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Synthesis of pH Dependent Pyrazole, Imidazole, and Isoindolone Dipyrrinone Fluorophores using a Claisen-Schmidt Condensation Approach
Published on: June 10, 2021
Protonated macrobicyclic hosts containing pyridine head units for anion recognition
David Esteban-Gómez1, Carlos Platas-Iglesias, Andrés de Blas
1Dpto. Química Fundamental, Facultade de Ciencias, Universidade da Coruña, Campus da Zapateira s/n, 15071A Coruña (Spain). mayter@udc.es
Two new macrobicyclic receptors show high selectivity for chloride anions over other halides and exhibit notable sulfate-to-nitrate binding selectivity, explained by DFT calculations and structural analysis.
Area of Science:
- Supramolecular Chemistry
- Anion Recognition
- Host-Guest Chemistry
Background:
- Macrobicyclic receptors are crucial for selective ion binding.
- Developing receptors with high selectivity for specific anions is an ongoing challenge in supramolecular chemistry.
Purpose of the Study:
- To synthesize and characterize novel macrobicyclic receptors for anion recognition.
- To investigate the selectivity of these receptors for various anions, including halides, sulfate, and nitrate.
- To elucidate the binding mechanisms using experimental and computational methods.
Main Methods:
- Synthesis of two macrobicyclic receptors (L1 and L2) with pyridine head units.
- Spectrophotometric titrations in acetonitrile (MeCN) to determine association constants.
- X-ray crystal structure analysis of selected anion complexes.
- Density Functional Theory (DFT) calculations (B3LYP/LanL2DZ) to rationalize binding trends.
Main Results:
- Protonated receptors L1 and L2 effectively bind anions.
- Halide binding affinities follow specific sequences: Cl(-) > Br(-) > I(-) > F(-) for L1 and Cl(-) > F(-) > I(-) > Br(-) for L2.
- High selectivity for chloride over bromide and iodide was observed.
- Significant selectivity for sulfate over nitrate was demonstrated.
- DFT calculations confirmed the role of cavity size and hydrogen bonding in selectivity.
Conclusions:
- The synthesized macrobicyclic receptors exhibit remarkable selectivity for chloride anions.
- These receptors demonstrate a high preference for sulfate over nitrate.
- Binding selectivity is governed by a combination of optimal geometric fit and specific hydrogen bonding interactions.
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