Application of Electrochemical Impedance Spectroscopy to the Study of Dioleoyl Phosphatidylcholine Monolayers on Mercury

Abstract

Electrochemical impedance spectroscopy has been applied to the analysis of the behavior of monolayers of dioleoyl phosphatidylcholine (DOPC) on a mercury electrode. Experiments were carried out in electrolytes KCl and NaCl (0.1 mol dm(-3)) and Mg(NO3)2 (0.05 mol dm(-3)), and the frequency dependence of the complex impedance was estimated between 65 000 and 0.1 Hz at potentials -0.4 to -1.5 V versus Ag/AgCl 3.5 mol dm(-3) KCl at uncoated and coated electrode surfaces. Experiments were also carried out in the presence of gramicidin A (gA). Between the potentials of -0.4 and -0.7 V, the DOPC monolayer behaves as an almost ideal capacitor with little frequency dispersion. At more negative potentials, the impedance data show the formation of defects (-0.7 to -0.85 V), ingression of electrolyte into the layer (capacitance peak approximately -0.935 V), reorientation of phospholipid-water structures (capacitance peak approximately -1.0 V), and initiation of phospholipid desorption (approximately -1.3 V). gA interaction with the phospholipid monolayer at -0.4 V is shown as an additional low-frequency element. A general "one capacitor model" in a RC series equivalent circuit is developed incorporating the frequency dispersion of the capacitance, distribution of the time constants of the dispersion, and a coefficient related to the interface between the solution and the coated electrode. This latter coefficient is the most robust and decreases at potentials approaching those coincident with the DOPC phase transitions.

Quantification of t-tubule area and protein distribution in rat cardiac ventricular myocytes

“…Figure 3 shows that increasing the mole fraction of cholesterol in the DOPC monolayer results in a decrease in its specific capacitance, to ~1 μF/cm 2 (0.56 of control); at 0.3-0.4 mole fraction cholesterol. Increasing cholesterol content above 0.4 mole fraction caused no further decrease in specific capacitance; indeed a small increase occurred, concurrent with phase separation (Whitehouse et al, 2004). Thus it appears that high cholesterol in the t-tubule membrane could decrease its specific capacitance, resulting in a smaller fractional loss of capacitance than of tubular membrane following detubulation.…”

“…Monolayers of dioleoyl phosphatidylcholine (DOPC) and DOPC + cholesterol were prepared as described previously (Bizzotto & Nelson, 1998;Cohen-Atiya et al, 2006;Nelson & Auffret, 1988;Whitehouse et al, 2004) by spreading 13 μl of a DOPC + cholesterol mixture in pentane (HPLC grade, Fisher Scientific Chemicals Ltd) at the argon-electrolyte interface in an electrochemical cell. A 2.55 mmol/l working solution of DOPC was obtained by dilution of a 63.7 mmol/l stock solution (Avanti Lipids).…”

“…The extrapolation of the RC semi-circle to the Im Y ω -1 axis at low frequency gives the zero frequency capacitance (C) of the RC circuit which is the specific capacitance of the monolayer. These methods applied to the specific capacitance of DOPC monolayers are described in detail (Whitehouse et al, 2004).…”

Substituents modulate biphenyl penetration into lipid membranes

“…In this study the C/A was graphically determined from the complex capacitance plots and expressed as specific frequency independent capacitance (FIC sp ). In the case of the phospholipid coated Hg electrode, any additional circuit element (second semicircle and "tail") at lower frequencies outside of RC is reflective of ionic penetration [54] and physical modifications of the phospholipid monolayer respectively [53].…”

Interaction of Bispyridinium Compounds with Phospholipid Layers in Presence and Absence of Electric Field

“…All potentials in this paper are quoted versus the potential of the above Ag/AgCl reference electrode. In the impedance-frequency measurements, a solution resistance of around 280 -300 ohms was recorded for the cell [20,21]. Diagnostic plots of the impedance data showed it to be that of an RC series circuit as before [20,21].…”