Influence of the temperature in the adsorption of sodium dodecyl sulfate on phosphatidylcholine liposomes

The influence of the temperature on the adsorption of monomeric and micellar solutions of the anionic surfactant sodium dodecyl sulfate (SDS) on phosphatidylcholine (PC) liposomes was investigated using the fluorescent probe 2-(p-toluidinyl)-naphthalene-6-sodium sulfonate (TNS). The number of adsorbed molecules was quantified by measuring changes in the electrostatic potential (Psi(o)) of the liposomes/probe during an incubation with SDS at varying temperatures. At low surfactant concentrations (from 0.05 to 0.25 mM), the increase in temperature reduced the number of surfactant molecules incorporated per vesicle regardless of the incubation time, whereas at high surfactant concentrations (from 0.50 to 1.0 mM) the incubation time has an opposite effect on this process. Thus, after 10s, the surfactant adsorption decreased with temperature, yet it increased progressively with time. The adsorption was linear with temperature below critical micellar concentration (CMC) of SDS and this linear tendency did not change above CMC. This suggests an adsorption of SDS monomers regardless of the surfactant concentration.