Chiral anion recognition using calix[4]arene-based ureido receptors in a 1,3-alternate conformation

The introduction of chiral alkyl substituents into the lower rim of calix[4]arene immobilised in the 1,3-alternate conformation led to a system possessing a preorganised ureido cavity hemmed with chiral alkyl units in the near proximity. As shown by the ¹H NMR titration experiments, these compounds can be used as receptors for chiral anions in DMSO-d ₆. The chiral recognition ability can be further strengthened by the introduction of another chiral moiety directly onto the urea N atoms. The systems with double chiral units being located around the binding ureido cavity showed better stereodiscrimination, with the highest selectivity factor being 3.33 (K _L/K _D) achieved for N-acetyl-ʟ-phenylalaninate. The structures of some receptors were confirmed by single crystal X-ray analysis.

Modified Calix[4]crowns as Molecular Receptors for Barium

A series of modified calix[4]crown-6 derivatives was synthesized to chelate the heavy group 2 metal barium, which serves as a non-radioactive surrogate for radium-223/-224; radionuclides with promising properties for radiopharmaceutical use. These calixcrowns were functionalized with either cyclic amide moieties or with deprotonizable groups, and the corresponding barium complexes were synthesized. Stability constants of these complexes were measured by using NMR and UV/Vis titration techniques to determine logK values of >4.1. Further extraction studies were performed to characterize the binding affinity of calixcrowns to radioactive barium-133. Additionally, the ligands containing cyclic amides were investigated regarding their rotational barriers by using temperature-dependent NMR measurements.

Calix[4]arenes containing a ureido functionality on the lower rim as highly efficient receptors for anion recognition

Calix[4]arenes bearing diaryl urea moieties with electron-withdrawing substituents on both sides can bind selected anions (AcO⁻, BzO⁻, H₂PO₄⁻) even in highly competitive solvents such as DMSO-d₆.

Chiral anion recognition by a ureido-thiacalix[4]arene ligand immobilized in the 1,3-alternate conformation

Tetranitrothiacalix[4]arene can be easily transformed into 1,3-alternatetetraalkoxy derivatives using the Mitsunobu reaction. The introduction of chiral alkyl groups leads to a receptor capable of chiral recognition of anions.

Cyclodextrin–calixarene co-polymers as a new class of nanosponges

Novel nanosponge materials, obtained by co-polymerization of cyclodextrin and calixarene derivatives, have been characterized by various techniques and tested for the removal of model pollutants from aqueous solution.