Electrophoretic light scattering studies of chitosans with different degrees of N-acetylation

Electrostatic properties of three chitosans with fractions of N-acetylated units (F(A)) of 0.01, 0.13 and 0.49 were examined by electrophoretic light-scattering technique (ELS) and (1)H NMR spectroscopy. From the dependency of mean electrophoretic mobilities on pH, the pK(a) values were calculated. Despite their large differences in chemical composition, all chitosans had similar pK(a) values of 6.5-6.6. All chitosans also showed the same polyelectrolyte behavior when apparent pK(a) values were calculated according to Katchalsky and plotted as a function of the degree of ionization alpha. The intrinsic pK(a) values (pK(0)) extrapolated to zero charge were about 9. The results derived from an independent (1)H NMR study of the same chitosan samples showed no effect of F(A) on titration behavior of chitosan, confirming the results obtained by ELS.