ELECTROKINETIC BEHAVIOR OF F(AB')(2) FRAGMENTS ADSORBED ONTO POSITIVELY AND NEGATIVELY CHARGED POLYMER COLLOIDS

The aim of the present work is to study the electrokinetic behavior of F(ab')(2) molecules adsorbed onto positively and negatively charged p olystyrene beads, in order to determine the role played by the electro static interactions in F(ab')(2) adsorption onto polymer colloids. Pos itively (JL8) and negatively (JL1) charged polystyrene beads were prep ared by emulsion polymerization. JL8 was prepared using an ate-initiat or, the average diameter of the particles was 195 +/- 5 nm with a surf ace charge density of 53 +/- 2 mC m(-2). JL1 was prepared according to the shot-growth procedure of emulsion copolymerization of styrene and sodium styrene sulfonate, giving beads with a high monodispersity and an average diameter of 168 +/- 8 nm with a surface charge density of -(40 +/- 2) mC m(-2). Adsorption isotherms at low ionic strength and d ifferent pH were performed. In all cases the adsorption isotherms show ed well-defined plateaus. The JL8 sample showed a higher adsorption of F(ab')(2) molecules over a range of pH. This latex sample reached a m aximum adsorption at pH 7, whereas the JL1 sample showed a maximum at pH 5. The isoelectric points of F(ab')(2)-latex complexes were 7.5 and 4.5 for JL8 and JL1, respectively. The effects caused by the resuspen sion-pH, ionic strength and degree of protein coverage were studied. M obility values were dealt with using the most recent theoretical appro aches given by Ohshima and Kondo to obtain information about the prote in layer.