Interactions of Surfactants with Biomimetic Membranes. 1. Ionic Surfactants

Abstract

When impregnated with esters of fatty acids, nitrocellulose filters can be used as a biomimetic membrane. They are easy to make, cheap, and may be used not only as an imitation of biological membranes but also as a sensor to characterize surfactant interactions with dirty fabric. These impregnated filters when fixed in a thermostatically controlled chamber separated into two compartments that contain stirred aqueous solutions by the filter, may be considered as a simple model of a laundry machine. The results revealed that the addition of ionic surfactants into one of the solutions led to the formation of transmembrane electrical potential that is proportional to the logarithm of surfactant concentration. Thus, our biomimetic membranes can be used as electrochemical sensors to detect and measure surfactant concentration. When concentration is near the critical micelle concentration (CMC), a new phenomenon was observed, i.e., spontaneous oscillations of both transmembrane potential and transmembrane current, which mimics the opening and closing of aqueous channels in biological membranes. A further increase of surfactant concentration les to a sharp 100-fold decrease of transmembrane electrical resistance and the disappearance of any transmembrane voltage. This effect, explained by the washing out of fatty acids from the pores, may be used for screening and development of new detergents.

Interactions of Surfactants with Biomimetic Membranes—2. Generation of Electric Potential with Non-Ionic Surfactants

“…Finally, a few words regarding possible practical applications. In a previous paper [ 7 ], we mentioned that our experimental system and surfactant-induced processes were similar to washing in a laundry machine and can be used to screen new surfactants and detergents. In addition, the fact that the extremum changes in the transmembrane electric potential are proportional to the log of uncharged surfactant concentration when it changes by three orders of magnitude may be useful in the analytical chemistry of these surfactants, which is usually done by titration.…”

“…The methods used were described previously [ 7 ]. Millipore-mixed cellulose filters (0.45 μ and 0.05 μ pore size) were impregnated with liquid isopropyl myristate and placed vertically in a Teflon chamber, separating the chamber into two cylindrical halves.…”

“…Earlier work by Rosen et al [ 6 ] supported the hypothesis that interfacial properties, such as adsorption and penetration through cell membranes, determine the biological toxicity of anionic and nonionic surfactants. In our previous article, we described the interactions of ionic surfactants with oil-impregnated nitrocellulose filters [ 7 ]. When cationic cetyl ammonium bromide (CTAB) was added into one of the solutions separated by the membrane, it led to several interesting effects that were dependent on concentration.…”