No abstract

We have found that 1,10-diaza-4,7,13,16-tetraoxa-18-crown-6 with a carboxylate cap and a hydrophobic dodecanoyl group (1) acts as a new class of ion carrier for membrane transport. The rate of K+ transport across a chloroform liquid membrane was significantly affected by pH of the OUT aqueous phase: The rate decreased with increasing or decreasing pH, providing a maximum at around pH 5. The main species of 1 in the neutral pH region should be zwitterionic 1±, so that one may rationalize the pH-rate profile in terms of (i) “enforced ion release” due to protonation of the ring nitrogen and (ii) high lipophilic nature of zwitterionic 1±. The efficiency of 1 was further demonstrated by active K+ transport from the basic IN aqueous phase to the neutral OUT aqueous phase. Also, 1 was capable of carrying amino acids in the presence of alkaline earth metal cations. These results suggest that, being different from conventional anion-capped crown ethers, the aza crown ethers carrying the N-substituted carboxylate cap exhibit a new class of ionophore functions.

Das Disulfid (IIa) zeigt gegenüber (Ia) eine verbesserte Extraktionsfähigkeit für Alkalikationen, wobei der transferierte Anteil bei K+ besonders hoch ist (92.5%).