Anion-Π Meets H-Bonding: Tuning Synergy Through the Flexibility-to-Preorganization Transition in Anion Receptor...

Area of Science:

• Supramolecular Chemistry
• Anion Recognition
• Organic Synthesis

Background:

• Anion recognition is crucial in biological and chemical processes.
• Designing receptors that utilize synergistic interactions like hydrogen bonding and anion-π interactions is an active research area.
• Understanding the impact of molecular preorganization and rigidity on binding affinity is key for developing efficient anion sensors and extractants.

Purpose of the Study:

• To synthesize and investigate a series of receptors incorporating urea and pentafluoropyridine motifs.
• To evaluate the synergistic effects of hydrogen bonding and anion-π interactions in anion recognition.
• To assess the influence of molecular preorganization and rigidity on receptor binding performance.

Main Methods:

• Synthesis of three receptors with varying spacers (flexible 1, rigid 2 and 3) using a two-step protocol.
• Computational analyses including density functional theory (DFT) and noncovalent interaction (NCI) plots.
• Experimental characterization using nuclear magnetic resonance (NMR) spectroscopy, mass spectrometry, and collision-induced dissociation.

Main Results:

• All synthesized receptors demonstrated complexation with chloride ions via dual urea and π-anion sites.
• Receptor 3, featuring enhanced structural rigidity, exhibited superior binding efficacy due to steric strain and additional C-H···Cl- interactions.
• NMR titrations and mass spectrometry data corroborated DFT predictions, establishing a binding strength order of 3 > 2 > 1.

Conclusions:

• Synergistic hydrogen bonding and anion-π interactions are effective for anion recognition.
• Structural rigidity significantly enhances receptor binding efficacy for anions.
• The developed receptors show promise for applications in anion sensing and separation technologies.