Electromigration of Chitosan D-Glucosamine and Oligomers in Dilute Aqueous Solutions MOHAMMED AIDER, † JOSEPH ARUL, † ALEXANDRU-MIRCEA MATEESCU, ‡ SERGE BRUNET, § AND LAURENT BAZINET* ,† Institute of Nutraceuticals and Functional Foods (INAF), Department of Food Sciences and Nutrition, Laval University, Que ´bec, Que ´bec, Canada G1K 7P4. Department of Chemistry and Biochemistry, Universite ´ du Que ´bec a ` Montre ´al, CP 8888, Succursale A, Montre ´al, Que ´bec, Canada H3C 3P8, ISM Biopolymer Inc., 220, Denison E. Granby, Que ´bec, Canada J2H 2R6 The electromigration behavior of chitosan D-glucosamine and oligomers with a degree of polymerization from 1 to 6 in dilute aqueous systems containing either NaCl or KCl salt at 0.01, 0.05, and 0.1 M at pH values from 2 to 9 was evaluated. The results showed that the electromigration of the chitosan D-glucosamine and oligomers did not change by changing the type of salt in the running medium and that the pH had a significant effect on the direction of migration under an external electric field. In addition, the increase in the ionic strength of the medium caused a significant decrease on the absolute value of the electrophoretic mobility, and the highest values of the electromobility were observed in water. However, the ionic strength had no significant effect on the electrophoretic mobilities at pH 2 in comparison with the other pH values. The dimer showed the highest electrophoretic mobility in the alkaline zone of the pH. At pH values lower than the pK a of the D-glucosamine, the chitosan D-glucosamine, and oligomers migrated toward the anode, where the amine groups are protonated and carry positive charge. At higher pH values, chitosan D-glucosamine and oligomers migrated toward the anode, even though they did not carry any electric charge. The contribution of the difference in the dielectric constants between the solvent and the solute to this phenomenon was highlighted. It was shown that the glucose moiety contributes to the direction of migration of the chitosan D-glucosamine and oligomers under alkaline conditions and that the difference in the dielectric constant of glucose and the solvent accounts for the direction and the extent of electromobility. KEYWORDS: Electrophoretic mobility; chitosan; D-glucosamine; oligomers; dielectric constant 1. INTRODUCTION Since the early 1990s, glucosamine has been widely promoted as an active molecule for the treatment of osteoarthritis and subjected to placebo-controlled studies. Glucosamine is a bioactive amino sugar that is present in all human tissues and is thought to promote the formation and repair of cartilage and has been shown to reduce the progression of diseases such as osteoarthritis and significantly lessen pain from arthritis (1- 5). This substance is the principal compound of the glucosami- noglycans that form the matrix of the connective tissues. Glucosamine could be combined with other glucosaminoglycans, since it helps to maintain the viscosity in the articulation and stimulates cartilage recovery (6). Glucosamine and chitosan oligomers of low molecular weight (with degree of polymeri- zation up to 7) were shown to be absorbed easily into the human intestine (7) because of their low molecular weight. Their use as dietary supplement in human food has become quite common, and for this reason, the study of the various characteristics of these biomolecules is of great interest (8). There are two principal methods for the production of chitosan oligomers: acid and enzymatic hydrolysis (9, 10). Acid hy- drolysis is nonspecific and leads to the formation of chitosan D-glucosamine and oligomers with a low degree of polymeri- zation. They are generally monomers and oligomers with a low degree of polymerization, as well as polymers of high molecular weights. On the other hand, the enzymatic hydrolysis of the chitosan by an enzyme such as a chitosanase makes it possible to produce oligomers of desirable range of polymerization, and the product of the hydrolysis is a mixture of oligomers of a narrow range of molecular weights (11-13). Considering the interest for chitosan oligomers of specific molecular weights for food, nutraceutical, and biopharmaceutical industries, ef- fective separation technologies for their production are needed. For this purpose, chromatographic techniques are generally required, but they are expensive. Alternative techniques such as preparative electrophoresis and membrane filtration are at the present time being studied for the production of bioactive * Corresponding author. Phone: 418-656-2131, ext 7445. Fax: 418- 656-3353. E-mail: laurent.bazinet@aln.ulaval.ca. † Laval University. ‡ Universite ´ du Que ´bec a ` Montre ´al. § ISM Biopolymer Inc. 6352 J. Agric. Food Chem. 2006, 54, 6352-6357 10.1021/jf060165c CCC: $33.50 © 2006 American Chemical Society Published on Web 07/22/2006