Surface properties of liposomes mixtures of phosphatidylcholines and phosphatidylethanolamines

MARIA BELEN SIERRA *; VIVIANA I. PEDRONI; MARCELA A. MORINI; ANIBAL DISALVO; LAUREANO ALARCON; GUSTAVO A. APPIGNANESI

Villa Carlos Paz

Congreso; SAB2013, XLII Reunión Anual de la Sociedad Argentina de Biofísica; 2013

SAB Sociedad Argentina de Biofísica

BLM15 p.36 Phase properties studies of mixtures of DMPC/DPPC and DMPC/DMPE performed by means of differential calorimetry and fluorescence microscopy, determined the existence of phase segregation as a function of temperature and composition. It is inferred from these studies that the phases in contact produce areas of contact, which affect surface properties of the membranes in contact with the aqueous medium. However, there are few systematic studies about the surface potential that arise from the presence of segregated phases. Thus, in this paper the zeta potential of multilamellar liposomes of DMPC/DPPC and DMPC/DMPE mixtures was determined at 50ºC and 60ºC respectively, which are the phase transition of the lipids, in a 1mM KCl medium. For the DMPC/DPPC zeta potential discontinuities are observed as mole fraction of DPPC increases. Two mole fractions show particularities, which coincide with what was reported for these mixtures in gel state [1] and with bigger sized liposomes. Since these lipids are miscible in the whole range of molar fractions, the results could be explained as a consequence of the organization of polar headgroups at the lipidic interphase. This conclusion is also supported by the behaviour of unilamellar and multilamellar mixtures of DMPC/DMPE where the polar headgroup plays an important role in the stabilization due to steric factors being this influence more noticeable than the one related to the change of length of the hydrocarbon chain, as shown by the DMPC/DPPC mixtures. Results are in agreement with Makino [2] proposal for the placement of PC headgroups on the liposome interphase according to its phase state.