High-Affinity Anion Binding by Steroidal Squaramide Receptors

Exceptionally powerful anion receptors have been constructed by placing squaramide groups in axial positions on a steroidal framework. The steroid preorganizes the squaramide NH groups such that they can act cooperatively on a bound anion, while maintaining solubility in nonpolar media. The acidic N...

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Bibliographic Details
Published in:Angewandte Chemie 2015-04, Vol.127 (15), p.4675-4679
Main Authors: Edwards, Sophie J., Valkenier, Hennie, Busschaert, Nathalie, Gale, Philip A., Davis, Anthony P.
Format: Article
Language:eng ; ger
Subjects:
Affinity
Anionen
Anions
Binding
Carriers
Chemistry
Constants
Correlation
Extraction
Ionophore
Membranen
Molekülerkennung
Receptors
Supramolekulare Chemie
Thioureas
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Summary:Exceptionally powerful anion receptors have been constructed by placing squaramide groups in axial positions on a steroidal framework. The steroid preorganizes the squaramide NH groups such that they can act cooperatively on a bound anion, while maintaining solubility in nonpolar media. The acidic NH groups confer higher affinities than previously‐used ureas or thioureas. Binding constants exceeding 1014 M−1 have been measured for tetraethylammonium salts in chloroform by employing a variation of Cram’s extraction procedure. The receptors have also been studied as transmembrane anion carriers in unilamellar vesicles. Unusually their activities do not correlate with anion affinities, thus suggesting an upper limit for binding strength in the design of anion carriers. Die Vororganisation von Squaramiden auf einem Steroidgerüst verstärkt ihre ohnehin starke Bindung an Anionen noch weiter. Diese Einheiten binden Tetraalkylammoniumsalze mit Affinitäten von mehr als 1014 M−1 in Chloroform. Das ist ein neuer Rekord bei der Anionenerkennung durch ungeladene Rezeptoren.
ISSN:0044-8249
1521-3757
DOI:10.1002/ange.201411805