Allosteric Coextraction of Sodium and Metal Ions with Calix[4]Arene Derivatives 3. Effect of Propyl Groups on Size-Discrimination for the Second Coextracted Ion

A calix[4]arene derivative containing two propyl groups and two acetic acids at each distal position has been synthesized and investigated for alkali metal extraction in individual and competitive systems. In an individual system, lithium ion simultaneously loads on a single molecule of the extraction reagent up to 200%, while sodium and potassium ions load up to 150% and 100%, respectively. In a competitive system, sodium as the first ion and lithium as the second among three ions each load up to 100%. The peak shift of the extraction reagent by using ¹H-NMR spectroscopy was investigated to elucidate the extraction mechanism of alkali metals in individual and competitive systems. The complex structures and extraction reactions for three ions are proposed from the results obtained. Size discrimination is observed not only for extraction of the first ion, but also the second ion as facilitated by an allosteric effect. Coordinatively-inert propyl groups provide a narrow coordination space for the discrimination of the second coextracted ion.