Polycomplexes of Bovine Serum Albumin with Poly[2-Methacryloyloxy) Ethyl]Trimethyl Ammonium Chloride

Complex formation between bovine serum albumin and water-soluble synthetic cationic polyelectrolyte poly[2-methacryloyloxy)ethyl]trimethyl ammonium chloride has been studied in aqueous solutions by turbidimetric and viscometric methods. It was found that the structure of polycomplex is compact and its stability strongly depends on the environment. Formation of insoluble polycomplexes is observed in solutions with low ionic strength and pH, higher than 5.0. This pH value corresponds to the isoelectric point of the protein, so at lower pH the biopolymer macromolecules gain the positive charge and not able to be bound by the positively charged macromolecules of poly[2-methacryloyloxy)ethyl]trimethyl ammonium chloride. An increase of pH within 5.0-11.0 leads to further stabilization of polycomplex because of appearance of additional negative charges on biomacromolecules, caused by ionization of acidic groups. It was found that the main forces, which are responsible for the complexation, are electrostatic interactions. The intensity of the complexation is dependent on the solution concentration, pH and ionic strength. In solutions with high ionic strength (I=0.2, 1.0) the mixing of the reagents does not lead to the formation of insoluble polycomplexes. The observed dependence is connected with the screening of electrostatic interactions between macromolecules of the biopolymer and synthetic polyelectrolyte by small ions present in solution.