Ion transport properties of cyclic and acyclic neutral carrier-containing membranes

The K(+)-valinomycin permselective membrane provides a standard system for describing the normal current-voltage and current-time responses of the "closed circuit shuttle" carrier mechanism. The responses of a selection of cyclic and acyclic carrier-systems have been measured and compared with the standard system responses. Deviations from expected normal behavior suggest that failure of Donnan exclusion is caused by use of high-permittivity plasticizers and too few fixed sites in the membrane supports. The closed circuit shuttle model has been extended to allow for failure of Donnan exclusion, consumption of free carriers, and additional transport by extracted salts. The predicted limiting currents and current-time responses show many features of failure of Donnan exclusion.