| Regional Biophysics Meeting 2005, March 16-20, Zreče, Slovenia | [MembBiophys] |
The incorporation of cationic surfactant cetylpyridinium chloride (CPC), into giant phospholipid vesicles prepared from 1-palmitoyl-2-oleoyl-phosphotidylcholine (POPC), was examined at various concentrations of the lipid component. The lipid concentration was determined by a spectrometric method. The potentiometric method based on surfactant-selective electrode was used for the determination of surfactant concentration in the external solution. From these results, the amount of surfactant incorporated in the membrane per mole of lipid (parameter β) and the partition coefficients Kc and KS were calculated. A three stage process of surfactant-induced solubilisation of phospholipid vesicles was observed. In the first stage, surfactant incorporates into bilayers by forming stable lipid-surfactant mixed vesicles, which become saturated with CPC at a value βsat larger than 0.8. In this region, the effective partition coefficient KS,1 was calculated. The beginning of the disintegration process (the second stage) is indicated by the formation of pores at the poles of a vesicle and followed by the appearance of myelin-like bilayer structures. The second stage is characterized by the partition coefficient KS,2 Large values for partition coefficients have been found: KS,1 and KS,2 are of the order of magnitude 1×105 mol/L and Kc is larger than 1×106. Fluorescence measurements have shown that the second stage in the solubilisation process does not involve mixed micelles. These are formed only in the third stage, which is the complete solubilisation of POPC vesicles. The corresponding critical micellization concentration decreases with increasing lipid concentration.
Email: vesna.arrigler@biofiz.mf.uni-lj.si
Address: Institute of Biophysics, Faculty of Medicine, University of Ljubljana, Lipičeva 2, SI-1000 Ljubljana, Slovenia