No abstract

Mono,arenes in the cone, partial cone and 1,3-alternate conformations have been synthesised and their complexation ability towards selected anions has been studied. The structure-anion complexation ability relationship has been systematically monitored. A new type of very efficient ligands based on diureido-calix [4]arene in a 1,3-alternate conformation with pronounced bonding ability towards carboxylates was designed.

A simple explicit relation linking 1H NMR chemical shifts and mixing enthalpy has been found for systems that form 1:1 complexes by hydrogen bonding. Starting from relatively general assumptions, we have derived two forms of this relation. The first form is represented by proportionality between the solution enthalpy of the proton donor and the chemical shift change of its active hydrogen atom. The second form is mediated by the relative extent of hydrogen bond formation, η1,rel, a quantity that can be directly evaluated from measurements of either the 1H NMR chemical shift or the mixing enthalpy. The validity of both relation forms has been convincingly demonstrated for 12 systems formed by a strong proton donor (halothane [1-bromo-1-chloro-2,2,2-trifluoroethane] or trichloromethane) and an oxygen- or nitrogen-containing proton acceptor (aliphatic or alicyclic ether, piperidine).

The interaction of natural α-, β-, and γ-cyclodextrins (CDs) with 14 hydrophobic ionic moieties of ionic liquids (ILs) was systematically examined in dilute aqueous solutions using isothermal titration microcalorimetry (ITC) and NMR spectroscopy. The studied cationic and anionic moieties involved some recently developed heavily fluorinated structures, as well as some others of common use. To isolate the effect of a given ion, the measurements were performed on salts containing the hydrophobic IL ion in question and a complexation-inactive counterion. Additional ITC experiments on ILs whose both cation and anion can interact appreciably with the CD cavity demonstrated that to resolve the effect of individual ions from such data is generally a tricky task and confirmed the superiority of the isolation strategy adopted for the purpose throughout this work. The binding constant, enthalpy and entropy determined at 298.15 K for the 1:1 (ion:CD) inclusion complex formation range in broad limits, being 0 < K < 2 × 10(5), 0 < -Δ(r)H°/(kJ·mol(-1)) < 44, and -28 < TΔ(r)S°/(kJ·mol(-1)) < 14, respectively. The stabilities of complexes of perfluorohexyl bearing ions with β-CD belong to the highest ever observed with natural CDs in water. The established binding affinity scales were discussed in both thermodynamic and molecular terms. The concepts of hydrophobic interaction and guest-host size matching supported by simple molecular modeling proved useful to rationalize the observed widely different binding affinities and suggest possible binding modes. Enthalpy and entropy contributions to the stability of the ion-CD complexes were found to compensate each other considerably obeying more or less the linear compensation relationship marked by existing literature data on binding other guests to natural CDs. As outliers to this pattern, the most stable complexes of -C(6)F(13) bearing ions with β-CD were found to receive an enhanced inherent entropy stabilization due to extraordinarily high extent of desolvation occurring in the course of binding.

Alkylation of thiacalix[4]arenes with ethyl bromoacetate led to high yields (≈60%) of corresponding tetraacetates in various conformations (cone, partial cone, 1,3-alternate) depending strictly on the carbonate (Na, K, Cs) used for the reaction. The complexation ability of new compounds was studied by 1H NMR.