MOLECULAR-INTERACTIONS AT BIOINTERFACES - A STUDY OF LIPID ADSORPTION

The study of the behaviour of biointerfaces is of great interest becau se it enables us to gain a much better understanding of the interactio ns between different biological compounds. Superficial processes are s trongly dependent on such interactions. In the present work, we have f ocused our attention on the adsorption of a cationic lipid onto differ ent colloidal polymer systems. Subsequently, the coadsorption of this lipid and an immunoprotein (F(ab')(2)) was performed trying to achieve stable latex particles. The aim was to obtain a structured interface similar to that of a simple biological membrane. Mainly, we have place d emphasis on the study of interaction forces that govern lipid adsorp tion when we change the dielectric constant in the medium. In order to obtain homogeneous aqueous lipid solutions some ethanol was added to samples. The adsorption isotherms were carried out at different experi mental conditions, changing the ethanol contents and the pH of the env ironment. Moreover, the electrokinetic behaviour and the colloidal sta bility of these biocomplexes were studied, and both yielded highly com patible results. The adsorption of lipid onto polymeric sorbents is an irreversible process that takes place rapidly. The preferential inter action between the lipid and polymeric surfaces is electrostatic. Only in those samples with low alcohol concentration, hydrophobic forces t ake place weakly. Lipid-surface interactions are influenced by the nat ure of buffer ions. The colloidal stability of the systems decreases a s the amount of the adsorbed lipid is higher. Sequential coadsorption experiments showed that the lipid molecules adhere both to the polymer surface and to the previously adsorbed immunoprotein.