Chymotrypsin–poly vinyl sulfonate interaction studied by dynamic light scattering and turbidimetric approaches

The formation of non-soluble complexes between a positively charged protein and a strong anionic polyelectrolyte, chymotrypsin, and poly vinyl sulfonate, respectively, was studied under different experimental conditions such as pH (1–3.5), protein concentration, temperature, ionic strength, and the presence of anions that modifies the water structure. Turbidimetric titration and dynamic light scattering approaches were used as study methods. When low protein–polyelectrolyte ratio was used, the formation of a soluble complex was observed. The increase in poly vinyl sulfonate concentration produced the interaction between the soluble complex particules, thus inducing macro-aggregate formation and precipitation. Stoichiometry ratios of 500 to 780 protein molecules were found in the precipitate per polyelectrolyte molecule when the medium pH varied from 1.0 to 3.5. The kinetic of the aggregation process showed to be of first order with a low activation energy value of 4.2 ± 0.2 kcal/mol. Electrostatic forces were found in the primary formation of the soluble complex, while the formation of the insoluble macro aggregate was a process driven by the disorder of the ordered water around the hydrophobic chain of the polymer.