Colloidal nanoparticles of sodium polygalacturonate prepared by nanoprecipitation

Polygalacturonic acid (PGA), being the backbone of pectins, governs their aggregation that is widely applied in industry. The PGA aggregation was studied by dynamic and static light scattering within a limited space of sodium polygalacturonate nanoparticles obtained by nanoprecipitation (drop-wise addition of alkaline solution of PGA to an ethanol bath). With increasing buffer's pH from 4.0 to 9.1, the colloids changed their form from elongated to spherical one, as indicated by decreasing the structure-sensitive ratio R_g/R_h from 1.7 to 1.1. Molecular mass-per-unit-length determined in Holtzer coordinates decreased from 5000 to 1600 Da nm^-1 with increasing pH, suggesting partial disintegration of helical bundles due to electrostatic repulsion. Kratky plots also pointed out partial disintegration of the PGA junctions with increasing pH. Nonmonotonic dependence of the colloidal radius of gyration R_g on [NaCl] characterized the osmotic regime characteristic of annealed polyelectrolytes and thus confirmed the star-like structure of junctions.