A new series of supramolecular assemblies is obtained through the interaction of 3-pyridylmethyl-calixarenes and copper or zinc ions. The complexes formed are characterized both in solution and in the solid state. The results offer appealing insights into how the steric crowding of the lower rim and different coordination modes of the metal centers have a great impact on the overall architecture of the complexes with the formation of monomeric, dimeric, or oligomeric/polymeric species.

The binding features of a sulfonato-calix[4]arene with pyridinium-based gemini guests have been investigated in water at physiological condition by NMR spectroscopy. Results provided converging evidence showing that guests having different size, shape and flexibility formed water-soluble homodimeric supramolecular capsules. The remarkably large encapsulation efficiency of the anionic calixarene host towards these bis(pyridinium) gemini guests results from the favourable combination of electrostatic and hydrophobic interactions. The introduction of short and rigid spacers between the two positively charged heads of the guest improves the efficiency of the capsule formation. The insertion of a substituent into the pyridinium ring of the guest dramatically affects both the association constants and the binding modes.

An entry from the Cambridge Structural Database, the world’s repository for small molecule crystal structures. The entry contains experimental data from a crystal diffraction study. The deposited dataset for this entry is freely available from the CCDC and typically includes 3D coordinates, cell parameters, space group, experimental conditions and quality measures.

Negatively charged gemini guests in the presence of a tetracationic host trigger the formation of self-assembling structures at physiological pH in water generating entities of the HG and H(2)G type (H = host and G = guest). ITC measurements show that the gemini guests are included via concerted electrostatic and hydrophobic interactions and that the formation of the HG adduct is enthalpically driven while the formation of the capsular entity (H(2)G) is driven by entropy gain. It is shown that the efficiency of capsule formation is influenced by the number of -CH2- units contained in the spacer and that spacers with an even number of methylene groups seem to be the best templating agents. In line with the above picture, MD simulations and DFT calculations show that the entropic contribution strongly depends on the length of the polymethylenic spacer. In the solid state, for the HG assembly three different structures are revealed by single crystal X-ray diffraction; the flexible interacting units create multiple interactions reaching the optimum balance between inter-and intramolecular energies. To the best of our knowledge, these are the first structures ever reported for water-soluble calixarenes and organic anions.

Two calix[4]arene receptors containing two or four 3-pyridylmethyl pendants at the lower rim and fixed in the cone conformation have been synthesised. Their complexes with Cu2+ and Zn2+ have been studied via UV-vis absorption spectroscopy in acetonitrile; H-1 NMR spectra provide further insights into the binding sites and show that the macrocycles suitably arrange their structure to meet the coordination features of the metal ion. Both ligands form with both Cu2+ and Zn2+ multiple complex species with large stability. The large binding constant values allow to drive the system to the formation of the desired species by appropriately selecting the metal/ligand ratio. The host-guest binding properties of N-methylpyridinium (NMPy) with both the free ligands and their metal complexes have been investigated by H-1 NMR spectroscopy in CDCl3/CD3CN (9:1, v/v). The metal ions do not negatively affect the affinity of the calixarenes for NMPy and also allow for the formation of systems with multiple cavities available for guest inclusion, thus paving the way to new heteroditopic receptors for molecular recognition in solution.

Water-soluble homodimeric capsules resulting from the electrostatic and hydrophobic interactions between a tetracationic calixarene receptor and gemini guests having the negatively charged ends separated by a (-CH2-)(n) (n=2-6) spacer are reported. The formation of the supramolecular capsules occurs through concerted hydrophobic and electrostatic interactions between the charged and aromatic groups of the guests and the host as indicated by H-1 NMR and DOSY NMR data. The different size of the guests may strongly affect the stability of the capsule. The surprising features of these host-guest systems disclose new paths for the design of more efficient anion-templated capsules in highly competitive media such as water.

Two new chiral calix[4]arene-salen ligands 1a,b, based on calix[4]arene platforms in 1,3-alternate conformation, have been prepared by a new general synthetic pathway. Their Mn(III) complexes, 3a,b have shown fairly good efficiency in the asymmetric epoxidation of styrene and substituted styrenes, whereas excellent catalytic activity and selectivity were observed with rigid bicyclic alkenes, namely 1,2-dihydro-naphthalene and substituted 2,2'-dimethyl-chromene. The higher catalytic properties of 3a may be ascribed to the more rigid and inherently chiral structure as proved by molecular modelling, NMR spectroscopy and X-ray data of the similarly structured UO2 complexes 2a,b.

A gemini guest having both aromatic units and negative charges induces the self-assembling of a homodimeric capsule when interacting with a positively charged calixarene at pH 7.

The inclusion of organic anions by the water-soluble tetracationic calix[4]arene TAC4 has been studied at neutral pH by 1H NMR and isothermal titration calorimetry. The aromatic anions are better included than their aliphatic analogues. The ΔH° and ΔS° values show that the inclusion processes are mostly enthalpically driven and entropically unfavoured; they also show that an enthalpy–entropy compensation balances the gain in one contribution against a corresponding loss in the other.

Self-aggregation processes are rarely reproducible owing to their dependence on various experimental parameters (aging of stock solutions, their concentration, concentration of working solutions, ionic strength, etc.). However, by enucleating the dependence from one parameter (in this case, the dependence of aggregation from the concentration of the working solutions), it has been possible to hierarchically control self-aggregation of the protonated form of tetrakis-(4-sulfonatophenyl)-porphyrin.

The interaction of a tetracationic calixarene (TAC4) with dianionic guest (BS) in water was studied with NMR, nano-ITC and ESI-MS experiments; the convergent evidence provided by these different techniques shows that the addition of a suitable guest molecule triggers the formation of a homodimeric capsule in aqueous neutral solution.

A cationic calix[4]arene derivative binds both aliphatic and aromatic, carboxylate and sulfonate anions in aqueous solution thanks to concerted electrostatic and hydrophobic interactions. The sulfonate guest inclusion is affected by the different mobility of the host caused by the pH change. (C) 2009 Elsevier Ltd. All rights reserved.

The inclusion of ethylammonium, N-methylpyridinium cations and native L-alpha-amino acids by the water-soluble pentasulfonatocalix[5]arene 1 has been investigated at neutral pH by H-1 NMR. The complexation behavior has been compared with that of the homologous tetrasulfonatocalix[4]arene 2. Unlike host 2, host 1 exhibits high selectivity in the recognition of the investigated guests.

A cationic calix[4] arene derivative binds both aliphatic and aromatic anions in aqueous solution thanks to concerted electrostatic and hydrophobic interactions. H-1 NMR and potentiometric data show that the host flexibility changes as a function of pH. H-1 NMR and isothermal titration calorimetry (ITC) studies, also supported by ESI-MS data, show that inclusion yields supramolecular complexes of the guest subset of host type only. Binding becomes weaker as the pH increases due to rigidification of the host in neutral aqueous solutions, and is enthalpically favoured for all the supramolecular complexes, regardless of pH.

Sulfonato groups were introduced into the backbone of a dipyridyl-based calixarene to obtain a novel water-soluble compound able to complex Co(II) and Cu(II). Spectrophotometric titrations pointed out that the new ligand complexes Co( II) and Cu( II) in water, but with stoichiometries and stabilities that are different from the analogous water insoluble calixarene. (C) 2007 Elsevier Ltd. All rights reserved.

20- and 40-membered macrocyclic mono and dinuclear uranyl complexes 11–13 incorporating salen and (R)-BINOL units have been designed and synthesized starting from 4-tert-butylphenol in eight steps. NMR measurements (COSY, NOESY/EXSY) indicate that such complexes in solution are involved in conformational equilibria, which for the 20-membered derivatives are observable already at room temperature (k1=300s−1 at 300K) and which are probably related to a flipping motion of salicylaldehyde units. T-ROESY experiments suggest that in solution, the dinuclear complexes do not assume structures wrapped around the metal ions.

Crystallization and crystal structure analysis of chlorohydrates of either tri- or tetracationic copper porphyrins, namely copper(5,10,15-tris(N-methyl-pyridinium-4-yl)-20-pyridine-porphyrinato) (1) and copper(5,10,15,20-tetrakis(N-methyl-pyridinium-4-yl)-porphyrinato), respectively, have been performed. Two crystalline forms, 2 and 3, of the latter have been obtained under different preparation conditions. A novel kind of slipped stack chains of these cationic porphyrins has been detected. The pronounced saddle conformation of the porphyrin reveals pi-like interactions between the peripheral pyrrole Cb-Cb- "double bond" and the metal center. DFT calculations on the isolated porphyrins clearly show the HOMO orbitals with the correct topology to yield a bonding interaction among the stacked porphyrin units. To our knowledge, a slipped stack chain of positively charged porphyrins has never been previously reported, if the arrangement of faced units of monocationic metalloporphyrins or phthalocyanins is excluded.

Two chromatographic stationary phases, obtained by covalently linking two suitably derivatized calix[4]crown-6 and calix[4]crown-5 receptors onto silica gel, are described here. A study of their chromatographic behaviour as well as their surface composition is reported. The packing materials exhibit high selectivity toward alkali metal ions. Complete separations of Cs+ from K+ and Na+ were obtained when using a water/methanol mixture (80:20) as the mobile phase. In these conditions, a selectivity factor Cs+/Na+=4.10 was achieved with the silica gel-bound calix[4]crown-6. The degree of coverage of the activated silica-gel surface following the covalent attachment of the macrocycle was estimated by mean of X-ray photoelectron spectroscopy (XPS). This technique allows the first few monolayers of the material to be analysed and thus is to be preferred to conventional Elemental Analysis for similar studies. Three methods for an adequate correction of the XP signals for the presence of organic contaminants are suggested and critically compared.

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