Biopolymer Adsorption, with Special Reference to the Serum Albumin-Polystyrene Latex System

A study has been made of the adsorption of human serum albumin (HSA) on emursifier-free, negatively charged polystyrene (PS) latices. The adsorption has been followed directly and microcalorimetrically. Important variables are: pH, temperature, csalt and the surface charge a0 of the latex. Although all adsorption isotherms have a platform, the Langmuir theory is inadequate to account for them. Distinction must be made between the initial stages of adsorption, solely determined by the HSA-PS interaction and the later stages, where lateral interaction between adsorbed HSA molecules plays also an important role. The adsorption platform as a function of pH is maximal in the isoelectric point. Here the adsorbed amount is roughly compatible with side-on native HSA molecules. Both below and above the i. e. p. adsorption proceeds in a more unfolded conformation but a spread monolayer is never reached. The adsorption is largely driven by a net entropy gain, both in the initial and later states of the process. Besides this, there is a recognizable influence of the electrostatic attraction between the latex surface and local positive excesses inside the molecule