ADSORPTION OF BSA ON HIGHLY CARBOXYLATED MICROSPHERES - QUANTITATIVE EFFECTS OF SURFACE FUNCTIONAL-GROUPS AND INTERACTION FORCES

In order to elucidate the relations between the amount of surface func tional groups and interaction forces, BSA adsorption experiments were performed, using highly carboxylated PS/PMAA microspheres as well as c onventional ones. Two kinds of interaction forces were considered in t his study, hydrogen bonding and hydrophobic interactions, while ionic interactions were assumed to be small or constant, Hydrophobic interac tions were dominant in the low N-c (number density of surface carboxyl groups) region, below 1 carboxyl group nm(-2), and were relatively se nsitive to pH, while hydrogen bonding was dominant in the high N-c reg ion, above 2 carboxyl groups nm(-2), irrespective of pH, The transitio n region between these two interaction forces was 1 similar to 2 carbo xyl groups nm(-2) on the surface of a microsphere, When comparing the two extremes of hydrophobic interaction and hydrogen bonding, the latt er was stronger, which was different from earlier studies, It can be e xplained that the conventional carboxylated microspheres do not have e nough carboxyl groups on their surfaces, Adsorption constant K diminis hed as N-c increased, which means that the affinity itself is reduced by hydrogen bonding, Adsorbed layer thicknesses calculated from the C- m (adsorbed amount in equilibrium) were 4.66 similar to 7.08 nm; this means that the BSA molecules exist between the side-on and end-on mode . (C) 1996 Academic Press, Inc.