Silicon-Bridged Bis(12-crown-4) Ethers as Ionophores for Sodium Ion-Selective Electrodes
2025
Shoichi Katsuta | Yoshiyasu Ino | Hiroto Wakabayashi
A new Na+ ionophore with two 12-crown-4 moieties on silicon atoms and hydrophobic hydrocarbon groups on silicon atoms has been synthesized. The silicon-bridged bis(12-crown-4)s were easily obtained in high yield by simply mixing dichlorodiorganosilane and 2-hydroxymethyl-12-crown-4 under room temperature and nitrogen atmosphere. Seven compounds with different hydrocarbon substituents were synthesized. To investigate their properties as ionophores, PVC membrane-type ion-selective electrodes incorporating them were prepared, and the ion selectivity coefficients were determined. The typical selectivity sequence is Na+ >: K+ >: Rb+ >: Cs+ >: NH4+ >: Li+ >: Ca2+ >: Mg2+ >: H+. The magnitude of selectivity depends on the structures of hydrocarbon substituents on the silicon atoms. The compound with two 2-ethylhexyl groups has particularly good Na+ selectivity, and the performance of the electrode is equal to or better than that of an electrode using a commercially available Na+ ionophore, malonate-bridged bis(12-crown-4). The electrode also showed better-aging stability than that of another known Na+ ionophore, tetraethyl 4-tert-butylcalix[4]arene-O,O&prime:,O&Prime:,O‴:-tetraacetate, indicating high utility.
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