Autoorganización en sistemas biomoleculares: efecto de la concentración iónica en la distribución de tamaños de liposomas de DPPC.

Abstract

In this work we have studied the distribution of both the size and the zeta potential of liposomes prepared with the lipid Dipalmitoylphosphatidicholine (DPPC) in solutions at pH 7 with different ionic strengths. The ionic strengths correspond to salt concentrations of 0mM to 200mM in steps of 50mM. The liposomes were prepared by the hydration and sonification method. While their characterization was performed by tracking the particle trajectories. The concentration of liposomes was initially determined with the absorbance at 230nm. The mean values of liposome diameters in solutions with salt concentrations of 50mM to 200mM were comparable to each other, with values close to 132nm. However, for liposomes in buffer-phosphate a lower mean size was obtained. Therefore, in this sample, the particles had on average a smaller hydrodynamic radius. The liposomes presented a predominantly positive surface charge. Since, the electrophoretic mobility distribution and potential mostly presented values in the negative range. This is consistent with the fact that the choline group of the lipid which is on the liposome surface and therefore in contact with the medium has a positive charge at pH 7. In addition, the average potential in the 0mM and 50mM samples were not statistically equal to each other. For 100mM to 200mM, the average potentials were found to be close to -45mV. Particularly, for 0mM the zeta potential was statistically less negative than in the other cases. This can be explained by the fact that in the absence of sodium chloride the only negative ions present are phosphate ions.