Anion binding studies of fluorinated expanded calixpyrroles

Area of Science:

• Supramolecular Chemistry
• Organic Chemistry
• Analytical Chemistry

Background:

• Calix[n]pyrroles are macrocyclic compounds known for their anion binding capabilities.
• Fluorination of calix[n]pyrroles is explored to modulate their chemical properties and binding affinities.
• The synthesis of dodecafluorocalix[6]pyrrole was previously unreported.

Purpose of the Study:

• To investigate the anion binding properties of fluorinated calix[n]pyrroles (n=4-6).
• To synthesize and isolate the dodecafluorocalix[6]pyrrole.
• To compare the binding affinities of fluorinated and non-fluorinated calix[n]pyrroles.

Main Methods:

• Synthesis via condensation of 3,4-difluoro-1H-pyrrole and acetone.
• Isothermal Titration Calorimetry (ITC) for binding studies in solution.
• (1)H NMR titration for association constant determination.
• Single-crystal X-ray diffraction for solid-state structural analysis.

Main Results:

• Successful synthesis and isolation of dodecafluorocalix[6]pyrrole.
• Octafluorocalix[4]pyrrole shows enhanced binding affinities for anions compared to its non-fluorinated analog.
• A trend of increased relative affinity for bromide over chloride was observed with increasing macrocycle size.
• X-ray diffraction confirmed hydrogen bonding interactions in solid-state anion complexes.

Conclusions:

• Fluorinated calix[n]pyrroles are effective anion binders in aprotic solvents.
• Macrocycle size influences the selectivity of anion binding.
• The study provides insights into the structure-activity relationship of fluorinated calix[n]pyrroles for anion recognition.