Étude de la mobilité électrophorétique des oligomères de chitosane et leur fractionnement par électrodialyse avec membrane d'ultrafiltration (EDUF)

Authors: Aider, Mohammed
Advisor: Bazinet, Laurent; Mateescu, M. A.
Abstract: The aim of this project was to study the electrophoretic mobility of chitosan oligomers and to apply the results to separate them in an electrodialysis with ultrafiltration membrane (EDUF) system. The first sub-objective was to study the electrophoretic mobilities of D-glucosamine and chitosan oligomers (dimer, trimer, tetramer, pentamer and hexamer) under various conditions of pH, salts and added ionic strengths. pH values from 3 to 9 and ionic strength of 0.01, 0.05 and 0.1 M of NaCl and KCl were studied. The same measurements were carried out in deionised water as a medium without any added ionic strength. Chitosan oligomer electrophoretic mobility decreased by increasing pH and ionic strength. The highest values were recorded in water followed by those in NaCl or KCl with an ionic strength of 0.01 M. The lowest values were recorded at an ionic strength of 0.05 and 0.1 M. The dimer was the most mobile oligomer followed by the monomer. No difference was observed between the mobilities of the oligomers with degree of polymerisation (DP) of 3 and more. The second sub-objective consisted to study the electrophoretic mobility of chitosan oligomer mixture composed by dimers, trimers and tetramers at different concentrations. pH values from 2 up to 12, added ionic strength of 0.01, 0.05 and 0.1 M of NaCl were studied. Electrophoretic mobility was also carried out in water as medium with zero added ionic strength. At a concentration of 3%, the chitosan oligomer mixture showed the highest electrophoretic mobility at pH 2 and 3 with an average value of 2.009 ± 0.105 x 10-6 m2/V.s. At pH 4, 5 and 6, the electrophoretic mobility was stable with an average value of 1.225 ± 0.051 x 10-6 m2/V.s. By increasing the pH, electrophoretic mobility decreased because of the deprotonation phenomenon of the amine group. By decreasing the concentration, the electrophoretic mobility decreased. Following these fundamental studies, the separation by an electrodialysis with ultrafiltration membrane (EDUF) system of a chitosan oligomer mixture was studied. The third sub-objective was to study the effect of ultrafiltration membrane molecular weight cut-offs on chitosan oligomers electromigration rates and kinetics. Five cellulose ester ultrafiltration membranes of 500, 1000, 5000, 10000 and 20000 Da MWCO were used. The membrane molecular weight cut-off had a significant effect on the electromigration rate of each chitosan oligomer, as well as on the possibility of their separation. The dimer showed the highest electromigration rates with average values which varied from 5.71 ± 0.95% up to 14.45 ± 1.43% with 1000 and 20000 Da MWCO UF-membranes, respectively. The effect of the processing time and the oligomers chain length was interpreted. Following this objective, an UF-membrane of 10000 Da MWCO was selected for the future objectives. The fourth sub-objective was to study the effect of the pH on the electromigration rate of the studied oligomers and their kinetics. pH 4 and solution flow velocity of 0.5 cm/s (300 mL/min) were used. pH had a significant effect on the electromigration rate of the oligomers and the possibility of their separation. After 4h of treatment, the dimer showed the highest electromigration rates with mean values of 11.50 ± 4.33, 10.61 ± 0.21, 8.30 ± 0.34 and 5.52 ± 0.38% at pH values of 4, 5, 6 and 7, respectively. Trimer electromigration rates were lower than that of the dimer. Between pH 4 and 7, it migrated with mean values of 8.52 ± 1.45 and 0.83 ± 0.43%, respectively. The effect of the processing time, electrophoretic mobility and oligomers chain length were interpreted. It was possible to obtain a fraction composed by the dimer and trimer at pH 4 and 5 until 2 and 3h, respectively. At pH 6, the tetramer did not migrate during the 4h of treatment. At pH 7, it was possible to obtain dimer pure fraction until 2h of treatment. No electromigration was observed at pH 8 and 9. In the fifth sub-objective, the effect of the applied external electric field (2.5, 5 and 10 V/cm, corresponding to an applied volatage of 5, 10 and 20 V, respectively) to the electrodialysis with ultrafiltration membrane (EDUF) system and solution flow velocity (2.77, 8.33 and 13.88 cm/s corresponding to flow rates of 100, 300 and 500 mL/min, respectively) on the electromigration rate and kinetics of the oligomers were studied. The solution flow velocity did not show any effect on the electromigration rate of the oligomers whereas the applied electric field strength had a significant effect on both electromigration rate and separation of the studied oligomers. At 2.5 V/cm, it was possible to obtain a solution composed only by the dimer and trimer until 2 h of treatment. Using and electric field strength of 2.5 V/cm, the dimer migrated with an average rate of 10.20 ± 3.04% and the trimer with an average value of 8.52 ± 1.66%. By increasing the electric field strength up to 5 and 10 V/cm (voltage of 10 and 20 V, respectively), there was no separation of the studied chitosan oligomers.
Document Type: Thèse de doctorat
Issue Date: 2007
Open Access Date: 13 April 2018
Permalink: http://hdl.handle.net/20.500.11794/19689
Grantor: Université Laval
Collection:Thèses et mémoires

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