Electrochemistry of Biomimetic Membranes - Applications of Electrochemistry and Nanotechnology in Biology and Medicine - page 158

Figure 5. Plot of Z Z ' against Z Z ” (M plot) for the same tBLM as in Fig. 3 . The
solid curve is the best fit of the equivalent circuit shown in Fig. 3 to the impedance
spectrum, using the same R and C values. The dashed curves are the contributions
to Z Z ' from the different RC meshes; proceeding along the positive direction of the
abscissas, these curves are ascribed to the lipoic acid residue, the tetraethyleneoxy
moiety, the lipid bilayer moiety, and the aqueous solution bathing the tBLM. 3
deconvolution. This is due to an appreciable difference between
the time constants of the four RC meshes, which are evenly dis-
tributed over a frequency range covering seven orders of magni-
tude. The capacitance of the solution interposed between the work-
ing and the counter electrode is of the order of 1 nF cm -2 . If it is
disregarded by simulating the aqueous phase by a pure resistance,
the contribution of the solution to the M plot is represented by a
vertical straight line. As a matter of fact, the radius of the semicir-
cle simulating the solution is not infinitely large, and its curvature
is often clearly visible. The RC mesh of the aqueous solution does
not depend on the architecture of the tBLM. Hence, the corre-
sponding semicircle can be excluded, at least partially, from the 0
plot in order to better visualize the contribution from the other