TIME-DEPENDENT VARIATION IN AC-IMPEDANCE OF LIPID-IMPREGNATED MEMBRANE FILTERS

We measured and analyzed time-dependent variation in the a.c. impedance of lipid-impregnated membrane filters. By changing the lipid concentration of the membrane and the salt concentration of the aqueous solution surrounding the filter, we could determine how the lipids in a decane solution rearrange their order in lipid-impregnated membrane filters. The results showed that the electrical characteristics of such filters change gradually with time; from this we inferred the formation of bilayer-like micromembranes. In addition, we verified the effectiveness of cholesterol and octadecylamine in improving membrane stability, resulting in a longer life-span of the micromembranes. Finally, we present a scenario for the time-dependent behavior of a lipid-decane system that is within a skeleton consisting of a cellulose matrix of a membrane filter. The results yielded knowledge about what occurs within lipid-impregnated membrane filters and the mechanism for membrane stabilization. Hence, such filters will help us explore model systems that simulate certain biological membrane systems. The time-dependent variations in characteristics of such lipid-impregnated membrane systems were previously unknown, even though such systems have been recognized as stable and feasible candidates for simulating biological functions.