Influence of polyelectrolytes on dynamic surface properties of fibrinogen solutions

The interactions between fibrinogen and polyelectrolytes in the surface layer of their mixed solutions were studied by measurements of the dynamic surface tension and surface elasticity as a function of surface age, polyelectrolyte concentration and solution pH. A flexible and negatively charged polyelectrolyte - sodium polystyrolsulfonate (PSS) - influenced the kinetic dependencies of the surface properties both below and above the isoelectric point, where fibrinogen is positively and negatively charged, respectively, indicating the formation of protein/polyelectrolyte complexes. At the same time, the addition of a more rigid and positively charged polyelectrolyte - polydiallyldimethylammonium chloride (PDADMAC) - to fibrinogen solutions resulted in noticeable changes of the studied dynamic surface properties only at pH values higher than the isoelectric point, while at lower pH values no interactions between the two solutes were observed. The formation of the protein/polyelectrolyte complexes did not lead to noticeable changes of the protein tertiary structure in the surface layer and all the kinetic dependences of the dynamic surface properties were monotonic.