Discrimination between Butylammonium Isomers by Calix[5]arene-Based ISEs

Area of Science:

• Supramolecular Chemistry
• Analytical Chemistry
• Electrochemistry

Background:

• Calixarenes are macrocyclic compounds with tunable properties.
• Ion-selective electrodes (ISEs) are crucial for chemical sensing.
• Developing selective ionophores is key for accurate potentiometric measurements.

Purpose of the Study:

• To evaluate penta-O-alkylated p-tert-butylcalix[5]arenes as ionophores in ISEs.
• To assess their performance in detecting n-butylammonium ions.
• To investigate selectivity towards butylammonium isomers and other ions.

Main Methods:

• Synthesis and characterization of five penta-O-alkylated p-tert-butylcalix[5]arenes.
• Fabrication and testing of liquid membrane ion-selective electrodes (ISEs).
• Potentiometric measurements, (1)H NMR competition experiments, and frequency response analysis.

Main Results:

• ISEs based on ionophore 2 exhibited the highest potentiometric selectivity and detection limits (up to 3 × 10⁻⁶ M).
• Selectivity order for ionophore 2: n-butylammonium ≫ iso-butylammonium > sec-butylammonium > tert-butylammonium.
• Ionophores 3-5 showed lower selectivity due to affinity for Na⁺, confirmed by NMR.

Conclusions:

• Penta-O-alkylated p-tert-butylcalix[5]arenes, particularly ionophore 2, are effective ionophores for n-butylammonium detection.
• Ionophore 2's mechanism involves a favorable kinetic-controlled process for linear butylammonium interaction.
• Understanding ionophore-analyte interactions is critical for ISE design.