Electrokinetic properties of n-tetradecane/ethanol emulsions with DPPC and enzyme lipase or phospholipase A2

The electrokinetic properties of n-tetradecane/ethanol emulsions in the presence of dipalmitoylphosphatidylcholine (DPPC) and enzyme (lipase Candida cylindracea or phospholipase A2) were investigated. Applying the dynamic light scattering zeta potentials and effective diameters of the emulsions droplets were determined as a function of pH and enzyme concentration. Investigation of the electrokinetic phenomena in the presence of phospholipids and enzymes are important for better understanding processes occurring in biological and pharmaceutical systems at interfaces like solid surfaces, cell membranes and oil–water interfaces. Generally, it was found that the presence of DPPC molecules decrease the negative zeta potentials of n-tetradecane droplets and the charge repulsion. Lipase presence increases the negative zeta potentials of n-tetradecane/DPPC (in ethanol) droplets at acidic and natural pH. In the buffer (pH 8) and pH 12 small decrease in the negative zeta potential of n-tetradecane/DPPC droplets is visible. On the other hand if PLA2 enzyme is used small increase in the negative zeta potential of n-tetradecane/DPPC (in buffer) droplets occurs. It is believed that the differences in the enzyme effect on the measured parameters result from hydrolysis reaction and preferable pH of catalytic reaction. Possible reasons for the observed changes of zeta potential and effective diameter are discussed.