Short chain chitosan solutions: self-assembly and aggregates disruption effects

Light scattering and microscopy studies show that short chain chitosans (oligochitosans) are partially associated in dilute solutions in the pH range below critical point of phase separation. The observed structural diversity of solutions (spherical and fibril-like aggregates, and molecularly dispersed systems – “true solution”) depends on purification procedure. It is shown that oligochitosan samples having molecular weights below 12 kg · mol⁻¹ form aggregates of constant sizes and can be selected into a series of oligochitosans of a peculiar aggregation behavior. Comparing the results of different methods (light scattering, microscopy, and HP SEC) it is concluded that initial supramolecular structures occurring in oligochitosan solutions are disrupted under shear action in the course of HP SEC and viscometric measurements, and that the additional factor promoting structural rearrangments during filtration through a porous membrane is the interaction of aggregates with pore surfaces. The results discussed in terms of modern theories of polyelectrolyte solutions are indispensable for better understanding of the mode of oligochitosan antibacterial and antifungal activities and preparation of its injectable compositions.