Effect of Sonication on the Thermotropic Behavior of DODAB Vesicles Studied by Fluorescence Probe Solubilization

Abstract

The effect of sonication on fluorescence probe solubilization in cationic vesicles of dioctadecyldimethylammonium bromide (DODAB) was investigated by steady-state fluorescence of pyrene (Py), trans-diphenylpolyenes-diphenylbutadiene (DPB), diphenylhexatriene (DPH), and their corresponding 4,4 0 -dialkyl derivatives 4B4A and 4H4A fluorescence probes. The data indicate that sonication affects the bilayer polarity, the melting temperature (T m ), and the cooperativity of the melting process due to changes in vesicle morphology. The effect of temperature on the fluorescence intensity and yielding U f and anisotropy \r[ shows that the ionizable probes 4B4A and 4H4A are solubilized close to the vesicle interfaces, whereas the non-ionizable DPH and DPB are deeper in the bilayers. Py solubilization indicates that sonicated vesicles exhibit less densely packed bilayers.

Modulation of Solvation and Molecular Recognition of a Lipid Bilayer under Dynamical Phase Transition

“…Relative to the negatively charged ANS, the neutral dye C500 incorporates deeper into the lipid bilayer exhibiting lower average rotational relaxation time ( t r h i, Table 1.) This variation in average rotational relaxation time for C500 is similar to the previously observed variation in fluorescence anisotropy [39] in DODAB vesicles, and may be ascribed to increased cooperativity of the melting process during transition from gel to liquid crystalline phase. [37,38] Furthermore, C500 displays lower mobility (higher t r h i) below and above the transition temperature, but a sharp decrease of t r h i is noted around this temperature (50 8C).…”

“…[37,38] Furthermore, C500 displays lower mobility (higher t r h i) below and above the transition temperature, but a sharp decrease of t r h i is noted around this temperature (50 8C). This variation in average rotational relaxation time for C500 is similar to the previously observed variation in fluorescence anisotropy [39] in DODAB vesicles, and may be ascribed to increased cooperativity of the melting process during transition from gel to liquid crystalline phase. On the other hand, the time-resolved anisotropy of ANS becomes faster upon subgel to gel and gel to liquid crystalline transition of DODAB vesicles (insets of Figure 2) which is reflected by decreasing average reorientational time (Table 1) indicating increased flexibility of the local environment of the dye.…”

Unusual location of the pyrene probe solubilized in the micellar solutions of tetraalkylammonium perfluorooctanoates

“…4,5,16,17 The following explanations can be summarized from many research papers: 3,[16][17][18] (i) the bulkiness and rigidity of uorocarbon chains, which induced smaller aggregation numbers 19 and thus relatively higher water penetration in micelles; (ii) the immiscibility between the hydrocarbon and uorocarbon species, which resulted in the less preferential partition of pyrene into uorocarbon micelles from an aqueous medium. As we all know, the uorescence spectra represent an average of the emission characteristics of the microenvironment among the distribution of the probes; 20 (iii) the location of solubilized pyrene was considered to be in the palisade layer of the micelles and closer to the micellar surface, where pyrene could more sufficiently contact with water.…”