Recognition ion-pairs

Receptor 14b was designed for ion pair recognition as it also contains a cavity suitable for cation complexation (ester groups on the lower rim). Similar recognition ability [17] was found for derivative 15 bearing additional crown ether units. In both cases the relationship between the cation present and the binding of anions was studied. 

Recently, ion-pair recognition has been attracting a lot of interest within the supramolecular community. This kind of molecular recognition is enabled by... 

Chart 2 Ion-pair recognition using ditopic salt-binding hosts. 

Fig. 2 Ion-pair recognition using ditopic salt-binding hosts. (Reprinted with pennission from Ref. [9] Copyright 2000, American Chemical Society.)...

Shi, X. Fettinger. J.C. Davis. J.T. Ion-pair recognition by nucleoside self-assembly Guanosine hexadecamers bind cations and anions. Angew. Chem.. Int. Ed. Engl. 2001.40. 2827-2830. 

As shown, in the majority of cases ion-pair recognition calls for receptors with separate cation- and anion-binding sites. On the other hand, an alternative approach could be to use noncovalent interactions to build the ion-pair receptor from multiple components and employ molecular self-assembly for ion-pair binding. 

B. D. Smith, Ion Pair Recognition by Ditopic Receptors, in Macrocyclic Chemistry Current Trends and Future, eds. 

Ion pairing between cations and anions is a barrier for the inclusion of cations into the pillar[5]arene cavity because strong ion-pairing prevents the complexation. Wang and co-workers synthesized a heteroditopic pillar[5]-arene containing one urea moiety (H5.15) for ion-pair recognition of alky-lammonium cations and counter anions (Figure 5.20). ... 

SAMs of calixarene derivatives have been demonstrated to possess recognition properties towards ions [69-77] and small organic molecules [78-83]. For example, in 2012 Li reported on calix[4]azacrown-based SAMs that exhibit ion-pair recognition properties towards l-butyl-3-methylimidazolium chloride [84], The calixarene-based SAM was produced by a click reaction between the azido-modified silicon substrate and the calix[4]azacrown. The authors demtmstrated by contact angle (CA) measurements that the calixarene-modified surface is superhydrophobic (CA= 154.6 3°). Upon immersion of the calixarene-based SAM in a l-butyl-3-methylimidazolium chloride solution, the CA drops to 10.1 3° (Fig. 37.14). On the other hand, no changes in the CA of the surface are observed in the presence of 1-butyl-3-methylimidazolium bromide and l-butyl-3-methylimidazolium hexafluorophosphate. The calix[4]azacrown modified SAM was therefore demonstrated to possess selective wettability response towards the l-butyl-3-methylimidazolium chloride ion-pair. 

Perraud O, Robert V, Martinez A, Dutasta J-P (2011) The cooperative effect in ion-pair recognition by a ditopic hemicryptophane host Chem Eur J 17 4177-4182... 

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