Effect of the incorporation of alkanols upon the properties of DPPC vesicles. Dependence with the solute concentration and topology

Diphenylhexatriene (DPH) and three 9-antroyloxy derivatives of stearic acid (AS) with the fluorescent moiety localized at different carbons of the stearyl chain, has been employed as fluorescent probes to study the changes produced in DPPC large unilamellar vesicles by the incorporation of several alkanols of different topology. From the modification of the fluorescence anisotropy of these probes, the effect of the alkanol incorporation upon different parts of the bilayer are evaluated. The biphasic behavior observed using AS probes is interpreted in terms of crowding the interface followed by a disorganization of the central parts of the bilayer. Differences in the behavior of the AS probes indicate that the fluidification of the central parts of the bilayer is considerably larger than the disorganization of the bilayer borders. The hypothesis that probes molecules create their own defects, where the fluorophore rotation is rather unhindered, is raised in order to explain the existence of fluorescence anisotropy maxima of two of the AS probes at relative low alkanol intravesicular concentrations.