Anion Effects on the Recognition of Ion Pairs by Calix[4]arene-Based Heteroditopic Receptors

Abstract

A novel heteroditopic receptor (5) based on a rigid calix[4]arene cavity bearing at the upper rim four arylsulfonamido binding sites has been synthesized. The binding abilities of this new host have been investigated in apolar solvents toward a series of tetramethylammonium salts (tosylate, chloride, acetate, trifluoroacetate, and picrate) and compared with those of monotopic and heteroditopic calix[4]arene-bis(crown-3)-based receptors 1 and 2 in order to evaluate the role of the anion on ion-pair recognition. While monotopic host 1 shows an efficiency order toward the different salts that increases when the anion is less interactive (Hofmeister trend), an opposite role of the counteranion on the recognition process was observed with host 5 (anti-Hofmeister trend). A more complex behavior is experienced by host 2, which shows a high and leveled efficiency for all the anions tested. The results obtained were explained on the basis of the different types of ion pairs present in the recognition process. Further information on the role of the anion were obtained by the "dual host" strategy utilizing the tri-n-butylthioureido derivative of tren 7, which forms a stable complex with chloride anion. The very high efficiency shown by these heteroditopic hosts opens new routes in supramolecular projects and is a very interesting tool in the molecular recognition of ion-pairs and its applications.

Janus‐Like Squaramide‐Based Hosts: Dual Mode of Binding and Conformational Transitions Driven by Ion‐Pair Recognition

“…Comparative NOESY and ROESY experiments (see the Supporting Information) revealed intramolecular contacts between NH b and three different protons of the cyclohexylidene ring, which indicates the spatial proximity of NH b to the cyclohexylidene residue of 4 . Moreover, the ROESY spectrum reveals intermolecular contacts between the butyl residues of TBAI and H a due to the spatial proximity between the aromatic portion of 4 and the TBA cations typical of associated ion pairs 26e. In contrast, the ROESY spectrum of a solution containing 4 and TBAT shows intermolecular contacts not only between the butyl chains of TBA and H a but also with H T and, significantly, between the two aromatic protons ArH a and ArH T .…”

Calix[4]arene Anion Receptors Bearing 2,2,2-trifluoroethanol Groups at TheUpperRim

“…The reaction is very efficient, clean and general for different calixarene derivatives. In fact, the trifluoromethylation of the monoformyl-(5), tetraformyl-tetrapropoxycalix [4]arenes (7) and of the diformylcalix [4]arene-crown-3 (21), -crown-4 (22) and -crown-5 (23) gave the trifiuoroethanol derivatives 6,8,24,25 and 26 in 73-98% isolated yields (Via B in Schemes 1 and 2). Vw 6 is particularly convenient in comparison to via A also because milder conditions are required and it is compatible with different functional groups w]-iich otherwise react with organolithium compounds.…”

Anion Receptors Based on Calixarenes

“…This result can be explained by the synchronous action of both sulphonamide and carboxamide functions during anion complexation which is enabled only in 27d. Similar structure 28a was designed as a heteroditopic receptor for the recognition of ion pairs [38] and it was found that the complexation of the corresponding tetramethylammonium salts strongly depends on the anion used. Derivative 28b bearing a methyl group on the amidic function does not show any complexation ability towards anions, thus proving the crucial role of NH bonds in the recognition process.…”