Electron spin resonance study of phosphatidyl choline vesicles using 5-doxyl stearic acid

Abstract

Harshness and skin irritation are related to surfactant–skin lipid interactions. Delipidization of the stratum corneum is caused by surfactant penetration into extracellualar lipid bilayers; disrupting the lipid microstructure and thereby impairing skin barrier properties. The mechanisms of interactions of sodium dodecyl sulfate (SDS) with lipid as a model membrane are investigated in this work by studying the vesicle to micelle structural transition, which occurs during such interactions of the membrane. The optical density of the phosphatidyl choline liposome was found to increase upon the addition of up to 2 mM SDS and then to decrease gradually on further increase in SDS concentration. Electron spin resonance (ESR) spectrum of 5-doxyl stearic acid (5-DSA) in liposome before and after interaction with SDS solutions at different concentrations showed the rotational correlation time of 5-DSA to increase markedly, possibly due to the penetration of 5-DSA into the lipid bilayers. SDS addition decreased the rotational correlation time of 5-DSA until it attained a constant value above a certain SDS concentration suggesting complete solubilization of liposome and formation of mixed micelles. The ESR spectrum of 5-DSA inside SDS micelle was also seen to be quite different from that obtained after complete solubilization of liposome and, this also indicates the formation of mixed micelles.