Bovine hemoglobin adsorption onto polymer latices

Abstract

The adsorption behavior of bovine hemoglobin (BHb) onto polymer latices was investigated. The latices used were hydrophobic polystyrene (PS) and hydrophilic copolymers; i.e., styrene (St)/2-hydroxyethyl methacrylate (HEMA) copolymer [P(St/HEMA)] and styrene/acrylamide (AAm) copolymer [P(St/AAm)]. All the latices were prepared without emulsifier and were highly monodisperse. From the measurement results of the surface characteristics for the latices, it was found that the hydrophilic diffuse layers of poly-HEMA and poly-AAm existed on the surfaces of P(St/HEMA) and P(St/AAm) latex particles, respectively. The initial slopes of the adsorption isotherms were greatly affected by pH change. The amount adsorbed onto the latices, except that onto copolymer latices at ionic strength 0.1, showed a maximum near the isoelectric point (iep, pH about 6.8) of BHb. These tendencies in BHb adsorption were similar to those in bovine serum albumin (BSA) adsorption. However, in the regions of pH < 4 and pH > 11, the amount of BHb adsorbed onto PS latex increased again. It was suggested that this re-increase in the amount adsorbed was correlated to the dissociation of BHb (tetramer) into its subunits (dimer and/or monomer) in these pH regions. Moreover, at a lower ionic strength (0.001), the BHb molecule showed a rather high adsorption onto PS latex even in the alkaline pH region. These results indicate that the BHb molecule has a stronger affinity for hydrophobic surfaces than the BSA molecule has. The amounts of BHb adsorbed onto hydrophilic copolymer latices were much smaller than that onto PS latex except in the iep region of the protein.