| Research Abstract |
The results obtained in the study period of 2000 - 2001 were summarized as follows:
1) In order to rationalize the mechanism of the complexation of chitosan with iodine and clearly interpret its specific molecular characteristics, we have investigated the effects of the factors responsible for the complexation, such as the degree of deacetylation (DDA), side-chain species, and molecular weight of chitosan, the concentrations of the reagents, etc., on the physicochemical properties (spectral characteristics, structure, etc.). For comparison, the physicochemical properties of the iodine complexes of amylose, cellulose, and N-methyl chitosan with structural types different from chitosan were examined. Furthermore, the biological functionalities of the CM complexes, i. e., the antibacterial assay for E. coli and wound healing assay for NIH/3T3 cell (mouse normal fibroblast) were probed.
2) The chitosan-iodine (CM) complex, which was prepared in acidic medium by our developed freezing-thawing
… More
method, exhibited absorption spectra with a peak at around 500-650 nm, and mutually split CD bands with opposite signs (+, -), regardless of the iodine/chitosan concentrations, temperature, DDA more than 50%, and molecular weight. These spectral characteristics were similar to those of amylose-iodine (Ami) complex, whose purple coloring is developed by the left-handed iodine/ iodide dimer exciton-coupled mechanism involving CT and CI. Furthermore, the resonance Raman and NMR spectroscopy measurements revealed that the iodine species responsible for the coloring of the Chl complexes is primarily ions, and the interaction sites in the D-glucosamine moiety in chitosan chains with bound iodine are hydroxyl groups on C-1, C-3, and C-4.
3)The ChI complex showed a unique characteristic of thermal hysteresis behavior, i. e., an irreversible reaction process involved in complexation and color formation, regardless ofDDA, side-chain species, and molecular weight. However, such as the behavior were not observed for the Ami and Cel complexes.
4)The structural studies based on analytical ultracentrifugation, and small-angle X-ray/neutron scattering for the Chl complexes revealed that the molecular assembly of extended chitosan chains plays a vital role in CM complexation, in which the CI complex forms an aggregate with a cylindrical structure composed of an inner polyiodide chain surrounded by an assembly of chitosan chains. The aggregate structural size was progressed with the reagent concentrations, following the increase in coloration ability.
5)The MD simulation predicted that the irreversibility and thermal hysteresis behavior of the Chl complexes is a result of the transition of chitosan in solution from a crystalline-like extended conformation to a compact folded conformation. As a future work, analysis of the transition of the compact folded form-crystalline-like extended form in the restoration of CI complexation induced by freezing, and the stoichiometry and kinetics of the complexation will be in progress.
6)At present, the information on the effective bioactivity for the CM complex has been obtained. The water-soluble N-methyl chitosan is predicted to have a bright prospect for multi-biofunctionality. The foregoing results have been reported in the published papers (4 subjects), proceedings (2 subjects), and the papers (20 subjects) in national and international science meetings. Less
|
