Investigations of DPPC effect on A1_2O_3 particles in the presence of (phospho)lipases by the zeta potential and effective diameter measurements

摘要

Adsorption of phospholipid (DPPC) from NaCl electrolyte solution (or from chloroform solution) on Al_2O_3 particles in suspension was investigated by means of the zeta potential and effective diameter measurements as a function of pH using dynamic light scattering. Al_2O_3 particles were precovered with an amount of dipalmitoylphosphatidylcholine sufficient to cover the alumina surface by the statistical mono- or bilayer (ML or BL). It was found that DPPC from NaCl solution was adsorbed on Al_2O_3 surface independently of phospholipid concentration, which resulted in decrease of the initial zeta potential of Al_2O_3 suspension. When alumina was precovered with DPPC from chloroform (ML or BL) some reori-entation of phospholipid molecules could take place. Despite the lowering of the zeta potential value in both cases (from both aqueous and chloroform solution) DPPC stabilized the Al_2O_3 particle aggregates, which resulted in smaller and smoother changes of the aggregate size during 2-experiment hours due to steric and electrostatic stabilization. In the next series of experiments the effect of enzymes (phos-pholipase A_2 or lipase Candida cylindracea) on the behavior of Al_2O_3/DPPC particles was studied. The kind of the enzymes, the hydrolysis products, which were palmitic acid and lysophosphatidylcholine (or glycerylphosphorylcholine), and pH changed the suspension zeta potential and influenced the stability of these systems. Lipase was found to be a more active enzyme than phospholipase. The electrokinetic parameters connected with the adsorption process and resulting from the enzyme action seem to be helpful for characterization of the Al_2O_3/DPPC suspension and the activity of the enzymes, which is discussed in the paper.