The subject of this report was to investigate headgroup h
ydration and mobilit
y of two t
ypes of mixed lipid vesicles, containing nonionic surfactants; straight chain Brij 98, and pol
ysorbat Tween 80, with the same number of ox
yeth
ylene units as Brij, but attached via a sorbitan ring to oleic acid. We used the fluorescence solvent relaxation (SR) approach for the purpose and revealed differences between the two s
ystems. Fluorescent solvent relaxation probes (Prodan, Laurdan, Patman) were found to be localized in mixed lipid vesicles similarl
y as in pure phospholipid bila
yers. The SR parameters (i.e. d
ynamic Stokes shift, Δν, and the time course of the correlation function,
C(
t)) of such labels are in the same range in both kinds of s
ystems. Each t
ype of the tested surfactants has its own impact on water organization in the bila
yer headgroup region probed b
y Patman. Brij 98 does not modif
y the solvation characteristics of the d
ye. In contrast, Tween 80 apparentl
y deh
ydrates the headgroup and decreases its mobilit
y. The SR data measured in lipid bila
yers in presence of Interferon alfa-2b reveal that this protein, a candidate for non-invasive deliver
y, affects the bila
yer in a different wa
y than the peptide melittin. Interferon alfa-2b binds to mixed lipid bila
yers peripherall
y, whereas melittin is deepl
y inserted into lipid membranes and affects their headgroup h
ydration and mobilit
y measurabl
y.
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