Cooperativity and Complexity in the Binding of Anions and Cations to a Tetratopic Ion-Pair Host

Cooperative interactions play a very important role in both natural and synthetic supramolecular systems. We report here on the cooperative binding properties of a tetratopic ion-pair host 1. This host combines two isophthalamide anion recognition sites with two unusual "half-crown/two carbonyl...

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Published in:Journal of the American Chemical Society Vol. 136; no. 20; pp. 7505 - 7516
Main Authors: Howe, Ethan N. W., Bhadbhade, Mohan, Thordarson, Pall
Format: Journal Article
Language:English
Published: WASHINGTON Amer Chemical Soc 21.05.2014
Subjects:
Amides - chemistry
Anions - chemistry
Binding Sites
Calcium - chemistry
Cations - chemistry
Chemistry
Chemistry, Multidisciplinary
Molecular Structure
Organometallic Compounds - chemistry
Physical Sciences
Science & Technology
HEMOGLOBIN
MOLECULAR RECOGNITION
CYCLODEXTRIN
ALLOSTERY
RECEPTOR
CHLORIDE ANION
MODEL
SELECTIVITY
METATHESIS
STRONTIUM
ISSN:0002-7863, 1520-5126, 1520-5126
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Summary:Cooperative interactions play a very important role in both natural and synthetic supramolecular systems. We report here on the cooperative binding properties of a tetratopic ion-pair host 1. This host combines two isophthalamide anion recognition sites with two unusual "half-crown/two carbonyl" cation recognition sites as revealed by the combination of single-crystal X-ray analysis of the free host and the 1:2 host:calcium cation complex, together with two-dimensional NMR and computational studies. By systematically comparing all of the binding data to several possible binding models and focusing on four different variants of the 1:2 binding model, it was in most cases possible to quantify these complex cooperative interactions. The data showed strong negative cooperativity (alpha = 0.01-0.05) of 1 toward chloride and acetate anions, while for cations the results were more variable. Interestingly, in the competitive (CDCl3/CD3OD (9:1, v/v)) solvent, the addition of calcium cations to the tetratopic ion-pair host 1 allosterically switched "on" chloride binding that is otherwise not present in this solvent system. The insight into the complexity of cooperative interactions revealed in this study of the tetratopic ion-pair host 1 can be used to design better cooperative supramolecular systems for information transfer and catalysis.
Bibliography:Australian Research Council
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ISSN:0002-7863
1520-5126
1520-5126
DOI:10.1021/ja503383e