STOICHIOMETRIC AND NONSTOICHIOMETRIC COMPLEX-FORMATION OF BOVINE SERUM-ALBUMIN POLY(DIMETHYLDIALLYL AMMONIUM-CHLORIDE)

Complexation between bovine serum albumin (BSA) and Poly(dimethyldiallyl-ammonium chloride) (PDMDAAC) was studied by static and quasi-elastic light scattering (QELS), electrophoretic light scattering and turbidimetric titration in dilute electrolyte solution. Both QELS and turbidimetric titration show that complexation occurs at pH greater than or equal to 4.6 for the ionic strength of 0.01 M. The results obtained support the following mechanism. Upon addition of PDMDAAC to BSA at I = 0.01 M, a stoichiometric complex is initially formed. Subsequent addition of polymer causes this complex to form a coacervate with concomitant charge neutralization. The stoichiometric complex was found by static light scattering to have 120 BSA bound per polymer chain. At higher ionic strengths (0.05 and 0.10 M), the initial complex is nonstoichiometric, and coacervates are formed by the aggregation of the complex. These coacervates are observed as ca 700 nm droplets by optical microscopy.