THE EFFECT OF HOFMEISTER IONS ON THERMODYNAMICS OF COMPLEX COACERVATION BETWEEN HYALURONIC ACID AND CHITOSAN

Franz Hofmeister's research in 1888 led to the discovery of the Hofmeister series, an ion series the effects of which on the behavior of aqueous protein solutions were found to be significant. Other biomacromolecules also had their stability in solution determined by the presence of Hofmeister series. With respect to thermodynamics, this work seeks to understand the impact of this series on the complexation and coacervation of hyaluronic acid (HA) with chitosan (CHI) at three distinct pHs (3.25, 5.25, and 6.25) and two different molecular weights (HA, 1200 kDa & 199 kDa). While light microscopy images were used to confirm that the HA/CHI mixtures led to coacervates and not just precipitate particles, turbidimetric titration experiments were used to optimize the conditions affecting coacervation such as salt type, pH and concentration of buffering agent and polyelectrolyte. It has been determined that isothermal titration calorimetry is useful for comprehending the thermodynamics of coacervation. Our results indicate the validity of the direct Hofmeister effect for cations and the reverse Hofmeister effect for anions. Furthermore, the salt screening effect is readily evident since the interaction between the two polyelectrolytes is strongest when salt is absent. Additionally, it was found that as pH was increased, there was a stronger interaction between the two macromolecules.