| Abstract
| - The adhesion of liposomes on a mercury electrode leads to capacitive signals due to the formation of islandsof lecithin monolayers. Integration of the current−time transients gives charge−time transients that can befitted by the empirical equation Q(t) = Q0 + Q1(1 − exp(−t/τ1)) + Q2(1 − exp(−t/τ2)), where the first termon the right side is caused by the docking of the liposome on the mercury surface, the second term is causedby the opening of the liposome, and the third term is caused by the spreading of the lecithin island on themercury surface. The temperature dependence of the two time constants τ1 and τ2 and the temperaturedependence of the overall adhesion rate allow determination of the activation energies of the opening, thespreading, and the overall adhesion process both for gel-phase 1,2-dimyristoyl-sn-glycero-3-phosphocholine(DMPC) and for liquid-crystalline-phase DMPC liposomes. In all cases, the spreading is the rate-determiningprocess. Negative apparent activation energies for the spreading and overall adhesion process of liquid-crystalline-phase DMPC liposomes can be explained by taking into account the weak adsorption equilibria ofthe intact liposomes and the opened but not yet spread liposomes. A formal kinetic analysis of the reactionscheme supports the empirical equation used for fitting the charge−time transients. The developed kineticmodel of liposome adhesion on mercury is similar to kinetic models published earlier to describe the fusionof liposomes. The new approach can be used to probe the stability of liposome membranes.
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