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Qualitative Identification of Carboxylic Acids, Boronic Acids, and Amines Using Cruciform Fluorophores
Published on: August 19, 2013
The squaramide versus urea contest for anion recognition.
Valeria Amendola1, Greta Bergamaschi, Massimo Boiocchi
1Dipartimento di Chimica Generale, Università di Pavia via Taramelli 12, 27100 Pavia, Italy.
Chemistry (Weinheim an Der Bergstrasse, Germany)
|March 12, 2010
Summary
This study explores squaramide receptors binding anions, revealing enhanced stability with halides due to unique hydrogen bonding. Squaramides show selective deprotonation with basic anions, unlike urea receptors.
Area of Science:
- Supramolecular Chemistry
- Anion Recognition
- Organic Synthesis
Background:
- Hydrogen bonding plays a crucial role in molecular recognition.
- Squaramide and urea derivatives are known anion receptors.
- Understanding receptor-ligand interactions is key for designing new functional molecules.
Purpose of the Study:
- To investigate the anion binding properties of a squaramide-based receptor (R(sq)).
- To compare the binding affinity and mechanism of R(sq) with a urea-based analog (R(ur)).
- To elucidate the role of hydrogen bonding and other interactions in complex formation.
Main Methods:
- UV/Vis and (1)H NMR spectroscopy titration experiments.
- X-ray diffraction studies on isolated complex salts.
- Computational analysis of electronic contributions.
Main Results:
- R(sq) forms stable 1:1 hydrogen-bonded complexes with halides and oxoanions.
- Halide complexes exhibit enhanced stability (1-2 orders of magnitude) compared to R(ur) due to bifurcated N-H and C-H hydrogen bonds.
- R(sq) shows selective deprotonation with strongly basic anions (F-, CH3COO-), forming dianion complexes, a feature less pronounced in R(ur).
Conclusions:
- Squaramide receptors offer superior halide binding affinity compared to ureas, attributed to synergistic N-H and C-H hydrogen bonding.
- Anion binding mechanisms differ: electrostatic interactions dominate with halides, while acid-base proton transfer is key for oxoanions.
- The squaramide framework facilitates charge delocalization, enhancing its Brønsted acidity and enabling deprotonation with strong bases.
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