Electrochemistry of Biomimetic Membranes - Applications of Electrochemistry and Nanotechnology in Biology and Medicine - page 154

independent of frequency, which would correspond to complete
control by R m . At the same time, I decreases tending to zero.
However, before this can occur, a further decrease in frequency
makes 1 /( Z C s ) >> R m , causing | Z | to coincide with 1 /( Z C s ). Hence,
the slope of the Bode plot becomes once again equal to -1 and I
tends to 90°. The solid curve in Fig. 2 is the best fit of the
C s ( R m C m ) R : equivalent circuit to the experimental plot. This Bode
plot is rather featureless. A Bode plot richer in features is obtained
by incorporating in the same tBLM the ion carrier valinomycin, a
hydrophobic depsipeptide that cages a desolvated potassium ion
shuttling it across the lipid bilayer. 3 In this case, the I vs. log f plot
exhibits an additional hump, as shown in Fig. 3 . We will show in
what follows that valinomycin allows an additional dielectric slab
of the tBLM to be disclosed.
Figure 3. Plot of log| Z | (solid circles) and I (solid triangles) against log f
(Bode plot) for a mercury-supported DPTL|DPhyPC bilayer incorporating
valinomycin from its 1.5u10 -7 M solution in aqueous 0.1 M KCl at -0.375 V
vs. Ag|AgCl(0.1M KCl). 3 The solid curve is the best fit of the equivalent cir-
cuit shown in the figure to the impedance spectrum, with C lar =92 nF,
R lar =0.126 G:, C s =20 nF, R s =0.155 M:, C m =73 nF, R m =2.2 M:, C : =0.95
nF, R : =170 :. Drop area= 2.2u10 -2 cm 2 .