Formation and characterization of supported hexadecanethiol dimyristoyl phosphatidylcholine hybrid bilayers containing gramicidin D
by Ha, Joomi; Henry, Charles Sherman; Fritsch, Ingrid
Polarization-modulation Fourier transform infrared reflection spectroscopy (PM-FTIR), ellipsometry, and a comparison of capacitance determinations by cyclic voltammetry and ac impedance have been performed on supported hybrid bilayers. The hybrid bilayers were constructed by fusion of vesicles of dimyristoyl phosphatidyl choline (DMPC), which form the top layer, with ethanol-rinsed, self-assembled monolayers (SAMs) of hexadecanethiol on gold, which form the bottom layer. A strategy for incorporating Gramicidin D (gD) which is 85% Gramicidin A, an ion channel forming polypeptide, is described. PM-FTIR reproducibly demonstrates that bilayers are, indeed, formed and that gD can be incorporated into the assembly from the phospholipid vesicles. X-ray photoelectron spectroscopy of-the bilayers showed evidence of the presence of DMPC and gD, although results were not reproducible, presumably due to sample damage during analysis. The capacitance in KNO3 solution for the gD-containing bilayer is higher than that for bilayers without gD. The opposite trend occurs for solutions containing Mg(NO3)(2). Experimental evidence appears to indicate that this effect is more likely due to compositional changes that gD induces in the bilayer rather than discrimination of ion permeation due to channel formation. Cyclic voltammetry (0.100 V/s scan rate) of SAM and SAM/phospholipid hybrid layers (measured at either 0.4 or 0.0 V vs Ag/AgCl saturated KCl) consistently gives higher capacitance values than ac impedance (at 0.0 V dc).
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