The addition of the ionophore dicyclohexano-18-crown-6 (DC18C6) to the bilayer of sodium 4-(1' -heptylnonyl) benzenesulfonate (SHBS) and sodium (4-(1' -nonylundecyl) benzenesulfonate (SNUBS) vesicles facilitates the transport of the alkali metal cations sodium, potassium and cesium at ionophore levels up to 1 ionophore per 25 vesicles. No facilitation is observed when DC18C6 is added to lecithin bilayers, or when a dibenzo-18-crown-6 analog with C11 side chains is added to SHBS bilayers. Based on these and previous (Hamilton and Kaler, 1987) observations, the proposed mechanism of crown ether action is the formation of non-specific ion channels in the bilayer. These channels are pores in the SHBS bilayer in which the crown ether occupies part of the pore wall. The energy of pore formation is reduced from 1.9 kJ/mol-Å (pure bilayers) to 1.3 kJ/mol-Å. The bilayer/water partition coefficient for DC18C6 was found to be 120.
Bibliographical noteFunding Information:
This work was supportedb y the National Science Foundation (Grant Number PYIA-8351179) and by the Standard Oil Company (Ohio) with matching funds under the National Science Foundation’s Presidential Young Investigator Program. For part of his tenure RTH was supportedb y Link Foundation and National Science Foundation Fellowships.