A new series of bis-macrocyclic bola-amphiphiles were prepared, and their transport activities in vesicle and planar bilayer membranes were evaluated. From vesicle experiments, the apparent kinetic order in transporter indicates that aggregates are the kinetically active species. Step-conductance changes observed in planar bilayer membranes indicate that the compounds act as channels. Multiple copies of the same channel form in which the conductance is controlled by the macrocyclic portions of the structures. The pores are ion-selective in the sequence Cs(+) > K(+) > Na(+) > Cl(-), controlled by the polar head-groups of the structures. The data are consistent with a model involving the formation of active dimers.

Macrocyclic receptor molecules can be designed to selectively bind a variety of host molecules, including metal cations and neutral molecules. This property can be uniquely exploited in separation processes, by using these compounds as carriers in transport through liquid membranes. The various types of liquid membrane systems are briefly discussed, and the attractive features of the supported (by a microporous polymer film) liquid membrane (SLM) are explained. The mechanical stability of the SLMs is dependent on several factors, including the type of polymer support, membrane solvent, and hydrophobicity of the carrier used. The rates and selectivity of transport are discussed in terms of membrane geometry, membrane solvent type, structure and concentration of the carrier, and the type and concentration of cations, and anions in both the source and receiving phases. Existing mathematical models in which these parameters have been incorporated, are compared with experimental data. Apart from a concentration gradient of the metal cation over the membrane, other driving forces, such as anion concentration, proton counter‐transport and redox‐active transport, are discussed.

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