Studies on depolymerization of chitosans having relatively high initial molecular weights by acid hydrolysis have been also reported [26�C28]. The present studies focused on fragmentation of chitosan for preparation of the sellectchem fragments having wide ranges of molecular weights using soft experimental conditions (concentration of HCl between 0.1 and 1M and temperature = 65��C). We report the effect of HCl (C = 0�C1.0N) on the average number of chain scissions (��), molecular weight distribution (polydispersity), and the DA of the fragments. A rapid method to estimate molecular weight of fragments while fragmentation process is continuing is proposed. 2. Materials and Methods2.1. MaterialsHigh viscosity shrimp-shell chitosan with a nominal DA of 25% was purchased from Nova-Chem. Ltd.

(Halifax, Nova Scotia, Canada) and was purified as follows: chitosan was dissolved in 0.2M HCl with constant stirring for 16 hours at room temperature. Suspended particles remaining in the solution were separated by centrifugation. The solutions were neutralized (pH, 7.8) with 1.0M NaOH. The chitosan particles suspended in aqueous medium were recovered by centrifugation, washed with deionized water several times, and dried by lyophilization. Acetic acid (HAc) and sodium acetate (NaAc) were of HPLC grade. CD3COOD and D2O were of analytical grade. All other chemicals were of analytical grade. 2.2. Fragmentation2.2.1. Kinetics Purified original chitosan was dissolved in 0.05M HCl with a constant stirring at room temperature for 12h. Hydrochloric acid with concentration of 2.3M was then added to chitosan solution.

Final HCl and chitosan concentrations in the latter solution were 0.5M and 1.0% (w/v), respectively. Hydrolytic fragmentation was carried out in a 1000mL spherical flask equipped with a vertical condenser at 65��C for 30h, while the solution was constantly stirred. A certain amount of the solution was drawn periodically and cooled down to 0��C immediately. One part of the solution was used to measure the solution viscosity at 25��C. Another part was used for recovery of chitosan fragments. The fragments have been used to measure intrinsic viscosity, the DA determination, and structural characterization. After fragmentation process, the fragments were recovered from chitosan suspension solutions as follows: the solution was neutralized with 1.0N NaOH.

The chitosan particles suspended in solution were precipitated by centrifugation, washed with deionized water, and recovered by lyophilization. 2.2.2. Effect of HCl Concentration Reactions were performed as before except that final HCl concentration was varied between 0.1 and 1.0M and reaction was AV-951 terminated after 5h. The reaction mixture was subsequently neutralized with 1.0M NaOH to recover chitosan fragments. The recovery procedure was performed as described in Section 2.2.1.2.3. Characterization2.3.1.