Structural changes in DODAC unilamellar liposomes by addition of sucrose esters monitored by using fluorescent techniques

The effect of the incorporation of the non-ionic surfactant sucrose palmitate in dioctadecyldimethylammonium chloride (DODAC) large unilamellar vesicles was studied by using several spectroscopic techniques. Significant changes in the liposome bilayer were detected prior to the formation of mixed micelles. Turbidity experiments show major growth in vesicle size. This behavior is rarely observed in large unilamellar vesicles. The vesicle size increase is accompanied by several alterations of the lipidic bilayer. Fluorescence of 6-dodecanoyl-2-(dimethylamino)-naphthalene (Laurdan) and pyrene incorporated in liposomes shows a dependence on sucrose palmitate addition, this is compatible with modifications of polarity and fluidity of its surroundings, probably due to a decrease in the bilayer water content. In contrast, diphenylhexatriene anisotropy changes indicate that deeper microenvironments are not substantially affected. In addition, changes in the quenching constant of pyrene and its derivatives by oxygen are indicative of the increase in oxygen solubility when the sucrose ester is incorporated in the liposome. These changes in the structure-dependent properties of DODAC liposome bilayer are explained by the location of the voluminous co-surfactant sucrose head groups on the liposome surface. © 2003 Elsevier B.V. All rights reserved.