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Title:
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Switching from Negative-Cooperativity to No-Cooperativity in the Binding of Ion-Pair Dimers by a Bis(calix[4]pyrrole) Macrocycle
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Author:
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Molina-Muriel, Ricardo; Aragay, Gemma; Escudero-Adán, Eduardo C.; Ballester, Pablo
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Abstract:
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We report the synthesis of a macrocyclic receptor containing two di-meso-phenylcalix[4]pyrrole units linked by two triazole spacers. The 1,4-substitution of the 1,2,3-triazole spacers conveys different binding affinities to the two heteroditopic binding sites. These features make the receptor an ideal candidate to investigate allosteric cooperativity in the binding of ion-pair dimers. We probed the interaction of tetraalkylammonium salts (TBA·Cl, TBA·OCN, and MTOA·Cl) with the tetra-heterotopic macrocyclic receptor in chloroform solution using 1H NMR spectroscopic titration experiments. The results obtained show that, at millimolar concentration, the addition of 2 equiv of the salt to the receptor’s solution induced the quantitative pairwise binding of the ion-pairs. The 2:1 (ion-pair:receptor) complexes feature different binding geometries and binding cooperativities depending on the nature of the alkylammonium cation. The binding geometries assigned to the complexes of the ion-pair dimers in solution are fully supported by X-ray diffraction analyses of single crystals. The thermodynamic features of the binding processes (separate or concomitant formation of 1:1 and 2:1 complexes), derived from isothermal titration calorimetry (ITC) experiments, are rationalized by combining the different ion-pair binding modes of the salt dimers with the dissimilar electronic properties of the two nearby heteroditopic binding sites of the receptor. |
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Publication date:
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2018-10-16 |
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Subject(s):
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54 |
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Rights:
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L'accés als continguts d'aquest document queda condicionat a l'acceptació de les condicions d'ús establertes per la següent llicència Creative Commons:http://creativecommons.org/licenses/by-nc-nd/4.0/ |
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Pages:
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13507 p. |
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Document type:
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Article
Article - Accepted version |
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DOI:
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10.1021/acs.joc.8b02449
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