Investigation of DPPC effect on SiO2 particles and in the presence of phospho(lipases) by zeta potential and effective diameter measurements

Abstract: Adsorption of dipalmitoylphosphatidylcholine (DPPC) from NaCl solution on SiO2 particles in suspension was investigated by means of zeta potential and effective diameter measurements as a function of pH using dynamic light scattering. Also, the zeta potential of DPPC aggregates in the same environment was measured. By comprising the results, it was found that DPPC adsorbs on the silica surface, which resulted in decrease of negative zeta potential of the silica suspension. However, DPPC stabilized the SiO2 particle aggregates, which resulted in smaller and smoother changes of the aggregate size during 2h-time experiments, probably due to steric stabilization. In the next series of the experiments the effect of enzymes (phospholipase A2 or lipase Candida Cylindracea) on the behavior of the silica/DPPC suspension was studied. The kind of the enzymes; the hydrolysis products, which were palmitic acid and lysophosphatidylcholine (or glycerylphosphorylcholine), and pH influenced the suspension zeta potential. The lipase was found to be a more active enzyme, both at natural pH=5.8 and pH=8. The evaluated parameters connected with the adsorption process and resulting from enzyme action seem to be helpful for further characterization of the silica/DPPC system, which is discussed in the paper. [Copyright &y& Elsevier]