Ivan Stibor

Novel biscalix[4]arene-based anion receptors

Novel biscalix[4]arene derivatives where two calixarene units are connected via one or two ureido bridges on the upper rim has been prepared. These compounds represent well preorganised cavities with interesting complexation abilities towards anions. The structure of bis-ureido derivative was proved by X-ray crystallography.

Conformational flexibility of a novel tetraethylether of thiacalix[4]arene. A comparison with the “classical” methylene-bridged compounds

Abstract Conformational analysis of a novel tetraethylether of thiacalix[4]arene by means of NMR spectroscopy is presented. Equilibrium between three dominant conformers paco, 1,3-alt and cone exists in CDCl3 solution at room temperature. Observed chemical exchange between conformers indicates higher internal flexibility of the title compound in comparison with similar methylene bridged analogues of tetraethylethers of calix[4]arene and p-tert-butylcalix[4]arene. The cone conformer experiences additional internal motions.

NMR and X-ray analysis of 25,27-dimethoxythiacalix[4]arene: unique infinite channels in the solid state

Abstract The conformational behaviour of 25,27-dimethoxythiacalix[4]arene was studied using NMR techniques and X-ray analysis. The title compound prefers a cone conformation in solution, while in the solid state it adopts a unique 1,2-alternate conformation thus creating a novel type of molecular channel held together by π–π interactions.

Macroscopic expression of molecular recognition. Supramolecular liquid crystalline phases induced by association of complementary heterocyclic components

Whereas the pure compounds are non-mesogenic, equimolar mixtures of the complementary components (5)–(7) and (11) present a liquid crystalline phase that may be attributed to the formation of the mesogenic supramolecular species (12).

Conformational behaviour of tetramethoxythiacalix[4]arenes: solution versus solid-state study

The conformational behaviour of simple thiacalix[4]arene derivatives was studied using a combination of NMR spectroscopy and X-ray diffraction analysis. The 25,26,27,28-tetramethoxythiacalix[4]arene was found to adopt an unprecedented solid-state structure, where the cone and 1,3-alternate conformers co-exist in the crystal lattice in the 3:1 ratio. This phenomenon reflects the basically distinct conformational behaviour of thiacalix[4]arene skeleton as compared with classical calixarenes.

Bis(amidopyridine)-linked calix 4 arenes: a novel type of receptor for dicarboxylic acids

Calix[4]arenes 1 and 2, functionalised on their upper rim with amidopyridine groups, have been synthesised. In the case of 1, a detailed binding study with a range of aliphatic and aromatic dicarboxylic acids has been carried out using H-1 NMR spectroscopy. The binding affinities are largely dependent upon the length of the alkyl spacer group, with the highest binding constant observed for dodecanedioic acid. The X-ray crystal structures of 1 and 2 reveal chain structures formed through intermolecular hydrogen bonds between amidopyridine moieties.

Diazo coupling: an alternative method for the upper rim amination of thiacalix[4]arenes

Abstract A common method for the introduction of amino groups into the upper rim of calix[ n ]arene—nitration and subsequent reduction of nitro derivatives—is not possible in the thiacalixarene series due to the easy oxidation of the sulphur bridges during the nitration step. Alternatively, thiacalix[4]arene reacts smoothly with diazonium salts to form the corresponding tetrasubstituted azo derivatives in high yields. These compounds can then be reduced to give upper rim amino substituted thiacalixarene derivatives.

Synthesis and spectroscopic properties of porphyrin-(thia)calix[4]arene conjugates

Calix[4]arene diacetate and tetraacetate together with their tetrathia-analogs served as starting compounds for the synthesis of novel porphyrin-calixarene conjugates. The introduction of monoaminotetraphenylporphyrin gave corresponding calixarene derivatives, bearing two or four porphyrin units on the lower calixarene rim. These compounds, immobilized in the cone conformation, possess interesting photophysical properties. The absorption and fluorescence emission spectra of the synthesized diporphyrins and tetraporphyrins reveal exciton coupling between the porphyrin units. The flexibility of the amidic bridges accounts for tuning of the degree of porphyrin coupling by the solvent polarity.

Upper rim substitution of thiacalix[4]arene

Abstract Upper rim bromination of thiacalix[4]arene has been achieved for the first time using a distally disubstituted thiacalix[4]arene as a starting material. Depending on the bromine:thiacalix[4]arene ratios, the corresponding dibromo- and tetrabromo derivatives were obtained which opens the door for subsequent derivatisation of the upper rim of thiacalix[4]arenes. Interestingly, direct bromination of tetraalkylated compounds did not yield brominated derivatives. The structure of the tetrabromo derivative in the 1,3-alternate conformation was proven by X-ray crystallography.

Synthesis of Novel Calixsugars: Calix[4]arene–Monosaccharide Conjugates Based on Amide Bonds

Abstract Novel calix[4]arenes containing two sugar moieties in the molecule have been prepared. Both components are connected through the amidic bonds on the lower rim of a calixarene unit preorganised in the cone conformation. This design leads to new chiral receptors with potential recognition ability towards suitable guest molecules.