Advantages of interfacial tensiometry for studying the interactions of biologically active compounds

Dynamic surface tensions of lipase in aqueous solutions at pH 7, in Na-phosphate solution at pH 9 and in basic phosphate buffer at pH 11 were measured at the water/air interface in a broad concentration range (10−8 to 10−5 M). Different lipase preparations were immobilized under various conditions in polyelectrolyte complexes (PEC) based on Na-poly(styrene sulfonates) (PSS) as polyanion and poly(diallyldimethylammonium chloride) (PDADMAC) as polycation. Strong lowering of the surface tension was observed for both two component and three component complexes. The dynamic surface tension of these systems allowed conclusions about the stability of the highly surface-active polyelectrolyte complexes which were formed under well defined conditions—pH value during complex formation, ionic strength, polyelectrolyte charge and polyelectrolyte ratio.