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.

No abstract

SynopsisThe crosslinked polystyrene beads which immobilized two terminal azophenoxide groups of an azobenzene-crown(24-crown-8)-azobenzene unit were synthesized. The polymer beads adsorbed Cs+ in the dark while they rapidly released Cs+ into the solution under UV-light irradiation, and the photoresponsive complexation occurred reversibly. On the other hand, the crosslinked polystyrene beads2which immobilized one terminal azophenoxide group of an azobenzene-crown (24crown-8) unit scarcely (or only to a smaller extent) exhibited such a photoresponsive behavior. Similarly, the polymer beads which immobilized two terminal azophenoxide groups of an azobenzene-crown (18-crown-6)-azobenzene unit reversibly adsorbed and desorbed K+ in response to UV-light irradiation. The novel photoresponsive behavior is ascribed to a conformational distortion of the crown rings which is induced by the photoisomerization of the azobenzene moiety, although the photoinduced polarity change of the polymer beads is not completely ruled out. The results suggest that the polymer support is useful as a "fixed point" to enforce the conformational changes of immobilized functional molecules.

Der Einfluß von Bestrahlung auf die Bindungsfähigkeit des an Polystyrol über p‐Chorrnethylgruppen gebundenen Crownethers (I) mit zwei Azobenzoleinheiten wird unter Verwendung von Cs‐p‐nitrobenzoat untersucht.