Selective Recognition and Precipitation of Cs⁺ ions from Aqueous Solutions

Ninhydrin is a widely used reagent in forensic science for the visualization of latent fingerprints and in biochemical research of amino acids. A spin-off from its classic use has revealed its unique ability in forming 3-dimensional vase-shaped compounds, which were thus named vasarenes, in a facile one-pot reaction with polyhydroxy aromatics¹. An intriguing characteristic of these structures is their selective affinity, binding and precipitation of ion-pairs of type M⁺F^-, where M being a large monovalent cation^2,3.

Our recent research has involved the design and synthesis of new analogues that are water-soluble, from polycarbonyl componds other than ninhydrin. The new ligands, which are readily obtained from alloxan and polyhydroxy aromatics, have shown a promising potential for the challenging task of binding and precipitation of the extremely soluble Cs⁺ ions from aqueous solutions. The binding process is highly selective; no other alkali metal ion reacts with these ligands. The specific affinity rests in a supramolecular interaction between the vasarene analogue and the large Cs⁺ cations.

From a practical point of view the new receptors may be used for the design of a sustainable salts-separation tool⁴.

(1) Almog, J.; Rozin, R.; Klein, A.; Shamuilov-Levinton, G.; Cohen, S. Tetrahedron 2009, 65 (38), 7954–7962.

(2) Almog, J.; Gavish-Abramovich, I.; Rozin, R.; Cohen, S.; Yardeni, G.; Zilbermann, I. Eur. J. Inorg. Chem. 2012, 2012 (28), 4427–4432.

(3) Bengiat, R.; Gil, M.; Klein, A.; Bogoslavsky, B.; Cohen, S.; Dubnikov, F.; Yardeni, G.; Zilbermann, I.; Almog, J. Dalton Trans. 2016, DOI: 10.1039/C5DT04171F.

(4) Bengiat, R.; Klein, A.; Gil, M.; Bogoslavsky, B.; Cohen, S.; Yardeni, G.; Zilbermann, I.; Almog, J. IUCrData 2016, 1 (2), x160261.