What anions do to N-H-containing receptors

Area of Science:

• Supramolecular Chemistry
• Anion Recognition
• Sensing Technologies

Background:

• Molecules with polarized N-H fragments act as hydrogen-bond donors for anion recognition in aprotic solvents.
• Pyrrole and urea subunits are common motifs in receptors designed for anion sensing.
• Understanding H-bond complex stability is crucial for designing effective molecular receptors.

Purpose of the Study:

• To investigate the stability of hydrogen-bond complexes formed between pyrrole and urea-based receptors and various anions.
• To correlate complex stability with the acidic properties of the receptors and the basic properties of the anions.
• To explore anion-induced deprotonation mechanisms and their signaling in chromogenic receptors.

Main Methods:

• Synthesis and characterization of pyrrole and urea-based receptors.
• Spectroscopic analysis (e.g., NMR) to study hydrogen-bond complex formation.
• Titration studies to determine binding affinities and deprotonation events with different anions.

Main Results:

• 1:1 complex stability is directly influenced by receptor acidity and anion basicity.
• Highly basic anions, particularly fluoride, can induce receptor deprotonation due to stable self-complex formation (e.g., [HF2]-).
• Chromogenic urea receptors exhibit color changes upon consecutive deprotonation of N-H fragments by excess anions like fluoride or hydroxide.

Conclusions:

• Receptor acidity and anion basicity are key factors governing hydrogen-bond complex stability in anion recognition.
• Anion-induced deprotonation is a viable mechanism, especially with strong bases, leading to potential signaling applications.
• Chromogenic receptors offer a visual readout for anion detection, with potential for sensing applications in aprotic media.