Beyond Size Complementary Factors in Anion-Tetralactam Macrocycle Complexes: From Intrinsic Gas-Phase to...

Area of Science:

• Supramolecular Chemistry
• Analytical Chemistry
• Computational Chemistry

Background:

• Macrocyclic receptors are crucial for selective anion recognition.
• Understanding anion-macrocycle interactions is key for developing sensors and separation technologies.
• Gas-phase studies provide fundamental insights into binding affinities, free from solvent effects.

Purpose of the Study:

• To evaluate the gas-phase affinities of various anions towards a model tetralactam-based macrocycle receptor (1).
• To determine the stability of anion-receptor complexes (1 + X-) against dissociation.
• To support experimental findings with theoretical calculations and predict solvent effects.

Main Methods:

• Gas-phase dissociation studies using mass spectrometry.
• Theoretical calculations employing density functional theory (DFT-PBE0).
• Symmetry-adapted perturbation theory (SAPT) for binding energy partition and electrostatic contribution scaling (1/εr approach).

Main Results:

• The macrocycle receptor (1) exhibited tailor-made gas-phase affinity for the chloride anion (Cl-).
• Complexes with salicylate anion (SA-) and hydrogen sulfate anion (HSO4-) were the weakest.
• Other anion complexes showed low stability dispersion (<1.2 kcal·mol⁻¹).
• High deformation energy and solvation energy differences explained discrepancies for F- and H2PO4- complexes in solution.

Conclusions:

• The tetralactam macrocycle (1) demonstrates selective binding for specific anions in the gas phase.
• Gas-phase binding affinities do not always directly translate to solution-phase stability due to solvation effects.
• Computational methods, combined with experimental data, are essential for understanding complex host-guest interactions.