Effect of Hofmeister ions on thermodynamics of complex coacervation of hyaluronic acid and chitosan

Abstract

The Hofmeister series is an ion series that was discovered to have significant effects on the behavior of aqueous protein solutions as a result of Franz Hofmeister's studies in 1888, and its effects on other biomacromolecules have also been investigated. This study aims to examine the effect of this series on the complexation and coacervation of hyaluronic acid (HA) with chitosan (CHI) polyelectrolytes in three different pH values (3.25, 5.25, and 6.25) and two different molecular weights (HA, 1200 kDa & 199 kDa) in terms of thermodynamics. While turbidimetric titration experiments were used to optimize conditions affecting coacervation such as salt type, pH and concentration of buffering agent and polyelectrolyte, images were taken by light microscopy to ensure that the HA/CHI system produces coacervates that could be used in areas such as encapsulation, tissue engineering, and not just precipitate particles. Isothermal titration calorimetry has been found suitable to understand the thermodynamics of coacervation. The results majorly agree with the direct Hofmeister effect for the cations and the reverse Hofmeister effect for the anions. In addition, the salt screening effect can be clearly observed as the interaction between the two polyelectrolytes are most intense in the absence of salt. It was also observed that the interaction between the two macromolecules was greater as the pH increases.