Abstract
A new method of metal-coordinating controlled oxidative degradation of chitosan leading to low molecular weight chitosan with uniform molecular weight distribution is reported in this paper. Chitosan is converted into chitosan-metal complex in which chitosan chain can be easily broken at weak points caused by coordinating bond. IR, UV, XRD, DSC and elemental analysis proved coordination between chitosan and the metal ion and the presence of weak points existing on the chitosan chain of complexes. Coordinating conditions (such as metal amount, speed of stirring, speed of metal salt addition) are controlled to obtain the complex with uniform metal distribution and uniform weak points distribution. H2O2 is added to break chitosan chain at those weak points to get low molecular weight chitosan. Degradative speed with different metal ion is different as follow: Cu 2+ > Co 2+ > Mn 2+ > Ni 2+ . With the increase of oxidant amount, temperature, and pH, and decrease of O2 content, degradative velocity increase. HPLC/GPC spectra show that degradative velocity of complexes is faster than that of chitosan, and the molecular weight distribution is much more narrow than that of chitosan. Low molecular weight chitosan and its complexes with Cu(II) or Co(II) possess good O2 .- scavenging activity.
Highlights
Chitosan, copolymer of 2-amino-2-deoxy-β (1,4)-D-glucose and 2-acetamido-2-deoxy-β (1,4)-Dglucose units, is N-deacetylated product of chitin which is the second most abundant natural polysaccharide
When degraded for 3 h, the intrinsic viscosity is 28, 405, 307, 590, and 763 mL.g-1 for CTS-Cu, CTS-Co, CTS-Mn, CTS-Ni and CTS respectively. This result shows that the intrinsic viscosity of all complexes decreases faster than that of chitosan, and that viscosity decrease velocity is different with the type of metal ion as: Cu2+ > Mn2+ > Co2+ > Ni2+
We have developed a new method for chitosan degradation called metal-coordinating controlled oxidative chitosan degradation
Summary
Copolymer of 2-amino-2-deoxy-β (1,4)-D-glucose and 2-acetamido-2-deoxy-β (1,4)-Dglucose units, is N-deacetylated product of chitin which is the second most abundant natural polysaccharide. Low molecular weight chitosan (LCTS) is especially important in medicine, food, cosmetics and agriculture because of its special physiological activity such as antitumor, antifungal, enhancing immunity, lowering cholesterol levels, water retention, and so on.. Low molecular weight chitosan (LCTS) is especially important in medicine, food, cosmetics and agriculture because of its special physiological activity such as antitumor, antifungal, enhancing immunity, lowering cholesterol levels, water retention, and so on.1-7 Effectiveness of these chemicals has been found to be dependent on their molecular size. Except degradation with chitosanase, which can get chitosan oligomer with 6-8 glucose residues, other methods often produce the low molecular weight chitosan with large molecular weight distribution, and so the yield of low molecular weight chitosan with particular molecular weight is low. An improved new method is needed to produce low molecular weight chitosan with narrow molecular weight distribution
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