Journal of inclusion phenomena

A new theoretical approach was recently addressed to predict cyclodextrin host–guest binding constants with the GFN2-xTB semiempirical quantum method. Within such a strategy, a set of starting supramolecular arrangements is automatically obtained through the UD-APARM software, and many optimized host–guest systems are used to obtain each binding constant. In the present work, within the scope of the multi-equilibrium treatment, we carried out a theoretical study concerning the host–guest systems formed with paraoxon (PRX), methyl-parathion (MPTN), and parathion (PTN) into α-cyclodextrin (α-CD), for which experimental data were addressed. Those guests correspond to pesticides in use, and their inclusion plays a role in remediation technology. The procedure for estimating binding constants for the host–guest system is discussed in terms of the ranges for the supramolecular parameters employed in exploring the GFN2-xTB Potential Energy Surface (PES). As a result, by investigating an unprecedented number of starting systems (3,076), we identified that proper exploration of the GFN2-xTB PES gives a reliable prediction of the binding constant in solution. Furthermore, with the study of different starting associations, for PTN/α-CD, we found an excellent linear correlation (R2 = 0.987) between GFN2-xTB data and experimental information, which, as in our previous study, supports the discussed methodology for application in predicting binding constants for CD-based host–guest systems.

Calix[4]arenes possessing electron-donating groups (OH and OR) at the lower rim when reacted with tosylated polyethers under basic conditions give the corresponding 1,3-disubstituted calix[4]arene-crown ethers 2a–2h, in good yields. The binding properties of the synthesized 1,3-bridged calix[4]arene-crown ethers for alkali metal cations have been investigated by atomic emission spectrometric analysis. It has been observed that recognition of sodium and potassium varies with the size of the polyether chain as well as the substituents on the free phenolics of the calix[4]arene-crown ether. The potassium/sodium selectivity seems to be governed primarily by the size of the crown ring, relative hydrophobicity and cation-π interaction capability to give efficiency order as 2a, 2d > 2 h > 2c, 2e > 2b, 2f > 2 g.

Cyclodextrins have been used as fluorescence enhancers in HPLC to improve thedetection limits of aflatoxins, cancerogens which can be found in severalfoodstuffs. In this work, a screening of several cyclodextrins has been performedin order to find the factors affecting the fluorescence enhancement. Evidence for formationof a 1 : 1 AF-CD inclusion complex has been achieved by titration and competitiveexperiments with adamantanecarboxylic acid and by fluorescence quenching by KI.Stability constants of the AF-CD complexes were evaluated.

The complex formation of the macrocyclic ligand hemicucurbit[6]uril with various salts has been studied in aqueous solution. Due to the low solubility of this ligand the formation of complexes results in an increase of the amount of ligand present in solution. From these measurements the stability constants of the complexes formed are calculated. Hemicucurbit[6]uril only forms cation complexes with cobalt(II), nickel(II) and the uranylion. All other cations examined e.g. silver(I), lead(II) and copper(II) do not form detectable complexes in aqueous solution. For a better understanding of the complexation behaviour some quantum mechanical chemical calculations are performed with Gaussian.

The action of sodium cyanide ongem -diphenyl-chloropropanone under phase transfer conditions in the presence of 15-crown-5 yields the title compound as a minor product. The crystal structure of this complex reveals that, in the solid state, the [15-crown-5-Na+] guest species is found within a loose cage of diphenylethyl diphenyl cyanoacetonate molecules with one open side of the cage blocked by an adjacent 15-crown-5 molecule. Colourless crystals of the compound belong to the monoclinic space groupP21/n witha = 12,255(2) Å,b = 13,005(1) Å,c = 23,433(2) Å, β = 95,92(1) ° andD c = 1.23 g cm−3 forZ = 4.

Two self-assembled compounds [Ni(C18H42N6)(C13H9N2O2)2]·2CH3CN (3) and [Cu(C18H42N6)(H2O)2](C13H9N2O2)2 (4) were obtained by the reaction of 4-(phenylazo)benzoate (pab−) with macrocyclic complexes [Ni(C18H42N6)](ClO4)2 (1) and [Cu(C18H42N6)](ClO4)2 (2), respectively (C18H42N6 = 1,8-dipentyl-1,3,6,8,10,13-hexaazacyclotetradecane, C13H9N2O2 = 4-(phenylazo)benzoate). Compounds 1–4 were characterized by elemental analysis, IR, UV–Vis, photoluminescence and single crystal X-ray diffraction. The nickel(II) ion in 1 has a square planar geometry by coordination with four nitrogens of a macrocyclic ligand with pentyl groups, while the copper(II) ion in 2 has a distorted octahedral geometry by coordination with four nitrogen atoms in a square planar configuration and two oxygens of two perchlorate ions. In 3, the nickel(II) macrocyclic unit binds two pab− ions in axial position. The coordinated pab− ions are involved in hydrogen bonds with adjacent pab− ions, which gives rise to a 1-D ribbonlike structure. The copper(II) ion in 4 coordinates two water molecules axially. In 4, pab− ions as anions in the solid state are involved in hydrogen bonding interactions with coordinated water molecules and offset face-to-face π–π interactions between the benzene rings of pab− ions, which leads to a 2-D sheet structure. Potassium 4-(phenylazo)benzoate and 4 show strong fluorescence bands at 402 and 467 nm, and 397 and 467 nm, respectively. However, no fluorescence bands in 3 are observed due to the coordination of pab− ion to nickel(II) ion.

The dielectric, thermodynamic and electric conduction behaviour of amorphous solids with three types of inclusions are described. In the first, or the self-inclusion in glasses, the features of dielectric relaxation due to localized rotational diffusion have a remarkable resemblance to those of the rotation of guest molecules in clathrate structures. But here, the availability of the various configurational states to molecules in the local regions makes a relatively greater contribution to the thermodynamic behaviour of a glass than is observed in clathrates. The number of such self-inclusions decreases as a glass spontaneously densifies on ageing. In this respect, the features attributable to such inclusions in a non-crystalline solid differ from those of a crystalline solid. In the second, - 20 A size inclusions or microdomains of strained a-AgI (bec lattice) are randomly distributed in AgI-AgP03 glasses. The electrical conductivity due to such inclusions follows a power law characteristic of site percolation with a percolation threshold of 0.3, critical exponent 3.3, vulnerability 4.8 and the number of contact sites 2.7. In the third, the part of the repeat unit of a randomly oriented poly(vinyl pyrrolidone) becomes incorporated as inclusions in the distorted, H-bonded, cage-like structures formed by the water molecules. The features of dielectric relaxation of water molecules in the solid aqueous solution of the polymer are similar to those of ice clathrates containing a guest molecule similar in size to pyrrolidone, but the respective temperature dependence of their rates differ.