On the surface properties of oleate micelles and oleic acid/oleate vesicles studied by spin labeling.

Dilute aqueous systems composed of sodium oleate micelles and sodium oleate/oleic acid vesicles were investigated as a function of pH by electron spin resonance spectroscopy with TEMPO-stearate TEMPO-stearamide as well as with a positively charged water soluble spin label, TEMPO-choline. The dynamics of the three TEMPO-spin labels were found to be sensitive to changes in the interfacial region of the aggregates as a function of pH. The results obtained are consistent with the formation of a hydrogen bond network (RCOO(-)↔HOOCR) at the surface of the sodium oleate/oleic acid system in the course of the transformation of micelles into the closed bilayers (vesicles). Vesicles formation below pH 10 was determined independently with a spin labeled glucose derivative.