Self-assembly of N-carboxyethylchitosan near the isoelectric point

For the first time the possibility to obtain nanostructures by self-assembly of chitosan polyampholytic derivative was demonstrated. The self-assembly of N-carboxyethylchitosan (CECh) took place only near its isoelectric point (pH 5.0-5.6). Out of the pH range 5.0-5.6, CECh aqueous solutions behaved as real solutions. Dynamic light scattering and atomic force microscopy analyses revealed that spherically shaped or rod/worm-like nanosized assemblies were formed depending on the polymer molar mass, pH value, and polymer concentration. CECh of two different molar masses was studied in concentrations ranging from 0.01 to 0.1 mg/mL. The structures from CECh of weight-average molar mass (Mw) 4.5 × 103 g/mol were spherical regardless the pH and polymer concentration. In contrast, CECh of high molar mass (HMMCECh, Mw = 6.7 × 105 g/mol) formed self-assemblies with spherical shape only at pH 5.0 and 5.6. At pH 5.2 spherical nanoparticles were obtained only at polymer concentration 0.01 mg/mL. The mean hydrodynamic diameter (Dh) of the obtained nanoparticles was in the range from 30 to 980 nm. On increasing the concentration, aggregation of the nanoparticles appeared, and at HMMCECh concentration 0.1 mg/mL, rod/worm-like structures were obtained.