Study of the complex coacervation mechanism between ovalbumin and the strong polyanion PSSNa: influence of temperature and pH.

We studied the complex between ovalbumin and long flexible poly-(sodium 4-styrene sulfonate) as a function of pH and temperature. We used various techniques [turbidimetry, conductometry, dynamic light scattering, viscosimetry, and ultra-small-angle light scattering (USALS)] to fully characterize the coacervate complex. Different phases of complexation versus temperature were determined by turbidimetric analysis (pHc, pHϕ1, and pHϕ2). The optimal protein/polyelectrolyte interaction occurred at pHopt 4. An increase in temperature made the hydrophobic interactions more favorable in the case of the soluble complex and complex coacervation phases (pH > pHϕ2). We systematically determined the activation energy to follow the conformational changes of the complex at different temperatures. At pHopt, the size of the formed complex showed a remarkable decrease with temperature increase. USALS was used to determine simultaneously the radius of gyration (Rg) and fractal dimension Df of the coacervate.