Studies on Synthetic Ionophores. VIII. Transport of Alkaline Earth Metal Ions by Polyether Carboxylic Acids through Liquid Membrane

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Abstract
Seven ω-hydroxy carboxylic acids bearing 2–5 ether oxygens with or without aromatic rings and five ω-alkoxy carboxylic acids bearing 2–6 ether oxygens with aromatic rings were employed as carriers for the active transport of alkaline earth metal ions as well as alkali metal ions through 1,2-dichloroethane or 1-hexanol as an organic liquid membrane. The relatively hydrophobic ω-hydroxy and ω-alkoxy carboxylic acids (logP>7) exhibited a high M2+ transport ability and selectivity over M+ through 1,2-dichloroethane, regardless of the number of ether oxygen. However, a marked selectivity among alkaline earth metal ions (Mg2+, Ca2+, Ba2+) was not observed. The less hydrophobic carboxylic acids (logP2+ through 1,2-dichloroethane. Ba2+ transport ability of the hydrophobic acids through 1-hexanol was lower than that through 1,2-dichloroethane. Linoleic acid in the presence of oligo- and polyethylene glycols showed efficient Ba2+ transport through 1,2-dichloroethane, although a long-chain fatty acid was not able to transport Ba2+ by itself.