Ion-pair Movement across Bilayer Membranes

WE have used bilayer lipid membranes (BLM) as models for biological membranes to study the transport of metal halides as ion-pairs. In the presence of iodine (I₂) we find¹ that various monovalent and divalent halides can readily move across BLM along a concentration gradient. The rate of transport increases as the size of the cation increases. As the membrane interior is thought to be of a liquid hydrocarbon nature, these results can be related to those of solvent extraction studies² which showed that various metal halides could be extracted efficiently from aqueous solutions into organic solvents; the extraction efficiency increases as the cation size increases.