Changes of zeta potential and particles size of silica caused by DPPC adsorption and enzyme phospholipase A2 presence

The changes in electrokinetic properties of silica suspensions in the presence of 1,2-dipalmitoyl- sn -glycero-3-phospshocholine (DPPC) were investigated via zeta potential, mean diameter and transmittance determinations. Silica particles were precovered with monolayer (ML) or bilayer (BL) of the phospholopid from chloroform solution (SiO 2 /DPPC) or covered by DPPC adsorption from aqueous solution (SiO 2 +DPPC). The zeta potential and mean diameter of SiO 2 /DPPC suspension were measured as a function of NaCl concentration and due to the phospholipase A 2 (PLA 2 ) action in 10 −3 M NaCl solution and buffer Tris at pH=8 and 9. It was found that the DPPC adsorption onto silica surface decreases its the zeta potential, however the suspensions were stable during the experiment time, probably because of steric stabilization. During PLA 2 enzyme action the changes in zeta potential were observed, which were caused by the hydrolysis products, especially palmitic acid molecules, which also had influence on the stability of these systems.