| The fragmentation of chitosan in aqueous solution was studied by the following methods: (i) hydrolysis with HCl; (ii) oxidation with NaNO2 and H2O2; (iii) sonication; (iv) microfluidization; (v) photochemical degradation with a laser beam; (vi) enzymatic hydrolysis (lysozyme, papain, lipases, pectinase and hyaluronidase). The results demonstrated that the concentration of chemical reagent was the dominant factor in chemical methods, while the ultrasonic power, the microfluidization pressure and the laser energy were in physical methods and the ratio of enzyme/chitosan concentration in enzymatic fragmentation. The polydispersity of the fragments did not broaden with a decrease in molecular weight, suggesting that larger macromolecules were preferentially fragmented. The chemical structure and the degree of acetylation were not altered significantly by the fragmentation processes. A double exponential decay function best described the kinetics results. Enzyme catalyzed depolymerization of chitosan exhibited substrate inhibition phenomenon. Solution properties of chitosan homologues in dilute and semi-dilute concentration were studied. The Martin constant (concentration dependence of solution viscosity) of chitosan were found to be 37.8 × 10–2 in 0.25 M HAc/0.25 M NaAc (poor solvent) and 15.0 × 10–2 in 0.1 M HAc/0.02 M NaCl (good solvent). The intrinsic viscosity of chitosan fragments solution was correlated with their molecular weight through the Mark-Houwink-Sakurada (MHS) equation, using a polydispersity correction factor. The following equation for chitosan having Mw in the range of 35–2220 kDa, in 0.25 M HAc/0.25 M NaAc solution is proposed: [η] = 1.57 × 10–4 MV0.79 = 1.49 × 10–4 MW0.79. |
