Refinement and quantification of potential oscillation by temporal and spatial control of ion transfer at a liquid/liquid interface

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Cyclic voltammograms for the transfer of K^+ facilitated by dibenzo-18-crown-6 were recorded at the interface between water containing lanthanide ion such as La^<3+> and 1,2-dichloroethane containing phosphatidylcholine (PC) and phosphatidic acid (PA). The mixed monolayer of PC and PA increased the barrier effect on the K^+ transfer, as compared with the compact layer composed of PC only. When the bulk concentration of PC and PA was 10 μM and 20 μM, the blocking effect was attained at maximum, and the potential range for the formation of the compact layer extended most widely to positive potentials. On the contrary, a further excess of PA resulted in the degradation of the compact layer. The electrochemical stability of the mixed compact layer was enhanced by an increase of pH. However, when pH was higher than 4.0, the blocking effect disappeared. The above results are discussed in relation to the complex formation of phospholipids with La^<3+> and the protonation to PC and PA.