Calix[4]pyrroles with Shortest Possible Strap: Exclusively Selective toward Fluoride Ion

Area of Science:

• Supramolecular Chemistry
• Organic Synthesis
• Anion Recognition

Background:

• Calix[4]pyrroles are versatile macrocyclic hosts with tunable binding properties.
• Developing selective anion receptors remains a significant challenge in chemistry.
• Short-strapped calix[4]pyrroles offer unique structural and electronic characteristics.

Purpose of the Study:

• To synthesize novel calix[4]pyrroles with the shortest possible straps.
• To investigate the anion binding selectivity of these new receptors.
• To explore the conformational aspects of anion binding using computational methods.

Main Methods:

• Organic synthesis of four new calix[4]pyrrole derivatives.
• Fluoride ion selectivity confirmed by 1H NMR spectroscopy.
• Binding affinities determined by isothermal titration calorimetry (ITC).
• Fluorescence spectroscopy used to study receptor-anion interactions.
• Computational modeling to elucidate binding modes and conformations.

Main Results:

• Successful synthesis of four novel calix[4]pyrroles with ortho-linked aromatic units.
• Demonstrated exclusive selectivity for the fluoride ion over other anions.
• Anion binding affinity was successfully modulated through strap functionalization.
• Computational studies revealed an unusual 1,3-alternate conformation for fluoride binding.

Conclusions:

• The synthesized short-strapped calix[4]pyrroles are highly selective fluoride ion sensors.
• Strap functionalization provides a means to tune anion recognition properties.
• The observed unusual binding conformation offers new perspectives on anion-macrocycle interactions.