Charge pulse studies of transport phenomena in bilayer membranes

Summary

The charge-pulse technique is applied to a study of valinomycin-mediated potassium transport across glycerol monooleate (GMO) bilayers. The theory, based on the Läuger-Stark model, is developed for the steady-state domain. The voltage dependences of the surface complexation reactions are also considered. The analysis of the data yields the following values for the rate constants:

$$\begin{array}{*{20}c} {k'_R = 2.6 \times 10^8 \times \exp \left[ {0.045\frac{F}{{RT}}V} \right]cm^3 moles^{ - 1} \sec ^{ - 1} ,} \\ {k'_D = 2.6 \times 10^5 \times \exp \left[ {0.045\frac{F}{{RT}}V} \right]\sec ^{ - 1} , k_s = 2.6 \times 10^4 \sec ^{ - 1} and k_{MS} /k_D > 4} \\\end{array}$$

With the exception of this last ratio, all the values agree well with previously published data. The implication of the exponential term, 0.045, is that the plane of reaction for the surface complexation actually occurs a small distance within the membrane dielectric. If one presumes that the reaction plane is about half way between the plane of adsorbed complex and the membrane-water interface, one deduces that the complex “feels” only about 80% of the applied voltage across the membrane.