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Allosteric and Electrostatic Cooperativity in a Heteroditopic Halogen Bonding Receptor System
Andrew J Taylor1, Andrew Docker1, Paul D Beer1
1Chemistry Research Laboratory, Department of Chemistry, University of Oxford, 12 Mansfield Road, Oxford, OX1 3TA, UK.
Chemistry, an Asian Journal
|December 14, 2022
Summary
This study reveals how specific receptor designs enhance alkali metal halide ion-pair recognition. Allosteric pre-organization and halogen bonding significantly boost anion binding affinity, crucial for developing advanced ion-pair receptors.
Area of Science:
- Supramolecular Chemistry
- Chemical Sensing
- Host-Guest Chemistry
Background:
- Developing heteroditopic receptors for selective ion-pair recognition is challenging.
- Understanding cooperativity mechanisms in ion-pair binding is essential for receptor design.
- Halogen bonding (XB) and hydrogen bonding (HB) offer distinct interaction modes.
Purpose of the Study:
- To delineate the mechanisms of cooperativity in alkali metal halide ion-pair recognition.
- To compare the efficacy of XB and HB receptors in ion-pair binding.
- To investigate the role of cation size and receptor pre-organization on anion binding affinity.
Main Methods:
- Synthesis of a heteroditopic XB receptor with benzo-15-crown-5 (B15C5) moieties and an analogous HB receptor.
- 1H NMR titration studies to investigate cation, anion, and ion-pair binding.
- Analysis of binding affinities and cooperativity effects based on NMR data.
Main Results:
- The XB receptor demonstrated a significant enhancement in halide anion binding affinity (≥700-fold) with potassium and rubidium cations.
- This enhancement is attributed to allosteric pre-organization via B15C5 cation complexation and favorable electrostatics/XB interactions.
- A diminished affinity enhancement (15-fold) was observed with sodium, where only electrostatic contributions to cooperativity were possible.
Conclusions:
- Allosteric pre-organization is a key strategy for enhancing ion-pair recognition, particularly with larger alkali metal cations.
- The combination of electrostatic attraction and halogen bonding significantly improves anion binding affinity.
- Future high-fidelity heteroditopic ion-pair receptor development should incorporate allosteric pre-organization, electrostatic attraction, and XB-mediated anion recognition.
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