferrocene derivatives by the water-soluble hostp-sulfonato-calix[6]arene was investigated using electrochemical and¹H-NMR spectroscopic techniques. The electrochemical results indicate that both oxidation states of the guests are bound to the calixarene host, although the oxidized (ferrocenium) forms are complexed more strongly than the reduced (ferrocene) species.¹H-NMR spectroscopic data indicate that the complexation phenomena involves the inclusion of the guest's ferrocene moiety into the flexible calixarene cavity.This paper is dedicated to the commemorative issue on the 50th anniversary of calixarenes.     

A Preliminary Investigation of the Solution Complexation of 4-Sulphonic calix[n]arenes with Testosterone

The complexation between water soluble calixarenes and testosterone has been studied. Stability constants of the host guest complexes of 4-sulphonic calix[n]arenes (n = 4, 6 and 8) with testosterone in water and buffers (pH 5.8, 7.3 and 10.0) were determined from phase solubility curves. These solubility curves indicated that the complexes were all of the A_L type. The constants were in the range 26–341 M^-1, dependent on the size of the calixarene and the pH of the solutions.     

Bis(calixcrown)tetrathiafulvalene receptors

A new class of electroactive receptors has been synthesized, built by covalent association of five subunits: two calixarene platforms for spatial organization, two polyether 3D cavities for cation binding, and one electroactive TTF unit to probe the complexation event. Sodium complexation induces rigidification of the molecular assembly, as shown by 1H NMR titration and single-crystal X-ray crystallographic studies on free receptor 14 and a corresponding complex with two bound sodium atoms per receptor (15-(NaPF6)2). The calixarene units in these receptors change from a pinched cone conformation in the free ligand to a symmetrical cone in the complex. Cyclovoltammetric studies validated the electrochemical recognition concept of these five-member assemblies.     

Complexation and extraction behavior of trivalent indium with multiple proton ionizable p�Ct-butylcalix[5]arene pentacaarboxylic acid derivative: a new efficient solvent extraction reagent for indium

Complexation behavior of plural ion-exchangeable p?Ct-butylcalix[5]arene pentacarboxylic acid derivative towards trivalent indium has been investigated along with its monomeric analog from weakly acidic media into chloroform. The cyclic structure of calixarene ligand providing certain cavity and cooperativity of functional groups significantly affect the complexation behavior and calixarene derivative is an excellent extractant over monomeric analog. The extraction mechanism is ion exchange and carboxylic acid groups are adequate functional sites for extraction. Mononuclear and/or polynuclear species of indium and monomeric or bridged dimeric species of calixarene are involved in complexation and the composition of extracted complex varied with solution pH. One mole of calix[5]arene derivative tend to extract 3.5 mol of indium. The loaded indium was quantitatively back extracted with 1 mol dm^?3 hydrochloric acid solution.     

Investigation of Metal Ion Complexation of π-Coordinate Calixarene Derivatives by Electrospray-Ionization Mass Spectrometry

Complexation of π-coordinate calix[4]arene derivatives toward soft metal ions, silver and thallium (I) ions, has been studied by electrospray-ionization mass spectrometry. Competitive metal–ion complexation of three calix[4]arene derivatives demonstrates a significant effect of olefinic substituents and its location on the silver ion complexation, but there was no effect of them on the thallium ion complexation. The stability constants for the metal ion complexes of the calixarene derivatives in methanol have been successfully determined by a mass-spectrometric method using 18-crown-6 as the reference ligand.     

Binding behaviour and solubilisation of p-sulfonatocalixarenes to cinchona alkaloids

In this study, we investigated the binding behaviours of three water-soluble p-sulfonatocalixarenes with four cinchona alkaloids in aqueous and phosphate buffer solutions (pH 7.2 and 2.0). The complexation stability constants obtained by fluorescence titrations were comparatively discussed from several aspects: host cavity, pH effect and ionic strength. Among three hosts, p-sulfonatocalix[4]arene (SC4A) forms the most stable complexes with cinchona alkaloids, especially in acidic aqueous conditions. Furthermore, SC4A was elected as model drug carrier for cinchona alkaloids, where solubilisation by the complexation of SC4A and mimic release from the calixarene cavity in the presence of negatively charged micelles were initially studied.     

Complexation of bipyridinium guests in the cavity of Acyclic Cucurbit[n]uril receptor

A series of bipyridinium guests have been synthesised, and their inclusion complexes with acyclic CB[n]-type receptor have been investigated by NMR, UV-Vis spectroscopy, and X-ray diffraction. Novel [3]pseudorotaxane was formed by C-H ^… O, π-π and ion–dipole interactions. The impact of their complexation on the equilibrium between monomer and dimer of bipyridinium cation radicals has also been studied by UV-Vis-NIR and EPR spectroscopy. Upon reduction, the bipyridinium units linked by flexible pentylene chain preferred the formation of the dimer in the presence of acyclic CB[n]-type receptor, whereas those connected by rigid xylene bridge were suppressed as monomeric form due to the steric effect.     

Complexation of calix[4]arenehydroxymethylphosphonic acids with amino acids. Binding constants determination of the complexes by HPLC method

Host–Guest complexation process of calixarenehydroxymethylphosphonic acids with 10 amino acids in solution H₂O/MeCN (99:1) had been studied. Binding constants of the inclusion complexes from the dependence between capacity factors of the Guest and the calixarene-Host concentration in the mobile phase had been calculated. It was shown the binding constants depend on the nature of the amino acid residue, conformation of the calixarene skeleton, quantity of phosphoryl groups at the upper rim. In accordance with molecular calculation the complexation is determined by the electrostatic interactions between the positively charged nitrogen atom of amino acid and the negatively charged oxygen atom of phosphonic group of calixarene molecule, hydrogen bonds, π–π, CH–π and solvatophobic, interactions.     

Molecular recognition thermodynamics of pyridine derivatives by sulfonatocalixarenes at different pH values

The complex stability constants (Ka) and thermodynamic parameters (DeltaG degrees, DeltaH degrees, and TDeltaS degrees) for 1:1 complexation of water-soluble calix[4]arene, thiacalix[4]arene, and calix[5]arene sulfonates with pyridine and their methylated derivatives have been determined by means of isothermal titration calorimetry at pH 2.0 and 7.2 at 298.15 K, and their binding modes have been investigated by NMR spectroscopy. The results obtained show that sulfonatocalixarenes afford stronger binding ability toward pyridine guests at pH 2.0, attributable to the positive electrostatic interactions and the more extensive desolvation effects, but present higher molecular selectivity at pH 7.2 owing to the strengthened C-H...pi interactions. The pH-responsible binding ability and molecular selectivity are discussed from the viewpoint of electrostatic, pi-stacking, van der Waals interactions and size-fit relationship between host and guest. A close comparison further demonstrates that the C-H...pi interactions and van der Waals interactions play a more important role than pi...pi interactions in the present inclusion complexation.     

Calixarene Dimers as Host Molecules for Biologically Important Di‐ and Oligophosphates

A dimeric calixarene, with an aliphatic C₆‐bridge and six anilinium head groups at its upper rim, preferably complexes diphosphates and oligonucleotides with more than 10 bonds between both anionic moieties. Free binding energies correlate with the length of the aliphatic bridge in a roughly linear fashion. The binding event, which is monitored by fluorescence titrations and competition experiments, relies on Coulomb interactions, as opposed to a nonpolar variant with tert‐butyl instead of ammonium groups; here, hydrophobic forces prevail, rendering the calixarene dimer selective for less polar cofactors such as FAD. The best guest for the hexaanilinium dimer is found in ssDNA, which carries multiple copies of the optimal trinucleotide for maximum attraction towards the extended cationic host. The recognition event is also observed in the environment of a lipid monolayer, and provides a means to quantify dimer diphosphate interactions by measuring p/A shifts.